The necessary premise to obtain Zamak components for household appliances able to become an added value for the entire object is the creation of a relationship of understanding and trust between the die caster and the producer of appliances. In fact, only through the mutual exchange of expertise and knowledge it is possible to achieve optimal results, able to meet not only the customer’s requirements, but also the expectations of the final consumer.If you want to learn more about saving opportunities connected with the choice of the right die casting supplier we suggest you to read the post How the right die casting supplier can help your company’s VAVE. 

Advantages of Zamak components for household appliances

In the first part of this article we are analyzing the main advantages that result from the choice of zinc alloys for household appliances components with an eye to the needs of the household appliances producer and to the expectations of the final consumer. Thereafter we will present some brief case studies able to illustrate the processes and the strategic choices that have been adopted in order to obtain optimized products.

The advantages on the side of the household appliances producer that will be considered are:

• Co-design
• Functional beauty
• Design freedom
• Freedom of superficial treatments
• Finishing and assembly
• Cost reduction

  From the final consumer side we will consider the value added by zinc component in a household appliance in these regards:

• Appearance, quality, resistance
• Cleaning
• Recyclability
  

  Advantages from the producer’s point of view

  There are many advantages on the producer side, for some of them we will offer a more complete analysis while for others we will just discuss some details, providing indications on where to find articles that address these subjects more in detail.

Co-design

As anticipated, it is only through a relationship of understanding and trust that it is possible to question established methods and procedures in order to define new ones able to lead to an optimization of processes and products. To establish such a relationship it is necessary to choose a supplier of Zamak components for household appliances with the competences, the experience and the knowledge necessary to undertake, together with the customer, the co-design process. In fact the right supplier will be able to work on the design of the component suggesting optimization strategies for molds and filling flows, shapes and walls able to lead to the creation of unique and exclusive products.

To discover some of the co-design strategies that it is possible to implement to reduce weight, and as a consequence costs, of household appliances we suggest to read Weight reduction for white goods industry.

Functional beauty

The co-design process shall be led by the principle of functional beauty, which is the removal of unnecessary details aimed at improving the aesthetical qualities of the functional parts.

The achievement of functional beauty is synonym of true collaboration between designers and manufacturers, in fact it implies a joint and targeted action that allows the obtainment of results able to satisfy both sides.

To achieve functional beauty, thanks to the synergy achieved during the co-design phase, it is necessary to put at the core of the process the coexistence of functional and aesthetical elements without forgetting that, to obtain really valid results, it is necessary to consider options compliant with the die casting productive process.

In the article Functional beauty: the case of Nespresso KitchenAid Artisan 5KES0503  it is possible to find a more detailed definition of functional beauty and its exemplification through a case study.

Design freedom

Functional beauty and co-design are tools that help the producer of household appliances to obtain products able to meet his or her requirements. However, both the hot chamber die casting technology and the choice of zinc alloys allow a great design freedom. In fact through the die casting process it is possible to obtain complex and articulate shapes with very thin walls that allow the creation of unique components and customized details and shapes.

Freedom of superficial treatments

The surface of zinc alloys die casts is particularly suitable for superficial treatments and finishing. In fact components can undergo various kinds of treatments in order to achieve an external appearance that is appealing and customized according to the requests of the customer. These treatments are, for example, chrome plating, powder coating and liquid painting. Moreover, the advantage given by this kind of treatments is not only aesthetical but it results also in an augmented superficial resistance of the products, and, for extension, of their life time.

Finishing and assembly

Thanks to the introduction of automation, anthropomorphic robots and ad hoc realized machineries it is possible to automate a great number of secondary operations, such as assembly and finishing, and of quality control. The possibility to undertake these operations with a reduced contribution of personnel allows the customer to obtain ready-to-use components at a competitive price and with a reduced cycle time. Moreover, the development of automations and ad hoc machineries allows quality and compliance controls to be done quickly and in exemption from the risk of human error with a noticeable decrease of returns due to not compliance.

Costs reduction

Beyond the saving opportunities allowed by automation and accuracy in designing the mold and the filling flows, it is important to underline also the cost effectiveness resulting from the choice of zinc as raw material for the creation of die casts.

In fact zinc alloys are different from other metals or metallic alloys for their competitiveness in costs and production times. Zinc alloys do not require high temperatures to melt and, as a consequence, also the cooling times result reduced. These factors, in their turn, mean a cycle time that is short if compared to the one of other metals and in an increase of the productive capacity of the plant.

Zinc can be competitive also in comparison to plastic materials: for example, to obtain the stiffness and resistance of zinc, plastics have to be reinforced with glass fiber or with special polymers with a resulting increase of the costs for the material.

Advantages from the customer’s point of view

Customer experience is what the customer feels when approaching to a product. In defining the quality of this relationship there are a number of variables connected to the actual situation, but also to consumption and market trends. Specifically, for the relationship between the user and the appliance some important factors are: the performance of the product, its usefulness, appearance, texture, resistance, the global perception of the object and its alignment, or misalignment, to consumption trends.

Let’s now analyze some relevant factors, able to influence the customer experience for a home appliance and to determine the perception of value and quality of the object.

Appearance, quality, resistance

Zamak components for household appliances are able to convey good visual and tactile sensations. From a visual point of view an element made of zinc, which is coated or chromed, distinguishes itself from the rest of the body of the appliance resulting in a prominent and valuable element. Also from a tactile point of view a metal functional element gives feelings of greater reliability and resistance in comparison to the same component made of plastic. In this way it is possible to obtain a differential advantage given by the visual and tactile feelings of the user that result in a perception of value.

Cleaning

On the customer side an important aspect when choosing an appliance is the easiness of cleaning. To clean chromed zinc is easier than to clean other surfaces: the metal has an hard and smooth surface that lends itself well to be polished and on which it is easy to find, and to remove, stains and rings. The added value determined by an appliance that is easy to clean is not only aesthetical because, in this case, also cleaning variables intervenes, which are particularly important if the object is intended for the treatment of food.

Recyclability

In the last few years, consumers gained an always greater awareness in matter of environmental sustainability and recycle. The search for easily disposable products and with little environmental footprint has been able to modify markets that were solid and it caused changes in sales and supply chains. Household appliances, characterized by a quite long life time are an excellent source of recyclable materials. Zinc is a valuable material that offers the possibility to be recycled repeatedly and that allows C2C productive practice, namely the kind of production that from the beginning establishes the re-employment of the used materials. Therefore, for the consumer, choosing household appliances with zinc components proves to be a guarantee of recyclability and eco-friendly practices.

To know more about the advantages connected to recyclability in the production of Zamak components for household appliances we suggest you to read White goods: improving sales through sustainable choices.

Case studies

The household appliances with Zamak components can be large or small and intended for professional or domestic use.

Below we present three case studies, the first one is about a small coffee machine intended for the consumer market, the second one is about a professional coffee machine and the third one is about a component for white goods such as the hinge for washing machines.

Appliance for domestic use: coffee machine

Among the zinc alloy components for household appliances we would like to focus on a component of the coffee machine: the cup support, a functional component with a primary aesthetic quality.

The optimization of this product started with a PDCA study that made it possible to consider and to analyze all the phases of the process and to undertake the actions necessary to optimize it.

Thanks to the study it has been possible to identify the appropriate parameters for the regulation of the fusion and for the filling of the mold and the time intervals necessary to optimally complete the productive process. Thanks to the results of the analyses conducted during the simulation phase it has been possible to estimate the changes in the superficial quality and the cycle time variations depending on the temperatures of the mold.

Moreover, thanks to the results of the study, it has been possible to focus the attention on the most value adding actions to the entire productive process: this way it has been decided to make the production more effective with the introduction of an automation dedicated to the processing of the components.

In particular the automation concerned the superficial treatment of the cup support, a component that, due to its particular shape, could not undergo processing of the internal surface before chroming phase. For this reason it has been identified a mold filling that allowed the reduction to zero of the faults in the not workable part. Furthermore, already during the die casting phase, a superficial roughness such as to allow a good result of the subsequent chroming treatment was obtained.

To deepen this subject we suggest you to read the article Zinc Die Casting for small appliances: components for coffee machines and to watch the video Die casting for household appliances: coffee machines 

It is possible to gather more information on the future development of the coffee machines market reading the article Using zinc in die casting for smart coffee makers.

Appliance for professional use: coffee machine

Professional appliances have to meet the expectations of the workers that use them daily and of the consumers of the service made possible by the appliance.

The professional coffee machine we are discussing in this case study is an example of the above mentioned situation: the appliance has to be considered efficient by the professional but it also has to give the same impression to the less expert eye of the customers.

A challenge, in manufacturing components for this product, has been to realize a chromed wall with the name of the appliances brand imprinted on the surface.

The obtainment of a writing in relief directly during die casting does not allow the component to undergo the polishing operations that components to be chromed usually undergo. For this reason it has been implemented a strategy aimed at obtaining a surface suitable to be chromed right after die casting. Studies conducted with special simulation software allowed the right injection and outlet points to be found and to be moved to the internal wall of the component in order not to affect the surface quality. Moreover, filling flows have been optimized to obtain a surface without air inclusions and porosity and the vacuum valve allowed a further reduction of these faults bringing the scrap rate close to zero.

Only zinc could have allowed this result: with other materials such a thin relief and a superficial quality such as to guarantee an excellent result of the galvanic treatment without previous preparations could have not been obtained.

On International Zinc Association website it is possible to read a data sheet of this product with a brief description of the optimization process  undertaken for its components.

White goods: washing machine

The hinges for the washing machine porthole are a functional component that can be produced in zinc. An interesting aspect, related to the realization of this product, is the necessity to assemble plastic bushings on the die cast. To optimize this productive process  it has been found the solution to design an automation able to perform the necessary semi-automatic assembly operations. Thanks to the system controlled remotely by PLC it is possible to place the hinges in different positions according to the version to be assembled. The introduction of this automation allowed the reduction of the cycle time and of the manual contribution of the operator with a consequent cost reduction. Moreover, automation has allowed precise outputs to be obtained, compliant with high qualitative standards.

For more information and to watch the machine for the semi-automatic assembly in action watch the video Bruschi – Die casting for household appliances: hinge for washing machines.

These are just some of the components for household appliances that it is possible to produce in Zamak, in fact, as mentioned above, the great versatility of the material allow a wide range of solutions to be created.

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Zinc alloys are an excellent material for the production of resistant, aesthetically appealing and complex shaped components: they can indeed be used to meet the requests of various and different industries, from automotive to building sector, ensuring high performance standards, both from a functional and an aesthetical point of view. Taken into account the different characteristics required by each sector it is therefore fundamental to conduct a thorough analysis of zinc alloys with the aim of identifying the most appropriate one for the purpose we would like to reach, examining the requirements of the product and looking for a zinc alloy with the right properties to meet these demands.

In order to conduct this analysis it is essential to know zinc alloys classification, which can be divided into two main categories: ZAMAK alloys, whose name is composed of the word Alloy followed by a number on the basis of their sequential development, and zinc alloys classified with the prefix ZA, which have a remarkable higher percentage of aluminum compared to the previous ones and are therefore provided with a greater resistance.

At the beginning ZAMAK was a trademark registered by New Jersey Zinc Co., the first company to use this specific alloy, but with the passing of time it has been chosen as the common name to define all zinc alloys for die casting. Only with the development of numerous types of alloys the nomenclature of zinc alloys has become more structured, as we have seen with the distinction between ZAMAK and ZA alloys: however, ZAMAK is still considered the most common and conventional name to indicate a zinc alloy.

This acronym indeed defines a zinc alloy composed of four main metals: zinc, aluminum, magnesium and copper (Kupfer in German). These elements occur in zinc alloys in different percentages: alloys indeed differ on the basis of the concentration of each metal, thus showing different characteristics that affect the features of the diecast. These characteristics are crucial for the choice of the most suitable zinc alloy for one’s own technology and production process. ZAMAK can indeed be worked with different production processes: hot chamber die casting, cold chamber die casting, spin casting, sludge casting and gravity die casting. In this article we are going to focus on the best zinc alloys for hot chamber die casting, the technology that Bruschi employs for its business.

The main zinc alloys used for hot chamber die casting are:

• Alloy 2
• Alloy 3
• Alloy 5
• ZA8

ZA8 is the only alloy, among the previous ones, that does not belong to ZAMAK classification because it contains a high quantity of aluminum that categorizes it as ZA: it is however an especially suitable alloy for hot chamber die casting and for this reason it has been included in this analysis.

As anticipated, these alloys have different compositions: they are indeed composed of the same elements but they are dosed in different percentages, so as to enhance specific characteristics such as resistance or fluidity. The following table shows the composition of the previously listed zinc alloys, defined by the European regulations EN 12844 European Standard for Zinc Alloy Castings and EN 1774 Zinc and zinc alloys – Alloys for foundry purposes – Ingot and liquid:

Zinc alloys chemical composition

The table highlights the different concentrations of the materials in the different zinc alloys, especially aluminum and copper concentrations: these two elements are indeed the ones that mainly influence the characteristics of the alloys.

Zinc alloys for hot chamber die casting

Alloy 2

Alloy 2 is characterized by high resistance and hardness: it is indeed the most resistant alloy among all zinc alloys. Aluminum percentage is equivalent to that of Alloy 3 and Alloy 5, while copper quantity is definitely higher: it can reach 3,3% and it is precisely this high copper percentage that provides an excellent resistance to the alloy. However, over time such a high amount can lead to the alteration of specific characteristics of the alloy: during metal aging it is indeed possible to observe some issues related to dimensions, such as a small dimensional variation. Furthermore, due to aging, the alloy can be subjected to performance decrease, which can reach levels similar to those of aluminum alloys: as a matter of fact, the main disadvantage when employing Alloy 2 is related to performance reduction, particularly a reduction of ductility over time. Despite this performance loss caused by aging, Alloy 2 is an excellent material for die casting thanks to its exceptional castability and creep performance, as well as its ability to maintain high resistance and hardness standards also during long-term aging.

Alloy 3

Alloy 3 is the most popular zinc alloy in North America: it is indeed the mostly used alloy because of its excellent castability and dimensional stability over time. Alloy 3 has a superior dimensional stability compared to the other alloys, however this high stability degree is only significant when very narrow tolerances are required. As far as resistance is concerned, Alloy 3 is characterized by a low percentage of copper that implies a lower resistance compared to the other zinc alloys but, at the same time, it reduces the likelihood of alterations due to material aging, thus avoiding dimensional shrinkage and maintaining a constant performance over time. This zinc alloy is also perfect for the production of components that need surface treatments, such as plating, painting and chroming.

Alloy 5

Alloy 5 is the most commonly used zinc alloy in Europe. This alloy has outstanding castability properties and, compared to Alloy 3, it contains a slightly higher copper percentage that gives the alloy a superior resistance and hardness, as well as a better creep performance. This higher copper quantity is though responsible, as previously seen, for an inferior ductility that can affect the processability of the alloy during secondary operations such as bending, riveting, pressing or crimping. Similarly to Alloy 3, Alloy 5 is an excellent choice for products that require surface finish treatments.

ZA 8

ZA8, as suggested by the classification ZA and not Alloy, is characterized by a chemical composition that has a high aluminum amount, considerably higher compared to the other zinc alloys. This high aluminum concentration provides the alloy with a superior resistance, hardness and creep performance in relation to the other alloys, except for Alloy 2 that has very similar features. ZA 8, like the other alloys, is appropriate for surface finish processes such as chroming and painting.

Main characteristics of zinc alloys

Through the analysis of the chemical composition of zinc alloys it is therefore possible to define which alloy is the most appropriate for one’s own sector, not only on the basis of mechanical and physical properties of zinc alloys, but also with regard to the features of the product that has to be realized.

The choice of the best zinc alloy for hot chamber die casting indeed starts from an examination of the characteristics of the component:

• Which are its most significant features?
• Is it an aesthetical or a functional product?
• Will it undergo surface treatments?
• Does it require a higher resistance or a greater dimensional stability?

Answer similar questions and therefore conduct a careful analysis of the requirements of the product is indeed the first step for the choice of the raw material.

Once the main characteristics of the product have been identified, it is possible to analyze the properties of the different zinc alloys.

As their previous descriptions report, the most significant characteristics of zinc alloys are castability, resistance, hardness, dimensional stability, creep performance and suitability for surface treatments. Now we will see these properties in detail.

Castability

The four zinc alloys mainly used for hot chamber die casting have all an excellent castability: it is exactly this feature that makes them specifically suitable for hot chamber die casting. High castability levels allow the die caster to produce components characterized by very thin walls, which are lighter compared to components produced with other metals. This ability to obtain minimum thickness leads also to a remarkable saving in terms of costs.

Resistance and hardness

Zinc alloys with the highest resistance and hardness are Alloy 2 and ZA8. Alloy 2 indeed contains a high copper percentage that gives it a particular resistance, while ZA8, despite having a copper amount similar to that of Alloy 5, is more resistant and hard thanks to the extremely high aluminum percentage (8,0-8,8%). These two alloys are therefore perfect for the production of components that need a great resistance and hardness but do not require specific dimensional parameters.

Dimensional stability

On the contrary, products that need a high dimensional stability over time should be produced using Alloy 3 or Alloy 5. These two alloys have indeed the right copper percentage to ensure a good resistance, while at the same time assuring dimensional stability over time. They are an excellent choice for the production of components with very complex shapes that require minimum dimensional shrinkage in order not to compromise the functionality of the product as time goes by. Thanks to this balance between resistance and dimensional stability Alloy 3 and Alloy 5 are the most widely used zinc alloys respectively in North America and Europe.

Creep performance

As far as creep performance is concerned, the most efficient alloys are Alloy 2 and ZA8. However, also Alloy 5 has a good creep performance, superior to that of Alloy 3, consequently it is more suitable to be used at high temperatures under a continuous stress.

Surface treatments

All zinc alloys listed in this post are appropriate for surface treatments: high fluidity of ZAMAK allows the die caster to apply various kinds of finishes, from chroming to powder coating. Zinc components can be worked in order to achieve almost every type of surface finish desired, thus obtaining aesthetically appealing products thanks to a shining chrome finish or a painting with intense and vivid colors, as well as smooth and silky surfaces thanks to satin finishing.

How to choose the most appropriate zinc alloy

Ultimately, to choose the most appropriate zinc alloy for one’s own product it is essential to focus on two main concepts: which are the characteristics that the final product should have and which are the properties of the zinc alloy that are fundamental to achieve these characteristics. If the component must be specifically resistant because it will be exposed to a high stress during its life cycle, then it will be more advantageous to choose Alloy 2 or ZA8. On the contrary, if the component needs a high dimensional stability level because it has very narrow tolerances, then it will be more convenient to choose Alloy 3 or Alloy 5.

Each product has specific and unique technical features that must be carefully examined in order to identify the most suitable zinc alloy, thus enhancing as much as possible the final outcome. The die cast supplier is consequently a valuable help when looking for the best zinc alloy to use because, thanks to the experience gained in different sectors and to the deep knowledge of the raw material, he or she can give precious advice for the achievement of the requested performance.

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1. DESIGN FREEDOM

Zinc, more precisely zinc alloys (ZAMAK), is a material that allows the production of components having nearly any type of shape. Thanks to zinc it is possible to obtain very thin surfaces that could not be achieved with other materials, such as aluminum. This results in a wider freedom in the design of a component, with consequent uniqueness and distinctiveness of the produced piece. Zinc thus represents an exceptional metal for the manufacturing of components which result complex from a shape perspective.

The following table contains zinc and aluminum values of minimum wall thickness: 

By choosing zinc for the production of small appliances it is possible to achieve several advantages related to the quality of the components, as zinc alloys present stable shrinking and high resistance. For example, compared to plastic materials, zinc presents a better typical precision and a superior yield and tensile strength (Table 1): these features result in a higher design freedom, not to mention remarkable qualities of the final product.

Table 1 – Typical Precision, Yield Strenght and Tensile Strenght values for zinc and plastic materials

2. HIGH END AESTHETICAL TREATMENTS

Several superficial treatments can be applied on zinc alloys. Specifically, it is possible to enhance aesthetical characteristics of the components through treatments which transform the product and improve its finish. The main aesthetical treatments realizable on zinc are:

• Galvanic treatments: polished chrome finish, satin chrome finish, different colors finish
• Liquid Painting
• Powder coating
• Special treatments to avoid material wear

Furthermore, specific treatments that take advantage of the physical properties of the alloy can be realized on zinc components. Among the mentioned treatments, powder coating is a brilliant example of an aesthetical treatment achievable through powder electro-deposition and cooking at high temperatures (around 200°C). This type of coating permits to obtain a better texture to the touch compared to painting. Realizing this treatment on a zinc component lends to it a significant added value.
Materials treatments generally follow the trends of the reference sector. A limitless variety of solutions that can be applied to zinc can help to fulfil this variable requirement.

3. SUPPLIER’S SUPPORT

A customer that relies on a qualified zinc supplier can discover in its vertical experience the ability of working on design too and to recommend to its customers innovative layouts and special finishes. This service, known as co-design, is the collaboration between client and die casting supplier, which aims to realize a product with specific functions and mechanical features that is at the same time compliant with manufacturing processes. Co-design can help designers to deeply understand zinc properties and to fully take advantage of their supplier’s know-how.
Zinc is a versatile material that allows experimenting with shapes and designs, thus permitting the conception and creation of unique and original pieces. As zinc die casting represents a very vertical market, its suppliers have a deep and vertical knowledge of the subject and can support customers in the production of distinctive pieces. The adaptability of zinc alloys proves especially helpful as far as small appliances are concerned: whereas other products are more standardized and creative design is limited, small appliances turn out to be a suitable product to test zinc versatility. As they are composed of several components, it is possible to imagine a wide variety of solutions with the use of zinc alloys, thus implementing the appearance, the performance and the distinctiveness of a product.

4. CUSTOMER EXPERIENCE

A further aspect that has to be taken into consideration when selecting a material is the customer experience. The relationship between end user and product consists of several variables, such as performance and usefulness, but also visual appearance, texture and durability. Zinc components convey excellent perceptions in terms of visual impact and touch feeling. A product made of zinc is more likely to be perceived as clean, resistant and of top quality.
As regards these features, it is essential to consider that the consumer has access to the use of small appliances through handles and buttons. If the body of the product is made of plastic, the handle or the button should be made of zinc, in order to offer the user a different experience in the use of the product. These details enhance the customer experience and make the difference in the customer’s choice of a product.

5. CLEANING OF COMPONENTS

From the end user’s point of view the ease of cleaning of a product is an aspect that influences the purchasing choice. For example cleaning chromed zinc components is easier compared to other surfaces, because they present a hard, solid and smooth surface. A product with these characteristics simplifies the cleaning process, making it quicker and more efficient: this results in a benefit for the consumer. Not only chromed zinc components are easy to clean, but they also convey a perception of neatness and brightness that impacts on the consumer’s eye. These qualities make zinc components stand out compared to other surfaces.

6. ZINC RECYCLABILITY

Virtuous companies are increasingly looking for sustainability. To support a sustainable development it is advisable to use recyclable materials, one of which is zinc. Zinc alloys can be re-melted and re-used several times without detriment to their properties. Normally the use of re-melted zinc alloys is limited to roughly 50% and this enables to completely exhaust production scrap. Today the implementation of this recycling system allows recycling a great number of zinc die casting scraps. Zinc thus represents a material with very low toxicity, not energy intensive to produce and recyclable. These properties make zinc an “environmentally friendly” material. 

7. REDUCED LEAD TIME

Lead time is the period of time that a company needs to fulfill a customer’s request in terms of supply. Logically, a short period translates into quicker results and a more satisfied client. In order to achieve this condition, zinc represents an efficient material thanks to its reduced cycle time. As a matter of fact, lead time is a concept related to cycle time: the period of time required to complete the manufacturing of a product, including every single process that leads to the finished product. Considering the cycle time of a product it is therefore possible to assume its related lead time. By choosing zinc instead of other materials, such as aluminum and plastic, lead time will be shortened, resulting in a more efficient and quicker service.
As mentioned above, cycle times related to zinc alloys die casting are lower compared to cycle times of aluminum alloys and plastic materials. In the first case, aluminum is molded at significantly higher temperatures, therefore the cycle time is superior due to cooling range. As far as plastic is concerned, it has superior filling times.
Below a table indicating values of cycle times of zinc alloys, aluminum alloys and plastic materials.

Table 2 – Typical production speeds and Broad production speed range for zinc, aluminum and plastic materials 

CASE STUDY N.1

Bruschi produces several components for coffee machines. In this specific case a client has contacted Bruschi to realize a cup holder tray for a coffee machine. The tray has been entirely realized in zinc and completely chromed. The entire surface of the component is considered aesthetical surface because the exterior is visible to the user’s eye and the interior becomes visible when the consumer removes the plastic cover and has access to the internal part of the tray to clean it.

The chrome process is composed of preliminary phases for the piece preparation. Particularly, the component has to be cleaned and polished through the use of rollers, tapes and scraping material. It is necessary to clean the internal part of the component too. For this reason Bruschi has conceived some alterations to the technological process that have allowed the achievement of an equivalent result.

Bruschi managed to solve the problem and produced a cup holder tray made of ZAMAK, externally and internally chromed.

CASE STUDY N.2

In this second case a client has requested to Bruschi the production of chromed handles for coffee machines. The complexity of realizing this component lied in its layout, in productivity and in the superficial quality. The handle was a particularly critical component because the standard mold cavities layout did not allow achieving the performance and costs level demanded by the client. Thanks to the experience and the expertise of Bruschi’s designers, Bruschi has conceived an alternative method to supply the mold. Designers have thus created a new mold that was compliant with the criteria demanded. Thanks to the new layout costs and performance levels have reduced.

In conclusion, the use of zinc for the production of coffee machines components generates remarkable advantages. By preferring the employ of zinc it is possible to design and create a functional and aesthetical product, able to combine design freedom and high-end aesthetical treatments, together with a proper balance between costs and production levels.

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You can find a full list of discussed topics in our first post on the subject, by clicking here.

CASE STUDIES AUTOMOTIVE: Surface aesthetical quality

The subjects of this case study are the thin plates in car vents that direct and control air flow in the car’s passenger compartment.

The vents for air flow control are usually made of plastic, but the object of our case-study is the central plate, used by the driver to direct the other air ducts and therefore made in alloy.

This product poses challenges especially for the surface aesthetical quality, because of its exposed position in plain sight inside the passenger compartment, the high-end car on which the vent will be installed and possibly the criticalities of surface treatment after die casting.

OBJECTIVE AND PHASES OF THE SIMULATION

The simulation analysis will thus focus on engineering an optimal flow through the feeders to avoid defects such as flow marks and blisters in the product.

In the first phase of the process we studied the effect of various runner configurations, one by one, to identify the runner with the best characteristics. Then we improved the shape of the runners, especially at the entry of the die.

The objectives sought in the various phases of the simulations were:

• Filling consistency of the die according to a main flow direction
• Decrease of the probability of cavitation to increase the speed of flow
• Reducing the filling time and keeping the alloy at a high temperature during this phase
• Absence of air bubbles in the product

RESULTS

In the study of product surface quality, the main parameter to consider is temperature. The temperature must be maintained the highest and the most consistent possible throughout the duration of die filling up to the end of filling process, especially in parts of the product that will be in full sight.

The images portray the analysis results at filling cycle end: the temperature is sufficiently high and homogeneous, with even better characteristics in the top surface, which requires a higher level of quality since it will be visible in the compartment of the car it will be installed in.

From the velocity field analysis it is possible to observe the feed direction and the speed modulus at the die entry point: a particularly critical point because it is often subject to cavitation phenomena, causing die wear.

By looking at the picture, we can notice filling consistency and that the last volumes to be filled are close to the overflows, allowing the exit of the first alloy arrived in the die, because the temperature will be lower.

The velocity field, depending not only on the runner geometry but also on boundary conditions at die entry level, has been obtained by using process parameters common for die casting this kind of product. The speed pattern is sufficiently low even in the vicinity of the gates. This has a positive effect on manufacturing because it will allow to apply higher filling parameters without the risk of premature wear of the die.

The next image shows that the impact of the runners is well balanced: the two runners, identified by red and blue colorings, fill the die in a consistent manner. Proper functioning of the small runner on the left is confirmed: the presence of the orange color, as small as it is, is necessary to avoid flow marks.

The influence of runners (orange liquid) should be reduced but not zero: it’s presence may be necessary in order to avoid flow- marks in the entry zone.

And finally, the field that shows trapped air indicates a favorable situation: the air contained in the casting is not an issue because it distributed evenly across the volume and concentrated only at the sprues, granting the achievement of requested surface aesthetical quality.

All of these analysis confirm that the design and the filling system are optimized to obtain the best esthetic quality, granting a smooth surface that can undergo the required coating and contribute to the perceived value of car interior.

In conclusion, the simulation study allowed us to assure the best surface aesthetical quality for air flow vents, by analyzing four main factors: main flow direction, speed of flow, filling time and temperature, absence of air trappings. Thanks to the analysis of these factors, it was possible to optimize the casting process by redesigning the shape of the runners and thus to fulfill the requested levels of esthetic quality.

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Bruschi is a committed supporter of a service called co-design: a collaboration between customer and supplier that aims to obtain results which fully satisfy both sides. Client and supplier can thus exchange information and opinions, in order to focus on critical issues, technical characteristics and requested quality of the product. This service is fundamental to create a product compliant with the manufacturing process, technical functionalities and aesthetical characteristics that satisfy both costumer and supplier. The coexistence of functional and aesthetic features in a single product has always represented a central concern for Bruschi, which has led to the conception of the business philosophy of functional beauty. According to this philosophy, a product is composed of functional elements and aesthetic characteristics that coexist and influence each other.

The intersection of co-design and functional beauty, together with its engineers’ expertise and manufacturing processes, allowed Bruschi to produce Nespresso KitchenAid Artisan 5KES0503, a design coffee machine which led the company to the victory of the prestigious European Zinc Die Casting Competition for design in 2016.

CO-DESIGN

As previously stated, co-design is a collaboration between client and die casting supplier and it is fundamental to obtain a product that can satisfy technical requirements of functionality and be at the same time in compliance with the process of die casting. This kind of approach is strictly related to the partnership between supplier and customer: co-design makes it possible to analyze every detail of product design and process design in depth and it helps strengthening the cooperation day by day. By applying this approach, every stylistic excess and useless characteristic will be eliminated: once only functional part remains, it is possible to concentrate all the efforts on improving the appearance of the mechanical part, granting eye-catching products. This method helps to improve the production process, to cut costs and to have beautiful products fitting the theory of functional beauty.

FUNCTIONAL BEAUTY

According to Bruschi, functional beauty is based on the removal of needless details while focusing on enhancing the aesthetic qualities of the remaining functional parts. The coexistence of aesthetics and performance is the core of functional beauty: a cosmetic requirement can therefore become a functional advantage and vice versa. These theories come to life through the collaboration between Bruschi and Kitchen Aid, thanks to the common efforts on the choices of alloy and shapes of the covers, on the way to reduce weight and on the surface finishing with the idea of reducing the useless parts and to improve aesthetically the functional parts.

THE CASE OF NESPRESSO KITCHENAID ARTISAN

Zinc is the ideal material to deliver this concept, since it can be used to obtain both strictly functional components and highly aesthetical external parts, and everything between these two extremes. This adaptability of the material is best perceived in our ZAMAK housing for Nespresso KitchenAid Artisan. This designer coffee machine is composed of eight zinc pressure die cast parts, with weights between 2.2 kg and 75 g.

Bruschi collaboration with KitchenAid began with their idea of creating a new coffee machine characterized by stunning shapes and innovative finishing: the design included round and sinuous shapes that were to be enhanced by a bright red powder coating.

Surface finish was another focal point: the new design needed to catch the eye of consumers and the choice of KitchenAid signature color, also known as Bright Candy Apple red, would have guaranteed the result. However, the application of a powder coating would surely enhance every imperfection in surface finish.

CHOICE OF THE MATERIAL

During the co-design process, the first choice was what material to use to embody the philosophy of functional beauty: the selected alloy should have been apt to cast complex shapes and resist to the finishing and painting treatments required, in order to satisfy both functionality requirements and aesthetics of the product.

ZP5 was chosen over other materials for its excellent surface finish, strength, ability to cast very fine details and feel of quality at touch. The desired shapes would have been unachievable with other metals, since die casted zinc allows to create smaller draft angles, smaller and longer cored holes and thinner wall sections, while keeping the surface smooth.

This is an excellent example of how the functionality of the chosen alloy influences the beauty of the product: the creativity of designers would have been limited by material functionality and mechanical characteristics, preventing them from the creation of bold, innovative designs.

NO MACHINING

As the main goal was to achieve an ideally smooth surface, Bruschi team worked together with KitchenAid designers to create a beautiful design, with minimum machining and assembly work. Through a deep analysis of tolerances and shapes in joint positions, all of the eight parts were casted with no further need for machining operations. A study of draft angles of matching parts allowed to avoid any further operation in assembly process, granting the aesthetical continuity KitchenAid designers were aiming for: casting tolerances of 0.05mm between assembly holes were achieved, requiring no further adjustment during assembly and almost no secondary operations.

Furthermore, this purely cosmetic quality resulted in two functional advantages: the reduced machining brought cost reduction in the component production and the compatibility of the parts became a quick quality control, since it allows to instantly recognize deformed or defected casts.

SURFACE FLATNESS

The last challenge concerned surface flatness: these difficulties were overcome through a close collaboration between Bruschi team and KitchenAid technicians. Defining together the criticalities helped in finding the best way to deal with them from design phase, avoiding mistakes in prototyping and reducing scraps.

In order to obtain the necessary surface quality the internal structure of the die cast should have been excellent and free of porosity, since during powder coating process the castings are heated up to around 200° C. In addition, the extractors and injection points must have been placed on the internal side of the component, to avoid leaving traces on the external surface.

For this reason, the right position of injection point and overflows were designed with MAGMASOFT, to guarantee the correct filling of the cavity while avoiding air entrapping and undesired porosity. The use of a simulation software to determine the positioning of extractors and injection point granted the right filling without leaving any marks on the surface.

To further reduce the risk of air trappings, Bruschi applied under vacuum die-casting: the use of vacuum valve allows the production of castings with no problem of blistering or bubble creation, resulting in a close to zero reject rate.

All of these efforts payed off: at the end of thermal curing of the powder coating, flatness of the surface was still within a tolerance of 0.3mm. An amazing result that is additionally enhanced by the luster of the final red varnish.

KITCHEN AID ENDORSEMENT

At the end of cooperation with Bruschi, Darrin Keiser – Kitchen Aid Small Appliances Global Senior Quality Manager – was satisfied and impressed with the result and declared: “My experience with Bruschi has been a very gratifying journey. From the early days of the project where we had to choose a supplier with highly capable people, methods and manufacturing process, it was clear to me that Bruschi was a winning choice. Its team is committed to the high quality expectation our brand is associated with.”

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ZINC TECHNICAL SPECIFICATIONS

The large majority of die castings requires specific processes to meet aesthetic appearance requirements, to enhance wear resistance or provide a protective barrier against corrosion: most parts have to be improved with secondary operations before being shipped.

Some metals are more suitable for undergoing galvanic treatments, varnishing and painting than others: one such metal is zinc. Zinc is a quite dense metal, really durable and stronger when compared to different materials such as polymers. Die casted zinc also allows to create smaller draft angles, smaller and longer cored holes and thinner wall sections, thus conveying the possibility to develop innovative shapes. This, together with the possibility to use unconventional surface finishes offers a competitive advantage over competitors. By choosing to work with zinc, designers can choose between a wide range of surfaces treatments, giving different finishes and surface improvements.

Designers and project managers are always looking for new ways to improve products: a collaboration with a supplier could help them identify criticalities in design or solve pre-existing issue. In a co-design kind of collaboration, the supplier should suggest its client the best way to optimize the product for finishing, based on its expertise.

CHOICE OF MATERIAL & RELATIVE FINISHES

During the collaboration, the first step is selecting the right type of alloy and evaluating its performances while taking in account the final use of the component. The first point to be cleared is whether the component is going to be used indoor or outdoor:  in second case, a corrosion resistance treatment shall be considered. There are different types of corrosion depending on chosen metal and the surrounding environment. You can learn more about corrosion by reading this post.

Another issue to take in account is the necessity for a cosmetic finish: depending on the final application of the component, clients could request varnishing, painting, enamel, chroming or plating.

Once analyzed every technical aspect, it is important to study advantages of different kind of finishing such as zinc black, C&E conversion coatings, sprayed and baked liquid coatings, copper-tin-zinc electroplate, copper-nickel-chrome electroplate, mechanical plating, and epoxy and polyester powder coatings.

Zinc Black

In this process a thick black phosphate is conferred to the casting as an obstruction against humidity and corrosive environments. It is usually a pre-treatment where zinc plating is followed by a black chromate conversion coating.

C&E Conversion Coatings

These treatments are chemical immersions that give a protective film on the zinc surface. Their aim is to protect parts during storage or in indoor environments. Usually conversion coatings are followed by waterproofing substances or varnish to widen the range of their applications.

Sprayed & Baked Liquid Coatings

These types of coatings include different chemistries such as epoxies, polyesters, phenolic and urethanes.

Copper-Tin-Zinc Electroplate

The outcome of this process is a dull and silvery finish on the zinc surface. It gives zinc a correct protection but the finish turns to a black appearance.

Copper-Nickel-Chrome Electroplate

This finishing is one of the best against corrosion. It protects zinc surface against the acidity of subsequent baths, then is able to uniform the zinc surface finish and assure it a good electrical conductivity.

Mechanical Plating

This procedure regards placing parts in a drum with metal powders desired and a chemical activator, then tumbling these parts until the desired thickness of coating is reached. The coating is created thanks to a mechanical and chemical action. The advantage of this process is that it can be applied on all surfaces, also on inside corners. Final colorations depend on different metal combinations.

Epoxy and Polyester Powder Coatings

These coatings are used as powders in dry electrostatic process and then fused in an oven. Not using solvents during the process is an advantage, since it prevents the formation of solvent-caused defects

This list is not comprehensive of all the possible finishing, but it is just a selection of the most common zinc die casting finishing.

Now we will present a selection of case studies where these technologies have been implemented with a tailor made cut, thanks to the collaboration between client and supplier.

CASE HISTORIES

The use of Zamak in die casting processes allows a series of finishes, which would be impossible to obtain with other alloys, leading to products with both high technical coefficient and important aesthetic value.

Bruschi has a 70 years-experience with clients among several industries, which include automotive, lightning engineering, household electrical appliance, doors and windows locks. Having an extensive know-how that covers different fields allows the designer to provide alternative solutions borrowed from other industries and always ensuring top quality in material, processes, manufacturing and products durability.

CASE STUDY 1 – New finishing to avoid blistering

An important automotive player asked to Bruschi to produce a component already produced by other suppliers. Client wanted new solution to develop this particular component, because it had a scrap rate of over 25% due to blisters appearing after treatment of galvanic coating.

Bruschi worked focusing its efforts, involving its supplier network, to avoid blistering. The solution has been achieved by changing the finishing: turning from galvanic coating to passivation. This means a great saving in terms of scrap rate caused by blistering, that has decreased from 25% to only a few parts per million.

CASE STUDY 2 – New finishing to improve SST resistance

An important automotive player asked Bruschi a solution to improve the salt spray test resistance of an existing component that was already made in Bruschi to be assembled on subcompact cars. For the new project, the component should receive better treatments in order to meet requirements of luxury cars. In general, regarding surface of the component, the SST resistance is given by a particular kind of finishing.

For subcompact cars the resistance guaranteed was 120 hours, thanks to a surface treatment called Fe/Zn: however, this treatment was not suitable for luxury cars. To reach the new goal Bruschi had to push the resistance to 1000 hours.

Thanks to Bruschi expertise and supplier network, the client reached its goal by implementing a special galvanic treatment, which allowed SST resistance for over 1000 hours to salt spray test.

CASE STUDY 3 – Special painting instead of mat chrome treatment

For an important client in locks sector Bruschi developed a different process in order to decrease the scrap rate. In details, client required a mat chrome surface treatment on its components but, due to their complex geometry characterized by a high number of angles, it was impossible to guarantee the requirements requested and the scrap rate was out of control.

In collaboration with its suppliers network, particularly with the painter and a chemical company, Bruschi developed special paint to assure the same characteristics to components without the mat chrome treatment. By changing the technology the client had the same components, but less scrap rate.

These case studies prove the importance of surface finishing and how a collaboration with suppliers can help with reducing scrap rate by finding alternative solutions or creating tailor made surface treatments to obtain the best performances out of a component.

If you are interested in the topic of metal finishing, you can read our other posts on the topic:

1- Focus on Surface Finishing

2- Processing techniques for metal finishing

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First of all, it is important to point out that surface finish is different from surface finishing: the first refers to the texture of a surface, for example whether it feels smooth or rough at the touch, while the second one identifies all the industrial processes aimed at changing the surface texture.

Surface finishing include a wide range of industrial processes that can modify the surface of a manufactured item, product or component to reach and improve a property or a characteristic. Except for components made of noble metals, almost all metal parts need finishing after manufacturing. Different finishes can be chosen for different reasons: to improve the appearance of a product, to enhance chemical resistance, corrosion resistance or wear resistance, to improve or modify electrical conductivity, to remove burrs and other flaws and to modify surface texture.

Sometimes more than one of treatment can be applied at the same time, for functional or aesthetic reasons: for example, in order to achieve the best result, aesthetical treatments like chroming or varnishing are usually preceded by special treatments to prepare surface. There are different kinds of processing techniques: some can be used as a last step of finishing while others are used to prepare surface for secondary surface treatments. The choice of treatment depends on product design and on client’s requirements. Thanks to these kind of treatments, it is possible to prevent surface defects caused by external agents, that could damage the product.

Another reason to apply surface finishes is to improve a part functionality: for example, machining processes are used not only to smooth out sharp edges, but they can also increase roughness to grant a better grip on handles and similar components.

As stated before, most metals products requires finishing processes: the majority of aluminum, magnesium and zinc die castings will receive at least one post-casting finishing, depending on specifications of durability, protection and aesthetic requirements.

One of the most common processing used in die casting is deburring: burrs are extremely common and they constitutes a cutting hazard because of their sharpness. There are different techniques to remove burrs, from hand-made deburring to thermal deburring, done with specific machines. Deburring is often followed by a conversion coating to remove any remaining oil, die-cast release agents and other contaminants.

The conversion coating process consists in creating a coating on the surface of a metal part by making the surface react with a chemical. This coating is mostly used as preparation and primer for the final painting, but in some cases, it can be used as final finish: especially for functional components that will not be seen after assembly, the use of only one finishing can grant cost savings.

Nevertheless, sometimes strictly functional components can require more than one treatment too: when there are strict functional specifications, such as corrosion protection and heat dissipation, it is recommended to use a combination of conversion coating and functional coating to meet clients’ requirements.

To achieve the best result and avoid discovering after casting that a component is not suitable for a certain treatment, it is advisable to consult a supplier already in product design phase, as we will see in the next part.

THE IMPORTANCE OF COLLABORATION FOR SURFACE TREATMENTS

Today’s technology allows to obtain die casting products with excellent surface finishes. To achieve the best results and manage costs, it is essential to know in advance every process that should be applied to the product.

Applying surface finishing to die cast products involves multiple variables: forecasting eventual problems and finding solutions makes it possible to improve manufacturing time and increase saving, guaranteeing requested quality.

In manufacturing terms, products are defined by precise specifications and surface finish depends on functional or aesthetic requirements. Even if the most relevant aspect of product design is the final purpose of a component, it should be taken in account that treatments result can be influenced by shapes or geometry of products, and even cause surface defects.

For this reason the collaboration between costumers and supplier should be constant in every phase of product development through a co-design activity, in order to spot critical shapes and obtain a simpler and more defined process. This allows, for example, carrying out proper modifications of critical surfaces, edges and mounting features, to obtain components that require minimum surface preparation prior to application of a final coating. Design modifications are not always possible but, if feasible, they can lead to consistent enhancement in surface finishes quality.

As said before, it could be advisable to plan post-casting finishing process during design phase. In fact, design features impact directly on achieving particular surface finish: for example, the presence of hollows on the component could cause lacks of painting. To know more about painting defects, click this link.

A partnership between casting supplier and its customer can thus improve not only post-casting processing, but also final functional or aesthetical surface treatments, such as painting or galvanic treatment.

SOME SUGGESTIONS ON HOW TO OBTAIN A BETTER OUTCOME

As said above, there a few precautions that can help obtain better finishing results. Here are a few pieces of advice that can be applied before casting to obtain concrete advantages in terms of product design and finishing. It is a list of suggestions that can simplify processes, cutting extra costs during production phase and finishing.

Parting lines

Parting lines are one of the unavoidable consequences of die casting: where the two halves of the mold meet, a parting line will be formed. An early consultation with supplier on aesthetic features assures proper placement of necessary parting lines, to conceal trimmed visible edges and eliminate the need for post-casting edge polishing.

Countersinks

To assure integrity of tapped holes’ surface edge, leading threads can be protected from deburring or polishing with countersinks or counterbores placed on die cast holes for machining.

Wall thickness

Where needed and feasible, wall thickness can be created on bosses to avoid scuffing on surrounding painted surface areas.

Ribs

Well-designed ribs improve die fill and avoid resulting sink marks on surfaces. Short and stocky bosses optimize metal flow and insure integrity of the feature.

Radius

Using the maximum allowable radius for all internal and external corners improves cavity filling and makes it possible to reach all part’s surfaces with vibratory deburring equipment.

Housings

A good design of housings diecast corners can also assure complete filling of the die cavity and corners integrity.

Cast-in textured surfaces

During die construction cast-in textured surfaces can be produced on selected areas of a component by special preparation of the die.

These are just a few of the most common suggestions to improve the final outcome of surface finishing process and to reduce wastes during die casting, but an experienced supplier will be certainly capable of suggesting the most fitting solution for each product. Since there are multiple variables to consider related to a specific product, it would be impossible to make general suggestions applicable to all circumstances, for each case deserves deep attention.

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When products require a high aesthetic impact, painting is often the best choice thanks to its versatility: not only does it offer a wide variety of colors, but it also determines the final texture of the product. Different painting processes make it possible to achieve matt textures, shiny textures and even metallic textures at a lower price than galvanization. Moreover, painted products gain extra surface resistance thanks to additional layers and to passivating treatments preceding coating.

However, like every industrial process, there are many factors that can compromise the final result. When working with die casting, some errors are more common than others. For example:

• Hue variation
• Fizzing
• Blisters
• Deformation
• Peeling
• Lack of paint
• Pitting
• Thin or scarce layer
• Orange peel

Now we are going to describe these defects, along with their causes and how to prevent them.

Hue variation

Hue variations can affect a single component, which could present different colors in some areas or darker shades, but they can also affect different batches of the same product, so that the first batch would be of a different hue than the followings.

These discoloring can be caused by expired or poorly stored powder, by fumes blackening some parts of the product, by variations in temperature or in baking time between each batch.

During painting, components are heated up to ease the application of powder painting and could be exposed to UVA rays or heated up again, depending on the treatment and the required finishing. Because of this, it is fundamental that time and temperature set for the first batch are exactly the same as the following batches and that they aren’t changed during the production. In addition, temperature control should be performed with carefully calibrated pyrometers.

Fizzing

Fizzing appears like small bubbles, very similar to blisters but smaller in dimensions. They are usually in groups and sometimes bubbles can have a central hole. In most cases they are caused by water or solvents trapped in porosities on the piece surface and emerged after heating.

These trappings can be avoided by carefully cleaning and drying the components, for example by pre-heating them up to 100°C or by using warm air instead of steam to dry them.

Blister

Blisters look like bubbles adhering on the metal surface, usually not bigger than 8 mm. Generally, blisters aren’t properly a defect in painting, but defects in die casting caused by air trappings and porosity laying under the surface that emerged after component’s heating.

In order to avoid this problem, it is possible to improve the distribution of porosity in casting through the use of a simulation and to test each component by pre-heating it before moving on with the painting phase. As an alternative, it is possible to reduce baking time and use the lowest temperature possible to avoid blisters from emerging.

Deformation

This kind of defect is rarer than the previous one, but it is still important to know how to identify it: it occurs when a component can’t bear the heat and creeps after baking, or when painting supports apply an excessive strength on the component, deforming it. It can be caused by some defects in die casting process or by a bad design.

To avoid this problem, it is advisable not to use high temperatures and to check positioning on the hangers and strength applied by supports. In some cases it could be necessary to modify the product design: asking suggestions to a trustworthy supplier would be advisable, to make sure that the design is suitable for the chosen industrial processes.  This may sound like a simple advice, but it can prevent further complications and improve the overall functionality of the component.

Peeling

Peeling are areas in which the paint coating was applied unevenly or is easily removable. This usually happens due to surface contamination caused by oils, fats, oxides, powders but also fingerprints. It is an easily avoidable problem: a careful cleaning and the use of gloves to manipulate each component should be enough to prevent the formation of this defect.

Lack of paint

This defect is typical of electrostatic powder painting: with this particular technique, an electric field is generated between the tip of the painting gun and the component. Normally this helps powder paint to stick to the surface evenly, but when a component has sockets, hollows or ducts on the surface, a Faraday Cage could form and  make the electric field head toward low resistivity zones, such as channels edges, dragging along powder painting particles. As a result, there will be heaps of paint on the borders of the hollow, and a lack of it on the internal surface.

To avoid these situations and make sure that varnish may reach the inside of hollows, it is advisable to reduce painting gun voltage: as a consequence, strength of the electric field near the component surface will decrease too, improving penetration rate of particles through Faraday cage by weakening the force pulling particles towards hollows’ borders.

When designing a component destined to electrostatic powder painting, it is advisable to avoid deep hollows and steep curves, to prevent the Faraday cage effect.

Pitting

Pitting looks like small granules underlying paint coating. They usually appear in groups and are caused by presence of dust on the component. To avoid their formation it is necessary to assure a meticulous cleaning of both working environment and  components, even in storage phases, by cleaning them with electrostatic cloth or with compressed air.

Thin or scarce layer

The expression identifies those zones in which the paint coating is transparent or inadequate, which are usually located near the edges of a component. They can be caused by scarce quantity, linked to a low powder dosage, or by wrong spraying parameters, unsuited for the component shape.

In addition, there could be problems with grounding that cause interferences between electric field, preventing the correct sticking process. For all of these cases, the solution is controlling and correcting process parameters and defects.

Orange peel

As the name suggests, this defect makes the painted component surface similar to orange peel: instead of being polished and smooth, it displays small bulges that makes it feel rough to the touch. It is a defect caused by excessive thickness of the painting layers: in order to prevent it, it is necessary to check the correct operation of nozzles and their positioning, and to modify system settings to spray a thinner layer.

To sum up, we have listed the most common defects in die casting painting processes, analyzing for each of them the root cause and explaining how to prevent them. To avoid this kind of defects, the best solution is to relay on expert and trusted suppliers, capable of suggesting the best kind of pre-finishing for the desired painting process.

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Surface finishing has a crucial role in zinc alloy components production: often the main reason to choose Zamak for a component is the wide range of finishing and colorings available, either through plating or painting. For this reason it is important to know and learn to prevent defects linked to the final surface quality of the diecast.

Die casting surface treatments defects can be linked to many different causes, ranging from the quality of the casting to issues in pre-finishing or finishing phases. The term pre-finishing includes all the operations necessary to prepare the product for following treatments of electrodeposition or painting, such as deburring, vibrating, cleaning and polishing. Depending on the root cause, the kind of defect may vary, but some are more common than others.

Among the most widespread defects in die casting surface treatments, we find blisters and pitting: they can be caused by a number of factors, therefore it may be necessary a more in-depth analysis to identify the cause and proceed to correction.

In addition to blisters and pitting, there are three types of surface defects easily recognizable: burnings, nodules and flaking.

Blisters

Blisters look like small bulges on the surface of the components and their dimension can vary depending on the cause of their formation. They can be caused by errors in casting, pre-finishing phases or during electrodeposition.

Casting blisters

This kind of blisters can be caused by contaminants in the alloy, such as lead and cadmium, or by intergranular corrosion, but they can also be linked to defects in casting such as cold laps and surface porosity.

In this case, blisters are round-shaped and big, and they feel hard to the touch. For a better analysis it will be necessary to cut the blister with a sharp blade: it will be then possible to observe that, by sectioning the blister, the diecast will be cut too. These traits identify blisters formed due to underlying porosity in die casting phase: in order to solve this issue, it will be necessary to reduce surface porosity.

Pre-finishing blisters

As stated above, not all blisters are caused by casting defects: some can form due to errors in pre-finishing phases. For example, during the preparation of a piece for electrodeposition, special attention should be dedicated to the detection of oxidation, corrosion and other superficial contaminants. If the surface isn’t perfectly clean, groups of round blisters will form after electrodeposition: by cutting through these blisters, the underlying metal will be left exposed and, observing its section at a microscope, it would be easy to spot  the oxidated layer that caused the defect.

In order to avoid these situations, it is advisable to prevent delays between casting, cleaning and electrodeposition so as to reduce the chance of surface oxidation. When this is not possible, for example when relaying on an external supplier, another way to prevent blistering is to apply a corrosion inhibitive solution to the components and remove it right before plating. If, despite taking all the mentioned precautions, traces of oxidation are found on the surface, it is possible to remove it through mechanical vibrating or cleaning it with acids.

Blisters caused by electrodeposition

Another easily recognizable kind of blister is the one caused by a lack of adherence between nickel and copper layers, or between nickel and chrome. These blisters often pop up in large groups, have an irregular shape and can be found on the whole surface of the component, sometimes far from one another. Unlike casting blisters, they are soft and squishy and, after removal, the underlying copper or nickel coating will be visible.

The formation of these blisters can be prevented by making sure that the copper layer is sufficiently thick, by leaving the shortest possible time lapse between nickeling and copper plating and by regularly checking baths for contaminants.

Pitting

Unlike blisters, pitting is always caused by mistakes during pre-finishing or finishing phases. They look like small lumps whose shape and position can vary depending on the root cause. There are 4 main causes of pitting: solvents or corrosive liquids on the surface, gas trappings and hydrogen bubbles in the galvanic bath.

When pitting is due to solvent residues that prevent the correct adherence of copper layer, lumps will be disposed in circle or chains, whereas when the cause is an unexpected splash of corrosive liquid, pitting will be distributed in an irregular shape.

In the first case, to solve the problem it is possible either to modify the degreasing system, or to add a cooling bath between degreasing phase and plating phase. Temperature plays a crucial role in these phases: sometimes it can be enough to lower the temperature of the casting or to wait longer between liquid and steaming treatments to prevent the formation of pitting.

Instead, when pitting appears in irregular shapes, the solution can be to control the source of splashes and fix it, or to apply a thicker copper layer so as to cover the defect.

Sometimes pitting can be randomly disposed and look like small craters with high edges: this happens because during the nickel-plating phase some hydrogen bubbles in the galvanic bath stick to component’s surface. The presence of these bubbles can be caused by different factors:

• Inadequate mixing of galvanic bath
• Low level of surfactants
• Oily layer on the surface of nickeling bath
• Dust particles sticking to the piece’s surface

To prevent the formation of this defect, it will be necessary to monitor the amount of surfactants and the mixing of the galvanic bath, in addition to protecting the surroundings to prevent infiltration of powders.

One last kind of pitting is caused by the presence of gas and bubbles in the galvanic bath: bubbles stick to the surface of the component, creating round and deep pitting, close to each other and covering the whole surface. To prevent the formation of these defects, it will be necessary to spot the gas source and to check baths’ state.

Sometimes the solution itself is naturally rich in gas, which gets released as soon as the mixture reaches a certain temperature. In times like these it is possible to remove gas by overheating the solution, bringing it to an higher temperature than the one requested for galvanization process and cooling it down again before using it.

Burnings

They look like a brown spot and a burnt crown, and are caused by a high pitch in current density or by a contamination of the bath: this contamination can derive from the use of the solution, because during the plating process some zinc particles may detach from the component and alter the solution.

To avoid these formations is then sufficient to periodically change the bath mix or to dilute the solution by adding more electrolytes.

Nodules

Nodules look like small bumps that make the surface of the casting grainy: they derive from particulate matter depositing on the piece or in the nickel-plating tank. To avoid these formations it is advisable to periodically filter galvanic mixture and to be careful when cleaning the pieces.

Flaking

Flaking is caused by a faulty attachment of the external nickel layer: it looks like compact and long vines, with different shapes and dimensions. They are easily scratched with nails or a blade, and when removed, they leave the underlying coating on display.  

The root causes of these defects are identifiable thanks to their position: if detaching is formed between copper and nickel coatings, it may be caused by contaminated solution, delays in the process or insufficient activation. Flaking can also be formed between polished layer and semilucid nickel layer, and their cause is to be found in the passivation of the semilucid coating, whereas if the formation is located inside the polished nickel layer, it is usually due to flicks or current interruptions during the plating.

Generally, to avoid the creation of flaking it is necessary to keep the solution pure, or to monitor the current flow to avoid interruptions during the process.

To sum up, we have seen how working with chroming and electrodeposition on zinc alloy products can induce many surface defects that can be linked to casting defects or processing errors. Some can however be avoided through constant monitoring of galvanic baths and solutions, and a careful cleaning of the diecast and the working environment.

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