Industrialization of the product in zinc die casting

Industrializing a product means facing the entire design process taking into account the functional, qualitative and aesthetic specifications of the customer and of the construction technology, which in this case is the hot camber die casting of zinc alloys.

The industrialization of the product is therefore a complex process composed of various phases in which various departments intervene. Let’s analyze the delicate process that leads to mass production.

DFM

Already in the RFQ (Request For Quotation) phase, therefore still in the commercial phase, the project proposed by the customer is evaluated and analyzed in order to present an offer. Afterwards, once the sales process has been completed and the order from the customer has been received, the most substantial and vertical activities are undertaken. One of these activities is, for example, co-design: a phase in which the technical departments of the customer and of the supplier work together to optimize the product.

The study undertaken on the product, the co-design activity mentioned above, makes it possible to propose a series of activities aimed at increasing value and reducing costs, both as regards the product and the production process. The work carried out at co-design level culminates with the drafting of Design for Manufacturing, called in technical jargon DFM, a document that defines the most suitable shapes for the production process of the die cast and the tools that are necessary in the different phases of the process: mold, automations, frame for superficial treatments and others.

For a definition of DFM approved by the scientific community and for additional related information we recommend visiting the Society of Manufacturing Engineers website.

It is important to underline how the modifications suggested in this phase not only concern the aesthetic aspect or the functionality of the product, but also the resolution of problems emerged during the study phase: whether they are at product level, such as critical areas and deformation or too narrow tolerances, or at process level, for example it could be necessary to find alternative solutions for the configuration of the mold extractors.

For further information on DFM we suggest you to read the article Product design for die casting: how to speed up and optimize your DFM.

Kick-off

Once this initial phase has ended, it is time to bring together for a second time all the actors involved in the process with a meeting called kick off. The kick-off is the moment of the launch, typically it is a meeting called by the Project Manager in which all the departments involved in the realization of the project come together to discuss the production aspects. During the meeting, conducted by the Project Manager, the following areas intervene:

• Design: designers highlight the critical aspects of the product and the solutions identified at design level
• Quality: on the basis of the observations of the designers it identifies the elements on which it will have to focus its attention and the kind of analysis that it will be necessary to undertake to guarantee the respect of the requirements of the customer
• Production: it evaluates the technical aspects of the productive process and the relative criticalities, establishing machines, automations and processes necessary for the realization of the product
• Logistic: it manages the warehouse and its critical issues and the shipping of the goods to the customer
• Sales and marketing department: oversee communication with the customer at every stage of the project life, providing feedback on the progress of the processes

Kick-off is a very important moment because at the end of the meeting all the departments are ready to act together for the success of the project. At the end of the kick-off is therefore possible to start the construction of the tools necessary for production.

Sampling

During sampling phase the first samples, defined first off tool, are created. It is in this phase that the die casting mold and all the tools that will be necessary during mass production phase are tested.

All production departments contribute to the evaluation of the samples that are subsequently sent to the customer in order to obtain the approval.

Samples allow the verification of the compliance of the product to the requirements of the customer and the necessary analysis are undertaken by quality department and afterwards by the customer.

Samples, beside die casting process, can undergo different kinds of treatments. In some cases raw parts are sent to the customer, in other cases mechanical operations or superficial treatments are necessary.

In the case of superficially processed samples, external suppliers are involved. In this case it becomes necessary to carry out checks on the products arriving from suppliers and consequently on those delivered to the customer. In fact, it is important to monitor quality throughout the entire supply chain so as to guarantee to the customer products that are always compliant and that have passed strict controls.

Pre-Series

If sampling is aimed at the analysis of the quality and the dimensions of the samples the pre-series allows the verification, on a reduced scale, of the compliance to the established standards for the productive process.

In pre-series phase in fact the products are created with all the techniques and the processes that will be undertaken in phase of mass production allowing the verification of cycle time, of the production capacity of the plant and the respect of the parameters set in design phase.

Since the runs of the pre-series are limited and sometimes the product or the mold have to be subjected to modifications, in zinc alloys die casting it is advisable to carry out the pre-series, and the previous sampling, with prototypal molds. The prototypal molds do not have the lifespan of the molds for mass production but they are more suitable for the execution of modifications.

Importance of collaboration

We have seen how in the industrialization of the product expertise from different departments intervene at different levels and in different phases of the process. The operative bonds between the different departments become particularly evident in this phase and they are decisive in the functions of coordination, timing, management of the resources and project management.

Moreover, in industrialization phase the collaboration goes beyond the boundaries of the company and it involves customers and suppliers. In fact, the process of co-design can be undertaken only together with the customer and it is thanks to collaboration with the latter that it is possible to establish strategies aimed at reducing costs and at optimizing the product.

Also the collaboration with suppliers becomes fundamental because only through a careful monitoring of the entire production chain  it becomes possible to guarantee the quality of the products and to obtain the approval of the customer.

Conclusions

In this brief article we have described the phases that precede mass production of a component, then focusing on collaboration that is necessary for the success of any project, in particular in a delicate phase as the industrialization of a product.

In conclusion, we believe it is important to underline how, in this process, the Project Manager is a key figure that has to constantly monitor the processes and the contribution of every department verifying that, step by step, all the necessary operations are performed. It is only through the right collaboration that, in an articulate process composed by a number of steps, it becomes possible to achieve the goal in the best and efficient way.

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Introduction

In a previous post we discussed the importance of the metrology laboratory in a zinc alloys die casting productive plant. The metrology laboratory, in fact, assures the quality of the products throughout the production chain by guaranteeing the compliance to the requirements of the customer from a dimensional, structural and chemical point of view. The activities of the metrology laboratory described in the post Dimensional measurement: production control and reverse engineering are:

– Constant monitoring of each production cycle
– Fast checks of new projects and sampling
– Checks of projects that have undergone changes over time
– Control of parts incoming from external suppliers
– Reverse engineering, both on the product and the mold

To deepen these themes, we suggest you to read the post.

In this post we will instead examine different devices paying special attention to the need to choose the most appropriate tool on the basis of the characteristics and the requirements of the product.

Importance of the metrology laboratory

The presence of a metrology laboratory in the production plant is not enough to guarantee the quality of the products: in fact, this result can only be achieved through the employment of appropriate tools for the component to be tested. The set of devices must be up-to-date, advanced and comprehensive of different technologies, in order to allow the minimization of risks that is necessary to meet the requirements of the customer.

This is particularly true in a plant that employs zinc die casting technology for products intended for different market sectors: the variety of products corresponds to a diversification of the tools and of the technologies that the metrology laboratory needs in order to carry out its analysis.

To be specialized in different market sectors allows the competences acquired in a sector to be transferred in another and this is also true for the tests of the metrology laboratory. The choice of the tool in fact is not only determined by the requirements of the customer or by the necessary documentation in the different stages of a project, but it is also defined by the necessity to obtain the most indicative and effective data for the assessment of the compliance of a component with the design standards. The expertise acquired in the measurements of the components intended for a sector can then be transferred to the analysis that are necessary in another sector with advantages that affect the entire production chain.

The tools of the metrology laboratory

After depicting the importance of the metrology laboratory let’s now analyze the tools that allow the metrology tests to be complete and effective.

Industrial computed tomography

The technology of industrial computed tomography, referred to zinc alloys die casting, has a double usefulness. In fact, it allows defect analysis on the internal structure of the components aimed at detecting defects in the internal distribution of the material and thus at identifying porosity and air inclusions. Moreover, thanks to tomographic analysis, it is possible to evaluate the success of the assembly of components. In the case of the assembly of different materials the tomographic analysis allows a functional evaluation of the clearances between assembled parts and the verification of the absence of flaws such as air inclusions or deformations.

3D Scanner

3D Scanner is particularly suitable in the case of components with complex shapes. The device is less accurate than a Coordinate Measuring Machine (CMM), but it allows the capture, without contact, of all the visible surface of the measured object and it makes the comparison with the theoretical model possible. For this reason, whereas a test with CMM would be too time-consuming for the necessity of a complete reconstruction of the shape of the object, the 3D scanner allows the result to be obtained rapidly and effectively.

CMM

In a metrology laboratory CMM is surely the most common technology. The machine allows the selection of the desired areas and the execution of very accurate checks to be performed. For this reason, it is particularly suitable for the measurement of elements of components with simple shapes for which the tolerances are very narrow. However, the CMM does not guarantee the same results with different materials. In the case of zinc alloys, it is particularly suitable because the metal, differently from other materials such as plastics, does not run the risk of deforming during measurement.

Polyworks

Polyworks is the Innovmetric software that allows the tools of the metrology laboratory not only to be complete, but also complementary. What previously said about CMM and 3D scanner must not suggest that, during testing, a measurement method is to be chosen rather than another one. In fact, thanks to the software, it is possible to make the acquired data interact and to overlap the measurements of the 3D scanner with those of the CMM. For this reason, the software, allowing different data to interconnect, makes it possible to the metrology laboratory to unify its technologies for a complete and detailed final result.

UTM Machine

The Universal Testing Machine is the device employed in order to test tensile and compressive strength of a component. It is a very versatile machine that makes it possible to perform different kinds of tests on a wide range of materials and components. For example, concerning tests on zinc alloy die casts, the UTM is fundamental to work with the automotive sector. The verification of the resistance of products intended for this sector is in fact a fundamental part of the documentation that is necessary for the approval and the good outcome of projects.

In-line machine for the 100% dimensional control of production

This in-house designed and developed machine is intended to the verification of the compliance with the dimensional tolerances of automotive components. The device uses a camera for the detection of dimensions, volume and superficial quality of the components and a profilometer. The profilometer, thanks to laser technology, allows the reconstruction of the profile of the measured component and it is particularly useful for the reconstruction of the profile of complex shapes such as threads.

Other devices

Eventually, other common but fundamental devices in a Zamak die casts productive plant are the spectrometer, the density scale and the electronic microscope. The spectrometer allows the chemical composition of Zamak to be analyzed and it is of fundamental importance when, on the same machine, the mold is changed, and we move from the production of a component to that of another in different alloy. Thanks to the spectrometer in fact it is possible to verify that Zamak bath is concluded and that all the material employed in the process is the new one. The density scale is used to verify the compactness of the component and to exclude the presence of air inclusions or other similar flaws. Finally, the microscope makes it possible to detect superficial defects that would not be identifiable at sight, proving to be a valid aid in detecting cold laps, laminations, cracks and lakes.

For further information on the most common die casting defects we suggest you to read the article Die casting defects: internal and superficial.

Other tests

The various tests carried on in a metrology laboratory are aimed at measuring the dimensions of the components, their weight, the internal distribution of the material and their resistance. Moreover, other kinds of tests can be carried out, such as for example salt spray testaimed at evaluating the resistance of the component to environmental corrosion or the leak test that through the employment of dedicated tools, aims at verifying the absence of air inclusions in the component.

Conclusions

With this brief overview on the tools of the metrology laboratory we wanted to focus the attention on the importance of this department.

If you are interested in this theme and you want to be updated on the news of the sector we suggest you to visit Metrology News web site, an important online review rich in information on metrology tools and their employment in different industrial sectors.

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The case study concerns a component produced for the building industry and the related mold, which was built 10 years ago. Over the years the mold began to cause problems due to its wear condition: it was therefore necessary to study and examine mold design and to introduce significant changes, in order to reduce casting defects that emerged on the component.

In accordance with the lesson learned approach, Bruschi engineers have analyzed production performances of the component and defined new parameters on the basis of the knowledge they assimilated through the years. Furthermore, cutting edge technology, such as simulation software, has allowed Bruschi design department to foresee material reactions and to make accurate changes to mold design, in order to reduce casting defects. In this way, they have figured out new solutions with the aim of achieving a component that could meet the requested quality standards.

Elements that influence superficial quality of the diecast

Superficial quality of a component produced with die casting technology can, indeed, be determined by multiple factors, such as mold thermoregulation and temperature of the material injected in the cavity, but it mainly depends on the filling method of the feeder. The design of an appropriate feeder, which allows a symmetrical filling of the cavities, is therefore a fundamental requirement to avoid superficial defects on the product. On the contrary, an asymmetric or divergent feeder can cause air entrapment in the die cast, as well as areas with evident cold laps caused by irregular filling.

Case study

This case study is about a component that is part of a hinge for a door. After several years of component production with the first mold, the latter was worn out and it caused superficial defects on the product, such as cold laps, lack of material and porosity. Bruschi engineers have conducted an analysis of the parameters and of the geometry of the mold, after that they have identified the leading cause of the defects: the incorrect filling of the cavities. In order to solve this problem they have thus decided to design and build a new mold. With a view to reduce casting defects the design department has therefore modified mold design, more specifically feeder design.

Phase 1 – Simulation

The first phase of mold design project concerned simulation of the filling of the cavities with thermofluidodynamic simulation software Magmasoft, which allows foreseeing to a good approximation the behavior of the material during filling phase. With Magmasoft it is indeed possible to examine different parameters, such as temperature of the metal in every stage of the filling, air pressure in the cavity, material speed and presence of areas with air entrapments. For further information on simulation, here are some previous posts:

• Simulation for HPDC: surface aesthetical quality in automotive
• Simulation for HPDC: shrinkage porosity case study
• Simulation for HPDC: die maintenance and optimization of set up

Simulation has highlighted three main problems:

• Asymmetrical filling
• Divergent feeder
• Lack of homogeneity in the material temperature

To best define the corrective actions to implement engineers had to carefully observe product’s shape: the component has, indeed, a thicker upper section and a thinner lower section. The product’s geometry has thus requested a specific care during the design of the feeder because, in order to achieve a symmetrical and regular filling, it was necessary to add further elements that could facilitate the dynamic behavior of the filling fluid.

Phase 2 – Upper section design

Simulation phase has revealed that the filling of the upper section was asymmetrical and therefore caused air entrapment in the die cast, with consequent air bubbles presence on the component’s surface. The cause of the asymmetrical filling was ascribed to the different speeds at which the material started to fill the cavity. As a matter of fact, the fluid entered from the injection point with a high kinetic energy and continued its way by following the cavity geometry, which drove the material to fill specific areas that were thus quickly and more filled, reaching instead only at a later stage those areas that were not in the direction of the main flow.

The first problem to solve was therefore related to the asymmetrical entrance of the material in the gate: in order to symmetrize material entry in the cavity, designers have added a damper at the end of the main feeder. With the new configuration the flow, before dividing, fills the damper while losing kinetic energy and continues its way towards the cavity at a constant speed.

The second problem, still concerning the upper section of the die cast, was related to the divergence of the feeder in specific sections, thus causing the appearance of turbulences. Consequently, engineers have designed a convergent feeder, which has helped to better channel the material and to facilitate the filling of the cavity, thus reducing boundary layer separation.

Phase 3 – Lower section design

The lower section of the product is visibly different from the upper section. Indeed, it is a thinner part that, with the first mold, was filled by material at low temperatures thus causing the presence of cold laps and lack of material. By observing the component’s shape, it was indeed clear that a uniform filling was difficult to obtain, particularly in the lower section: the material filled in the first place the whole upper section, which is characterized by an important dimension, while it reached only at a later stage the lower section. Consequently, the material started to fill the lower section at a too cold temperature, such as not to guarantee an appropriate level of superficial quality.

With the aim of solving this problem, Bruschi team has designed a devoted feeding system through the addition of two auxiliary runners. The runners have been added to the lower section of the component in order to achieve a regular filling, by maintaining a stable material temperature in the entire die cast. The two auxiliary runners, as well as the main feeder, have been designed in order to obtain a symmetrical flow: to achieve this result engineers have added two further dampers to the auxiliary runners.

In addition to that, considering the particular shape of the product, in order to further facilitate the filling in the whole cavity, engineers have designed a partially tangential in-gate capable of channel the material in critical areas. The lower section presents, indeed, some inserts that, without this type of gate, could potentially obstruct the material flow, thus impacting on filling uniformity. This kind of solution therefore determines a better material distribution, by facilitating its entrance in the cavities and the reaching of the most critical areas.

Achievements

After having modified mold design engineers have conducted the simulation of the filling of the cavities with the software Magmasoft and have obtained excellent results: the previously observed critical issues have indeed remarkably decreased. Specifically, through the design of a new feeder, designers have achieved a higher filling uniformity, which has consequently determined the reduction of casting defects on the component’s surface.

This case study therefore confirms the importance of knowing how to draw on previous experiences for the resolution of new problems, by combining know how and technology in order to achieve increasingly outstanding results. Mold design and Magmasoft have allowed designers to test various solutions before proceeding with the actual production of the component, thus obtaining relevant benefits in terms of quality, time and costs.

To get updates on trends and innovations in the Zinc Die Casting industry, you are welcome to subscribe to our blog.

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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.

To get updates on trends and innovations in the Zinc Die Casting industry, you are welcome to subscribe to our blog.

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As the Journal of Industrial Engineering International reports, customers are more and more calling for environment-friendly products and this demand puts pressure on the whole supply chain, because it involves manufacturers, suppliers, retailers and customers. The latter are asking for a greener supply chain that promotes environmental protection and, at the same time, are also developing a well-defined purchasing behavior, which avoids unsustainable products and services. Businesses are therefore studying new methods in order to reach green supply chain management (GSCM), the integration of environmental issues and supply chain that results in reducing manufacturers’ impact on environment while enhancing an organization’s performance.

White goods recycling system

As far as white goods are concerned, emphasis is placed on their recycling cycle: manufacturers must therefore focus on materials. According to AHAM, the Association of Home Appliance Manufacturers, household appliances are increasingly being recycled: they are overtaken only by automotive industry as a source of recycled materials. The growing interest towards recycling has allowed to achieve significant results in the household appliances industry, also thanks to the United States Environmental Protection Agency, specifically with the Responsible Appliance Disposal (RAD) program, which in 2017 has recycled almost 70 million pounds of ferrous metals, 4 million pounds of nonferrous metals, 17 pounds of plastic and 3 million pounds of glass. As data highlight, consumers are increasingly aware of the importance of recycling and are more and more adopting a responsible and sustainable purchasing behavior: white goods industry is therefore continuously renovating and appliances’ manufacturers must face new challenges that environmental consciousness generates, developing products with recyclable materials through sustainable processes.

Metals recycling

White goods are characterized by a long life cycle, normally 10 to 18 years, and when they are no more usable they provide a consistent amount of recycled materials, specifically metals. As stated by The Global Metal Waste and Recycling Market report, the most recycled metals are iron, steel, aluminum, copper, lead and zinc; in addition to that, the report indicates the leading recycling industries, which are building, automotive, shipbuilding and consumer appliances. Metals are among the main materials that undergo a recycling process: they are perfectly suitable for recycling, indeed metals are valuable, can be easily transported thanks to their density and, furthermore, they present properties that allow them to be recycled repeatedly. In the U.S. metal recyclers manage thereabouts 120 million tons of recycled metal every year, with the metal recycling industry having registered nearly $27 billion in 2018.

Zinc recyclability

White goods are complex machines composed of several elements and different materials, among which zinc represents an intelligent and recyclable choice. As a matter of fact, zinc has exceptional metallurgical and chemical properties that remain unchanged also after recycling process, making zinc a suitable material for a wide range of modern products, such as white goods and small appliances.

To calculate zinc recycling rates experts rely on two main methods: the End of Life (EoL) recycling rate and the Recycled Content. Usually EoL is preferred because it measures the quantity of available zinc recovered at the end of product life and recycled, whereas the Recycled Content approach considers the amount of recycled material in a given product. Recent analyses report that around 45% of zinc at the end of life is estimated to be recovered and recycled; in developed regions, such as Europe and North America, this percentage reaches 50%.

Typical Recycling Rate Indices

What is more, zinc not only is itself recyclable, but also contains numerous substances that are recyclable: this quality certifies zinc as Cradle-to-Cradle (C2C), a concept inspired by nature that promotes circular economy. According to this approach a product is designed already considering future reuse and, at the end of its life, it is seen as a new source instead of waste: materials and elements that compose the product are thus recovered and again inserted into the processing cycle.

Zinc benefits in white goods manufacturing

Taking into consideration customers’ request for quality products manufactured with sustainable practices, zinc constitutes an ideal material for white goods components. Indeed, zinc presents high recycling rates and excellent aesthetical quality, combining two of the most demanded characteristics by end-users. Highlighting zinc properties can therefore be an efficient promoting strategy, thus meeting customers’ expectations, providing environmental-friendly solutions and improving selling rates.

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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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Considering the metrology room as a part of production process is an advantage: it becomes an integral part of the process, such as the design of the die, machine setting or finishing, not just a post-production control.

In terms of production the metrology room inside of die casting plant allows to manage important activities, such as:

– Constant monitoring of each production cycle
– Fast check of new projects and sampling
– Getting an overview about projects that have undergone changes over time
– Control of parts incoming from external suppliers
– Reverse engineering, both for the product and the die

To achieve these goals, a complete range of tools and innovative machines is needed, complementing the precision of a traditional CMM system with a 3D scanning one, combined with the most advanced software for inspection and statistics, allows to accomplish a complete dimensional control.

Following, you can find an analyses regarding applications of a metrology room inside die casting process.

Constant monitoring of each production cycle
Pieces are dimensionally tested when they are still in the production cycle to ensure the correct quality. Products are taken directly from the die casting machine for dimensional and statistical controls: to cyclically evaluate the dimensional quality and, in general, to continue monitoring the reliability of the process.

Fast check of new projects and sampling
A constant dimensional control activity, especially in the project start-up phase or sampling phase, it is strictly necessary to reduce time and costs. Having a metrology room inside the plant allows real-time control of the pieces produced to immediately confirm the precision of the process or, in the opposite case, to have a real-time response in order to make changes or updates in production cycle.

Getting an overview about projects that have undergone changes over time
In case of dies or products previously designed and developed by a different supplier, it could be necessary to analyse and check them to ensure the dimensional quality required by the customer. In fact, without similar controls, the new supplier could face the same issues. This kind of analysis is essential to avoid this situation. Instead, by getting a complete analysis of the project, the new die caster will be able to act directly for updates, ranging from simulation software to machine settings.

Control of parts incoming from external suppliers
Having a metrology room inside of die casting plant could be also really useful in case of complex products, that need to be assembled with other components from a different supplier. In fact, in addition to the control of produced pieces, it is important check all the other parts of the product. This method assures to minimize risks for the customer.

Reverse engineering 
Dimensional measurements are very important in case of reverse engineering actions, both on parts and dies. It can be a helpful activity in order to analyse the market, or pieces already in production, or rebuild a component starting from the die. This methodology can be applied on different purposes, to speed up some projects.

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It is important to remember that not every defect can be avoided during die casting phase, but it is necessary to focus on mold design. This happens because during production phase it is possible to act on a limited number of parameters and sometimes to solve a problem the designer can only modify mold design.

Die casting defects : explaining their characteristics

Casting defects are caused by an incorrect filling or solidification phase and they can be divided into two category:

Internal:

• Gas porosity
• Shrinkage porosity
• Inclusions

Superficial:

• Cold laps
• Laminations
• Blister
• Cracks
• Lakes

Internal defects

These kind of die casting defects are more difficult to find and are responsible for weakening component structural resistance.

Gas porosity

Due to fluid high speed during filling phase turbulences are generated, these turbulences can include air or other gases. During solidification phase, if gas concentration is not homogeneous inside casting, air bubbles generate cavities which weaken resistant sections of component.

These cavities are rounded and can be shiny or opaque, depending on gas type entrapped during filling phase: for example air, water or lubricant.

Shrinkage porosity

Shrinkage porosity defects are created during solidification and cooling phase of casting. They are created due to material shrinking and for this reason are widely spread in massive parts.

During solidification phase, the material tend to move near colder zones, for this reason, due to different temperature between casting surface and core, cavities are concentrated inside the part. The morphology of these cavities has an angular shape.

In some cases there is the risk of creating cavities on component surface if part and runner geometry is suitable for hot spot setting up.

Inclusions

In zinc alloys intermetallic compound can be created: in particular the most common is FeAl₃, which is a compound of iron and aluminum.

Is important to say that these compound are tougher and have a different colour than zamak alloy: for this reason can cause problems during following phases of mechanical and finishing process.

Moreover with components under mechanical fatigue stress concentration and cracks can be created.

Superficial defects

These kind of casting defects are visible and worsens component surface and its aesthetical quality.

Cold laps

Cold laps are the most common die casting defects: they are caused by irregular flows and low temperatures. Cold laps include a wide selection of defects such as flow marks or lack of material. Depending on defect rate components can have a poor surface quality or in the worst case it can be incomplete.

This phenomenon is generated from matching two or more flows of material which, due to low temperature, oxide formation and dirt inclusion, flows welding is incomplete or absent.

Laminations

Laminations can be classified as part of cold laps category. They are generated from overlapping of two layers which are always separated during filling phase.

These defects are difficult to detect after die casting, while they appear after finishing or pre-finishing operations like tumbling and sand blasting. During these phases, the impact between inserts and casting causes lifting of subtle zinc layers.

In the middle of these layers other fluids and dirt of die casting process like lubricant or oil can be hidden. These substances can come out during surface treatment like painting or galvanization and worsen the outcome.

Blisters

During mould filling phase, air inside the mould and machine is compressed, and one part is ejected from the casting using vacuum valve, chill vent or overflows. Air remained inside the component can be dissolved inside the melted metal with an homogeneous distribution. Due to many turbulences, air is concentrated creating high pressure cavities.

Very often, if the component does not have high temperature extra operations, this die casting defect is hidden and causes diminishing of component strength; otherwise in processes like powder painting where the temperature is higher, gases inside the casting expand and generate bubbles on the surface.

Cracks

Cracks are material breakage caused by stress inside and outside the material.

The first ones are created during solidification and cooling phase: due to cavity geometry material is not allowed to shrink in its natural directions, what results is residual stress that can generate cracks inside the mould or deformations after ejection.

The second ones are caused by external forces on components: these forces can be found during parts ejection from the mould or cutting phase.

Lakes

These kind of defects are seen in aesthetical components: are caused by different solidification time of the filled metal which in some part of the casting generates a different skin from the surface. This area is fine grained and appears different from the rest.

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