Cost reduction strategies in zinc die casting

Cost reduction in zinc die casting can be implemented in different ways. In fact, zinc is a versatile metal that, if manufactured with the right technologies, allows saving not only in absolute terms, because it allows the die caster to save the time, energy and raw material that are required in the process, but also compared to other metals.

In the production of die-casts it is possible to implement cost reduction by:

•  Choosing zinc instead of other metals or other metal alloys
•  Optimizing the productive process
• Designing processes and components together with the customer through co-design methods

  When it comes to save during die casting process it is also important to choose the right die caster, if you want to learn more on the matter read How companies can save while selecting the die caster.

Advantages of zinc: chemical and physical qualities and characteristics, melting temperature, circular economy

Zinc alloys usually employed in the die casting process have some properties that make them competitive if compared to other metals. These are chemical-physical properties that allow the reduction of costs related to productive processes and to the subsequent stages, such as, for example, those of disposal and recycling. Let’s analyze these characteristics in detail.

Chemical-physical qualities and properties

In the die casting process different zinc alloys are employed. The most common of those alloys are Alloy 2, 3 and 5, and they are chosen for the production of different components depending on their chemical-physical properties. In fact, according to the percentage and the relative values of the metals that are contained in them, the alloys have different characteristics that make them more or less appropriate to realize different typologies of products. For example, if the component is a safety product the alloy that guarantees the greatest resistance to wear, corrosion and pressure, yield strength and dimensional accuracy is to be chosen. In case of a technical component, for which it is often important to achieve details and thin ribs, the Zamak to be preferred will be the most fluid because it will be capable of spilling over the mold in the most uniform way. In this way it will be possible to obtain thin walls thickness that is essential to guarantee the functionality of products. Finally, for aesthetical products Zamak alloys able to ensure the best surface quality and the best performance if subject to subsequent processing and finishing, are to be preferred. Therefore it is very important to know the chemical-physical characteristics of the different zinc alloys in order to choose the most suitable for the production of a specific component. Only in this way, in fact, it is possible to make a winning choice and obtain, with reduced scrap rates, quality die casts that need a reduced number of finishing and further processing.

If you want to discover more about different zinc alloys and how to take advantage of their specific characteristics read the articles The best zinc alloys for hot chamber die casting and Zamak molding in hot chamber die casting: chemical composition.
To deepen your knowledge about the advantages of zinc in comparison to other metals read The importance of zinc die casting in automotive industry and Coating, plating and other kind of surface treatments.

Melting temperature

One chemical-physical property that has a great impact in terms of cost reduction is the melting temperature of Zamak. The melting point of Zamak, in fact, is low and this allows hot chamber die casting. Differently from aluminum, which has a higher melting point and that is cold chamber die cast, Zamak allows energy saving provided by the different technological process used to melt the material. There are further advantages related to time that are connected to hot chamber die casting: hot chamber die casting is a faster process than cold chamber die casting and, as a consequence, it has an increased productivity. Another saving factor related to melting temperature is that the mold, subjected to lower temperatures, is affected by less wear and, for this reason, has a longer lifetime, with beneficial effects especially in large scale production.

Circular economy

In this brief review of the qualities of zinc in comparison to other metals one last property has to be mentioned: recyclability. Zinc, in fact, fits in circular economy processes and therefore meets the recent trends toward environmental sustainability. Zinc recyclability is not only an advantage for the final consumer, who can recycle products and appliances, but it is also an important factor of cost reduction for the die caster. In fact, if the agreements with customer allows it, zinc can be re-melted and, in controlled percentages, it can be reintroduced in the productive process with evident consequences in terms of reduction of scrap rate and of optimization of the productive processes.

If you wish to learn more about the possibility of recycling Zamak click here.
If you look for insights on zinc circular economy we suggest you to read Zinc life cycle: how it contributes to circular economy.

Productive process optimization

In regards to cost reduction in die casting not only the properties of zinc are important but also the productive process with which the metal is manufactured. Die casting techniques and machineries have to be up to date with technological development in order to be efficient, for this reason constant research and innovation are necessary. It is also important to have effective supply chain and logistic managment, if you want to learn more click here.

For a general overview about these topics we suggest you to read the article Production process improvement in the die casting industry. If you wanto to deepen your knowledge on the  analysis necessary to optimize the productive process read the article How die casting companies can help you save time and budget.

Automation and cycle time

An important step to achieve cost reduction is, for example, the introduction of automation in the productive process. In fact, automation makes the system more efficient by diminishing the percentage of scrap and allowing the operators to deal with activities with a greater added value.

Moreover, the acquisition of automation is closely related to the capability of updating and implementing the productive machineries. Thanks to the purchase of new machineries activities that used to be manual become automatic with a resulting diminishing in lead time, cycle time and scrap rate and a noticeable increase in productivity. Cycle time, in particular, is very important in relation to cost reduction strategies: in fact diminishing cycle time means increasing OEE, the productive performance index of a plant, and, consequently, the production. In the specific field of hot chamber die casting the reduction of cycle time represents a further saving opportunity because, in a reduced cycle time, the thermal power that the melted material provides to the mold is increased with a resulting decrease of cold fronts and related defects.

If you want to learn more about automation and its importance for the production process read How automation helps improving the production process; if you want to discover more about cycle time and its optimization we suggest you to read How die casting cycle time optimization can help to reduce costs.

Simulation

Another strategy to optimize the productive process is to use simulation software that allow designers to forecast what is going to happen during the die casting process. Simulation is a useful instrument to prevent problems, errors and defects during the production of the die casts and it is, moreover, a fundamental aid during design, prototyping and testing phases.

You can find a study about the advantages of simulation in zinc die casting clicking here.

Quality certifications

A guarantee of optimization of the productive process and of the subsequent cost reduction is the achievement of quality certifications. Smeta 4 Pillars, for example, is a certification of qualitative standards, environmental management, company integrity, health and safety with a noticeable impact in terms of cost reduction. In fact, Smeta 4 Pillars through the sharing of standardized approaches improves and aligns the productive process safeguarding brand reputation and guaranteeing an ethical supply chain.

Co-design

Co-design consists in a series of activities aimed at increasing the value of the product and at improving it in terms of quality and efficiency. Often these activities do not result in an increase in production costs but, on the contrary, they result in a decrease in costs. Through co-design, if already implemented during designing phase, it is possible to agree with the customer on weight reduction, elimination of secondary operations, optimization of the mold and a number of other actions that directly lead to a noticeable cost reduction. Obtaining a drawing that is already optimized for mass production allows the customer to have a final product that is in line with expectations and with less risks and scraps. As a further assurance of cost reduction, already during co-design phase, it is possible to undertake a VA/VE value analysis and to optimize the process through the DFM. VA/VE value analysis is a method of problem solving that allows the effective identification of unnecessary costs making it possible to reduce them. DFM, Design for Manufacturability, is a feasibility study in which the design of the product is evaluated and in which adjustments, special treatments and structural modifications are proposed in order to make the optimization of the production possible.

For a deeper insight on co-design we suggest you to read the article Product design for die casting, if you want to deepen your knowledge on VA/VE read The zinc die caster impact on production costs reduction. 

The methods to implement cost reduction in zinc die casting and to optimize processes and products do not end here. However, by reading this article you should have had evidence of some important benefits of cost reduction.

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Productivity enhancement represents, indeed, an advantage both for the supplier and the client: on the one hand the supplier benefits from costs savings, while on the other hand the client can rely on a partner that offers quality performances in short times. Bruschi has always considered this subject a core aspect, as a matter of fact through the years Bruschi has taken several measures in order to achieve an ever-increasing process improvement.

How to reach process improvement

Process improvement can be developed through a well-defined action plan, which takes into consideration the complexity of elements that characterizes the production department. Production is indeed composed not only of machinery, but also of product design, technologies, operators and planning activities, to mention some of the most important components of this structured system. To improve the production process it is therefore crucial to have a comprehensive view of all these elements, in order to implement a strategy that is functional on multiple aspects.

As a consequence, the first step to take is the setting of the tools and of the adjustment actions that can impact on the improvement of the different stages of the production. In Bruschi the process improvement plan is composed of four central elements:

1. Automation

2. Simulation

3. Scrap reduction

4. Cycle time

1. Automation

The introduction in a production system of automated machinery equipped with state-of-the-art technologies generates relevant benefits in terms of reduced lead time, costs reduction and achievement of quality standards requested by clients. The replacement of workforce with automated systems allows, indeed, to obtain a faster process, consequently enhancing the whole lead time. In addition to that, automation leads to a reduced likelihood of error compared to manual operations. This translates into a relevant production costs reduction, which is further increased thanks to energy and material saving that automation generates. The introduction of automated machinery in the production department produces another significant advantage that allows quality control improvement, too. As a matter of fact, operators that previously dealt with manual operations on the component thanks to automation can take responsibility for other activities with a higher added-value, such as quality control.

A process improvement project of a specific component, for a client of the sector of small appliances, has obtained excellent results in terms of increased productivity and decrease of manual activities of operators. Process improvement project has been developed in order to solve a situation of misalignment between production capacity and client’s demand. Through the introduction of automated systems this gap has been narrowed, thus achieving an optimized cycle time. After several studies and researches it has been possible to apply some changes to the process, which have brought to significant benefits: an increase of 33% of production capacity and a decrease of -95% of manual activities made by operators.

For more detailed information on automation consult the post below:

• How automation helps improving the production process
• The Importance Of Automation Optimize The Production Time

2. Simulation

Simulation of the die casting process represents another essential element that impacts on process improvement: with simulation software engineers can indeed foresee material reactions inside the mold. This process is feasible thanks to a thermos-fluid dynamic analysis of the mold, known as CFD simulation (Computational Fluid Dynamics), which allows the engineer to detect potential defects, such as cold laps and hot spots, on the die cast. The simulation stage proves especially helpful to obtain an optimized mold design before starting with the production process. During this stage it is indeed possible to select the best mold design parameters to apply, so that potential defects on the piece are previously detected and, consequently, production costs and further mechanical operations are reduced.

If you are interested in simulation, here are additional posts on this topic:

• The Benefits Of Simulation In Die Casting Design
• Die Casting Simulation For Shrinkage Porosity Prediction
• How To Use Die Casting Simulation For Cost Reduction
• Hpdc Simulation For Die Casting Process Optimization
• Die Casting Simulation A Casting Process Optimization
• Hpdc Simulation Benefits For Die Casting
• Simulation For Hpdc Surface Aesthetical Quality In Automotive Case Study
• Simulation For Hpdc Shrinkage Porosity Case Study
• Simulation For Hpdc Die Maintenance And Optimization Of Set Up

3. Scrap reduction

Scrap reduction can be achieved through an accurate planning of the whole production process of a component. First of all it is necessary to carry out a product and process analysis that focuses on the causes of scrap. To identify these causes engineers must use simulation software to foresee every stage of the production, from design to finishing operations. Once again simulation proves to be an indispensable tool for zinc die casting process improvement, because it allows engineers to avoid defects and to check technical properties before starting with the component production, thus producing a consistent costs and lead time reduction. Once scrap causes have been figured out it is possible to proceed to the outlining of potential solutions to apply, identifying the most relevant steps in the production process and constantly checking them.

To know more about scrap reduction, here are extra posts on the topic:

• How To Reduce Scrap In Die Casting Process
• Simulation For HPDC Scrap Reduction Case Study

4. Cycle time

The expression cycle time defines the period of time required to produce a product. Cycle time represents a central variable in the production of a component because a reduced cycle time results in a reduced lead time, which is the period of time needed to accomplish a customer’s request in terms of supply. An optimized lead time generates an increase in the client’s satisfaction, because it allows the supplier to meet deadlines and standards demanded by the client. As a consequence, in order to guarantee a rapid and efficient service, cycle and lead time have to be enhanced to the maximum extent possible. Cycle time can be shortened paying attention to different aspects of the production process, especially to simulation stage and to technological systems of the production department. First of all, as already mentioned, it is important to simulate production and defining the best process parameters to apply for the production process. In this way potential defects will be avoided from the very beginning and, consequently, it will be possible to eliminate further mechanical operations. Another core element for cycle time shortening is the technological system of the foundry, whose technological innovation level can generate relevant time reduction during the production process. As a matter of fact, automated machines lead to optimized cycle times and to more accurate operations, discriminating factors for the achieving of performances requested by customers. Furthermore, periodical checks on machinery help understanding how cycle time can be further improved.

Check the posts below to learn more about cycle time:

• Process Optimization For Die Casting Cycle Time Reduction
• How Die Casting Cycle Time Optimization Can Help To Reduce Costs

Why process improvement is crucial for a business

Process improvement is a crucial element in the management of a business because it leads to production costs reduction and faster productive processes. With the aim of reaching these benefits it is therefore necessary to introduce automated technology and simulation software in the production process, and to optimize scrap reduction and cycle time. With the outlining of a precise process improvement plan lead time can be shortened and, as a result, client’s satisfaction will be increased.

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This post is part of a series in which we explain the importance of simulation for HPDC (High Pressure Die Casting) through the presentation of real life cases.

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

CASE STUDY DIE MAINTENANCE: automotive industry

The product we are going to analyze in this post is a steering lock housing assembly for automotive industry.

The critical part was the upper cover of the steering block assembly, containing an electronic card. The part itself was not flawed at first, but soon the signs of mold erosion started to show up. The erosion of the mold left distinctive marks on the surface of the component: these irregular dark spots were the sign of die wear.

The identified die wear was caused by the high speed of flow during the filling phase and by the specific geometry of the part. The consequences of poor die maintenance are rather severe as they can bring on a malfunctioning of the part, caused by surface spurs resulting from die wear, in addition to increasing the need for maintenance work. In order to solve the problem, a simulation of the filling process was run.

OBJECTIVE AND PHASES OF THE SIMULATION

The objective of the simulation was to identify opportunities for slowing down or eliminating erosion on an existing die: to achieve the wanted result, our engineering department run an analysis of alternative feeder solutions.

The first step was to identify the cause of erosion: erosion is caused by the development and non-stationary implosion of alloy bubbles against the surface of the die. Due to high speeds of the flow through the narrow ducts in proximity of feeder, the pressure falls below the vapor pressure of the alloy, causing it to evaporate instantaneously.

Subsequently, the alloy enters the die with a larger cross section than the feeders, causing an expansion that reduces the speed of the flow. The pressure rises rapidly causing the implosion of vapor bubbles and freeing up energy. This entire process is called cavitation and is the main cause of wear to the internal surface of the die.

RESULTS

The filling velocity field represents the speed of the flow when it initially enters the control volume.

Since cavitation is a non-stationary process that takes place in the first phase of filling, which is also the phase of highest instability, the study of filling velocity field represent the highest opportunity to identify the critical areas.

As the following images show, the new geometry positively influences the expansion of the flow, mitigating the velocity gradients along the green line.

Internal part of the housing

The area with largest cavitation is in the center of the field, where the green line demarcates the separation between two areas with different speeds. Exactly in this area, because the flow slows down and pressure increases, the alloy bubbles implode and damage the die.

With the new feeder duct the green line is moved generating a broadening of flow diffusion. This broadening should shift the cavitation area and reduce the risk of cavitation because of the lower speed gradient in the critical area of the die.

External part of the housing

The green line moved on the fixed side of the die as well, broadening the diffusion and diminishing the transversal speed gradient.

In conclusion, the use of simulation allowed to identify the critical area in which cavitation was occurring and to design a broaden flow to shift cavitation, preventing wear of the die and reducing the need of die maintenance.

We will now move on with the next case study, which focuses on small domestic appliances and set up parameters optimization.

CASE STUDY OPTIMIZATION OF SET UP PARAMETERS: small domestic appliances

The subject of our second case study is a chrome plated handle. The product is a component for a pad type coffee machine: in this case there was not a problem to fix, but it was necessary to identify the correct filling of the die to optimize the production.

In order to achieve a high level of esthetical quality, the die has to be maintained at very high temperatures: high temperature in the die reduces alloy cooling during the filling phase, reducing flow marks. However, high temperatures implies longer cooling time: as a consequence, the cycle time expands because of the prolonged solidifying phase of the part. Therefore, it is necessary to establish an operating temperature range that allows a high quality level while keeping the cycle time as low as possible, to increase productivity.

Once identified, the die casting conditioning parameters can be set to keep the die within the range. These conditioning parameters are entry temperature and the type of coolant.

OBJECTIVES AND PHASES OF THE SIMULATION

The objective of the simulation is to estimate the change in surface quality and cycle time at the varying of die temperatures.

Die temperature depends on two factors: the geometry of the conditioning circuit, defined in engineering phase, and the temperature and nature of the coolant applied in production phase.

In the simulation, a homogeneous die temperature was imposed in proximity of the cavity. Surface quality has been determined by the average value of the alloy temperature at the end of the filling phase, whereas the production cycle has been derived from the necessary time for the component to solidify and cool to a temperature of 340°C.

The evolution of the two quantities has been calculated across a series of simulations in which the temperature was made variable.

RESULTS

The following graph clearly indicates the results of the series of simulations. Technically, this is not an optimization analysis because the two monotonously increasing curves do not allow to find an absolute minimum or maximum: it can be considered as a tradeoff analysis to define the optimal temperature range.

The 180 – 228°C temperature range is where the surface quality curve grows most significantly, while the product cycle time stays fairly constant before increasing almost exponentially.

For these reasons we choose the range within bandwidth of about 10°C, placed at the extreme right of the interval (218°C < T < 228°C).

In this case, simulation of the component has helped determine the ideal die temperature range to obtain the required surface quality, guiding the setting of entry temperature and the choice of the coolant.

In conclusion, throughout this series of post we have seen different applications of simulation for die casting: scrap reduction, optimization of esthetical quality, improvement of mechanical characteristics, improved die maintenance and optimization of set up parameters are only some of the many advantages offered by the use of this technology.

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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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VA/VE Analysis History

In 1961, in his book “Techniques of Value Analysis and Engineering”, American engineer Lawrence D. Miles stated:

 “Value analysis is a problem-solving system implemented by the use of a specific set of techniques, a body of knowledge, and a group of learned skills. It is an organized creative approach whose purpose is the efficient identification of unnecessary costs, i.e. cost that provides neither quality nor use nor tool life nor appearance nor customer features.”

The term Value Analysis / Value Engineering originated in the early days of technique development and its first approach was to increase value, rather than to reduce costs. Therefore there was a need to analyze value.

Lawrence D. Miles continues:

“Value analysis approaches may assist all branches of an enterprise-engineering – manufacturing, procurement, marketing, and management – by securing better answers to their specific problems in supplying what the customer wants at lower production costs. Quite commonly, 15 to 25 per cent and often more of manufacturing costs can be made unnecessary without any reduction in customer values by the use of this problem-solving system in significant decisional areas.”

VA/VE is an extremely powerful approach with over a century of worldwide application and it can be applied to any cost generating areas with equal success.

Il VA/VE è un approccio estremamente efficace con oltre un secolo di applicazioni in tutto il mondo e può essere applicato ad ogni area che genera costi con lo stesso successo.

Value Analysis / Value Engineering Definitions

Value Analysis – VA

What is value?

Different customers will answer to that question in different ways. The value of a product can be the performance of its functions or its aesthetic beauty, when applicable and needed. As a general statement high level performances, capabilities, emotional appeal, style, all compared to cost is commonly what we consider as value.

Therefore Value = Function / Cost

Value Analysis is a standardized, multi-skilled team approach which aims at identifying the lowest cost way and ensuring the highest worth to accomplish the functions of a product, process or service. Value analysis means to assess product functions and value-to-cost ratios, and to find opportunities for costs reduction.

Value Engineering – VE

As we said above, Value Analysis is the application of several techniques to identify the functions of a product (or service) and provide them at the lowest cost.

Value Engineering refers instead to the design stage. This approach is generally used for new products, therefore the same principles and techniques to pre-manufacturing stages such as concept development, design and prototyping are applied.

To sum up, VA / VE is an orderly and systemic method to increase the value of an item, which can be a product, system, process, procedure, plan, machine, equipment , tool, service or working method. Function analysis is part of VA as its purpose is to identify product functions compared to cost and price; design and construction assessment is done through VE with the goal of  eliminating elements which are not contributing to function.

Product’s function should not be conceived solely as its application and practical uses: it can also include aesthetic factors, or the union of the two following dictates of functional beauty philosophy: this theory is based on the coexistence of aesthetics and performance. What matters the most in drafting a VA / VE is that the function is clearly defined, so that it can be analyzed in detail and sub-segmented to make the analysis easier.

If you are interested in functional beauty, Bruschi is going to give a lecture on the topic: click here to learn more.

In VA/VE the function of a product or service, defined by customers to meet their requirements, is identified, the monetary value for that function is established, the specified performance and requested reliability provided at the lowest Iife-cycle cost.

Following a VA/VE approach it is possible to increase customer satisfaction and add value to the investment.

Even the best and most innovative designs can age and become uncompetitive: in these cases VA/VE can support both customers and suppliers in finding and optimizing any value mismatches in products, components, processes, projects or low performing functions.

A correct segregation between necessary and unnecessary functions of products leads to a creative development of alternative ways of accomplishing them – as requested by customers – at lower cost.

VA/VE enables a company to highlight areas that need to be analyzed and improved, with a standardized method which generates ideas and alternatives, considerably increasing the value of goods and services.

A project completed with VA/VE technology is more successful and efficient than a project developed without that approach, because goals and requirements are pursued in a customer centric way. VA/VE is almost unlimited in identifying area of potential savings, as it can be used to reach quality, improve efficiency and reduce risks, in a cost saving way.

VA/VE Approach & Main Steps

According to the principles of “Techniques of Value Analysis Engineering” there are different phases of VA/VE:

• Exhaustive accumulation of information and identification and improvement of assumptions.

• Penetrating analysis. What senses of direction does this informative provide us with? What specific problems will, when solved, bring important cost benefits?

• Creative mental activity, in which all judgement is temporarily deferred to form the roots of a variety of different solutions to each of the specific problems developed in the preceding analysis.

• Judgment-type mental activity, in which what results from creative thought is searched for ideas roots to minimize disadvantages and maximize advantages sufficiently to meet the need for cost and/or operation improvement.

During the information phase, the project and its requirements are analyzed, and then the function analysis studies the possible room for improvement. In the creative stage ideas to increase performances are developed: from the resulting list of ideas only a short set is evaluated in order to find the ones with best potential to reach the goal. The following step is development of alternatives and their presentation to decision makers and, eventually, implementation.

VA/VE tools are extremely powerful and fundamental to reach objectives such as decreasing costs, improving quality and shortening time-to-market.

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The connection between the injection system and the shot entry is composed of two main elements: the feed and the runner. Their structure and size have a crucial impact on the casting flow, since different shape can bring about different results and help in reducing the risk of defects in the die casted product.

Runner positioning

To define the ideal position of the runner it is necessary to keep in mind that molten metal should cover the shortest distance possible to avoid premature cooling. Because of this, it is usually suggested to direct the flow towards the smallest side of the cavity, or to take advantage of ribs and branches to ease cavity filling. When dealing with more than one shot entry, it is important that flows are not convergent, since that would cause an energy loss and the formation of turbulences and air trappings: therefore, it is best to design the runner to obtain parallel or divergent flows.

Runners position it is also crucial to keep under control the distribution of shrinkage porosity. It is impossible to avoid porosity, but it is possible to manage it. In fact, in order to obtain a disperse and uniform porosity the shot entry should be placed in correspondence to the thinner parts of the casting, while in order to obtain a reduction of the porosity in a massive zone the shot should be placed next to the thicker parts of the casting.

Moreover, the flow should be directed towards those zone with high quality requirements: to obtain a high surface quality it is needed that the cast should be as direct as possible. These precautions lead to a better control of shrinkage porosity and thus to a casting process optimization.

Design and dimension of runners

Another important element to consider is the shape of the runners. Normally the most used shape is trapezium, but for some high tolerance alloys, such as Zamak, runners with circular cross-sections can be used: this reduces energy dissipation, thus preserving flow’s temperature.

During the designing phase, the ratio between the runner’s section and the shot entry should be kept in mind, but there is no universal rule: the choice depends on the wanted result. Smaller runners allow for a saving of both material and energy, but require more power from the injection system and are more subjected to premature solidification. On the other hand, larger runners require more material and energy, but have higher hydraulic efficiency and increase the thermic value of the mold. Therefore, they require also a longer cooling time which could have a negative impact on the cycle time.

Moreover, the cross-section of the runner should be decreasing in size through their whole length, and this applies also to branches:  the entering section should be equal or larger than the exiting one. If the main branch splits to two runners with the same cross-section, the resulting runners should also be of the same size, and their sum should be equal or smaller than the main branch.

Another issue regarding the design of the runner could be the presence of sharp edges and the discontinuity of flow deviations, the most critical points in the design of the runners. They should be avoided to prevent the formation of turbulences. When working with compound dies a particular attention should be given to construction and assembly errors, because the formation of bottlenecks and bulges could damage the metal flow. This kind of mistakes can be fixed in the tool shop, allowing for a recovery of the original functionality of the mold.

Finally, it is important that the volume of the runners will let the metal flow in the cavities at the same time, and that is why their length must be constant.

To allow the casting to be evenly distributed in all the cavities, it is necessary to attach the main runner to the injector with a feed.

The feed

The feed is a junction needed to pass from the squared section of the injection channel to the thin one of the shot entry. There are many different types of feeds and each one has different advantages, but all have the same main functions: to make the passage between the channel and the entry more gradual, so as to contrast metal tendency to withdraw from walls, and to direct metal flow.

The most common models of feed are the fan feed and the double tangent feed:

• The fan feed creates a narrow flow with a higher speed in the middle. Because of this, it is more suitable for short and thick shot entries, and it is ideal for small angles;
• The double tangent feed produces a larger flow, with higher speed at the sides. Because of this, it is more fitting for long and thin shot entries and offers larger angles;

Independently form the chosen type of feed, the section should be linearly decreasing from the channel to the shot entry. This means that it is not enough to use a trapezium-based feed, but it will be necessary to curve either the base surface or the side’s surface.

Pro and Cons of a straight feed

The term “Straight feed” identifies those feeds with a straight trapezium base and curved sides. The main advantage of this kind of feed is that the opening angle is the same as the half-opening of the feed, making it easier to remove the runners, while the main disadvantage is the tendency to work with a cold shot entry. Moreover, the flow generated by this feed has a narrower leading front and thus the metal has a tendency to withdraw from the walls.

Pro and Cons of a curved feed

The curved feed is a feed characterized by straight sides and a curved base. It is ideal when it is necessary to have a stronger flow to the sides, but the opening angle is harder to calculate and it causes the formation of small parts that require removal. The flow created by this kind of feed has an higher speed in the middle and metal tends to stick to the walls.

After learning about their strengths and weaknesses, it should be clear that, just like the runners, the type of feed should be chosen depending on the wanted result, on the power of the injection machines and on other secondary conditions. By allowing a better control of the casting flow and reducing the risk of air trapping formations, the feed is a fundamental tool for casting process optimization.

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THE STANDARD CYCLE

The term “die casting cycle time” is used to identify the time lapse between the beginning of an injection cycle and the next one. It can be obtained through a summation of the partial times in the die casting process. The standard cycle can be divided in the following phases:

• Injection time:

The piston follows a defined route at 1^st phase speed, through which the material is pushed up to the nozzle; it will then be accelerated by a nitrogen expansion in the accumulator in order to reach 2^nd phase speed, leading to the filling of the mold cavity.

• Die casting technical time:

It includes both compacting and cooling phases, thus involving metal change of state, from molten to solid. A compacting phase is necessary to compensate the volume reduction caused by phase transection.

• Mold shifting/lubrication time:

It is the sum of mold opening and closing time, extractor’s forward and backward movements and mold lubrication time. The lubrication can be manual, done with a Cartesian system or  with fixed nozzles.

• Control time (optional):

It can vary depending on the piece-release system of choice. When the withdrawal is done by a robot, it would be advisable to choose a control system based on photocells. In a free-fall on balance system it will be necessary to set the expected weight on the scale, in order to detect eventual missing parts that could be left inside the mold.

At the end of the die casting cycle, further operations of runners and overflow removal are needed and, for some critical products, further refinishing. Some of these operations can be executed manually by a worker, while others -such as threading- require a dispatching of the raw piece to third-part firms.

Alternatively, it is possible to integrate the production line with anautomated system in line with the casting machine. By using automated machines for scrap removal it is possible to save man-hours, which can be invested in different ways, for example in Kaizen activities.

Another viable optimization can be achieved by integrating automations in the die casting machine for precise machining, such as threading, thus reducing WIP’s transit time in the plant. Thanks to this integrated automatic machineries, capable of complex machining, it is possible to reduce lead time and to fulfill client’s request more easily.

The time necessary to complete the whole automation cycle adds (or overlaps) to die casting cycle time, and together they form the standard cycle time for a determined product.

HOW TO MEASURE COMPANY PERFORMANCES

In order to quantify a company performances, it is possible to rely on 2 indexes:

• The first one is OEE (Overall Equipment Effectiveness), a percentage measure obtained by multiplying availability, performance and quality. The index refers to the productive return of the plant;
• The second one is OTIF (On time in Full), which expresses as a percentage the logistic ability of a company to send the requested quantity of products at the expected time and place;

The optimization of cycle time increases the OEE value by rising the efficiency. Moreover, thanks to a systematic reduction of production time, more machine-hours are available, allowing the company to fulfill a bigger number of orders without changing the plant opening hours.

As stated above, OEE is composed of 3 factors:

• Availability: the relation between available machine time and operating machine time;
• Performance: the relation between produced pieces and producible pieces;
• Quality: the relation between pieces and produced pieces;

Frequently the improvement in die casting cycle time also affects the quality of the casting. A time reduction implies an increased number of injection per hour, which intensifies mold thermal input produced by the molten metal. This leads to an improvement in the surface quality of the casting, since it decreases the number of cold fronts responsible for cold laps on the surface.

There are many advantages achievable by an effective cycle time optimization, that can enhance the whole production. In the next paragraph we are going to explain in detail some techniques for time cycle improvement.

HOW TO OPTIMIZE DIE CASTING AND AUTOMATION CYCLE TIME

First of all, it is necessary to define whether to intervene on the die casting cycle or on the automation cycle. In an ideal production cycle the two coincide, which means that the process are all parallelized and there are no bottlenecks.

In order to define the priority of an intervention a Pareto chart of partial times can be used: the chart is composed of an histogram representing the distribution rate of a phenomenon, displayed in decreasing order so as to permit instantaneous identification of the main factors. After a graph analysis it will be possible to spot the critical points in need of optimization: we are going to choose the highest impact elements.

Once the graph is defined, we need to proceed with a separation between independent processing time and dependent processing time.

The term “independent processing time” is used to define actions that occur in series, one after the other. The reduction of an independent processing time entails an immediate reduction of the cycle time.

On the contrary, dependent processing time define those operations that occurs at the same time as a different one; the reduction of a dependent processing time without a reduction of the main process from which it depends, does not create a variation in the cycle time.

• Revising independent processing time: automation with robotic withdrawal

Once decided to reduce automation time, the next step will be to film the whole cycle of the robot, from withdrawal to dump. Thanks to this shooting, it will be possible to write a complete list of the robot’s movements and operations, along with their exact duration. Starting from these data, it will be defined whether to intervene on the movement speed or on their trajectory.

The movements done by a withdrawal robot through the course of a working cycle are: aligning with the machine columns, entering the press area, withdrawal of the diecasted product, exiting from the press area, transit to the check point and dump.

Before proceeding to the actual optimization, some simulations are run in order to form die casting cycle time hypothesis, and afterwards decide how to intervene: sometimes it is sufficient to alter  speed of movement, some others it will be necessary to remove superfluous movements.

•  Optimization of die casting time

Die casting process optimization is more challenging, since the majority of the process requires a fixed amount of time, for example in operations like piston compression and casting cooling. Examples of possible improvements in this phase are:

• Cooling time
  It can be reduced modifying the mold’s thermoregulation through the use of water/oil cooling units; in other words, a reduction of waiting time of the cast in the mold can be compensated by a reduction of T° in the thermoregulation fluid.
• Die casting duration
  A prefilling function can be a useful support, since the saving per cycle can be assimilated by the duration of the first phase of injection. The movement of the piston in the 1^st phase is then transformed from independent time to a dependent time, bounded to mold closing.

For a better chance of optimization it is possible to intervene on the extraction time (start delay, course speed, return speed, return delay, number of runs), mold opening/closing (opening/closing speed, aperture run) and lubrication (start delay, duration).

When working with an automation system, the necessity of synchronizing movements of the robot to the new schedule should be taken in account. The optimization of cycle time can be highly variable and bring to a 20-30% time reduction or greater, thus leading to a good economical saving for the company.

To learn more about production cycle time optimization, please take a look at our other posts on the topic.

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This is a widely discussed topic among the industry specialists: since the very first stages of mould filling various mistakes can occur, for example caused by a too quick metal solidification that can damage the final result. All of this can be forecasted and avoided thanks to HPDC simulation, thus improving the entire productive process and leading to consistent time and costs reduction.

The complexity of die casting process

When considering metal melting process a thermo-fluidodynamic biphasic simulation is needed, because metal processing process is composed of both kinetic and dynamic phenomena, heat transfer and phase transition from liquid to solid. In addition to that, the heat transfer is both of the convective kind, thus related to movements of the fluid, and the diffusive kind, determined by the heat shift between fluid and mould.

In order to face these issues the best solution is a simulation software.

Especially in the case of HPDC simulation (High Pressure Die Casting) mould complexity and machines parameters increase the number of variables to take in account during the simulation. Moreover, the productive process is continuous and based on quick cycles of high pressure fillings and cool down phases. These features, added to the intricate shapes and the shallowness of some products, highly increase the numeric complexity of the simulation.

After these premises, it is plain that the simulation process cannot be straightforward either: the equations used in the process can be solved only through an analytic approach only in a few and limited circumstances. For this reason is necessary to use a numerical methodology that requires a conspicuous use of computational resources. The numerical approach involves management of a discrete domain (the finite space in which the studied element lies) and a simplification of the equations.

The domain is turned into a so-called mesh: a calculation grid composed of different sized cells. A balance equation is written for each of these cells, to build up the global system and to be solved by the simulator. Higher the number of the cells and smaller their dimension, the more precise and lengthy will be the simulation.

The employment of specific programs plays a fundamental role to achieve the best possible results: programs like MagmaSoft, a CFD simulation software designed for foundries are based on a LES (Large Eddy Simulation) numerical scheme, enabling the user to compute without approximation the turbulence of vortexes of medium and large size, thus leading to quickly and precisely re-enact the studied phenomenon.

Why preliminary studies for die casting matters

Those who study the process of die casting through simulation cannot avoid the comparison with reality. Only the observance of the real process permits to identify defectiveness in the product and to classify them, so that they can be studied, reproduced and avoided, thus achieving better surface aesthetical quality. Furthermore, an in-depth and empirical analysis of the real-life phenomenon is fundamental for setting the boundary values. Their determination, in addition to being necessary for the closure of the numerical system, determines the closeness of the simulated model with reality.

Through the use of a HPDC simulation, the following defects can be studied and prevented:

• Porosity
• Cold Laps (due to low temperature in filling phase)
• Presence of air in the diecast
• Metallic inclusions determined by the presence of foreign bodies in the molten material
• Cavitation issues or mould erosion
• Scrap reduction

Each of these possible issues is linked to physical aspects of the system detectable in the simulation, such as speed, pressure and temperature: porosity, for instance, is caused by material distribution in the mould and is therefore linked to the speed of injection, to air pressure in the mould and to heat distribution during solidification. Through the use of simulation it is possible to foresee the formation of vacuum pockets that may decrease the solidity and aesthetic of the product. Click here to read about a case study of shrinkage porosity reduction in a component.

Another occurrence in which the simulations proves particularly efficient is in forecasting the possible damages caused to the mould by cavitation: there is a risk that the mould may undergo a major erosion if subjected to pressure variations. Because of this, it is necessary to analyze in depth the object geometry, drawing duct with strategical shapes and positions.

HPDC Simulation: comparison with reality

The expert should then research the causes of the anomalies in the physical qualities of the fluid, analyzing accordingly to the case and matching the mathematical data given by the simulation with the extra value of practical experience and know-how. By comparing the expected data provided by the simulation with the effectual results, two main goals are achieved:

• on one hand, it increases the understanding of the physical phenomenon causing the faultiness and helps the researcher with finding a suitable solution, for there may be many possible ones;
• on the other hand, it increase the interpretational ability of the researcher, leading to a better knowledge of which fields or combination of fields allow to identify critical values linked to faultiness creation;

The more experienced the software user is, the better the results.

If you want to keep up-to-date with die casting industry news, take a look at other simulation posts and please subscribe to the blog.

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New goals and targets are constantly shifting to respond to market trends. It is essential to leverage multiple disciplines and competencies in order to be able to reach the global customers’ casting product expectations and manufacturing needs.

How Die Casting Simulation can lead to Savings

A smart casting process optimization requires flexible variables, with the ability to update information and data in order to adapt to the changing business environment.

Each team involved in the process must collaborate with other teams in order to identify and develop cost-effective, innovative, and simple to use methodologies; therefore, innovative thinking and creativity should be encouraged in order to facilitate solutions for difficult manufacturing situations.

Let’s now dive into die casting simulation issues.

The importance of the collaboration between suppliers and customers

When a supplier works closely with its customer and viceversa, each component of the process can be optimized to perfection:

– product or component co-design
– die casting simulation
– tooling
– manufacturing processes
– mould design
– complementary works
– shipment procedures

Such collaboration guarantees great results in terms of high quality production and cost optimization.

If the customer aims at getting better products at lower costs, the manufacturer needs to be selected carefully and involved early enough in the process to enable collaboration not only in the design, but also in the entire decision making process.

A joint effort between suppliers and customers is a win-win solution to meet the market needs.

This can be true for several fields, but in particular concern Zinc Die Casting. From design to finishing there are many variables to manage, therefore a good process design is crucial to reach product integrity and quality.

In fact die casting simulation is therefore a fundamental stage to ensure best results in the most efficient way possible.

In this post is underlined the first phase of product or component co-design from the angle of die casting simulation.

Die casting simulation allow the designer to foresee with a good precision all material reactions inside the mould cavity among a thermos-fluid dynamic analysis of the mould. This kind of analysis is called CFD simulation (Computational Fluid Dynamics).

Concerning mould temperature, using this kind of software, is possible to identify possible defects such as cold laps and hot spots, and is possible to simulate temperature exchanges during the solidification phase and mould opening.

Numerical steps, in this particular phase, are fundamental. For this reason is necessary to start with die casting simulation that can help specialists to identify the best mould design parameters since the very beginning, obtaining an important cost reduction.

A proactive approach of designer can avoid and anticipate problems such as flow marks and blisters, cold laps, porosity, shrinkage porosity, lakes, and shot to shot inconsistency.

It is important to say that simulation allows to identify the correct balance between speed and temperature and geometry of overflows and runners in order to prevent any issue or defects in high pressure die casting.

Tools for casting process optimization

There are several applications available nowadays to maximize both the profit margin and the quality of the casting process: the use of die casting simulation software improves the collaboration among designers and engineering team, ensuring that all components leaving the development department are suitable for casting and can be manufactured in an economical process.

This kind of technology offers a virtual version of the casting process from filling to solidification and porosity prediction, in order to obtain reliable and high-quality products avoiding the costs of trials and the production of expensive moulds or patterns.

The die casting simulation examines mould filling, solidification and cooling, therefore residual stresses and distortion, as well as microstructure formation and property distributions can be assessed.

Within the main benefits of simulation in die casting you can include:

– Avoiding defects that arise from gas porosity, shrinkage, turbulence, etc.

– Filling process optimization to provide a fast but smooth and controlled flow

– Time savings thanks to efficient gate design and sizing

– Material cost and waste reduction

– Reduction of cycle times and maintenance costs

– Minimization of start-up costs through modifications to patterns or tooling

– Improved communication within suppliers and customers

Having a comprehensive and effective simulation tool enables the implementation of smart processes and optimized casting layouts.

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The most relevant benefit of automation is the reduction of workload for the operators, but it proves also beneficial in terms of energy and materials savings.  Automation can therefore lead to production process improvement, enhancing accuracy, precision, productivity, robustness, consistency of outputs and quality.

Automation can be implemented through different tools, such as mechanical, hydraulic, pneumatic, electrical, electronic devices and computers, usually used together.

Automation in Bruschi

Bruschi has introduced automatic systems in its foundry to improve production time during the production process. Several operations that are carried out by workmen can be replaced with automation.

Since its establishment Bruschi has always been innovative in terms of automation, but in 2011 this concept has been widen with important investments.

Indeed, in 2011 automation was implemented with new robots ABB with IRC5 control: controls that are the productive unit of governance of the robot. In this way it is possible to use remote assistance to have access to all the functions of the robot to control and maintain it.

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Bruschi previously had an outdated system that needed to be improved and innovated. Consequently, Bruschi decided to create a new installation: the management purchased a cooling tower and created around it a complex system: a project was outlined, pumps and water tanks were built and the cooling tower was finally activated in order to save time and energy. Once the operator decides to create a program, he will need a PLC that is possible to set up with incomes and outcomes depending on the aims. This program has a lot of advantages, but the most important is to email the responsible during breakdown. In this way the operator can solve the problem promptly.

Simulation in Bruschi is really important because with this tool it is possibile to examine the mold before the production process starts and to simulate what the organization of the production will be.

This software is made by ABB company and with it it is possible to do the pre-installation operations: try it in preview, decide if something has to be modified, reduce installation and set up time using offline technology, it is possible to do it in the office instead of directly in the field.

Between 2016 and 2017 Bruschi has purchased three new robots. The idea is to use a new control system with better performances than the one already used in Bruschi.

Everything is possible thanks to qualified people and a large amount of investment that Bruschi does in terms of automation and robotics.

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