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The importance of zinc die casting in automotive industry

by Marcello Cazzaniga August 6, 2018

The process of zinc die casting is highly popular for making parts in building and industrial fields, but its most common application is in automotive industry. In fact, cars have different parts that can be crafted through die casting, so much so that the modern process of die casting originally started for automotive industry.


 zinc die casting in automotive

 

With casting process there is often no need of further machining after casting: not only its accuracy is up to 99.8%, but casted products also can be used raw, since they have a pleasant finish. Zinc die casting usage is almost 28% in automotive industry, followed by building and hardware sectors.

Zinc has become one of the most important metals in automotive parts industry, especially for products like door lock housing, pawls, retractor gears and pulleys in seat belt system, but also for the camshaft and sensor components. By using this metal and its alloys, it is possible to reach a strength, ductility and malleability that will not be possible with other materials.

Moreover, zinc can be the right choice to obtain high quality aesthetic components, with  strict tolerances impossible to achieve with other materials, and to obtain embossing and grooves for mechanical or gear components.

Automotive zinc die casting components

As said before, automotive industry is the most common application of die casting: by using zinc and its alloys is possible to produce components capable of reaching high aesthetic quality , with strict and narrow tolerances for shapes morphology. Zinc alloy is also used for plating purposes because of its many benefits, such as enhancing the already impressive anti-corrosion zinc properties.

Hereunder you can find a selection of examples of what is possible to produce with zinc plating:

  • Interior aesthetic parts
  • Sunroofs parts
  • Mechanical parts
  • Engine and other under-the-hood components
  • Power steering systems
  • Brake parts and systems
  • Air-conditioning components and systems
  • Chassis hardware
  • Parts in seat belt system
  • Climate control components
  • Fuel systems

In the next paragraph, we will proceed with a list of zinc alloys advantages.

Zinc alloys advantages

Zinc alloys in die casting allows to develop products and to simplify production, providing a durable end-product. Zinc strength, ductility and stability allows specialists to obtain a better and more resistant product. It is this high ductility that makes zinc ideal for die casting process, in which it is necessary to sustain pressure and expansion without fracturing. Other zinc alloys advantages are used in die casting, such as:

  • Electrical and thermal conductivity
  • Raw material low cost
  • Strong stability, which grants a long-lasting end product with high quality finishing properties
  • Thin walls: they contribute to corrosion resistance for end products, increasing their durability in harsh environment
  • Economical for small parts
  • Low melting point, which means it requires less energy for production
  • Dies have a longer tool life
  • Complex geometries and quality finishing: by using zinc it is possible to cast intricate, thin walled and technically demanding parts with high precision
  • Top quality coating and chrome plating: zinc die casting components are fit for electroplating

 

Zinc vs other materials

Each alloy has its own characteristics in terms of physical and mechanical properties: these factors are fundamental to determine longevity, strength and functionality of products. Product complexity, its wall thicknesses and the required precision will influence how castable it is: these elements should be considered main points to better organize a die casting production.

There are different methods of die casting, depending on design application and metal choice: hot chamber or cold chamber are just two of them. Hot chamber die casting is ideal for metal with low melting temperatures, for example zinc or magnesium, while cold chamber processes are used for alloys such as aluminum, which have higher melting temperatures.

Zinc alloys compete with other materials in die casting industry: aluminum, cast iron, machined brass, machined steel and magnesium, together with zinc, are the most commonly used metal in die casting products. Choosing alloys is a tough operation: the die caster has to analyze application, material density, tensile strength, yield strength, melting temperature and elasticity to obtain a better outcome with all its functional and aesthetical requirements.

1. Zinc alloys vs Aluminum

One of the main difference between aluminum and zinc alloys is zinc low melting temperature and its need for lower pressure during die casting. For these reasons zinc alloys are the most castable ones. Having a low melting temperature allows zinc die casting tools to last longer, and since dies are expensive, using them for a longer time is a cost-effective approach to high volume of production.

Moreover, zinc can be cast with HPDC, which is less expensive than cold chamber process; by using HPDC it is possible to increase production speed. Aluminum alloys, on the other hand, are normally casted with cold chamber procedure, which is less productive than hot chamber process used for zinc.

In addition, zinc is more suitable for very detailed castings and very little machining or finishing work is needed after ejection of the component from die: low pressure and low melting point reduce thermal shock during casting, giving a smoother surface to the component. Moreover, the superior zinc formability and machinability gives costs advantages in finishing and assembly operations.

There is another downside to aluminum die casting: it tends to produce sparks after impacting against iron or steel. This forbids its use in risky environment where explosive atmospheres can develop. Instead, zinc is a non-sparking material and thus it is free from this risk and it is suitable even for those environments.

In general, zinc has a better precision, smaller draft angles, smaller and longer cored holes, much longer tools life, thinner wall sections possible, superior tensile strength, better machinability, better formability, lower casting costs, superior pressure tightness, more finishing options and it is a non-sparking material when compared to aluminum.

2. Zinc alloys vs cast iron

Zinc, in comparison to cast iron, has lower casting costs, more precision and superior thermal and electrical conductivity. However, it is difficult to compare cast iron with zinc alloys because there are a large range of materials for iron casting, each with different properties, so that is impossible to strictly define them.

3. Zinc alloys vs machined brass

Zinc alloys have lower process costs, lower material costs, less process scrap and equivalent or superior tolerances achievable than machined brass. As before, the term brass regards a wide range of cast materials, with many different mechanical properties and is impossible to define each of them.

4. Zinc alloys vs machined steel

Compared to machined steel, zinc has lower process costs, a superior corrosion resistance and equivalent or superior tolerances achievable.

5. Zinc alloy vs magnesium die castings

One of the main differences between magnesium and zinc alloys is that zinc alloys need lower pressure and temperature for casting. Unlike magnesium, which requires a special treatment for corrosion resistance and finishing, zinc alloys have excellent corrosion resistance and a better surface right after being ejected from the die.

Magnesium has a really low density and, just like zinc, magnesium alloys can be die casted using HPDC: for this reason, they have faster cycle times than aluminum. However, zinc properties are superior to those of magnesium in every aspect.

Zinc, when compared to magnesium, has lower processing costs, lower draft angles, better precision, superior stiffness, superior tensile strength, better corrosion resistance, superior formability, longer tool life, more finishing options and it is a non-sparking material.

CASE STUDIES

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

Bruschi has 70 years of experience with clients of several industries, including automotive, lightning engineering, household electrical appliance, doors and windows locks. Having a wide know-how that extends from one field to another allows the designer to provide his clients with alternative solutions inspired from other industries and always ensuring top quality in material, processes, manufacturing and durability.

In addition, an analysis phase preceding mold design leads to proposals aimed at reducing scraps,  minimizing production costs.

Hereunder a selection of case studies focused on automotive sector.

 

CASE STUDY n° 1 – New finishing to avoid blistering

An important automotive player asked Bruschi to produce a component in order to find a solution for its scrap rate: it was already being produced by another supplier, but it had a scrap rate of over 25% due to blistering, appearing after treatment of galvanizing coating.

Bruschi worked focusing its efforts, involving its supplier network, to avoid blistering. The solution was to  change the finish: shifting from galvanizing coating to passivation. This meant a great reduction of scrap rate caused by blistering, that decreased from 25% to only a few parts per million.

 

CASE STUDY n° 2 – New finishing to improve SST resistance

An important automotive player asked Bruschi a solution to improve the salt spray test resistance of a  product. The component needed a higher SST resistance for a new project, in which the component would become part of luxury cars.

The SST resistance is given by a particular kind of finishing, called Fe/Zn: for subcompact cars the guaranteed resistance is 120 hours. However, this treatment was not suitable for luxury cars. The new goal was to push the resistance up to 1000 hours. Thanks to Bruschi expertise and network, our client reached its goal by applying a special galvanic treatment, which improved SST resistance to over 1000 hours.

 

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