OEM die-casting processes make net-shape components in lower density metals, and lend themselves to a combination of high strength, low cost (for moderate to high volume), low material wastage and quite often reduced follow-on processes, compared with other casting techniques.

The process family uses multipart metal die cavity tools, into which molten metal is poured or injected and then cooled/solidified. This injection process can be fed by gravity or by pressure – and the pressures can be as high as 1000kg/cm2

Melt of virgin and recycled material is performed using electrical, gas or ther heating and the melt is purified by slag removal and de-gassing (to reduce inclusions and porosity in the resulting parts). The degree of automation of this aspect of the process is variable from fully manual to fully automatic. Repeatability of raw material and its processing is key to part quality and consistency.

The barely cooled, cast part is then ejected from the tool die, usually by ejector pins built into one of the tool die halves, which are operated as part of the tool opening sequence. Limited cooling time ensures maximum production rates.

OEM die-casting process options

Gravity OEM die-casting

This uses a hard-tooled mould casting process, where the molten metal is poured from a melt crucible or ladle into the mould. The mould cavity fills under gravity and  filling can be improved by tilting and/or vibrating the die. Undercuts, and cavities can be incorporated into the component form with the use of sand cores. This process offers better surface finish than sand casting and better mechanical properties, both due to rapid cooling and solidification.

This can offer a higher casting rate and lower cost per part than sand casting, however, the relatively costly metal dies are a cost factor. This process offers the possibility of lower gas porosity, and finer grain sizes than green-sand casting.

Gravity OEM die-casting is often a manual process, with the molten metal added with the use of a ladle. However, for some high volume applications it is also possible to mechanics the die filling, using equipment that requires low operator skill.

This process is suitable for relatively high precision parts, although surface quality can be variable and hand finishing (usually referred to as fettling) is usually required.

Low pressure OEM die-casting

This process is essentially identical to gravity OEM die-casting, but it is performed in sealed channel casting machines which pump the molten metal into the cavity. It offers better quality and repeatability of parts than by gravity feed – as well as better surface finish and less post casting fettling.

In particular, shrinkage can be better managed by maintaining feed pressure during the crystal growth phase of early solidification – forcing in additional molten charge to compensate for the reduced part volume resulting from cooling.

Tooling and casting machines are both considerably lower cost in low pressure manufacturing – the clamping forces holding the tool closed, the strength of the die sets and the wear resilience of the die materials are all considerably eased.

High pressure OEM die-casting

High pressure OEM die-casting offers the highest precision and quality of outcomes and excellent surface finish qualities – faithfully reflecting the surface finish of the cavity.

Part precision is excellent and shrinkage distortion is minimal to no-existent, once the process is optimised and the pre-processing of the melt is perfected.

The high pressure of injection requires very strong tooling and the largest clamping forces – making this the highest cost of setup. However, when the costs are amortised over large production runs, this still results in part costs that are of the same magnitude as the raw material costs – making this a highly cost effective option for very complex, high strength and cosmetic parts.

Service differentiators

OEM die-casting engineering expertise

Design engineering in OEM die-casting is constantly evolving, so engaging early with knowledgeable and experienced OEM die-casting suppliers who can advise and assist in Design for Manufacture is important for optimal outcomes. From material selection to choosing the optimal process and eliminating secondary operations, a capable OEM service provider will work with you in the design process, through tooling development and into mass production.

High quality die tooling development/production

One of the biggest differentiators between OEM die-casting companies is the thoroughness and care in the tooling process. Whether the tools are multi-slide or more conventional 2 and 3 plate devices, dies must be designed and built for reliability, long shot-life and maintainability. Built from high grade specialists steels, bothe pre-hardened and post manufacture heat treated, they must be built to withstand a high number of shots and maintain the component integrity throughout production. Downtime costs money and disrupts production, so look for OEM suppliers who warrant their tooling services for production pace and shot-life.

Factors such as runner type and location, gate shape, size, number of overflows and position of the mould cooling system are important die design parameters. Factors such as alloy

composition, melt temperature, die surface temperature, injection pressure and the weight of the parts are the critical manufacturing parameters, which must be planned for in the tooling development and manufacture.

Consideration must be given to choosing hot chamber or cold chamber processes – often driven by design requirements, material choices, productivity goals and cost constraints.

Proven track record in mass production

Look for your OEM supplier to have a track record with significant international customers, excellent quality processes and great record keeping and up to date equipment. If you need the largest parts – up to 80kg in Aluminium – look for them to have die-casting machines from Ida Group, in Italy – or local equivalents, which are slowly increasing in availability.

Ideally, your chosen OEM will want to introduce you to one or more of their happy customers – and they’ll be able to show you high quality tooling and components made for such customers – within the limits imposed by client confidentiality.

Communication processes and time to production

Your team needs to collaborate with the OEM part and die designers and the manufacturing management quickly, across time zones and language issues. Look for your OEM die-casting supplier to have the resources and attitude to support your project, and accommodate your culture and business practices without language barriers.

Material options

The low and high pressure die-cast process is used to produce parts from Aluminium, Magnesium, Copper and Zinc and a wide range of specialist alloys.

Aluminium OEM die-casting alloys

Aluminium and its alloys are the most commonly applied OEM die-casting raw materials, and aluminium alloys are best suited to cold-chamber casting. Alloys usually contain Silicon, Copper, and Magnesium. They are lightweight but strong and offer great dimensional stability, so they’re the right choice for complex, fine-featured parts which are cost constrained. Aluminium alloys provide good corrosion resistance, component ageing properties, temperature resistance, and high levels of thermal and electrical conductivity.

Common alloys employed are;

380 – General-purpose alloy, good castability and mechanical properties. It is used in a very wide variety of products, from automotive motor/gearbox casings to electronics enclosures.

390 – Excellent wear resistance and fatigue and peening resistance. Initially developed automotive engine blocks and is also widely used in machine components where vibrations are present.

413 – Among the best casting properties – low viscosity at moderate melt temperatures. Used for hydraulic cylinders and low corrosive fluid handling equipment.

443 – More ductile than other alloys, used for components that require plastic deformation after casting – such as swaged parts or parts with integrated rivets.

518 – Somewhat more ductile than most alloys, but with great corrosion resistance. Used widely in aircraft components, ornamental hardware, and escalator treadplates.

Magnesium OEM die-casting alloys

Magnesium widely used in OEM die-casting. Lighter and more machinable than Aluminium alloys, ideally suited where weight and extensive post machining or surface finishing are factors.

Magnesium die-casting alloys are suitable for hot-chamber processing, making them faster to process than Aluminium alloys. Magnesium is generally alloyed with Aluminium, Zinc, Manganese, and Silicon.

Common magnesium alloys are;

AZ91D – General-purpose alloy with good castability, corrosion resistance, and strength-to-weight ratio. Used for mechanical and power-train components, consumer products.

AM60: An alloy with good castability, strength, vibration dampening, and ductility. It is used in automotive components such as seat frames and panels.

AS41B and AE42 (rare earth alloys) –  Higher temperature resistance, great creep and corrosion resistance, good ductility. Both alloys are found in automotive engine and EV motor parts.

Zinc OEM die-casting alloys

Zinc alloys are a major category of die-casting materials. Suited to hot-chamber processing, zinc is the most easy to process and manufacturer forgiving, it has benefits like good impact strength, ductility and great palatability. Zinc alloys are gentle on the die faces, being low abrasion and aggressiveness in the melt, resulting in high tool shot-life.

Zinc is higher density than Aluminium and magnesium and is generally alloyed with Aluminium, Copper, and Magnesium.

Common zinc OEM die-casting alloys are:

Zamak 3 -General-purpose alloy that is easy to cast and offers excellent dimensional stability. Uses include ceiling fan and plumbing components.

Zamak 2 – Slightly stronger and more expensive than Zamak 3, due to the added copper content. It is often used to produce low volume cavity parts for plastic injection moulding.

Zamak 5 – Close in composition to Zamak 3 but with greater tensile strength and lower ductility. Used for products like small automotive parts and wheel balancing weights.

Conclusion

OEM die-casting is a flexible and low cost method of producing highly repeatable, strong and light components at manageable costs. Used appropriately, OEM die-casting services can provide components that serve in a wide range of industrial applications.