What is investment casting?

There are some common processes that are used for mass-producing metal parts. As an Investment Casting specialist, we often get asked by engineers what investment casting is and why should they use this process over and above any of the others. 

In this article we will go through the investment casting process and identify some pros and cons associated with it.

What is Investment Casting?

Also known as lost wax casting, the investment casting process dates back over 5000 years. Today it offers the capability to produce light weight and complex components while minimising waste energy consumption and subsequent machining.

Essentially, investment casting involves pouring a liquid metal into a hollow ceramic mould. Once the liquid metal has cooled and solidified, it is extracted from the mould cavity. The process, up to the pouring of the metal is what makes the investment casting technique unique and delivers a better surface finish than conventional sand-casting methods.

The investment casting process

A wax mould or pattern is made by injecting molten wax into a die. Wax patterns are then ‘invested’ or dipped into a high-grade ceramic slurry before being coated by a further layer of ceramic particles (which are slightly larger) to create a thick ceramic mold. 

The wax inside the ceramic mold is then melted away in a high-pressure steam boiler (hence the name lost wax) and replaced with the final component material. Steel or aluminium is melted down and poured into the ceramic fired and pre heated mold. This allows for the metal to run into intricate areas of the pattern.

Once the mold is fully cooled and the metal has solidified, the ceramic is removed leaving the cast component. Often, the investment casting process can provide an adequate surface finish however mating faces may need to be machined for improved accuracy or sealing properties. 

What is investment casting used for?

The applications for investment casting are limitless. Its total flexibility makes it possible for highly complex parts to be made relatively simply with consistency and accuracy. With these benefits it is hard not to specify the limits of components that can be cast.

The aerospace and defence, automotive, engineering and oil & gas industries are some of the business sectors that benefit from investment castings, making components such as gear box assemblies, engine components, tools, valves and pumps.

What are the main pro’s and con’s of investment casting?

In our blog article, you can read more about the detail behind the advantages of investment casting, but here we identify the main pro’s and con’s.

Pro’s

• Fine surface finish, resulting in shorter lead times and cost savings from no machining requirements
• Superior dimensional accuracy in production which reduces flaws and waste
• Supports fine details and complex parts which allows for greater freedom of design
• Easy to detect and rectify faults 
• Very versatile, suitable for a variety of metals and can produce most casting shapes from the process.
• Can be used to produce prototypes prior to die casting tooling investment

Con’s

• Whilst higher production levels can be achieved with low repeat costs, the initial preparation of wax pattern tooling can be time consuming and expensive depending on the complexity of the component being produced. 
• The cycle of manufacture doesn’t lend itself to super-fast, high volume turnaround times. 
• It is generally better suited to  components with a combined mold weight of below 100kg.

Weighing up the pros and cons, there are some projects where using the investment casting process makes total sense, depending on things like the design requirements, the quantity of parts and the timescales involved, the con’s may be outweighed by the pro’s. 

Rest assured, that with over 70 years’ experience in investment casting, the team here at PI Castings are well equipped to advise you on the best manufacturing solution for your project, if you have one in mind, please get in touch with our team on 0161 9255160.