An Overview of Investment Casting and its Key Benefits

Published - 31st Jan 2024

Helping you choose the right manufacturing method for your component

Precision investment casting is at the core of Investacast’s metal castings business. We are a leading UK casting foundry with over 50 years’ of experience in the art and science of investment casting, enabling us to become a global supplier of high-quality castings for performance-critical applications.

Investment casting is a precision manufacturing process capable of meeting demanding specifications and finishes. As an expert casting company, we have extensive knowledge and understanding of the benefits of different methods of casting, including how to Design for Manufacture, and how to achieve the optimal balance between cost and fitness for purpose.

In this article, we will explain the benefits of the investment casting process to help you identify whether it is right for your application. 

What is Casting?

Casting is a well-established method of manufacturing which can produce parts in sizes, quantities and finishes suitable for a wide range of industrial sectors. 

The metal casting process starts with the creation of a 3D master die used to create a bespoke mould or ‘pattern’ in a repeatable process. Once the mould is complete, molten material is poured into the cavity created by a pattern to create the final product. When the material cools, it is removed from the mould and can be finished to the required specifications.

What is Investment Casting?

Investacast specialises in Investment Casting, a process that dates back over 5,000 years and has evolved to deliver many of the high-quality components used around us every day. The process takes its name from the application of a ceramic coating (the ‘investment’) onto a sacrificial pattern to form the mould.

Also known as ‘lost wax’ casting, because the wax used to form the pattern is ‘lost’ (melted away) to reveal the solid mould, investment casting is one of the oldest known metal-forming techniques. Ancient lost wax casting used materials such as beeswax and clay to produce copper, bronze and gold items much faster than through smithing or abrasion. 

The process has evolved significantly, particularly with the need for ever-tighter tolerances and increasingly complex components. Today, patterns are made from specialist waxes or plastics, or are 3D printed by sophisticated machines, and expert casting companies like Investacast can produce highly complex parts in specialised alloys for a wide range of commercial and industrial applications.

What are the key stages in Investment Casting?

Investment casting requires an expert understanding of the properties of materials involved at every stage of the process, which takes several days to complete.

Tooled metal master die

First, perfect tooling is required to produce a master die that can be used to create the expendable wax patterns which will then be invested to form solid ceramic moulds.

Creation of wax patterns

Wax patterns are created from the original 3D master die or tool. The patterns are assembled onto a ‘runner’, chosen based on the feed requirements for that part. At Investacast, this runner incorporates our special ‘quick release’ hanger attachment system, designed in-house to aid removal of the mould from the shelling line. 

The investment process

The wax assembly is then repeatedly dipped or ‘invested’ in layers of liquid slurry alternated with dry ceramic stucco to build up a semi permeable layer that will dry to form a solid shell. Care must be taken to ensure that the slurry is at the precise temperature and viscosity to form the right thickness and quality of investment for the eventual casting of your specific component.

The dipped and coated runner carrying the invested wax patterns is then air dried slowly over several days. Carefully controlled conditions allow it to dry consistently and form a ceramic shell of the required thickness. 

Wax removal by autoclave

The sacrificial wax is removed by heating the assembly in an autoclave, calculated to melt the wax without causing it to expand and break the mould. The ceramic shell is fired to sinter the mould, partially fusing the ceramic and removing the binder. This also pre-heats the mould ready for pouring.

The Pour

The hot ceramic mould can now be carefully filled with molten metal. The foundry team must ensure that the metal or alloy is at exactly the right temperature for the best pour (which will depend on the type of material being cast), and that the process of clamping, pouring, and rotating the moulds is handled correctly to deliver molten metal at the right temperature throughout the casting.

Finishing

After cooling for several hours, the ceramic shell can finally be mechanically removed to reveal the cast metal parts. Individual cast parts can then be finished as required, including shot blasting and heat treatment, machining and so on.

Inspection and testing 

Throughout the process, monitoring takes place to check the quality of the casting and that the final cast part meets specifications. This includes non-destructive testing.

Why choose Investment casting?

Investment casting allows us to create highly intricate and complex components with virtually any alloy. It produces excellent dimensional accuracy, high integrity and a fine surface finish. 

Here are some further reasons you might choose to produce your part using investment casting:

Versatility of design

Investment casting offers exceptional design flexibility. Complex components can be cast to near net shape, including internal shaping, undercuts and slots, and complex passageways. The capability to cast thinner walls than are possible in other processes such as sand casting may be key, as it can lead to lower overall weight or improved efficiency. Features such as logos, names and numbers can also be incorporated.

Versatility of materials

Most alloy bases such as ferrous, aluminium, nickel, copper and cobalt can be cast using the investment casting process. Some of these alloys are either very difficult to machine and process or almost impossible to machine economically, so investment casting is the manufacturing process of choice for components using these materials. 

At Investacast we have significant experience in casting difficult alloys such as nickel-based superalloys. These superalloys exhibit excellent creep strength, oxidation resistance, corrosion resistance and fracture toughness, but can be technically difficult to cast and machine. 

Range of sizes

At Investacast we can cast a wide range of parts, from small to large – for example we have cast parts weighing from as little as 10g to parts that weigh 30Kg (not including the runner).

Wide-ranging applications

Investment casting can be used in a wide variety of industries thanks to the range of metal alloys that can be cast in this way. Most metal alloys, including aluminium, bronze, steel and nickel, are well suited to investment casting and it is used in a wide variety of industries to produce many different components, from turbine blades through to safety interlocks and camera housings.

Tight tolerances

Cast parts can be highly accurate, reducing the need for further refinement. Investment castings can be held to much tighter tolerances than sand castings or forgings: close dimensional tolerances down to + – 0.15mm/25mm can be achieved through investment casting.

Exceptional surface finish

Investment casting gives a very smooth finish thanks to the ceramic mould, typically offering 1.6 Ra to 3.2 Ra surface finish as cast. This can significantly reduce the amount of secondary machining required compared to other manufacturing processes such as sand casting or forging.

Flash or parting lines can appear where products are cast using a two-part mould, such as those used in sand casting. Investment castings will also have parting lines, created by the two halves of the die and sliders. However, these are minimal and can be removed by post processing if the criticality of the part requires it, i.e. for cosmetic reasons.

Investacast offers a range of further finishes depending on the application, including:

• Steel shot blast
• Pickling and passivation
• Electropolishing
• Glass bead blast
• E-coat
• Light aluminium oxide
• Powder coating/ painting

All our castings are inspected and tested using CMM (Coordinate Measuring Machine) and standard equipment such as micrometers, verniers and gauges before dispatch, to ensure they meet specifications.

Faster production, lower cost

Quicker lead times are possible thanks to the immediate high-quality finish of investment castings, even when thousands of units are produced. Any reduction in post-production machining means quicker delivery and lower labour costs for your parts. 

Rapid prototyping

Investacast’s rapid prototyping service allows companies to turn innovative ideas into successful products quickly and efficiently. We offer casting simulation to ensure your product is validated through the casting process, and rapid production of prototypes to mitigate any risks when transitioning to production tooling.

Once the wax pattern has been produced a prototype product can be produced quickly, allowing designers to appraise their product before expensive tooling is manufactured. Investment casting of a single unit or small production run is possible – such rapid prototyping can reduce the lead times for test products by up to 75% compared to production tooling methods.

Low tooling costs

The investment casting process has much lower tooling set-up costs than gravity die or high pressure die casting, which require permanent casts to be manufactured. For this reason, it is sometimes used for pre-production runs for high-volume pressure die cast products.

Repeatability

The quality of investment castings is maintained from casting to casting, providing a very reliable product and low-cost repeat runs.

Sustainability

At Investacast, we strive to act in an environmentally responsible way in our foundries. Investment castings are created to near net shape, so the amount of material waste from production is minimal – this can be important for customers too, where more expensive alloys like nickel and cobalt alloys are used. 

We also reclaim and recycle almost all the wax (the reclaimed wax is sent away for processing and then used as runner wax). Metal used in the process, such as for the runner, is reused as remelt where applicable (at controlled levels) and any contaminated metal is sent away for recycling. 

In summary: Investment Casting has many benefits

Investment casting has developed into a reliable and versatile manufacturing method for precision castings for performance-critical applications.

Whether you are looking for a rapid, low-volume prototype, or require mass production of your component, Investacast can provide expert advice and casting expertise. We offer end-to-end solutions through our UK casting foundry in Devon and a global sourcing network spread throughout Asia and Europe – contact us now to find out how investment casting with Investacast can work for you.

Call us on +44 (0) 1271 866200 or email [email protected] to find out how Investacast can help you.