What is investment casting?
In our world today, investment castings are all around us. Whether you are driving your car, using a DIY tool or playing a game of golf, you are using investment castings. From turbine blades through to gears, medical equipment and golf club heads, investment casting is used to produce a whole host of components in many different industrial sectors.
In this blog, we will look in detail at this highly versatile and popular technique and find out how the process works.
Why choose investment casting?
In very basic terms, investment casting, also known as lost-wax casting or precision casting, involves creating a wax pattern and using this to produce a ceramic mould. The ceramic shell mould is then fired and filled with molten metal to produce the metal 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 – reducing the need for secondary machining.
The process can be traced back more than 5000 years to ancient China and Egypt where beeswax was used to craft jewellery and ornaments. These days, we use more sophisticated polymers and refined techniques, but the fundamental process remains largely unchanged.
How the process works
The first stage is to create a wax pattern – which is an exact replica of the final product. Each casting requires a sacrificial wax pattern.
The wax pattern is manufactured using a specially created wax injection tool. This pattern is attached to a tree-like assembly. It is then coated in a liquid ceramic slurry (the investment) before a dry ceramic granular layer (stucco) is attached. This is dried in environmentally controlled conditions. Additional coatings are added before the investment reaches the required thickness to withstand the rigours of the casting process.
The term “investment casting” is used to describe the process of ‘investing’ or coating the wax pattern with the ceramic material.
The ceramic shell dries before steam is used to remove the wax. It is then fired at high temperature to harden the material, a process that doubles the mechanical strength of the shell.
While still hot, the shell is filled with molten metal, which then cools and solidifies. The ceramic shell is mechanically removed to reveal the cast metal product beneath. The casting is removed using cutting or plasma techniques. Any minor finishing can then take place.
Quality control is essential and, once finished, the casting is inspected using modern CMM equipment techniques to ensure that it meets the required drawing specifications.
