Precision Investment Casting, also referred to as lost wax casting, is a process in which metals are casted into different shapes using wax and ceramics to act as the mould for the casting. This is one of the oldest known techniques for metal casting and has stood the test of time over centuries.
It finds usage in various industries like firearms industry, energy industry, gas and oil and even food industry. While many debate upon the strength and durability of this form of casting, doubting mainly that this method might provide weaker metal shapes as compared to forging or metal fabrication, these doubts have been laid to rest since aerospace, defence and medical fields have trusted equipment that are made from Precision Investment Casting.
As mentioned earlier, the process for Precision Investment Casting requires wax and ceramics to be the mould for the main metal. This is done in a very simple yet precise way (hence the name) and the steps are:
• Pattern Formation –Manufacturing of the wax pattern is the very first step involved in investment casting. Here it should be mentioned that wax is preferred over plastic, because wax melts easily and can be reused for another casting which is again a beneficial point from costing aspect. Special aluminium moulds are made to cast the pattern and this requires some trial and error, because factors like shrinking of the wax, the ceramic or even the metal should be incorporated.
• Assembly – For Precision Investment Casting, there are two ways to assemble the cast, one being single moulds and the other being tree formation. One of the main advantages of this method is that since there is no need to open the master cast, you can work with many intricate shapes for creating a mould. After the design is arranged, the wax is poured in to fill up the shape.
• Shell Building – For the tree formation, a ceramic pouring cup is attached to the end of the main bar that acts as the roots. This is then dipped in the refractory slurry that is made up of fine silica, sand and water. Once the initial layer of ceramic coating is formed, the set is then covered with sand and left to harden up.
• Dewaxing – This next step is crucial for Precision Investment Casting, as it involves much patience and precision. The hardened mould is turned upside down and then heated to a temperature of 200°F to 375°F which causes the shell to harden more and the wax to melt and be drained completely. This then gives birth to the cavity that will be used to cast the metals.
• Pouring and Solidification – Once all the wax is cleared out, the ceramic cavity is further heated to a temperature of 1000°F to 2000°F and the metal casting in poured into this hot and hardened casting as this helps with the easy flow of the metal into even the minute detailed section of the cast. This is then left to solidify.
• Cutting – After the metal has solidified and the shape has been taken, the outer ceramic casting is then cut off or broken away. Any residual sand is dusted away.
• Customisation – The final step is the customising of the design unless it was already set in a designed mould.
Like every other manufacturing process, the Precision Investment Casting too comes with its set of pros and cons, but the pros definitely outrun the cons. While some may say that this method is more time consuming and requires great skill and precision to achieve the end result, the good news is that the hard work that is done in the manufacturing process makes sure that you do not run the risk of damaging the end result while forming a shape out of it.
Intricate designs can be cast as one with this method. This process is known for its excellent accuracy in terms of dimensions and detailing, and the alloys that can be used are of a wider range. Though it does cost more when it comes to production, people do pay for quality products.
Being one of the oldest methods, the Precision Investment Casting surely has stood the test of time and kept growing and finding more and more manufacturers tuning to this method to belt out premium grade metal designs.