CRP is introducing Windform PS, a new polystyrene-based material that is optimised for the creation of selective laser sintered (SLS) disposable patterns for rapid casting.
CRP's R&D department has been involved in rapid casting since 1997, when the company began to study laser sintering technology for the manufacture of disposable patterns using polycarbonate and Trueform materials.
Although these materials were not suitable for titanium alloy pouring, because the high ash content remaining inside the shell reacted with the titanium alloys, producing porosity, they proved suitable for steel and aluminium alloys.
CRP therefore decided to develop new materials for sintering rapid casting patterns, and partnered with DTM in 1998 to be the first to use rapid casting for hard to cast shapes such as F1 uprights and gearboxes, and alloys such as titanium. They say they were first to optimise a polystyrene material for laser sintered patterns, known as Castform.
That year, CRP also began to optimise the engineering process and the manufacturing process, studying titanium rapid casting, based on the combination of rapid prototyping (RP) technology, to manufacture the disposable pattern, and investment-casting technology (lost wax casting) with titanium alloys.
CRP has utilised Castform from DTM for many years. Their R&D department built on DTM's knowledge and experience in rapid prototyping, casting and machining to become experts in the rapid casting process. This work has led to CRP being recognised as a leader in the use of rapid casting for motor sport applications throughout the world. These efforts have now yielded a breakthrough in this arena, namely Windform PS.
Windform PS is a new polystyrene-based material able to produce complex investment casting patterns. The sintered patterns are porous in order to allow wax infiltration, making them easy to handle and finish.
Windform PS patterns can undergo the typical rapid casting procedure, including autoclaves and flash firing steps, low-temperature furnaces and vacuum plaster casting methods.
Compared to other polystyrene materials available on the market, Windform is said to offer:
* Improved surface quality and details reproduction
* Less 'curling' effect on the first layers
* Very low ash content, making it suitable for highly reactive alloys such as titanium, aluminium, magnesium, steel and nickel-based alloys
It is particular suited for the foundry and RP market since the main applications are complex investment casting patterns and casting with highly reactive alloys, in addition to typical cast alloys.
The casting structure is formed of an aggregate of grains, or polyhedral crystallites, which produce isotropy compensation, a solid metal that is isotropic. Thanks to isotropy, predictions for component performance made using finite element analysis are said to be very close to the real behaviour of the part.
Rapid casting with laser-sintered patterns also allows complete shape conception freedom, needing no even supports and reducing undercut and tool path problems during CNC machining. It also allows for optimisation of the project to the working conditions, making it possible to create a product along its mechanical stress axes, and to obtain excellent reproduction of all details of the RP pattern, with tolerances and surface finish equivalent to high-quality fully machined parts.
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