Thursday, 27 June 2013

3D Printing for Sand Casting - Part Two

 The Journey to Find Cost Efficient Aluminium Rapid Cast Parts Continued.

Over the past few years we have had several parts designed and cast using the sand casting process. 

The detail of the parts required are usually relatively simple.  We provide engineering drawings to a foundry in West Molesey, F Bullet & Co,  their pattern shop takes the drawing and makes a wooden master part.  Depending on the number of parts required, the master may be manufactured from other materials such as resins or even polymers.

Sand Casting

The pattern makers job is highly skilled, taking into consideration the flow of the molten material through the mould, shrinkage, draft angles as well as making sure the part cools as evenly as possible to prevent stress concentrations which could lead to cracks forming. 

In the past when we have had complicated geometry, say a 3D curved surface for example, we have sent the CAD off for investment casting. (as  I covered in the last blog)

The parts come back to a high accuracy and the surface finish is also really good.   I have never considered giving highly complex parts to a sand casting pattern shop as complex surfaces are not always possible to be fully represented on engineering drawings to allow the skilled pattern maker to create the wooden master by hand.  The investment casting process has the benefits of  3D CAD file that are sent directly to a wax printer.  Complex surfaces, geometry and features are all replicated extremely accurately via the wax 3D printer, something that is simply not possible to do sometimes using the traditional pattern makers approach.

In our design office here at JNDC we have a 3D printer that is usually running three or four days a week. All the parts printed are used for checking the design of prototypes as well as creating fully working plastic prototypes, however, it is limited to printing in "plastic".

For us here at the office the printer has been an invaluable tool for research and development.  There are so many 3D printing companies out there now that offer really low prices for plastic parts so we have never really used the printer for such a purpose.  We were "early adopters" of buying an in house 3D printing machine, but these days the cost of the machines have dropped so much, more and more companies, universities, colleges and schools are all now buying in the technology.

Below is a photo of a job that has just finished printing.

Parts just finished, still in the  printer.

Parts in situ with all the support material

Here I have removed all the support material 

This got me thinking.... why not use these plastic parts for the masters in the sand casting process?

Clearly it's not as simple as just printing out a part and handing it to the foundry and getting a metal part back.  Next blog I will start to open up this area further and explore what changes are needed to the CAD to allow the master parts to be printed and used directly as the master in the sand casting process.

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