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.

Friday, 14 June 2013

The Journey to Find Cost Efficient Aluminium Rapid Cast Parts. Part One - The Dilemma

We are an engineering design consultancy based in Kingston. Engineering is our work and hobby. So to put it mildly we enjoy what we do and we are always on the lookout for new processes and ideas to help us along our way. In-house we have a 3D printer which is a fantastic asset for prototyping initial ideas that can be shown to clients in a physical form and then tweaked as required.

Often we require rapid cast metal parts. In the past we have designed in CAD and then sent the 3D files to a company that has a special wax printer that can print out a wax master allowing the part to be investment cast. This process , using the lost wax technique, is one of the oldest casting methods known.

Typically parts takes a few weeks to manufacture, the process is quite involved as the wax printing takes quite some time to create resulting in an expensive process.

Below illustrates the different stages required to achieve the aluminium parts using the example of a seat pad.

The seat pad was modelled from plaster to achieve the optimum shape required. Using a 3D scanner the pad was scanned and the data was transferred into Solidworks.
CAD rendering of the seat pad including an inscription of a finger print.

To show the stresses of the design finite element analysis was used to test the CAD model.

The CAD was sent off to create a wax replica using a 3D wax printer (similar to a prototyping machine).

This is then attached to a central wax stick to form the assembly and mounted onto a pouring cup. In this case the wax replica was also finished so as to produce a higher quality result.

A shell is built by immersing the assembly in a liquid ceramic slurry and then into a bed of fine sand forming several layers.

The end results of the investment cast process. The ceramic is then dried in the oven.

The ceramic is dried while the de-waxing occurs as the wax is melted out in an autoclave. This creates a negative impression of the assembly. The shell mould is then fired in a high temperature oven.

The final part (sorry no photos) involves casting as the shell is filled with molten aluminium. When this has cool  and solidified the ceramic shell is broken off and then cut away from the central assembly.

The end result is the aluminium part identical to the original wax replica.

We were really pleased with the quality of the parts, the tolerances were good and the surface finish was impressive, just what we were looking for. However, they took around 2 to 3 weeks to be completed and the process was also extremely expensive. 

This got us all thinking to explore some different routes for a low cost alternative shorter process.
The following blogs over the course of the next few months will be our ideas and thoughts on what went well as well as wrong and most importantly of all if we managed to create a more cost effective part to the same quality.

Friday, 7 June 2013

JNDC Achieves ISO 9001:2008 For the 5th Consecutive Year

The Kingston based  engineering design consultancy JNDC Ltd has achieved the internationally recognised ISO 9001:2008 establishing it as one of the leaders in its field.

The independent assessment demonstrates the commitment to customer service and quality in delivery.

ISO 9001 was first introduced in 1987 and requires organisations to demonstrate that they do what they say they do and that they have a quality management system in place to ensure consistency and improvement; leading to high levels of performance and customer satisfaction. Certified organisations are committed to continuous improvement and are assessed annually to ensure progress is being maintained.

JNDC's Operations Director Dean Carran said, 'We are particularly pleased to have achieved ISO 9001:2008 certification as it underlines our ongoing commitment to our customers and our focus on quality.  Not many customers get to see their suppliers’ ‘back-office’ activities.  This recognition demonstrates we can provide a quality solution from quotation to delivery.'

Established within the aerospace industry JNDC provide mechanical design solutions within areas such as tooling, fabrication and manufacturing techniques.  JNDC's expertise has allowed them to expand into areas such as new product development, re-life and redesign in markets such as consumer products, medical devices and industrial equipment. Using the latest 3D CAD modelling, finite element analysis, testing, prototyping and development facilities JNDC's engineers and product designers have the capability to offer a competitive price with outstanding quality and service.