Prototyping, 3D printing, additive manufacture, whatever we choose to call it now offers a wide variety of options and importantly capabilities. Which one is ‘best’ depends on what you are trying to achieve.

Define and prioritise your goals

So, step one, define and prioritise your goals. These should include delivery, cost, quantity, accuracy, surface finish, and material for starters. Now given this to work with, we can start to narrow down the options.

Time considerations

The first consideration ironically has got to be delivery. If the parts are required same day then this will usually set a geographic radius and narrow the options to someone who will have a machine idle waiting to jump on your job as soon as it arrives.

A perfect example happened to us yesterday, we received a request for 6-off small parts to be available for collection later that day or latest first thing the following morning. Material had to be robust, geometry was simple, accuracy good. This was achieved by CNC turning and the parts were in our hands just after midday.

Getting things done quickly is not just about the process but about machine loading and willingness of the supplier to go that extra mile and make things happen….and of course a little bit of luck!

Increase the delivery slightly and there would have been other equally applicable options.

Costs and budget

Secondly, budget is of increasing importance, as there are now printers in existence that range from a few hundred pounds to hundreds of thousands of pounds. These deliver a huge range of materials and accuracies as well as quality. This is not to denigrate the lower end printers, just to highlight that suppliers will invest serious sums of money to achieve a quality level. If you don’t need this then there are options to reduce cost, the difficulty is frequently in understanding or specifying the acceptable concessions.

How many do you need?

Number three is quantity, which is going to affect process selection due to the associated economics and timescales. One hundred parts in three days can be resolved several ways and is very dependent on material, geometry and surface finish requirements. For example, laser sintering (SLS) will be faster than fused deposition modelling (FDM), but both options would be thwarted by specifying a gloss finish.

The final touches

Accuracy can also be affected by machine type but also part design, orientation, process selection and monitoring. The application is likely to impose requirements for parts to fit together, for example bearing location diameters, although the option of using a secondary process always exists. If the layer thickness is greater than the desired accuracy on a feature, then build orientation becomes important and must be specified.

Surface finish is a function of the process, material and calibration. For example, whilst laser sintering gives great material properties, the surface finish is not as good as Stereolithography. If parts are for airflow modelling or cosmetic this may be an issue that needs to be taken into consideration.

Material choice has huge ramifications and knowing the production intent is always useful. Specifying a metallic part over a polymer will immediately have cost and lead-time implications, as will any ‘finishing’ work that is required, be that anodising or painting. So, if the part is purely required for an assembly trial, can a polymer be substituted?

Analysis support

At Plunkett Associates we are working through this kind of analysis all the time, looking for what will meet your goals and what trade-offs are necessary. The importance of knowing how each of these factors impacts your requirement will help us to help you.

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Plunkett Associates
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