By Gary on 04/10/17 | Category - Informative


I think we can all agree that 3D printing (additive manufacturing) is grabbing headlines at the moment largely because there are so many affordable 3D printing machines appearing on the market and so many technologies and additive materials.  Subtractive manufacturing on the other hand is much less in the public eye but worth discussing in this article.

So, is additive or subtractive manufacturing something you should be considering for your next product?  Let’s look at the basic types of additive technologies to get started.

Stereolithogrophy(SLa) is a process where resin is cured with light in layers.  The advantage of this method is accuracy and quality of finish.  The disadvantages of this method is material choice and ultimately material strength.  SLa parts may have a support structure that needs to be removed. This is the most expensive process.

Selective Laser Sintering (SLS) is a process where powdered material is fused by a laser in layers.  The advantage of this method is strength of material and accuracy.  The disadvantage is material choice and surface finish.  SLS parts require no support structure as the part is supported by the powder that it sits in.  This process is cheaper than SLa.

Fused deposition modelling (FDM) is where an extruded plastic filament is fed into a heated nozzle and melted into position in layers. The advantages of this method are low cost, availability of inexpensive printers and material choice and strength. The disadvantages are slow build speed, low accuracy and poor surface finish.  FDM parts typically have a support structure but this can be done with a second material that is water soluble.

There are other types of 3D printing technology but in basic terms you either fuse powder, cure resin or melt filament using different methods.  So which method do you choose?  Do you buy a printer and do it yourself or do you choose a supplier and buy from them?  Let’s look at the key differences between the technologies and how you might use them.

FDM parts will be cheapest but lowest accuracy and are the most easily printed on your own sub £5k printer.  This method may not be good enough for customer visible parts although the technology is improving all of the time so this may change.  The quality of parts from a sub £1000 printer will be of poor quality, poor repeatability and poor strength where parts produced on a more expensive printer would be much better.  I would recommend looking at machines with a double filament nozzle and good resolution.  This type of printed part is typically used to make low cost prototype parts during a development programme or low cost jigs and fixtures.

SLA parts are typically used for high quality prototyping at the end of a development project to verify fit and function of a design prior to going into full production tooling. The parts are generally not tough, strong, flexible or UV stable enough to be used in full production and are expensive to produce.  The parts need to be stabilised with IPA and then cured with UV light before use.  SLA parts are commonly made on more expensive machines used by bureau services.

SLS parts are very strong, flexible or tough and are low enough in cost to be usable for production parts.  For customer facing parts a vibro finish would need to be applied to improve surface finish.  SLS parts can be dyed to a number of colours but typically they are either left off-white or black.  Again, SLS parts are commonly made on larger more expensive machines used by bureau services.

So what about subtractive manufacturing?  As the name suggests, this is about removing material to create a part rather than adding it. This typically relates to machining or CNC machining of metal and plastic parts but would also cover laser cutting, waterjet cutting and sheet metal punching and forming.  There is little in the way of affordable units for in house subtractive manufacturing bar a few small CNC desktop prototyping units so this is typically sourced from 3rd party specialists or is integral to the business you are running. Parts made by a subtractive method are as accurate as you need them to be and the choice of materials is limited only by what you can cut.  Prices are high to higher depending on quantity and accuracy.

So should you buy a machine and make parts in house or use a supplier or bureau service?  Buying parts in will give you the best quality and variety of parts in the best materials but at inflated prices, as the supplier has to make profit and pay for the investment they have made in their 3D printers.  Making parts in house means a capital outlay of between £2k and £10k.  You need to do the maths to work out what’s best for you.

If you are considering purchasing a 3d printing machine to produce production parts, I would be inclined to go with SLS as there is no support structure to remove and the parts can be nested together very efficiently, making the parts cheaper.  Take a look at Sinterit.

If all you are interested in is accuracy, then you would be better off with an SLa printer, so something like the Formlabs Form 2.  SLa parts made using the right resin can be used for casting, so ideal for jewellery makers.

If you just want to explore 3D printing and what it could do for your business, then I would suggest getting on board with a mid-priced FDM machine, so something like an Ultimaker 3. Finally, if you are an individual looking to play with 3D printing on a budget then a low cost sub £500 machine can be had.

Let’s now consider traditional production manufacturing techniques.  The media have made lots of noise about the future of 3D printing and how we will be using it to produce parts for production.  I’m sure they are right but we are not quite there yet.  If you are planning on producing highly customisable products in low quantity then consider 3D printing as an option. If you want to make strong accurate parts in low volume then subtractive manufacturing would give you the accuracy and strength of materials required.  But if you want to mass produce parts in plastic with little or no customisation then look at traditional techniques like injection moulding, blow moulding, die-casting and extruding.  This type of manufacturing requires an upfront investment to create the tools that make the parts, so this is only suitable for quantities of around 1000 or higher.

So where does this leave us?  Every product and every company will have different requirements, high volumes; low volumes; customisation; accuracy; strength; surface finish; colour and more often than not ‘low cost’, so it’s safe to say that I can’t impart enough knowledge or wisdom in this blog to allow you to make a decision about manufacturing your next product.  I hope I have given you some insight into the different technologies and what might be worth considering for your next product.

One last thing I want to end on. I think the most interesting aspect to the additive manufacturing story lies in using the process to make the tools that make the mass produced parts.  Mass produced parts are moulded from a metal tool that is costly and slow to make using subtractive manufacturing methods.  This means that to mass produce a part requires a large up-front cost.  A recent trip to a 3D printing show revealed some interesting developments in this area where 3D printing materials are being developed to replace that metal tool and therefore lower the upfront cost and time to mass produce parts.  I will be keeping a very keen eye on these future developments!

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