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3D Printing Vs Injection Moulding Vs Machining

Speaking to a friend recently- one who works in Engineering nonetheless- it became clear to me that those who are not embroiled in the world of FDM 3D Printing still have misconceptions about the technology and its current place in the market.

Said friend kept on using the stereotypical buzz word that is typically associated with FDM 3D Printing- ‘Prototyping’. In industry this is not a falsehood, there are countless companies who use FDM 3D printing as a Prototyping tool. However, to stop using the technology after the Prototyping stage is perhaps where the technology is not being exploited to its maximum potential.

Rewind five years and the material options for 3D printing were stunted at two- PLA or ABS. PLA, although very easy to tune in and print with, cannot be described as an Industrial plastic, and therefore applications are limited. ABS possesses the mechanical properties to hold up to Industrial applications. For FDM technology to be a success, it needed to ease in other Thermoplastics as well. Today, the range of 3D printable Thermoplastics is extensive. PET-G, Nylon 12, various Composites etc. Typical machined plastics such as Acetal or Polyethylene are still not common or easy to print with, however it is only a matter of time before these become fully available as well.

My pro 3D printing argument had jumped over the material hurdle. However, my friend had a counter argument prepared- ‘but it takes a long time to print something compared to Injection Moulding or Machining, so it ultimately costs more money’.

With this statement he was both right and wrong. The run time of a 3D Printed object 99 cases out of 100 will be longer than both Injection Moulding and Machining, but it is the total cost and time that needs exploring. Set up time for FDM 3D Printing is significantly less than Injection Moulding or Machining in most cases. Having worked in a machining environment- one which incorporated expensive metrology equipment to minimise set up time- a 3hr set up time per operation was common place. This is 3hrs where the machine is idle and not making money. With the right expertise, most 3D Printing jobs can be set up ‘offline’ whilst the machine is printing another job.

In terms of run time, Injection Moulding is considerably shorter than both 3D Printing and Machining. However. the cost of producing a Mould Tool is very high, something that neither of the other technologies require.

Therefore, it becomes clear that at lower quantities, 3D Printing certainly has a cost advantage over both Machining and Injection Moulding. A representative example is shown:

In this example it is assumed that the Cost per Hour for the three technologies are equal. The Run Time for the 3D Printed part is three times greater than the Machined part and 100 times greater(!) than the Injection Moulded part. Based on this, you would be forgiven for thinking that 3D Printing is not a cost-effective solution for this product. However, when referring to the Graph, it shows that 3D printing is the most inexpensive manufacturing solution at quantities between 1 and 5. As the quantities increase, the two more conventional manufacturing technologies are cheaper, due to their significantly lower Run Times.

This example is only representative, but a good indicator of how long set up times and expensive mould tools drive up the price of low batch quantities. It is at these low volumes where 3D Printing is under-utilised.

FDM 3D Printing does have other limitations such as tolerancing, surface roughness and its anisotropic nature. However, for certain parts it is a technology which should be a final solution and not simply a ‘Prototype’.

In my next blog post, I will be discussing some of the more advanced 3D Printable Thermoplastics- such as ESD and Conductive Materials- and exploring their applications.

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