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True that it is a ‘disruptive’ technology, because it changes the way engineers conceive, develop and design products. But while it can produce parts that were previously unthinkable, it is not always the best manufacturing option.
From CNC to DMLS
The very words 3D printing hold connotations of innovation and the future. So people often ask to ‘3D print a piece’ (that would’ve previously been produced using technologies such as CNC machining) without paying due attention to the consequences.
Asking questions should be the first step of a project
When potentially turning to 3D printing, it’s a good idea to ask questions and look for answers so as not to run into problems, such as overspending the budget or not respecting the timeline. You should ask yourself: what are the considerations when designing for CNC and DMLS (Direct Metal Laser Sintering) parts? Which is the most economical solution for my project? How many pieces will I have to produce? What finishes are needed to achieve the desired final quality?
Design and build considerations
The cost of 3D printing is always proportional to the material used. It does not matter if any material is then removed (being only functional to the build of the part, such as the support structure that prevents any collapse during the production phase) – the designer who wants to optimise a design for 3D printing should minimise all material consumption; improving the geometry and volume not only of the component, but also of the support structure. And of course they will have to analyse the required functionality of the part and reconstruct the geometry based on that too. All the time being mindful of timescales, type of post-production required, and overall cost.
The necessary enemy
The supports are the ‘necessary enemy’, usually lengthening the construction and finishing time of the part. Despite them being removed after the build, they are indispensable to the production of a high-quality part, and can be summarised as follows:
- they support new layers, in particular if they are facing downwards or overhanging
- they absorb and dissipate process heat
- they anchor the workpiece to the construction plate, thus holding against pressure and reducing deformations
- they keep the most delicate parts steady during construction and subsequent processing phases.
In the examples above – a piece produced first by CNC machining (figure 1), then in DMLS 3D printing with a non-optimised design (fig. 2) and finally printed after the design optimisation process (fig. 3). The main goal was to optimise the design of the part to make it functional but economically sustainable. The resulting design was able to:
- reduce the volume by 80%
- reduce the projection by 12%
- reduce the volume of material to 5% of the CNC machined volume, compared to a reduction to 88% in the non-optimised project.
We calculated that optimising the design of the part for 3D printing has produced some significant advantages:
- reduced printing time by 84%
- increased the number of units produced at the same time (in the machine) by more than 100%
- reduced finishing time by 80%
- reduced the unit cost by 75%.
Ultimately, the two technologies are mutually alternative in the production phase of the part, but they are complementary if you consider how CNC machining is still the technology needed in post-production after DMLS (such as for the removal of supports or required surface finish).
For more information, please take a look at the following design tip on designing parts for DMLS: https://www.protolabs.co.uk/resources/design-tips/designing-for-direct-metal-laser-sintering/
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.