Fed up with layers? Need a better cosmetic finish without paying the earth?
Additive manufacturing, with all the technical advances and media publicity within 3D printing, is certainly booming! Prototyping through methods, such as Stereolithography (SLA) or Selective Laser Sintering (SLS), give obvious time advantages over some of the more traditional methods, such as CNC machining, but have their own limitations such as accuracy and material choice.
Be aware however, that the huge leaps in the additive manufacturing sector has forced other technologies to re evaluate the way they work to remain competitive. Updated software has meant CNC machining is now able to deliver parts that are smooth, primed and often fully cosmetically finished for only a little more than the standard SLA or SLS part.
This brings huge advantages to someone who needs a high cosmetic finish to their prototype or equally to someone who wants to follow with a production run of parts..jpg "CNC machined prototype part")
All technologies have advantages and disadvantages and people will always have preferences; what we would like to show you are the merits and therefore the relevant applications so you can make an informed choice depending on your requirements and specific part needs. Here we will consider CNC machining alongside additive manufacturing.
CNC Machining vs Additive Manufacturing
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Additive Manufacturing |
CNC machining |
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Material options |
There are limitations although options are increasing and include metals, plastics, ceramics and composites. |
Nearly unlimited. |
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Part size |
Machines that are readily available can run parts to build sizes 650 x 750 550mm. Bigger machines are available but costs and build times then start to escalate. |
Bigger machines are far more readily available and therefore cost is not dependent on part size. |
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Part Complexity |
Nearly unlimited. As long as there is CAD data the design can be achieved. |
Limited. As complexity increases so does the number of set ups and tool changes. High aspect ratio features, deep slots and holes in square corners can be a challenge. |
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Feature detail |
Can produce sharp inner corners and features with high aspect ratios. |
Inner complexities are a challenge but part to part accuracy and surface finish is excellent. External sharp edges, smooth blends and clean chamfers on parts are not a problem. |
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Accuracy |
0.125 to 0.75mm As dimensions increase so does the inaccuracy. |
0.0125 to 0.125mm High accuracy and precision. |
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Repeatability |
Moderate. Temperature, humidity, orientation and placement are amongst the many factors that can affect the quality of the part. |
Good. Part to part accuracy is one of the strengths of CNC machining especially if the tool and materials are unchanged. |
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Surface finish (plastics) |
SLA Ra 5-25 microns. SLS Ra 15-35 microns. Post finishing is required to achieve some smoothness due to layering and rough surface finish, however care must be taken not to affect the dimensional accuracy of the part. Note post finishing processes add time and cost. |
Ra 0.5 to 5 microns. High cosmetic surface finishes are easily achieved. |
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Leadtime |
The ability to cope with complex designs means Additive Manufacturing processes are usually quick, however increased quantities of parts means a far longer leadtime than through other manufacturing techniques. |
The more complicated the part the longer the leadtime for low numbers of parts, however once the design has been finalized, increased numbers of parts can be made in a much shorter space of time. |
So, time, quality, quantity, cost – all factors to be considered when considering the best process for your prototype project. If in doubt give us a call and we will be more than happy to discuss the best way forward for your individual requirement.
