Graphite Additive Manufacturing Accuracy

As engineers, the accuracy that can be repeatably achieved with 3D Printing technologies has long been an obsession with us. At first glance, variability can seem daunting with no obvious reason and it’s all too easy to accept that’s just the way things are.

Through a passion to always do better and improve, we have studied and gained a depth of understanding which enables us to build the most accurate parts possible.

There are many things that affect accuracy and repeatability when additively manufacturing.

  • Environment: Room humidity and temperature stability.
  • Component: Geometry, orientation, and placement in the build envelope.
  • Machine: Calibration, machine service standards, laser power and build parameters.
  • Material: Type, quality, and shrinkage characteristics.

If everything on this list is controlled well, you will find repeatable accuracy of parts to be very high. When introducing lots of different part geometries, shrinkage is the single most common reason for variability. Building a production run of a component and ‘dialling’ everything in to achieve the required accuracy is relatively straight forward. Building a 1-off component and expecting the tolerance to still be high, is more of a challenge. Unlike casting or injection moulding, 3D Printing behaves very differently due to the very nature of building layer by layer.

The thermal effects of sintering powder (SLS) and chemical effects curing a resin (SLA) lead to shrinkage properties for a given material. Although this will have a known % shrinkage value, variation in thin and thick sections and the chosen orientation can cause very different results for the same part. An experienced operator can make an educated guess on how a part will behave, but it will still be difficult to know if a tolerance will be met first time. This is why many companies quote ‘typical’ tolerances, and ‘geometry dependant’.

Here are our top tips to designing for, and getting the most out of your chosen machine.

  • Understand and communicate any critical tolerances. (This could change the chosen build orientation)
  • Keep the machine regularly serviced and calibrated.
  • Build and measure frequent calibration parts. (We’d recommend every build or at least once a week).
  • Understand the characteristics of the machine/material and choose the part orientation carefully.

About us specifically……

By recording and analysing many thousands of part measurements, we understand what is typical and possible. We are pleased to publish these figures and give more data and facts around what tolerances we are working to.

 Typical Tolerance (achieved >95% parts)Guaranteed Tolerance (all delivered parts)Enhanced Tolerance
SLA±0.10% (min 0.13mm)±0.40% (min 0.25mm)Please call to discuss any specific tolerance requirements
SLS±0.13% (min 0.15mm)±0.50% (min 0.30mm)
MJF*±0.30% (min 0.20mm)±0.50% (min 0.35mm)
*MJF accuracy is based on the data provided from HP validated by in-house analysis.

For jobs that don’t have a specified tolerance, we at minimum, will build and measure an X,Y,Z calibration part and verify that the machine is dialled in and working within our expected standard. This gives a very good level of part accuracy and repeatability. Where specific tolerances need to be met for certain components, this can be arranged. We’ll review the customer specified tolerance, component, and batch size, then determine how this can be achieved. This could be straight from the machine after dialling-in, may require some fettling by hand or CNC machining as a secondary operation.

Please talk to us about your challenges and requirements, and we’ll see how we can help.

Review and download our Accuracy Guidelines Document here.


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