GlossaryKind of term: Manufacturing termMachining printed parts
What is post-machining of printed parts?
Machining printed parts means machining an additively built part until its dimensions, faces, fits and threads meet the drawing.
It applies to printed parts in metal and in plastic. The printing process gives the shape but rarely the size and roughness that fits, sealing faces, locating faces and threads need; those surfaces are printed with machining allowance and cut afterwards. In metal printing, removal from the build plate, support removal and a heat treatment usually come before machining. Who carries out those steps varies by supply chain.
What does machining printed parts depend on?
How much allowance is needed and how the part behaves in machining depends on the printing process, the material and the build orientation. Powder-bed processes usually need less allowance and leave a smaller size deviation than directed energy deposition (DED), including wire arc additive manufacturing (WAAM). Residual stress from printing can be released when the part comes off the build plate or during machining and distort it; in metal, stress relieving on the build plate limits that. Porosity can be exposed at the surface after machining. Hardness and machinability differ from wrought material of the same alloy and can vary with build direction.
How does machining printed parts work in practice?
Clamping and alignment often take the most extra time. A printed part often has no flat or cylindrical surface to clamp on; a fixture, soft jaws shaped to the part or printed-on clamping lugs that are removed later are common. Because the shape can vary slightly from piece to piece, the work origin is often probed per piece rather than set once. Agree with the designer which features are datums and how much allowance sits on which faces, and have datum features printed where possible. The print model with allowance is a different geometry from the final model and the drawing; you machine to the drawing. What that costs per piece depends on quantity, the clamping solution and how much the pieces vary.
What is machining printed parts often confused with?
Machining printed parts is not hybrid manufacturing: in hybrid manufacturing printing and cutting alternate in one machine, here a finished print is machined separately. Nor is it the same as post-processing a print, such as blasting, heat treatment or hot isostatic pressing: those change the surface or the material but do not bring the part to size.
Frequently asked questions
How much allowance does a printed part need?
That depends on the printing process, build orientation, material and the tolerance on the face. Enough to remove the roughness and size deviation of printing completely; agree it per face with the designer or the print supplier. Too little allowance leaves rough patches.
How do you clamp a printed part without a flat face?
With a fixture or soft jaws shaped to the part, or with clamping lugs or a margin printed on and removed later. Such a clamping solution is a one-off cost; how you spread it over the pieces is a convention of your estimate.
Why does aligning printed parts take more time?
Because the pieces can differ slightly from one another. You then probe the datum per piece and shift the work origin, whereas with wrought or drawn stock the origin is often set once per batch.