3D Printing Process Principles and Technical Standards for Engineering Product Evaluation

3D Printing Process Principles and Technical Standards for Engineering Product Evaluation

Additive manufacturing has left the prototype stage, and buyers now judge printed parts against the same mechanical, dimensional and compliance criteria used for moulded or machined components. This note covers how the three mainstream processes work, the tolerances and material data engineers can design against, and the standards that belong in a supplier evaluation file.

1. Working Principles

FDM extrudes 1.75 mm filament through a heated nozzle, fusing roads to the previous layer by thermal diffusion. Since bond strength depends on nozzle and chamber temperature, parts are anisotropic: strength across layer lines reaches about 55 to 75 percent of the in plane value.

SLA and DLP cure photopolymer resin layer by layer with a laser or projected UV mask. Resolution is set by spot size and layer height rather than nozzle diameter, giving the tightest finish, but parts need washing and post cure, and aged resin turns brittle unless an engineering grade is specified.

SLS and MJF fuse polymer powder with a laser or infrared fusing agent. The powder bed supports the part, so no support structures are needed, overhangs are unlimited and parts can be nested for volume runs. PA12 remains the workhorse for functional end use parts.

2. Capability and Verification

Tolerance claims must be tied to a measurement method. ISO/ASTM 52902 defines test artefacts for geometric capability, while ISO 2768 covers non critical features. Request per lot: artefact deviation, roundness and flatness, minimum feature size and hole shrinkage. FDM holes under 4 mm need 0.1 to 0.2 mm negative compensation; SLS shrinkage of about 3 percent is compensated in the build file.

3. Material Data for Design Calculations

These follow ISO 527-2 or ASTM D638 tensile testing and ISO 75 heat deflection testing. Apply a safety factor of at least 2.0 on the weakest axis, not on the datasheet XY value.

4. DfAM Design Rules

• Minimum wall: 1.2 mm FDM, 0.8 mm SLA, 1.0 mm SLS; load bearing walls 2.4 mm and above.
• Overhang below 45 degrees from vertical to avoid support marks; SLS has no limit.
• Mating clearance: 0.3 mm sliding, 0.15 mm press fit after trial.
• Holes: 2 mm minimum in FDM with 0.2 mm compensation, teardrop profile on horizontals.
• Threads: pilot hole plus brass heat set insert for parts opened more than ten times.
• Internal fillet 3 mm minimum to cut stress concentration; orient the build so tensile load runs in the XY plane.

5. Standards Checklist

6. Evaluation Workflow

1. Define load case, temperature, chemical exposure, service life and cosmetic class.
2. Screen processes against the requirement matrix, including anisotropy and tolerance class.
3. Select material from test data, then confirm with printed coupons for tensile and thermal checks.
4. Run a DfAM review: wall, overhang, clearance, inserts, build orientation.
5. Print a capability artefact lot and measure against ISO 2768-m or the drawing GD and T scheme.
6. Qualify functionally: static load to 1.5 times working load, ISTA 3A drop test, thermal cycling.

7. Conclusion

Evaluation is reliable when process physics, tolerance class, material data and compliance are stated together and verified with artefacts and coupons. Request the artefact report, batch certificates and RoHS plus REACH declarations for the technical file. Our team runs FDM, SLA and SLS programmes at 0.05 mm resolution with dimensional reports per lot. Send your drawing and load case for an evaluation.