Designing EV Prototype Parts for 3D Printing

The problem

Student EV teams and start-ups rely on 3D printing for brackets, covers and test fixtures, but parts designed as if they were machined often warp, fail along layer lines or do not fit. Designing for the process from the start saves material, time and broken prototypes, and teaches the trade-off between a quick print and a functional part.

Objectives

• Choose three example prototype parts and define their loads, fits and environment.
• Model each part with print orientation, minimum wall, overhang and hole-tolerance rules in mind.
• Use configurations to try clearance values and create a fit test coupon.
• Check strength with a simple static study using orthotropic thinking, and validate by a physical test.
• Export STL or 3MF, print, measure and record the design-to-print deviation.

What you need

Key concepts

Anisotropy

FDM parts are weaker across layers than along them because layers bond less well than the extruded filament itself, so orientation must put the main stress along the layers.

Overhang angle

Faces leaning beyond about 45 degrees from vertical usually need support material. Designing chamfers instead of flat overhangs avoids supports.

Print clearance

Holes print smaller and pins larger than modelled, so mating features need a deliberate clearance found by test coupons on the actual printer.

Infill and perimeters

Most strength comes from the outer perimeters, so wall count often matters more than infill percentage for brackets.

Step-by-step guide

1. 1

   Pick parts and requirements

   Choose three example parts for an e-scooter prototype: a handlebar display mount, a bracket that holds a charging inlet to the body, and a snap-on cable clip. For each, write the load (for example a 2 kg display with a 3 g vibration allowance), the fits needed, the operating temperature and whether it is for a quick look or functional testing. This decides material, as PLA softens at lower temperatures than PETG or ABS.

   Checkpoint: A requirement table for each part with load, fit, temperature and chosen filament.

2. 2

   Print a calibration coupon

   Model a fit-test coupon with a row of holes and pins at nominal diameters such as 5, 8 and 10 mm, plus a slot. Create configurations with clearances of 0.1, 0.2, 0.3 and 0.4 mm using a Design Table driven from Excel. Print it in the same orientation and material as the real parts and record which clearance gives a sliding fit and which a press fit on your printer.

   Checkpoint: A measured table of printed hole and pin sizes against nominal, giving a clearance value to use in the real parts.

3. 3

   Choose build orientation

   For each part, decide which face sits on the bed. Put the main bending stress along the layers, keep cosmetic faces off the support side, and minimise supports. Use Draft Analysis with the build direction as the pull direction: faces shown as needing draft beyond about 45 degrees will be unsupported overhangs. Sketch the orientation in a reference plane so it stays visible in the model.

   Checkpoint: Each part has a recorded build orientation, with the reason linked to load direction or surface finish.

4. 4

   Model the display mount

   Model a clamp around an example 22 mm handlebar with a split ring, a single M5 bolt and a plate for the display. Use a wall of at least four perimeters at your nozzle width, fillets of 2 mm or more at the clamp root, and ribs to stiffen the plate. Replace flat overhangs with 45 degree chamfers so no support is needed. Apply the clearance from the coupon to the bolt hole and add a hex nut trap.

   Checkpoint: The model has no feature thinner than the stated minimum wall and the draft analysis shows no unsupported overhangs.

5. 5

   Model the inlet bracket and clip

   Model the charging inlet bracket with bosses for heat-set inserts, sized to the insert manufacturer's recommended hole, because printed threads wear quickly. Model the cable clip as a cantilever snap fit, calculating the allowable deflection from the strain limit of the material so it does not crack. Orient the clip so the snap arm is printed along the layers. Add a small fillet at the root of the snap arm to reduce stress concentration, and print one spare clip to test to failure.

   Checkpoint: Snap-fit deflection is checked with a cantilever strain formula and stays under the example material limit.

6. 6

   Run an indicative strength check

   Run a static study on the display mount using a linear elastic material with a conservative modulus and strength for printed PETG or PLA, added to a custom material library. Fix the clamp bore, apply the display load with a 3 g factor and use mesh control at the clamp root. Remember the model is isotropic while the print is not, so treat the factor of safety as indicative and aim higher, for example above 3.

   Checkpoint: Indicative factor of safety above the stated target, and the location of peak stress identified for the physical test.

7. 7

   Export and slice

   Save each part as STL or 3MF with a fine resolution setting so curves are smooth, and preview with Print3D if available. In the slicer, set the agreed orientation, perimeter count, infill and layer height, and note print time and mass. Compare the slicer mass with SOLIDWORKS Mass Properties, remembering infill makes the print lighter than a solid model. Save the slicer project alongside the CAD file so every print can be repeated with the same settings.

   Checkpoint: Print time, filament mass and settings are logged for each part, and no unexpected supports appear in the slicer preview.

8. 8

   Print, measure and test

   Print the parts and measure critical dimensions with a caliper: clamp bore, bolt hole, insert bosses, overall length. Fit the display mount to a bar of the same diameter and hang the example load; if a pull test rig is available, load to failure and note where it breaks. Fit the clip on a cable bundle ten times and inspect the arm for whitening or cracks.

   Checkpoint: Measured deviations recorded for every critical dimension, and the failure location compared with the simulation hot spot.

9. 9

   Iterate and document

   Adjust clearances, fillets or orientation from the test results and print a second version. Record the changes as configurations or a revision so the history is visible. Write a short design guide for your team covering the clearance, minimum wall, overhang and insert rules you measured, and include photos, CAD images and the measured-versus-modelled table in the report. Keep the failed version 1 parts and label them, because photos of real failures make the report far more convincing.

   Checkpoint: Version 2 parts fit and pass the load test, and a one-page printing design guide is produced from your own measurements.

Testing & validation

• Coupon measurements give a clearance value used consistently in the parts.
• No unsupported overhangs remain beyond the stated angle.
• Snap-fit strain is within the material limit by calculation.
• Physical load and fit tests pass, and failure locations are compared with simulation.
• Measured dimensions are within a stated band of the CAD values.

Expected results

Three functional printed EV prototype parts with CAD models, fit and load test results, measured deviations and a short printer-specific design guide.

Take it further

• Compare FDM with resin or SLS prints for the same parts.
• Design a printed drill or assembly jig for a battery module.
• Test the effect of perimeter count on bracket stiffness with a simple rig.

Viva and review questions

Learn it at DIYguru

These DIYguru courses and programmes teach what this project needs.