Heat Staking Design Guide

This guide covers the boss and stud geometry, the head profile choices, the resin selection, and the design rules that decide whether your heat-staked joint forms cleanly or fails on the line. It is written for moulding designers, mechanical engineers, and process engineers who need to specify a stake-able feature on a part that is not yet in production. Get the boss right at the moulding stage and most heat staking failures disappear before they have a chance to happen.

The guide is grounded in production data from the impulse heat staking presses U.S. Heatstake builds for automotive, medical, electronics, and consumer applications. Where there is a "best practice" number, it is a real number from real production parts, not a generic textbook figure that may or may not match your resin.

Topics Covered

Boss diameter and wall ratios (how much wall section you need around the boss to avoid sink and cracking); stud height and volume calculations (the stud has to contain enough plastic to form the head, but not so much that the head spreads beyond the clearance hole); formed head profiles (flush for cosmetic surfaces, dome for general use, hollow for high-clamp applications, flared for thick or composite parts); clearance hole sizing relative to the boss and head; draft and corner radii; material compatibility (which resins stake well, which need special tooling, which should be staked differently); multi-up tooling considerations; and the failure modes that come from getting any of the above wrong.

Boss Geometry Rules

The shortest version: the boss outside diameter should sit on a wall section at least equal to the boss wall thickness, with a generous radius at the base to avoid stress concentration; the stud volume above the part surface should equal the desired formed head volume; the clearance hole in the captured part should be 0.005″ to 0.015″ larger than the boss diameter on a side, depending on tolerances. Get those three right and the head forms predictably the first time.

Material Compatibility

Heat staking works on essentially all thermoplastics: ABS, PC, PC/ABS, nylon (PA6, PA66), polypropylene, polyethylene, acetal, PPS, and most engineering grades. Glass-filled grades stake but give a slightly rougher head finish; consider cosmetic implications. Thermosets do not stake — they char rather than flow. PTFE and PEEK either will not work or need specialist tooling and parameters.

Common Failure Modes

The big ones: cracked or split bosses (usually wall section too thin, or stud volume too high for the boss); under-formed heads (not enough plastic in the stud, or tip not seated correctly); over-formed heads (too much plastic, or tip dwelling too long — impulse control eliminates this); witness marks on cosmetic surfaces (hot-probe style continuous heat — impulse cool-on-retract eliminates this); inconsistent joint quality (resin drift or operator drift — energy-per-joint control eliminates this). See Common Heat Staking Failures for the full troubleshooting list.

Get a Design Review

Send a part drawing as part of any quote request and we include a design review at no charge — boss geometry, stud volume, head profile, resin compatibility, and any red flags before tooling is cut. Contact us to start.