Injection Molding Boss Design Checker

Screen boss wall thickness, outside diameter and base radius using the adjacent wall and actual fastener or insert diameter.

Formula and method

Boss-wall ratio = boss wall / nominal wall × 100. Diameter ratio = boss OD / fastener or insert diameter. Base-radius screen = entered radius ≥ 0.2 mm.

Inputs and units

Use CAD section dimensions at the boss base and the actual production fastener or insert diameter. The reference screen uses 40–60% boss wall, at least 2× outside-to-fastener diameter and a boss-to-wall transition radius of at least 0.2 mm.

Worked example

A 3 mm nominal wall, 1.5 mm boss wall, 4 mm fastener, 8 mm outside diameter and 0.75 mm base radius gives a 50% boss-wall ratio, 2× diameter ratio and a 0.75 mm radius; 3 of 3 checks pass.

When to use it

Use before a fastening concept is frozen and before choosing insert installation or screw-forming parameters.

How to interpret the result

A pass means the entered ratios meet this preliminary geometry screen. It does not establish pull-out, torque, weld-line strength, insert temperature or assembly durability.

Assumptions and limitations

Boss geometry is resin-, fastener-, insert- and load-specific. Draft on inner and outer walls, coring, gussets, steel thickness, bottom thickness and distance to nearby walls need separate review.

Validation guidance

Obtain fastener or insert supplier design data, test the intended assembly in molded material, and review sink, fill, ejection and steel access with the moldmaker.

FAQ

Does a passing screen approve the part for tooling?

No. It creates a traceable CAD review record. Formal DFM, material review, mold design, simulation where appropriate, and molded-part validation remain required.

Sources

Protolabs wall-thickness guidance · Protolabs injection-moulding design guide · Covestro connecting-element guidance