Rubber Molding Design Guidelines and Review

Rubber Molding manufacturing is facilitated by either extruding, pressing or pouring a liquid into a mold. Most rubber products made from vulcanized rubber with sulfur at high temperature during the molding process or after extruding.

are a block or sheet of rubber into a form or mold tool which represents the desired geometry of the molded rubber part. The rubber material is then cured by applying heat energy which actives a chemical reaction of the rubber material.

Typical parts that are manufactured by rubber molding include: O-rings, seals, grips, caps, covers, hose adapters, gaskets, buttons, handles, knobs, roller, bumpers, hydraulic and pneumatic components, and many other geometries. Most any 2-D shapes of shallow depth are possible.

Design guidelines: Rubber can be molded into very complex shapes and geometries, however small changes in a rubber geometry may allow the part to be manufactured using more economical processes, such as rubber extrusion. It is always a good ideal to keep your geometry as simple as possible while keeping the critical fit features in the same molded part. In general critical features manufactured in the same setup (any manufacturing process) is a good ideal in minimize tolerance accumulation.

When designing your part, and you have verified that rubber molding is the target manufacturing process, consider where the molding die parting line will be on your part. Be sure to define the location and minimum draft angle as required by your molding job-shop. Because rubber is flexible, a draft angled geometry may not be required, however for some very soft rubber materials the more draft the better.

Carefully consider your surface finish or appearance requirements. A smoother surface may drive individual parts costs high as well as part rejection.

Attempt to keep your part geometry symmetrical and wall thickness uniform and avoid sharp corners and other geometries that result in an area that will significantly cool slower or faster than adjacent areas. In general, features or areas that cool slower will have a larger shrinkage rate resulting dips or craters for selected materials. Inserts or other parts and materials may be molded into and placed within the post molded part.

General:

Avoid sharp corners requirements in the geometry
Avoid deep undercuts and other complex geometries
Avoid overhangs
Geometries that will require additional manufacturing processes. i.e. trimming, hollowing and other post molding steps. These tend to increase part costing and rejection rates.

Materials - Typical for Rubber Molding:

EPDM
Natural Rubber
Nitrile Compounds
Silicon Rubber
Urethane Rubber
Latex
Neoprene
Styrene Butadiene
Isobutylene Isoprene
Fluorosilicone
Many others

As always, Engineers Edge recommends consulting with the rubber molding engineering staff before finalizing your design geometry.