Design Tips for Custom Plastic Molding

Plastic is possibly the most versatile manufacturing material available today, which is why custom plastic molding is such a popular manufacturing choice. Variations in formulas among different plastics allow an endless array of material properties to allow manufactured items to have exactly the structural features needed.

Plastic has characteristics different from other manufacturing materials and considering those qualities when designing a custom plastic molding can create a more durable finished product at a lower cost.

Wall thickness

Custom plastic moldings can be created for a wide range of wall thickness. Whether a design needs walls as thin as a soda bottle or thick enough to provide significant weight bearing, plastics manufacturers can easily provide the mold needed.

The problem arises when a design requires differing wall thicknesses. When a custom plastic molding cools, thick walls cool more slowly than thin ones. This can cause the finished product to warp or create stresses that will lead to failure later in the manufacturing process or when in the hands of the consumer. It is always better to use uniform wall thicknesses throughout the design.

The wall thickness issue can be particularly pronounced at corners and radii. It is important that the radii of the inside wall and outside wall of a curved piece be measured from the same point so that the thickness remains uniform throughout the custom plastic molding.

Since thick pieces require not only more material but also more injection time and more cooling time, it is more cost effective to use thin pieces when possible. The use of ribs or gussets in a custom plastic molding can add stiffness to a thin section and eliminate the need for a thick wall. The ribs should be 1/2 to 2/3 of nominal wall thickness, with a height less than 3 times thickness.

Design with the mold in mind

Although custom plastic molding can easily be made of complex shapes, the designer must not forget that the piece will have to be extracted from the mold. Parts should be designed with tapering in the direction of the opening or closing of the mold to facilitate easy removal of the finished piece.

Consider dimensional tolerances carefully when drafting the piece. Tighter tolerances mean increased cost and slower manufacture. For small regions that require extremely tight tolerances for critical operation, it is often more cost effective to use post molding processes such as machining to bring the measurements within tolerance.

Consult the experts

Although product inventors have intimate knowledge of their products' designs, sometimes that vision doesn't match the realities of manufacturing processes. By partnering with a manufacturer with experience in custom plastic molding, inventors are given access to an information resource that should not be ignored. The manufacturer's engineers may have created similar designs for other customers and have already solved technical problems that inventors are facing.

With a few careful design decisions, many products can be produced for a fraction of the cost that would have been required before custom plastic molding existed.

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