The plastic product design process offers many versatile solutions and unique benefits, but it’s a practice that depends on the strength of its design. The injection molding part design must be developed to maximize the efficiency inherent in high-volume molding. Plastic injection product and plastic injection mold design, tool building, plastic material selection, and Injection molding manufacturing process are the four key factors that go into making a high-quality plastic injection molded part. During both the injection and cooling stages of the manufacturing process, below are several factors that may affect the quality of the final product and the repeatability of the manufacturing process.

Use a uniform wall thickness throughout the part (if possible) is essential to avoid thick sections. Wall thickness between 1.2 mm and 3 mm is a safe value for most materials. The next table summaries specific recommended wall thicknesses for some of the most common Injection Molding materials:

If sections of different thicknesses are required, make the transition as smooth as possible using a chamfer or fillet. In this way, the material filling will be much better.

The wall thickness specified typically should meet application requirements, moldability, and agency requirements. From a cost standpoint, the thinnest wall utilizes the least material and results in the fastest molding cycle times.

Ribs increase the moment of inertia in a design, which in turn will increase the bending stiffness of a part without adding thickness. Rib should not exceed 70% nor lower 50% of part wall thickness; both scenarios can cause sinking in the surface of your part. We also have to pay attention to the rib height, location, and degree of the draft for ease of ejection. Proper rib design involves five main issues: thickness, height, location, quantity, and moldability.

A boss is included in the part design to accommodate part assembly through screws or pins. Generally, the thickness should be as same as the ribs. The outside diameter of the bosses should remain within 2.0 to 2.4 times the outer diameter of the screw or insert. Thicker bosses will create sink defects as the part cools, but a boss-rib combination can eliminate sink marks. By using ribs to connect the boss to a side wall, this method of part design will provide the strength necessary to support screws and inserts. Also, adding small radii to break the sharp corners will significantly reduce stress concentrations. And as with ribs, the boss also needs to have some draft to aid in ejection.

Usually, the boss hole should extend to the base-wall level, even if the full depth is not needed for assembly. If the boss hole is too long, we may have filling problems, knit lies, or surface blemishes. If the boss hole is too short, we may have a sink mark on the part surface.

Draft angles must be included in the part design. It allows you to remove the part from a mold. The draft needs to be in an offset angle, parallel to the opening and closing of the mold. Surfaces formed by slides may not need a draft angel if the steel separates from the surface before ejection. The mold finish, resin, part geometry, and mold ejection system determine the amount of draft needed. Generally, polished mold surfaces require less draft angel than surfaces with machined finishes. When you allow for as much draft angel as possible, you make it easier to release parts from the mold. One or two degrees of drafts, along with 1.5 degrees per .25 millimeters depth of texture, should enough.

Other factors need to be considered when you do the plastics engineered product design for the injection molding, such as parting lines, threaded fasteners, snap-fit joints, living Hinges, and undercuts. Avoiding undercuts altogether might be the best option in molding design. Undercuts always increase the mold cost, complexity, and maintenance requirements of the mold. A smart redesign can often eliminate undercuts.