Many of the problems faced by injection molders can be prevented if a few basic concepts are followed in component design. Among them:
You should maintain the thickness of the wall to the best of your ability. Even a difference of just 15 to 25 percent in thickness can cause sink marks to form in the thicker parts in the case of such a difference. At worst, voids may form and this may adversely influence overall performance.

In providing rigidity, stepped sections are often introduced (for example, corrugated roofing sheets), and even box sections may be rigidized by curving their corners slightly in order to keep their thickness the same. Introducing ribs and bosses to your design could result in sink marks and it may not be possible to avoid them. It's a smart idea to make the ribs and bosses two-thirds the thickness of the wall and to make the holes penetrate into the wall one-third as deep as the ribs.

The thickness of the wall should be kept to a minimum to allow for strength and rigidity to be achieved. Using multiple gates can probably solve problems relating to filling molds by keeping material use to a minimum and ensuring the shortest possible cycle time. A simple assembly method for two or more components can always reduce the time spent on undercuts and reentrant shapes.

This raises costs in mold production as well as in molding time. This can be achieved by avoiding the need for core operations on the side. In particular, interference fits provide a secure connection between two components by engaging strongly with one another (cf. the poppet bead). Friction, hot-plate, or ultrasonic welder is also an option, but, in general, bonding with a solvent or solvent-based adhesive is not recommended for custom molders due to fire and toxicity hazards, as well as problems with solvent recovery.

If possible, avoid using molded-in inserts. Staked or spring-clip inserts are more easily made by injection molding and work better in blind holes. The insert molding process is generally the most expensive and wasteful process, both for the operators and for the machines. Give the largest possible radius.

The stresses induced by sharp corners, both internal and external, are natural, but a radius of 0.06 in (1-5mm) reduces the situation significantly and may increase the impact strength by five or ten times. Designers may require difficult-to-manufacture components. "Occasionally, so rarely, actually, that it makes one feel uneasy to mention it, designers have come up with things that are just a teeny-weeny bit difficult to create.

The English language would be poorer without those relish challenges of this kind. In some cases, designers may be ignorant of a component's service conditions, ignorant of a material's performance in service, and ignorant of the many factors involved in contributing to an effective plastic product.

It is critical to educate, but even more critical to consult and cooperate. It is imperative that end-users, component designers, mold designers, and molding technologists maintain regular contact to avoid many of these problems.