What should you consider when designing a plastic product? 1/2

Developing a product can take months or even years. Once the design is finalized, it’s shared with a plastic injection molding company, and naturally, you’d prefer to have the finished product in hand as soon as possible. However, it can be a major setback if changes are required after the process has begun.

When it comes to injection molding, certain fundamental elements must be considered during product design to achieve the best possible outcome.

1. Choose the right plastic material

The first step is selecting a suitable plastic material. With an overwhelming number of options available, each with its own unique properties, advantages, and limitations, the choice depends on the product’s application, environment, and desired characteristics. For more details on selecting the right material, check out our blog on different types of plastics.

2. Design rules to follow

The next step involves applying key design principles. In this blog, we explore a few essential rules for designing products for the injection molding process.

Key product design rules

1. Ensure proper and uniform wall thickness

The wall thickness of a plastic product significantly impacts its mechanical performance, appearance, manufacturability, and cost. Achieving an optimal wall thickness often involves balancing factors such as impact resistance versus material use, flexibility versus stiffness, or functionality versus aesthetics.

Wall thickness also affects the injection molding process. Thick walls can lead to warping, shrinkage, or sink marks during cooling, while thin walls may result in incomplete filling or trapped air, creating weak spots. Both scenarios increase the likelihood of defects in the final product.

An increase of just 10% in wall thickness can lead to a 33% improvement in stiffness. Using ribs or rounded edges can enhance stiffness without increasing wall thickness. The recommended wall thickness generally falls between 2 and 3 mm, though acceptable thickness also depends on the material chosen.

2. Avoid sharp corners

During injection molding, molten plastic is injected into the mold under high pressure. Sharp corners hinder material flow and require higher pressure, which can create unnecessary stress within the product.

Sharp corners are also more prone to deformation during cooling and material shrinkage. Incorporating a radius to round off sharp edges in the design helps distribute internal stress more evenly, reducing the risk of defects. Additionally, sharp corners can increase mold manufacturing costs.

3. Include draft angles

To ensure the product can be easily removed from the mold during ejection, draft angles are essential. Without a draft angle, walls, ribs, or protrusions that run parallel to the mold’s opening direction may shrink and stick to the mold, causing complications.

A draft angle involves adding a slight taper to the walls of the product, typically at least 0.5 degrees. Larger draft angles enhance product quality and reduce mold wear over time.

Products with textured surfaces require greater draft angles to prevent damage during ejection. The type of plastic material used also influences the required draft angle.

Proactively address design changes

A well-thought-out product design that adheres to these rules is crucial for ensuring that the design can be successfully and cost-effectively produced via injection molding.

Once the mold is created, making changes becomes challenging, time-consuming, and expensive—sometimes even impossible. By contrast, modifying a product drawing during the design phase is relatively straightforward.

Prototyping can help test the design or iterations before committing to production. We recommend taking extra time to refine the design and involving an experienced injection molding partner early in the process.

In the long run, a well-designed product saves time, money, and resources while delivering better quality.