Top Six Capabilities Designers Want in Custom Rotational Molders

Over the years, I’ve designed many rotational molded parts and projects. And I’ve worked with dozens of molders throughout the country. Although the process is called rotational molding, each molder is actually unique. Their work is based on a plan layout, staff, equipment, business model, preference of resins and capabilities.

The United States claims to have more than 400 rotational molders, but only a small percentage of this list are willing or capable of molding complex custom molded plastic parts.

Many custom molders, for example, require high production minimum orders before quoting a potential project. Some molders limit part size, tool complexity or wall thickness to specific requirements, which happen to be consistent with their machinery, production setup and cycle times.

There are custom molders who are exclusively dedicated to molding low-cost functional parts. These are items that do not have to comply with aesthetic requirements, tight tolerances or any assembly operations.

The Most Important Attributes as a Custom Rotational Molder

 So what do product designers and industrial designers seek in custom molders? The following is my ideal list of criteria in a few brief paragraphs:

  • Molders who are willing to mold parts in quantities as low as 50 to 300 annually are extremely attractive to designers. Many applications require complex, expensive parts that are used in analytical equipment, medical devices or other specialty products. These have annual quantities typically less than 500 per year. Although the yearly quantities may be attractive to most molders, the value for these products is typically quite high.
  • Designers often look for molders with a good support team. This would include application engineers, manufacturing engineers, and possibly tool designers to provide technical support throughout the development process. These individuals are also extremely beneficial during production startup to aid in identifying problems typically encountered during first article inspection.
  • A great asset for molders is a well laid out manufacturing facility. That means clean floors, well-organized material handling systems, logical inventory layout, clean equipment, and safe working conditions. The general appearance of the plant will make an important and lasting first impression. A clean well-organized facility typically implies quality parts and efficient production operations or part of the corporate culture.
  • A wide variety of aesthetically appealing products with complex features and high quality are a great selling point for molders. Designers always look for examples of products that demonstrate a molder’s capabilities, creativity and technical sophistication.
  • Molders who quickly respond to questions posed by designers typically get preferential treatment because of their cooperation. Throughout the design process, designers are often curious about approximate cost for tooling, parts and basic capabilities of the molder. Some molders are willing to provide estimated tooling costs for a particular design, as well as assist in some basic design questions. Designers tend to favor these molders because of their generous and cooperative policies.
  • Excellent QC equipment, methods and procedures are great assets for a molder who is trying to emphasize quality as well as production consistency. Molders that describe quality assurance policies with specific terms will obviously be favored by designers who want parts molded to their specifications.

Hopefully, this shortlist of decision-making attributes will provide some guidelines in advance of your next project. I welcome feedback from all of you who may agree or disagree. Let me know what you think. Email to: