Factors Affecting Resin Selection for Injection Molded Parts

Resin selection is critical for injection molded components. All too often, customers come to us with a material specification that has not accounted for all environmental factors…. After a short time in the field the end user says, “My part is cracking…. Why?” The answer is typically that the end user did not reveal all of the environmental conditions up front. It is imperative to know under what conditions an injection molded part will be used.

Some questions to ask include: .

• Will this part be subjected to extreme temperatures?
• Will it be placed under any constant friction or forces?
• Will the part undergo sterilization? If so what type? Specifics are needed… At what dose? How many times? Is discoloration going to be an issue?
• Does the application require UV additive for outdoor use?
• Will any chemicals, cleaning agents or lubricants be used in the environment?
• Is flame retardant required? If so at what level? UL HB? UL V-0?
• Are there any regulatory or medical compliance requirements that apply? REACH, ROHS, FDA, USP Class VI, ISO 10993, California Proposition 65?
• Will the part need to endure impact in the field? This adds the question of whether the part has been designed for impact resistance… Another topic entirely!
• Finally… How can the requirements be met while staying within the established budget?

The only way to mitigate the risks is to know as much as possible during the design phase. After the mold is produced, material options are limited especially if tolerances are tight and shrinkage of alternate materials are not comparable to the original chosen resin. By working together with all concerned parties, it is possible to get the design right up front and to select an appropriate material. Knowledge is critical and it is important for the end user, engineers and customers to collect and supply as much information as possible prior to producing a mold and moving to the production phase of a project.