The chosen plastic/composite for a component is one of the most common causes of failure in many products. Time after time reported field failures have to do with assemblies not lasting in their overall environment. Selection of plastic/composites and the information in the specification sheets are paramount to these shortfalls. When you add in processing and unforeseen operational conditions, failure is not as surprising as it should be. Working closely with your injection molding partner can help mitigate some of these failure modes.
- Plastic/Composite Selection
Careful selection of plastic/composites is essential for avoiding the financial costs and loss of reputation that can accompany a field failure and possible recall.
Data sheets are highly effective tools for identifying the best family of plastic/composites for a particular application, and may even allow engineers to select a particular grade of plastic/composite. However, many specifications are ranges (and some quite large ranges) and well thought out testing to determine how, in your particular application, that plastic/composite will react. Your injection mold and molding partner will likely have experience with that plastic/composite and how it functions in other customers’ applications.
- Plastic/Composite molding
The molding process that a plastic/composite sees during its conversion from resin to custom shape must also be taken into account. When molten resin is shot into a mold, the physical stresses can result in a degradation to the plastic/composite properties. Additionally, the temperatures a resin seeing during molding must be characterized. The transition from solid to liquid is accomplished through heat, but the heat is both radiant and friction based. This additive effect plus the heat generated by thousands of pounds of force being used to inject the resin into the mold can result in temperatures much higher than recommended. This requirement typically necessitates additional testing after manufacture to determine if a plastic/composite’s properties have shifted from its baseline specifications.
Plastic/composite data sheets routinely include a disclaimer indicating that the data is merely typical for the plastic/composite and shouldn’t be used for design purposes.
Designers and engineers often put too much credence in the specification and do not take note of the disclaimer. Early in the product’s design requirements document phase, the operating temperature can rule out for testing, when in fact the temperatures seen during storage and delivery must be considered. Often times the standardized testing protocols are written around room temperatures, which may differ significantly from the finished assembly’s experienced conditions.
Pay particular attention to a data sheet’s use of minimums and maximums. When a data sheets refers to a capability “exceeding” a certain number, that real number may be far outside your desired operating conditions. You may have been looking for a number in excess of their minimum, but not to the magnitude that may be experienced.
Using an injection molding partner that can help guide you in selection of your plastic/composite is a good first step in developing a desired design outcome. An injection molding partner that is well versed in the plastic/composite selection, from both a mold design AND processing viewpoint, augmented by what their other customers have seen in their use of the plastic/composite, will help maintain or even reduce your product development timeline. Developing a component test specification as well as a finished assembly test specification will help identify what requirements you need to incorporate. Devising a test that will assure you the selection, processing, handling and use of your selected plastic/composite will not just meet but exceed your AND YOUR CUSTOMERS’ expectations with bring dividends in the long run.