Because of low cost, low weight to strength ratio, improved mechanical and structural properties plastic materials are becoming preferred choice over traditional metals. Plastic materials are available in various grades with wide variety of physical, thermal and mechanical properties.
Because of vast availability of grades, plastic material selection is becoming a complicated task. In this article we will discuss plastic material selection process for required application.
Commonly used Plastic Materials :
|S. No||Polymer||Full Form|
|7||HDPE||High Density Polypropylene|
|8||PEEK||Low Density Polyether ether ketone|
General Guidelines for Material Selection :
Material selection is one of the most challenging task for plastic product design engineers. Material selection process requires good understanding of product application, polymers, additives and their properties.
After careful consideration of product application and material properties, few materials are shortlisted. And Final material is selected based on product verification and validation.
Required Plastic Properties
Following plastic part properties need to be considered based on required product applications :
All types of mechanical loads encountered on plastic parts during its complete life-cycle need to be considered.
Part structure, thickness and size also affects selection of material. For example, For larger size parts with small thickness (0.5 mm) polycarbonate cannot be a good choice because of its low flowability.
Projected Plastic Part Life
Projected plastic part life is also affected by plastic material.
Extreme working conditions such as working temperature, relative humidity, and exposure to chemicals affects the selection of plastic material. For example, for high temperate applications PC is a good choice compared to ABS.
Exposure of parts with chemicals needs to be considered during initial stages of part design.
Plastics are non-conductive in nature. But now a days if required conductive plastic blends are also available.
Conductive plastic blends improves EMI shielding but reduces antenna performance.
Temperature, moisture, and UV sun exposure affect plastic part properties and appearance. The end-use of a product determines the type of weather resistance required like outdoor parts must withstand continuous outdoor exposure and perform in the full range of weather conditions.
For example, UV Radiation can yellow or degrade many plastics. If part will be exposed to a radiation source, we can consider painting or using a UV-stabilized resin.
Product aesthetic requirements also affects material selection. For example to achieve good surface finish PC and ABS are better choices than PP and nylon. To achieve clear transparent finish PC and acrylic is used.
Required approvals from various agencies like : FDA, MIL, NSF, USDA, Level of UL 94 retardant rating requirement(5VA, 5VB, V0, V1, V2, HB) need to be checked.
Various plastics gives different tolerances and variability during manufacturing. For example, with ABS and PC we can achieve close tolerance whereas with PP its not feasible.
Assembly process also affects material selection. For example, adhesives works best with ABS and PC. Whereas for Nylon and HDPE we require special adhesives. Its easy to ultrasonic weld PP and ABS compared to Nylon and PC.