Processing Polymers

MANUFACTURING MOLDING-PROCESS TRADEOFFS 

Figure 1 shows a brief overview of the tradeoffs between each of the following processes: Injection, Extrusion, and Compression Molding. You will notice that the lowest stress during process pertains to Compression Molding, which very useful with the correct tooling, required material stability, and tight tolerance machining.

THREE COMMON CONVERSION PROCESSES 

INJECTION MOLDING

• Begin with a lower viscosity material so that it can flow easily into a mold. 
• Forcing the polymer through a small opening so directionality of fibers develops. 
• The polymer cooled quickly to get the material out of the mold fast, resuling in a shape that stores increased internal stress and less dimensional stability of the final shape. 

EXTRUSION MOLDING

• Begin with a higher viscosity material. 
• Similar to IM, slowly force the polymer through an opening so some directionality develops 
• Cooling of the polymer occurs quite slowly. while resulting in reduced internal stress and provideing improved dimensional stability of the final shape. 

COMPRESSION MOLDING

• Begin with a free flow poder loaded in a mold and apply pressure and proper heat. 
• Zero directionality occurs resulting in a very dimensionally stable material. 
• This process, which is slower, yields a lower internal stress as compare to IM & EM. 

THE SAME RESIN: WHY ARE THE MECHNICAL PROPERTIES SO DIFFERENT? 

See Figure 2. Review the three columns on the far right of the chart as compared to the Victrex Resin processed via Injection Molding. The three filled PEEK samples, shown above, display nominal values which differ by process; hence, it is important to understand which process will provide the correct properties needed for your application.

HOW DOES PLASTIC DATA AFFECT YOUR MATERIAL SPECIFICATIONS? 

CONSIDER THE DATA YOU ARE USING: 

• How were the test samples generated?
• Determine which process will be used to achieve the correct test values needed.
• Resin suppliers always provide data based on injection molded samples.
• Most shape converters take the “easy way out” and provide Resin data.

TEST MATERIALS IN A QUALITY LABORATORY FAMILIAR WITH THE INDUSTRY MATERIAL PROPERTY DATA IS GENEERATED FROM THE ACTUAL STOCK SHAPE 

WHEN WRITING MATERIAL SPECIFICATIONS: 

• Consider writing around machinable shape data.
• Consider the final shape and associate the process required.
• Determine whether or not you are dealing in small or large production needs.
• Consider asking for batch data on the shape being produced.

Perhaps this overview will enhance your understanding of the impact that each polymer process yields using the same basic polymer compound shown here – PEEK with 30% carbon fiber.

CONTACT PORT PLASTICS FOR ALL YOUR NEEDS IN TERMS OF POLYMERS FOR THE ENERGY MARKET.