Polypropylene (PP) is a BPA-free, lightweight plastic with exceptional fatigue resistance and toughness. These properties make it a popular material for use in a wide range of applications across the automotive, packaging, and consumer product industries.
Polypropylene (PP) is a semi-crystalline thermoplastic that comes in two different forms; it can be composed of homopolymers or copolymers. Homopolymer polypropylene is the most generic grade whereas copolymer polypropylene has varying degrees of ethylene mixed into it. CNC machining in polypropylene may be more challenging than with other common plastics due to its tendency to gall and melt. Polypropylene’s excellent chemical resistance and fatigue strength make it especially useful for flexible parts and parts that are exposed to corrosive environments.
|Application||BPA-free food containers, electrical equipment, household appliances|
|Advantages||Low density, chemically resistant to a range of acids and bases, high fatigue resistance|
|Disdvantages||Not suitable for high-temperature applications, degrades under exposure to UV light|
|Lead Time||Lead time is generally a minimum of 3 days. However, this can increase depending on complexity and manufacturing origin.|
|Tolerances||Machining tolerances of 0.005” (0.13 mm) are achievable.|
|Wall Thickness||A minimum wall thickness of 0.03” (0.8 mm) is achievable. This can vary depending on the ratio of wall thickness to planar dimension.|
|Max Part Size||The maximum size of the part is determined by the machines available and the complexity of the part.|
While CNC machining in polypropylene is challenging due to its tendency to gall and melt, homopolymer polypropylene offers a range of benefits for CNC machined parts. Its slick surface makes it ideal for mechanical items like gears and its fatigue resistance means that thin features such as living hinges are easy to incorporate into designs.
|Tensile Strength, Yield (MPa)||Elongation at Break (%)||Hardness (Rockwell R)||Heat Deflection Temperature (C)||Glass Transition Temperature (oC)|
Polypropylene parts are a natural off-white color. PP does not accept surface finishes like paints very well. Its hydrophobic nature also makes it very difficult to dye.
CNC machining in polypropylene can be cost-effective thanks to the low cost of the material. However, reducing excessive machine and post-processing time is critical to keeping costs low. One way this can be achieved is by keeping tolerances standard for plastic and composite machining:
This is especially important because machining plastics can cause warping from the heat generated during material removal.