Companies around the world use CNC machining to craft high-quality components from diverse materials like ceramics, wood, and composites. Metal and plastic take the forefront in mass production, with metals enjoying wider machinability. Machinists can adeptly tackle issues in metals by adjusting speeds, feeds, tools, and more.
However, plastics prove a distinct challenge. Methods effective on steel, brass, aluminum, and titanium struggle to yield the same outcomes. Resulting are subpar finishes and imprecise dimensions, causing rejection of numerous parts.
Understanding the unique complexities of plastic machining and common pitfalls is crucial. This article presents key insights into mastering plastic CNC machining. By incorporating these expert tips, you’ll elevate the quality of your plastic machining endeavors.
Table of Contents
• The Challenges of Plastics Machining
• 4 Tips for Precision Machining Plastics
#1 – Minimize Clamping Forces
#2 – Use the Right Cutting Tool
#3 – Stay Cool
#4 – Know Your Material
• Plastic CNC Machining With Gensun
The Challenges of Plastics Machining
CNC machining plastic parts of plexiglas
Generally speaking, the two biggest challenges that machinists face when working with plastics are poor surface finishes and dimensional changes. Any tool chatter, rubbing, or poor chip formation can cause gouges and scratches in the plastic surface that affect the surface finish.
Anything that causes the plastic to compress or expand during machining can affect the machinist’s ability to meet precision tolerances when the part reverts to its original shape after machining.
Most of the quality issues that arise when CNC machining plastics come from one or more of these sources:
Poor chip formation: Softer plastics can be prone to “flowing” around your cutting tool instead of forming chips. Much like pushing a finger into wet clay, the plastic simply deforms around the cutting tool instead of breaking off. Meanwhile, harder plastics can fracture unpredictably, especially near edges where larger chunks can break off and leave a small cavity.
Deformation from clamping: The stress applied to a plastic part during clamping can cause it to elastically deform. After the part has been machined and unclamped, the plastic part may be out of tolerance when the clamped portion returns to its original shape.
Poor chip ejection: Plastic chips can “gum up” the flutes of drilling and milling tools if they aren’t quickly removed from the cutting area. Poor chip ejection reduces cutting efficiency and causes rubbing that rapidly raises the temperature of the surrounding plastic.
Heat deflection temperatures: Many plastics have low heat deflection temperatures, which can cause them to soften dramatically. Then they deform easily in response to forces from clamping, cutting, or even just gravity.
Thermal expansion: Thermal expansion in polymers can be much greater than commonly machined metals, which causes them to expand when overheated and shrink afterward, potentially missing tolerance requirements.
Chemical reactivity: Different polymers are susceptible to different solvents, which can cause them to dissolve or simply just swell. Machine shops will need to be aware of what chemicals can be used around the polymers they are working with.
Moisture absorption and retention: Similar to chemical reactivity, some plastics can absorb a lot of moisture, causing them to swell. Even the humidity in the air can cause some plastics to expand out of tolerance.
Transparency: Clear polymers, like acrylic, ABS, and polycarbonate, can appear foggy or faded if machining leaves them with a rough surface finish. Some polymers are even susceptible to degradation from UV light exposure.
It is important to note that some plastics are more susceptible to certain problems during machining than others. One plastic may have a high moisture retention rate, while another plastic is prone to overheating. Some plastics may even produce toxic fumes when overheated. This makes it important to choose the right plastic for your application.
4 Tips for Precision Machining Plastics
CNC machining ABS plastic mini wheels
To overcome the most common quality issues encountered when CNC machining plastic components, machinists should consider these expert tips.
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