How to machine plastic in CNC?

Key Guidelines for Plastic CNC Machining

Plastic CNC machining is a subtractive manufacturing process. A solid block of plastic is placed against a moving cutting tool that removes material from the block. The cutting tool follows a set path, guided by a digital design file, to shape the final part. CNC machining is a popular method for creating plastic components. With this process, you can quickly produce thousands of uniform and precise parts with incredibly tight tolerances.

You can create many different types of plastic parts using CNC machining, including:

• Medical devices, such as dental surgical guides and cardiac implants
• Components for the food and beverage industry, such as spray bars and assembly line pieces
• Semiconductor components, such as electrical insulators and watertight seals
• Automotive and aerospace industry components, such as fire blockers, valve seats, and pump gears

Depending on the CNC machining method—CNC drilling, CNC turning, or CNC milling—engineers must follow different guidelines to produce superior plastic CNC machined parts. In this article, we will break each down.

Plastic CNC Turning

CNC turning involves holding a plastic piece on a lathe, which rotates against the cutting tool. Many forms of CNC turning exist, each with specific purposes and results. For instance, straight or cylindrical CNC turning is best for large cuts, while taper CNC turning creates a cone-like shape.

Specific guidelines for creating plastic parts with CNC turning machines include:

• Minimize rubbing by ensuring cutting edges have a negative back rake.
• Use generous relief angles for cutting edges.
• Polish top surfaces to help reduce material buildup and achieve a better surface finish.
• Utilize fine C-2 grade carbide inserts.

For rough cuts, a feed rate of 0.015 IPR is recommended. For more precise final cuts, a feed rate of 0.005 IPR is advised. Product teams should also note that clearance angles, rake angles, and side angles will change depending on the material used in CNC turning.

Plastic CNC Milling

CNC milling is a computer-controlled process that uses a cylindrical rotating tool, called a milling cutter, to remove material from a solid workpiece. CNC milling machines can be categorized into two broad types: 3-axis mills and multi-axis mills. 3-axis mills move either the cutting tool or the workpiece along three linear axes—left to right, back and forth, up and down—suitable for simpler designs. Multi-axis mills, which may have four or more axes, are ideal for creating plastic parts with complex geometries.

Guidelines for creating plastic parts via CNC milling include:

• Use carbon tooling when machining thermoplastics reinforced with glass or carbon fibers.
• Utilize clamps to achieve higher spindle speeds.
• Create rounded internal corners and pockets with end mills to mitigate stress concentration.

Plastic CNC Drilling

CNC drilling involves using a drill bit to create holes in a plastic block. The spindle, which secures the block, lowers onto it to drill the appropriately-sized holes. Various types of drill presses can be used with a CNC drill, including upright, bench, and radial CNC drill presses.

When creating plastic components via CNC drilling, keeping drill bits sharp is critical. Dull or incorrectly shaped drills can exert excessive stress on the part, causing tooling problems and performance issues. For most thermoplastics, a 90 to 118° drill bit with a 9 to 15° lip angle is recommended. When drilling acrylic, a 0° rake is preferred.

Effective chip ejection is essential as poor chip removal can cause friction and heat buildup. CNC drilling generates more heat than other CNC machining processes; therefore, heat reduction is crucial to minimize stress and damage. To safely remove a CNC drill without damaging the part, ensure the drilling depth does not exceed three or four times the drill diameter and reduce the feed rate when the drill nears exit.

Plastic CNC Machining With SyBridge

Following the guidelines in this article can help you successfully create plastic parts through CNC drilling, turning, and milling. However, these guidelines are just that—guidelines! Depending on the complexity of your project, you may need to adjust these recommendations to fit your specific manufacturing requirements.

A seasoned manufacturing partner like SyBridge can assist you in making informed decisions regarding plastic CNC machining. Our team offers expert advice throughout the entire manufacturing process, considering all necessary guidelines. At SyBridge, we are committed to helping you produce the best possible CNC machined plastic parts. Ready to elevate your project? Contact us today.

CNC Machining Plastic: 4 Essential Tips You Should Know

Companies worldwide utilize CNC machining to craft high-quality components from various materials, including ceramics, wood, and composites. Metal and plastic lead in mass production, with metals having broader machinability. Machinists can adeptly handle issues with metals by adjusting speeds, feeds, tools, and more.

However, plastics present a unique challenge. Methods effective for steel, brass, aluminum, and titanium may not yield the same outcomes with plastic, resulting in subpar finishes and imprecise dimensions that cause numerous parts to be rejected.

Understanding the complexities of plastic machining and common pitfalls is crucial. This article shares key insights into mastering plastic CNC machining. By incorporating these expert tips, you can enhance the quality of your plastic machining efforts.

The Challenges of Plastics Machining

Generally, the two biggest challenges machinists face when working with plastics are poor surface finishes and dimensional changes. Tool chatter, rubbing, or poor chip formation can result in gouges and scratches on the plastic surface, affecting the finish.

Any factors causing the plastic to compress or expand during machining can hinder the ability to meet precision tolerances when the part returns to its original shape.

Quality issues in CNC machining plastics often arise from:

• Poor chip formation: Softer plastics may flow around the cutting tool instead of forming chips, while harder plastics can fracture unpredictably, leading to small cavities.
• Deformation from clamping: Stress during clamping can cause elastic deformation, affecting tolerance when the part returns to its original shape.
• Poor chip ejection: Plastic chips can clog flutes of drilling and milling tools if not quickly removed, reducing cutting efficiency and increasing temperatures.
• Heat deflection temperatures: Many plastics have low heat deflection temperatures, leading to significant softening and deformation under stress.
• Thermal expansion: Thermal expansion in plastics can be greater than that of metals, causing them to expand with heat and shrink upon cooling, potentially leading to tolerance issues.
• Chemical reactivity: Different polymers react differently to solvents, which can dissolve or cause swelling in plastics, necessitating knowledge of compatible chemicals.
• Moisture absorption: Certain plastics can absorb moisture, leading to swelling and potential tolerance deviations.
• Transparency: Clear polymers may become foggy if not finished properly; some can degrade from UV exposure.

It is important to note that some plastics are more susceptible to certain machining issues than others. Selecting the right plastic for your application is crucial.

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4 Tips for Precision Machining Plastics

To address the most common quality issues encountered when CNC machining plastic components, consider these expert tips.

#1 – Minimize Clamping Forces

Machinists familiar with metals may overcompress plastic parts to prevent movement. Overclamping can create impressions or induce stress, leading to further deformation once the part is unclamped. Use the minimum force necessary and consider jigs that reduce stress on the plastic.

#2 – Use the Right Cutting Tool

Dull tooling, improperly angled edges, and flute design affect cutting effectiveness. Choosing the right cutting tools is vital for achieving efficient cutting and high-quality surface finishes.

#3 – Stay Cool

Excess heat buildup can lead to various quality problems in plastics. Keeping the part cool is essential. High-pressure coolant jets can maintain temperatures while removing plastic chips efficiently.

#4 – Know Your Material

Each plastic behaves differently, so the cutting parameters that work for one type may not be effective for another. Machinists should research and experiment with specific plastics to understand their machining reactions. The Titans of CNC Machining YouTube channel offers many useful tips for working with common plastics.

Plastic CNC Machining With Gensun

This article covers only a fraction of the knowledge required to overcome the challenges of machining plastics. Each polymer requires specialized experience for high-quality results.

Fortunately, the machinists and engineers at Gensun have extensive experience with various materials, including metals and plastics. We provide top-quality CNC machining services to produce your parts on time and within budget.

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