CNC Plastic Machining: Custom CNC Machined Parts Fabrication

Most of the time, a typical representation of CNC machining includes handling a metallic workpiece. But while CNC machining is frequently used with plastics, one of the frequently used machining techniques in a variety of industries is CNC plastic machining.

The availability of a large variety of plastic materials has led to the acceptance of CNC plastic machining as a manufacturing process. Furthermore, the process becomes faster, more accurate, and appropriate for producing parts with tight tolerances with the introduction of computer numerical control. To what extent is your knowledge of CNC plastic machining? This article goes over available techniques, materials that work with the process, and other things that can support your project.

CNC Machining with Plastics

Various machinable plastics find application in the production of parts across diverse industries. The choice of plastic depends on its specific properties, with certain options, like nylon, possessing exceptional mechanical qualities that enable them to substitute for metals. The following are some commonly used plastics in custom plastic machining:

ABS (Acrylonitrile Butadiene Styrene)

ABS is a lightweight material often utilized in CNC machining due to its notable impact resistance, strength, and ease of machinability. Despite its commendable mechanical properties, ABS exhibits lower chemical stability, making it susceptible to greases, alcohols, and other chemical solvents. Additionally, pure ABS, without additives, has limited thermal stability, leading to combustion even after the removal of a flame.

Pros

• Lightweight yet mechanically robust.
• Highly machinable, making it a preferred material for rapid prototyping.
• Low melting point, suitable for various prototyping processes like 3D printing and injection molding.
• High tensile strength.
• Durable, ensuring an extended lifespan.
• Affordable.

Cons

• Emits hot plastic fumes under heat, requiring adequate ventilation to prevent gas buildup.
• Low melting point may cause deformation from the heat generated during CNC machining.

Applications
ABS is a widely used engineering thermoplastic in the realm of rapid prototyping services, owing to its excellent properties and cost-effectiveness. It finds application in the electrical and automotive industries for crafting items such as keyboard caps, electronic enclosures, and components of car dashboards.

Polyamide (Nylon)

Nylon, also known as polyamide, is a low-friction plastic polymer characterized by its exceptional impact, chemical, and abrasion resistance. With notable mechanical properties, including a high tensile strength, durability, and hardness, specifically 76 MPa and 116R respectively, nylon stands out as a preferred material for CNC machining. This versatility enhances its applicability in the automotive and medical part manufacturing sectors.

Pros

• Exhibits excellent mechanical properties.
• Boasts a high tensile strength.
• Cost-effective.
• Lightweight polymer.
• Resistant to heat and chemicals.

Cons

• Shows low dimensional stability.
• Prone to absorbing moisture.
• Susceptible to strong mineral acids.

Applications
Nylon proves to be a high-performing engineering thermoplastic, finding application in both prototyping and the production of actual parts in the medical and automotive industries. Components crafted from this CNC material include bearings, washers, and tubes.

Acrylic (PMMA)

Acrylic, also known as PMMA (Poly Methyl Methacrylate), is a popular choice in plastic CNC machining, primarily for its optical properties. This plastic polymer is characterized by its translucence and scratch resistance, making it suitable for industries that require such features. Beyond its optical qualities, acrylic exhibits excellent mechanical properties, showcasing toughness and impact resistance. Its cost-effectiveness has positioned acrylic CNC machining as an alternative to other plastic polymers like polycarbonate and glass.

Pros

• Lightweight.
• High chemical and UV resistance.
• Excellent machinability.
• High chemical resistance.

Cons

• Limited resistance to heat, impact, and abrasion.
• Prone to cracking under heavy loads.
• Not resistant to chlorinated/aromatic organic substances.

Applications
Acrylic finds application as a substitute for materials like polycarbonate and glass. This versatility extends its use to the automotive industry for crafting light pipes and car indicator light covers, as well as other sectors for manufacturing solar panels, greenhouse canopies, and more.

POM (Delrin)

POM, also known as Delrin in commercial terms, is a highly machinable CNC plastic material favored by many CNC machining services for its strength and resistance to heat, chemicals, and wear and tear. Various grades of Delrin exist, with Delrin 150 and 570 being widely relied upon due to their dimensional stability.

Pros

• Among the most machinable CNC plastic materials.
• Excellent chemical resistance.
• High dimensional stability.
• High tensile strength and durability, ensuring a longer lifespan.

Cons

• Poor resistance to acids.

Applications
POM is employed across diverse industries. In the automotive sector, it is used for manufacturing seat belt components. The medical equipment industry utilizes POM for producing insulin pens, while the consumer goods sector employs it in crafting electronic cigarettes and water meters.

HDPE

High-Density Polyethylene (HDPE) is a thermoplastic renowned for its robust resistance to stress and corrosive chemicals. It boasts superior mechanical properties, including a tensile strength of 4000 PSI and hardness (R65), surpassing its counterpart, LDPE, and making it a preferred choice for applications with stringent requirements.

Pros

• Flexible and easily machinable.
• High resistance to stress and chemicals.
• Excellent mechanical properties.
• High durability, ensuring an extended lifespan.

Cons

• Poor UV resistance.

Applications
HDPE finds versatile applications, including prototyping, the creation of gears, bearings, packaging, electrical insulation, and medical equipment. Its suitability for prototyping arises from its quick and easy machinability, coupled with its cost-effectiveness for creating multiple iterations. Additionally, HDPE is an ideal material for gears due to its low coefficient of friction and high wear resistance. It also serves well for bearings as it is self-lubricating and chemically resistant.

LDPE

Low-Density Polyethylene (LDPE) stands out as a tough and flexible plastic polymer with notable chemical resistance and low-temperature properties. Widely applied in the medical part manufacturing industry, LDPE is instrumental in the creation of prosthetics and orthotics.

Pros

• Tough and flexible.
• Highly corrosion-resistant.
• Easily sealable using heat techniques like welding.

Cons

• Unsuitable for parts requiring high-temperature resistance.
• Low stiffness and structural strength.

Applications
LDPE is frequently utilized in producing custom gears and mechanical components, as well as electrical components like insulators and housings for electronic devices. Its application extends to parts requiring a polished or glossy appearance. Moreover, LDPE’s low coefficient of friction, high insulation resistance, and durability make it an ideal material for high-performance applications.

PTFE (Polytetrafluoroethylene or Teflon)

Polytetrafluoroethylene (PTFE), commonly known as Teflon, stands as a high-performance plastic CNC machining material celebrated for its exceptional mechanical and chemical properties, rendering it suitable for various commercial products. This plastic polymer boasts a low coefficient of friction, resistance to chemicals, UV rays, and fatigue, in addition to anti-adhesive properties, making it a preferred choice for coating non-stick pans.

Pros

• Resistant to chemicals and light.
• Low coefficient of friction.
• Anti-adhesive properties.

Cons

• Inferior mechanical properties compared to other materials.
• Limited thickness options with 2-inch-thick rods and plates.

Applications
Teflon’s anti-adhesive properties find application in the production of non-stick pans. Beyond culinary uses, it is employed in creating gaskets, semiconductors, and heart patches.

PEEK (Polyether Ether Ketone)

Polyether Ether Ketone (PEEK) is a plastic polymer distinguished by unique mechanical properties, including high chemical resistance, wear and tear resistance, and heat resistance up to 260°C. This lightweight, recyclable, and biocompatible material serves as a versatile alternative to certain metals in part manufacturing.

Pros

• Excellent mechanical properties.
• Recyclable.
• Biocompatible.
• Lightweight and capable of enduring harsh environmental conditions.

Cons

• Not resistant to UV light.
• Unsuitable for marine applications.
• Considered expensive.

Applications
PEEK is applied in part manufacturing where plastic flexibility is required while maintaining the mechanical properties of metals. Common applications include pistons, airplane engine parts, and dental syringes.

Polycarbonate (PC)

Polycarbonate (PC) stands as a robust yet lightweight plastic polymer, featuring heat retardant and electrical insulating properties. Similar to acrylic, it can effectively replace glass due to its inherent toughness and transparency.

Pros

• More efficient than most engineering thermoplastics.
• Naturally transparent with light-transmitting capabilities.
• Easily takes on color.
• High tensile strength and durability.
• Resistant to diluted acids, oils, and greases.

Cons

• Degradation after prolonged exposure to water over 60°C.
• Susceptible to hydrocarbon wear.
• Tends to yellow over time after extended exposure to UV rays.

Applications
Polycarbonate, owing to its light-transmitting properties, is employed as a glass substitute in various applications. This includes the production of safety goggles, CDs/DVDs, surgical implements, and circuit breakers.

Polyethylene

Polyethylene, a lightweight and robust plastic CNC material, is recognized for its impact resistance, stiffness, and flexibility. It boasts excellent dielectric properties and comes in various grades, such as LDPE, HDPE, and UHMW PE, each with unique applications.

Pros

• Lightweight without compromising mechanical strength.
• High tensile strength.
• Low moisture absorption.
• Non-staining and non-toxic.
• High machinability.
• Resistant to acids and alkalis.

Cons

• Releases hot plastic fumes when subjected to heat, requiring proper ventilation.
• Low melting point can lead to deformation from heat generated by the CNC machine.

Applications
Polyethylene finds extensive use in the pharmaceutical, construction, chemicals, and food industries. Examples of products and parts crafted from this material include squeeze bottles, wire and cable insulation, and toys.

PVC (Polyvinyl Chloride)

Polyvinyl Chloride (PVC) is a widely utilized material in CNC machining, known for its high durability and versatility. Resistant to moisture, chemicals, and abrasion, PVC is valued for its ease of machining, allowing for precise creation of parts and components through cutting, drilling, milling, and turning. Another advantage lies in its cost-effectiveness, making PVC an affordable choice for various applications.

Pros

• High corrosion and chemical resistance.
• Acts as an electrical insulator.
• Exhibits high machinability.
• Tasteless, odorless, and non-toxic.

Cons

• Limited heating stability.
• Potential release of toxic fumes during machining due to high heat.
• Requires proper ventilation to prevent gas buildup.
• Low melting point can cause deformation from heat generated by the CNC machine.

Applications
PVC’s chemical inertness makes it widely applicable across diverse industries, with the specific application depending on the PVC type. Flexible PVC is suitable for manufacturing electrical wire insulation and flooring. In contrast, rigid PVC is employed for crafting components like rings, rollers, pads, pipe, and valve components.

Note: If you’re uncertain about the most suitable plastic material for your CNC machining project, feel free to contact us for assistance.

Methods of CNC Plastic Machining

CNC plastic part machining employs computer-controlled machines to precisely shape plastic polymers into desired products through subtractive manufacturing. This process ensures tight tolerance, uniformity, and accuracy, employing various methods:

CNC Turning

CNC turning involves securing the workpiece on a lathe and rotating it against a cutting tool by spinning or turning. Different types of CNC turning include straight or cylindrical turning for large cuts and taper turning for cone-like shapes. Guidelines for plastic CNC turning include negative back rake on cutting edges to minimize rubbing, generous relief angles, polishing for improved surface finish, and adjusting clearance, side, and rake angles based on the plastic material. Adjusting feed rates can enhance precision in final cuts.

CNC Milling

CNC milling utilizes a milling cutter to remove material from the workpiece to achieve the desired part. There are 3-axis mills for simple designs and multi-axis mills for complex geometries. Guidelines for plastic CNC milling include using carbon tooling for thermoplastics reinforced with carbon or glass, increasing spindle speed with clamps, creating rounded internal corners to reduce stress concentration, cooling directly on the router, selecting rotational speed, and deburring plastic parts post-milling for improved surface finishing.

CNC Drilling

CNC drilling in plastic machining involves creating holes using a drill mounted with a drill bit. The drill bit’s size and shape determine the hole size and chip evacuation. Types of drill presses include bench, upright, and radial. Guidelines for plastic CNC drilling encompass using sharp drill bits to prevent stress on the workpiece, selecting appropriate drill bits based on thermoplastic types, ensuring easy chip ejection, employing a cooling system to dissipate heat, and carefully removing the CNC drill to avoid damage, especially when the drilling depth is less than three or four times the drill diameter. Adjusting the feed rate during the exit phase is crucial.

Alternative Processes to Plastic Machining

In addition to CNC plastic part machining, various rapid prototyping methods offer alternative approaches. These include:

Injection Molding

Injection molding stands as a widely used mass-production process for plastic workpieces. In this method, molds crafted from aluminum or steel, depending on durability needs, are filled with molten plastic. Once the plastic cools, it takes on the shape defined by the mold. Injection molding is effective for both prototyping and actual part production, proving cost-effective for intricate and simple designs. The resulting parts often require minimal additional work or surface treatment.

3D Printing

3D printing, a prevalent prototyping method, is extensively employed in small-scale businesses. This additive manufacturing process encompasses technologies like Stereolithography (SLA), Fused Deposition Modeling (FDM), and Selective Laser Sintering (SLS), targeting thermoplastics such as nylon, PLA, ABS, and ULTEM. The process involves creating 3D digital models and building the desired parts layer by layer, akin to plastic CNC machining. However, 3D printing minimizes material wastage and eliminates the need for tooling, making it particularly suitable for intricate designs.

Vacuum Casting

Vacuum casting, also known as polyurethane/urethane casting, utilizes silicon molds and resins to replicate a master pattern. This rapid prototyping process ensures the creation of high-quality plastic copies. These copies serve purposes such as visualizing ideas or identifying design flaws during the troubleshooting phase.

Industrial Applications of CNC Plastic Machining

The widespread use of plastic CNC machining in various industries is attributed to its advantages in terms of accuracy, precision, and tight tolerance. Key industrial applications of this process include:

Medical Industry

Plastic CNC machining plays a crucial role in the production of machined parts for the medical sector, including prosthetic limbs and artificial hearts. Its remarkable accuracy and repeatability enable compliance with the stringent safety standards of the industry. The versatility of material options and the capability to produce complex shapes contribute to its prominence in medical applications.

Automotive Components

In the automotive industry, both designers and engineers leverage plastic CNC machining for the rapid production of automotive components and prototypes. Plastic, known for its lightweight properties, is widely used in crafting custom CNC plastic parts such as dashboards. This not only contributes to reduced fuel consumption but also takes advantage of plastic’s resistance to corrosion and wear. Additionally, the malleability of plastic facilitates the creation of components with intricate and complex shapes.

Aerospace Parts

For the precision-driven aerospace sector, CNC machining is the preferred method in designing, testing, and manufacturing various aerospace machined parts. Plastic materials are particularly favored due to their suitability for complex shapes, strength, lightweight nature, and high resistance to chemicals and heat, meeting the stringent requirements of aerospace applications.

Electronic Industry

The electronic industry benefits significantly from CNC plastic machining, primarily for its high precision and repeatability. This process is actively employed in crafting CNC-machined plastic electronic parts such as wire enclosures, device keypads, and LCD screens. The ability to consistently achieve precise dimensions makes it an ideal choice for meeting the intricate demands of electronic components.

Determining When to Choose Plastic CNC Machining

Selecting the most appropriate plastic manufacturing process can be a complex decision. Consider the following factors to determine whether plastic CNC machining is the optimal method for your project:

Plastic Prototype Design with Tight Tolerance

If your project involves creating parts with designs that demand tight tolerances, CNC plastic machining is the preferred method. Conventional CNC milling machines can achieve impressively tight tolerances, reaching approximately 4 μm.

Plastic Prototype Requires Quality Surface Finish

When your project demands a high-quality surface finish without the need for additional finishing processes, CNC machining is advantageous. Unlike 3D printing, which may leave layer marks, CNC machining delivers a superior surface finish.

Plastic Prototype Requires Special Materials

Plastic CNC machining offers versatility in material selection, accommodating a wide range of plastics with special properties like high-temperature resistance, high strength, or high chemical resistance. This flexibility makes it ideal for creating prototypes with unique requirements.

Products in the Testing Stage

During the testing stage, constant modifications are often necessary. CNC machining, relying on 3D models, facilitates easy changes. This allows designers and manufacturers to swiftly create functional plastic prototypes, enabling thorough testing and troubleshooting of design flaws.

Economical Option Needed

If cost-effectiveness is a crucial consideration, plastic CNC machining is a suitable choice. Plastics are generally more affordable than metals and other materials like composites. Moreover, the precision of computer numerical control makes the process cost-effective, especially for intricate and complex designs.

CNC Plastic Machining Services

Since CNC plastic machining is fast, accurate, and ideal for producing parts with tight tolerances, it is a widely used process in industry. We discussed available techniques, various CNC machining materials that are compatible with the process, and other things that may be helpful for your project.

Depending on your needs, we can assist you in creating various parts for real-time use or rapid prototyping through our custom plastic CNC machining services.

We offer a number of plastic materials that are suitable for CNC machining, and the selection process is both rigorous and efficient. Please feel free to consult with us.