Polycarbonate CNC Machining

Polycarbonate, also known as PC, is an amorphous thermoplastic that softens before reaching its melting point. It is characterized by transparency, impact resistance, strength and lighter weight compared to glass, which makes it an excellent alternative to this material. Polycarbonate is also capable of withstanding higher temperatures than acrylic, which allows it to be easily machined to create a variety of custom components, especially when using CNC milling technology.

This guide provides an overview of polycarbonate, including its key properties, typical applications, machining tips, and available surface finish methods for polycarbonate parts.

What is polycarbonate?

Polycarbonate (PC) is a type of thermoplastic that is distinguished by its excellent optical transparency, high mechanical strength, excellent impact resistance and outstanding resistance to deformation under load. The material is available in FDA-approved versions and variants with additives to improve its load-carrying properties and abrasion resistance.

Thanks to its amorphous structure, polycarbonate has low crystallinity and exceptional optical transparency, which allows it to outperform many types of glass in terms of visible light transmission. For this reason, polycarbonate is used as an alternative to glass in many fields, including automotive lighting, impact-resistant windows, aerospace (e.g., military fighters, laboratory lenses), electrical circuits, and more. Polycarbonate is distinguished not only by its extraordinary impact resistance even at extreme temperatures, but also by its high machinability. It is easy to form and thermoform, which makes it possible to achieve precise tolerances without much difficulty.

Properties of polycarbonate

Polycarbonate, with its unique properties, is widely preferred in a variety of industrial and commercial applications. The key features of this thermoplastic are crucial when selecting the right grades and processing methods, which in turn can significantly increase the efficiency of production processes.

Optical transparency: Thanks to its amorphous structure, polycarbonate offers outstanding optical properties, being a frequently used replacement for glass thanks to its refractive index of 1.548. It retains its transparency even after coloring.

High strength and hardness: Polycarbonate is prized for its unparalleled impact resistance and toughness, allowing it to withstand external impacts, cracks, and splits. Its strength lasts in a temperature range of -20°C to 140°C, making it ideal for parts that require high reliability and durability.

Machining: Due to its heat resistance and durability, polycarbonate is very easy to machine.

Transmittance: Typical polycarbonate can transmit about 90% of light, making it an excellent choice for applications that require high transparency, such as medical components, prototypes, and decorative items.

Lightweight: Compared to other thermoplastic materials or glass, polycarbonate stands out for its exceptional lightness.

Thermal stability: Polycarbonate remains stable up to 135°C. For applications requiring higher thermal resistance, stability can be increased by adding flame retardants.

Dimensional stability: It has the characteristics of high dimensional stability and shrink resistance, with a low shrinkage rate of 0.6% – 0.9%.

FDA Compliance: As an FDA-compliant material, polycarbonate is a key choice for the medical and food industries.

UV Resistance: Special grades of polycarbonate can block 100% of sunlight, offering exceptional UV resistance.

Chemical resistance: Reinforced polycarbonate grades exhibit excellent resistance to oils, waxes, aliphatic hydrocarbons, greases, and dilute acids.

Coating Capabilities: Polycarbonate parts can be coated with anti-static, hard and matte layers, as well as UV and anti-fog coatings.

However, polycarbonate also has some limitations, such as susceptibility to scratches, yellowing when exposed to UV radiation, and challenges associated with secondary finishing operations. Parts may also tend to collapse or create voids in thicker segments. To prevent this, it is recommended to divide thick parts into thinner segments, which can be more cost-effective given the cost of raw materials and processing time.

Polycarbonate grades

Polycarbonate is available in a variety of grades, each designed to meet specific industrial and commercial requirements. Here is an overview of the most common types of polycarbonate:

Glass-Filled Polycarbonate: This type of polycarbonate is ideal for industrial applications, where it often replaces metals. It contains 10 to 40% glass fibers, which significantly increases its strength compared to standard polycarbonate. It is chosen for its high strength and impact resistance, making it an excellent alternative to metals and other engineering plastics.

General Purpose Polycarbonate: Has comparable transparency to glass and impressive strength. Thanks to its polished surface, this grade is often used where aesthetics are key. In addition, it has an outstanding resistance to aging caused by UV radiation.

Machine-Grade Polycarbonate: This grade is distinguished by good dimensional stability, impact resistance, high modulus of elasticity and excellent electrical properties. Parts made of this material are ideal for applications that require intensive production effort.

Each of these polycarbonate grades is designed to meet specific needs, offering a wide range of possibilities for engineers and designers in a variety of industries.

What is polycarbonate treatment and how does it work?

Polycarbonate machining is a subtractive process that involves removing excess material from a polycarbonate block to achieve a specific shape and finish. One of the most popular machining methods is the use of CNC (Computer Numerical Control) technology.

This process begins with the polycarbonate block being accurately cut using a suitable method or combination of machining methods, such as CNC milling, CNC turning, CNC cutting, or laser cutting. The choice of a specific technique or a combination of them depends on the specific production requirements. After cutting and shaping the polycarbonate, the surface finishing step begins, which is necessary to achieve the aesthetic appearance of the final product.

Why CNC Process Polycarbonate?

There are many advantages to using polycarbonate in the CNC machining process, making it the preferred material for many industrial applications. Here are some key reasons why polycarbonate is so valued:

High strength and wear resistance: Polycarbonate has excellent load-bearing capacity and wear resistance, which makes it resistant to extreme temperatures. This feature makes it an ideal material for parts that have to withstand harsh operating conditions.

Exceptional machinability: Polycarbonate is highly machinable, which makes it perfect for precision CNC machining. Its properties allow for easy forming and cutting, which is crucial when creating complex shapes and details.

Excellent transparency: Thanks to its exceptional transparency, polycarbonate is the ideal material for the production of transparent components such as safety glasses, windows or light covers. This feature makes it a popular choice where both aesthetics and functionality are important.

Electrical insulation: Polycarbonate is a popular choice for applications that require electrical insulation, thanks to its dielectric properties. It is biologically inert, which further expands its use in the electronics and electrical industries.

Cost: Polycarbonate offers relatively low costs, making it an attractive material for a wide range of industrial applications. Its affordability, combined with its strength and versatility, makes it a popular choice for production in both large and small runs.

In conclusion, polycarbonate is a versatile material that, thanks to its unique properties, is used in many industrial fields, from electronics to automotive, offering not only strength and durability, but also aesthetics and economy.

Tips for processing polycarbonate

CNC machining of polycarbonate is a process that, despite its simplicity, requires the observance of certain rules and techniques to ensure high quality and precision of the finished products. Here are some key tips to help you increase the efficiency of CNC polycarbonate machining:

1. Use sharper tools: To ensure a smooth machining process, it is important to use milling machines with sharp blades and an effective chip removal system. It is also recommended to use a vacuum cleaner if the machine is equipped with one to ensure cleanliness during operation.
2. Choose the right tool: For the best machining results, choose carbide (HSS) tools with the right diameter. For panels up to 5 mm thick, a tool diameter of 4 mm is recommended, for panels with a thickness of 5-10 mm – a diameter of up to 6 mm, and for panels over 10 mm thick – tools with a diameter of 8-10 mm are the most suitable.
3. Stable material fixation: Providing stable support for both the panel and the machine is crucial. The panel should be placed on a hard surface, to avoid vibration, it is recommended to use a wooden board. In addition, provide adequate support for the top of the panel so that it is firmly pressed against the work surface, which can be achieved with strips and clamps.
4. Optimize speeds and feeds: Start machining at maximum speed and feed rates that ensure accuracy, then gradually adjust these parameters for best results. The immersion rate of the tool can vary from 20 to 120 IPM (inches per minute), depending on the tool used.
5. Use coolant: The use of coolant is crucial for chip elimination and heat dissipation. There are two main types of coolants available: high-pressure air current, which is a simple and effective solution, and clean water, which provides better performance for deep grooves.
6. Mill in multiple steps: For thick sheets, it is recommended to mill in several steps to ensure a clean edge finish. Thin panels up to 5 mm thick can be machined in a single pass, but for better edge finishing, it is recommended to machine in the opposite direction to the rotation of the tool. Panels up to 10 mm thick are best milled in two steps, and thicker ones in four, with a slightly slower speed recommended in the last step to achieve the perfect finish.

Following these guidelines can significantly improve the quality and efficiency of polycarbonate CNC machining, providing a precise and aesthetically appealing finish to your products.

Surface finish of treated polycarbonate

Removing scratches from polycarbonate surfaces is a key step in the finishing process to improve the aesthetics and functionality of finished products. There are three main polishing methods that can be used to achieve a smooth and glossy surface: buffering, steam polishing, and hand polishing.

Caching

Buffering is a mechanical polishing method that uses a rapidly rotating polishing wheel, typically made of cotton. It is an effective technique for polishing large, straight surfaces, offering fast and effective results. However, compared to steam polishing, buffering may not provide such a pronounced gloss effect.

Steam polishing

This method consists in evenly covering both the external and internal surfaces of polycarbonate parts, which allows to achieve a uniform gloss over the entire treated surface. Steam polishing is particularly suitable for components with complex shapes and details, where traditional methods may not be effective.

Hand polishing

This is a traditional method that involves manual polishing of the surface with sandpaper of various grits. The process begins with the use of thicker sandpaper, which is gradually replaced by paper with less and less grit until the desired gloss is achieved. Although hand polishing can be more time-consuming and labor-intensive compared to other methods, it can achieve extremely high gloss, especially on polycarbonate parts.

Summary

Choosing the right polishing method depends on a number of factors, including the size and shape of the polycarbonate part, the desired finishing result, and the time and financial resources available. Buffering offers speed and efficiency for large, straight surfaces, steam polishing is ideal for complex shapes, while manual polishing provides the highest level of control and quality finish, especially on small or particularly delicate parts.

Autor: Tomasz Matuszek; Dział Marketingu - Firma Gulajski