What Is Polycarbonate?
Polycarbonate (PC) is an amorphous thermoplastic that softens before melting and doesn’t have a specific melting point. Polycarbonate is available mainly in black and clear bar stock and sheets. Similarly, polycarbonate is a versatile and durable alternative to standard glass when you need parts with excellent light transmission thanks to its amorphous composition, excellent clarity, low weight, and relatively low crystallinity. Unlike other plastics, like acrylic, Polycarbonate is heat-resistant and impact-resistant.
Properties of Polycarbonate
PC is a versatile engineering plastic with excellent material properties. Although polycarbonate is supplied in different grades, below are some of its common mechanical properties:
- High Fracture Toughness and Impact Resistance: Polycarbonates are known for their exceptional toughness and resistance to impact, making them commonly used material in high-performance applications.
- Resistance to UV radiation: Specific grades of polycarbonate offer exceptional UV light resistance because they are specially engineered to resist 100% sunlight exposure.
- High Normal Temperature and Fire Resistant: Polycarbonate can withstand temperatures as high as 140°C, making it ideal for medical applications that require repeated sterilization.
- Chemical Resistance: Polycarbonates exhibit high chemical resistance to alcohols, oil greases, inorganic acids, and aliphatic hydrocarbons.
- Excellent dimensional stability: This engineering thermoplastic has a low shrink rate between 0.6 – 0.9% and can maintain its dimensions in most conditions.
- Translucency and Optical Clarity: The amorphous structure of the polycarbonate thermoplastic allows it to offer exceptional transparency and optical clarity. Besides, it will enable precisely 90% light transmittance, and its refractive index of 1.548 makes it a widely used alternative to glass.
Commonly Used Types of Polycarbonate
Polycarbonate plastics are available in different grades, each with a distinct combination of mechanical properties suitable for specific purposes across industries. Here are typical grades of polycarbonate used in CNC machining:
- General Purpose Polycarbonate
This grade of polycarbonate has incredibly high toughness and similar transparency to glass. The general-purpose polycarbonate is perfect for aesthetic purposes due to its polished surface. Besides, its excellent UV resistance makes it a suitable material for outdoor applications.
- Glass-Filled Polycarbonate
Glass-filled polycarbonate is a robust grade of polycarbonate with high impact strength and toughness, making it a perfect alternative to engineered plastic and metals. Thanks to its 10-40% glass fiber content, which reinforces the strength of standard polycarbonate, it is a suitable replacement for metals when manufacturing industrial-grade components.
- Machine Grade Polycarbonate
This polycarbonate grade exhibits impressive dimensional stability, excellent electrical properties, a high modulus of elasticity, and impact resistance. Components made with machine-grade polycarbonate are commonly found in applications that demand substantial fabrication efforts.
- AMGARDTM Polycarbonate
The AMGARDTM polycarbonate is an extraordinary engineering plastic that combines silver ions into the material to prevent microorganisms’ growth on the surface. This polycarbonate grade is perfect for making medical devices and equipment, protective shields, and similar applications requiring bacteria or mold-free surfaces.
- TUFFAK Polycarbonate
TUFFAK is a versatile polycarbonate plastic variant that is twice the strength of glass. It is compatible with various manufacturing techniques, such as CNC machining and thermoforming. TUFFAK polycarbonate exhibits impressively high dimensional stability and compatibility with adhesives, paints, and solvents.
Benefits and Limitations of CNC Machining Polycarbonate
CNC machining polycarbonate parts offer extensive benefits such as:
- Polycarbonate comes in various formulations, including FDA-compliant and glass-filled variants. Hence, you can find the perfect match for your project’s requirements.
- Machined polycarbonate parts exhibit minimal moisture absorption and have higher melting points.
- Polycarbonate is suitable for high-demand applications such as protective gear and bullet-resistant glass due to its high impact resistance and tensile strength.
- Variants of polycarbonate are intrinsically transparent and lightweight, can transmit light effectively, and accept colors without compromising their transparency.
- Polycarbonate has good machinability and excellent heat deflection temperature.
Irrespective of the vast benefits of using polycarbonate for your CNC machining project, here are some of the common limitations:
- Polycarbonate components are susceptible to scratching and are only compatible with a few finishing options, such as coating and vapor polishing.
- Polycarbonate is prone to softening and deforming at high temperatures. Excessive heat generated during machining can lead to poor dimensional accuracy, surface finish issues, and part deformation.
- PC is an abrasive material, which can cause rapid tool wear during machining. This increases tooling costs and may require frequent tool changes or special tool coatings.
- CNC-machined polycarbonate parts turn yellow due to extended exposure to UV light.
- Large polycarbonate components may be difficult to machine due to the material’s tendency to warp or deform under its own weight or during clamping.
Applications of CNC Machined Polycarbonate Parts
CNC-machined polycarbonate parts are commonly used in different industries since polycarbonate grades offer various of desirable properties. Below are typical applications of CNC polycarbonate parts:
Automotive
Polycarbonate provides the excellent impact strength and fracture toughness required to make quality and reliable automotive components. Manufacturers in the automotive industry often use polycarbonates when producing transparent or translucent components that can handle high impact, such as bulletproof windows, turning signal lenses, and headlights.
Healthcare
Machined polycarbonate parts are used in different areas of the healthcare sector, ranging from dialysis machine housings to incubators. Moreover, polycarbonates have remarkable dimensional stability, heat resistance, and toughness. Hence, machined medical PC parts can withstand FDA-approved sterilization methods such as autoclaving and radiation.
Surgical instruments, blood filters, oxygenators, and fluid reservoirs are typical polycarbonate parts used in the medical industry. In addition, polycarbonate’s transparency helps doctors monitor and track blood infusions more easily.
Household Appliances
Polycarbonate is ideal for producing household appliances like electric shavers, hair dryers, blenders, and refrigerators. Other common uses of polycarbonate include food containers, fuse boxes, protective gear, television enclosures, greenhouses, skylights, machine guarding, and roofs.
Finishing Options for CNC Machined Polycarbonate Parts
Polycarbonate is compatible with a few surface finishes since the material can scratch easily. These surface finishes help improve the physical properties of machined PC parts for end-use applications. Here are possible finishing options for polycarbonate:
As-Machined
As-machined is a standard and cheaper finish requiring no further post-processing treatment for machined parts. Although as-machined parts may possess tiny and visible surface tool marks or scratches, the finishing represents a more economical and faster manufacturing option. However, an as-machined finish doesn’t provide an optically transparent surface on polycarbonate parts, even though a machining PC with diamond tooling can provide optical clarity. Consequently, clients must specifically request this finish in the quoting process as it may increase machining costs.
Vapor Polishing
CNC machined parts often have visible tool marks, which affect the product’s appearance. Vapor polishing typically removes tool marks and scratches by exposing the machined PC parts’ surface to a solution that reacts and melts the part’s surface, causing the material to flow and fill visible tool marks.
Although the CNC machined polycarbonate parts’ surface is typically translucent, it can become nearly opaque if it melts during machining. Vapor polishing is an ideal post-processing option that evens the part’s surface, giving a uniform high gloss or optically clear look. However, this surface finish is unsuitable for applications that demand components with optical clarity.
Buffing
This mechanical finish improves the surface of machined polycarbonate parts by removing tool marks. It involves polishing the part’s surface with a rapidly spinning cotton polishing wheel. This method is highly efficient in finishing large parts with simple external surfaces. However, buffing provides a less clear polishing effect on machined polycarbonate than vapor polishing.
Scratch-Resistant Coating
One of the downsides of using polycarbonate is its tendency to scratch easily. Applying coatings on CNC machined polycarbonate parts helps enhance its scratch-resistance and optical clarity properties.
Expert Tips for CNC Machining Polycarbonate
Polycarbonate is one of the relatively costly CNC plastics. Here are some expert tips for achieving the best results in polycarbonate CNC machining:
Mill in Steps
Expert machinists recommend milling thicker polycarbonate sheets in multiple steps to attain a clean and consistent edge finish. You can mill thin panels of about 5 mm thickness in a single pass. However, it is essential to mill in the opposite direction of the cutting tool’s rotation to achieve a cleaner milling edge.
However, AT Machining experts advise milling panels with about 10 thicknesses in two steps and thicker panel sections in four steps. Additionally, run the cutter at a reduced speed during the fourth step for an improved edge finish and avoid melting.
Use CNC Cutters with Sharp Edges
Aside from polycarbonate being susceptible to chipping and stress cracking during machining, using cutters with dull/blunt edges can deteriorate the finish of your machined polycarbonate parts. Even though PC exhibits good machinability, it is essential to use sharp CNC cutting tools to ensure smooth polycarbonate machining and reduce stress on the material. Furthermore, you can use a vacuum or blower to extract the chips that can build up and interfere with the machining process.
Choose the Right Cutting Tool with a Compatible Diameter
Use a CNC cutter with the proper diameter to achieve the best polycarbonate CNC machining results. Experts often recommend milling polycarbonate with a single-edged carbide (HSS) CNC tool for an excellent finish.
- Use a 4 mm diameter cutter when machining panels with a 5 mm or less thickness.
- Choose a cutter diameter of 6 mm at most when working with panels with thickness between 5 – 10 mm.
- Machine panels thicker than 10 mm using a cutter with a diameter between 8 – 10 mm.
Apply Cutting Fluids
Applying cutting fluids during polycarbonate CNC machining helps mitigate heat buildup, extract chips, and avoid material melting. Machining experts at AT Machining utilize non-aromatic water-miscible coolants in machining polycarbonate. It helps achieve machined polycarbonate parts with desired surface finishes and tighter tolerances. More notably, using coolants during polycarbonate CNC machining ensures extended tool life.
Set Proper Feet and Speed Rates
It is advisable to start polycarbonate CNC machining with the maximum RPM (Rotation per Minute) and feed rates that can achieve accuracy to ensure optimal machining. Then, slowly reduce the feed rates and speeds to achieve optimal machining results. However, depending on the tool types, the required plunge rate may vary from 20 to 120 IPM.
Conclusion
Polycarbonate CNC machining is a popular manufacturing process for producing precision plastic parts with standard cutting tools like drills and end mills. When the machining parameters are suitable, the process becomes relatively easier than machining acrylic and other common thermoplastics. However, this guide has provided more tips on achieving the best results in CNC machining polycarbonate.
AT-Machining is a reliable custom CNC machined polycarbonate parts supplier to rely on whenever you need custom PC parts and prototypes. We can deliver superior quality polycarbonate parts with tight tolerance and superior surface finish that fit the client’s preference and industry standards. Our certified engineers and machinists leverage our state-of-the-art CNC facility and expertise to deliver quality machined products. Worry not about your products meeting stringent industry standards; we are ISO 9001:2015 certified. Submit your CAD file now for instant quotes on custom-machined polycarbonate parts.
