CNC polycarbonate into precise components for engineering applications. You’ll find that this engineered grade thermoplastic offers exceptional impact resistance, up to 250 times stronger than glass. Moreover, it maintains dimensional stability across temperatures from -40°C to 120°C.
When you machine polycarbonate, it means you’re working with a material that combines optical clarity with mechanical strength. It is naturally transparent. It can transmit up to 90% of visible light. The material machines cleanly with appropriate tooling and cutting parameters.
However, you’ll face specific challenges during machining. Polycarbonate generates significant heat. So, it requires careful chip evacuation and coolant management. The material’s hygroscopic nature means you must store it properly to prevent moisture absorption. Internal stresses can cause cracking if you don’t control feed rates and tool geometry.
Engineers often prefer CNC polycarbonate for protective covers, medical device housings, and automotive components. It can achieve tight tolerances, typically ±0.05mm, with standard machining equipment. Sharp carbide tools and moderate cutting speeds prevent melting and gumming. Let’s get deeper into details about CNC polycarbonate machining, alloys, and properties.
What is CNC Polycarbonate?
CNC polycarbonate is a polycarbonate thermoplastic shaped through computer numerical control machining. The material features a high flexibility that’s almost impossible to break. It can withstand 250 times more impact than glass. It stays clear even when forces that would break most plastics try to break it. This combination makes it very useful when your design needs both strength and visibility.
In the process, a rotating cutter is used to remove material with a precision of microns. You program exact tool paths that cut raw polycarbonate sheet or rod into the shape you want. CNC machining allows you to adjust your design without having to buy expensive tools, unlike moulding. You can make 10 parts or 1000 with the same level of accuracy.
The choice of grade depends on the actual use case. It can bear high temperatures from -40°C to 120°C, which is important for outdoor and automotive uses. However, it may absorb 0.15% of moisture, so you should expect some small changes in size. It has a tensile strength of 65 MPa, which makes it strong enough to hold up in thin-walled areas.
You’ll find its extensive use in protecting delicate electronics in tough places. Medical companies use it for making fluid chambers and housings that can be sterilized. Besides, it is used in aerospace interiors for window assemblies and safety barriers.
Material Properties Overview
Understanding polycarbonate’s characteristics helps you make optimal design decisions. Here, we provided a table below that presents key physical and chemical properties you’ll reference during specification.
| Property | Value | Unit |
| Physical Properties | ||
| Density | 1.20 | g/cm³ |
| Tensile Strength | 60-70 | MPa |
| Flexural Modulus | 2,300 | MPa |
| Impact Strength (Izod) | 600-850 | J/m |
| Glass Transition Temperature | 147 | °C |
| Continuous Service Temperature | 115-120 | °C |
| Light Transmission | 88-90 | % |
| Refractive Index | 1.586 | – |
| Water Absorption (24 hrs) | 0.15 | % |
| Chemical Properties | ||
| Chemical Formula | (C₁₆H₁₄O₃)ₙ | – |
| Dielectric Strength | 16-18 | kV/mm |
| Flammability Rating | V-2 to V-0 | UL94 |
| Acid Resistance | Poor | – |
| Alkali Resistance | Moderate | – |
| Solvent Resistance | Poor | – |
Commonly Used Types of CNC Polycarbonate
This section has provided some of the common polycarbonate grades useful for machining.
General Purpose Polycarbonate
These grades are used in everyday household items. Machining them requires a speed of about 200 to 400 m/min with little heat buildup. Additionally, this allows 90% of the light through while also being able to withstand impacts of 600–850 J/m. When you need reliable performance without paying much, it’s usually 30–40% less expensive than specialized grades.
Glass-Filled Polycarbonate
When you add glass to polycarbonate, it turns the base material into a strong structure that can handle heavy loads. The addition of glass makes the material 3 times stiffer and lowers its thermal expansion to 2–3 × 10⁻⁵/°C. The reinforcement allows you to make your designs with thinner walls, which cuts the weight by 25% to 35%. During machining, glass fibers generate high heat and reach temperatures far higher than 300°C. It can have an impact on your tool’s life span.
Machine Grade Polycarbonate
Machine-grade polycarbonate can endure internal stresses that often cause cracks. The material has been pre-conditioned with controlled molecular orientation. This orientation keeps the material dimensionally stable through thermal cycling. This grade has tolerances of ±0.013mm over 300mm spans, and there is no stress relief after machining. When your parts require micrometre-level accuracy, it’s a go-to option. Its use is common in making medical devices and optical components.
AMGARD™ Polycarbonate
AMGARD™ polycarbonate prevents ballistic threats while keeping things clear for security purposes. You’ll choose a thickness between 19 and 76 mm based on the level of threat, which can be anything from a 9 mm handgun to a 7.62 mm rifle. The material’s layered structure absorbs impact energy gradually, which stops spalling on the protected side. It is used by banks, embassies, and armored vehicles. In these applications, lives depend on the transparent barrier’s performance.
TUFFAK Polycarbonate
TUFFAK polycarbonate has been proven to last for decades in the field and has modern coextruded protective layers. It has special UV absorbers that keep it from turning yellow for more than 10 years outside. The coating that resists scratches has a pencil hardness rating of 3H, which is important for glazing applications that get a lot of traffic. TUFFAK is a good choice when replacement costs are higher than original material costs. This applies to stadium roofs, machine guards, and transit shelters.
Benefits and Limitations of CNC Machining Polycarbonate
CNC Polycarbonate machining makes precise parts without requiring costly mold tooling. However, it presents certain limitations during cutting. You will need to weigh its great qualities against the machining limitations to see if it is right for your needs.
Pros
Exceptional Impact Resistance in Finished Parts
Machined polycarbonate parts retain their toughness after CNC machining. They can perform well under high-stress situations without breaking, unlike aluminum or acrylic. Some plastics become brittle when they are machined, but this material does not. They maintain their effectiveness in demanding environments.
Design Flexibility Without Tooling Investment
CNC machining allows you to adapt to design changes between production runs without having to purchase new tools. You can easily move a mounting hole or change the thickness of a wall by modifying the program. This is most important during the development phase. When making fewer parts, about 1,000 units, CNC is usually more economical than injection molding.
Tight Tolerance Capability for Precision Work
Modern CNC machines can consistently achieve tolerances down to ±0.025mm. It offers high accuracy in complicated shapes like pockets, bores, and curved surfaces. This accuracy level is needed for the proper assembly and function of medical housings and optical parts. The process makes shapes that molding can’t make.
Cons
Heat Generation During Cutting Operations
When you cut polycarbonate, it melts easily and makes sticky chips that get stuck in your tools. When you cut it aggressively at temperatures over 150°C, you’ll see the material start to soften. This leads to poor quality surface finish, size variation, and tools that break too soon. These issues can be avoided by using the right coolant and slow feeds, but production rates will slow down as a result.
Moisture Sensitivity Affecting Dimensional Stability
Polycarbonate stock absorbs moisture, which changes its size by 0.1–0.2%. So, wet material parts may crack or warp over time. Before machining critical parts, you need to dry the sheets at 120°C for a few hours. Putting things in sealed containers with desiccant keeps them from getting wet again after machining.
Surface Finish Challenges and Post-Processing Requirements
Even with sharp cutters, tool marks can still be seen on machined polycarbonate surfaces. To make clear parts look clear, you’ll need to do secondary polishing. Flame polishing, vapor treatment, or diamond turning will take a lot more time. Parts that need perfect surfaces cost 40% to 60% more than basic machined parts.
Applications of CNC Machined Polycarbonate Parts
CNC-machined polycarbonate provides both strength and clear visibility. They are preferred when standard materials can’t meet your safety and performance needs. Here are some of the common parts/components made from polycarbonate.
Fluid Chambers and Housings for Medical Devices
Polycarbonate housings keep the diagnostic equipment safe from damage and dirt. These products can go through 134°C autoclave cycles without warping or losing their size. For visual inspection during operation, the fluid chambers in dialysis and blood analysis equipment need to be clear. The material doesn’t crack when it comes into contact with isopropyl alcohol and hydrogen peroxide disinfectants over and over again.
Machine Safety Guards and Protective Barriers
Industrial machines need guards that keep operators safe while allowing them to watch the process. Usually, 6 to 25 mm thick sheets of polycarbonate are used to make barriers for CNC mills and robotic cells. These guards can take hits from broken tools or parts that have been ejected without breaking. A 12mm thick guard prevents a 1kg projectile traveling at 15 m/s. The projectile does not penetrate the guard.
Aerospace Interior Components and Window Assemblies
FAR 25.853 flammability standards define that aircraft cabins need to be made of lightweight materials. You make overhead bin doors and instrument covers that pass strict burn tests. Polycarbonate cockpit windows can handle bird strikes at speeds of up to 400 knots. The material works well at high altitudes up to -55°C and on tarmac up to 70°C.
Automotive Lighting Lenses and Sensor Housings
Headlamp lenses require smooth surfaces for proper light distribution. These surfaces must meet ECE regulations. You can machine complicated Fresnel patterns and reflective geometries all at once. LIDAR sensor covers need to control the wall thickness to within ±0.05mm to keep the signals from getting messed up. When stones hit polycarbonate lenses at 110 km/h, they don’t break.
Electronic Enclosures for Harsh Environments
Polycarbonate outdoor control panels offer high resistance to UV rays, chemicals, and rough handling. It is used in enclosures for railways and boats, where it’s hard to find replacements. The material has a dielectric strength of 16 kV/mm. This prevents electrical tracking in high-voltage applications. IP67-rated housings keep circuits safe in oil field instruments that are exposed to saltwater spray.
Optical Components and Light Diffusers
Machined polycarbonate diffusers are used in LED assemblies to get rid of hot spots and make the light even. To reduce light scattering losses, you keep the surface finish below 0.4 Ra. For machine vision lenses to work properly, the tolerances must be ±0.013mm. Polycarbonate’s refractive index makes it good for uses where glass would be too heavy and break too easily.
Finishing Options for CNC Machined Polycarbonate Parts
Machined polycarbonate surfaces rarely meet final specifications without additional finishing. You’ll select post-processing methods based on optical requirements, surface durability needs, and production economics.
As-Machined Finish
As-machined surfaces retain visible tool marks and achieve surface roughness between 1.6-3.2 Ra. You’ll see striations from cutter paths that scatter light in transparent sections. This finish suits non-critical applications like mounting brackets and internal structural components. It saves cost, reaching 30-40% compared to polished alternatives when optical clarity isn’t required.
Flame Polishing
Flame polishing melts the surface layer using a hydrogen-oxygen torch to eliminate tool marks. You can achieve optical clarity approaching 88-90% light transmission in 15-30 seconds per surface. The process requires skilled operators to prevent overheating, bubbling, or dimensional distortion. Edge finishing on cut polycarbonate sheets universally uses this method for crystal-clear results.
Vapour Polishing
Vapour polishing exposes parts to methylene chloride or other solvent vapours that soften the surface. It controls exposure time between 5-60 seconds, depending on initial surface roughness and desired clarity. Aside from this, it creates uniform finishes across complex geometries, including internal passages and recessed features. Parts obtained with glass-like surfaces require a 24-48 hour drying time before handling.
Diamond Turning
Diamond turning uses single-crystal cutting tools. It can achieve surface roughness below 0.025 Ra. It provides optical clarity of 1-2 microns. This makes it suitable for lens applications. The process demands vibration-isolated equipment and precisely controlled cutting parameters, including 0.025mm depth of cut. However, the costs increase 3-4 times over conventional machining but eliminate secondary polishing operations.
Annealing
In the annealing process, polycarbonate stocks are heated to 130-140°C for 1-4 hours, depending on thickness and complexity. The process prevents stress cracking when parts contact solvents or experience mechanical loading. Critical components like pressure vessels and safety shields require annealing before deployment.
Effective Tips for CNC Machining Polycarbonate
Successful polycarbonate machining requires specific techniques that differ from standard plastic processing. You’ll achieve better results by controlling heat, managing material preparation, and selecting appropriate tooling strategies.
Pre-Dry Material Before Machining
Polycarbonate absorbs 0.15 to 0.35% of its weight in moisture from the air. This changes its size. So, you need to dry the sheets for 3 to 4 hours at 120°C before machining critical parts.
Until you’re ready to process the dried material, keep it in sealed containers with desiccant. Parts that are machined from wet stock start to crack under stress within 48 to 72 hours of being finished.
Use Sharp Carbide Tools with Proper Geometry
The sharpness of the tool affects the finish of the surface and keeps the material from melting while cutting. Carbide cutters with positive rake angles of 5 to 10 degrees are best for removing chips cleanly.
A tool edge radius of less than 0.025mm makes cutting forces and heat go down a lot. Don’t wait until your tools break; instead, get new ones as soon as you notice they’re getting dull.
Control Cutting Speed and Feed Rates
Cutting at speeds between 200 and 350 m/min is the best way to keep productivity high and heat low. The feed rates you use will be between 0.10 and 0.25 mm/tooth, depending on the tool’s diameter and the depth of the cut.
If you feed too slowly, the parts will rub against each other and get hot. If you feed too quickly, the parts will chip, and the finish will be bad. So, always keep an eye on chip formation because stringy chips mean that too much heat is being generated.
Apply Compressed Air or Mist Coolant
Compressed air is useful for clearing chips and preventing thermal stress from happening when liquid coolant comes into contact with them. You apply pressure of 5 to 6 bars to the cutting area to get rid of chips.
Mist coolant systems work when you need better cooling but don’t want to risk thermal shock. Never flood cool polycarbonate because temperature differences cause cracks to form right away.
Machine in Multiple Light Passes
In general, big or heavy cuts make too much heat. They usually melt things and leave a rough surface. Instead of trying full-depth operations, you should cut to a depth of 1 to 2 mm.
Multiple passes spread out the heat generation evenly over time. It lets the material cool down between cuts. Final finishing passes at a depth of 0.2–0.5 mm give a better surface quality.
Support Thin Sections with Proper Fixturing
Unsupported polycarbonate bends under cutting pressure. This causes dimensional errors and chatter marks. You need to use vacuum tables and custom supports to fix the thin walls from both sides. Until all machining is done, keep the support material attached. Then take it off carefully. Parts that are less than 3mm thick need to be carefully handled so they don’t bend while in use.
Allow Parts to Cool Before Measurement
Machined polycarbonate requires 2-4 hours of cooling to ambient temperature before accurate measurement. You’ll see dimensional variations of 0.05-0.15mm if measuring immediately after cutting. Thermal expansion coefficients of 6.5 × 10⁻⁵/°C create significant errors in warm parts.
Partner with FastPreci for Precision Polycarbonate Machining
FastPreci offers CNC-machined polycarbonate components with tolerances down to ±0.05mm for critical applications. Our engineers understand polycarbonate’s unique machining challenges, including heat management and moisture sensitivity. Our 3-axis and 5-axis CNC centres handle complex geometries from prototypes to large-scale production volumes.
We machine all polycarbonate grades, including general purpose, glass-filled, and specialised variants like AMGARD™ and TUFFAK. You receive parts in 2-3 days for rapid prototyping or scaled production runs. Our finishing capabilities include vapour polishing for optical clarity, flame polishing for edge transparency, and hard coatings for excellent durability.
Our quality control ensures dimensional stability and stress-free parts ready for assembly. So, you benefit from all aspects, from designing to finishing, under one roof.
