Machining Plastic – UHMW
What is UHMW
UHMW, or UHMWPE, is short for Ultra-High Molecular Weight Polyethylene, a type of polyethylene.
UHMW Properties – Pros
1) Excellent wear resistance:
● 3 to 7 times higher than carbon steel, it is one of the most wear-resistant plastics known
● Ideal for high friction and wear environments
2) Self-lubricating
● The friction coefficient is 0.05-0.11, which is 1/2 of PA6 when water is used as lubricant; it is second only to PTFE when there is no lubricant
● No additional lubrication required in many applications, reduce maintenance costs
● Suitable for sliding or moving parts
3) Good impact resistance
● It remains tough at low temperatures (-200°C)
● The impact energy absorption value is the highest among all plastics, so the noise damping is very good
● A good option for high impact environments
4) Chemical stability
● Good resistance to acids, alkalis, solvents (except concentrated nitric acid) at 20°C to 80°C without any abnormal phenomenon
● Commonly used in corrosive environments
5) Low temperature resistance
● Still maintain good performance in low temperature environment (such as -80°C)
● Can be used in freezing or low temperature conditions
UHMW Properties – Cons
1) Difficult manufacturing:
● It has poor fluidity during manufacturing and requires higher temperature and pressure due to a high molecular mass, which causes high cost and low efficiency
● Limits its application in some fields
2) Large thermal expansion coefficient
● In an environment with large temperature changes, the material has poor dimensional stability due to a large thermal expansion coefficient, prone to deformation or cracking
● Not suitable for high-precision dimensional control
3) Non-heat resistant
● Typically, the maximum operating temperature is usually limited to about 80°C to 100°C
● Susceptible to aging and degradation in high temperature environments, losing its original performance
4) UV sensitivity
● Sensitive to UV rays
● Prolonged exposure to sunlight can cause it to degrade and become brittle
● Not recommended for outdoor environments
5) Poor adhesion
● Weak bonding between UHMWPE and other substances when manufacturing composite materials
● Affecting the performance of composite materials
6) Low hardness and strength
● A relatively low hardness and strength
● Not a good option for applications required to withstand larger loads or higher hardness
UHMW Applications
Property | Applications |
Wear & impact resistance | ● Textile machinery components: shuttle pickers, shuttle rods, gears, couplers, flower sweeping rods, buffer blocks, eccentric wheels, rod sleeves, swinging back beams and other impact-resistant wear parts etc ● Papermaking machinery components: wipers, water suction box covers, guide plates, hydrofoils, compression parts, joints, sealing shafts, deflectors, scrapers, filters, etc ● Conveyor devices components: guide rails, slider seats, fixed plates, etc ● General machinery components: gears, cams, impellers, rollers, pulleys, bearings, bushings, sleeves, pins, gaskets, seals, elastic couplings, screws, pipe clamps, etc |
Self-lubricating & Poor adhesion | ● Powder linings: silos, hoppers, chutes and other return devices; sliding surfaces, rollers, etc. Storage hopper linings for silo linings such as coal hoppers and powder product hoppers ● Agricultural and construction machinery components: anti-wear plates, brackets ● Stationery and sports goods: skating sleds, sled boards, etc |
Chemical stability | ● Warm water containers for solar equipment ● Chemical industry parts: sealing filler plates, packing materials, vacuum mold boxes, pump parts, bearing bushings, gears, sealing joints, etc ● Transportation pipelines ● Food conveying systems, ice machine components and other related machinery and equipment ● Medical artificial body parts |
Others | ● Ship parts, extremely low-temperature mechanical parts, etc |
UHMW Process Selection
1) Recommended process
● CNC machining (most commonly used):
– Tools: carbide or diamond coated cutter, large front angle design (reduce cutting heat)
– Parameters: low speed (≤200m/min), snack depth (0.1~0.3mm), fast feed
– Cooling: compressed air (water cooling is prohibited to avoid water absorption and deformation)
● Pressure sintering molding: directly sinter powder into blanks or simple parts
● Hot compression molding: heating the plate and then press molding (such as liners, rails)
2) Not recommended process
● Injection molding/extrusion (extremely high melt viscosity, requires special equipment)
● Laser cutting (easy to melt and uneven edges)
UHMW CNC Machining – Common defects and solutions
Defect Type | Cause | Solution |
Surface melting / burning | ● High cutting heat causes partial melt ● Tool blunting or slow feeding, generating frictional heat | ● Use sharp tools (diamond coating or carbide tools) to keep the cutting edge free of wear ● Parameter optimization: low speed (≤200m/min), fast feed (≥0.1mm/tooth), avoid tool dwelling ● Forced cooling: use compressed air to blow chips |
Burr / Fibrosis Edge | ● UHMW is extremely tough, and the material is pulled rather than sheared when the tool cuts ● The tool back angle is too small or the cutting edge is not sharp. | ● Use a new tool when fine finishing, tools with large rake angles (≥20°) is preferred ● Use reverse milling (the tool cuts into the material from the outside to reduce burrs) ● Manual trimming after machining (lightly scrape the edge with a sharp blade; or other hand deburring tools, silicon carbide paper) |
Dimensional instability (rebound/deformation) | ● Low elastic modulus and elastic recovery after machining (rebound amount 0.1-0.3mm) ● Clamping force is too large resulting in local deformation | ● Machining in stages: roughing with allowance (0.3mm) → natural cooling → fine finishing (0.1mm depth of cut) ● Fixture optimization: use vacuum suction cups or soft jaws to avoid mechanical extrusion and deformation ● Compensation design: pre-drill small holes during hole machining, reamer for final machining (hole diameter compensation 0.05-0.1mm) |
Rough surface/ chatter marks | ● Tool vibration or uneven feed ● Material elasticity causes tool deflection | ● Use short-edged tools (overhang < 4 times tool diameter) to reduce vibration ● Polishing: 600# sandpaper for rough polishing → diamond abrasive paste for fine polishing |
Tips
1) Tool selection:
● Use 2-edge end mill for rough machining and single-edge spiral mill for fine machining (reduce cutting force)
2) Clamping notes:
● Avoid using metal fixtures for direct extrusion, and use soft rubber sheets to disperse pressure.
3) Emergency treatment of defects:
● If it has melted: use a sharp scraper to remove the molten mass, and then finish it at low speed
● If the size is out of specification: use a hot air gun to locally heat (≤80℃) to fine-tune the shape
Conclusions
Key points to machine UHMW
● Heat control: low speed, fast feeding, forced air cooling
● Rebound preventing: staged machining to compensate for the amount of rebound
● Suppress burrs: reverse milling + sharp tool + manual trimming
FAQ
1. Is UHMW a good choice for my part?
● You can refer to UHMW properties and applications above
● The fastest and easiest way is to send us the drawings and product application, our engineering team will evaluate accordingly
2. Which material is better for my product, HDPE or UHMW?
When UHMW is preferred
● High wear resistance: such as guide rails, gears, bearing bushings and other parts with frequent friction
● Precision machining: high surface finish is required (such as medical equipment parts)
● Impact resistant environment: such as handling tools, bumpers
When HDPE is preferred
● Low-cost simple parts: such as containers, shells and other non-load-bearing parts
● Rapid prototyping: HDPE is easier to cut and suitable for proofing
