Machining Plastic Parts Luke Kwisnek Patrick Slater Matt Jackson

Objective Differences between metal and plastic Differences between metal and plastic Materials Materials Advantages Advantages Disadvantages Disadvantages

Outline Why Machine Plastics Why Machine Plastics Process Considerations Process Considerations Material Considerations Material Considerations

Why Machine Plastic? Cost Effective Cost Effective Low Volume Production Low Volume Production Secondary Operations Secondary Operations Material Limitations Material Limitations Thermosets Thermosets Composites Composites Ultra-High Mw Materials Ultra-High Mw Materials

Machining Plastics vs Metals Ventilation Concerns Ventilation Concerns Annealing Annealing To Avoid Warpage To Avoid Warpage Robust Fixturing Robust Fixturing Tooling Considerations Tooling Considerations Sharper Sharper More Clearance (“Rake”) More Clearance (“Rake”)

Factors Affecting Cutting Action In Plastics Heat Heat Thermal Conductivity < Metal Thermal Conductivity < Metal Resists Compressive Fracture Resists Compressive Fracture Factors Promoting Tensile Fracture: Factors Promoting Tensile Fracture: Sharp Tools Sharp Tools Large Rake Angles Large Rake Angles

Factors Affecting Cutting Action In Plastics Chip Formation Chip Formation Want Continuous Flow Type Want Continuous Flow Type Smooth and Continuous Smooth and Continuous High Elastic Deformation High Elastic Deformation

Process Specific Considerations

Lathe Cutting Tooling Tooling Standard Tool Materials Standard Tool Materials High Rake Angle High Rake Angle Water Soluble Coolants Water Soluble Coolants Close Chucking and Follow Rests Close Chucking and Follow Rests Prevent chatter Prevent chatter

Lathe Tool Bit Terminology

Milling Tooling Tooling Standard Tool Materials Standard Tool Materials High Clearance High Clearance Water Soluble Coolants Water Soluble Coolants Slower Cutting Feeds Slower Cutting Feeds Same as Metal Otherwise Same as Metal Otherwise

Drilling/Reaming Tooling Tooling Wide, Highly Polished Flutes Wide, Highly Polished Flutes Large Helix Angles Large Helix Angles Point angles of 60-90° (included) Point angles of 60-90° (included) 120° for PMMA and PVC 120° for PMMA and PVC Dimensional Concerns Dimensional Concerns Thermal Expansion Thermal Expansion Drill Oversize Drill Oversize

Drill Terminology

Reamer Terminology

Tapping/Threading Tooling Tooling Same Tools as Metal Same Tools as Metal Blunt Withdrawal Edges Blunt Withdrawal Edges Speeds Speeds 50 ft/min Most Plastics 50 ft/min Most Plastics 25 ft/min Filled Materials 25 ft/min Filled Materials

New Cutting Technologies Water Jet Water Jet Ultrasonic Ultrasonic Laser-assisted turning Laser-assisted turning

Material Specific Considerations

Machining Neat Plastics Teflon, Acetal, Acrylics Teflon, Acetal, Acrylics Generous Rake Generous Rake Low Cutting Speeds (< 1m/min) Low Cutting Speeds (< 1m/min) Nylon Nylon Continuous Chips Continuous Chips Rake, Depth and Speed Rake, Depth and Speed Annealing Annealing Standard Standard Double Anneal (Teflon) Double Anneal (Teflon)

Machining Thermosets Base Resin Mixtures Base Resin Mixtures Phenolic, Urea, Melamine, Silicone Phenolic, Urea, Melamine, Silicone Most similar to metal Most similar to metal High speeds and feeds High speeds and feeds Finishing required Finishing required

Machining Reinforced Plastics Fiber-Reinforced Plastics (FRPs) Fiber-Reinforced Plastics (FRPs) Base Materials Base Materials Polyesters, Polyamides, Expoxy Resins Polyesters, Polyamides, Expoxy Resins Matrix (Filler) Materials Matrix (Filler) Materials Glass, Carbon, Aramid Fibers Glass, Carbon, Aramid Fibers

Machining Reinforced Plastics cont. Usage Limitations Usage Limitations Chip/Dust Production Chip/Dust Production Surface Details Surface Details Unique Modes of Failure Unique Modes of Failure Different Fracture Characteristics Different Fracture Characteristics

Chip Characteristics Powder Ribbon Brush

Fracture Characteristics

Machining Reinforced Plastics cont. Tooling Tooling Longer Life With K-Carbide Longer Life With K-Carbide Cutting Speed 38 m/min Cutting Speed 38 m/min Single Crystal Diamond Tooling Single Crystal Diamond Tooling Better Life Better Life Cutting Speed 426 m/min Cutting Speed 426 m/min

Conclusion Cost Effective Cost Effective Low Volume Low Volume Difficult to Mold Materials Difficult to Mold Materials Promote Tensile Fracture Promote Tensile Fracture Continuous Flow Chips Continuous Flow Chips Generous Rake Generous Rake Sharp Tools Sharp Tools Low Cutting Speeds Low Cutting Speeds