MACHINING OF CARBON FIBER COMPOSITES USING CVD

1
MACHINING OF CARBON FIBER COMPOSITES USING CVD

• J. Zimmer, E. Koik, K. Bennett
• sp3 Cutting Tools Inc.
• May 6, 2008

2
CFC Machining Challenges

• Large Stiff Fiber Bundles
• Relatively Soft Low melting Point Corrosive
  Resins
• Fiber Fraying
• Layer Delamination
• Popcorn Effect

3
Typical CFCMachining Operations

• Endmilling
• Side Cutting
• Plunging
• Slotting
• Drilling
• Spot Facing
• Turning (rare)

4
The Ideal CFC Cutting Tool

• Very Sharp Edge
• Surface finish, fraying and heat reduction
• Tough Strong Edge
• Tool edge chipping reduction
• Feed rate increases
• Compression Cut Geometry
• Fraying reduction
• Large Open Smooth Flutes
• Chip evacuation
• Compromise is Required

5
Classical Machining Solutions

• Diamond Cut Burrs
• Single Point Tools
• High dust, low lifetime
• Wear away material
• Grinding Wheels
• Poor Tolerance Control
• High dust, low lifetime

• Low Helix Angle Carbide Routers
• High Wear Rate
• Single Flute PCD Routers
• Low Feed Rate
• Chatter problems

6
New Diamond Tool Solutions

• Diabide (diamond coated carbide)
• Multiple geometry choices
• Various edge treatments
• Large Open Flutes Possible
• Marginal Edge Sharpness
• Optimal Machining Conditions are not intuitive
• Less Predictable Failure Modes

• TFd (thick film CVD diamond)
• Brazed Solid Diamond
• Sharp, Tough Edges
• Variable helix and rake angles
• Open Flutes not easy
• 2 or 3 Flute PCD
• Embedded Edges
• Expensive
• Not Chemically resistant

7
Comparison Criteria

• All Tools and Machining Conditions Must Provide
• Acceptable Results for the Following
• Cut Quality
• Minimal Fraying
• Adequate Surface Finish
• Minimal Delamination
• Wear Rate and Durability Targets
• Machining Cost Targets
• Productivity Targets

8
CFC Cut Quality

• Tool Design and Machining Conditions Drive Cut
  Quality
• Designs and machining conditions are Type and
  Application Specific
• Rivet hole drills different from honeycomb panel
  drills, etc.
• Chip control in slotting is more critical than
  edge trimming

9
Diamond Wear Rate and Durability

• CFC Wear Rate on Diamond is Predictable if Tool
  Durability is High
• 20-30 nm / swept inch
• Durability is material, tool design and machining
  condition dependant
• Coatings must be thick enough to be self
  supporting
• PCD is subject to pullouts, cobalt leaching and
  chipping
• TFd is subject to chipping
• Chip flow and chip evacuation must be controlled
• Durability can be designed into the tool

10
Tool Durability vs.Diamond Thickness
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Productivity and Cost Targets

• Machining Costs are more than just tool lifetime
• Tool Life
• Tool Cost
• Tool Setup and Replacement times
• Productivity is more that just tool lifetime
• Tool Lifetime
• Machining times
• Setup Times
• Feed Rates
• Machine Uptime

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Drilling Tool Life vs. Costs
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Productivity by Tool Type
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Conclusions

• Uncoated Carbide
• Wears out very rapidly.
• Conventional Coatings (including DLC)
• Wear through quickly.
• Tool then performs like Uncoated Carbide.
• Thin Diamond Coatings and Diamond on many
  conventional tool shapes is not much better than
  uncoated carbide.

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Conclusions

• DIAbide (Diamond Coated Carbide) tools can be
  designed to provide both durability and cost
  advantages in some applications
• PCD Tools Can Outlast Diabide Tools in some
  applications but do not necessarily provide the
  lowest machining costs because of tool
  fabrication costs.
• The cobalt (Co) in the PCD matrix can be leached
  by the CFC resins. Diamond grains then drop out
  accelerating the wear.

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Conclusions

• TFd shows the longest life of the 3 types of
  Diamond Tools.
• Experience has shown TFd to outlast PCD by 1.5X
  to 2X or more.
• TFd Tools can be fabricated into flexible complex
  geometries without expensive fixtures or starting
  substrates
• TFd Tools can be used under more aggressive
  conditions which results in greater productivity