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Agie Charmilles Group
+GF+
INTERTECH 2006
EDM Technology To cut PCD Materials
Presented by
Eric OstiniProduct Manager
Outline
Goal of the presentation• What is PCD
• PCD applications that commonly used Wire EDM
• Understand the key elements to cut PCD by Wire EDM
• Performances on PCD
What is PCD ?
PCD (Poly-Crystalline Diamond) is a composite material made up of crystals of synthetic mono-crystalline diamond bound solidly together by means of a technique called sintering. The binder is usually Cobalt, and the diamond crystals are a few microns in size.
Typically;Fine Grain PCD = 2 to 4 μmMedium Grain PCD = 5 to 10 μm Coarse Grain PCD = 25 μm >
Poly crystalline diamond is used for manufacturing and marketing diamond chips of large dimensions that can be used by industry.
What is Sintering?
This consists in creating a part by using a powder of materials as the raw material. The powder plus the binder are pressed together in a mold. This is then heated to a temperature slightly below the temperature of fusion of the powdered material. This results in the creation of metallurgical bindingsbetween the grains of the powder to form a solid part.
What is PCD ?
Characteristics of PCDPCD has an excellent abrasion resistance( may last 50 to 200 times more than tungsten carbide)
Substantial increase in the working life of the tool. (before sharpening)Higher machining speedReduced down time (fewer tool changes)Lower wear = greater accuracy and repetitively on the parts machined
Use of PCDPCD is used to produce cutting tools for non ferrous or non metallic abrasive materials.
Wood composite (furniture)Ceramic ( buildings)Aluminum alloys (automotive)Medical
Wire
PCD
FIL
PCD
Wire
Water
PCD
WireWater
PCD
Cobalt
How is PCD eroded with Wire EDM
In a first phase, the cobalt conductor is eroded
Next, the high temperature around the cobalt transforms – on the surface - the diamond into graphite, making it a conductor
This layer of graphite facilitates the erosion of the diamond
Effects of Wire EDM on PCD
Dissolution of CobaltCobalt is a material that is highly sensitive to corrosion. It dissolves easily in water especially when subject to the phenomenon of electrolysis that is sometimes observed on spark erosion These defects are confined to the places where the electrical fields are strongest.The seriousness of the defects depends on the type of spark generator, the conductivity of the dielectric and the duration of submersion
PCD
Tungsten carbide
substrate
1
2
1) Undercut below the top surface of the PCD which weakens the cutting edge
2) Undercut at the interface PCD/carbide tungsten (harmless)
PCD
CARBIDE
Effects of Wire EDM on PCD
PCD is a sintered material sensitive to EDM process
When cutting PCD, the key point is to preserve the top surface integrity.
Pitting on the top surface affects the cutting edge quality and so, the tool life.
No damage
SEM Mag x 500
E3
E9
Smartscope (optic)
Effects of Wire EDM on PCD
Top view (optical) of PCD layerAffected zone may be 100 microns after roughing
Surface roughness, Ra = 0.53 μm
Wire EDM trim-cut CTB 010 edge
Surface roughness, Ra = 0.12 μm
Ground CTB 010 edge
50 μm 50 μm
Rake face
Clearance face
Rake face
Clearance faceClearance face
Edge Quality of Wire EDMed and Mechanically Ground PCD Edges
Cutting tool wear rate Workpiece surface finish
0
0.05
0.1
0.15
0.2
0 2000 4000 6000
WEDM1WEDM2Ground1Ground2
0
0.2
0.4
0.6
0.8
1
1.2
0 2000 4000 6000
WEDM1WEDM2Ground1Ground2
Distance (m) Distance (m)W
orkp
iece
sur
face
ro
ughn
ess,
Ra
(μm
)
Flan
k w
ear,
VB (μ
m)
Initial difference in wear rate and surface finish; difference becomes less significant with increased cutting distance
Performance of Wire EDM and Mechanically Ground PCD Edges in MMC Machining
Wire EDM trim-cut CTB010 edge Ground CTB010 edge
100 μm100 μm
Wear Surfaces on Wire EDMed and Mechanically Ground PCD Cutting Tools
EDM Technology available for PCD
Provides the right settings to finish the tools with no need to grind it later.
Top surface
Polished PCDSurface Finish
obtained is 0.4 μm Ra
Good Cutting Edge integrity
Carbide
Machining Technology For fine grain PCD
Sequence for 0.008” wire
Rough
Skim 1
Finish skim 2
Finish skim 2
Finish skim 3
Finish skim 4
X 1000 X 500Edge quality
Edge regularity (top view)
PCD Edge quality
PCD
Carbide
Technology for Draw die
Rough
Skim 1
Finish skim 1
Sequence
X 1000X 50
2 main controls for this application: Edge condition and surface finish
Dedicated technology for draw die
PCD machining results
X180
Rough pass1st Skim pass
Roughing E3:Affected zone: ≈30 μmCutting speed: 1.8 mm/min.
1st Skim pass E9:Affected zone: ≈20 μmCutting speed: 3 mm/min.
2nd Skim pass E20:Affected zone: ≈5 μmCutting speed: 4 mm/min.
Tools manufactured with PCD materials can be economically processed using erosion techniques (Wire EDM)
A large degree of control exists over erosion rate and tool edgequality. For all erosion processes, it is a matter of achieving the correct balance by optimising the Wire EDM generator settings
Some degree of care is required to ensure optimum tool quality and to avoid edge undercut (with water-based dielectrics); minimise immersion times, ensure correct water resistively, etc.
In certain applications, eroded PCD edges may be comparable to mechanically ground edges, in terms of tool wear rates and workpiece surface finish
Conclusion