Agie Charmilles Group

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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