INTERTECH EDM Technology To cut PCD Materials. Presented by. Eric Ostini Product Manager +GF+ Agie Charmilles Group

Transcription

1 INTERTECH 2006 EDM Technology To cut PCD Materials Presented by Eric Ostini Product Manager Agie Charmilles Group +GF+

2 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

3 What is PCD? PCD (Poly-Crystalline Diamond) is a composite material made up of crystals of synthetic monocrystalline 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 μm Medium 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.

4 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 bindings between the grains of the powder to form a solid part.

5 What is PCD? Characteristics of PCD PCD 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 speed Reduced down time (fewer tool changes) Lower wear = greater accuracy and repetitively on the parts machined Use of PCD PCD is used to produce cutting tools for non ferrous or non metallic abrasive materials. Wood composite (furniture) Ceramic ( buildings) Aluminum alloys (automotive) Medical

6 How is PCD eroded with Wire EDM Cobalt Wire Water In a first phase, the cobalt conductor is eroded PCD FIL Wire Water PCD PCD Next, the high temperature around the cobalt transforms on the surface - the diamond into graphite, making it a conductor Wire This layer of graphite facilitates the erosion of the diamond PCD

7 Effects of Wire EDM on PCD Dissolution of Cobalt Cobalt 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 CARBIDE 1 2 PCD Tungsten carbide substrate 1) Undercut below the top surface of the PCD which weakens the cutting edge 2) Undercut at the interface PCD/carbide tungsten (harmless)

8 Effects of Wire EDM on PCD No damage PCD is a sintered material sensitive to EDM process E9 When cutting PCD, the key point is to preserve the top surface integrity. E3 SEM Mag x 500 Pitting on the top surface affects the cutting edge quality and so, the tool life. Smartscope (optic)

9 Effects of Wire EDM on PCD Top view (optical) of PCD layer Affected zone may be 100 microns after roughing

10 Edge Quality of Wire EDMed and Mechanically Ground PCD Edges Wire EDM trim-cut CTB 010 edge Rake face Ground CTB 010 edge Rake face Clearance face Surface roughness, R a = 0.53 μm Clearance face 50 μm Surface roughness, 50 μm R a = 0.12 μm

11 Performance of Wire EDM and Mechanically Ground PCD Edges in MMC Machining Cutting tool wear rate Workpiece surface finish Flank wear, VB (μm) WEDM1 WEDM2 Ground1 Ground2 Workpiece surface roughness, R a (μm) WEDM1 WEDM2 Ground1 Ground Distance (m) Distance (m) Initial difference in wear rate and surface finish; difference becomes less significant with increased cutting distance

12 Wear Surfaces on Wire EDMed and Mechanically Ground PCD Cutting Tools Wire EDM trim-cut CTB010 edge Ground CTB010 edge 100 μm 100 μm

13 EDM Technology available for PCD Provides the right settings to finish the tools with no need to grind it later. Top surface Polished PCD Carbide Surface Finish obtained is 0.4 μm Ra Good Cutting Edge integrity

14 Machining Technology For fine grain PCD Finish skim 4 Finish skim 3 Finish skim 2 Finish skim 2 Skim 1 Rough Sequence for wire Edge regularity (top view) Edge quality X 1000 X 500

15 PCD Edge quality PCD Carbide

16 Technology for Draw die Dedicated technology for draw die Finish skim 1 Skim 1 Rough Sequence X 50 2 main controls for this application: Edge condition and surface finish X 1000

17 PCD machining results Roughing E3: Affected zone: 30 μm Cutting speed: 1.8 mm/min. 1 st Skim pass E9: Affected zone: 20 μm Cutting speed: 3 mm/min. Rough pass 1 st Skim pass X180 2 nd Skim pass E20: Affected zone: 5 μm Cutting speed: 4 mm/min.

18 Conclusion 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 edge quality. 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