International Journal of Machine Tools & Manufacture 42 (2002) 331–334

Study on PCD machining

Pei-Lum Tso*, Yan-Gang LiuDepartment of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan, ROC

Received 7 June 2001; accepted 3 September 2001

Abstract

Polycrystalline diamond, PCD, is known for its superior characteristics such as hardness, toughness and wear resistance. However,due to these factors, manufacturing PCD tools is a difficult material removal process. Using quantitative analysis, this study comparesthe machining effect on a PCD V-cutter including EDM and grinding. The conclusions show that grinding is better than EDM formachining PCD, and with proper parameters, the PCD will be less damaged and retain its superiorities as a cutting tool. In addition,this study presents a beginning for research on understandings of principles in cutting PCD. It may be useful for toolmakers toproduce a high quality and reusable PCD tools. 2002 Published by Elsevier Science Ltd.

Keywords: Polycrystalline diamond; PCD tool; V-cutter

1. Introduction

Polycrystalline diamond, PCD, is manufactured by ahigh pressure and high temperature process that yieldsdirect diamond-to-diamond bonding within a matrix ofcobalt metal. It is currently used in the industry for cut-ting tools of difficult-to-machine materials because of itssuperior characteristics. In printed circuit board (PCB)applications, many kinds of PCD tools are used, such assaw blades, V-cutter and edge trimmer etc. as shown inFig. 1.

There has been much research on PCD and its appli-cations. Kanada [1] developed high strength PCDespecially for cutting tools. Bertagnolli and Vale [2] ana-lyzed residual stresses in thick PCD cutters. Bailey andCook [3] demonstrated the advantages of using PCDdrills in the aerospace industry. However, there is rela-tively little research on the manufacturing of PCD tools.Cassidy [4] presented PCD grinding optimization bymeans of PCD inserts. By observation of scanning elec-tron microscope (SEM) on the insert edge, the studycompared the effect of working parameters like grindingwheel speed, infeed rate and oscillation frequency.

This study presents the effect of manufacturing pro-cesses including electric discharge machining (EDM)

* Corresponding author. Fax:+886-3-572-2840.E-mail address: pltso@pme.nthu.edu.tw (P.-L. Tso).

0890-6955/02/$ - see front matter 2002 Published by Elsevier Science Ltd.PII: S0890-6955 (01)00131-6

and grinding on a PCD tool, the V-cutter, named becauseof the ‘V’ shaped grove left on the board after cutting.The specification is 120 mm in diameter, 20 mm inthickness and 20 teeth with PCD tips of CTB 010 madeby De Beers. To sever a PCB, a pair of V-cutters is usednecessarily and their working condition is 18,000 rpm,10–15 mm/min infeed and 0.5 mm cutting depth.

2. Methodology

Because the cutting process of a V-cutter is non-con-tinuous, the impact and fatigue load from PCB serves ateach PCD tooth. With finer surface condition this cuttingedge has better ability to resist impact and fatigue dam-age because of fewer material imperfection under thesurface. Besides, with lower surface roughness, therewill be less cutting heat caused by friction between tooland workpiece, which is the dominant factor of PCDdamage. It is believed that surface roughness plays animportant role in assessing the fabricating effect of aV-cutter.

The PCD teeth of the V-cutter were manufactured byVollmer QM erosion machine and Ewag grindingmachine, with different parameters, respectively. Thenusing optical experiment WYCO measured surfaceroughness (Ra) of five teeth in each sample and averagedthe measurements for comparing.

332 P.-L. Tso, Y.-G. Liu / International Journal of Machine Tools & Manufacture 42 (2002) 331–334

Fig. 1. PCD tools used in PCB.

Fig. 2. SEM pictures of PCD surface.

3. Results

SEM pictures of the PCD surface after EDM andgrinding are presented in Fig. 2. The surfaces, observedwith the same scale, have great differences. Surfaceintegrity from grinding is superior to EDM. Fig. 3 showsthe surface roughness from different EDM modes, whichare superfinish, finish, mean and standard. Rt, maximumroughness, varied evenly with erosion intensity. Therelation between Ra and erosion intensity seemed to beless clear than with Rt. Ra represents the mean value ofsurface profile, whereas Rt reveals the height differencesof measuring profile. We may therefore infer thatstronger erosion intensity creates more severe PCD dam-age.

Fig. 3. PCD surface roughness with EDM mode.

On the other hand, grinding quality was affected byboth diamond wheel and grinding parameters. The grind-ing results using different diamond grit grades are shownin Fig. 4. Certainly, the finer diamond wheel will pro-duce a better PCD surface, for both perpendicular andparallel grinding directions. Wheel velocity, infeed andoscillation rate are the grinding control parameters, andFigs. 5 and 6 identify those effects. With lower wheelvelocity, infeed and oscillation rate, we can obtain a finerPCD surface. This may be explained that while grinding,diamonds on the wheel cut the diamonds in PCD, likea moving rock hitting a still one, and the PCD is dam-aged. So if there is less contact between PCD and dia-mond wheel (with lower velocity and oscillation rate atthe same infeed), a better PCD surface should result. In

Fig. 4. PCD surface roughness with diamond wheel.

333P.-L. Tso, Y.-G. Liu / International Journal of Machine Tools & Manufacture 42 (2002) 331–334

Fig. 5. PCD surface roughness (Ra) with grinding parameters (wheelvelocity=20 m/s; infeed=0.2 mm/min; diamond mesh 1000).

Fig. 6. PCD surface roughness (Ra) with grinding parameters(S1=0.2; S2=0.5) (oscillation rate 20 mm/min; diamond mesh 1000).

Table 1Manufacturing effect of grinding parameters

Reduction ratio Improvement rate (Ra)

Oscillation 75% (80–20) 35% (166–108)Infeed 60% (0.5–0.2) 41% (183–108)Wheel velocity 20% (25–20) 32% (159–108)

Fig. 8. Abnormal wear of V-cutter tooth.

Fig. 7. Normal wear of V-cutter tooth.

addition, comparing these three parameters in Table 1,the wheel velocity plays the most important role ingrinding PCD.

4. Discussion

Fig. 7 shows the normal wear of a V-cutter tooth,which can be reground and then reused. However, iffragmentation and breakage of the diamond layer occurs,as shown in Fig. 8, the tooth cannot be used further,shortening the working life of the V-cutter.

In this study, the roughness, Ra, of EDM surfaceranges from 0.27 to 0.4 µm, and the ground surfaceranges from 0.1 to 0.25 µm. Used on a FR4 circuitboard, the cutting distance of a ground V-cutter is up to20,000 m. An EDM V-cutter, however, cuts only about5000–6000 m because of the abnormal wear. It may lendsupport to the assumption that surface roughness, Ra, isan indication of the V-cutter using life.

We may therefore conclude that grinding machiningproduces better PCD V-cutter than EDM. However, withinadequate grinding parameters, it can harm the PCDadversely. From optical microscope, a scratch caused bygrinding is easily seen on the PCD surface, which may

334 P.-L. Tso, Y.-G. Liu / International Journal of Machine Tools & Manufacture 42 (2002) 331–334

lead to tooth breakage while cutting. The other conditionis the damage of grinding heat. A dark zone is observedat the tip of the PCD tooth. In this situation, the charac-teristics of PCD material may be transformed, such asby carbonization.

Using proper grinding parameters, it is believed thatPCD will be less damaged and keep its superior charac-teristics so that a high quality and reusable PCD toolmay be manufactured.

5. Conclusions

1. Grinding makes a finer PCD surface than EDM. Theaverage roughness, Ra, of EDM surface ranges from0.27 to 0.4 µm, and the ground surface is from 0.1to 0.25 µm.

2. A ground PCD V-cutter can cut FR4 PCB about threetimes longer length than an EDM one.

3. Velocity of the diamond wheel is the most importantfactor on grinding PCD.

4. Under normal grinding conditions, less contactbetween PCD and the diamond wheel can provide abetter PCD surface.

References

[1] Y. Kanada, Development of a tougher grade of polycrystalline dia-mond cutting tool, Int. J. Jpn. Soc. Pre. Eng. 33 (1) (1999) 6–9.

[2] K. Bertagnolli, R. Vale, Understanding and controlling residualstresses in thick polycrystalline diamond cutters for enhanced dura-bility, INTERTECH 2000.

[3] M.W. Bailey, M.W. Cook, The future of ultrahard machining inthe aerospace industry, INTERTECH 2000.

[4] R. Cassidy, PCD Grinding Optimization, INTERTECH 2000.