PROGRESS IN NATURAL SCIENCE Vol .15 , N o .9 , September 2005 Cutting tool materials for high speed machining＊ LIU Zhanqiang ＊＊ and AI Xing (School of Mechanical Engineering , S handong University , Jinan 250061 , China) Received Feb ruary 22 , 2005 ;revised March 28 , 2005 Abstract High speed machining (HSM)is one of the emerging cutting processes, w hich is machining at a speed significantly higher than the speed commonly in use on the shop floor .In the last tw enty years, high speed machining has received g reat attentions as a technological solution for high productivity in manufactu ring .This article review s the developments of tool materials in high speed ma- chining operations, and the properties, applications and prospective developments of tool materials in HSM are also presented . Keywords: tool materials, high speed machining. High speed machining processes can produce plications fo r each type of the material . more accurate parts , as well as reduce the costs asso- ciated w ith assembly and fixture storage by allow ing several procedures to be combined into a mo nolithic one[ 1] .There has been a stro ng resurgence of interest in high speed machining technology , so that it has become one of the most promising advanced manufac- turing technologies in the last tw enty years .Hig h speed machining technology has already been applied to many manufacturing industries such as the aviation and aerospace industry , automobile industry , mould industry to cut steel , cast iron and its alloys , alu- minum and magnesium alloys , super alloy s of nickel- based , cobalt-based , ferrous-based , titanium-based , Fig .1 . Variety of tool materials in high speed machining. etc .and composite materials[ 2] .The applications of 1 .1 Diamond high speed machining are continuing to rapidly ex- pand . Diamond has the highest hardness, heat co nduc- In o rder to explore the w ide applications of hig h tivity among the substances and is excellent in chemi- speed machining , recent developments and applica- cal stability .The four types of diamonds being used tions of the tool materials in hig h speed m achining are as cutting tools are industrial grade natural diamond presented in this paper . (ND), synthetic single crystal diamond , poly crystal- line diamond (PCD), and chemical vapor deposition 1 Recent developments of tool materials in (CVD) diamond coating (including thin-film and [ 4] high speed machining thick-film diamond coating s) . M any ty pes of tool materials , ranging from dia- Natural diamond is the most expensive tool ma- monds to ceramics and to high speed steel (HSS), are terial .Because the ex tremely sharp edge of a blade is used as cutting tools in today' s machining industry[ 3] obtained , natural diamond is m ainly used in some ul- (see Fig .1).It is important to be aware that differ- tra-precision m achinings , such as the machining of ences in properties do exist among tool materials (see micro-mechanical parts , retro reflectors , navigating Table 1), these differences determine the correct ap- gy roscopes, and hard disc chips , etc . ＊ S upported by National Natural S cience Foundation of China (Grant No .50375089), Fok Ying Tung Education Foundation (Grant No.91054), the Natural S cience Foundation of Shandong Province, China (Gran t No .Y2003F06), and the Program for New Century Excellent Talents in Univer- sity ＊＊ To w hom correspondence should be addressed .E-mail:melius@sdu .edu .cn 778 w ww .tandf.co .uk/journals Prog ress in Natural Science Vol .15 No .9 2005 Table 1 . Main properties of some tool materials Properties Diamond CBN Cemented carbide Cerm et Silicone nitride Alumina Density(106 kg/ m3) 3 .5 3 .5 14 .5 6 .8 3 .2 4 .2 Hardness(Hv) 10000 5000 1500 1600 1600 2500 Strength (kg/ mm2) — 110 250 200 120 40 Young modulus(104 kg/ mm2) 10 .5 7 .3 60 40 3 .1 3 .6 Thermal conductivity (W/mK) 2000 (single crystal) 50 76 13 40 20 Synthetic single crystal diamond has good di- mension, shape and function stability .It is mainly used in machining of wood , for exam ple , w ood floor- board coated with Al2O 3 . PCD is obtained with some binders such as cobalt pow ders by sintering under ultra-high pressure and high temperature under w hich condition the diamond is chemically safe .This sintered diamond body shows excellent abrasion resistance w ith the cutting of the nonferrous metals as well as nonmetallic material and is taking an active part as the high accuracy , hig h ef- Fig .2 . S tructures of diamond and CBN . ficiency cutting tool for the difficult processing sub- materials with hardness greater than H RC 45 such as stances such as the Al-Si alloy and cemented carbide . automobile parts , the engine blocks and gears, CVD diamond coating tools are w ell suited fo r shafts , bearing s.Generally speaking , PCBN machin- the high speed machining of aluminum and other non- ing operations should be run dry .It can be run at cut- ferrous alloys such as copper , brass , bronze , and ting speeds above 2000 m/min in machining of gray abrasive advanced composites such as g raphite , car- cast iron materials .The largest recent g row th in the bon-carbon , g lass-fiber reinfo rced plastics , and car- use of PCBN inserts is in the area of high speed hard bon-filled phenolics[ 5 —9] .CVD thin-film diamond can machining —in particular , the finish machining of be applied to such complex tool geometries as inserts steel-alloy automotive engine compo nents , such as w ith chip breakers , solid end mills , routers , and gears , shafts and bearings , w hich have hardness be- drills.Thick-film diamond coating tools currently tw een HRC 60 and H RC 65 .These parts have tradi- find their use in high speed machining of high-eutec- tionally been ground to very tight dimensional toler- tic aluminum alloys[ 10, 11] . ances and a fine surface finish . 1 .2 CBN The mechanical and therm al properties of CBN are influenced largely by the kinds and addition quan- Cubic boron nitride (CBN)is synthesized artifi- tities of the binders that are used in the case .The cially under the condition of the high pressure and bond phases of PCBN are Co , Ni or TiC , TiN , high tem perature as the same as the diamond .It is al- Al2O3 , etc .The CBN grain size and bond phase af- so similar to diamo nd in its polycry stalline structure fect the PCBN machining perform ances .PCBN w ith (see Fig .2). low co ntent CBN (50 %—65 %)is mainly used in finishing hardened steel (HRC45-65), while high CBN has sm all reactivity w ith the iron system content CBN (80 %—90 %)is used in high speed materials and is mo re chemically and thermally stable rough , semi-finishing of nickel and chromium cast than those of the diamond .Because of these proper- iron , intermittent machining of hardened steel, hard ties , the CBN has been paid attention as the tool m a- metal, sintered metal, and heavy alloy , etc . terial that is useful fo r machining of iron sy stem m a- terials for w hich the diamond is unable . The binder-less sintered CBN w hich does not in- clude any binder is developed recently[ 12—14] .The Polycry stalline ty pe CBN (PCBN)has an ex cel- binder-less CBN is synthesized by controlling the con- lent characteristic for cutting tools to machine the cast dition of the CBN particle to be fine particles having iron and heat resisting alloy , and the iron system hard high therm al conductivity , excellent thermal stabili- Prog ress in Natural Science Vol.15 No .9 2005 w ww .tandf.co .uk/journals 779 ty , high hardness and streng th even under hig h tem- of composites and super alloy materials used in the perature .The binder-less CBN cutting tool is now aerospace industry , such as nickel-based alloy s , but considered as the cutting tool m aterial of the nex t are not suitable for machining of cast irons and steels. generation . 1 .4 TiC(N)-based cemented carbides 1 .3 Ceramic cutting tool TiC (N )-based cemented carbides are mostly Ceramics are non-metallic materials.Some ad- compose of titanium carbon nitride (TiCN )w ith a vantages of ceramic tools are ex tremely high resis- nickel or cobalt bonder[ 21] .They are hard and chemi- tance to abrasive w ear , cratering , and extremely hig h cally stable , which leads to hig her w ear resistance . temperature hardness[ 15] .There are tw o major classes Cermets w ork in materials such as steels and ductile [ 22] of ceramic tool materials available :alumina (A12O3)- irons that produce a ductile chip .Their increased based ceramics and silicon nitride (Si3N 4)-based ce- speed capability enables them to machine carbon ramics . steels, stainless steels, ductile irons , and cast irons at high cutting speeds and to produce better surface finishes . Alumina-based ceramics has g ood chemical sta- The most common cermets are :(1)TiC-based bility and low affinity w ith ferrous metals .It is there- [ 23] fore not susceptible to adhesion .The solubility of alu- carbide such as TiC +Ni o r M o w ith high wear re- mina in iron is only one fifth of that of tungsten car- sistance , and TiC +TaC +WC +Co w ith hig h frac- bide (WC).Hence , alumina-based ceramics is with ture toughness , (2)TiN-based carbide w ith enhanced low diffusio n wear and very high anti-oxidization . fracture toughness , and (3) TiCN-based carbide How ever , alumina-based ceramics has low er (TiCN +NbC)with higher w ear resistance and ther- strength , fracture toughness , thermal conductivity , mal shock resistance .Cermets are very suitable for and thermal shock resistance .It has better perfor- high speed finish machining of steel alloys and cast irons .