Development of Super-hard Cutter Material Feng Huiying, Li Xiaojing

Transcription

1 Applied Mechanics and Materials Online: ISSN: , Vols , pp 3-7 doi:.4028/ Trans Tech Publications, Switzerland Development of Super-hard Cutter Material Feng Huiying, Li Xiaojing Mechanical Department, Henan Polytechnic Institute, Nanyang ,China Keywords: tool materials; performance; finished quality Abstract. Super-hard tool material is a main research point of mechanical engineering because of excellent performance. The development of technology for high-speed cutting process could enhance the machining quality and surface precision. It is a difficulty thing to get higher finished surface for traditional machining process. However, the super-hard cutter material could enhance the finished performance of tool material. For example, the wearing resistance, high stability of PCD (polycrystalline diamond) and PCBN (poly cubic boron nitride) can get more information for obtaining higher finished surface quality. The author introduces super-hard cutters materials (PCD and PCBN) development, and discusses several material properties. The features of materials used in different cutting fields are discussed. Introduction With the quick development of the automotive industry, the wear resistance of forming tools during the production process has obtained quick improvement[1]. In order to get high performance, thermally sprayed hard material coatings are one possible solution. However, the surface quality of the coated materials is not sufficient to be used during the production process. In order to achieve high surface qualities and small form errors, the coatings have to be machined mechanically. For this purpose, grinding is a capable and flexible process that can additionally induce compressive stresses into the surface. Coated tools is better in strength and toughness of cemented carbide or high speed steel (HSS) based on the surfaces, the use of vapor deposition method of coating a thin layer of wear resistance of refractory metals or non-metallic compounds (also coated In ceramics, diamond and cubic boron nitride and other super-hard materials, blade) obtained[2]. Fig.1 shows the common hard coating tools material in industrial fields. Fig.1 The material of common hard coating tools Super-hard cutting tool material refers to synthetic diamond and CBN (cubic boron nitride) or other special cutting material with the high hardness performance that close to natural diamond. Due to high expensive of natural diamond, most practical production often use artificial polycrystalline diamond (PCD), polycrystalline cubic boron nitride (PCBN), and their composite materials[3]. Diamond is the world most hard material at present. The diamond tool with excellent performance of high hardness and high wear resistance and high thermal conductivity, has been widely applied in nonferrous metallic and nonmetallic processing, especially, super-hard cutting All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (# , Pennsylvania State University, University Park, USA-18/09/16,14:20:09)

2 4 Energy Research and Power Engineering tool material used in Aluminum and silicon alloy high-speed machining, such as car engine, gearbox and cylinder block and head of the machining process of the piston, etc, the diamond tool is irreplaceable main cutting tool. In recent years, due to the popularity of NC machine and the high speed development technology of NC machining, and the high efficiency, high stability, long life processing the application of the growing popularity of diamond tools. The diamond tool will be an indispensable important tool for NC machining[4]. Fig.2 shows the relationship of tool performance and tool coating materials Fig.2 Relationship of tool performance and tool coating materials Cubic boron nitride (CBN) is the boron nitride with grain isomers, its structure is similar with diamond, with the hardness up to 8000~9000HV, heat-resistant degree up to 80~14 and good abrasion resistance. The polycrystalline cubic boron nitride (PCBN) is the polycrystalline material that sintered by combination of CBN particlesin in high temperature and high pressure, therefore, the material noncrystalline not only can replace with hardened steel (45~65HRC), bearing steel (60 ~ 64HRC) and HSS (63 ~ 66HRC), machined by hard cast-iron coarse turn and fine turn, but also qualified for high temperature alloys, thermal spraying materials, carbide and other difficult-to-machine materials of high-speed cutting processing. Super-hard Cutter Performance Characteristics High hardness and resistance. Mono-crystalline diamond cutters can get high machining accuracy and efficiency at high-speed cutting because of its high hardness and high compressive strength, good thermal conductivity and good abrasion resistance[5]. Although polycrystalline diamond (PCD) is joined in diamond sintering mixture, its hardness and abrasive resistance are still lower than the mono-crystalline diamond Owing to its structure mixed orientation fine grain[6]. Table 1 The hardness of various tools material Type Hardness (HV) carbon tool steel 8~830 alloy tool steel 8~840 high-speed steel 820~870 hard alloy 820~930 ceramics 1500~20 PCBN 3000~5000 PCD 8000 CBN 8000~9000 diamond 000 Table 1 gives all sorts of cutters hardness. Visible, the hardness of PCD is 8000HV which is about 8-12 times for cemented carbide. Micro hardness of CBN micro powder is 8000 ~ 90 HV, The hardness of PCBN sinter is generally 3000 ~ 5000 HV.

3 Applied Mechanics and Materials Vols According to abrasive resistance and intensity of materials, Fig.3 give the order of cutters materials. We can see, Diamond (especially PCD) has the highest abrasive resistance. But it will show brittleness which make PCD cutter easy to be destroyed, and the lowest strength in all material when It is impacted for its cleavage plane. PCBN has more excellent performance than traditional cutter material (such as ceramic). Its abrasive resistance rank only second to the diamond, worse than PCD, the abrasive resistance is about 50 times of hard alloy cutter, is 30 times of coated hard alloy cutter, is 25 times of ceramic cutter. The strength is Close to ceramic. Abrasive resistance Intensity PCD&CVDD 1 PCBN 2 TiC aluminium ceramics Whisker reinforce ceramic Silicon nitride ceramics Cermet 6 CVD alumina coated carbide CVD three-phase carbide PVDcoated carbide 9 Uncoated carbide High-speed steel Fig.3 Comparison of different materials tool abrasive resistance and intensity Good thermal conductivity. The diamond has the highest of thermal conductivity in all kinds of tool material. The coefficient of heat conductivity of PCD is 700W/mk, which is 1.5 ~ 9 times of hard alloy and higher than PCBN and copper. Therefore PCD cutting transfer heat very quickly; The thermal conductivity of CBN rank only second to the diamond, which is 3.2 times of diamond and 20 times of hard alloy. Ratio of heat conductivity coefficient of CBN and ceramic is 37:1, Thermal diffusion rate ratio is 65:5, with the rise of temperature, PCBN thermal conductivity coefficient is ever-increasing, The high thermal conductivity of PCBN cutter can decrease the temperature of point of a knife, reduce tool wear, be helpful for machining accuracy. The chemical stability. There are affinity between Carbon and iron, Diamond produces chemical reaction with iron under the high temperature,so diamond is not suitable for machining iron and iron alloys parts usually, Which greatly restricted the diamond applications. The chemical inertia of CBN is particularly big, it not react with iron when 1200~1300 degrees, but only produces chemical reaction with carbon beyond 2000 degrees. It is stable for acid and alkali in neutral and reducing gas surroundings, the bonding and diffusion for various materials is much less than hard alloy, Therefore PCBN tool is especially suitable for machining steel materials. Low friction coefficient. The friction coefficient between different materials and CBN or PCD is only 0.1 ~ 0.3(the friction coefficient of hard alloy is 0.4 ~ 1).Friction coefficient is reduced with the cutting speed improved. therefore super-hard cutter can reduce cutting force and cutting deformation, improve cutting surface quality obviously. Good thermal stability. Thermal expansion coefficient of PCD only is ~ 118.6, equal to 1/5times of hard alloy. So the thermal deformation of PCD cutter is small, machining accuracy is higher; Because the hardness of PCBN at 800 is higher than hardness of ceramic and hard alloy at normal, PCBN cutter can be used cutting high temperature alloys and hardened steel at 3~5 times speed higher than hard alloy. Super-hard Materials Cutter Applications PCD cutter and PCBN cutter global sales growth in recent decades. According to survey, PCD cutter s global sales rose to $4.8 billion in 2008 gradually from the $40 million in 1980, The annual sales trend of PCBN cutter is increasing in Europe, Japan, North America and China. Among them,

4 6 Energy Research and Power Engineering annual sales growth speed in European is the highest; the research and development of PCBN cutter has just begun in recent years In China, it has been increased to $60 million until 20. The application of PCD cutter used mainly in the following two aspects: (1) Difficult-to-machine non-ferrous metal materials processing: Common cutter processing often produce tool wear and low efficiency, but PCD cutter can process casting and forging parts at high efficient and high-speed, and accomplish rough and fine grinding in one operation, which especially suitable for precision grinding of forming, copy and fixed size, and make the quality and efficiency of grinding improve several times and dozens of times. (2)Difficult-to-machine nonmetal materials processing: PCD cutter very suitable for difficult-to-machine nonmetal materials processing, such as stone, hard carbon,carbon fiber reinforced plastics (CFRP), man-made plank and so on[6]. Hard alloy has high hardness and wear resistance, Using super-hard materials instead of conventional silicon carbide and corundum abrasive can prevent the workpiece surface burn, crackle, deep metamorphic layer and improve machining efficiency and saving grinding cost. The application of CBN and PCBN cutter performance show below aspects: (1) Hard machining, turning instead of grinding: PCBN cutter can obtain good surface roughness with high hardness and red hardness, PCBN cutter turning quenched steel can realize turning instead of grinding. For example automobile, motorcycle gears hole processing, Many materials is 20CrMnTi, carburizing and quenching, hardness is 60~62HRC,Precision is IT6, surface roughness is 0.8µm. Traditional process:machining heat treatment grinding. The process of turning instead of grinding using super-hard cutter: rough machining heat treatment finishing machining. One grinding can only processing 0 small gears, and new technology using PCBN cutter turning can processing 400 small gears. (2) High speed cutting, high stability machining: Grey cylinder hole machining is one of the critical process in the automobile engine on the production line, which request that cylinder hole has high machining size precision, small surface roughness, good stability, high speed cutting and long cutter service life for the production processing fast rhythm. Using PCBN tools can realize engine cylinder hole high-speed cutting and high stability. (3) Dry-type cutting, clean machining: Processing cast-iron cylinder using PCBN cutter can realize turning replacing grinding, and avoid environmental pollution that is caused by cutting (grinding) fluid and ash of grinding wheel. Its processing parameters are V=200m/min, f=0.1mm/r, a p =0.2~1mm, machining surface roughness is Ra 1.6µm, precision is IT6, cutter life between two cutter sharpening greater than 0parts, Scraps can be recycled, which accord with cleaner production requirements. Summary At present, super-hard cutter has been effectively used because of its good processing quality in manufacturing. With the theoretical research of tools More deeply and further promotion of application technology, PCD and PCBN cutter in the super-hard cutter field will become more and more important, it can be expected that super-hard cutter application scope will expand rapidly. References [1] Fuming Deng, Qiwu Chen. PDC super-hard composite cutter materials and its application[m]. Beijing: Chemical industry press [2] Zili Kou. Development and application of super-hard cutter[j]. Journal of Tool technology, 2000, 4(34) [3] Jihong Wang. Super-hard cutter material broad application prospect [J]. Journal of electromechanical product development and innovation, 2002, (5):61-62

5 Applied Mechanics and Materials Vols [4] Bingjun Chen, Shaomao Hu. Super-hard cutter material research and development trend[j]. Journal of cutter and mould cutting.2005,9 (34) [5] Qishun Bai, Yingxue Yao, etc. The development of polycrystalline diamond (PCD)[J]. Journal of tool technology, 2002, 3 [6] Jingying Zhang,Qixun Yu. The development and application of Polycrystalline cubic boron nitride cutter materials[j]. Journal of mechanical engineers, 3, 2008