激光熔覆技术制造立铣刀的实验研究
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摘要
刀具表面强化处理是提高刀具耐磨性及其使用寿命的重要途径之一，而用激光对刀具进行表面强化处理来替代高速钢刀具常规炉中热处理方面的研究也已取得成效，并在工业上得到了应用。另一方面，激光熔覆技术已经在小范围的零部件中取得了应用，国内外目前在用激光熔覆来获得局部耐磨涂层从而提高材料耐磨性能的研究也已卓有成效。本文在这两个研究方向的墓础上找出它们的结合点，对立铣刀激光熔覆技术的工艺及机理进行了研究，成功的采用Nd：YAG激光熔覆技术在普通钢基体上制造出了性能良好的立铣刀螺旋刃带。
采用同步送粉技术，对以钻基合金粉末系列为主的18种粉末配方进行实验研究，结果表明No．9熔覆层质量较好，硬度及抗弯强度均与常用铣刀材料高速钢W18Cr4V相当，是比较理想的熔覆立铣刀螺旋刃带的粉末配方。
采用6kW CO_2激光器、1kW Nd：YAG激光器和同步送粉熔覆技术从工艺性、开裂性、经济性三个方面进行了CO_2激光和Nd：YAG激光的熔覆特性对比研究，得出Nd：YAG激光更适合于小面积的立铣刀激光熔覆。在此基础上，采用No．9粉末配方研究了Nd：YAG激光的熔覆工艺。分析总结了工艺参数对熔覆层形状参数和质量的影响规律，在模拟铣刀刃带形状的台阶槽试板上进行了熔覆实验，并对工艺参数进行了优化。
试验结果表明，当激光工艺参数选取不当时，激光熔覆层中极易出现裂纹，偶见夹杂和气孔等缺陷。在本实验条件下，直径微小的气孔对熔覆层质量没有影响，并有可能成为显微裂纹的终止点。观察贯穿裂纹的断口形貌，发现这种裂纹一般是从熔覆层和基体结合界面的外侧起裂，并以此为源头扩展，裂纹的扩展方向呈放射状，在裂纹扩展面上Si、O等杂质元素含量很高。
用优化的参数获得了无缺陷、形状系数及硬度分布满足立铣刀工作要求的熔覆层。采用光学显微镜、扫描电子显微镜观察熔覆层显微组织形貌，用X射
线衍射法测试熔覆层相组成。结果表明，熔覆层组织细密，主要是由C。的过
饱和固溶体及呈骨状分布的碳化物组成。与W18Cr4V相比，硬度、抗弯强度和
耐磨性均相当。
最后，根据立铣刀坯材的形状特点，选取了适合制造立铣刀的专用设备，
研究了激光熔覆制造立铣刀过程中实际遇到的工艺问题，最终在45钢铣刀坯材
上成功的熔覆出了无裂纹、成形良好、硬度分布满足要求的立铣刀。然后，根
据GB／T12204．3－90进行了切削性能试验，实验结果表明激光熔覆制造的立铣刀
切削性能满足铣削的要求。
Surface treatment is one of the most important methods to improve the wear-resistance and durability of cutter. Successes have been achieved both in the research in laser surface treatment and in industrial applications. On the other hand, laser cladding has been used on local areas of parts. Scientists have gained great achievements in the research of obtaining local coatings by laser cladding in order to enhance the wear-resistance of materials. This paper finds their links on the basis of both aspects. Then we research the process of laser cladding and successfully clad helical blades of end mill with Nd: YAG laser yielding good performances.
Firstly, eighteen types of co-based series of powder formula as laser cladding materials have been investigated by using synchronous powder feeding system. Experimental results show that the formula of No.9 is the best one to be used for the cladding layer of end mill because of its good coating quality, high micro hardness and equivalent bending strength compared with W18Cr4V which is commonly used to make end mill.
Secondly, we do a comparison research on the cladding behaviors of CO2 laser and Nd: YAG laser by using 6 kW CO2 laser system and 1kW Nd: YAG laser system. Experimental results show that Nd: YAG laser is more fit for the laser cladding of end mill because of its limited working area. Based on that, Nd: YAG laser cladding process is studied by using No.9 formula, the effect of processing parameters on shape and quality of coatings is also analyzed and summarized. Then cladding experiments are processed on the simulacrum and technical parameters are optimized.
At the same time, experimental results show that the crack tendency will be
high by using improper processing parameters. The pore or impurity is seldom. In this experiment, tiny pores do no harm to the quality of the coating and probably prevent microcosmic cracks from extending. The fracture surfaces of impenetrate cracks are researched. Results show that this kind of crack originates in the outboard of the interface and extends radially. The content of silicon and oxygen is high in the crack fracture surface.
After that, with optimal parameters, satisfying cladding layer is achieved. Then, by means of optical microscope and SEM, the microstructure of the coating is investigated; by means of x-ray diffraction, phase composition is measured. Experimental results show that fine microstructure is mainly composed of Y cobalt, a cobalt and osseously distributed carbides. Compared with W18Cr4V, the micro hardness, bending strength and wear resistance is equivalent.
Finally, according to the shape character of end mill, special equipments are properly choose. Some problems encountered during the procedure of laser cladding are researched and finally the crackless end mill with well shape and satisfying hardness distribution is manufactured on 45 steel substrate. And its cutting performance is fine according to the national standards.
采用同步送粉技术，对以钻基合金粉末系列为主的18种粉末配方进行实验研究，结果表明No．9熔覆层质量较好，硬度及抗弯强度均与常用铣刀材料高速钢W18Cr4V相当，是比较理想的熔覆立铣刀螺旋刃带的粉末配方。
采用6kW CO_2激光器、1kW Nd：YAG激光器和同步送粉熔覆技术从工艺性、开裂性、经济性三个方面进行了CO_2激光和Nd：YAG激光的熔覆特性对比研究，得出Nd：YAG激光更适合于小面积的立铣刀激光熔覆。在此基础上，采用No．9粉末配方研究了Nd：YAG激光的熔覆工艺。分析总结了工艺参数对熔覆层形状参数和质量的影响规律，在模拟铣刀刃带形状的台阶槽试板上进行了熔覆实验，并对工艺参数进行了优化。
试验结果表明，当激光工艺参数选取不当时，激光熔覆层中极易出现裂纹，偶见夹杂和气孔等缺陷。在本实验条件下，直径微小的气孔对熔覆层质量没有影响，并有可能成为显微裂纹的终止点。观察贯穿裂纹的断口形貌，发现这种裂纹一般是从熔覆层和基体结合界面的外侧起裂，并以此为源头扩展，裂纹的扩展方向呈放射状，在裂纹扩展面上Si、O等杂质元素含量很高。
用优化的参数获得了无缺陷、形状系数及硬度分布满足立铣刀工作要求的熔覆层。采用光学显微镜、扫描电子显微镜观察熔覆层显微组织形貌，用X射
线衍射法测试熔覆层相组成。结果表明，熔覆层组织细密，主要是由C。的过
饱和固溶体及呈骨状分布的碳化物组成。与W18Cr4V相比，硬度、抗弯强度和
耐磨性均相当。
最后，根据立铣刀坯材的形状特点，选取了适合制造立铣刀的专用设备，
研究了激光熔覆制造立铣刀过程中实际遇到的工艺问题，最终在45钢铣刀坯材
上成功的熔覆出了无裂纹、成形良好、硬度分布满足要求的立铣刀。然后，根
据GB／T12204．3－90进行了切削性能试验，实验结果表明激光熔覆制造的立铣刀
切削性能满足铣削的要求。
Surface treatment is one of the most important methods to improve the wear-resistance and durability of cutter. Successes have been achieved both in the research in laser surface treatment and in industrial applications. On the other hand, laser cladding has been used on local areas of parts. Scientists have gained great achievements in the research of obtaining local coatings by laser cladding in order to enhance the wear-resistance of materials. This paper finds their links on the basis of both aspects. Then we research the process of laser cladding and successfully clad helical blades of end mill with Nd: YAG laser yielding good performances.
Firstly, eighteen types of co-based series of powder formula as laser cladding materials have been investigated by using synchronous powder feeding system. Experimental results show that the formula of No.9 is the best one to be used for the cladding layer of end mill because of its good coating quality, high micro hardness and equivalent bending strength compared with W18Cr4V which is commonly used to make end mill.
Secondly, we do a comparison research on the cladding behaviors of CO2 laser and Nd: YAG laser by using 6 kW CO2 laser system and 1kW Nd: YAG laser system. Experimental results show that Nd: YAG laser is more fit for the laser cladding of end mill because of its limited working area. Based on that, Nd: YAG laser cladding process is studied by using No.9 formula, the effect of processing parameters on shape and quality of coatings is also analyzed and summarized. Then cladding experiments are processed on the simulacrum and technical parameters are optimized.
At the same time, experimental results show that the crack tendency will be
high by using improper processing parameters. The pore or impurity is seldom. In this experiment, tiny pores do no harm to the quality of the coating and probably prevent microcosmic cracks from extending. The fracture surfaces of impenetrate cracks are researched. Results show that this kind of crack originates in the outboard of the interface and extends radially. The content of silicon and oxygen is high in the crack fracture surface.
After that, with optimal parameters, satisfying cladding layer is achieved. Then, by means of optical microscope and SEM, the microstructure of the coating is investigated; by means of x-ray diffraction, phase composition is measured. Experimental results show that fine microstructure is mainly composed of Y cobalt, a cobalt and osseously distributed carbides. Compared with W18Cr4V, the micro hardness, bending strength and wear resistance is equivalent.
Finally, according to the shape character of end mill, special equipments are properly choose. Some problems encountered during the procedure of laser cladding are researched and finally the crackless end mill with well shape and satisfying hardness distribution is manufactured on 45 steel substrate. And its cutting performance is fine according to the national standards.
引文
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2 宋增平．刀具制造工艺．机械工业出版社，1987：306～330
3 袁哲俊，刘华明主编．刀具设计手册．机械工业出版社，1999：19～415
4 G．E．凯恩．切削刀具新的发展方向．机械工业出版社，1987：44～51
5 J.-Y. Jeng, M.-C.Lin. Mold fabrication and modification using hybrid processes of selective laser cladding and milling. Journal of Materials Processing Technology,2001,110:98～103
6 郭伟，徐庆鸿等．激光熔覆的研究发展状况．宇航材料工艺，1998，2：33～35
7 李强，欧阳家虎等．材料表面激光熔覆进展．材料科学与工艺，1996，4(4)：22～36
8 李文，关振中．激光熔覆技术及其界面问题发展评述．金属热处理学报，1997，18(2)：45～50
9 肖荣诗，王智勇等．同步送粉大功率激光表面宽带熔覆技术．应用激光，2000，20(3)：115～116
10 杨洗陈．万瓦级激光大面积自动涂覆系统．中国激光，1996，23(8)：696
11 杨洗陈，王宝琦等．万瓦级激光熔覆宽带扫描转镜的研究．光电子激光，1996，7(5)：279～282
12 De. Pascale O, et al. Controlled surface temperature laser heat-treating. Optics and Lasers in Engineering. 1985(8): 97
13 Idem. Coating characterization in controlled surface temperature laser heat-treating, Ibid,1988(8):97
14 Idem. The use of plane polarized beams in controlled surface temperature laser heat-treating. Ibid, 1989(10):97
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