外文翻译--制造业用于提高表面光洁度和减少切削力的抛丸清理机

Micro shot blasting of machine tools for improving surface finish and reducing cutting forces in manufacturing D.M. Kennedy *, J. Vahey, D. Hanney Faculty of Engineering, Dublin Institute of Technology, Bolton Street, Dublin 1, Ireland Received 5 January 2004； accepted 3 February 2004 Available online 13 April 2004 Abstract Micro blasting of cutting tips and tools is a very effective and reliable method of advancing the life of tools under the action of turning, milling, drilling, punching and cutting. This paper outlines the ways in which micro blasted tools, both coated and uncoated have benefited from shot blasting and resulted in greater productivity, lower cutting forces, improved surface finish of the work pieces and less machine downtime. The process of micro blasting is discussed in the paper. Its effectiveness depends on many parameters including the shot media and size, the mechanics of impact and the application of the shot via the micro shot blasting unit. Control of the process to provide repeatability and reliability in the shot blasting unit is discussed. Comparisons between treated and untreated cutting tools are made and results of tool life for these cutting tips outlined. The process has shown to be of major benefitto tool life improvement. 2004 Elsevier Ltd. All rights reserved. Keywords: Micro shot blasting； Surface finish； Machine tools 1. Introduction Many modern techniques have been developed to enhance the life of components in service, such as alloying additions, heat treatment, surface engineering, surface coating, implantation processes, laser treatment and surface shape design. Processes such as thin film technology, plasma spraying, vacuum techniques depositing a range of multi-layered coatings have greatly enhanced the life, use and applications of engineering components and machine tools. Bombardment with millions of micro shot ranging in size from 4 to 50 lm with a controlled process can lead to dramatic operating life improvements of components. Standard shot peening was first used in a production process to extend the life of valve springs for Buick and Cadillac engines in the early 1930s 1,2 but prior to this it was a well known process used by blacksmiths and sword makers overtime to improve the toughness of the cutting edges of their tools and weapons. Today, cutting tips and tools can be greatly improved by the process of micro shot blasting their surfaces to induce compressive residual stresses. The operating life of tools such as drills, turning tips,milling tips, punches, knife edges, slicers, blades, and a range of other working parts can also benefit from this process.Standard components, such as springs, dies, shafts, cams, and dynamic components in machines and engines can be enhanced by this process. The fatigue life of compressor components for example, treated by shot peening have increased dramatically as reported by Eckersley and Ferrelli 3. Other factors such as improved fatigue resistance, micro crack closure, reduced corrosion and an improved surface finish can also be designed into components as a result of this the peening process. Not only can improvements be made to the surface finish of the cutting tips and tools but also the surface finish of the work pieces machined with these tools have improved as a result of this technique. Engineering materials such as tools steels, carbides, ceramics, coated carbides, through to polymers and even rubbers (elastomers) can benefit. The key requirement for this process is to develop anautomated micro blasting process to fit inside a spraybooth or standard shot blasting booth. Shot material, size and mass, operating pressures, operating velocities, kinetic energy, density and coverage time will need to be perfected and optimised for a range of materials. The process is a line of sight method but can be applied to complex surface shapes such as the tips of drill bits. 2. Method of operation One of the primary ways that components fail in ervice is through fatigue. This is closely associated with cyclic stresses and accelerated by tensile stresses, micro crack propagation and stress corrosion cracking. Cracks reduce the cross section of a material and eventually it will fail to support the applied loads. One simple method of reducing failure by fatigue is to arrest these tensile stresses by inducing compressive stresses into a surface. The benefits obtained with shot peening are a direct result of the residual compressive stresses produced in a component. A typical shot striking a surface is shown in Fig. 1. Any applied tensile loads would have to overcome the residual compressive stresses before a crack could initiate as described by Almen 4. Poor machining of materials can result in residual stresses accruing at the surface. Rough surfaces have deeper notches, where cracks can initiate due to tensile stress concentrations at these points. Many standard machining processes such as grinding, milling, turning, and coating processes such as electroplating induce residual tensile stresses in surfaces and this can lead to early failure of components. Further tensile loading in service would lead to early failure and this can be prevented by shot peening and micro blasting of component surfaces. Micro shot blasting will change the following in a materials surface: (i) resistance to fatigue fracture； (ii) resistance to stress corrosion； (iii) a change in residual stresses； (iv) modification of surface finish. It is a cold working process involving bombarding powders such as ceramics, glass and metals of mainly spherical shapes against surfaces and can be used in conjunction with other processes. The main stages involved in this dynamic process include elastic recovery of the substrate after impact, some plastic deformation of the substrate if the impact pressure exceeds the yield stress, increased plastic deformation due to an increase in impact pressure and finally some rebound of the shot due to a release of elastic energy. Some critical design characteristics of the micro shot peening process include the shot size, shape, hardness, density, durability, angle of impact, velocity and intensity. All of these parameters will influence the residual compressive stresses produced in the substrate. 3. Experimental work Tool materials such as Tungsten Carbide, High Speed Steels used in milling and turning tools were subjected to the micro peening process using different shot media (ceramic and glass bead) and shot size. Tests prior to and following the blasting process were conducted to ascertain any improvements resulting from the process. The micro shot peening unit is shown in Photo 1 it incorporates an air filter, pressure regulator and gauge, air flow regulator, pressurised blast media container and a venturi blast nozzle for directing the stream of micro shot. The unit is PLC controlled and a stepper motor, used to drive a lead screw, is used to move the blast nozzle across the sample in order to control media shot coverage. The blast nozzle can also be rotated to allow shot media to strike the samples at different angles. Tests undertaken include surface finish and roughness measurement, machining tests on standard lathes and mills, hardness tests, cutting forces on turning operations, tool wear and the determination of surface finish of the work pieces machined. Figs. 2 and 3 show a typical high speed steel (HSS) tip prior to and following the micro shot peening process using ceramic bead at a pressure of 5.5 bar. 4. Experimental results Testing of treated and untreated cutting tips and tools was conducted on HSSs for turning and milling as well as coated and uncoated carbide inserts. A dynamometer was used to measure cutting forces on the turning tool (Lathe). The cutting process consisted of a depth of cut of 2 mm on a standard bright mild steel specimen over a length of 750 mm while milling tests consisted of machining a 25_25_150 mm piece of mild steel using a depth of cut of 1 mm with a slot milling cutter of 18 mm diameter. Surface roughness measurements were conducted on the machined components prior to and after machining to establish whether the treated cutting tips had superior performance to the untreated tips. Micro Hardness testing was also carried out to establish if there was any increase in surface hardness due to the micro shot peening process. The impact angle of the shot was set at 90_ as this provides the optimum compressive layer 5. The shot velocity on impact with a surface is largely dependent on the nozzle size, the air pressure and the distance from the substrate. The exposure time was adequate to give sufficient coverage of the substrate and this was determined by the Almen strip saturation time, work piece indentation time and visual appearance. Harder materials such as carbides will obviously require longer exposure time or harder shot media. The micro peening media used was a ceramic bead of approximately 40 lm diameter providing high impact strength and hardness (NF L 06-824, approximately 60 HRc). 4.1. Micro hardness tests Combined Vickers micro hardness tests gave the results in Table 1. for both treated and untreated HSS cutting tips. 4.2. Surface roughness values In all surface roughness tests conducted, the micro blasted surface gave an improved surface roughness value. Surface roughness and profile tests were carried out on both a Talyor Hobson Tallysurf instrument and a non contact surface profileometer. Surface roughness details of a typical untreated HSS cutting tip and a treated one are shown in Figs. 4 and5 and Table 2 shows the results of surface measurement values for other cutting tips and tools and workpieces. Fig. 6 shows an uncoated carbide cutting tip which was not subjected to micro blasting. The flank wear was measured using an optical microscope and the value recorded was 150 lm after 676 s of machining. Fig. 7 shows an uncoated carbide tip subjected to micro blasting. The flank wear in this case is only 90 lm for the same machining time. and5 and Table 2 shows the results of surface measurement values for other cutting tips and tools and workpieces. Fig. 6 shows an uncoated carbide cutting tip which was not subjected to micro blasting. The flank wear was measured using an optical microscope and the value recorded was 150 lm after 676 s of machining. Fig. 7 shows an uncoated carbide tip subjected to micro blasting. The flank wear in this case is only 90 lm for the same machining time. 4.3. Dynamometer tests Figs. 8 and 9 show the comparison for Dynamometer results for HSS in the treated (micro blasted) and untreated states with relevant comments. Similar profiles are shown for coated and uncoated turning tips in both the treated (micro blasted) and untreated conditions in Figs. 1013. In all cases, the micro blasted tips provided an increase in cutting tip life with lower cutting forces recorded. 5. Conclusions This research work has shown that micro shot blasting of cutting tips and tools has a very positive effect on component surfaces by increasing toughness, operating life, improving hardness and surface finish. From the tests conducted, it is obvious that the process affects the residual stresses at or near the surface in a beneficial way by inducing compressive stresses on the substrates tested. The micro blasting process is very simple to apply and economical to use. The mechanical properties of the substrates will determine the type of treatment, i.e. shot hardness, velocity and duration of application in order to obtain maximum benefits from this process. In some cases, authors have reported a 4 10 fold improvement in fatigue life in a range of dynamic machine parts subjected to standard shot blasting. Further testing will need to be conducted at the micro shot blasting stage to obtain similar benefits. Other applications for the micro blasting process are currently being investigated and rubber based products that are subjected to fatigue and wear are being tested in order to remove the surface voids that act as stress concentrations in these materials. References 1 Impact. Bloomfield, CT: Metal Improvement Company； Fall 1989. 2 Zimmerli FP. Heat treating, setting and shot-peening of mechanical springs. Metal process； June 1952. 3 Eckersley JS, Ferrelli B. Using shot-peening to multiply the life of compressor components. In: The shot peener, International newsletter for shot-peening surface finishing industry, vol. 9, Issue No. 1； March 1995. 4 Almen JC. J.O. Almen on hot blasting. General motors test, US Patent 2,350,440. 5 Champaigne J. Controlled shot peening. Elec Inc., Report； 1989. 制造业用于提高表面光洁度和减少切削力的抛丸清理机 摘要 在旋转，铣削，钻孔，冲孔和切削运动中，微抛丸切削技巧和工具是一种提高工具寿命的非常高效并且可靠的方法。本文概述了应用微抛丸工具的方式，微抛丸对有无镀膜工件的益处，并且创造了更大的生产力，降低了切应力，提高了工件的表面光洁度，减少了机器的停机时间。本文对微抛丸过程进行了讨论。它的效率取决于包括弹丸媒体和型号在内的许多参数，碰撞力学和通过微抛丸单元的弹丸的应用程序。对控制流程提供的可重复性和可靠性的爆破装置进行了探讨。处理和未经处理的刀具的做出了对比，切 割技巧对刀具寿命的影响做出了概述。这个过程体现了提高工具寿命的主要好处。 2004 爱思唯尔有限公司保留所有权利。 关键词 :微喷丸清理 ,表面光洁度 ；机床 介绍 许多现代技术已经开发出来加强服务组件的寿命，例如添加合金，热处理，表面工程，表面涂层，移植过程，激光治疗以及表面外形设计。例如薄膜技术，等离子喷涂，沉淀多层涂料的真空技术都大大加强了寿命，工程和应用程序组件和机床使用。通过控制过程用数以百万计的大小在 4 到 50 微米的微抛丸撞击可以显著提高组件的使用寿命。标准喷丸技术首次使用时在 20 世纪 30 年代提高别克和凯 迪拉克引擎气门弹簧的生产过程中，但在此之前该技术就是被铁匠和刀制造商所熟知的来提高他们工具和武器切削刃韧性的过程。当今，切割技巧和工具可以通过微抛丸清理它们的表面的过程来引导压缩参与应力而被大大提高。钻头，车削头，铣削头，冲头，刀刃，切片机，叶片以及一系列的其他工作部分都可以受益于该过程。 机器和引擎中的标准组件，例如离合器，柴油机，轴，凸轮以及动态组件等都可以通过该过程提高。由 Eckersley和 Ferrelli所述， 例如压缩机组件的疲劳寿命通过抛丸处理可以显著增加。其他因素，例如抗疲劳强度，微裂纹闭合， 减少腐蚀以及提高表面光洁度都可以被作为喷丸的结果而被设计进组件当中。不仅可以做到切削刀具表面光洁度的提高，而且由这些刀具加工的工件的表面光洁度作为该技术的一个成果也得到了提高。工程材料中，例如工具钢，硬质合金，陶瓷，涂层硬质合金，通过聚合物甚至橡胶（弹性物）都可以受益。这个过程的关键要求是开发一个自动化微抛丸的工艺过程来适用于喷漆柜或者标准抛丸位置。 抛丸材料，大小和质量，操作压力，操作速度，动能，密度，覆盖时间都要被完美优化一系列材料。这个过程是一种视线方法却可以应用于复杂外形例如钻孔。 操作方法 服务组 件损坏的主要原因之一是疲劳使用。这是与循环应力密切相关 ,加速了抗拉应力，微裂纹扩展和应力腐蚀开裂。裂纹减少材料的横截面，最终它将无法支持应用加载。减少疲劳的失败的一个简单方法是通过诱导压应力到表面来停止这些拉伸应力。抛丸加工直接产生的好处是一个组件产生的残余压应力。典型的镜头的表面是图 1所示。在由阿尔门 4描述的裂纹出现之前，任何应用拉伸加载将不得不克服残余压应力。 不良的加工材料会导致残留表面压力积累。粗糙表面有更深层次的等级，在这些点，由于拉应力会产生裂纹。 许多标准磨削，铣削、车削和涂层工艺例如电镀 等加工过程，在表面产生残余拉应力，这可能会导致早期失效的组件。进一步拉伸加载服务会导致早期失效，这可以防止喷丸加工和微抛丸组件表面。 微抛丸处理将改变以下材料表面： 1. 抗疲劳断裂； 2. 抗应力腐蚀； 3. 残余应力的变化； 4. 修改的表面光洁度。 这是一个包括轰击粉末的冷加工过程，例如陶