微径铣刀及微细铣削技术的研究进展

介绍了微径铣刀在制造工艺、刀具性能、刀具材料和涂层技术方面的研究进展;讨论了微细铣削技术在表面粗糙度及毛刺、切削力、刀具磨损及寿命等切削机理以及对微小零件加工能力的研究成果和发展前景。     

Performance assessment of microwave treated WC insert while turning AISI 1040 steel

This study attributed to post treatment of tungsten carbide (WC) inserts using microwave irradiation. Tungsten carbide inserts were subjected to microwave radiation (2.45 GHz) to enhance its performance in terms of reduction in tool wear rate, cutting force surface roughness and improvement in tool life. Performance of tungsten carbide insert is very much affected by machine operating parameters i.e. speed, feed and depth of cut. An attempt has been made to investigate the effects of machining parameters on microwave treated tool inserts. This paper describes the comparative study of machining performance of untreated and microwave treated WC tool inserts used for turning of AISI 1040 steel. Machining performance has been evaluated in terms of flank wear, cutting force, surface roughness, tool wear mechanisms. Critical examinations of tool wear mechanisms and improvements in metallurgical properties such as microstructural change, phase activation of WC grains were identified using scanning electron microscope (SEM). Results obtained from the turning using the microwave treated tool inserts showed a significant reduction tool wear thereby enhancing the surface quality of workpiece.     

Tribological compatibility and improvement of machining productivity and surface integrity

Machining process productivity and machined part quality improvement is a considerable challenge for modern manufacturing. One way to accomplish this is through the application of PVD coatings on cutting tools. In this study the wear rate and wear behavior of end milling cutters with mono-layered TiAlCrN and nano-multilayered self-adaptive TiAlCrN/WN PVD coatings have been studied under high performance dry ball-nose end-milling conditions. The material being machined in this case is hardened H13 tool steel. The morphology of the worn surface of the cutting tool has been studied using SEM/EDX. The microstructure of the cross-section of the chips formed during cutting was analyzed as well. The surface integrity of the workpiece material was also evaluated. Surface roughness and microhardness distribution near the surface of the workpiece material was also investigated. The data presented shows that achieving a high degree of tribological compatibility within the cutting tool/workpiece system can have a big impact on tool life and surface integrity improvement during end milling of hardened tool steel.     

Influence of cryosoaking period on wear characteristics and surface topography of M35 tool steel

Cryogenic treatment affects tool steels wherein alteration in microstructural features like phases, uniform precipitation of carbides is observed. In this work, improvement in wear resistance of cryotreated material with microstructural features and surface roughness of material has been correlated. Samples of AISI M35 steel were hardened at 1200°C, followed by triple tempering at 555°C in the salt bath, subsequently subjected to cryogenic treatment at minus 185°C for varying cryosoaking period (4–32?h) followed by soft tempering at 100°C. Such samples were characterized for hardness, microstructure, carbide density, wear rate and surface roughness. A correlation of carbide density and roughness has been established with wear resistance.     

Crankshaft surfaces: Finishing methods,surface characterization and their influence on wear

In the gasoline or diesel internal combustion engine the surfaces which the crankshaft presents to the connecting rod and the main bearings are very important in determining the wear rate of the bearings. Nodular iron crankshafts, which are now used almost exclusively in automotive gasoline and diesel engines, are particularly sensitive to variations in finishing technique. The microstructure of the nodular iron crankshaft contains spherical graphite nodules surrounded by ferrite. When improperly finished, the ferrite can form a burr which protrudes above the surrounding surface. The prevalence, size and directionality of these ferrite burrs have a marked influence on the wear rate of the bearings. A large burr lying in the unfavorable direction can act as a file on the soft bearing material. Burrs can also impede formation of a suitable oil film, causing high bearing wear rates and reduced service life.     

Machining performance of a grooved tool in dry machining Ti-6Al-4 V

In this paper, dry machining experiment of Ti-6Al-4 V was carried out to investigate the machining performance of a grooved tool in terms of its wear mechanisms and the effects of cutting parameters (cutting speed, feed rate, and cutting depth) on tool life and surface roughness of the machined workpiece. The results showed that chip-groove configuration substantially improved the machining performance of cutting tool. The main wear mechanisms of the grooved tool were adhesive wear, stripping wear, crater wear, and dissolution-diffusion wear. The resistance to chipping was enhanced due to the decrease of contact pressure of tool-chip interface. And the resistance to plastic deformation of tool nose was weakened at the cutting speed of more than 60 m/min. The appropriate cutting speed and feed rate were less than 70 m/min and 0.10 mm/r, respectively. With cutting speed increasing, the surface roughness of machined workpiece decreased. A high feed rate helped the formation of higher surface roughness except 0.21 mm/r. When cutting depth increased, tool nose curvature and phase transformation of workpiece material had great impact on surface roughness.     

The dependence of tool overhang on surface quality and tool wear in the turning process

In the turning process, the importance of machining parameter choice is increased, as it controls the surface quality required. Tool overhang is a cutting tool parameter that has not been investigated in as much detail as some of the better known ones. It is appropriate to keep the tool overhang as short as possible; however, a longer tool overhang may be required depending on the geometry of the workpiece and when using the hole-turning process in particular. In this study, we investigate the effects of changes in the tool overhang in the external turning process on both the surface quality of the workpiece and tool wear. For this purpose, we used workpieces of AISI 1050 material with diameters of 20, 30, and 40 mm; and the surface roughness of the workpiece and tool wear were determined through experiments using constant cutting speed and feed rates with different depth of cuts (DOCs) and tool overhangs. We observed that the effect of the DOC on the surface roughness is negligible, but tool overhang is more important. The deflection of the cutting tool increases with tool overhang. Two different analytical methods were compared to determine the dependence of tool deflection on the tool overhang. Also, the real tool deflection values were determined using a comparator. We observed that the tool deflection values were quite compatible with the tool deflection results obtained using the second analytical method.     

Friction and adhesion of stainless steel strip against tool steels in unlubricated sliding with high contact load

The strong tendency of stainless steel to adhere to other metals and to work harden makes it particularly difficult to form. A new slider-on-strip tribometer was used to study the tribological behaviour of traditional and new tool materials. The tribometer allows friction, workpiece adhesion on the tool surface and wear to be studied under conditions with low sliding speeds and high contact pressures. Several tool steels were tested using cold rolled stainless steel strip as a workpiece material. The results showed that the composition of the tool steel does not have a marked effect on the friction between the tool and the workpiece. However, the surface roughness and topography of the tool have a marked effect. Polishing of the tool surface to reduce the surface roughness reduces the friction between the tool and the workpiece.     

Tool-wear mechanisms in hard turning with polycrystalline cubic boron nitride tools

Hard turning is a turning operation performed on high strength alloy steels (45R_a0.1 μm). Extensive research being conducted on hard turning has so far addressed several fundamental questions concerning chip formation mechanisms, tool-wear, surface integrity and geometric accuracy of the machined components. The major consideration for the user of this relatively newer technology is the quality of the parts produced. A notable observation from this research is that flank wear of the cutting tool has a large impact on the quality of the machined parts (surface finish, geometric accuracy and surface integrity). For components with surface, dimensional and geometric requirements (e.g. bearing surfaces), hard turning technology is often not economical compared with grinding because tool-life is limited by the tolerances required (i.e. high flank wear rate).

The aim of this paper is to present the various modes of wear and damage of the polycrystalline cubic boron nitrides (PCBN) cutting tool under different loading conditions, in order to establish a reliable wear modeling. Flank wear has a large impact on the quality of the parts produced and the wear mechanisms have to be understood to improve the performance of the tool material, namely by reducing the flank wear rate. The wear mechanisms depend not only on the chemical composition of the PCBN, and the nature of the binder phase, but also on the hardness value and above all on the microstructure (percentage of martensite, type, size, composition of the hard phases, etc.) of the machining work material. The proposed modeling is in a generalized form of the extended Taylor’s law allowing to prediction of the tool-life as a function of the cutting parameters and of the workpiece hardness. The effects of these factors on tool-wear, tool-life and cutting forces are discussed in the paper.     

The microstructure and wear behaviour of friction stir processed AISI 430 ferritic stainless steel

ABSTRACT

The microstructure and wear behavior of Friction Stir Processed (FSPed) AISI 430 ferritic stainless steel were analyzed in the present study. FSP was performed with a tool rotation and advancing speeds of 1400?rpm 16?mm/min respectively by employing a tungsten carbide tool. The FSPed microstructure consisted of a mixture of ferrite and martensite. After FSP, microhardness increased with respect to that of the as-received material. The wear resistance of the FS processed material was significantly enhanced if compared to that of the as-received substrate. According to the SEM analyses of the worn surfaces and wear debris, a combination of adhesive wear and delamination was observed in the case of the base metal. The wear mechanism shifted to mild adhesive wear after FSP. The superior wear resistance of the FS processed AISI 430 steel was attributed to the pronounced grain refinement and to martensite formation in the stir zone.     

Effect of material microstructure and tool geometry on surface generation in single point diamond turning

There is a strong desire in industry to improve surface finish when performing ultra-precision, single point diamond turning (SPDT) to reduce the amount of post process polishing required to meet final product specifications. However there are well known factors in SPDT which limit achievable surface finish. This paper focuses on the role of material microstructure, including grain boundary density and the presence of inclusions, as well as tool design on surface roughness using the concept of size effect. Size effect can be described as an interplay between the material microstructure dimension and the relative size of the uncut chip thickness with respect to the cutting edge radius. Since one of the controllable parameters in size effect is grain size and dislocation density, controlled studies were performed on samples whose microstructure was refined by mechanical strain hardening through rolling and a friction stir process (FSP). The use of the ultra-fine grained workpiece prepared using an FSP was observed to reduce side flow as well as grain boundary and inclusion induced roughness. The role of tool geometry on material induced roughness was investigated using a tool with a rounded primary cutting edge and a flat secondary edge. The use of the flat secondary edge was observed to improve surface finish when machining a flat surface. This improvement was primarily attributed to a reduction in side flow and material microstructural effects. By combining these approaches an average surface roughness R_a value of 0.685 nm was achieved when SPDT a flat surface. Furthermore the custom tool has the potential to significantly improve the productivity of SPDT by allowing for a much higher feed rate while still achieving a high quality surface finish.     

微铣金属表面微沟槽结构的粗糙度及形貌分析

为了提高和改善微沟槽表面质量,设计了高速微铣削实验,研究了微沟槽底面表面粗糙度和侧壁残留毛刺的变化规律。从理论角度引入了已加工表面的形成机理,建立了微观表面粗糙度理论模型,提出了刀具跳动对侧壁形貌变化影响的规律。利用三轴联动精密微细铣削机床加工微细直沟槽,并选取主轴转速、轴向切深、进给速度、刀具跳动量和材料组织结构为研究因素。采用多因素正交实验和极差分析法,对表面粗糙度值进行数值分析。铝合金,钢和钛合金三类微沟槽底面对应的最佳表面粗糙度值变化范围分别为1.073~1.481 μm,0.485~0.883 μm,0.235~0.267 μm;无刀具跳动钛合金微沟槽壁毛刺的最大高度为7.637 μm,而当刀具存在0.3 μm的径向综合跳动量时对应的微槽壁毛刺的最大高度为21.79 μm。铣削参数对表面粗糙度值的影响按从大到小依次为进给速度、主轴转速、轴向切深,且随着进给速度和轴向切深的增大,表面粗糙度值增大;随着主轴转速的增大,表面粗糙度值先减小后增大;在相同加工条件下,若微圆弧刀刃无磨损,微刀具的跳动量对微直沟槽侧壁表面质量有较大影响。同时,不同金属材料特性也是影响微沟槽表面质量的潜在因素。     

AN EXPERIMENTAL INVESTIGATION ON WEAR ASPECTS OF TAPPING OPERATION ON HARDENED STEELS

Tapping is one of the most intensively used operations for internal threads with diameters below about 15 mm. When a tap fails, the workpiece has a significant added value. The present work investigates some aspects of wear and performance when solid carbide coated taps M10 × 1.5 cut hardened AISI H13 and AISI D2. The results indicated that it was possible to make threads on hardened AISI D2, although the number of holes was essentially low and tool breakage was often. Threads on hardened AISI H13 was possible with reasonably low tool wear. Cutting surface presented some indication of small flaws due to the adhered material on the taps.     

In-cycle monitoring of tool nose wear and surface roughness of turned parts using machine vision

Tool wear has been extensively studied in the past due to its effect on the surface quality of the finished product. Vision-based systems using a CCD camera are increasingly being used for measurement of tool wear due to their numerous advantages compared to indirect methods. Most research into tool wear monitoring using vision systems focusses on off-line measurement of wear. The effect of wear on surface roughness of the workpiece is also studied by measuring the roughness off-line using mechanical stylus methods. In this work, a vision system using a CCD camera and backlight was developed to measure the surface roughness of the turned part without removing it from the machine in-between cutting processes, i.e. in-cycle. An algorithm developed in previous work was used to automatically correct tool misalignment using the images and measure the nose wear area. The surface roughness of turned parts measured using the machine vision system was verified using the mechanical stylus method. The nose wear was measured for different feed rates and its effect on the surface roughness of the turned part was studied. The results showed that surface roughness initially decreased as the machining time of the tool increased due to increasing nose wear and then increased when notch wear occurred.     

AN EXPERIMENTAL INVESTIGATION ON WEAR ASPECTS OF TAPPING OPERATION ON HARDENED STEELS

Tapping is one of the most intensively used operations for internal threads with diameters below about 15 mm. When a tap fails, the workpiece has a significant added value. The present work investigates some aspects of wear and performance when solid carbide coated taps M10 × 1.5 cut hardened AISI H13 and AISI D2. The results indicated that it was possible to make threads on hardened AISI D2, although the number of holes was essentially low and tool breakage was often. Threads on hardened AISI H13 was possible with reasonably low tool wear. Cutting surface presented some indication of small flaws due to the adhered material on the taps.     

Study of face milling of hardened AISI D3 steel with a special design of carbide tools

This paper studies the impact of a special carbide tool design on the process viability of the face milling of hardened AISI D3 steel (with a hardness of 60 HRC), in terms of surface quality and tool life. Due to the advances in the manufacturing of PVD AlCrN tungsten carbide coated tools, it is possible to use them in the manufacturing of mould and die components. Experimental results show that surface roughness (R_a) values from 0.1 to 0.3 μm can be obtained in the workpiece with an acceptable level of tool life. These outcomes suggest that these tools are suitable for the finishing of hardened steel parts and can compete with other finishing processes. The tool performance is explained after a tool wear characterization, in which two wear zones were distinguished: the region along the cutting edge where the cutting angle (κ) is maximum (κ_max) for a given depth of cut, and the zone where the cutting angle is minimum (κ?=?0) that generates the desired surface. An additional machining test run was made to plot the topography of the surface and to measure dimensional variations. Finally, for the parameters optimal selection, frequency histograms of R_a distribution were obtained establishing the relationship between key milling process parameters (V_c and f_z), surface roughness and tool wear morphology.     

Cutting performance of nano-crystalline diamond (NCD) coating in micro-milling of Ti6Al4V alloy

Hard coatings are an important factor affecting the cutting performance of tools. In particular, they directly affect tool life, cutting forces, surface quality and burr formation in the micro-milling process. In this study, the performance of nano-crystalline diamond (NCD) coated tools was evaluated by comparing it with TiN-coated, AlCrN-coated and uncoated carbide tools in micro-milling of Ti₆Al₄V alloy. A series of micro-milling tests was carried out to determine the effects of coating type and machining conditions on tool wear, cutting force, surface roughness and burr size. Flat end-mill tools with two flutes and a diameter of 0.5 mm were used in the micro-milling process. The minimum chip thickness depending on both the cutting force and the surface roughness were determined. The results showed that the minimum chip thickness is about 0.3 times that of the cutter corner radius for Ti₆Al₄V alloy and changes very little with coating type. It was observed from wear tests that the dominant wear mechanism was abrasion. Maximum wear occurred on NCD-coated and uncoated tools. In addition, maximum burr size was obtained in the cutting process with the uncoated tool.     

Wear test for bulk metal forming using a radionuclide technique

Various parameters influence tool life, such as the tool material and the workpiece material, the lubricant, the tool pressure, the initial surface roughness, the relative velocity between the tool and the workpiece and the temperature. Usually investigations of tool wear require great experimental effort. Therefore a new testing procedure was sought which permits the wear to be identified from a small number of workpieces. There are two methods using radioisotopes which in principle satisfy these conditions: neutron activation analysis and tool surface activation.Experiments showed, however, that commercial steels do not satisfy the demands concerning material purity which is a precondition of neutron activation analysis.The use of surface activation offers a suitable technique for wear measurements which may be carried out continuously during a test. It is important that the position of maximum wear is exactly known and that the wear particles are carried away from the place of origin without further interaction with the tribosystem.     

Case Studies on Tribological Behavior of Coated Cutting Tools

Plasma surface engineering is a very promising way to enhance performance of metal cutting tools. The advantage of PVD coatings include increase the tool life, improve the roughness of machined surfaces, increase the cutting speed, etc.

This paper studied some new multiphase materials and multilayer structures of coatings based on TiN and TiC, ZrN, (Ti,Al)N,Al-Si-N. The change of contact conditions on cutting by coated tools, specific features of wear of tools with complicated geometry (like drills), effect of cutting conditions and workpiece materials on tribological behavior of indexable inserts during lathe turning and plain rotary were discussed.     

Performance comparison of conventional and wiper ceramic inserts in hard turning through artificial neural network modeling

Hard turning with ceramic tools provides an alternative to grinding operation in machining high precision and hardened components. But, the main concerns are the cost of expensive tool materials and the effect of the process on machinability. The poor selection of cutting conditions may lead to excessive tool wear and increased surface roughness of workpiece. Hence, there is a need to investigate the effects of process parameters on machinability characteristics in hard turning. In this work, the influence of cutting speed, feed rate, and machining time on machinability aspects such as specific cutting force, surface roughness, and tool wear in AISI D2 cold work tool steel hard turning with three different ceramic inserts, namely, CC650, CC650WG, and GC6050WH has been studied. A multilayer feed-forward artificial neural network (ANN), trained using error back-propagation training algorithm has been employed for predicting the machinability. The input?Coutput patterns required for ANN training and testing are obtained from the turning experiments planned through full factorial design. The simulation results demonstrate the effectiveness of ANN models to analyze the effects of cutting conditions as well as to study the performance of conventional and wiper ceramic inserts on machinability.