Capability of high pressure cooling in the turning of surface hardened piston rods

An experimental study was performed to investigate the capabilities of dry, conventional and high pressure cooling (HPC) in the turning of surface hardened piston rods used in fluid power applications. Machining experiments were performed using coated carbide tools at cutting speeds up to 160 m/min. The cooling capabilities are compared by monitoring of chip breakability, process regions of operability, cooling efficiency, tool wear, tool life and cutting forces. Test results showed that dry cutting could not be performed due to long and ductile chips that were formed for all investigated cutting conditions. In comparison to conventional cooling the significant increase of cutting speed and feed rate region of operability was recorded when machining with HPC. Tool life analysis proved a five times increase in tool life when machining with HPC. Furthermore HPC also improved chip breakability and reduced coolant consumption.     

基于切削技术的金刚石刀具磨损特征分析

金刚石刀具的磨损情况决定其使用寿命。用金刚石PCD刀具切削6061-T6镁铝合金工件,通过不同切削速度、切削深度、振动频率、刀具后角时的切削力及切削温度变化,研究不同刀具前后角、进给量、切削转速时的工件表面粗糙度及刀具磨损面积。结果表明:金刚石刀具的切削力和切削温度随切削速度、切削深度的增加而增大,随振动频率的增加而减小;刀具后角增大,金刚石刀具的切削力呈先下降而后缓缓上升趋势,但对切削温度的影响很小。当刀具前角为10°,刀具后角为8°,切削速度为0.46?m/s,切削深度为28?μm,进给量为0.10?mm/r,切削转速为4100?r/min,振动频率为22?kHz,切削振幅为9?μm时,金刚石刀具的磨损面积最小,磨损程度最低,使用寿命最长,但工件的表面粗糙度稍高。      

Temperature of internally-cooled diamond-coated tools for dry-cutting titanium

The role of cutting fluids is well known for the importance of removing heat from the cutting edge, lubricating the sliding chip contact and transporting the metal chips away from the cutting zone. Dry machining leads to increased cutting temperatures and higher wear rates resulting in shorter tool life; this is particularly evident in the cutting of high strength materials. Diamond coated cutting inserts are not usually considered for machining titanium due to rapid oxidation of the coating at the temperatures typical of titanium machining. This paper examines the formation of hot-spots on the rake face during dry and near-dry turning of titanium using conventional cemented carbide inserts. Machining performance is assessed by measurement of tool wear and tool life. Trials with an internally cooled tool with a specially designed, diamond coated insert have shown that the heat from the cutting operation can be rapidly diffused over the entire surface of the insert and thus successfully drawn away from the tool via closed loop recirculation of coolant through the tool holder. This enables wear to be inhibited by management of rake face temperature to keep it below the critical temperatures at which these prominent wear mechanisms operate. Measurements of change in coolant temperature before and after circulation are used to quantify the heat removed from the cutting process. The low friction coefficient and high thermal conductivity of diamond, assisted by the indirect cooling, results in longer tool life whilst maintaining high standards of surface finish.     

Mechanism of minimum quantity lubrication in high-speed milling of hardened steel

The rapid wear rate of cutting tools due to high cutting temperature is a critical problem to be solved in high-speed machining (HSM) of hardened steels. Near-dry machining such as minimum quantity lubrication (MQL) is regarded as one of the solutions to this difficulty. However, the function of MQL in HSM is still uncertain so far which prevents MQL from widely being utilized in the machining of hardened steels. In this paper, the mechanism of MQL in HSM of hardened steel is investigated more comprehensively. Comparing with dry cutting, the tool performance can be enhanced by MQL under all cutting speeds in this study. It is found that MQL can provide extra oxygen to promote the formation of a protective oxide layer in between the chip–tool interface. This layer is basically quaternary compound oxides of Fe, Mn, Si, and Al, and is proved to act as diffusion barriers effectively. Hence, the strength and wear resistance of a cutting tool can be retained which leads to a significant improvement of tool life. It is found that there exists an optimal cutting speed at which a stable protective oxide layer can be formed. When cutting speed is lower than this speed, there is less oxide layer and the improvement of tool life is less apparent. As the cutting speed is far beyond the optimal value, the protective layer is absent and the thermal cracks are apt to occur at the cutting edge due to large fluctuation of temperature. Resultantly, application of MQL is inappropriate in the extreme high-speed cutting condition irrespective of its little increase in tool life. Based on this study, it is concluded that the tool life can be effectively improved by MQL in HSM of NAK80 hardened steels when cutting parameters are chosen properly.     

Analytical modeling and experimental investigation of tool and workpiece temperatures for interrupted cutting 1045 steel by inverse heat conduction method

Cutting temperature is a key factor which directly affects tool wear, workpiece integrity, and machining precision in high speed machining process. The interrupted cutting process consists of several periodical characteristics, such as cutting force and time varying heat source. Induced cutting temperature models with time varying heat flux are developed in this paper to predict temperature distribution at tool inserts and workpiece during interrupted cutting process. A set of interrupted cutting experimental installation is designed to verify the proposed models. The comparison of predicted and measured results for 1045 steel in interrupted cutting processes shows reasonable agreement. The measured temperature of both the tool inserts and workpiece increase firstly and then decrease as the cutting speed increases. The peak temperature of the workpiece appears at 1500 m/min, while the peak tool inserts temperature appears at 1250 m/min approximately. Heat flux is calculated by the inverse heat conduction method. The applicability of Salomon's hypothesis to the temperature of tool inserts and workpiece is discussed during the interrupted cutting process. The dropped temperature at high cutting speed is mainly caused by that heat flux into tool inserts decreases and heat transfer time is not enough after the critical cutting speed.     

Investigations of yield stress,fracture toughness,and energy distribution in high speed orthogonal cutting

This paper presents a novel prediction method of the yield stress and fracture toughness for ductile metal materials through the metal cutting process based on Williams' Model [38]. The fracture toughness of the separation between the segments in serrated chips in high speed machining is then deduced. In addition, an energy conservation equation for high speed machining process, which considers the energy of new created workpiece surfaces, is established. The fracture energy of serrated chips is taken into the developed energy conservation equation. Five groups of experiments are carried out under the cutting speeds of 100, 200, 400, 800 and 1500 m/min. The cutting forces are measured using three-dimensional dynamometer and the relevant geometrical parameters of chips are measured with the aid of optical microscope. The experiment results show that the yield stress of machined ductile metal material presents an obviously increasing trend with the cutting speed increasing from 100 to 800 m/min while it decreases when the cutting speed increases to 1500 m/min further. Meanwhile, the fracture toughness between the chip and bulk material displays a slightly increasing tendency. In high speed machining, the fracture toughness of the separation between the segments in serrated chips also presents increasing trend with the increasing cutting speed, whose value is much greater than that between the chip and bulk material. In the end, the distribution of energy spent in cutting process is analyzed which mainly includes such four portions as plastic deformation, friction on the tool–chip interface, new generated surface and chip fracture. The results show that the proportion of plastic deformation is the largest one while it decreases with the cutting speed increasing. However, the proportions of energy spent on new created surface and chip fracture increase due to the increasing of both the chip's fracture area and the fracture toughness.     

An experimental technique for the measurement of temperature fields for the orthogonal cutting in high speed machining

Cutting temperature and heat generated at the tool-chip interface during high speed machining operations have been recognized as major factors that influence tool performance and workpiece geometry or properties. This paper presents an experimental setup able to determine the temperature field in the cutting zone, during an orthogonal machining operation with 42 CrMo 4 steel. The machining was performed with a gas gun, using standard carbide tools TiCN coated and for cutting speeds up to 50 ms^-1. The technique of temperature measurement was developed on the principle of pyrometry in the visible spectral range by using an intensified CCD camera with very short exposure time and interference filter at 0.8 μm. Temperature gradients were obtained in an area close to the cutting edge of the tool, along the secondary shear zone. Effects of the cutting speed and the chip thickness on the temperature profile in the chip were determined. Maximum chip temperature of about 825 °C was found, for cutting speed close to 20 ms^-1, located at a distance of 300 μm of the tool tip. It was established that this experimental arrangement is quite efficient and can provide fundamental data on the temperature field in materials during orthogonal high speed machining.     

Cutting Performance and Wear Behavior of AlTiN-and TiAlSiN-Coated Carbide Tools During Dry Milling of Ti-6Al-4V

Machining, especially dry machining of titanium alloys, has been one of the most significant challenges for carbide cutting tools. In this study, aluminum-rich AlTiN coating, as well as TiAlSiN nanocomposite coating, were successfully employed for dry milling of Ti-6Al-4V alloy with high efficiency and long tool life. At the cutting speeds of 150 m/min and 200 m/min, the tool life of the TiAlSiN-coated tool exceeds that of AlTiN-coated tool by 32 and 66%, respectively. The wear modes for both coated tools include the uniform flank wear, smooth wear, chipping, coating and substrate flaking, crater and notch wear, and the wear mechanisms include adhesion, diffusion, oxidation and crack. Among them, the wear mechanism is dominated by the adhesion and oxidation wear. As compared with AlTiN coating, TiAlSiN coating exhibits better mechanical properties and oxidation resistance, which contribute to a better cutting performance, fewer thermal cracks and smaller and uniform workpiece chips during the dry milling of Ti-6Al-4V alloy.     

A comparative study of the cutting forces in high speed machining of Ti–6Al–4V and Inconel 718 with a round cutting edge tool

Titanium alloy Ti–6Al–4V and nickel-based superalloy Inconel 718 have been widely employed in modern manufacturing. The published literature on high speed machining (HSM) of the two materials often involves different machining set-up, which makes it difficult to directly apply the research findings from one material to the other to select the most appropriate tool geometry and cutting conditions. A comparative experimental study of HSM of Ti–6Al–4V and Inconel 718 is conducted in this paper using the same machining set-up. The scope of this study is limited in high speed finish machining, where the tool edge geometry plays a significant role. The experimental set-up and the methods of measuring the cutting forces and the tool edge radius are introduced. A total of 40 orthogonal high speed tube-cutting tests were performed, involving five levels of cutting speeds and four levels of feed rates. Based on extensive experimental data, the similarities and differences between HSM of Ti–6Al–4V and Inconel 718 are quantitatively compared and qualitatively explained in terms of four quantities: (1) the cutting force F_c, (2) the thrust force F_t, (3) the resultant force R, and (4) the force ratio F_c/F_t. A total of 12 empirical regression relationships are obtained.     

High-speed machining of titanium alloys using the driven rotary tool

Machining of titanium at high cutting speeds such as from 4 m/s to 8 m/s is very challenging. In this paper, a new generation of driven rotary lathe tool was developed for high-speed machining of a titanium alloy, Ti–6Al–4V. The rotary tool was designed and fabricated based on the requirements of compact structure, sufficient stiffness and minimal edge runout. Cylindrical turning experiments were conducted using the driven rotary tool (DRT) and a stationary cutting tool with the same insert, for comparison in the high-speed machining of Ti–6Al–4V. The results showed that the DRT can significantly increase tool life. Increase in tool life of more than 60 times was achieved under certain conditions. The effects of the rotational speed of the insert were also investigated experimentally. Cutting forces were found to decline slightly with increase of the rotational speed. Tool wear appears to increase with the rotational speed in a certain speed range.     

Failure mechanisms of TiB2 particle and SiC whisker reinforced Al2O3 ceramic cutting tools when machining nickel-based alloys

In this paper, Al₂O₃/TiB₂/SiC_w ceramic cutting tools with different volume fraction of TiB₂ particles and SiC whiskers were produced by hot pressing. The fundamental properties of these composite tool materials were examined. Machining tests with these ceramic tools were carried out on the Inconel718 nickel-based alloys. The tool wear rates and the cutting temperature were measured. The failure mechanisms of these ceramic tools were investigated and correlated to their mechanical properties. Results showed that the fracture toughness and hardness of the composite tool materials continuously increased with increasing SiC whisker content up to 30 vol.%. The relative density decreased with increasing SiC whisker content, the trend of the flexural strength being the same as that of the relative density. Cutting speeds were found to have a profound effect on the wear behaviors of these ceramic tools. The ceramic tools exhibited relative small flank and crater wear at cutting speed lower than 100 m/min, within further increasing of the cutting speed the flank and crater wear increased greatly. Cutting speeds less than 100 m/min were proved to be the best range for this kind of ceramic tool when machining Inconel718 nickel-based alloys. The composite tool materials with higher SiC whisker content showed more wear resistance. Abrasive wear was found to be the predominant flank wear mechanism. While the mechanisms responsible for the crater wear were determined to be adhesion and diffusion due to the high cutting temperature.     

5G覆铜板叠层复合材料高效切磨工艺试验研究

为解决5G覆铜板叠层复合材料板材现有的冲压剪切工艺毛刺飞边严重的问题,提出采用烧结金刚石开槽薄片砂轮切磨工艺替代剪切工艺的方法,在分析设计开槽砂轮结构参数的基础上,研制相应的烧结金刚石开槽薄片砂轮,试验研究不同工艺参数对切磨过程上下表面覆铜层加工毛刺的影响规律和磨削区温度的变化规律.试验结果表明:单位Z向磨削力随磨削速...     

Experimental investigation on the performance of nanoboric acid suspensions in SAE-40 and coconut oil during turning of AISI 1040 steel

Machining is one of the most fundamental and indispensable processes in manufacturing industry. The heat generated in the cutting zone during machining is critical in deciding the workpiece quality. Though cutting fluids are widely employed to carry away the heat in machining, their usage poses threat to ecology and the health of workers. Hence, there arises a need to identify eco-friendly and user-friendly alternatives to conventional cutting fluids. The present work features a specific study on the application of nanosolid lubricant suspensions in lubricating oil in turning of AISI 1040 steel with carbide tool. SAE-40 and coconut oil are taken as base lubricants and boric acid solid lubricant of 50 nm particle size as suspensions. Variation of cutting tool temperatures, average tool flank wear and the surface roughness of the machined surface with cutting speed and feed are studied with nanosolid lubricant suspensions in lubricating oil.     

An integrated thermo-mechanical-dynamic model to characterize motorized machine tool spindles during very high speed rotation

High speed machining (HSM) is a promising technology for drastically increasing productivity and reducing production costs. Development of high-speed spindle technology is strategically critical to the implementation of HSM. Compared to conventional spindles, motorized spindles are equipped with built-in motors for better power transmission and balancing to achieve high-speed operation. However, the built-in motor introduces a great amount of heat into the spindle system as well as additional mass to the spindle shaft, thus complicating its thermo-mechanical-dynamic behaviors. This paper presents an integrated model with experimental validation and sensitivity analysis for studying various thermo-mechanical-dynamic spindle behaviors at high speeds. Specifically, the following effects are investigated: the bearing preload effects on bearing stiffness, and subsequently on overall spindle dynamics; high-speed rotational effects, including centrifugal forces and gyroscopic moments on the spindle shaft and, subsequently, on overall spindle dynamics; and the spindle dynamics on the cutting point receptance. The proposed integrated model is a useful tool for differentiating quantitatively different effects on the spindle behaviors. The results show that a motorized spindle softens at high speeds mainly due to the centrifugal effect on the spindle shaft.     

Physics based modelling of interface temperatures in machining with multilayer coated tools at moderate cutting speeds

A new thermal model is presented for turning with tools with multilayer coatings. In the previous paper [Int. J. Mach. Tools Manuf. 43 (2003) 1311] devoted to the thermal problems in dry turning of steels with tools treated with multilayer coatings with an intermediate Al₂O₃ layer new analytical models for estimating the heat partition to the chip and the average interface temperature were derived and the predictions were compared with experimental results. In this paper, a physics based modelling concept has been applied to both the individual layer and the composite layer approach to develop an estimate of the average and the maximum steady-state chip-tool interface temperatures in orthogonal turning. Different approaches for determining the heat partition coefficient for sliding bodies of defined thermal properties were tested. Experiments using the work and the tool as the thermocouple pair have verified that the proposed models accurately predict the temperatures for uncoated and coated tools for a range of cutting speeds. As a result a new computational algorithm, for predicting with reasonable accuracy the average and peak values of the temperatures at the chip-coating/substrate interface at cutting speeds up to 200 m/min, has been recommended.     

Modelling chip formation of alloy 718

The aim of this article is to investigate the effect of different fracture criteria on the chip formation process, focusing on the formation of segmented chips and what happens around the cutting edge. Furthermore, it is investigated how well the finite element model is able to capture the transition from continuous to segmented chip formation in alloy 718. Machining alloy 718 at lower cutting speeds (below 50 m/min) the chip produced is long and continuous. At higher cutting speeds (above 100 m/min) the chip produced is segmented. The conclusion from this study is that the transition from continuous chip to segmented chip is caused by both thermal softening and material damage. Furthermore it is concluded that a fracture criterion with a hydrostatic dependency shall be used for accurate modelling of chip segmentation.     

陶瓷刀具高速干切削加工数值仿真研究

陶瓷刀具在高温作用下会产生自润滑现象,可起到减摩、抗磨作用.论文以Al2O3陶瓷刀具为例,在高温下刀具表面产生自润滑薄膜,利用有限元分析软件DEFORM-3D,建立高速切削AlSI——1045模型,分析Al2O3陶瓷刀具在高速切削加工时,产生自润滑现象所需切削速度,以及在高速切削时,刀具表面的主切削力、应力分布、温度分布和刀具的磨损状态等.研究表明:当切削速度为270m/min,时,刀具表面温度高达842℃,能够产生自润滑现象.     

Advancing Cutting Technology

This paper reviews some of the main developments in cutting technology since the foundation of CIRP over fifty years ago. Material removal processes can take place at considerably higher performance levels in the range up to Q_w = 150 - 1500 cm³/min for most workpiece materials at cutting speeds up to some 8.000 m/min. Dry or near dry cutting is finding widespread application. The superhard cutting tool materials embody hardness levels in the range 3000 - 9000 HV with toughness levels exceeding 1000 MPa. Coated tool materials offer the opportunity to fine tune the cutting tool to the material being machined. Machining accuracies down to 10 μm can now be achieved for conventional cutting processes with CNC machine tools, whilst ultraprecision cutting can operate in the range < 0.1 μm. The main technological developments associated with the cutting tool and tool materials, the workpiece materials, the machine tool, the process conditions and the manufacturing environment which have led to this advancement are given detailed consideration in this paper. The basis for a roadmap of future development of cutting technology is provided.     

渗硼对Ti(C,N)基金属陶瓷刀具性能的影响

采用粉末冶金法制备了Ti(C,N)基金属陶瓷,并用固体渗硼法对其进行了渗硼处理。研究了渗硼后金属陶瓷的微观组织和力学性能以及渗硼对切削性能的影响。结果表明:Ti(C,N)基金属陶瓷的渗硼层组织由硼化物层、扩散层和基体区组成。渗硼使金属陶瓷的表面硬度提高,抗弯强度降低。渗硼使金属陶瓷刀具在切削速度为200 m/min时的使用寿命提高约1倍;在300 m/min切削速度下,渗硼对延长金属陶瓷刀具的使用寿命没有明显作用;切削速度增至400 m/min时,渗硼使金属陶瓷刀具的使用寿命变短。强烈的热冲击是导致高速切削条件下渗硼层耐磨性降低的主要原因。渗硼层有效地减轻了金属陶瓷刀具表面发生的粘结,并抑制了刀具的扩散磨损和氧化磨损。     

Thermal modeling for white layer predictions in finish hard turning

Part thermal damage is a process limitation in finish hard turning and understanding process parameter effects, especially, tool wear, on cutting temperatures is fundamental for process modeling and optimization. This study develops an analytical model for cutting temperature predictions, in particular, at the machined-surfaces, in finish hard turning by either a new or worn tool.A mechanistic model is employed to estimate the chip formation forces. Wear-land forces are modeled using an approach that assumes linear growth of plastic zone on the wear-land and quadratic decay of stresses in elastic contact. Machining forces and geometric characteristics, i.e. shear plane, chip–tool contact, and flank wear-land, approximate the heat intensity and dimensions of the shear plane, rake face, as well as wear-land heat sources. The three heat sources are further discretized into small segments, each treated as an individual rectangular heat source and subsequently used to calculate temperatures using modified moving or stationary heat-source approaches. Temperature rises due to all heat-source segments are superimposed, with proper coordinate transformation, to obtain the final temperature distributions due to the overall heat sources. All heat sources are simultaneously considered to determine heat partition coefficients, both at the rake face and wear-land, and evaluate the final temperature rises due to the combined heat-source effects.Simulation results show that, in new tool cutting, maximum machined-surface temperatures are adversely affected by increasing feed rate and cutting speed, but favorably by increasing depth of cut. In worn tool cutting, flank wear has decisive effects on machined-surface temperatures; the maximum temperature increases 2–3 times from 0 to 0.2 mm wear-land width. White layers (phase-transformed structures) formed at the machined-surfaces have been used to experimentally validate the analytical model by investigating tool nose radius effects on the white layer depth. The experimental results show good agreement with the model predictions.The established model forms a framework for analytical predictions of machined-surface temperatures in finish hard turning that are critical to part surface integrity and can be used to specify a tool life criterion.