Design,fabrication and properties of a self-lubricated tool in dry cutting

Micro-holes were made using micro-EDM on the rake and flank face of the cemented carbide (WC/Co) tools. Molybdenum disulfide (MoS₂) solid lubricants were filled into the micro-holes to form self-lubricated tools (ML-1 and -2). Dry cutting tests on hardened steel were carried out with these self-lubricated tools and conventional tools (ML-3). The cutting forces, the tool wear, and the friction coefficient between the tool–chip interface were measured. It was shown that the cutting forces with ML-1 and -2 self-lubricated tools were greatly reduced compared with that of ML-3 conventional tool, the ML-1 self-lubricated tool with one micro-hole in its rake face possessed the lower friction coefficient at the tool–chip interface; while the ML-2 self-lubricated tool with one micro-hole in its flank face revealed more flank wear resistance. The mechanism responsible was explained as the formation of a self-lubricating film between the sliding couple, and the composition of this lubricating film was found to be MoS₂ solid lubricant, which was released from the micro-hole and smeared on the rake or flank face, and can be acted as lubricating additive during dry cutting processes.     

Effect of micro-textured tools on machining of Ti–6Al–4V alloy: An experimental and numerical approach

In this work, an attempt is made to reduce the detrimental effects that occurred during machining of Ti–6Al–4V by employing surface textures on the rake faces of the cutting tools. Numerical simulation of machining of Ti–6Al–4V alloy with surface textured tools was employed, taking the work piece as elasto-plastic material and the tool as rigid body. Deform 3D software with updated Lagrangian formulation was used for numerical simulation of machining process. Coupled thermo-mechanical analysis was carried out using Johnson-cook material model to predict the temperature distribution, machining forces, tool wear and chip morphology during machining. Turning experiments on Ti–6Al–4V alloy were carried out using surface textured tungsten carbide tools with micro-scaled grooves in preferred orientation such as, parallel, perpendicular and cross pattern to that of chip flow. A mixture of molybdenum disulfide with SAE 40 oil (80:20) was used as semi-solid lubricant during machining process. Temperature distribution at tool–chip interface was measured using an infrared thermal imager camera. Feed, thrust and cutting forces were measured by a three component-dynamometer. Tool wear and chip morphology were captured and analyzed using optical microscopic images. Experimental results such as cutting temperature, machining forces and chip morphology were used for validating numerical simulation results. Cutting tools with surface textures produced in a direction perpendicular to that of chip flow exhibit a larger reduction in cutting force, temperature generation and reduced tool wear.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.     

Machinability of titanium alloys (Ti6Al4V and Ti555.3)

Near-beta titanium alloys like Ti555.3 are increasingly being used in aeronautics replacing in some critical applications the most common Ti6Al4V. However, these near-beta titanium alloys have a poor machinability rating which needs to be overcome so as to maintain at least the same productivity levels as in Ti6Al4V.This paper presents the machinability results carried out for Ti555.3 compared with the commonly used Ti6Al4V. The aim of this research work is to understand tool wear mechanisms when machining Ti555.3. Analysis of variables such as cutting forces, chip geometry and tool wear shows that: (I) greater difficulty is encounterd when machining Ti555.3 alloy compared with Ti6Al4V alloy which can be machined at higher speeds up to 90 m min^?1; (II) there was a correlation between the mechanical properties of work material, tool wear, and component forces; (III) the occurrence of the diffusion process leads to the formation of a layer of adhered material composed of Ti and TiC on the tool's rake face for both Ti alloys.     

Electro-spark coatings for enhanced performance of twist drills

Surface engineering approaches are being increasingly employed for enhancing the effective life of twist drills with a view to reduce machining costs. The electro-spark coating (ESC) technique provides a promising means of depositing wear resistant coatings that can potentially enhance the performance of these tools. However, it is often necessary to also optimize the machining conditions for coated tools to achieve an enhanced tool life. In the present investigation, varying spindle speeds were employed at a fixed vertical feed to evaluate the performance of WC-8Co ESC coated HSS drills in comparison to bare HSS drills. The number of holes drilled before reaching a preset average flank wear (0.5 mm), or catastrophic failure of the drill, was taken as the measure of tool life. The drill flank wear, monitored at regular intervals, as well as the cutting torque and thrust measured for all holes, were considered to be the key criteria for optimizing the cutting conditions. Results indicate that the WC-8Co coated drill tool life can be increased by a factor of more than 5, depending on the machining conditions selected. Furthermore, flank wear of the drill was found to increase rapidly at the end of drill life. Cutting torque data was also found to provide a useful indicator for predicting the end of tool life.     

Fabrication techniques and cutting performance of micro-textured self-lubricating ceramic cutting tools by in-situ forming of Al2O3-TiC

In this study, different geometric micro-textured ceramic tools (MST-0, MST-1, MST-2) are designed using the software AdvantEdge (AE). The designed tools are used to perform FEM (finite element modelling) simulation of the cutting process. The simulation results show that, compared with the traditional non-texture tool (MST-0), applying the appropriate shape and size of micro-texture to ceramic cutting tools can significantly reduce the cutting force, decrease the cutting temperature and improve the cutting performance of the tool. Additionally, an experimental study was conducted that involved the fabrication of hot-pressing sintered micro-textured self-lubricating ceramic tools (MST-1, MST-2) by means of in-situ forming method. Furthermore, cutting tests to compare the cutting performance of the micro-textured self-lubricating ceramic tools with the traditional non-textured tool (MST-0) were performed. The results indicate that the in-situ formed micro-textured ceramic cutting tools can effectively reduce the cutting force, the cutting temperature, and the rake face wear. During the cutting process, the abrasive grain of graphite that is placed into the micro-texture by in-situ forming is squeezed into the microstructure. Thus, the graphite overflows from the microstructure under abrasive grains and covers the rake face. This helps to reduce the friction between the chip and the rake face, which further reduces the cutting force and temperature, and improves the cutting performance of the tools. The texture pattern orientation of the micro-texture also affects the cutting performance of the tool. It is found that the best cutting performance is obtained by the transverse micro-texture tool.     

Effect of femtosecond laser pretreatment on wear resistance of Al2O3/TiC ceramic tools in dry cutting

A femtosecond pulsed laser (pulse width: 120 fs, wavelength: 800 nm and repetition rate: 500 Hz) was used for the pretreatment on the rake face of Al₂O₃/TiC ceramic cutting tools. The evolution of surface morphology of pretreated cutting tools irradiated with different pulse energies was measured by scanning electron microscope (SEM) and atomic force microscope (AFM). Dry cutting tests were carried out with these pretreated tools and conventional tools on hardened steel. The effect of pulse energy on the wear resistance of these pretreated tools was investigated. Results show that the cutting forces have no significant difference between laser pretreated tools and the conventional tool; the cutting temperatures of laser pretreated tools were slightly reduced compared with the conventional tool. Meanwhile, we found that the laser pretreated tools increased the adhesions of chips on the rake face, but they can significantly improve the wear resistance of the rake face; and laser pulse energy was found to have a profound effect on the wear resistance of the laser pretreated tools.     

Influence of oxygen on the tool wear in machining

High temperatures generated in machining are known to facilitate oxidation wear. A controlled atmosphere chamber was developed to investigate the effects of oxygen on tool wear and high speed machining tests were conducted on air and in argon. Cemented carbide, cermet and cubic boron nitride tooling was used on alloyed steel, hardened tool steel and superalloy Alloy 718. Machining in argon resulted in higher flank wear, higher cutting forces, and larger tool–chip contact length on the rake face. However, in hard machining, argon atmosphere reduced rake cratering. Transmission electron microscopy of tools worn on air showed formation of nanocrystalline Al₂O₃ film on the rake when machining aluminium containing Alloy 718, while no oxide films was detectable in the other cases.     

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.     

Magnetic abrasive finishing of cutting tools for machining of titanium alloys

Uncoated carbide tool surfaces are conditioned using magnetic abrasive finishing (MAF) to improve the tool wear characteristics by reducing friction between the tool and chip. The configuration of the magnetic particle chains that drive the abrasives plays an important role in surface finishing with minimal damage to the tool cutting edges. Roughnesses of less than 25 nm Ra on the flank and nose and less than 50 nm Ra on the rake can be achieved. In turning of Ti–6Al–4V alloy rods (at 100 m/min cutting speed), MAF-processed tools exhibited tool lives of up to twice as long as unprocessed tools.     

Turning characteristics of titanium alloy Ti-6Al-4V with high-pressure cutting fluid

This study investigates the effect of high-pressure cutting fluid on the turning characteristics of Ti-6Al-4V alloy. A noncoated carbide tool was used to measure the cutting temperature using a tool-work thermocouple technique, and the cutting characteristics were evaluated with respect to the cutting temperature, chip breakability, and tool wear. Furthermore, the viability of TiAlN/AlCr₂O₃-coated tool was examined. The coolant jet when placed towards the cutting zone on the rake face is effective in reducing the cutting temperature because of the reduction in the chip-tool contact length. Based on this result, tools with a textured rake face were examined.     

Tool life and tool wear in the semi-finish milling of inclined surfaces

Functional die and mold components have complex geometries and are made of high hardness materials, which make them difficult to machine. This work contributes to a better understanding of this type of process and of the wear mechanisms of tools used in semi-finishing operations of hardened steels for dies and molds. Several milling experiments were carried out to cut AISI H13 steel with 50 HR_C of hardness using the high-speed milling technique. The main goal was to verify the influence of workpiece surface inclination and cutting conditions on tool life and tool wear mechanisms. The main conclusions were the inclination of the machined surface strongly influences tool life and tool wear involves different mechanisms. At the beginning of tool life, the wear was caused mainly by abrasion on the flank face plus diffusion and attrition on the rake face. At the end of tool life, the mechanisms were adhesions and microchipping at the cutting edge.     

硬质合金刀具正交车铣TC4钛合金磨损形貌及机制分析

在车铣复合加工中心Mazak Integrex 200Y上,切削速度为v=150、200 m/min及干式切削条件下,采用硬质合金刀具H13A对钛合金TC4进行正交车铣(顺铣)磨损试验。研究表明高速正交车铣钛合金时,正常磨损阶段前刀面出现不同程度切屑黏结及积屑瘤,后刀面主要以黏结磨损为主,磨损相对均匀;急剧磨损阶段,前刀面切屑黏结加剧,形成连续切屑,缠绕刀具;后刀面由于黏结作用刀具材料被切屑黏结物带走,形成黏结凹坑。刀具磨损的主要原因为黏结磨损、氧化磨损,通过X射线电子能谱(XPS)证明刀具磨损表面有TiO_2、WO_3和Co_3O_4等氧化物生成,分析其对刀具磨损的影响。     

铝含量对AZ系列镁合金机械加工性能的影响

研究铝含量对AZ系列铸造铝合金机械加工性能的影响。为评价该合金的机械加工性能,测量切削操作过程中的切削力以及表面粗糙度,以及研究显微组织和拉伸性能。结果表明：添加2%铝含量的镁合金具有最佳的拉伸性能。随着铝含量增加到2%以上,由于晶界上析出金属间化合物β-Mg17Al12,切削力会随延展性的降低而降低。切削力也会随着切削速度的增加而增大,这是由于在加工过程中切削工具的尖端有侧面生成。     

High speed ball nose end milling of γ-TiAl alloys

Following a brief review on the development and intended application of γ-TiAl for aeroengine components, the paper details statistically designed machinability experiments involving high speed ball end milling in order to benchmark 4th generation alloy Ti–45Al–8Nb–0.2C against Ti–45Al–2Mn–2Nb +0.8%vol. TiB_2, which has been the prime focus of machinability evaluation and associated publications. Testing utilised 8 mm diameter, solid WC, AlTiN coated ball nose end cutters in a factorial design and involved measurement of cutting temperatures and workpiece surface roughness in addition to tool life and cutting forces. The trials established alloy Ti–45Al–8Nb–0.2C as providing a ∼25% increase in tool life based on a maximum flank wear criteria of 300 μm. On average, alloy Ti–45Al–2Mn–2Nb +0.8%vol. TiB₂ had a surface roughness Ra of ∼0.1 μm higher than Ti–45Al–8Nb–0.2C with values <0.6 μm Ra possible. Maximum cutting temperatures for Ti–45A–8Nb–0.2C measured using infra red pyrometry were ∼250 °C at a cutting speed of 160 m/min for a new tool, rising to ∼430 °C at a cutting speed of 340 m/min with a tool that had 300 μm of flank wear. For both γ-TiAl alloys, fracture/pullout was observed on every milled surface that was assessed and varied from a few microns to a few millimeters depending on test operating levels, within general, higher cutting speeds and tool flank wear levels causing an increased level of damage.     

Face milling of the EN AB-43300 aluminum alloy by PVD- and CVD-coated cemented carbide inserts

Two commercially available WC-6Co cemented carbide substrates (Extramet EMT100 and Pramet H10), were industrially coated with PVD TiB₂ or CVD diamond. Subsequently, the coated inserts were submitted to dry sliding tests (slider on cylinder contact geometry) against the aluminum alloy EN AB-43300, for preliminary performance ranking and identification of basic wear mechanisms. The best substrate/coating combination (CVD-Diamond coated Extramet EMT100) was then tested in face milling EN AB-43300 with milling tool characterized by two different geometries (A and B), using PCD inserts as a reference for comparison. In milling tests, the influence of both insert geometry and cutting fluid feed rate were taken into account. The geometry of the tool was identified as the main parameter in influencing the tool performance. In particular, in the case of the A geometry, the relative flank wear of CVD coated tools increased abruptly during the test due coating detachment, whilst with the B geometry no catastrophic failure of the CVD coated insert was observed. The influence of Cutting Fluid Feed Rate (CFFR) also changed with tool geometry: in particular, with the B geometry, which allowed to obtain the best results with the CVD coated inserts, a decrease of CFFR from 100 to 25% did not affect significantly the wear resistance of CVD-coated inserts and allowed to maintain the roughness of the workpiece (R_a) below 0.6 μm, notwithstanding a slightly increased tendency towards the formation of Al-based transfer layers.     

基于微磨削方法的微织构刀具制备与切削性能研究

目的研究表面微织构对硬质合金刀具切削性能的影响。方法采用微磨削方法在硬质合金刀具前刀面加工出具有不同结构参数的横向、纵向和交叉微织构,通过AL6061切削试验和有限元切削仿真,研究表面微织构对硬质合金刀具的切削温度及刀具磨损的影响。结果采用V形金刚石砂轮微磨削方法能够加工出几何形状规则且表面质量良好的表面微织构。与无织构刀具相比,微织构刀具的切削温度明显降低,高温区域明显减少,其中横向织构刀具降温效果最为显著。微织构刀具的切削温度随沟槽间距的增大而升高,沟槽间距为150μm时,切削温度最低。表面微织构能够有效减轻刀具前刀面的粘结磨损,横向织构刀具减摩抗粘效果最好,且采用较小的沟槽间距更利于减轻刀具的粘结磨损。随着切削速度的增加,表面微织构的抗粘结作用更加明显,当切削速度为150 m/min时,沟槽间距为150μm的横向织构刀具的切屑粘结面积最小。结论在横向、纵向和交叉织构刀具中,沟槽间距为150μm的横向织构刀具切削性能最好,即降温效果、抗粘结性能最为显著。     

Performance of carbide tools with textured rake-face filled with solid lubricants in dry cutting processes

Surface texturing with different geometrical characteristics was made on the rake face of the WC/Co carbide tools, molybdenum disulfide (MoS₂) solid lubricants were filled into the textured rake-face. Dry cutting tests were carried out with these rake-face textured tools and a conventional tool. The effect of the texture shape on the cutting performance of these rake-face textured tools was investigated. Results show that the cutting forces, cutting temperature, and the friction coefficient at the tool-chip interface of the rake-face textured tools were significantly reduced compared with that of the conventional one. The rake-face textured tool with elliptical grooves on its rake face had the most improved cutting performance. Two mechanisms responsible were found, the first one is explained as the formation of a lubricating film with low shear strength at the tool-chip interface, which was released from the texturing and smeared on the rake face, and served as lubricating additive during dry cutting processes; the other one was explained by the reduced contact length at the tool-chip interface of the rake-face textured tools, which contributes to the decrease of the direct contact area between the chip and rake face.     

PCD刀具高速干式切削铜合金的磨损研究

使用PCD刀具对锡青铜合金材料进行高速干式切削试验,分别采用扫描电镜（SEM）、X射线能谱仪（EDS）对刀具的磨损形貌进行观察和磨损区域化学成分进行分析,并以此研究了PCD刀具的磨损机理。结果表明:在高速干式切削条件下,PCD刀具主要表现为前刀面的片状剥落和后刀面的轻微破损;同时还伴随着机械应力和热应力冲击下的脆性破损,出现崩刃、切削刃整体断裂以及前后刀面的大面积剥落。刀具磨损的主要原因是高温作用下的氧化磨损和扩散磨损。      

Effects of Mo2C,Ni binder and laser surface modification on WC inserts for turning Ti-6Al-4V

The effects of rapid pulse electric current sintering (PECS), Ni as a Co binder substitute, Mo₂C additions and laser surface modification (LSM) on the microstructure, mechanical properties and machining performance during roughing and finishing turning of Ti-6Al-4 V were investigated. Additions of Mo₂C reduced the carbide grain size from 0.65 ± 0.01 μm to 0.5 ± 0.01 μm in liquid phase sintered (LPS) WC-Co/Ni cermets, with the PECS manufactured WC-0.5Cr₃C₂–3.5Mo₂C-10Co (wt%) having the highest hardness. The LSM technique produced a ~2.5 μm self-carbide coating, increasing the surface hardness of all the samples. LSM was done to improve abrasion, attrition and thermal wear resistance. Turning was done at cuttings speeds (v_c) of 45–120 m/min, depths of cut (a_p) of 0.25–2.0 mm and feeds of 0.15–0.2 mm/revolution, under lubricated conditions. The developed inserts were compared to TH10 (an industrial reference), and performance was assessed by cutting forces, tool wear and tool life. The liquid phase sintered WC-0.5Cr₃C₂-10Co (wt%) and WC-0.5Cr₃C₂–3.5Mo₂C-10Co (wt%) inserts had longer tool lives than TH10 during roughing at a cutting speed (v_c) of 45 m/min, depth of cut (a_p) of 2 mm and feed of 0.2 mm/revolution, although TH10 had the best tool life during finishing (v_c = 120 m/min, a_p = 0.25 mm and feed =0.15 mm/revolution). Generally, LSM had a negligible effect on tool life, WC-Ni based inserts had the shortest tool lives and LPS inserts performed better than PECS inserts.