淬火钢加工用PCBN新材料的研制

结合淬火钢加工特点及PCBN烧结原理,设计开发了一种适于淬火钢加工用CB–600新材料。运用扫描电子显微镜(SEM)观察、切削实验、以及客户实际使用等方法对CB–600、国内同类产品FP–1及国外同类产品DP–1进行了性能对比分析。SEM检测结果表明:CB–600与DP–1均具有均匀致密的组织结构。连续车削淬火钢实验表明:CB–600具有较好的耐磨性,其后刀面磨损量比DP–1大40%,比FP–1小68%。断续车削实验表明:CB–600和FP–1经过4万次断续冲击后切削刃完好无崩损,而DP–1经过2.7万次断续冲击时发生较大崩刃。客户实际使用表明:CB–600能够加工的淬火钢零件件数比FP–1多1倍以上。因此,CB–600具有较优异的淬火钢加工性能。     

Determination of forces in high speed blanking using FEM and experiments

The increasing demand for micro-formed and stamped parts such as connectors in the electronic industry is forcing manufacturers to push the speed limit of conventional press technologies to improve throughput. Designing dies/tooling for higher speeds and obtaining extended tool life requires a thorough understanding of the process. This paper discusses an experimental study of the interaction between punch, stripper plate and sheet material at various blanking velocities up to 1600 mm/s. The effect of velocity on punching force is also studied. A methodology to obtain high strain and strain rate dependent material flow stress data using blanking test and finite element modelling is presented.     

On the measurement and prediction of temperature fields In machining AISI 1045 steel

Infrared microscopic measurements of the temperature fields at the tool-chip interface in steady-state, orthogonal, machining of AISI 1045 steel are presented for a range of chip thicknesses The measurements are verified using an energy balance method and simple finite difference calculations (see [14]) These results are compared to the predictions of a finite element calculation using a commercial package for three different material models obtained from the literature Results are highly dependent on the material model and friction behavior, indicating that caution be used when finite element analysis is to predict rather than interpret machining temperatures.     

Improving surface integrity in orthogonal machining of hardened AISI 52100 steel by modeling white and dark layers formation

In machining of hard parts, surface integrity is one of the most specified customer requirements. Often, the major indications of surface integrity are surface roughness and residual stresses. However, the material microstructure also changes in machined-hardened steels, and it must be taken into account for improving product performance. In this paper, a hardness-based flow stress and an empirical model for describing the white and dark layers formation were developed and implemented in a FE code. The proposed model was validated by comparing the predicted results with the experimental evidences.     

Tool wear when turning hardened AISI 4340 with coated PCBN tools using finishing cutting conditions

Tool wear is one of the most important aspects in metal cutting, especially when machining hardened steels. The present work shows the results of tool wear, cutting force and surface finish obtained from the turning operation on hardened AISI 4340 using PCBN coated and uncoated edges. Three different coatings were tested using finishing conditions: TiAlN, TiAlN-nanocoating and AlCrN. The lowest tool wear happened with TiAlN-nanocoating followed by TiAlN, AlCrN and uncoated PCBN. Forces followed the same pattern, increasing in the same order, after flank wear appears. At the beginning of cutting, there was no significant difference amongst the coated tools, only the uncoated one showing higher cutting force. Ra values were between 0.7 and 1.2 μm with no large differences amongst the tools. Finite element method (FEM) simulations indicated that temperature at the chip–tool interface was around 800 °C in absence of flank wear, independently of coating. In that range only the TiAlN coating oxidize since AlCrN needs higher than 1000 °C. Therefore, due to a combination of high hardness in the cutting temperature range and the presence of an oxidizing layer, TiAlN-nanocoating performed better in terms of tool wear and surface roughness.     

Investigation of the torque characteristics in vibration tapping of hardened steel

Vibration tapping is presented in this paper to solve this problem, as high-speed steel tap is incapable of tapping small-hole (M3) in hardened steel (50HRC). Theoretical analysis with fracture mechanics indicates that the impact effect of the tap on the workpiece results in increased II-type stress intensity factor and extended micro cracks, leading to lower plastic deformation, reduced cutting forces and a much lower tapping torque, and the torsional rigidity of the tap is enhanced in vibration tapping as proved by dynamic analysis. The experimental results show that with well chosen amplitudes, tapping torque decreases as vibration frequency increases, and tapping torque increases as net cutting time ratio increases, where net cutting time ratio influences the tapping torque more significantly. Vibration tapping is then proved to be a practical solution to the problem of small-hole tapping in hardened steel.     

Chip morphology of normalized steel when machining in different atmospheres with ceramic composite tool

Dry cutting tests in air and nitrogen atmospheres with a ceramic cutting tool were carried out on normalized AISI 1045 steel. SEM and EDX techniques are employed to observe the chip morphology and tribological mechanisms are simultaneously discussed. The finite element model of chip formation was created to determine the effective stress and strain distributions in the chip and workpiece. Compared in nitrogen, the friction coefficient in air was reduced when the cutting speed is at 160 m/min and the feed rate is 0.1 mm/r. Experimental data and observation revealed the formation of a lubricating film at the tool-chip interface, which related to the difference chip morphology in air and nitrogen.     

Ductile shear failure damage modelling and predicting built-up edge in steel machining

This paper reports an improved ductile shear failure model for steels and its application, through finite element simulations, to predicting the conditions for built-up edge formation in steel machining. The model has two parts, a standard damage accumulation law and (the improved part) how damage affects the steel's flow stress after failure. The accumulation law includes a strain to failure with inverse exponential dependence on hydrostatic pressure and reducing in a blue-brittle temperature range. The flow stress after failure remains finite in compressive hydrostatic conditions, to create a friction resistance to shear across the failure surface. Predictions of built-up edge formation depend strongly on strain hardening behaviour. This affects the hydrostatic stress field in the chip formation region. Simulations show the general features of built-up edge formation (a finite cutting speed range with an upper limit determined by increased ductility with temperature and a lower limit determined, depending on conditions, by insufficient heating for blue-brittleness, lower chip/tool friction or a change to unsteady chip formation). The simulations are tested against previously published observations of built-up edge formation in orthogonal cutting of a Russian steel equivalent to AISI 5130. To extend the work to a wider range of steels requires more data to be gathered on individual steels’ damage accumulation law coefficients. Also, at this stage, the simulations only predict the conditions (cutting speed, uncut chip thickness) in which built-up edge forms. They are not able to follow the growth of the built-up edge to its final shape.     

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.     

Prediction of tool and chip temperature in continuous and interrupted machining

In this paper, a numerical model based on the finite difference method is presented to predict tool and chip temperature fields in continuous machining and time varying milling processes. Continuous or steady state machining operations like orthogonal cutting are studied by modeling the heat transfer between the tool and chip at the tool—rake face contact zone. The shear energy created in the primary zone, the friction energy produced at the rake face—chip contact zone and the heat balance between the moving chip and stationary tool are considered. The temperature distribution is solved using the finite difference method. Later, the model is extended to milling where the cutting is interrupted and the chip thickness varies with time. The time varying chip is digitized into small elements with differential cutter rotation angles which are defined by the product of spindle speed and discrete time intervals. The temperature field in each differential element is modeled as a first-order dynamic system, whose time constant is identified based on the thermal properties of the tool and work material, and the initial temperature at the previous chip segment. The transient temperature variation is evaluated by recursively solving the first order heat transfer problem at successive chip elements. The proposed model combines the steady-state temperature prediction in continuous machining with transient temperature evaluation in interrupted cutting operations where the chip and the process change in a discontinuous manner. The mathematical models and simulation results are in satisfactory agreement with experimental temperature measurements reported in the literature.     

PCBN刀具干车淬硬钢时倒棱前角对切削力和刀具磨损的影响

PCBN刀具磨出负倒棱是为了加强刀具的刃口强度，以减少刀具加工时可能出现的破损情况。本文通过对PCBN刀具加工淬硬轴承钢GCr15的一系列试验数据加以分析，得出倒棱前角和切削力、刀具磨损之间的关系，进而得出在实际加工情况下应该采用的最佳倒棱前角值。试验表明：当倒棱前角取15度且切削速度为125m／s时，刀具具有最好的加工效果，不但切削力可以达到最小值，刀具磨损最轻，而且刀具寿命也达到了最大值。     

Modeling of white layer formation under thermally dominant conditions in orthogonal machining of hardened AISI 52100 steel

This paper presents a finite element model for white layer formation in orthogonal machining of hardened AISI 52100 steel under thermally dominant cutting conditions that promote martensitic phase transformations. The model explicitly accounts for the effects of stress and strain, transformation plasticity and the effect of volume expansion accompanying phase transformation on the transformation temperature. Model predictions of white layer depth are found to be in agreement with experimental values. The paper also analyzes the effect of white layer formation on residual stress evolution in orthogonal cutting of AISI 52100 hardened steel. Model simulations show that white layer formation does have a significant impact on the magnitude of surface residual stress and on the location of the peak compressive residual stress.     

Experimental study on ultrasonic elliptical vibration cutting of hardened steel using PCD tools

Diamond tools cannot usually be applied for machining hardened steels while applying conventional cutting technique. As an alternative, ultrasonic elliptical vibration cutting (UEVC) technique was successfully applied for obtaining mirror surface on such steels using single crystal diamond (SCD) tools. In order to reduce production cost without compromising mirror surface quality, polycrystalline diamond (PCD) tools may be tested against highly expensive SCD tools. However, study on machining of hardened steel using PCD tools applying the UEVC technique has not yet been reported. The current research presents an experimental study on UEVC of hardened stainless steel (a typical Stavax, hardness 49 HRC) using the PCD tools. Face turning experiments were carried out to investigate the effects of three machining parameters: nominal depth of cut, feed rate, and nominal cutting speed on output performances such as cutting force, tool flank wear, surface roughness, and chip formation. Experimental results show that nominal cutting speed has very strong influence on the output performances, compared to the other two parameters. The surface roughness improves with a decrease in cutting speed. A mirror-like surface of approximately 804 mm² with a roughness value R_a of 11 nm was achieved at a lower cutting speed. Theoretical explanations have been given to support the results drawn from the UEVC experiments. It can be concluded that, while applying the UEVC technique, the inexpensive PCD tools instead of the SCD tools can be effectively applied to obtain optical surface for producing precise molds from the hardened steel.     

PcBN加工淬硬钢刀具材料的研究

介绍了立方氮化硼刀具材料( PcBN)的制备过程,并制备了六种不同配方的样品加工淬硬钢.通过切削实验和性能检测,发现PcBN刀片在加工淬硬钢时cBN浓度起着关键作用,切削同样的路程,低浓度PcBN的后刀面磨损量小.经扫描电镜观察,CoAl合金粉能够提高PcBN烧结刀具材料的致密度.测量耐磨性时,证明用于金刚石复合片PC...     

Modelling the effects of tool-edge radius on residual stresses when orthogonal cutting AISI 316L

Tool-edge geometry has significant effects on the cutting process, as it affects cutting forces, stresses, temperatures, deformation zone, and surface integrity. An Arbitrary-Lagrangian–Eulerian (A.L.E.) finite element model is presented here to simulate the effects of cutting-edge radius on residual stresses (R.S.) when orthogonal dry cutting austenitic stainless steel AISI 316L with continuous chip formation. Four radii were simulated starting with a sharp edge, with a finite radius, and up to a value equal to the uncut chip thickness. Residual stress profiles started with surface tensile stresses then turned to be compressive at about 140 μm from the surface; the same trend was found experimentally. Larger edge radius induced higher R.S. in both the tensile and compressive regions, while it had almost no effect on the thickness of tensile layer and pushed the maximum compressive stresses deeper into the workpiece. A stagnation zone was clearly observed when using non-sharp tools and its size increased with edge radius. The distance between the stagnation-zone tip and the machined surface increased with edge radius, which explained the increase in material plastic deformation, and compressive R.S. when using larger edge radius. Workpiece temperatures increased with edge radius; this is attributed to the increase in friction heat generation as the contact area between the tool edge and workpiece increases. Consequently, higher tensile R.S. were induced in the near-surface layer. The low thermal conductivity of AISI 316L restricted the effect of friction heat to the near-surface layer; therefore, the thickness of tensile layer was not affected.     

PCBN刀具断续车削淬硬钢的试验研究

为了探索PCBN刀具在断续切削条件下刀具的破损规律,选用两种不同的PCBN刀具,在不同强度的断续方式及不同的切削速度下,对淬硬钢进行车削试验研究。根据试验条件,观察了刀具前、后刀面的磨损及破损情况,分析了刀具的失效机理,比较了刀具的切削寿命。结果表明：断续强度严重影响PCBN刀具的使用寿命,断续强度越高,刀具寿命越低;在相同强度的断续条件下,切削速度影响刀具的使用寿命,切削速度越高,刀具的寿命越低;本实验所用的断续条件下,刀具的失效判据为崩刃。     

Cutting forces and surface finish when machining medium hardness steel using CBN tools

Cutting forces generated using CBN tools have been evaluated when cutting steel being hardened to 45–55 HRC. Radial thrust cutting force was the largest among the three cutting force components and was most sensitive to the changes of cutting edge geometry and tool wear. The surface finish produced by CBN tools was compatible with the results of grinding and was affected by cutting speed, tool wear and plastic behaviour of the workpiece material.     

Tool wear and machining performance of cBN–TiN coated carbide inserts and PCBN compact inserts in turning AISI 4340 hardened steel

PCBN is the dominant tool material for hard turning applications due to its high hardness, high wear resistance, and high thermal stability. However, the inflexibility of fabricating PCBN inserts with complex tool geometries and the prohibitive cost of PCBN inserts are some of the concerns in furthering the implementation of CBN based materials for hard turning. In this paper, we present the results of a thorough investigation of cBN plus TiN (cBN–TiN) composite-coated, commercial grade, carbide inserts (CNMA 432, WC–Co (6% Co)) for hard turning applications in an effort to address these concerns. The effect of cutting speed and feed rate on tool wear (tool life), surface roughness, and cutting forces of the cBN–TiN coated carbide inserts was experimented and analyzed using analysis of variance (ANOVA) technique, and the cutting conditions for their maximum tool life were evaluated. The tool wear, surface roughness, and cutting forces of the cBN–TiN coated and commercially available PCBN tipped inserts were compared under similar cutting conditions. Both flank wear and crater wear were observed. The flank wear is mainly due to abrasive actions of the martensite present in the hardened AISI 4340 alloy. The crater wear of the cBN–TiN coated inserts is less than that of the PCBN inserts because of the lubricity of TiN capping layer on the cBN–TiN coating. The coated CNMA 432 inserts produce a good surface finish (<1.6 μm) and yield a tool life of about 18 min per cutting edge. In addition, cost analysis based on total machining cost per part was performed for the comparison of the economic viability between the cBN–TiN coated and PCBN inserts.     

Cryogenic machining as an alternative turning process of normalized and hardened AISI 52100 bearing steel

Environmental and health friendly technologies with economic justification have nowadays an increasing importance in global industrial trends. Idea of global sustainable development dictates cleaner and less health hazardous machining processes. With these limitations in mind, the main issue is now to change the way mechanical components are being machined and move to alternative technologies that could moreover increase the machining performance. Cryogenic machining is one possibility to reach this goal. It consists of a system for cutting (turning, milling, etc.) assisted by liquid nitrogen, which enables a clean process with possible lower production costs and higher productivity. This article presents the results of turning hardened and normalized bearing steel AISI 52100 (DIN 100Cr6), comparing conventional flood and dry with cryogenic machining. Turning results show drastic improvements in tool lifetime (up to 370%) for cryogenic machining of normalized bearing steel 100Cr6 and reduction of thermal residual stress inducements in case of hardened bearing steel 100Cr6, while tool life is also extended.     

DP980激光焊接温度场模拟及力学性能研究

采用光纤激光焊接高强钢DP980,并对温度场分布进行有限元计算。结果表明焊缝中心热循环温度高达3204 ℃,迅速冷却后形成马氏体组织,硬度较母材提高30%,抗拉强度达到了1115.7 MPa,延伸率相对母材下降49.1%。回火区应力应变曲线存在明显的屈服平台,抗拉强度（850.7 MPa）明显低于母材（986.9 MPa）。焊接接头抗拉强度为母材的87.1%,延伸率为母材的32.7%。焊接接头拉伸试样和杯突试样均断于回火区。焊接接头的杯突值较母材下降32.58%,母材主应变值高于焊接接头。