6-Axis control cutting of overhanging curved grooves by means of non-rotational tool with application of ultrasonic vibrations

This paper presents a new machining method that efficiently cuts overhanging curve grooves on wall surfaces without causing a collision between the tool and the workpiece. It also describes the development of software for 6-axis control grooving and the effect of applied ultrasonic vibrations (USV) in cutting overhanging grooves (OHG). In general, rotational tools are used to produce grooves, thus resulting in long circular arc segments at the cutting end points, as well as placing restrictions on the manufacture of grooves with continuous change in curvature, while ensuring that they do not overshoot the side clearance angle of the cutting edge with the groove. The study aims at machining OHGs presently impossible to machine by conventional methods. From the experimental results, it was found that the new machining method, which is 6-axis control cutting using a non-rotational tool with the application of USV, is capable of cutting an OHG on wall surfaces correctly.     

A fine tool servo system for global position error compensation for a miniature ultra-precision lathe

There is an increasing demand for single-point diamond turning to manufacture micro components as well as micro features on a large workpiece surface. In order to obtain high accuracy and a fine surface finish of the large area workpiece, position control of machine tool has become the main concern to achieve the high precision position control. A coarse-fine servo system is able to provide a cost-effective solution. This system can provide information on the entire guidance errors profile data and simultaneously compensate the error in real-time by using the fine position control technique. In this study, a piezoelectric actuator based fine tool servo (FTS) system has been developed and it has been incorporated with a miniature ultra-precision lathe. A cost-effective position sensitivity detector (PSD) is integrated in the FTS design, which is able to measure the global straightness error of the translational slide accurately. The detected error signals are compensated by the FTS during the turning process. For better tracking performance, a proportional-integral (PI) feedback controller has been implemented and tested in this study. Experimental results show that the developed FTS can effectively and successfully compensate the micro waviness error which is caused by the x-axis translational slide of the miniature ultra-precision lathe.     

Tool wear control in single-crystal diamond cutting of steel by using the ultra-intermittent cutting method

Excessive tool wear is a major drawback to the ultraprecision cutting of steel with geometrically defined single-crystal diamond tools. This paper presents a new approach to reduce this wear. In general, the wear of the diamond tool is due to chemical reactions such as diffusion into the steel, oxidation, graphitization, and carbide formation under cutting conditions of high temperature and high pressure. To suppress these types of chemical reactions, the contact time between the diamond tool and the steel in the cutting process was controlled by intermittent cutting method such as fly-cutting or milling. A series of intermittent cutting experiments were carried out to control the tool–workpiece contact time in one cutting cycle by changing the cutting speed and cutting length in each cutting cycle. The experimental results showed that the diamond tool wear was highly dependent on the tool–workpiece contact time, regardless of the cutting speed, and that the wear was greatly reduced by decreasing the contact time to less than 0.3 ms under these cutting conditions. It is expected that steel can be successfully cut with a single-crystal diamond tool by controlling the tool–workpiece contact time.     

Modelling and simulation of chatter in milling using a predictive force model

A predictive time domain chatter model is presented for the simulation and analysis of chatter in milling processes. The model is developed using a predictive milling force model, which represents the action of milling cutter by the simultaneous operations of a number of single-point cutting tools and predicts the milling forces from the fundamental workpiece material properties, tool geometry and cutting conditions. The instantaneous undeformed chip thickness is modelled to include the dynamic modulations caused by the tool vibrations so that the dynamic regeneration effect is taken into account. Runge–Kutta method is employed to solve the differential equations governing the dynamics of the milling system for accurate solutions. A Windows-based simulation system for chatter in milling is developed using the predictive model, which predicts chatter vibrations represented by the tool-work displacements and cutting force variations against cutter revolution in both numerical and graphic formats, from input of tool and workpiece material properties, cutter parameters, machine tool characteristics and cutting conditions. The system is verified with experimental results and good agreement is shown.     

Effect of various parameters on the surface roughness of an aluminium alloy burnished with a spherical surfaced polycrystalline diamond tool

The effect of various parameters on the surface roughness of an aluminium alloy burnished with a spherical surfaced polycrystalline diamond tool are studied experimentally with a theoretical analysis. Problems in selecting the optimum burnishing parameters and some burnishing mechanisms are discussed. With suitable parameters employed, the new no-chip finishing process developed can eliminate or reduce the cutting marks left on the workpiece surface by diamond cutting tools, with its surface roughness reduced to Ra=0.026 μm from the original 0.5 μm.     

CVD金刚石涂层刀具切削性能与磨损机理研究

针对普通刀具切削质量差、刀具耐用度低等问题,对CVD涂层刀具制备方法及切削性能进行研究。首先以硬质合金刀具为基体通过CVD方法制备金刚石涂层,分析涂层表面形貌。然后在不同条件下进行铝合金材料的干式切削试验,分析金刚石涂层对切削力、切削温度以及工件表面粗糙度的影响规律。最后,通过对刀具磨损机理的分析,讨论涂层对刀具使用寿命的影响。研究结果表明,所制备的涂层刀具能够降低切削力和切削温度,大大提高刀具的切削性能和工件的表面质量,并能有效提高刀具使用寿命。     

人造金刚石新型槽刀的研制

本文针对硬质合金刀具切削中硅铝合金活塞槽存在的问题,研制出一种新型人造金刚石切槽刀。使用该刀,加工效率可提高二倍,加工成本降低62％,并且还提高了加工精度。从本文研究结果可以看出,人造金刚石刀具加工硅铝合金与硬质合金刀具相比,具有许多优点,是值得进一步开发和推广的刀具。本文不仅探讨了人造金刚石切槽刀的制造,还探讨了对刀具备参数的检测。     

Research Progress of Diamond Tool Machining Technology for Ferrous MetalsEI北大核心CSCD

金刚石刀具是超精密加工最理想的刀具之一,但在黑色金属超精密加工领域“石墨化”导致刀具快速磨损,其应用极大地受到了限制。首先,针对金刚石刀具的磨损机理进行介绍。然后,综述金刚石刀具切削黑色金属的几种常见方法,如刀具表面改性、工件表面改性、低温辅助切削、超声振动辅助切削等,通过研究实例来分析各方法的应用效果和存在问题,并从技术层面分析影响金刚石刀具在黑色金属加工领域发展的关键因素。最后,对金刚石刀具切削黑色金属未来的发展趋势进行探讨。总结金刚石刀具在黑色金属领域的加工方法,分析加工黑色金属时抑制金刚石刀具磨损的核心技术,对黑色金属的精密超精密加工具有重要的引领和推动作用。     

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.     

Using PCD for machining CGI with a CO2 coolant system

Polycrystalline diamond is widely used as a economic cutting material for machining non-ferrous materials such as aluminum. It is perceived that diamond cannot be used for cutting ferrous materials due to the high affinity of carbon to iron. Nevertheless, under certain conditions it is possible to use diamond materials for cutting ferrous metals. In order to avoid graphitization of the diamond matrix, it is necessary to keep the cutting temperature below the critical level of diamond graphitization. This paper presents the influence of a cryogenic CO₂ coolant strategy on the cutting process using PCD tools for cutting high strength compacted graphite iron (CGI). Investigations show, that tool wear behavior strongly correlates with the cutting speed, the cutting forces, cutting temperatures, and surface roughness of the workpiece. The test results show, that the tool life of PCD for cutting cast iron is dependent on the diamond grain size, the binder material, and the cutting parameters.     

Measurement of slide error of an ultra-precision diamond turning machine by using a rotating cylinder workpiece

Two measurement methods of using a rotating cylinder workpiece, which are referred to as the one-probe method and the two-probe method, respectively, are proposed for measurement of the horizontal error motion (X-directional error motion) of the Z-slide of an ultra-precision diamond turning machine. In the one-probe method, a displacement probe mounted on the opposite position of the turned (self-cut) cylinder workpiece with respect to the cutting tool is moved by the Z-slide to scan the workpiece being rotated by the spindle with its axis of rotation along the Z-axis. The Z-slide error can be obtained by an averaged output of the probe over one rotation without the influence of the spindle error and the surface form error of the cylinder. In the two-probe method, in addition to the displacement probe used in the one-probe method, another displacement probe is mounted at the position of the cutting tool. The rotating cylinder is scanned along the Z-direction by the two displacement probes simultaneously and the Z-slide error can be accurately measured by using the averaged output of the two probes over one rotation. Both the methods can measure not only the out-of-straightness component of the slide error but also the out-of-parallelism of the Z-slide axis with respect to the spindle axis. Experiments are carried out to verify the feasibility of the proposed methods.     

Analysis of orthogonal finish machining using tungsten carbide and diamond tools of different heat transfer coefficients

An orthogonal cutting model for finish machining, using diamond and tungsten carbide tools which have different coeffficients of thermal conductivity, was simulated and analyzed. It was assumed that the tool had a minute amount of tool flank wear. The distribution of strain rate and stress within the machined workpiece and the determination of the cutting force were obtained after simulation. The generation and distribution of temperature and stress within the chip through cutting of the workpiece were also acquired. In addition, the temperature of the tool, the workpiece and the chip during finish machining by the two different tools, that show the effects of the different friction coefficients of the diamond tool and the tungsten carbide tool on cutting, were compared. Finally, the cutting forces predicted by the model for orthogonal finish machining were compared with those obtained by experiment, and it appears that the present orthogonal finish machining model is reasonable.     

研磨刀架结构对金刚石刀具刃口质量的影响

金刚石刀具刃口锋利度和刀面表面粗糙度对所加工零件的质量有着重要影响。较好的研磨刀架结构将有助于降低因刀架而产生的振动扰动,获得高质量的刀具刃口。通过改进刀架结构,使刀具刃口锋利度从300 nm提高到了50 nm,表面粗糙度从15 nm提高到了0.5 nm,刀具刃口质量得到了明显改善。     

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。      

The influence of the microstructure of hardened tool steel workpiece on the wear of PCBN cutting tools

Due to the recent developments of advanced cutting tool materials in the superbarasive family, such as cubic boron nitride (CBN) tools, the interest in cutting hardened steels has increased significantly. High flexibility and ability to manufacture complex workpiece geometry in one set up is the main advantage of hard turning compared to grinding. The focus of this study is to investigate the performance and wear behavior of CBN tools in finish, dry turning of four different hardened steels, treated to the same hardness R_c = 54. The following four materials were machined: X155CrMoV 12 cold work steel (AISI D2), X38CrMoV5 (AISI H11) hot work steel, 35NiCrMo16 hot work steel and 100Cr6 bearing steel (AISI 52100). A large variation in tool wear rate was observed in the machining of these steels. The tool flank grooves have been correlated to the microstructure of these steels, namely the presence of various carbides. The chip study reveals that there is presence of different amounts of white layers in machining these steels.     

Effects of micro-milling conditions on the cutting forces and process stability

Determining stable cutting conditions for corresponding cutting tools with specific geometries is essential for achieving precision micro-milling with high surface quality. Therefore, this paper investigates the influence of the tool rake angle, tool wear and workpiece preheating on the cutting forces and process stability. An advanced micro-milling cutting force model considering the tool wear is proposed. The micro-milling cutting forces are predicted and compared with experimentally obtained results for two cutting conditions and four edge radii measured at different stages of the tool wear. It is found that the cutting forces increase by increasing the edge radius. It is also observed that the cutting forces are higher at a rake angle of 0° compared with a rake angle of 8°. The increase of the cutting forces is mainly associated with the change of the friction conditions between the tool and workpiece contact. Stability lobes are obtained for different edge radii, rake angles of 0° and 8°, initial workpiece temperature and different measured static run-outs. The predicted stability lobes are compared with the micro-milling force signals transformed into the frequency domain. It is observed that the predicted stability limits result in good correlation with the experimentally obtained chatter free conditions. Also, the stability limits are higher at smaller edge radii, higher preheating workpiece temperature and positive rake angles.     

金刚石薄膜与WC-Co硬质合金结合力的改善

利用SEM,XRD研究了Murakami溶液和H2等离子体处理对硬质合金表面形貌、物相结构的影响,并对硬质合金工具进行了复合金刚石薄膜涂层,采用压痕法和实际钻削实验检测了金刚石薄膜／基体间的结合力．结果表明,微米／纳米复合金刚石薄膜涂层分布均匀,具有低的表面粗糙度,Murakami溶液处理硬质合金可产生均匀的表面沟槽,其金刚石薄膜与基体间的临界载荷约为1．5kN,而用该方法制备的涂层钻头加工性能很差,H2等离子体处理促进了硬质合金基体表面的WC晶粒更加粗大、致密,其临界载荷超过1．5kN,用该方法制备的涂层钻头的加工性能优良。     

A study of the diamond tool wear suppression mechanism in vibration-assisted machining of steel

Inability of machining steel strongly inhibits the application of diamond machining in manufacturing industry, especially in the fields of ultra-precision and micro machining. In recent years, vibration-assisted machining (VAM) has been proved to be capable of efficiently suppressing the diamond tool wear in cutting steel. Currently, the prevailing speculation claimed by most researchers for such suppression is that the tool–workpiece flash temperature was reduced in VAM, which would slow the chemical reaction between iron on steel and carbon on diamond. However, the correctness of this speculation has not been proved by any experimental or theoretical research. In this paper, in order to understand the true wear suppression mechanism of diamond tools in VAM of steel, a study is conducted by measuring the workpiece temperatures and modeling the cutting energy consumption in both VAM and conventional cutting (CC). Based on the comparison results, it is concluded that the cutting temperature and energy consumption in VAM are not smaller than in CC, and hence the reduced diamond tool wear in VAM should not be caused by the claimed reduced temperature, especially when the material removal rate is very small. Finally, based on the EDS analysis and the comparison of experimental results under different air pressure, two probable reasons are proposed for the significantly reduced diamond tool wear in VAM of steel: (i) increase of gas pressure at the tool–workpiece interface and (ii) generation of an oxide layer on the freshly machined surface.     

Identification of machine–tool–workpiece system dynamics

The aim of this paper is to present a method to identify the dynamics of a structure composed of a milling machine, a tool and a workpiece. The excitation is obtained as a result of the interrupted cutting of a narrow workpiece width and single tooth milling operations. This provides a pulse-like cutting force. The three components of the cutting force and the relative motion between the tool and the workpiece are measured simultaneously. A method was developed to determine the nine terms of the structural transfer matrix under a single cutting operation and without any assumption on the excitation direction. The proposed method is experimentally validated.     

Comparison between multi-point and other 5-axis tool positioning strategies

A method of generating sculptured surfaces at multiple points of contact between the tool and the workpiece was developed and proven viable by the current authors in previous work. They denoted this finish machining method, “Multi Point Machining”, or simply MPM. This paper compares MPM with two other 5-axis tool positioning strategies; namely: the inclined tool, and the principal axis method. It is also compared with 3-axis ball nose machining. Comparisons are conducted using computer simulations and experimental cutting tests. Results obtained show that MPM produced scallop heights that are much smaller than those produced by the other tool positioning strategies.