铍铜合金断续切削后刀面磨损机理研究

目的研究断续切削过程温度变化对刀具粘结现象、涂层剥落和刀具磨损的影响。方法搭建了仿铣削加工的断续车削实验平台,采用热电偶法测量了断续切削过程中刀具后刀面在不同速度下的切削温度,利用带有能谱仪(EDS)的扫描电镜(SEM)观察后刀面随速度变化的磨损形貌并分析后刀面磨损区域的元素组成,阐述了后刀面温度和刀具磨损之间的联系,研究了Ti AlN涂层硬质合金刀具断续切削铍铜合金C17200时的后刀面磨损机理。结果随着切削速度的增加,刀具温度在v=500 m/min出现峰值,温度越高,后刀面的涂层剥落和粘结磨损现象越严重,涂层剥落和粘结磨损现象在切削速度为500 m/min时最严重,而后随着刀具温度的降低而减缓,切削速度600 m/min时的涂层剥落和粘结磨损现象相比500 m/min时有所减轻。结论断续切削过程中,刀具持续性地经受"负载-卸载"、"升温-降温"产生的高温、冲击和加工环境的不稳定性,是引起粘结现象、涂层剥落和刀具磨损的主要原因。涂层剥落和粘结磨损是导致铍铜合金断续切削刀具失效的主要磨损形式。     

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.     

Cutting performance of PVD-coated carbide and CBN tools in hardmilling

In this study, cutting performance of CBN tools and PVD-coated carbide tools in end-milling of hardened steel was investigated. In high-speed dry hardmilling, two types of CBN tools were applied: the CBN-rich type and an ordinary one. In the case of relatively low-speed milling, on the other hand, a few coated carbide tools were selected where four kinds of coating films, TiN, TiCN, TiAlN and multi-layered TiAlN/AlCrN, were deposited on the K10 and P30 grade carbide. The cutting performance was mainly evaluated by tool wear, cutting temperature, cutting force and surface roughness. In dry cutting of hardened carbon steel with the ordinary CBN tool, the cutting tool temperature rose rapidly with increase in cutting speed; and tool temperature reached approximately 850 °C at the cutting speed of 600 m/min. In the case of the CBN-rich tool, the cutting temperature decreased by 50 °C or more because of its high thermal conductivity. It is remarkable that tool wear or damage on a cutting tool was not observed even when the cutting length was 156 m in both CBN tools. In the case of coated carbide tools, the temperatures of TiN-, TiCN- and TiAlN-coated carbide tools rose as cutting proceeded because of the progress of tool wear, but that of TiAlN/AlCrN-coated carbide tool hardly rose due to little tool wear. When the base material was K10 grade carbide, tool temperature was lower than that of P30 with any coating. The tool flank wear depends considerably on hardness and oxidizing temperature of the coating film.     

A review of research related to Salomon's hypothesis on cutting speeds and temperatures

This paper is a review of literature which considers the theory put forward by Dr. Carl Salomon in 1931 that the temperature created by cutting metal increased with cutting speed up to a certain point and then started to decrease as the cutting speed continued to climb.The conclusion is that the theory is not valid for the tool–work interface temperature, but could be true for the surface temperature of the workpiece. More research needs to be carried out to verify this.     

An experimental method for studies of intermittent cutting at small cutting depths

Most devices for metal cutting experiments are designed to simulate continuous cutting at relatively large cutting depths. However, there is also a need for techniques to study the more complex situations prevailing in other important cutting operations like milling, sawing, hobbing, shaper cutting and grinding. These operations are characterized as being intermittent and having a relatively small and varying cutting depth per edge. In order to supply an experimental set-up for basic studies of chip formation and cutting forces under these conditions a new method for single stroke, single edge metal cutting has been developed.

The experiments are performed in a modified Charpy pendulum which offers force measurement and accurate selection of cutting speed and feed in the ranges typical of many intermittent cutting operations. The equipment is also provided with an excellent quick-stop mechanism to aid in chip formation studies.

The test method is described in detail and examples of metallographical and scanning electron microscopical studies of quick-stopped samples as well as registrations of specific thrust and cutting forces are presented.     

PcBN刀具材料在高速硬态切削中的应用研究

简要介绍了PcBN刀具材料的高压高温烧结制备方法及其物理力学性能特点、高速切削技术与硬态切削技术的特点以及PcBN刀具材料对高速硬态加工的适应性。分析和探讨了高速硬态切削对PcBN材料性能的要求,认为限制PcBN应用于高速硬态切削的主要是其高温力学性能,包括高温强度、高温硬度、高温韧性等。介绍了目前国外高速切削用PcBN材料的研究新进展,列举了PcBN刀具应用于高速硬态加工领域的实例,指出纳米级无任何粘结剂的PcBN刀具材料的开发与应用对推动我国的高速切削加工技术具有十分重要的意义。     

PcBN刀具连续车削淬硬钢性能的研究

为了研究PcBN刀具在干式连续车削条件下刀具的性能,选用两种不同的PcBN刀具,在不同切削速度及不同工件硬度条件下,对淬硬钢进行车削试验。在此基础上,对刀具前、后刀面的显微形貌特征进行了观察,分析了刀具的失效机理。结果表明:切削速度对刀具的切削寿命影响很大,随着切削速度的增加刀具寿命几乎线性下降。硬度也是影响刀具切削寿命的重要因素之一,当v190 m/m in时,刀具切削硬度为(64±1)HRC工件的寿命比相同条件下切削硬度为(61±1)HRC工件的寿命下降约40%~60%。刀尖温度随着切削速度的增加不多,切屑温度要比刀尖温度高出许多。在本试验中,刀具的失效判据为崩刃或后刀面平均磨损超过0.3 mm。     

陶瓷刀具断续车削淬硬钢失效形态研究

采用Al_2O_3/Ti(C,N)陶瓷刀具进行淬硬钢的断续车削正交试验,对不同切削速度下刀具的失效形态进行了对比。结果表明,低速时,刀具的失效形态主要是崩刃和前刀面剥落,疲劳破损影响较小。随着切削速度的增加,疲劳破损对刀具的影响逐渐增大。高速时,疲劳裂纹扩展引起的破损成为刀具主要失效形式。在不同切削速度下,刀具内部的应力水平不同,导致裂纹扩展速率及裂纹方向有所差异,疲劳特征则表现出不同形式。低速时疲劳特征表现为疲劳条带,而高速时的疲劳特征通常为疲劳弧线。     

Impact Resistance of PVD Films and Milling Performance of Coated Tools at Various Temperature Levels

Impact tests were conducted on coated cutting inserts, revealing that a temperature increase at first enhances the coating impact resistance, and then leads to its non-linear deterioration. On the other hand, milling investigations with coated cemented carbide inserts demonstrated that the cutting speed increase, up to a certain level, causes initially a significant improvement of the cutting performance. FEM calculations of the developed temperature and stress fields during cutting provided additional insights. The joint study and the subsequent correlation of the aforementioned results, renders the impact test as a convenient and efficient methodological tool for the characterization of coated tools' cutting performance.     

Cutting temperature of ceramic tools in high speed machining of difficult-to-cut materials

This paper deals with an experimental and analytical investigation into the different factors which influence the temperature distribution on Al₂O₃---TiC ceramic tool rake face during machining of difficult-to-cut materials, such as case hardened AISI 1552 steel (60–65 Rc) and nickel-based superalloys (e.g. Inconel 718). The temperature distribution was predicted first using the finite element analysis. Temperature measurements on the tool rake face using a thermocouple based technique were performed and the results were verified using the finite element analysis. Experiments were then performed to study the effect of cutting parameters, different tool geometries, tool conditions, and workpiece materials on the cutting edge temperatures. Results presented in this paper indicate that for turning case hardened steel, increasing the cutting speed, feted, and depth of cut will increase the cutting edge temperature. On the other hand, increasing the tool nose radius, and angle of approach reduces the cutting edge temperature, while increasing the width of the tool chamfer will slightly increase the cutting ege temperature. As for the negative rake angle, it was found that there is an optimum value of rake angle where the cutting edge temperature was minimum. For the Inconel 718 material, it was found that the cutting edge temperature reached a minimum at a speed of 510 m/min, and feed of 1.25 mm/rev. However, the effect of the depth of cut and tool nose radius was almost the same as that determined in the turning of case hardened steel. It was also observed in turning Inconel 718 with ceramic tools that, cutting forces and different types of tool wear were reduced with increasing the feed.     

Cutting performance of diamond tools during ultra-precision turning of electroless-nickel plated die materials

This study is an attempt (a) to observe the wear characteristic of diamond tool with 200 km cutting distance and to study the effects of wear on the surface roughness and cutting forces and (b) to optimize various cutting parameters such as depth of cut, feed rate, spindle speed and phosphorus content. The experimental results showed that tool wear was not so significant although some defects on rake face were observed after cutting 15.6 km. Further cutting showed that the surface roughness increases with cutting distance, and that the cutting forces were larger than thrust force at the beginning of cutting, but after cutting 130 km, thrust force became larger and increased rapidly. It was also observed that forces increase with the increase of depth of cut, spindle speed and feed rate, and decrease with the increase of phosphorus content of the plating. Depth of cut has no significant effect on surface roughness, while it increases with increase of feed rate and decreases with the increase of percentage of phosphorus content in the workpieces. In case of spindle speed, surface roughness decreases with the increase of spindle speed up to a certain value and then starts to increase with the increase of spindle speed.     

Intermittent metal cutting at small cutting depths—2. Cutting forces

Cutting forces in intermittent metal cutting at small cutting depths were investigated by single edge experiments. Single cutting strokes were performed in a modified Charpy pendulum tester which offers cutting and thrust force measurement and accurate selection of cutting speed and feed in ranges typical for many intermittent high speed steel (HSS) tool operations.

The cutting performance of a number of double rake HSS edges, with primary rake angles ranging from +20° (“parrot bill”) to −60°, all with a preground 0.1 mm flank length were tested in two steel grades (one plain carbon and one austenitic stainless). Some of the edge geometries were tested also in TiN coated condition. The relative performance of the different edges was investigated with respect to specific cutting and thrust forces. The influence of cutting length and depth, edge micro geometry, TiN coating and cutting speed is discussed specifically.

Among the most important observations were:

• The cutting and thrust forces at a fixed cutting depth may change significantly during the short (25–30 mm) cuts.

• The chamfer formed by a double rake geometry with negative primary angle increases the forces.

• For these chamfered tools the forces increase linearly with the projected flank length. TiN coating increases rather than reduces the forces during these short cuts.

The relationships between the varied parameters and chip formation phenomena like dead zone formation, chip curl and surface finish were presented in part 1 of this paper.     

陶瓷刀具断续车削淬硬钢切削力和切削温度的有限元分析

为揭示Al2O3/(W,Ti)C陶瓷刀具断续车削淬硬钢时的切削力、刀具温度以及刀具应力的变化规律及相互关系,采用有限元方法进行金属切削仿真。仿真结果表明,断续车削过程中,刀具承受十分明显的周期性机械载荷冲击与热载荷冲击;单个切削周期内机械载荷与热载荷的变化规律体现了两者的密切相关性以及时间上的不一致性;由于剪切角偏转的影响,刀具最大主应力显著增大,所以切出过程对刀具破坏的作用尤为严重。     

Intermittent metal cutting at small cutting depths—1. Dead zone phenomena and surface finish

Chip formation in intermittent metal cutting at small cutting depths was investigated by single edge experiments. Single cutting strokes were performed in a modified Charpy pendulum tester which offers force measurement, accurate selection of cutting speed and feed in the ranges typical of many intermittent high speed steel (HSS) tool operations. The pendulum is also provided with an excellent quick-stop mechanism.

The cutting performance of HSS tools in three widely used steel grades (including one plain carbon, one quenched and tempered and one austenitic stainless steel) was studied. A number of double rake micro geometries, with primary rake angles ranging from +20° (parrot bill) to −60°, all with a prepared 0.1 mm wear land were tested. The performance of the different edge geometries was investigated with respect to class of dead zone developed on the cutting edge, and its relation to chip curl and finish of the cut surface. The results are visualized in a dead zone map. The influence of cutting length, cutting speed, cutting depth and TiN-coating was treated specifically.

Among the most important observations were:

• the micro geometry of the edge influences the dead zone formation mechanism and hence the class of dead zone,

• the surface finish is strongly dead zone class dependent,

• the chip curl is determined by edge micro geometry and dead zone class.

The relationships between the varied parameters, generated dead zones and resulting cutting forces are presented in part 2 of this paper.     

Theoretical modelling and simulation of cutting forces in face milling with cutter runout

A new approach to theoretical modelling and simulation of cutting forces in face milling is presented. Based on a predictive machining theory, the action of a milling cutter is modeled as the simultaneous actions of a number of single-point cutting tools. The milling forces are predicted from the workpiece material properties, cutter parameters, tooth geometry, cutting conditions and types of milling. The properties of the workpiece material are considered as functions of strain, strain-rate and temperature in the cutting region. It takes into account the effect of the intermittent contact between each milling tooth and the workpiece on the temperature in the cutting region. It also takes into account the effect of cutter runout on the undeformed chip thickness. Milling experiments have been conducted to verify the proposed model. Good agreements between the experimental and simulated results are presented.     

Characterization and optimization of vibration-assisted drilling of fibre reinforced epoxy laminates

Vibration-assisted drilling (VAD) can reduce thermal and mechanical defects associated with drilling of composites. Machinability maps are presented to establish the effect of the process parameters (speed, feed, frequency, and amplitude) in the low frequency–high amplitude regime (<200 Hz, <0.6 mm) on the hole quality attributes. The optimized VAD conditions can reduce the cutting temperature by 50% and the axial force by 40% and produce delamination-free holes, without affecting productivity. It is demonstrated that the intermittent cutting in VAD redistributes the cutting energy over the engagement cycles. This enhances the tool cooling and substantially reduces the axial force component.     

切削参数对碳钢微量润滑切削温度的影响

为了了解切削参数影响碳钢微量润滑切削温度的规律,通过45钢的车削实验,利用自然热电偶测温,探明在干切削、传统浇注润滑和微量润滑条件下,不同切削参数对切削温度的影响及原因。实验结果表明:MQL切削温度随切削参数增大而上升,切削速度对MQL温度影响最大,切削深度影响最小;在低切削速度时,MQL冷却效果优于传统浇注润滑,在中、高速时,MQL冷却效果比浇注润滑差;MQL冷却能力随切削速度和进给量增大而减弱,不随切削深度而变化。     

碳纤维增强热塑性复合材料螺旋铣磨制孔损伤研究

目的 研究碳纤维增强热塑性复合材料(CFRTP)螺旋铣磨制孔的切削温度和切削力的变化趋势,以及典型制孔损伤的特点,并分析切削温度的下降对制孔损伤的影响。方法 采用螺旋铣磨的方法开展CFRTP的制孔试验研究,通过改变工艺参数研究切削温度、切削力的变化趋势,分析各类典型制孔损伤的特点、形成原因及随工艺参数的变化情况,并研究添加冷却辅助降低切削温度对抑制制孔损伤的效果。结果 随着刀具自转转速、公转转速和螺距的升高,切削温度分别升高了约46.43%、12.06%和95.97%;切削力随着自转转速的升高而降低,随着公转转速和螺距的升高而增大。当螺距达到0.45mm时,轴向力会有所下降。入口损伤和出口损伤主要以毛刺为主,损伤会随着各工艺参数的升高而加剧,孔壁损伤主要表现为涂覆、变形、裂纹等3种形式。添加冷却辅助后,制孔质量得到显著提高,高温下的刀具涂覆问题基本解决。结论 切削温度是影响CFRTP制孔质量的主要因素,切削温度的升高导致树脂基体软化,使得切屑形貌从粉末状转变为连续薄片状,进而对切削力产生影响,树脂软化对制孔损伤有着明显的影响。冷却辅助能够明显地降低切削温度,从而起到抑制损伤的作用。     

Heat generation and temperature prediction in metal cutting: A review and implications for high speed machining

Determination of the maximum temperature and temperature distribution along the rake face of the cutting tool is of particular importance because of its controlling influence on tool life, as well as, the quality of the machined part. Numerous attempts have been made to approach the problem with different methods including experimental, analytical and numerical analysis. Although considerable research effort has been made on the thermal problem in metal cutting, there is hardly a consensus on the basics principles. The unique tribological contact phenomenon, which occur in metal cutting is highly localized and non-linear, and occurs at high temperatures, high pressures and high strains. This has made it extremely difficult to predict in a precise manner or even assess the performance of various models developed for modelling the machining process. Accurate and repeatable heat and temperature prediction remains challenging due to the complexity of the contact phenomena in the cutting process. In this paper, previous research on heat generation and heat dissipation in the orthogonal machining process is critically reviewed. In addition, temperature measurement techniques applied in metal cutting are briefly reviewed. The emphasis is on the comparability of test results, as well as, the relevance of temperature measurement method to high speed cutting. New temperature measurement results obtained by a thermal imaging camera in high speed cutting of high strength alloys are also presented. Finally, the latest work on estimation of heat generation, heat partition and temperature distribution in metal machining is reviewed. This includes an exploration of the different simplifying assumptions related to the geometry of the process components, material properties, boundary conditions and heat partition. The paper then proposes some modelling requirements for computer simulation of high speed machining processes.     

High-speed rotary cutting of difficult-to-cut materials on multitasking lathe

This paper aims to realize the high-speed rotary dry cutting of an Inconel 718 at 500 m/min on a multitasking lathe which has an additional milling spindle with an X/Y/Z-axis and inclination control. A series of experiments were conducted and are discussed with respect to the tool face temperature analysis by FEM. It was verified that it is necessary to select an optimum inclination angle, tool rotation speed and tool diameter so as to enable the main cutting force direction to align with the highest rigidity direction of an applied rotary tool. Under preferable cutting conditions, the average tool rake face temperature measured by a thermograph camera was about 300 °C even at a high cutting speed of 500 m/min under dry cutting conditions, and the tool wear decreased dramatically compared with the conventional tools.