Adhesion analysis and dry machining performance of CVD diamond coatings deposited on surface modified WC-Co turning inserts

This paper investigates the effects of different surface pretreatments on the adhesion and performance of CVD diamond coated WC-Co turning inserts for the dry machining of high silicon aluminum alloys. Different interfacial characteristics between the diamond coatings and the modified WC-Co substrate were obtained by the use of two different chemical etchings and a CrN/Cr interlayer, with the aim to produce an adherent diamond coating by increasing the interlocking effect of the diamond film, and halting the catalytic effect of the cobalt present on the cemented carbide tool. A systematic study is analyzed in terms of the initial cutting tool surface modifications, the deposition and characterization of microcrystalline diamond coatings deposited by HFCVD synthesis, the estimation of the resulting diamond adhesion by Rockwell indentations and Raman spectroscopy, and finally, the evaluation of the dry machining performance of the diamond coated tools on A390 aluminum alloys. The experiments show that chemical etching methods exceed the effect of the CrN/Cr interlayer in increasing the diamond coating adhesion under dry cutting operations. This work provided new insights about optimizing the surface characteristics of cemented carbides to produce adherent diamond coatings in the dry cutting manufacturing chain of high silicon aluminum alloys.     

碳化硅晶须增强铝基复合材料精密加工表面微观形貌

通过采用聚晶金刚石PCD刀具对SiCw增强铝基复合材料在精密数控车床上进行加工试验,使用扫描电子显微镜SEM、原子力显微镜AFM和Talysurf-6型粗糙度轮廓仪对已加工表面进行微观形貌检测和分析,并采用EDAX能谱仪对已加工表面进行化学成分分析.结果表明:第三切削变形区中SiCw所处的不同位向与不同种类的已加工表面微观形貌形成高度的关联度,SiCw的位向是直接影响已加工表面质量的重要因素之一.在A～E五大类SiCw的位向中,A类(α=0°)位向最易使SiCw以直接切断型变形,产生最好的表面质量.E类(α=±90°,且β=0°或β=180.)位向最易使SiCw以拔出或压碎嵌入型变形,形成最差的表面质量.     

金刚石涂层立铣刀与PCD立铣刀切削铝合金性能研究

目的：研究金刚石涂层立铣刀和 PCD 立铣刀切削铝合金时,铝合金表面粗糙度以及刀具的使用寿命。方法通过实验比较1μm、5μm金刚石涂层四刃立铣刀和PCD立铣刀在高速干式切削条件下切削铝合金的性能,并通过走刀距离比较不同状态刀具的使用寿命以及在走刀过程中的粘刀情况,用表面粗糙度测量仪测量加工的铝合金表面粗糙度。结果1μm、5μm金刚石涂层立铣刀加工铝合金失效距离分别为25 m、75 m, PCD立铣刀加工铝合金96 m后失效;1μm、5μm金刚石涂层立铣刀切削铝合金表面粗糙度平均值分别为1.07μm、1.10μm,PCD立铣刀切削铝合金表面粗糙度平均值为0.80μm。结论5μm金刚石涂层立铣刀是1μm金刚石涂层立铣刀寿命的5倍,PCD立铣刀使用寿命最长;1μm、5μm金刚石涂层立铣刀切削铝合金表面较PCD立铣刀粗糙,在相同切削环境下切削铝合金时, PCD立铣刀使用寿命较金刚石涂层立铣刀提高,且在抑制粘刀方面效果十分明显。     

室温脱钴对PCD微观结构及力学性能的影响

为提高PCD使用过程中的热稳定性,选用硫酸-过氧化氢混合溶液在室温下对PCD进行脱钴处理,研究其脱钴机理及脱钴对PCD微观结构及力学性能的影响。通过SEM观察到PCD在室温脱钴48 h后表面出现较大深度的腐蚀坑,钴相基本被去除,上下表面脱钴深度分别为176 μm和162 μm;通过EDS可确定脱钴层剩余钴的质量分数为0.93%,而未脱钴层钴的质量分数为7.64%,表明87.83%的钴在实验中被硫酸-过氧化氢混合溶液溶解而去除。对PCD样品进行残余应力测量,脱钴之前的残余压应力为483.91 MPa,脱钴之后的残余压应力为330.35 MPa,后者相对前者减少31.73%,说明脱钴可以有效降低PCD内部残余压应力。      

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.     

超硬织构化刀具高速切削钛合金试验研究

目的研究高速切削钛合金过程中表面织构对刀具切削性能的影响。方法通过开展常规(无织构)和织构化聚晶金刚石(PCD)刀具高速切削钛合金试验,分析不同条件下切削力、摩擦系数、切削粘结的变化。结果增加切削速度能够有效降低PCD刀具的切削力和摩擦系数。当切削速度为16.485~175.84 m/min时,相对于无织构刀具,织构化刀具的干切削性能在总体上表现最佳,且织构化刀具在干切削时的进给抗力、主切削力和摩擦系数最大分别降低了约71.75 N、39.95 N、0.13。结论高速切削可以显著降低刀-屑界面的切削力、摩擦系数。织构化PCD刀具在低速下的干切削性能明显优于常规刀具,且优于低温润滑条件时的减摩效果。     

A study on micro-hole machining of polycrystalline diamond by micro-electrical discharge machining

Polycrystalline diamond (PCD), with its superior wear and corrosion resistance, is an ideal material for micro-hole parts in the field of microfabrication. This study investigated the micro-hole machining performance for PCDs by micro-electrical discharge machining (micro-EDM). A series of experiments were carried out to investigate the proper machining polarity and the impacts of micro-EDM parameters on machining performance. Experimental results indicate that negative polarity machining is suitable for micro-EDM of PCDs because of the protection brought over by the adhesion sticking to the electrode. An appropriate volume of adhesion on the tool electrode can help to increase the material removal rate (MRR) and reduce the relative tool wear ratio (TWR). By contrast, an excessive volume of adhesion can lead the machining into a vicious circle in which micro-holes are drilled with overlarge diameters. An optimal set of machining conditions was chosen among the investigated ranges of nominal capacitance and electrode rotation speed. An exemplary PCD through-hole, machined under the chosen optimal machining conditions, shows satisfactory machining results.     

PCD和HTi10刀具铣削CFRP试验研究

针对碳纤维复合材料(CFRP)难加工的特性,文中采用PCD和HTi10刀具进行了CFRP铣削试验,对加工过程中的铣削力、刀具磨损和表面粗糙度进行了分析。结果表明:PCD和HTi10刀具的铣削力和表面粗糙度变化规律一致,均随转速的增大而减小,随进给速度的增大而增大,但PCD刀具的铣削力更小,加工质量更好;与HTi10相比,PCD刀具的铣削力对刀具磨损更加敏感,更适合应用在加工环境较好的条件下。在CFRP加工过程中,粗加工时优选HTi10刀具,精加工时优选PCD刀具,宜选用高转速、低进给的切削参数。     

PCD刀具孔加工过程中的切屑控制方法

为消除PCD刀具孔加工过程中出现的划痕，通过分析划痕的类型和出现的原因，设计试验验证优化刀具角度和增加喷淋手段等方式对内孔表面质量的影响。结果显示:入口划痕产生的原因是粗加工刀具产生的铝环切屑残留在工件内，被精加工刀具再次切削时划伤工件内表面。优化喷淋方式对改善入口划痕效果较差；通过调整加工工艺，并优化精加工刀具刃口主偏角(从85°减小到48°)，可以减小铝环厚度并遏制铝环的形成。实际生产显示该方法可消除阀体成品中残留铝环的现象，提高内孔表面质量。      

Effects of electric discharge dressing parameters on polycrystalline diamond micro-tool surface topography and their micro-grinding performances

Polycrystalline diamond (PCD) micro-grinding tools are shaped by using different electro-discharge machining processes, among which wire electro-discharge grinding (WEDG) process is widely accepted due to its capability of producing highly precise, ultra-thin and dimensionally accurate tools. Observing the effects of different WEDG conditions on the tool surface and analyzing the tool's topographic features relevant to micro-grinding are of utmost importance. Current study deals with dressing of polycrystalline diamond tool blanks at different combinations of wire tension and discharge energy to observe the effects of dressing parameters on the tool surface morphology and statistics. Surface roughness, ridge type surface defects and diametrical error in the fabricated tool are analyzed with respect to discharge energy and wire tension. High wire tension produces tools with consistence surfaces and desired diameter. Binder material cobalt is efficiently melted and flushed out from the tool surface at high wire tension, which leads to proper segregation and protrusion of diamond abrasives from the surface. Static abrasive grit density measured by processing the 3D surface data of the tool is found to be ≈165–170 per mm, as compared to theoretically determined value of ≈200 per mm. Micro-slot grinding experiments are carried out on BK7 glass, to quantify the effects of the dressing parameters on the micro-grinding performances of the PCD micro-tools. Cutting forces for all the tools are found to be within 1 N whereas normal force exceeds beyond 1 N. Cutting forces are found to be higher for the tools dressed at high wire tension due to large diameter of the tool as compared to that of undersized tool obtained at low wire tension. Cutting nature is found to be mix of ductile-brittle for the machining conditions adopted in this paper.     

基体热处理使PCD刀具适于断续切削

聚晶金刚石（PCD）刀具的韧性较差,极少用于带有冲击性的断续切削加工,限制了其应用范围。为改良刀具性能,通过热处理工艺优化刀具基体,加固PCD和基体的结合,制成新型的PCD刀具。通过断续切削铝合金实验,分析新型刀具的使用寿命以及表面磨损状况。结果表明:刀具基体优化后,金刚石层与硬质合金基体之间的结合力提高,刀具抗冲击能力提高。新型刀具在切削128 min后没有出现崩刃现象,其磨损量仍在可控范围,适用于断续切削生产。      

Research of the Tribological Properties of the Surface on 16Mn Steel by Plasma Nitriding and S-N-C Plasmas Composite Treatment

Sulfide layer with certain thickness was made on the nitrided surface of 16Mn steel by means of plasma S-C-N composite treatment. Under half lubricated condition, friction coefficient and wear loss of LY12 aluminum alloy were measured in sliding against samples of 16Mn treated by cubrizing and sulphiding respectively; In order to avoid the transfer of aluminum to the steel that lead to the inaccurate measurement of wear loss of carburized samples, Grl5 steel was adopted as counterpart face to measure the wear loss of them. SEM and EDAX were used for the morphological and chemical characterization of the wear surface and longitudinal cross-sections beneath sliding surface of LY12 aluminum alloy cirque and the wear tacks of the carburized samples and sulphided samples. Results show: The surface roughness,wear rate, average friction coefficient and magnitude of friction fluctuations of LY12 aluminum alloy cirque sliding against sulphided sample were all lower than sliding against carburized sample; Compared with carburized layer, sulfide layer of 16Mn steel can not only efficiently prevent the occurrence of adhesion when sliding against LY12 aluminum alloy, but also greatly lower the wear loss when sliding against Gr15 steel.     

Investigation of Influencing Parameters for Tribological Conditions in Dry Forming Processes

Environmental awareness and a growing demand for efficient resource utilization encourage the realization of lubricant-free forming processes. A first step in accomplishing dry sheet metal forming is to gain knowledge about the changing tribological conditions and to identify the relevant influencing parameters. The commonly used flat strip drawing test was selected to investigate the tribological conditions in the flange area of deep drawing processes. The influencing factors of contact pressure and varying drawing velocities were analyzed under dry and lubricated conditions. Additionally,the tool and workpiece surfaces were characterized. Besides lubrication, the contact pressure mainly determines the tribological conditions. In lubricated tests higher normal pressure reduces friction, whereas without lubrication higher pressure results in slightly increasing friction. A changing drawing velocity affects the friction when lubricant is applied. In dry experiments, no influence of velocity was found. Results of surface characterization reveal adhesion as main wear mechanism under dry conditions. Based on the investigated influence of the process parameters, an increase in process understanding for dry forming operations is derived.     

Optimum Me-DLC coatings and hard coatings for tribological performance

In this study, hard coatings (TiN, TiCN, CrN, and CrCN) and Me-DLC coatings (Ti _x%-C:H and Cr _x%-C:H) were deposited on tungsten carbide (WC) substrate by multiarc physical vapor deposition (MAPVD) and unbalanced magnetron (UBM) sputtering, respectively. Counterbodies of the AISI 1045 steel cylinder and the AA7075T651 aluminum cylinder were used in the cylinder-on-disk, line-contact wear mode under dry condition; a counterbody of the AISI 52100 steel ball was used in the ball-on-disk, point-contact wear mode, under both dry and lubricated conditions. All wear tests were conducted with a reciprocating machine. After the tests, the most suitable coating for various counterbodies and test environments was selected. For the coating/1045 steel cylinder, the Ti_10%-C:H coating possesses excellent tribological characteristics. For the coating/7075T651 aluminum cylinder, hard coatings display excellent wear resistance. For the coating/steel ball, CrCN and CrN coatings display very little wear under both dry and lubricated conditions. On TiN and TiCN coatings, special wear mechanisms of material transfer, adhesion wear, and fatigue fracture occurred during initial tests under kerosene lubrication.     

Tapping of Al–Si alloys with diamond-like carbon coated tools and minimum quantity lubrication

The deep hole drilling and tapping of automotive powertrain components made of hypoeutectic Al–Si alloys are of considerable importance. This work investigates the dry and minimum quantity lubricated (MQL) tapping of Al–6.5%Si (319 Al) alloys as alternatives to conventional flooded tapping. Two types of tests were done in comparison with flooded tapping. In the first set dry tapping experiments were performed using diamond-like carbon (DLC) coated and uncoated HSS taps. HSS-dry tapping caused immediate tool failure within less than 20 holes due to aluminum adhesion, resulting in high forward and backward torques. DLC-dry tapping improved tool life considerably and exhibited small torques. The second set of tapping experiments used MQL and only uncoated HSS taps. The use of MQL at the rate of 80 ml/h produced similar average torques to flooded tapping, and a high thread quality was observed. DLC coatings’ low COFs against 319 Al limited the temperature increase during DLC-dry tapping to 75 °C. The low COF of DLC against aluminum was responsible for preventing built-up edge (BUE) formation and thus, instrumental in improving thread quality. The use of MQL reduced the tapping temperature to 55 °C. The mechanical properties of the material adjacent to tapped holes, evaluated using hardness measurements, revealed a notable softening in the case of HSS-dry tapping, but not for MQL tapping. The presence of sulphur and phosphorus-based additives in MQL fluids proved beneficial in preventing aluminum adhesion.     

A study on microgrinding of brittle and difficult-to-cut glasses using on-machine fabricated poly crystalline diamond (PCD) tool

Present study aims to investigate the feasibility of microgrinding difficult-to-machine glass materials with Poly Crystalline Diamond (PCD) tool, which is fabricated on-machine using micro-electrodischarge machining (micro-EDM). A detailed experimental investigation on the mechanism of the process including the effect of micro-EDM machining conditions on tool surface and the effect of grinding parameters on microgrinding performance are presented. In this context, a comparative study on the microgrinding performance of three glass materials (BK7, Lithosil and N-SF14) using on-machine fabricated PCD tool was carried out. It was found that during tool fabrication using micro-EDM process, higher discharge energy generates rougher surface and larger craters on the tool, which can provide higher material removal rate (MRR) during grinding but results in poorer surface finish on glass surface. In addition to micro-EDM conditions of tool fabrication, the roughness of the ground glass surface depends greatly on grinding parameters such as depth of cut, feed rate and tool rotational speed. The surface roughness increases with increasing axial depth of cut and feed rate, whereas higher rotational speed was found to improve the surface finish. Among three types of glass materials, BK7 glass was found to provide better performance in terms of the achieved surface finish and cutting force analysis.     

Evaluation of Vitreous and Devitrifying Enamels as Hot Forming Lubricants for Aluminum AA5083 Alloy

The adhesion of aluminum to tool surfaces during the hot forming of sheet aluminum alloys presents challenging tribological problems. Graphite and boron nitride are commonly used as aluminum adhesion mitigating solid lubricants for hot forming processes, but lubricant breakdown in high-stress areas, such as corners and bends, remains an issue compromising the quality of the formed parts as well as the tool life. Low-melting temperature enamels may provide an affordable and easy to apply alternative. In this study, vitreous (amorphous glass) and devitrifying (two phase crystalline glass) layers were deposited on the surface of sheet aluminum samples with a sedimentation technique. Enamel lubrication was effective in preventing aluminum transfer to the steel counterface. Hence, the prospect exists for the use of these enamels as aluminum workpiece lubricants in hot forming operations. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles Symposium held September 16-20, 2007, in Detroit, MI.     

PCD刀具加工有色金属的研究

本文主要研究PCD刀具加工有色金属时刃口及后刀面的刃磨质量对切削表面质量的影响。首先对PCD刀具切削有色金属模型进行了分析研究,然后分别采用金属结合剂金刚石砂轮、树脂结合剂金刚石砂轮和陶瓷结合剂金刚石砂轮刃磨出三把不同质量的PCD刀具进行了切削对比试验,并用扫描电镜对切削表面微观形貌进行了观察分析,发现加工有色金属时,PCD刀具后刀面与刃口刃磨质量对切削表面质量有着同等重要的影响作用。     

复合镀覆Ti—Ni金刚石的钎焊应用

镀覆技术的研究进展表明：经过真空微蒸发镀钛、钨的金刚石单晶或聚晶,可以采用化学镀或电镀的方法在钛或钨镀层上进一步镀覆镍、钴、铬等金属,这种复合镀层与金刚石界面强力冶金结合,并且可以采用各种钎焊方法实现金刚石与多种金属基体的焊接。复合镀覆的金刚石可用于各类表镶工具的制造,获得高出刃、高磨粘结合强度,使金刚石表镶工具的使用寿命和加工效率大幅度提高。     

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。