Grinding performance and workpiece integrity when superabrasive edge routing carbon fibre reinforced plastic (CFRP) composites

Data is presented for wheel wear, cutting forces and workpiece integrity when high speed routing 10 mm thick CFRP laminates using single layer electroplated diamond and CBN grinding points as opposed to standard end milling tools. A 60,000 rpm retrofit spindle was utilised to accommodate the 10 mm diameter wheels having grit sizes of 76, 151 and 252 μm employed under either roughing or finishing parameters. Wear of CBN points exhibited a near two-fold increase over diamond with a similar ratio for cutting forces. Despite use of flood cooling, point geometry when roughing compromised life and integrity due to excessive clogging.     

Development of ultra-fine-grain binderless cBN tool for precision cutting of ferrous materials

A new cutting tool was developed from ultra-fine-grain (<100 nm), binderless cubic boron nitride (cBN) material fabricated by transforming hexagonal boron nitride to cBN by means of sintering under an ultra-high pressure of 10 GPa at 1800 °C. The cutting edges of the newly developed cBN tool can be made as sharp as those of single-crystal diamond tools. In this experiment, cBN and single-crystal diamond tools of the same shape were compared by precision cutting tests using stainless steel specimens and steel specimens coated with an electroless Ni-P layer. The surface roughness (R_z) of specimen surfaces cut with the cBN tool by means of planing was approximately 100 nm for both the Ni-P-coated steel and stainless steel specimens. Though similar R_z values were obtained for Ni-P layers cut by the cBN and diamond tools, an R_z value exceeding 2000 nm was obtained for stainless steel cut by the diamond tool. High-precision surfaces with R_z values of 50–100 nm were obtained for stainless steel specimens cut with the cBN tool under high-speed milling (942 m/min) conditions. These results indicate that the newly developed cBN tool is useful for the ultra-precision or precision cutting of ferrous materials.     

Analysis of the manufacturing chain of CVD diamond coated shaft type cutting tools

Hypereutectic aluminium silicon alloys, e.g. casted AlSi17Cu4Mg, are commonly used in the automotive and aeronautical industries. These alloys consist of hard, abrasive silicon particles in a soft aluminium matrix and thus place high mechanical loads on the tool during machining processes. Polycrystalline Diamond or CVD (chemical vapour deposition) diamond based cutting tools can be used for the high speed machining of these alloys due to their high hardness and wear resistance. Diamond thin film coatings of different film morphologies are commonly applied on cemented carbide tools using Hot Filament CVD. The distinguishing characteristic to other coatings is utmost hardness resulting in high resistance to abrasion, low tendency to adhesion and low friction coefficient. The manufacturing of CVD diamond coated shaft type cutting tools is challenging due to the complex design of the cutting edges and the demanding stress behaviour during tool application. The influencing parameters of substrate type, chemical and mechanical substrate pre-treatment as well as diamond film modification on the tool cutting performance are discussed. The manufacturing route of CVD diamond coated thread milling drills is analysed with the use of material and tribological tests. The complex thread manufacturing tools are then applied in the machining of AlSi17Cu4Mg, whereby the tool performance is characterised with respect to their wear behaviour, the process forces and temperatures as well as the workpiece quality.     

On-machine dry electric discharge truing of diamond wheels for micro-structured surfaces grinding

Precision grinding with diamond wheels gives a promising alternative to achieve high quality micro-structured surfaces on optical molds. However, it is difficult to true these diamond wheels efficiently, because of the remarkable resistance property and the geometrical limitation of small wheel profile. In this paper, an on-machine dry-EDT method to precision shape and prepare diamond wheels with various profiles was proposed for micro-structured surface grinding. Firstly, the fundamental truing errors were analyzed based on the dry-EDT kinematics. And then the capabilities of dry-EDT truing for high abrasive concentration metal bonded diamond wheels were presented. Next, the effects of kinematic parameters variables on trued wheel profile accuracy were investigated. Finally, the micro-structured surfaces on SiC ceramic and tungsten carbide WC were ground by these trued diamond wheels. The experiments results showed that the arc-shaped diamond wheel (diameter of 200 mm) with 4 μm profile error (PV) and 1.0023 mm profile radius, and the V-shaped diamond wheel with 22.5 μm V-tip radius and 120.03° profile angle could be obtained by on-machine dry EDT. The kinematic parameters of dry-EDT have an important influence on truing profile accuracy of diamond wheels, especially for the tip of V-shaped wheel. The subsequent grinding show that the edge radius of V groove array on SiC is less than 2 μm, while the radius of included corner is around 55 μm. The PV error of ground arc groove array on WC is less than 5 μm. The surface roughness of ground micro-structured surface R_a is 142 nm and 97 nm for SiC and WC, respectively.     

Ultraviolet-laser-assisted precision cutting of yttria-stabilized tetragonal zirconia polycrystal

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is a promising biomaterial for use in dental and femoral implants. The current method for machining Y-TZP involves grinding after sintering. However, the grinding process is time consuming and therefore costly. To resolve these issues, this paper proposes a precision cutting process that utilizes a UV-laser-assisted machining method that requires no expensive cutting tools such as diamond tools. The UV laser is used to heat the Y-TZP, which improves its machinability. First, we performed experiments to determine that the most suitable machining temperature was 600 °C. A simulation was then used to determine the optimal distance between the tool edge and the laser spot. Finally, experiments using a UV laser were conducted to confirm the effectiveness of using a UV laser for machining. In these experiments, a Y-TZP sample was cut, and grooves were generated. The carved grooves were 20 mm long, 100 μm wide, and approximately 10 μm deep. Cutting without using a UV laser was also performed as a reference experiment. The results show that the use of the laser significantly decreased the number of large cracks from 14 to 3, the specific cutting energy by 35%, and the breakage of the tool edge. These results demonstrate the possibility of enhancing the productivity of Y-TZP products.     

Conditions for the in-situ formation of carbide coatings on diamond grains during their sintering with CuWC binders

In present work, self-assembled WC/W coatings on diamond grains, sintered with Cu matrix were firstly obtained by gas phase transport mechanism. Conditions for spontaneous coating formation were also determined. The coatings can improve adhesion strength between diamond grains and a binder. Discovered method can be used for production of heat sink and heat spreader devices, as well as cutting tools. As functional additives (precursors) for coating formation, WC and WO₃ were used. Morphology and composition of the coatings were identified by XPS, SEM, and TEM techniques. Coating consisting of mixture of metallic tungsten and tungsten carbide is formed on diamond when the Cu + WC binder is used. No coating is formed when copper is modified with WO₃ nanoparticles; introduction of 20% Fe to the binder leads to formation of a coating containing 100% tungsten in metallic form. Hence, conditions for formation of the tungsten (tungsten carbide) coating onto the diamond surface during sintering with a metal binder include the presence of a nucleating agent WC and a metal that catalyzes graphitization. It was found that the driving force for spontaneous coating formation is a chemically activated gas-phase mass transfer of WO₃ to the diamond surface, its chemisorption and subsequent reduction.     

等离子体技术在提高硬质合金工具上金刚石薄膜附着力方面的应用

金刚石薄膜具有优异的性能，作为切削工具表面的保护性涂层，可以大幅度提高工具的使用寿命以及加工精度。硬质合金是一种广泛使用的工具材料，在其表面沉积高附着力的金刚石薄膜时存在着困难。等离子体中离子、原子或分子具有高的反应活性，等离子体技术在金刚石薄膜的制备中有着广泛应用。利用等离子体技术可以极大的消除因金刚石薄膜与硬质合金基体之间存在热应力以及由硬质合金中的钴粘结剂在化学气相沉积金刚石薄膜过程中的促石墨化作用而产生的不利影响，提高金刚石薄膜与硬质合金基底之间附着力。本文综述了等离子体技术在提高硬质合金工具表面金刚石薄膜附着力方面的研究进展。     

A study on ultrasonic elliptical vibration cutting of tungsten carbide

Sintered tungsten carbide (WC) is a versatile metal matrix composite (MMC) material widely used in the tool manufacturing industries. Machining of this material with conventional cutting (CC) method is a real challenge compared to other difficult-to-cut materials. Ultrasonic elliptical vibration cutting (UEVC) method is a novel and non-conventional cutting technique which has been successfully applied to machine such intractable materials for the last decade. However, few studies have been conducted on cutting of WC using single point diamond tool (SPDT) applying the UEVC technique. This paper presents an experimental study on UEVC of sintered WC (～15% Co) using polycrystalline diamond (PCD) tools. Firstly, experiments have been carried out to investigate the effect of cutting parameters in the UEVC method in terms of cutting force, flank wear, surface finish while cutting sintered WC. The tests have revealed that the PCD tools in cutting of WC by the UEVC method results in better cutting performance at 4 μm depth of cut (DOC) as compared to both a lower DOC (e.g. 2 μm) and a higher DOC (e.g. 6 or 8 μm). Moreover, the cutting performance improves with the decrease in both the feed rate and cutting speed in the UEVC method like conventional turning (CT) method. A minimum surface roughness, R_a of 0.036 μm has been achieved on an area of about 1257 mm² with the UEVC performance. The CT method has also been employed to compare its cutting performance against the UEVC method. It has been observed that the UEVC method results in better cutting performances in all aspects compared to the CT method. Theoretical analysis on the UEVC method and analysis of the experimental results have been carried out to explain the reasons of better surface finish at 4 μm DOC and better cutting performance of the UEVC method.     

Nanocrystalline diamond coating tools for machining high-strength Al alloys

Diamond coating tools have been increasingly used for machining advanced materials. Recently, a microwave plasma-assisted chemical vapor deposition (CVD) technology was developed to produce diamond coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix. In this study, the nanocrystalline diamond (NCD) coating tools were evaluated in machining high-strength aluminum (Al) alloy. The conventional CVD microcrystalline diamond coating (MCD) tools and PCD tools were also tested for performance comparisons. In addition, stress distributions in diamond coating tools, after deposition and during machining, were analyzed using a 2D finite element (FE) thermomechanical model.

The results show that catastrophic failures, reached in all except one machining conditions, limit the NCD tool life, which is primarily affected by the cutting speed. In addition, coating delamination in the worn NCD tools is clearly evident from scanning electron microscopy (SEM) and force monitoring in machining can capture the delamination incident. At a high feed, coating delamination may extend to the rake face. Furthermore, SEM observations of coating failure boundaries show intimate coating-substrate contact. Though the NCD tools are inferior to the PCD tools, they substantially outperform the MCD tools, which failed by premature delamination. The diamond coating tools can have high residual stresses from the deposition and stresses at the cutting edge are highly augmented. Further machining loading causes the stress reversal pattern which seems to correlate with the tool wear severity.     

Investigation on the brazing mechanism and machining performance of diamond wire saw based on Cu-Sn-Ti alloy

Brazing connection between diamond particles and KSC82 carbon steel wire was established by the Cu-Sn-Ti alloy, and a diamond wire saw of 500 m in length and about 0.75 mm in diameter was fabricated. The brazing morphology of the diamond particles was observed using scanning electron microscopy (SEM), and the products and elemental distribution characteristics at the diamond brazed interface were analyzed by the energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The tensile mechanical properties of the brazed diamond wire saw was obtained through tensile tests, and the morphology of the fracture was observed using the SEM to analyze the tensile fracture mechanism. Further, the diamond wire saw was used for slice processing test of G663 granite, and the failure mode of the wire saw was analyzed. The results showed that there was Ti segregation at the diamond brazing interface, and that Ti₂C new phase was detected at the interface, where brazing connection of diamond particles was achieved through by reactive wetting. The tensile and yield strengths of the brazing diamond wire saw were 1289.08 and 923.18 MPa respectively, its plasticity was twice that of original KSC82 steel wire, and the tensile failure mode of the wire saw was ductile fracture. The stable cutting efficiency of the brazing diamond wire saw cutting the G663 granite with cross-sectional dimensions of 480 mm × 260 mm could reach 15 mm/min. There were three abrasive wear modes for the diamond particles of the wire saw working layer, including normal wear, shear fracture and separation, of which separation accounted for 14.3%. The reason for the separation of diamond was attributed to the oxidation of Ti element in Cu-Sn-Ti alloy and the fatigue crack initiation and growth at the diamond brazing interface.     

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.     

The history of hard CVD coatings for tool applications at the University of Technology Vienna

The history of chemical vapour deposition (CVD) started in the 19th century with the production of lamp filaments and by the Mond process for the nickel production. In the 20th century Van Arkel deposited metals from the gas phase for application in lamp industry.TiC was the first hard coating deposited by CVD in the 1950s. Nearly 20 years later Krupp Widia introduced the first commercial TiC coating on hardmetal tools.Prof. Richard Kieffer started with TiN deposition by the CVD process in the 1970s at the “Technischer Hochschule Wien” and Prof. Benno Lux continued with Al₂O₃- and diamond coatings.In the following years CVD processes for TiN, Ti(C,N), ZrC, (Ti,Zr)C, TiB₂, Al₂O₃, Ta_xC, Cr_xC_y, diamond, BN and BCN were investigated at the University of Technology Vienna.The depositions of new crystalline solid solutions (mixed crystals), nano-crystalline materials and nano-crystalline mixtures of phases have been research topics so far.     

Model of quality management of hard coatings on ceramic cutting tools

For the development and introduction of new coated cutting tools (i.e. new combinations of cutting materials and hard coatings), it is necessary to carry out a number of studies with the purpose of optimizing the coatings composition and processing procedures, and also to test new tools under working conditions. The aim of this paper is to establish a common model for environmentally oriented quality management in the use and development of coated ceramic cutting tools with new coating systems. The paper also presents an investigation of the results of tribological and cutting properties of the coatings deposited with the PVD and CVD techniques on cutting inserts made from (Al₂O₃ + TiC) tool ceramics. Tests were carried out on ceramic inserts, uncoated and PVD or CVD-coated, with gradient, mono-, multi- (nano) layers and multicomponent hard wear resistant coatings composed of TiN, Ti(C, N), (Ti, Al)N, (Ti, AlSi)N and Al₂O₃ layers.     

Grinding characteristics of diamond film using composite electro-plating in-process sharpening method

To finish a chemical vapor deposition (CVD) diamond film surface, composite electro-plating is introduced during the grinding process to sharpen the grinder, a method named as composite electro-plating in-process sharpening (CEPIS). In the grinding process, the grinder for the cathode and the nickel plate for the anode are connected to a DC power supply and immersed in an electrolyte solution containing diamond particles of 10 μm in size so that metal ions with diamond particles are deposited onto the grinder in process to expose fresh sharp grains. Results show that the removal rate of the diamond film increases with increasing current density. The removal rate of the diamond film at a current density of 7.5 ASD is 3.8 times higher than at 0 ASD as in the traditional grinding method. Based on the experimental results of the observations of the coated surface of the grinder and the variations in the coating thickness, a sharpening mechanism for the CEPIS method is deduced. This mechanism allows the coating thickness of the grinder to be increased with grinding time using the CEPIS method. The higher removal capability is achieved due to the higher active grit density.     

Micromachining of ceramic surfaces: Hydroxyapatite and zirconia

Computerised Numerical Control (CNC) precision machining can be employed as a fast and reproducible method for surface micropatterning. For biomedical applications an efficient and reproducible micropatterning of zirconia and calcium phosphate based materials is highly sought in order to guide implant interactions with surrounding biological tissues for a better osseointegration. Therefore, CNC precision machining of zirconia and hydroxyapatite substrates is investigated in this study and optimised process parameters are reported. By microgrinding and micromilling microgrooves with a minimum width of 100 μm were obtained and process parameters such as cutting tool diameter and feed velocity discussed. As all samples were sintered prior to the micropatterning process, the influence of sintering temperature on the pattern quality, size and hardness of the obtained samples are studied. Vickers hardness of the different sintered ceramic surfaces was measured to correlate the possible wear impact on the tip of the cutting tools. The stiffness and the hardness of the used cutting tools were measured and their effect on the cutting results was discussed. The pattern quality and the average roughness in the machined microgrooves were analysed by 3D-profilometry and imaged by SEM. Comparison of the two machining techniques yielded more defined and less fractured micropatterns for microgrinding. The process efficiency for both methods was limited by the economic life time of the tool tips. For CNC grinding the life time was downsized due to more pronounced abrasive wear. For both materials the hardness was the crucial process parameter, which was adjusted by the sintering temperature. For milling of zirconia the sintering should not exceed a temperature of 1100 °C to minimize tool wear. A temperature of lower 1200 °C is suggested for the milling of HA. For sintering temperatures higher than 1200 °C the machining of both ceramic surfaces was hardly possible. The feed velocity was found not having a significant influence on the obtained micropattern width. The preset line pitch of 100 μm was excellently reached for both applied machining processes. It was found that lower feed velocities and smaller tool diameters caused deeper micropatterns.     

ELID grinding characteristics of glass-ceramic materials

Zerodur glass-ceramic materials have been widely used in optical, opto-electronic and precision engineering industries; their efficient ultraprecision machining, with extremely low surface roughness and high form accuracy, is in great demand in those fields. The authors have been conducting studies on realizing high-quality surface and form accuracy of zerodur glass-ceramic materials efficiently by use of electrolytic in-process dressing (ELID) grinding process. This paper proposes a new grinding mode in which top surface and sides of zerodur block were ground by cylindrical surface and side surface of grinding wheel. Grinding experiments were carried out using #1200, #2000 and #4000 diamond cast-iron bond wheels, and grinding characteristics such as grinding performance, ground surface roughness, surface topographies and perpendicularity between ground surfaces were investigated. Experiments on grinding using #4000 wheel successfully produced smooth top surface and side surfaces that were about 10 nmRa in surface roughness, 1.5 μm/□400×400 mm² in flatness and 90°±6″ in perpendicularity. AFM observation of the ground surface also showed that material removal in the ductile mode occurs for fine abrasive wheels. The results showed that grinding was stable without severe clogging for wheels by choosing suitable ELID parameters and grinding conditions.     

The influence of tungsten carbide contamination from the milling process on PCD materials oxidation

The most popular polycrystalline diamond (PCD) is a compact with cobalt bonding phase. The thermal resistance of this material is rather low, up to 700 °C. The best way to obtain a higher thermal resistance for diamond compacts (PCD materials) is to limit cobalt content or to sinter the diamond either without a bonding phase or with a ceramic bonding phase. The second group of commercial PCDs, used mainly in rock drilling, are materials with the Si bonding phase. Because of their residual porosity, these materials are not used for metalworking applications, where low roughness value is required. The main focus of the studies presented was the influence of methods of mixture preparation on the microstructures and selected properties of diamond compacts. The traditional method of preparing diamond powders with a bonding phase is to use WC-Co millers. This method causes tungsten carbide contamination of the material, which in these materials decreases their resistance to oxidation during machining. The second aim of these researches was lowering the level of residual porosity. The presence of nanoparticles between diamond microsize particles limits the residual porosity of diamond compacts and improves the roughness properties of cutting tools, but the addition of nanopowders requires intensive milling for good distribution of the ingredients, which increases the WC-Co contamination. In these studies, mixtures containing 90 wt.% diamond with 10 wt.% nanometric TiB₂ powders were prepared with the use of the milling method and the ultrasonic method. The resulting mixtures were formed into discs (15 mm in diameter) by pressing in a steel matrix under the pressure of 100 MPa. The samples were heated using an assembly equipped with an internal graphite heater. The compacts were sintered at the pressure of 8.0 ± 0.2 GPa and the temperature of about 2000 °C in a Bridgman-type ultra high pressure apparatus. The density of the materials was measured. Hardness measurements were carried out with a Vickers apparatus at 9.8 N load. Young's modulus was measured using the ultrasonic method. Phase composition of the diamond compacts was identified by X-ray diffraction analysis. The method of the mixtures preparation has a strong influence on the microstructure and the properties of diamond compacts. The preparation of mixtures in a PULVERISETTE 6 Planetary mill with WC grinding balls results in tungsten contamination, and thus in the presence of WC, WB and W₂C_0,84 in the compacts. The ultrasonic method of mixing allows to receive diamond materials with nanometric bonding phases without tungsten contamination.     

Reinforcement architectures and thermal fatigue in diamond particle-reinforced aluminum

Aluminum reinforced by 60 vol.% diamond particles has been investigated as a potential heat sink material for high power electronics. Diamond (CD) is used as reinforcement contributing its high thermal conductivity (TC ≈ 1000 W mK^?1) and low coefficient thermal expansion (CTE ≈ 1 ppm K^?1). An Al matrix enables shaping and joining of the composite components. Interface bonding is improved by limited carbide formation induced by heat treatment and even more by SiC coating of diamond particles. An AlSi7 matrix forms an interpenetrating composite three-dimensional (3D) network of diamond particles linked by Si bridges percolated by a ductile α-Al matrix. Internal stresses are generated during temperature changes due to the CTE mismatch of the constituents. The stress evolution was determined in situ by neutron diffraction during thermal cycling between room temperature and 350 °C (soldering temperature). Tensile stresses build up in the Al/CD composites: during cooling <100 MPa in a pure Al matrix, but around 200 MPa in the Al in an AlSi7 matrix. Compressive stresses build up in Al during heating of the composite. The stress evolution causes changes in the void volume fraction and interface debonding by visco-plastic deformation of the Al matrix. Thermal fatigue damage has been revealed by high resolution synchrotron tomography. An interconnected diamond–Si 3D network formed with an AlSi7 matrix promises higher stability with respect to cycling temperature exposure.     

Study on removal mechanism and removal characters for SiC and fused silica by fixed abrasive diamond pellets

Fixed abrasive is known as a high-efficient and stable technique for fabricating various materials. This work studies the removal mechanism and removal characters of fixed abrasive diamond pellets (FADPs) for lapping SiC and fused silica. The critical sizes of diamond particles changing brittle fracture to ductile removal (with better surface roughness and less damages) are figured out for SiC (9.56 μm) and fused silica (0.53 μm). Multi-distribution models are presented and a mathematical removal model is built based on Preston law. Then, removal characters of FADPs are investigated, including removal profile, removal rate, linear removal, removal stability, surface roughness, subsurface damage etc. Results show that (i) the removal shape is predictable and the removal rate is highly correlative with diamond size, velocity and pressure; (ii) the cumulative removal is temporally linear and removal stability is within ±10%; (iii) SiC can be ductilely lapped by 1.5, 3, 5 μm pellets, with best roughness Ra=4.8 nm and a specular surface for optical metrology; (iv) removal of fused silica is mostly brittle fracture and it can change as semi-ductile by 1.5 μm pellets, with a non-specular or semi-specular surface which is hard for optical metrology; (v) subsurface damage is highly dependent on diamond size, but free to pressure and velocity. Finally, two engineering applications validated its feasibility in uniform or deterministic lapping/polishing of optical mirrors.     

硬质合金CVD金刚石涂层最新进展

金刚石因具有优异的物理化学性能被认为是理想的刀具材料。硬质合金基底上涂覆CVD金刚石薄膜有利于改善刀具的加工性能和寿命,但涂层和基底之间存在热膨胀系数差异以及合金中Co对沉积有不利影响,使得薄膜附着力较差。本文综述了近几年来各种提高CVD金刚石涂层刀具切屑性能的方法,从提高薄膜附着力和改善金刚石膜的质量两个方面进行了讨论。并介绍了国外较先进的CVD金刚石涂层刀具的应用,随着技术的不断成熟,CVD金刚石涂层将会有更为广泛的应用。