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.     

An evaluation of the evolution of workpiece surface integrity in hole making operations for a nickel-based superalloy

White layers and extensive material drag introduced during rough machining are regarded as detrimental to surface integrity. As such a sensible method for determining the amount of material to be removed in a roughing process would be to understand the relationship and interaction between roughing (i.e. drilling) and finishing (i.e. plunge milling) operations. Within this work non-standard cutting parameters were employed during the roughing process to generate a white layer and material drag up to a depth of 20 μm. Various plunge milling cutting strategies followed, with radius removal ranging from 25 μm to 250 μm in order to identify the amount of material removal necessary to eliminate the anomalies previously generated from mistreated surface history. The results show that finishing with a depth of cut between 50 μm and 125 μm removes all anomalies from the roughing process, leaving behind a negligible amount of material drag (3–4 μm). X-ray diffraction demonstrates significant tensile residual stresses (1000–2000 MPa) were generated in the axial and hoop direction by abusive hole drilling while subsequent plunge milling operation leaves compressive surface stresses in the region of ?500 MPa in both the axial and hoop directions; in both cases the depth of the surface stresses extended to around 125 μm from the drilled surface. It was also found that a depth of cut of 25 μm was not sufficient to recover the abused surface; this was due to intense material drag accompanied by surface cracking (i.e. 2 μm depth). The research shows that understanding the interaction between successive cutting operations can provide a suitable machining route to fulfil the industrial quality requirements in terms of the machined surface mechanical/metallurgical properties.     

High efficiency slicing of low resistance silicon ingot by wire electrolytic-spark hybrid machining

As the semiconductor industry requires the cutting of silicon ingots into wafers, the slicing of large, ultra thin wafers is one of the main technologies to prevent wastage. Recently, apart from conventional inner diameter (ID) blade and multi-wire saw methods, wire electrical discharge machining (WEDM), which has no cutting force, has been introduced to this area and low resistance silicon may be sliced by WEDM. In this paper, a novel approach, based on wire electrolytic-spark slicing strategy using hybrid oil/aqueous electrolyte, combining electric discharge and anodic etching into a single process, is investigated experimentally. Some improvements, such as a new wire winding system, hybrid electrolyte and high efficiency pulse generator, have been adopted in a kind of high speed (HS)-WEDM machine. Experiments have been conducted to evaluate the machining rate, surface quality and wafer thickness of low resistance (0.5–3 Ω cm) mono-crystalline silicon. It has been demonstrated that with properly selected electrical parameters and electrolyte, a maximum machining rate of 600 mm²/min can be obtained and with a wafer thickness less than 120 μm. Furthermore, in comparison with WEDM, heat affected zone and harmful metal residues are considerably diminished, which provides significant theoretical and experimental support for future applications.     

Experimental evaluation of minimum quantity lubrication in near micro-milling

This paper presents the performance of the minimum quantity lubrication (MQL) technique in near micro-milling with respect to dry cutting on the basis of tool wear, surface roughness and burr formation. The effects of tool materials, oil flow rate and air flow rate on tool performance in MQL cutting are also studied. It is found that the application of MQL will significantly improve the tool life, surface roughness and burr formation compared to those in dry cutting based on slotting tests with micro-end mills on a meso-scale machine tool. It is also observed that the values of surface roughness are close related to the tool-wear conditions in micro-cutting. Based on the experimental results, it is presumed that the maximum allowable tool flank wear of the 600-μm micro-tool is 80 μm while the surface finish quickly deteriorates after the tool flank wear reaches 80 μm and the tool breaks soon after the tool wear reaches 100 μm. The optimal lubrication conditions in this study are oil flow rate of 1.88 ml/h and air flow rate of 40 l/min. It is also found that the air flow rate has a more significant influence on tool life than the oil flow rate under MQL conditions in this study.     

Slicing,cleaning and kerf analysis of germanium wafers machined by wire electrical discharge machining

This paper investigates the slicing of germanium wafers from single crystal, gallium-doped ingots using wire electrical discharge machining. Wafers with a thickness of 350 μm and a diameter of 66 mm were cut using 75 and 100 μm molybdenum wire. Wafer characteristics resulting from the process such as the surface profile and texture are analyzed using a surface profiler and scanning electron microscopy. Detailed experimental investigation of the kerf measurement was performed to demonstrate minimization of material wastage during the slicing process using WEDM in combination with thin wire diameters. A series of timed etches using two different chemical etchants were performed on the machined surfaces to measure the thickness of the recast layer. Cleaning of germanium wafers along with its quality after slicing is demonstrated by using Raman spectroscopy.     

On the precision single-point diamond machining of polymeric materials

This paper is a continuation of long duration research and it reports about new results in the investigation of wear of natural monocrystalline diamond cutting tool in single-point precision and ultraprecision machining process of thermoplastic amorphous polymeric materials for various application, e.g. for photon-optical and bioengineering applications. In these investigations we have been using up-to-date methods and devices, including atomic force microscope, interferometers and optical profilers, 3D topographic analysis systems, optical-polarizable microscope, etc. Wear criterion was chosen as the technological criterion of the diamond tool cutting wedge clearance face wear (h_cf < 0.6 μm), what allows to provide high quality level of the machined surfaces of articles from polymers.     

Effect of metal coating on machinability of high purity germanium using wire electrical discharge machining

This paper reports on the research of wire electrical discharge machining (WEDM) as a cutting process for n-type high purity germanium (HP Ge). WEDM requires sufficient electrical conductivity of the work piece for discharges to occur. Owing to the very high material resistivity of HP Ge (32.8 Ω cm), the electrical conduction is too low for WEDM to be efficient. To temporarily enhance the conduction, metals (aluminum and nickel) were deposited on the HP Ge on 1 or 2 sides with various thicknesses (1.0, 2.0, and 3.0 μm) using sputter deposition. This shortens the path of conduction between the HP Ge and the WEDM ground and also serves to trigger the discharges. Machining experiments were performed to determine the correlation between the slicing rate and locally enhanced HP Ge through various discharge energies (potential voltage: 150, 200, 250 and 300 V and capacitance: 1, 3.3, 5.5, 9.9 and 21.4 nF). From the results, the obtained maximum slicing rate is 7.7 mm²/min for Al coating (2 sides, 1.0 μm thickness) at high energy (300 V, 21.4 nF), which is improved as much as 27 times over uncoated HP Ge. The fastest cutting without creating subsurface microcracks was measured as 1.12 mm²/min performed at 150 V and 9.9 nF. Additional slicing experiments at reverse polarity (positive wire and negative work piece, uncommon polarity for WEDM) were performed at 150 V and various capacitances. The experiment proved that there were rectifying contacts at the metal coating surface. It was found that under identical EDM settings, a faster slicing rate also showed a reduction in kerf size due to less lateral discharge energy. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were used to investigate microcracks and to analyze surface impurities.     

Electrodeposited Ni microcones with a thin Au film bonded with Au wire

In wire bonding, the bonding quality between the substrate Au film and metal wire has an effect on productivity and reliability. Au film thickness is important for substrate bondability. It is required to reduce the Au film thickness as thin as possible without deteriorating the level of bondability to cut down extremely high cost of Au consumption. In this study, electrodeposited Ni/Au microcones were fabricated and thermosonic bonded with Au wire. The thickness of Au film was only 0.05 μm. Bonded with Au wire 17.5 μm in diameter, the 0.4 μm-height microcones showed excellent and stable bondability with average pull strength 6.29 gf and small standard deviation. Microscopic observation showed that Ni/Au microcones inserted into Au wire effectively, thus insertion weld between microcones and Au wire was formed. Pull fracture scanning electron microscopy (SEM) images showed an improvement of stitch bonding quality when using Ni/Au microcones. Mechanism of bonding process between the Ni/Au microcones and Au wire was put forward by three stages.     

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.     

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.     

Mechanical properties of as-fabricated and 2300 °C annealed tungsten wire tested up to 600 °C

Recent efforts dedicated to the mitigation of tungsten brittleness have demonstrated that tungsten fiber-reinforced composites acquire pseudo ductility even at room temperature. Crack extension and fracture process is basically defined by the strength of tungsten fibers. Here, we move forward and report the results of mechanical and microstructural investigation of different grades of W wire with a diameter of 150 μm at elevated temperature up to 600 °C. The results demonstrated that potassium doping to the wire in the as-fabricated state does not principally change the mechanical response, and the fracture occurs by grain elongation and delamination. Both fracture stress and fracture strain decrease with increasing test temperature. Contrary to the as-fabricated wire, the potassium-doped wire annealed at 2300 °C exhibits much lower fracture stress. The fracture mechanism also differs, namely: cleavage below 300 °C and ductile necking above. The change in the fracture mechanism is accompanied with a significant increase of the elongation to fracture being ~ 5% around 300 °C.     

Microstructure and mechanical properties of biomedical Co–29Cr–8Mo alloy wire fabricated by a modified melt-spinning process

A modified in-rotating-water spinning process has been applied for producing the alloy wire of Ni-free Co–29Cr–8Mo suitable for biomedical use. The microstructure and tensile properties of the as-spun and heat-treated wires were investigated using backscattered electron microscopy, X-ray diffraction analyses and tensile tests. The microstructure of the as-spun wire exhibits a cellular structure and evolves into an equiaxed and fine-grained structure with an average grain size of several micrometers, containing σ-phase precipitates after heat treatment at 1373 K. Grains increase in size and reach an average diameter ranging from 10 to 20 μm at 1473 K. The crystal structure of the as-spun wire changes from face-centered cubic to strain-induced hexagonal close-packed martensite through wiredrawing. The wiredrawing, combined with heat treatments, improves the mechanical properties of the as-spun wire. The present modified melt-spinning process is an effective method to produce Ni-free Co–Cr–Mo alloy wire for biomedical applications.     

A new 3D multiphase FE model for micro cutting ferritic–pearlitic carbon steels

A new three-dimensional multiphase finite element computation model is proposed for the simulation of micro drilling two-phase ferritic–pearlitic carbon steels in order to understand the cutting, ploughing, tribological and heat transfer mechanisms at the microscale. Based on the Split-Hopkinson-Pressure-Bar technique, a constitutive material law has been developed to model the thermo-mechanical material behaviour including the effect of the microstructure. Micro drilling tests using solid carbide twist drills with different diameters (d = 50 μm to 1 mm) were performed on ferrite–pearlite two-phase steel AISI 1045 for the verification of the developed 3D FE computation model regarding chip formation, feed force, and torque.     

A novel magnetic actuator design for active damping of machining tools

Parts and cutting tools with large structural flexibility experience both forced and chatter vibrations during machining, resulting in poor surface finish or damage to the machine. This paper presents the design principles of a novel 3 degrees of freedom linear magnetic actuator which increases the damping and static stiffness of flexible structures during machining. The proposed actuator can deliver 248 N force in two radial (x, y) directions and 34 N×m (torque) in torsional (θ) direction up to 850 Hz. The force and torque reduces to 107 N and 14.5 N×m at 2000 Hz, hence it can actively damp a wide range of structural modes. The magnetic force is linearized with respect to the input current using magnetic configuration design strategy. Loop shaping controllers are designed for active damping of boring bar vibrations. The static and dynamic stiffnesses of the boring bar were considerably increased with the designed actuator, leading to a significant increase in chatter-free material removal rates during cutting tests.     

The role of beam dispersion in Raman and photo-stimulated luminescence piezo-spectroscopy of yttria-stabilized zirconia in multi-layered coatings

Laser beam dispersion affects the resolution of Raman and photo-stimulated luminescence piezo-spectroscopy measurements of transparent materials. In this paper, we investigate the lateral spreading of the laser beam and the axial sampling depth of Raman spectroscopy measurements within thermal sprayed yttria-stabilized zirconia (YSZ) thin coatings. The lateral diameters of the laser beams (λ = 632.8 nm and 514 nm) reach approximately ～160 μm after travelling through a thickness of 200 μm of air plasma sprayed (APS) YSZ and ～80 μm after travelling through 120 μm of electron beam physical vapour deposited YSZ. The Raman spectroscopy sampling depth was found to be between 30 and 40 μm in APS YSZ. The beam dispersions within these two coatings were simulated using the ray-tracing software ZEMAX to understand the observed scattering patterns. The results are discussed with respect to the application of these two spectroscopic techniques in multi-layered thermal barrier coating systems.     

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.     

Experimentation on MR fluid using a 2-axis wheel tool

This paper is focused on magnetorheological (MR) fluid assistive polishing of optical aspheric components. MR fluid is a functional mixture of non-colloidal magnetic particle of micrometer size suspended in a host fluid, with the special property that its viscosity can be varied by the application of a magnetic field. This paper introduces the basic principles of the methodology and presents experiment results on MR fluids using a 2-axis wheel-shaped tool supporting dual magnetic fields. Mathematical models taking into account the pressure and the tool velocity are derived. The experiments serve to evaluate the effects of process parameters on material removal and performance using a K9 glass parabolic lens of 60 mm diameter as work-piece. It is shown that surface roughness can be reduced from an initial value of 3.8–1.2 nm after 10 min of polishing. The form errors can also be improved from an initial 2.27 μm rms and 7.89 μm peak-to-valley to become 0.36 μm rms and 2.01 μm peak-to-valley after 60 min of polishing.     

Effect of initial particulate and sintering temperature on mechanical properties and microstructure of WC–ZrO2–VC ceramic composites

Owing to improving the mechanical properties of cemented carbides in high speed machining fields, a new composite tool material WC–ZrO₂–VC (WZV) is prepared from a mixture of yttria stabilized zirconia (YSZ) and micrometer VC particles by hot-press-sintering in nitrogenous atmosphere. Commercial WC, of which the initial particle sizes are 0.2 μm, 0.4 μm, 0.6 μm and 0.8 μm, is mixed with zirconia and VC powder in aqueous medium by following a ball mill process. The sintering behavior is investigated by isostatic pressing under different sintering temperature. The relative density and bending strength are measured by Archimedes methods and three-point bending mode, respectively. Hardness and fracture toughness are performed by Vickers indentation method. Microstructure of the composite is characterized by scanning electron microscopy (SEM). The correlations between initial particles, densification mechanism, sintering temperature, microstructure and mechanical properties are studied. Experimental results show that maximum densification 99.5% is achieved at 1650 °C and the initial particle size is 0.8 μm. When temperature is 1550 °C and particle size is 0.4 μm, the optimized bending strength (943 MPa) is obtained. The best hardness record is 19.2 GPa when sintering temperature is 1650 and particle size is 0.8 μm. The indention cracks propagate around the grain boundaries and the WC particles fracture, which is associated with particle and microcrack toughening mechanism.     

Amorphous magnetoelastic sensors for the detection of biological agents

Freestanding amorphous magnetoelastic (ME) biosensors were fabricated by two ways. One type with larger size, 2000 × 400 × 15 μm, 1000 × 200 × 15 μm and 500 × 100 × 15 μm, was made from an ME Fe40Ni38Mo4B18 ribbon, the other with smaller size 200 × 40 × 4 μm was manufactured by dual beam sputtering and non-traditional microelectronic fabrication techniques. Both platforms were immobilized with JRB7 phage and were developed for the real-time in vitro detection of Bacillus anthracis spores. The experimental results show that the measured sensitivity of the ME sensors agrees with theoretical predictions and the specificity of ME sensors coated with JRB7 phage for B. anthracis spore species is excellent. The 200 × 40 × 4 μm biosensor was found to have a detection limit of 10² cfu/ml and sensitivity of 13.1 kHz/decade.     

Effect of hot rolled grain size on the precipitation kinetics of nitrides in low carbon Al-killed steel

The precipitation of nitrides plays a general role in the industrial processing of deep drawing quality Al-killed low carbon steels. In this paper, the effect of hot rolled grain size on the precipitation of nitrides has been analysed. To evaluate the effect of grain size on the nitride precipitation kinetics, thermoelectric power based investigations have been performed on hot and cold rolled specimens.In the hot rolled state, the precipitation of nitrides occurs more intensively in the fine grain size microstructure (average grain size = 9 μm) than in the large grain size microstructure (average grain size = 23 μm) until the precipitated fraction of nitrides reaches about 70%. In the cold rolled state the effect of grain size is much less significant; probably the precipitation process occurs simultaneously at the grain boundaries and along dislocations. According to the simulation results, significant differences can be found between the precipitated fraction of nitrides in fine and large grain size sheets coiled in the temperature range 550–650 °C. In this interval, the precipitated nitride fraction is about two times larger in a fine grain microstructure (9 μm) than in sheets with 23 μm average grain size. The local position in the coil also affects significantly the precipitated fraction of nitrides. In the outer ring of the coil, less than 20% precipitated fraction is predicted in coiling temperature range 550–700 °C. However, in the middle ring of a hot rolled coil, the precipitated fraction changes from 5% to 85% with increasing coiling temperature from 550 to 700 °C.