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.     

Effect of laminate configuration and feed rate on cutting performance when drilling holes in carbon fibre reinforced plastic composites

Composites use in the aerospace industry is expanding, in particular carbon fibre reinforced plastics (CFRP) for structural components. Machinability can however be problematic especially when drilling, due to CFRP's inherent anisotropy/in-homogeneity, limited plastic deformation and abrasive characteristics. Following a brief review on composites development and associated machining, the paper outlines experimental results when twist drilling 1.5 mm diameter holes in 3 mm thick CFRP laminate using tungsten carbide (WC) stepped drills. The control variables considered were prepreg type (3 types) and form (unidirectional (UD) and woven), together with drill feed rate (0.2 and 0.4 mm/rev). A full factorial experimental design was used involving 12 tests. Response variables included the number of drilled holes (wear criterion VB_Bmax ≤ 100 μm), thrust force and torque, together with entry and exit delamination (conventional and adjusted delamination factor values calculated) and hole diameter. Best results were obtained with woven MTM44-1/HTS oven cured material (3750 holes) while the effect of prepreg form on tool life was evident only when operating at the higher level of feed rate. Thrust forces were typically under 125 N with torque values generally below 65 Nmm over the range of operating parameters employed. Finally, the delamination factor (F_d) measured at hole entry and exit ranged between ～1.2–1.8 and 1.0–2.1 respectively.     

Characterization of the drilling alumina ceramic using Nd:YAG pulsed laser

Laser micromachining can replace mechanical removal methods in many industrial applications, particularly in the processing of difficult-to-machine materials such as hardened metals, ceramics, and composites. It is being applied across many industries like semiconductor, electronics, medical, automotive, aerospace, instrumentation and communications. Laser machining is a thermal process. The effectiveness of this process depends on thermal and optical properties of the material. Therefore, laser machining is suitable for materials that exhibit a high degree of brittleness, or hardness, and have favourable thermal properties, such as low thermal diffusivity and conductivity. Ceramics which have the mentioned properties are used extensively in the microelectronics industry for scribing and hole drilling.Rapid improvement of laser technology in recent years gave us facility to control laser parameters such as wavelength, pulse duration, energy and frequency of laser. In this study, Nd:YAG pulsed laser (with minimum pulse duration of 0.5 ms) is used in order to determine the effects of the peak power and the pulse duration on the holes of the alumina ceramic plates. The thicknesses of the alumina ceramic plates drilled by laser are 10 mm. Average hole diameters are measured between 500 μm and 1000 μm at different drilling parameters. The morphologies of the drilled materials are analyzed using optical microscope. Effects of the laser pulse duration and the peak power on the average taper angles of the holes are investigated.     

Dry and minimum quantity lubrication drilling of cast magnesium alloy (AM60)

Dry and minimum quantity lubrication (MQL) drilling of cast magnesium alloy AM60 used in the manufacturing of lightweight automotive components have been studied. The maximum and average torque and thrust forces measured during drilling using distilled water (H₂O-MQL) and a fatty acid-based MQL fluid (FA-MQL), both supplied at the rate of 10 ml/h, were compared with those generated during flooded (mineral oil) drilling. Tool life during dry drilling was inadequately short, due to excessive magnesium transfer and adhesion to the (HSS steel) drill causing drill failure in less than 80 holes. The use of MQL reduced magnesium adhesion and built-up edge formation, resulting in an increase in tool life as well as reductions in both average torque and thrust forces—prompting a performance similar to that of flooded drilling. The maximum temperature generated in the workpiece during MQL drilling was lower than that observed in dry drilling, and comparable to flooded condition. The mechanical properties of the material adjacent to drilled holes, as evaluated through plastic strain and hardness measurements near the holes, revealed a notable softening in the case of dry drilling, but not for MQL drilling. MQL drilling provided a stable drilling performance, which was evident from the uniform torque and force patterns throughout the drilling cycles and also resulted in desirable machining characteristics, including a smooth hole surface and short chip segments.     

Experimental characterization of micro-drilling process using nanofluid minimum quantity lubrication

This paper discusses the experimental characterization of the micro-drilling process with the nanofluid minimum quantity lubrication (MQL). The miniaturized drilling machine tool system is developed, and then a series of micro-drilling experiments are conducted in the cases of compressed air lubrication, pure MQL and nanofluid MQL. For the nanofluid MQL, nano-diamond particles having the diameter of 30 nm are used with the base fluids of paraffin and vegetable oils. For the micro-drilling process, an uncoated carbide twist drill having the diameter of 200 μm is used for making holes in the aluminum 6061 workpiece. The experimental results show that the nanofluid MQL significantly increases the number of drilled holes and reduces the drilling torques and thrust forces. In addition, the nanofluid MQL effectively eliminates remaining chips and burrs to enhance the quality of drilled holes.     

Effect of roll gap adjustment on exit cross sectional shape in groove rolling—Experimental and FE analysis

We machined work roll with groove worn down as well as groove with no wear. We then performed a pilot hot rod rolling test at temperature of 1000 °C using plain carbon steel (0.1% C) as the roll gap decreases from reference roll gap (6.5 mm) to 3.5 mm. To understand better the effect of roll gap (i.e., section height) adjustment on the exit cross sectional area (ECSA) variation of workpiece in a two-stand groove rolling process with wear is considered, we carried out a series of three dimensional finite element analysis. Results reveal that variation of ECSA is almost linearly proportional to roll gap change while the roll gap decreases from reference roll gap (6.5 mm) to 3.5 mm. In oval groove rolling, the exit cross sectional shape and area predicted by FEA is in a good agreement with those measured. In round groove rolling, however, some deviations between FEA and experiment are observed because of roll groove geometry coupled with cross sectional shape of incoming workpiece. In the two-stand groove rolling, the effect of roll gap adjustment at each stand on the exit cross section of workpiece is somewhat different, in comparison with single-stand groove rolling. The roll gap adjustment at the previous stand has a more influence on the ECSA of workpiece than that of the next stand.     

Comparison of the wear behavior of WC/(FeAl-B) and WC-Co composites at high temperatures

In this research, the sliding wear behavior of the hot pressed WC/40 vol%(FeAl-B) composites was investigated at temperatures ranging from the ambient one to those as high as 600 °C. The composites were then compared with hot pressed WC-40 vol%Co and commercial WC-16 vol%Co (H10F) in terms of their mechanical properties and high temperature wear behavior. It was found that the WC/(FeAl-B) composite recorded its maximum wear resistance at all the experimental temperatures, which was higher than that of WC-40 vol%Co at these same temperatures due to the higher hardness of the FeAl-B than that of the Co matrix. Also, WC/(FeAl-B) exhibited a higher wear resistance at lower temperatures and a more proper behavior at higher temperatures than did the commercial WC-16 vol%Co; this was attributed to the higher strength of the FeAl-B matrix at high temperatures. Examination of the wear surfaces revealed that abrasion was the wear mechanism in the commercial WC-16 vol%Co and WC/(FeAl-B) composites at both ambient temperature and 300 °C. At 400 °C, however, the wear mechanism was more of an adhesive one, while binder oxidation was observed at 600 °C.     

Sliding behavior and wear mechanism of iron and cobalt-based high-temperature alloys against WC and SiC balls

The sliding behaviors of two typical high-temperature alloys of GH2132 and GH605 against WC and SiC balls were investigated at environments from room temperature to 800 °C with a sliding speed of 50 to 125 m/min under a load of 10 to 20 N. The wear performances of high-temperature alloys, WC and SiC balls were rated and their mechanisms were discussed. The four sliding pairs exhibited the markedly different sliding behaviours, in which the GH2132/WC sliding pair had the maximum friction coefficient with 125 m/min under 10 N at room temperature. The variation trends of ball wear rates with the ambient temperature were at odds with those of friction coefficient. The higher friction coefficient did not always lead balls to suffer from the higher wear rate. The maximum worn depth approximated to 250 μm for the GH2132/WC sliding pair with higher friction coefficient. The GH605/WC sliding pair exhibited the lower friction coefficient and lower worn depth of plate. Whether at room temperature or high temperature, the GH605/SiC sliding pair significantly exhibited good wear resistance with a minor damage of ball and plate despite of its higher friction coefficient.     

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.     

Wear mechanisms of micro-drills during dry high speed drilling of PCB

In this paper, micro-drills with diameters of 0.1–0.3 mm were used to drill printed circuit boards (PCBs) with a highest spindle speed of 300 krpm. To study the wear mechanisms of PCB micro-drills, micro-drill morphology was observed, and the flank wear of the micro-drills was measured. The factors affecting flank wear were studied. In addition, hole wall roughness, nail head formation, and the accuracy of hole location were measured and analysed to determine how micro-drill wear influenced hole quality. It was found that abrasion was the main mechanism controlling the deterioration of cemented tungsten carbide micro-drills. The aggressive rubbing by glass fibre broken chips and reinforcing fillers, and the diffusion of cobalt caused abrasive wear of the flank, the chisel edge, the rake face, and the minor flank of the micro-drills. Resin that was softened by cutting heat would adhere to the micro-drills, which decreased chip removal and the accuracy of hole location. Micro-drill wear was inclined to cause nail heads and decrease the accuracy of hole location.     

Glass-forming carbazolylidene-containing hydrazones as hole-transporting materials

The synthesis, optical, thermal and photoelectrical properties of carbazole- and phenothiazine-containing hydrazones are reported. The ionization potentials of the films of the hydrazones, measured by the electron photoemission technique, range from 5.20 to 5.60 eV. Room temperature time-of-flight hole mobilities in the solid solutions of carbazole phenothiazine and carbazole carbazole hydrazones in bisphenol-Z polycarbonate exceeded 10^?5 cm²/(V s) at high applied electric fields.     

Prediction of effect of rolling speed on coefficient of friction in hot sheet rolling of steel using sliding rolling tribo-simulator

In order to reduce the rolling force and the roll wear, the lubricants have been used in hot rolling of steel. In order to evaluate the tribological behavior at the interface between roll and workpiece in hot steel rolling, it is important to measure the coefficient of friction and examine the effect of the tribological factors on the coefficient of friction. In this paper, the effect of the rolling speed on the coefficient of friction is investigated using the tribo-simulator testing machine for hot rolling developed by the authors. The workpiece used is SPHC. The roll material is SKD11 and the surface roughnesses are 0.05 μm, 0.2 μm and 0.8 μm. The rolling tests are carried out at a temperature of 800 °C during a rolling distance of 400 mm, changing the rolling speed from 15 to 70 m/min. The colza oil is used as a base oil and the emulsion concentrations are 0.1% and 3.0%. The coefficient of friction at an emulsion concentration of 3.0% is independent on the rolling speed. On the other hand, the coefficient of friction at an emulsion concentration of 0.1% decreases with increasing rolling speed in the lower range of rolling speed, but it increases in increasing rolling speed in the higher range of rolling speed.     

Abrasive slurry jet micro-machining of holes in brittle and ductile materials

This paper investigated the effects of elasticity and viscosity, induced by a dilute high-molecular-weight polymer solution, on the shape, depth, and diameter of micro-holes drilled in borosilicate glass and in plates of 6061-T6 aluminum alloy, 110 copper, and 316 stainless steel using low-pressure abrasive slurry jet micro-machining (ASJM). Holes were machined using aqueous jets with 1 wt% 10 μm Al₂O₃ particles. The 180 μm sapphire orifice produced a 140 μm diameter jet at pressures of 4 and 7 MPa. When the jet contained 50 wppm of dissolved 8 million molecular weight polyethylene oxide (PEO), the blind holes in glass were approximately 20% narrower and 30% shallower than holes drilled without the polymer, using the same abrasive concentration and pressure. The addition of PEO led to hole cross-sectional profiles that had a sharper edge at the glass surface and were more V-shaped compared with the U-shape of the holes produced without PEO. Hole symmetry in glass was maintained over depths ranging from about 80–900 μm by ensuring that the jets were aligned perpendicularly to within 0.2°. The changes in shape and size were brought about by normal stresses generated by the polymer. Jets containing this dissolved polymer were observed to oscillate laterally and non-periodically, with an amplitude reaching a value of 20 μm. For the first time, symmetric ASJM through-holes were drilled in a 3-mm-thick borosilicate glass plate without chipping around the exit edge.The depth of symmetric blind holes in metals was restricted to approximately 150 μm for jets with and without PEO. At greater depths, the holes became highly asymmetric, eroding in a specific direction to create a sub-surface slot. The asymmetry appeared to be caused by the extreme sensitivity of ductile materials to jet alignment. This sensitivity also caused the holes in metals to be less circular when PEO was included, apparently caused by the random jet oscillations induced by the polymer. Under identical conditions, hole depths increased in the order: borosilicate glass > 6061-T6 aluminum > 110 copper > 316 stainless steel. The edges of the holes in glass could be made sharper by machining through a sacrificial layer of glass or epoxy.     

Fabrication of a micro-pin array with high density and high hardness by combining mechanical peck-drilling and reverse-EDM

To fabricate circular cross-section micro-pin array with high hardness and high density in a fast and efficient way, a combined method of mechanical peck-drilling and reverse electrical discharge machining (reverse-EDM) is proposed in this research. First, a ball-cone-hole-magnet (BCHM) method is applied in high vibration cantilevered platform (HVCP) and quick release holder/jig to produce highly precise, fast and elastic positioning. Second, a micro-hole array with high density and different types of holes on a workpiece (brass material) is produced by a vibration-assisted mechanical peck-drilling (VAMPD), which includes the high vibration of workpiece created by HVCP and mechanical peck-drilling of micro-drill. This VAMPD can drill up to 1600 single-stage or multi-stage micro-holes, and the aspect ratio of the drilled one-stage micro-holes of Ø60 μm is up to ten. Finally, reverse-EDM is used to fabricate the micro-pin array made of tungsten carbide. In this process, the effects of the chip removal mechanism, the various micro-hole types, and the density of the micro-holes on the electrodes are investigated. The results indicate that the combination of multi-stage micro-hole electrodes and three chip removal methods (working fluid spraying, vibration-assisted electrode and shake-down type workpiece) can produce a 1600-micro-pin array with an average diameter below Ø30.00 μm, a length of 625.0 μm, and a pitch of 100 μm. Consequently, the proposed method of combining mechanical peck-drilling and reverse-EDM can fabricate a micro-pin array with high hardness, high density, high quantity, and uniform diameter in a fast and efficient way.     

Thiophene-based hydrazones as hole-transporting materials

The synthesis, optical, thermal and photoelectrical properties of thiophene-based hydrazones are reported. The HOMO levels in a solid state of thiophene-based hydrazones measured by the electron photoemission technique are ?5.25 eV and ?5.28 eV. Hole-drift mobilities of the solid solutions in bisphenol-Z polycarbonate (PC-Z) of the synthesized hydrazones were studied by the time-of-flight technique. Room temperature hole mobilities in the solid solution of thiophene-2-carbaldehyde N,N-diphenylhydrazone in PC-Z exceeded 10^?5 cm²/(V s) at high electric fields.     

Orbital electrode actuation to improve efficiency of drilling micro-holes by micro-EDM

This paper presents a novel machining technique for micro-EDM that actuates the EDM electrode on an orbital trajectory that is created by a 2-axis flexural micro-EDM head with a range of ±100 μm in both x- and y-directions. The orbital motion with its adjustable radius decouples the size of the hole to be drilled from the size of the electrode, allowing a range of hole sizes to be drilled. The orbital motion of the electrode increases the hole diameter proportional to the orbital radius, thereby creating a larger gap between the work piece and the electrode, which promotes increased flushing. For holes with large depth to diameter ratios, the increased flushing reduces electrode wear, creates a better surface finish, and eliminates the exponential reduction in material removal rates typical for EDM drilling.     

Influence of wire-EDM on high temperature sliding wear behavior of WC10Co(Cr/V) cemented carbide

This paper reports the friction and wear response of WC–10%Co(Cr/V) cemented carbide with different surface finishes, attained by grinding (G) and wire-EDM, respectively, during sliding experiments at 400 °C. For comparison, tests under the same conditions were carried out at 25 °C. The wear experiments were performed under a normal force of 14 N, which produced a Hertzian maximum pressure of 3.10 GPa, and a sliding speed of 0.3 m/s against WC–6%Co(Cr/V) balls of 6 mm diameter. At 25 °C the average values of the friction coefficients were 0.36 ± 0.04 and 0.39 ± 0.06 for the ground and wire-EDM surface finishes, respectively. The mechanical behavior of both systems at 25 °C was assessed by carrying out analytical calculations of the stress field created by a circular sliding contact under a spherical indenter, where the residual stresses were considered. The theoretical results are in agreement with the experimental data, indicating that the wire-EDM sample has a specific wear rate, which is approximately 3.1 times greater than that corresponding to the G sample at 25 °C. At 400 °C, an increase in the friction coefficients takes place up to values of 0.75 ± 0.1 and 0.71 ± 0.8, for the ground and wire-EDM surface finishes, respectively. The increase was associated to an adhesive mechanism, which is more pronounced for the G sample. However, for the wire-EDM sample this increase was more linked to a marked abrasive mechanism. The wear rates for both samples at 400 °C are similar to those obtained at 25 °C, which indicates that apparently the test temperature does not have an important effect on the wear rate. However, it is known that temperature influences considerably the residual stress nature. Therefore, these results were explained by taking into account the wear mechanisms between the tribopairs in view of the mechanical characteristics and the morphological features obtained from SEM coupled with EDS analysis.     

Effects of LaB6 addition on arc-jet convectively heated SiC-containing ZrB2-based ultra-high temperature ceramics in high enthalpy supersonic airflows

The performances of a ZrB₂–SiC–LaB₆ ultra-high temperature ceramic (UHTC) was investigated in high enthalpy supersonic air flow. The UHTC material reached and maintained steady-state radiative surface temperature of 1973 K (monitored by pyrometer) for 5 min, and survived the arc-jet plasma exposure without any optical evidence of mechanical damage. The oxide scale covering externally the sample evolved into different textures. Transient thermal analysis processed via CFD provided a good agreement between the numerical steady-state temperature and the temperature distribution obtained experimentally. The contemporary addition of LaB₆ and SiC to ZrB₂ had a detrimental effect on the overall oxidation resistance.     

Effect of graphene platelets on tribological properties of boron carbide ceramic composites

The friction and wear behaviour of hot pressed boron carbide/graphene platelets (GPLs) composites have been investigated using the ball-on-flat technique with SiC ball under dry sliding conditions at room temperature. The hardness and fracture toughness of the investigated materials varied from 18.21 GPa to 30.35 GPa and from 3.81 MPa·m^1/2 to 4.60 MPa·m^1/2, respectively. The coefficient of friction for composites were similar, however the wear rate significantly decreased ~ 77% in the case of B₄C + 6 wt.% GPLs when compared to reference material at a load of 5 N, and ~ 60% at a load of 50 N. Wear resistance increased with increasing GPLs content in regards to the present graphene platelets, which during the wear test pulled-out from the matrix, exfoliated and created a wear protecting graphene-silicon based tribofilm.     

Transparent conductive Sb-doped SnO2/Ag multilayer films fabricated by magnetron sputtering for flexible electronics

The effects of an embedded silver layer and substrate temperature on the electrical and optical properties of Sb-doped SnO₂ (ATO)/silver (Ag) layered composite structures on polyethylene naphthalate substrates have been investigated. The highest conductivity of ATO/Ag multilayer films was obtained with a carrier concentration of 1.5 × 10²² cm^?3 and a resistivity of 2.4 × 10^?5 Ω cm at the optimum Ag layer thickness and substrate temperature. The photopic averaged transmittance and Haacke figure of merit are 81.7%, and 21.7 × 10^?3 Ω^?1, respectively. In addition, a conduction mechanism is proposed to elucidate the mobility variation with increased Ag thickness. We also describe the influence of substrate temperature on the structural, electrical and optical properties of the ATO/Ag multilayer films, and propose a mechanism for the changes in electrical and optical properties at different substrate temperatures.