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.     

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.     

Analysis of micro-drilling of glassy ceramic Macor nozzles for scanning droplet systems

This paper presents a new approach called spindle-peak-frequency (SPF) for determining stable micro-drilling parameters. The novelty is that the approach does not require a force model, material behaviour of the workpiece, modal stiffness and damping of the drilling tools. The only required parameter is the natural frequency of the drilling tools, which is obtained by modal dynamic finite element analysis (FEA). Material constants for the Johnson–Cook material model for Macor are obtained and implemented into a FE model of orthogonal cutting to investigate the cutting mechanisms. The results have shown that the cutting mechanisms of the Macor are achieved by initiation and propagation of micro-cracks. Finally, the developed research methods have been implemented to manufacture Macor nozzles of scanning droplet systems where holes with diameter of 100 μm and aspect ratio of 10 have been successfully drilled which has increased the resolution by 5 times.     

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.     

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.     

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.     

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.     

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.     

Development of a reversible machining method for fabrication of microstructures by using micro-EDM

A new micromachining method for the fabrication of micro-metal structures by using micro-reversible electrical discharge machining (EDM) was investigated. The reversible machining combines the micro-EDM deposition process with the selective removal process, which provides the ability of depositing or removing metal material using the same micro-EDM machining system. From the discharge mechanism of micro-EDM, the process conditions of micro-EDM deposition were analyzed firstly. Using the brass and steel materials as a tool electrode, the micro-cylinders with 200 μm in diameter and height-to-diameter ratio of more than 5 were deposited on a high-speed steel surface. Then the machining procedure was transformed easily from deposition to selective removal process by switching the process conditions. Different removal strategies including micro-EDM drilling and micro-EDM milling were used in the machining. Micro-holes with 80 μm in diameter are drilled successfully in the radial direction of the deposited micro-steel cylinder. Also, a brass square column with 70 μm in side length and 750 μm in height, and a micro-cylinder with 135 μm in diameter and 1445 μm in height are obtained by using micro-EDM milling. Finally, the characteristics of the deposited material were analyzed. The results show that the material components of a deposited micro-cylinder are almost the same as those of the tool electrode, and the metallurgical bonding has been formed on the interface. In addition, the Vickers-hardness of 454Hv of the steel deposited material is higher when compared to the hardness of 200Hv of the raw steel electrode.     

Experimental evaluation of the lubrication performance of MoS2/CNT nanofluid for minimal quantity lubrication in Ni-based alloy grinding

A nanofluid minimum quantity lubrication with addition of one kind of nanoparticle has several limitations, such as grinding of difficult-to-cutting materials. Hybrid nanoparticles integrate the properties of two or more kinds of nanoparticles, thus having better lubrication and heat transfer performances than single nanoparticle additives. However, the use of hybrid nanoparticles in nanofluid minimum quantity lubrication grinding has not been reported. This study aims to determine whether hybrid nanoparticles have better lubrication performance than pure nanoparticle. A hybrid nanofluid consisting of MoS₂ nanoparticles with good lubrication effect and CNTs with high heat conductivity coefficient is investigated. The effects of the hybrid nanofluid on grinding force, coefficient of friction, and workpiece surface quality for Ni-based alloy grinding are analyzed. Results show that the MoS₂/CNT hybrid nanoparticles achieve better lubrication effect than single nanoparticles. The optimal MoS₂/CNT mixing ratio and nanofluid concentration are 2:1 and 6 wt%, respectively.     

Variation of temperature at the bottom surface of a hole during drilling and its effect on tool wear

The temperature at the bottom surface of a hole being drilled is measured by using an infrared-radiation pyrometer equipped with two optical fibers. One of the optical fibers is inserted into the oil hole of an internal coolant carbide drill and passes through the machine-tool spindle. This optical fiber is connected to another optical fiber at the end of the spindle. Infrared rays radiating from the bottom surface of the hole being drilled are accepted and transmitted to the pyrometer by the two optical fibers. Temperature increases as drilling progresses, and it increases considerably near the bottom surface of the workpiece. In case of a 10-mm-thick carbon–steel workpiece, temperature reaches 190, 250, and 340 °C at drilling depths of 6, 8, and 10 mm, respectively. To investigate the effect of the increase in temperature on drill wear, a series of 10-mm-deep blind holes are drilled in workpieces with thicknesses of 10 and 25 mm. Tool wear is greater when the drill cuts a hole at the bottom of a 10-mm workpiece than that when the drill cuts a hole at the mid-depth of a 25-mm workpiece. This indicates that the rapid increase in temperature near the bottom of the workpiece effects the progress of drill wear.     

Deep hole drilling using tools with small diameters—Process analysis and process design

This paper is focused on the drilling of bore holes with high length-to-diameter ratios and diameters less than 2 mm which are needed, for example, in medical and automotive applications. In the presented research, the influence of cutting data and tool design on tool wear and chip formation has been analysed. First the experimental set-up is described followed by an in-depth process analysis of the single-lip deep hole drilling process under investigation. The next section deals with a process combination, where laser and mechanical drilling are combined in order to improve process reliability and productivity.     

A microstructural investigation of the surface of a drilled hole in carbon steels

The microstructure of the surface of drilled holes generated under different drilling conditions in carbon steels has been investigated. It is found that the surface microstructure depends strongly on the drilling parameters and the hardness of the matrix. White etching layers, composed of an equiaxed nanocrystalline structure layer with an average grain size of the order of several 10 nm and a submicron grained layer containing fresh martensite along the depth, formed on the hole surfaces during drilling at moderate to high cutting speed in carbon steels with high matrix hardness. The existence of a high content of austenite at the hole surface suggests that dynamic phase transformation (DPT) from body-centered cubic to face-centered cubic occurred during high-speed drilling. It is proposed that the ultrafine structure layer on the surface of a drilled hole is produced by severe plastic deformation-induced DPT together with a large strain gradient and high strain rate.     

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.     

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.     

Periscope infrared thermography for local wall thinning in tubes

In this paper, a novel way to inspect local wall thinning in metal tubes with infrared thermography has been demonstrated. The first of its kind method utilizes a periscope-like reflector located deep inside a tube to mirror the radiated heat that flows across the tube thickness to an IR camera positioned outside the tube. Localized wall thinning was represented by partially drilled holes of different depths on a tube, of inner diameter 82 mm and outer diameter 91 mm. Feasibility studies were carried out through simulations using a finite element model. Experiments were performed to determine the thermal diffusivity of the material. Remaining thicknesses of the tubes in wall-thinned sections were found to be estimated reasonably well using measured time–temperature profiles obtained by flash method [Parker WJ, Jenkins RJ, Butler CP, Abbott GL. Flash method of determining thermal diffusivity, heat capacity, and thermal conductivity. J Appl Phys 1961;32:1679–84]. The good correlation found between model calculations and measurements vindicated the utility of a model-based approach to applications of pulsed IR thermography.     

CO2 laser micromachined crackless through holes of Pyrex 7740 glass

The drilling of glass through holes with a high aspect ratio is crucial for microsystems application, especially in the inlet/outlet connection of microfluidic devices for biological analysis or for the anodic bonded silicon-glass ones. Traditional glass drilling using mechanical processing and laser processing in air would produce many kinds of defects such as bulges, debris, cracks and scorch. In this paper, we have applied the method of liquid-assisted laser processing (LALP) to reduce the temperature gradient, bulges and heat affected zone (HAZ) region for achieving crack-free glass machined holes. The nominal diameters of circles from 100 to 200 μm were drawn for through glass machining test. Through-hole glass etching can be obtained by LALP for 10 passes of circular scanning in several seconds on conditions of a 6 W laser power, 76 μm spot size and 11.4 mm/s scanning speed. The ANSYS software was also used to analyze the temperature distribution and thermal stress field in air and water ambient during glass hole machining. The higher temperature gradient in air induced higher stress for crack formation while the smaller temperature gradient in water had less HAZ and eliminated the crack during processing. CO₂ laser micromachining under water has merits of high etching rate, easy fabrication and low cost together with much improved surface quality compared to that in air.     

Computer controlled system for dieless drawing of tool steel bar

This paper describes the computer controlled processing of AISI-O1 steel rod by a dieless drawing method. Both the operation of a purposely built machine and the results of an experimental programme are described. The machine consisted of elements to provide a drawing force, a PID controlled band heater and an air/water cooling system to carry out the novel bar production process. The untreated material in bar form of initial diameter, 5 mm, was drawn in the temperature range of 600–750 °C at drawing velocities of 2.5–5 mm/min and with air-cooling provided in the pressure range 2–4 × 10⁵ Pa. The process ratio, i.e. the ratio of the drawing velocity to the heat/cooling device movement velocity was varied between 0.35 and 1.33. A novel load-control algorithm was executed to ensure a steady-state process and a high tolerance on the final drawn diameter.     

Experimental and FEM study on sinking of miniature inner grooved copper tube

Miniature inner grooved copper tubes (mIGCT) which have an outer diameter less than 6 mm are in demand for the production of heat pipes. In this work, it is proposed to manufacture such tubes by a multi-stage tube sinking process with an initial mIGCT having an outer diameter of 6 mm. A FEM simulation approach is used to analyze stress, strain and damage distribution for the proposed process. For comparison, a smooth copper tube is also used in the simulation study. Furthermore, experiments are conducted to investigate plastic deformation of the grooves and teeth of the tube. Results show that the maximum stress and strain are occurred at the grooves area, while the maximum damage is located at the top of the teeth. The ratio of groove width to tooth width (β) is reduced after each drawing pass. Bonding, folding and segmenting, which represent potential flaws, have also been observed in the multi-stage tube sinking process, and are discussed.     

Development of micro-plasma transferred arc (μ-PTA) wire deposition process for additive layer manufacturing applications

Micro-plasma transferred arc (μ-PTA) deposition process has potential to meet requirements of the meso-sized fabrication and repair of the high value components. This paper reports on the development of μ-PTA as cost effective and energy efficient alternative process for small sized deposition with an overall objective to repair and/or remanufacture the defective dies and molds. An experimental setup was developed to deposit 300 μm diameter wire of AISI P20 tool steel on the substrate of the same material which is one of the most commonly used materials for making the dies and molds used for various applications. Two stage experiments were conducted to indentify the important process parameters generating regular and smooth single bead geometry. The process was further explored for highest possible deposition rate for fabrication of straight walls through multi-layer deposition. The μ-PTA deposition process was found to be capable of fabricating straight walls having total wall width of 2.45 mm and effective wall width of 2.11 mm. The deposition efficiency was found to be 87% for the maximum deposition rate of 42 g/h. The microscopic examination and micro-hardness measurements revealed that the deposited wall is free from cracks, porosity, and inclusions. This study confirms the capability of μ-PTA for ALM in comparison to the existing high energy deposition processes used for meso-scale fabrication and repair applications of the dies and molds. This work confirms that μ-PTA wire deposition process offers the advantages of the laser based processes at much lower cost and more energy efficiency thus making it potential alternative process for repair and remanufacturing of the defective dies and molds. Use of finer wire can further reduce the deposition size enabling μ-PTA wire deposition process to fabricate the miniaturized parts.