Innovative micro hole machining with minimum burr formation by the use of newly developed micro compound tool

The study focuses on the efforts for minimization of burr formation and improvement of hole surface roughness in micro through-hole machining. It deals with the development of micro compound tool which is consisting of a micro flat drill as the drilling part and a micro diamond-electroplated-grinding part for hole finishing. The finishing diameters of each drilling and grinding parts of the fabricated micro compound tool are 90 μm and 100 μm, respectively. The study focuses mainly on the effect of drill point angle and ultrasonic vibration applied during micro hole machining to the hole entrance and exit burrs formation. The used workpiece is made of stainless steel (SUS304) with a thickness of 100 μm. From the experiment, it was found that the tool having drill point angle of 118° resulted in a smaller burr formation although hole machining was conducted for 600 holes. Furthermore, the application of ultrasonic vibration during hole machining could improve the performance of the developed micro compound tool and decreased the burr size, especially the exit burr.     

Influence of overlap between the laser beam tracks on surface quality in laser polishing of AISI H13 tool steel

Polishing by laser beam radiation is a novel manufacturing process to modify the initial surface topography in order to achieve a desired level of surface finish. The performance of laser polishing (LP) is determined by an optimum combination of several key process parameters. In this regard, the overlap between two successive laser beam tracks is one of the important LP process parameters, which has a significant effect over the final surface quality. In the current study, influence of overlap between the laser beam tracks on surface quality was experimentally investigated during the laser polishing of AISI H13 tool steel. Surface areas were polished by using four different overlap percentages (e.g. 80%, 90%, 95%, and 97.5%) while applying the same energy density. The improvement of surface quality was estimated through the analysis of line profiling surface roughness R_a, areal topography surface roughness S_a, and material ratio function. Also, individual components of the surface quality, e.g. waviness and roughness, and their evolution during LP were statistically analyzed using the power spectral density and the transfer functions. Finally, as an example of the best achieved LP result, flat surface area was polished using optimum set of the process parameters improving surface quality by 86.7% through the reduction of an areal topography surface roughness S_a from 1.35 μm to 0.18 μm.     

An experimental technique to detect tool–workpiece contact in micromilling

There is a need for simple, accurate, and low-cost techniques to detect tool–workpiece contact (or tool touch-off) in micromilling operations. This paper presents a method that is based on monitoring changes in the power spectral characteristics of the spindle vibration signal. The accuracy of this contact detection method is evaluated under different conditions by measuring the overshoot of the tool into the workpiece surface. Specifically, the effects of tool geometry, workpiece surface roughness and hardness, tool wear, step size, and contact detection threshold on the overshoot are analyzed through experiments carried out on a 3-axis micromilling machine. The results show that the method is capable of sub-micron contact detection accuracy depending on the workpiece hardness, roughness, and contact detection threshold.     

The effect of spindle speed,feed-rate and machining time to the surface roughness and burr formation of Aluminum Alloy 1100 in micro-milling operation

This paper describes the characteristics and the cutting parameters performance of spindle speeds (n, rpm) and feed-rates (f, mm/s) during three interval ranges of machining times (t, minutes) with respect to the surface roughness and burr formation, by using a miniaturized micro-milling machine. Flat end-mill tools that have two-flutes, made of solid carbide with Mega-T coated, with 0.2 mm in diameter were used to cut Aluminum Alloy AA1100. The causal relationship among spindle speeds, feed-rates, and machining times toward the surface roughness was analyzed using a statistical method ANOVA. It is found that the feed-rate (f) and machining time (t) contribute significantly to the surface roughness. Lower feed-rate would produce better surface roughness. However, when machining time is transformed into total cut length, it is known that a higher feed-rate, that consequently giving more productive machining since produce more cut length, would not degrade surface quality and tool life significantly. Burr occurrence on machined work pieces was analyzed using SEM. The average sizes of top burr for each cutting parameter selection were analyzed to find the relation between the cutting parameters and burr formation. In this research, bottom burr was found. It is formed in a longer machining time compare the formation of top burr, entrance burr and exit burr. Burr formation is significantly affected by the tool condition, which is degrading during the machining process. This knowledge of appropriate cutting parameter selection and actual tool condition would be an important consideration when planning a micro-milling process to produce a product with minimum burr.     

Investigation of chipping and wear of silicon wafer dicing

Wafer dicing chipping and blade wear processes in transient and steady stages were investigated. Dicing blades with two different diamond grit sizes were used to cut wafers. In the cutting experiments, the dicing blades with two different diamond grit sizes were used to cut wafers and for a given type of wafer, the cooling water temperature, cutting feed speed, and rotational speed were fixed. The chipping size, blade surface wear area and surface roughness of the wafer were measured at cutting distances of 50, 150, 300, 975, 1350, and 1900 m, respectively. Cutting debris of cutting distances of 300 m and 1900 m was collected and analyzed. The correlation between blade surface properties and chipping size was investigated. Based on this experimental system, attention is to pay to examine the correlation between blade surface properties and chipping size for transient stage and steady stage. In transient stage, the roughness of dicing blade increases rapidly. This will rapidly increase the chipping size. In steady stage, the chipping size decreases slowly with the decreasing roughness of blade surface. This concludes that blade surface condition is an important factor that affects the chipping size. Moreover, in transient stage, diamond grits that are salient or less bonded to the blade detach leave caves on the blade surface which increases surface roughness of the blade and the chipping size. In steady stage, the heights of grits become even and the chipping size decreases accordingly.     

Effect of mechanical surface treatments on Ti–6Al–4V direct metal deposition parts

The effect of surface treatments, including aggressive milling, rotational burnishing, and nonrotational burnishing, on Ti–6Al–4V DMD (direct metal deposition) parts was investigated. Particular emphasis is on the question of whether these surface treatments could induce the plastically deformed and work-hardened layer that was proven to enhance the fatigue resistance of titanium alloys and was a key step for recrystallization. Through the microhardness examination and microstructure analysis, it was found that the rotational burnishing process was able to work harden the material deeper than 1000 μm, while the work-hardened layer generated by the nonrotational process was ∼600 μm and that for aggressive milling was less than 10 μm. Because surface finish is another critical factor for the resistance of fatigue crack initiation, it was also evaluated for these treatments.     

Aero-lap polishing of poly crystalline diamond inserts using Multicon media

Increasing use of poly crystalline diamond (PCD) inserts as cutting tools and wear parts is vividly seen in automobile, aerospace, marine and precision engineering applications. The PCD inserts undergo series of manufacturing processes such as: grinding that forms the required shape and polishing that gives a fine finish. These operations are not straight forward as PCD is extremely resistant to grinding and polishing. Single crystal diamond can easily be polished by choosing a direction of easy abrasion, but polishing a PCD imposes serious difficulties as the grains are randomly oriented. Prior research on polishing of PCD inserts includes electro discharge grinding (EDG), dynamic friction polishing and grinding by a vitrified bonded diamond wheel. The surface textures of PCD produced using an EDG process often contains: micro cavities, particle pullout, micro-grooves, chipped edges, cracks and gouch marks. While applying the dynamic friction polishing method the PCD material undergoes phase transformation and hence increased polishing rate was apparently seen. However the phase transformation of PCD deteriorates the strength of the insert. Furthermore the inserts produced using the dynamic polishing method often exhibits cracks, chip off and edge damage while using as a cutting tool. Therefore, a new method “aero-lap polishing” was attempted as it applies controlled amount of impinging force by which the surface damage can be significantly reduced. The study did establish an improvement of surface finish of PCD from R_a = 0.55 μm, R_t = 4.5 μm to R_a = 0.29 μm, R_t = 1.6 μm within 15–25 min of polishing time along with significant reduction in surface defects.     

Experimental Evaluation of Cutter Orientation When Ball Nose End Milling Inconel 718™

High-speed machining (HSM), specifically end milling and ball end cutting, is attracting interest in the aerospace industry for the machining of complex 3D aerofoil surfaces in titanium alloys and nickel-based superalloys. Following a brief introduction on HSM and related aerospace work, the paper reviews published data on the effect of cutter/workpiece orientation, also known as engagement or tilt angle, on tool performance. Such angles are defined as ±β_fN and ±β_f.Experimental work is detailed on the effect of cutter orientation on tool life, cutting forces, chip formation, specific force, and workpiece surface roughness when high-speed ball end milling Inconel 718™. Dry cutting was performed using 8 mm diameter PVD-coated solid carbide cutters with the workpiece mounted at an angle of 45° from the cutter axis.A horizontal downward (-β_fN) cutting orientation provided the best tool life with cut lengths ∼50% longer than for all other directions (+β_fN, +β_f, and –β_f). Evaluation of cutting forces and associated spectrum analysis of results indicated that cutters employed in a horizontal downward direction produced the least vibration. This contributed to improved workpiece surface roughness, with typical mean values of ∼0.4 μm Ra as opposed to ∼1.25 μm Ra when machining in the vertical downward (–β_f) direction.     

Water jet guided laser as an alternative to EDM for micro-drilling of fuel injector nozzles: A comparison of machined surfaces

To characterize the inner surface of the fuel injector nozzle holes drilled by EDM and water jet guided laser drilling (Laser Micro-Jet) a specifically conceived scanning probe microscopy technique with true non-contact operating mode was used. A difference in morphology of the drilled surfaces is evident from the acquired surface topography along the hole axis for the two compared drilling techniques. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity. Acquired maps confirm that electro-eroded surfaces are an envelope of craters randomly distributed with total excursion up to 1.7 μm with a crater size of 15 μm. While, the efficient melt expulsion and immediate cooling of water jet guided laser generates a peak to valley distance of 800 nm with a periodicity of 18 μm. Average R_q derived from the measured cylindrical surfaces was 450 nm and 150 nm for EDM and Laser Micro-Jet, respectively. Water jet guided laser drilling has proved to be a reliable alternative to EDM from the point of view of repeatability of the results and surface quality to facilitate the atomization of the fuel jet.     

Micro end mill tool temperature measurement and prediction

The objective of this work is to characterize the heat transfer in micro end mill tools during machining operations. This analysis will aid in the design of heat dissipation strategies that could potentially increase tool life and machining precision. Tool temperatures, above the unmachined workpiece surface, have been measured using an infrared camera during slot milling of aluminum (6061-T6) and steel (1018) with 300 μm-diameter two-flute tungsten carbide end mills. The measured temperatures compare favorably with temperature distributions predicted by a two-dimensional, transient, heat transfer model of the tool. The heat input is estimated by applying Loewen and Shaw’s heat partitioning analysis. Analysis of heat transfer in the tool found that 46 s into a cut conduction through the length of the tool, storage in the tool, and convection from the surface account for 41.5%, 45%, and 13.5% of the heat generated during machining. Thermal expansion and cooling strategies are discussed.     

High aspect ratio micromachining of glass by electrochemical discharge machining (ECDM)

Micromachining of glass is essential for several microfluidic components, micro-pumps, micro-accelerometers, micro-reactors, micro-fuel cells and several biomedical devices. Unique properties such as high chemical resistance, thermal stability and transparency give glass scope for additional applications. However, poor machinability of glass is a major constraint, especially in high aspect ratio applications of glass in microsystem technology. Micro electrochemical discharge machining (micro ECDM) is an emerging nontraditional fabrication method capable of micromachining ceramic materials like glass. While surface features less than 100 μm have been successfully machined on glass, machining high aspect features is a challenge. Machining accuracy at high depths is severely affected due to overcut and tool wear. In this paper, high aspect ratio microtools fabricated in-house have been used for deep microhole drilling on glass using low electrolyte concentration. An aspect ratio of 11 has been achieved. The results show that lower electrolyte concentration reduced overcut by 22%, thus increasing the aspect ratio of the micro holes. Lowering the electrolyte concentration also reduced the tool wear and hole taper by 39% and 18% respectively.     

Analysis of machined surface quality in a single-pass of ball-end milling on Inconel 718

The ball-end milling process is widely used for generating three-dimensional sculptured surfaces with definite curvature. In such cases, variation of surface properties along the machined surface curvatures is not well understood. Therefore, this paper reports the effect of machining parameters on the quality of surface obtained in a single-pass of a ball-end milling cutter with varying chip cross-sectional area. This situation is analogous to generation of free form cavities, pockets, and round fillets on mould surfaces. The machined surfaces show formation of distinct bands as a function of instantaneous machining parameters along the periphery of cutting tool edge, chip compression and instantaneous shear angle. A distinct variation is also observed in the measured values of surface roughness and micro-hardness in these regions. The maximum surface roughness is observed near the tool tip region on the machined surface. The minimum surface roughness is obtained in the stable cutting zone and it increases towards the periphery of the cutter. Similar segmentation was observed on the deformed chips, which could be correlated with the width of bands on the machined surfaces. The sub-surface quality analysis in terms of micro-hardness helped define machining affected zone (MAZ). The parametric effects on the machining induced shear and residual stresses have also been evaluated.     

Evaluation of the effectiveness of low frequency workpiece vibration in deep-hole micro-EDM drilling of tungsten carbide

The application of micro-electrical discharge machining (micro-EDM) in deep-hole drilling is still limited due to the difficulty in flushing of debris and unstable machining. Present study introduces a simplistic analytical model to evaluate the effectiveness of low frequency workpiece vibration during the micro-EDM drilling of deep micro-holes. In addition, experimental investigation has been conducted to validate the model by studying the effects of workpiece vibration on machining performance, surface quality and dimensional accuracy of the micro-holes. The effect of vibration frequency and amplitude for three different settings of aspect ratios has been studied experimentally. Moreover, the vibration experiments have been conducted at different levels of gap voltages and capacitances in order to understand the effect of electrical parameters and effectiveness of low-frequency workpiece-vibration at different levels of discharge energies. It has been shown analytically that the effectiveness of low frequency workpiece vibration during micro-EDM drilling can be evaluated by a parameter ‘K_v’ (ratio of maximum acceleration of the vibrating plate in gravitational direction to gravitational acceleration ‘g’), which can be determined from the vibration frequency, amplitude and phase angle of the vibrating workpiece. The theoretical model reveals that for K_v > 1, the position of debris particles will be above the workpiece; thus can be flushed away from machined zone effectively. The experimental reasons for improved micro-EDM drilling performance at the setting of K_v > 1 are found to be the increased effective discharge ratio, reduced short-circuits and improved dielectric flushing. The experimental results also reveal that the low frequency vibration is more effective at the low discharge energy level, thus making it more suitable for micro-EDM. Considering the effect on both the machining characteristics and micro-hole accuracy parameters, vibration frequency of 750 Hz and amplitude of 1.5 μm was found to provide improved performance for the developed vibration device.     

Experimental investigation of the machining induced residual stress tensor under mechanical loading

Residual stress induced by machining is complex and difficult to predict, since it involves mechanical loads, temperature gradients or phase transformation in the generation mechanism. In this work, an experiment with a statistical design for the residual stress tensor was performed to investigate the residual stress profile on a machined surface. In order to understand the generation mechanism of residual stress in machining, three variables and workpiece materials were carefully selected to focus on the mechanical loads and avoid the temperature gradients and phase transformation on the machined surface. The mechanical loads considered here included the chip formation force at the primary shear zone and the plowing force at the tool tip–workpiece contact. Depths of cut and rake angles were selected to alter the chip formation force, and the tool tip radius was designed to emphasize the plowing effect. The workpiece material was aluminum 3003. The experimental results showed that the chip formation force provides basic shapes of the residual stress profile for a machined surface. It decides the depth of the peak residual stress below the surface. However, the plowing force was the dominating effect on the surface residual stress, causing high stresses on the surface. The plowing force can shift the surface stress from tensile to compressive. Additionally, the measured stress tensor proved that in-plane shear stress exists for the machined surface.     

Study on machinability of a stellite alloy with uncoated and coated carbide tools in turning

Stellite alloys, which have been widely used in the aerospace, automotive and chemical industries, are hard-to-cut cobalt-based materials. This study investigates the machinability of stellite 12 alloys with uncoated carbide cutting tool grades YG610 (K01-K10) and YT726 (K05-K10/M20) and SANDVIK coated carbide tool SNMG150612-SM1105 under dry cutting conditions. Both wear mechanisms and failure modes of the uncoated and coated tools were investigated with turning experiments. The results show that the coated tool SM1105 remarkably outperforms the uncoated tools; and the cutting tool YG610 generally outperforms YT726 under all cutting conditions. Built-up edge was found with YG610 in some cutting conditions and with SM1105 at cutting speed of 16 m/min. Tool surface burning marks were observed on YT726 at relatively higher cutting speeds. Wear develops slowly with coated tools SM1105 until VB reaches 0.2 mm at most conditions (except at v = 43 m/min, f = 0.25 mm/r). Excessive tool flank typically resulted in tool breakage at the cutting edge for uncoated tools. Abrasive and adhesive wear of cutting tools were observed at low cutting speeds while diffusion and chemical wear occurred at higher cutting speeds.     

High speed ball nose end milling of hardened AISI A2 tool steel with PCBN and coated carbide tools

High speed machining (HSM) of tool steels in their hardened state is emerging as an attractive approach for the mold and die industry due to its potential for significant cost savings and productivity improvement. An experimental study was conducted to investigate the tool wear mechanism and surface integrity in high speed ball nose end milling of hardened AISI A2 tool steel using coated tungsten carbide and polycrystalline cubic boron nitride (PCBN) tools. It is found that coated carbide tools can only be used at low speed (120 m/min) while high content PCBN tools are suitable for HSM range (470 m/min). PCBN tools produce a damage free workpiece with better surface finish and less work hardening. Despite the higher tool cost, HSM with PCBN tools lead to reduction in both total cost and production time per part.     

Self-registration methods for increasing membrane utilization within compression-sealed microchannel hemodialysers

More than 1.2 million people worldwide require regular hemodialysis therapy to treat end stage renal failure. Current hemodialysis systems are too expensive to support at-home hemodialysis where more frequent and longer duration treatment can lead to better patient outcomes. The key cost driver for hemodialysers is the cost of the hemodialysis membrane. Microchannel hemodialysers are smaller providing the potential to use significantly less membrane. Prior work has demonstrated the use of sealing bosses to form compression seals in microchannel hemodialysers. In this paper, estimates show that the percentage of the membrane utilized for mass transfer is highly dependent on the design and registration accuracy of adjacent blood and dialysate laminae. Efforts here focus on the development of a self-registration method to align polycarbonate laminae compatible with compression sealing schemes for membrane separation applications. Self-nesting registration methods were demonstrated with average registration accuracies of 11.4 ± 7.2 μm measured over a 50 mm scale. Analysis shows that the registration accuracy is constrained by tolerances in the embossing process. A dialysis test article was produced using the self-nesting registration method showing a measured average one-dimensional misregistration of 18.5 μm allowing a potential 41.4% of the membrane to be utilized for mass transfer when considering both microchannel and header regions. Mass transfer results provide evidence of a twofold to threefold increase in membrane utilization over other designs in the existing literature.     

基体表面状态对硅烷环氧杂化树脂涂层/2024铝合金间附着力影响

目的研究不同表面状态对硅烷环氧杂化树脂涂层/2024铝合金间附着力影响规律。方法结合硅烷环氧杂化树脂涂层的综合性能与实际应用情况,选取4种常见的预处理方式来改变基体表面状态,采用拉拔测试仪测试不同基体表面状态(基体表面p H值、基体表面粗糙度、基体表面能),涂层/基体间的附着力值,研究基体表面状态对该涂层/基体间附着力的影响关系。结果基体表面状体影响涂层附着力的根本原因是基体表面能、基体表面p H值和基体表面粗糙度。结论对于硅烷环氧杂化树脂涂层,其表面处理方式可用热碱清洗方法代替传统铬酸盐钝化;当硅烷环氧杂化树脂涂层喷涂厚度为30μm时,将铝合金基体表面粗糙度控制在Ra=4.75μm左右,可保证涂层有好的附着性,附着力值为8.84 MPa。     

Investigating surface roughness,material removal rate and corrosion resistance in PMEDM of γ-TiAl intermetallic

Titanium aluminide intermetallics offer an attractive combination of low density and good oxidation, corrosion and ignition resistance with unique mechanical properties. In this study two series of machining tests are designed. Firstly the powder mixed electrical discharge machining (PMEDM) of γ-TiAl by means of different powders such as aluminum, chrome, silicon carbide, graphite and iron is performed to investigate the output characteristics of surface roughness and topography, material removal rate (MRR), electrochemical corrosion resistance of machined samples and also the machined surfaces are investigated by means of EDS and XRD analyses. Secondly after selection the aluminum powder as the most appropriate kind of powder, the current, pulse on time, powder size and powder concentration are changed in different levels for overall comparison between EDM and PMEDM output characteristics. In the first setting of input machining parameters, aluminum powder improves the surface roughness of TiAl sample about 32% comparing with EDM case and also aluminum particles with the size of 2 μm, in the second setting of input parameters lead to 54% enhancement of MRR comparing with EDM case. The electrochemical corrosion results show that, corrosion resistance of the samples which are machined by graphite and chrome powders respectively are about three and two times more than the sample which is machined without powder.