Machining Micro Research Articles

Prediction of dimension error based on the deflection of cutting tool in micro ball-end milling

Micro milling forces can easily induce bending deflection when machining micro complex components, which makes the tool center deviate the desired trajectory and causes dimension error. So this study is mainly focused on analysis of dimension error in micro ball end milling. The analytical prediction model of dimension error is proposed based on the deflection of micro ball-end milling cutter induced by micro milling forces, which referenced to Euler Bernoulli cantilever beam equations. The micro milling forces acting on ball end milling cutter can be acquired by numerical integration. And the proposed models using two-section and three-section cantilever beam equation separately were analyzed by comparison. The proposed machining deflection’s error prediction model is validated by micro ball end mill on stainless steel workpiece. The experimental results show that the model based on three-section cantilever beam equation has a better correlation with the simulation results. The proposed theoretical model offers a basis for controlling machining deflection as well as manufacturing process optimization.

Precision machining of high aspect-ratio rotational part with wire electro discharge machining

Precision and micro rotational parts are widely used in various industries, such as micro probes for medical instruments, contact pins for micro assembly applications, micro electrodes for micro Electrical discharge machining (μ-EDM) or micro Electro-chemical discharge machining (μ-ECDM). In this research, a uniform annular area layer by layer feeding strategy was proposed to fabricate high aspect ratio, small radii rotational components on a conventional Wire electrical discharge machining (WEDM) machine equipped with an auxiliary spindle. The uniform annular area layer by layer feeding strategy consisted of the roughing and finishing stages. First, the theoretical Material removal rate (MRR) and radial infeed rate for each layer were determined for the roughing stage, and the theoretical surface roughness, Rz in the finishing stage was researched. Then, a series of optimization experiments were conducted to investigate the influence of the parameters on MRR and the machined surface roughness. A group of pin electrodes were machined by applying this feed strategy with the optimized parameters, and the minimum diameter of the pin electrodes was 40 μm with an aspect-ratio of 60. Finally, micro electrodes for an injection nozzle were achieved with this novel process and a qualified injection nozzle for powder metallurgy was fabricated with the machined micro electrodes.

Study in dimension precision of micro straight thin wall with Ti-6Al-4V titanium alloy under mesoscale

Deflection problems are important causes of deterioration to the dimensional precision of machining micro thin-walled components. Under mesoscale, the deflection of the cutting tool and micro thin-walled workpiece model is established based on the Euler-Bernoulli cantilever beam theory. Then a novel average thickness prediction model of micro straight thin wall is set up considering the runout, cutting tool, and workpiece deflection. Afterwards, based on experimental data, the model is modified by introducing a scale factor K. This modified model has been calibrated and validated with Ti-6Al-4V titanium alloy, and it can provide very accurate prediction results for the micro straight thin wall at average thickness. In addition, the law of micro thin wall milling forces is also studied. In the end, the effect of different micro straight thin-walled stiffness on micro thin-walled dimensional accuracy is analyzed. The study found that for the thickness of micro straight thin walls, 100 μm is an inflection point to distinguish dimension precision between macroscale and mesoscale.

Communication—Electrochemical Micro-Machining with Adjustable Resistance

In electrochemical micromachining technique using ultra short pulses, the pulse duration is the only effective control parameter of the machining resolution. Here, we added an adjustable resistance in the equivalent circuit of the electrochemical micromachining. The machining resolution depends on both the pulse duration and the adjustable resistance. So, the adjustable resistance can be taken as another control parameter for the machining resolution. As the adjustable resistance increases, the machining resolution can be improved. This technique was used for machining micro beams, and a good machining resolution was achieved.

Fabrication of micro-rotating structure by micro reciprocated wire-EDM

Micro rotating-structure manufacture has been largely carried out using a variety of processing methods. However, it is difficult to achieve the high-precise machining of the micro rotating structure due to the material constraints and the geometrical limitation of the free-form profile. This paper discusses the fabrication of micro-rotating structure using micro reciprocated wire electrical discharge machining (wire-EDM). To ensure machining accuracy, a gravity takeup for maintaining constant wire tension and a unit for suppressing the wire vibration are designed and fabricated, respectively. Besides, the effects of processing parameters on rotating groove width are investigated by conducting preliminary experiments, showing that high open voltage, discharge capacitance and revolving speed, and low discharge resistance and wire tension cause larger rotating groove width. Nevertheless, the rotating groove width firstly decreases with the reference voltage and feed rate increase in the initial stage and then increases when applying higher values. Based on the preliminary experiments, the proper processing parameters are determined and are used for machining micro bellows core-mould. Ultimately, the micro bellows core-mould is successfully machined by micro reciprocated wire-EDM, exhibiting high machining accuracy, excellent geometric shape and uniformity. Specifically, the machining errors along the axial direction and the radial direction of the micro bellows core-mould are less than 1.4 µm and 2.3 µm, respectively.

Experimental investigation of the influence of chip interference on burr height in machining micro V-grooves on electroplated copper roll die

The roll-to-roll imprinting technology is considered as the most promising process for manufacturing large-area microstructured surface in a high-precision, high-efficiency and low-cost way. However, the existence of cutting burr of microstructures on roll die will deteriorate the quality of microstructures on target surface in roll-to-roll imprinting processing. For electroplated copper material, this article presents the influence of chip interference on burr in cutting process. The parameter that illustrates the level of chip interference is deduced. The influences of cutting depth and included angle of V-shaped diamond tool on burr height of V-grooves are revealed by analyzing the chip interference. A series of experiments are carried out to verify the theoretical study. The results show good agreement between theoretical derivation and experimental analysis. The reason for chip interference of cutting process is made clear. Then, the optimal process of multi-step cutting process was given as the guidance to enhance the surface quality of micro V-grooves on electroplated copper roll die. With the optimal cutting parameters, the high-quality surface of micro-prism array is achieved.

Optimization of EDM process in machining micro holes for improvement of hole quality

Electrical discharge machining (EDM) or micro EDM found successful for production of micro holes on ceramics, hard metal and alloys. In the present study, experimental investigation and parametric optimization are carried out on EDM process for producing micro holes of diameter 500 µm on stainless steel (grade 304).Current (I), gap voltage (V) and pulse on time (T on) are considered as process parameters and are optimized for improving hole quality [i.e., overcut (OC) and taper angle (θ)]. Statistical regression models are developed for predicting OC and θ and effects of parameters are studied using surface plots. The optimal parameters are obtained for single as well as multiple performance characteristics. The traditional Taguchi analysis is used for optimization of each objective individually. This work presents the application of Taguchi optimization for simultaneous minimization of over cut (OC) and taper angle (θ) for improvement of hole quality in drilling micro holes. The optimal level of factors based on analysis of means (ANOM) with highest signal to noise (S/N) ratio is found as (i.e., I1 − V3 − T on2). This corresponds to parametric combination being 10 A, 50 V and 150 µs for I, V and T on respectively that produce improved hole quality with minimum overcut and taper angle. The obtained result is compared with desirability analysis and found that it is closer.

An Experimental Study of the Effects of Electrode Shapes on Micro-EDM Performances

In this paper, experiments were conducted to investigate the effects of cylindrical electrode and helical electrode on the micro electrical discharge machining (EDM) performances during micro-hole machining of titanium alloy. The results show that the material removal rate (MRR) and the tool wear rate (TWR) increase with open circuit voltage, regardless of electrode shapes. Compared to the cylindrical electrode, helical electrode can result in higher MRR and lower relative tool wear ratio (RTWR). It can be concluded that the helical electrode is more suitable than cylindrical electrode for machining micro parts.

Influence of machined surface roughness on thrust performance of micro-nozzle manufactured by micro-milling

This paper describes an investigation of the effects of machined surface roughness on micro-nozzle performance through computational fluid dynamics (CFD) simulations and experiment. Firstly, both ball end mill and taper end mill were used in the finish micro-milling processes for micro nozzles where different surface quality were obtained. A residue surface model for micro-nozzle was proposed and used in CFD simulation. The simulation results show that the increase of roughness causes that the outlet velocity decreases, total pressure drops and boundary layer thickness increases. The roughness increasing also leads to the deterioration of thrust performance of the micro nozzle. Secondly, a thrust measuring apparatus was designed and manufactured to evaluate the thrust performance of the machined micro nozzle. The thrust was measured at different inlet pressure for the machined micro-nozzles with different surface roughness. The measurement results indicate that the simulation results were consistent with the experiment. The nozzle with small roughness can achieve better thrust performance. Actual thrust fluctuation was caused by the incremental turbulent intensity with surface roughness.

Investigation on surface residual stress distribution and evaluation of engineering ceramics in rotary ultrasonic grinding machining

Residual stress of engineering ceramics is one of surface integrity evaluation indexes affecting the parts’ strength properties. Rotary ultrasonic grinding machining is the most powerful machining method for engineering ceramics with better surface integrity. The residual stress field distribution is changed due to micro cracks which are inevitable in the process. A residual stress distribution model of machined surface micro crack tip has been established in the paper. And the experimental results enable us to obtain surface residual stress distribution of engineering ceramics in rotary ultrasonic grinding machining. Then, we propose an evaluation parameter called confidence stress tolerance to evaluate surface residual stress characteristic. Preliminary results indicate that surface residual stress distribution is in line with the normal distribution. Confidence stress tolerance is an effective parameter to improve the evaluation reliability. Furthermore, precision and affecting factors of confidence stress tolerance evaluation have also been investigated.

Stability analysis for micro-milling nickel-based superalloy process

Nowadays, there is strong demand for micro parts and components which are able to function properly at high temperature in the fields of aerospace, biomedicine, and energy and power. Nickel-based superalloy with good comprehensive thermal performance is well fit for the requirement of micro parts and components. Micro-milling is a novel processing technology for machining micro and high-precision parts with high temperature resistance and it can be applied to manufacture nickel-based superalloy micro parts. Nickel-based superalloy is a kind of typical difficult-to-machine material and chatter tends to occur during its micro-milling process. Chatter damages machining precision and efficiency during the process. Considering the influences of multiple regenerative effect, minimum cutting thickness, and elastic recovery of processed surface, dynamical model of micro-milling process of nickel-based superalloy is built and chatter stability is analyzed in the time domain. Based on the stability lobes, cutting parameters to avoid chatter can be gained. Consequently, machining precision and efficiency are improved.

Analysis of Combined Parameter Effects and Profile Study of Micro Hole in Micro EDM Drilling

In this current work, the combined effect of micro EDM's process parameters was studied on Material Removal Rate (MRR). The selected input drilling parameters for experimental works are voltage, capacitance and sparkgap. The experiments were conducted based on the full factorial design methodology. The experimental results show that, with increase in both voltage and capacitance the MRR increases. With simultaneous increase in capacitance and sparkgap, the highest MRR is achieved at highest capacitance and lowest sparkgap values. Similarly, with the simultaneous increases in voltage and sparkgap the highest MRR is obtained at highest voltage and lowest sparkgap. The micro hole study was also performed to verify the geometry of the drills. Based on the SEM observations of micro hole profile, a smooth surface finish and straight edges have been obtained. The shape of the machined micro hole matches with the profile of the tool electrode.

Improvement of Geometrical Accuracy of Micro Holes Machined Through Micro Abrasive Jet Machining

Assembling of various parts and subassembly needs the closer attention on the geometrical accuracy of the part apart from the dimensional tolerances. Micro holes machined through micro abrasive jet machining are tapered, resulting in poor cylindricity. Cylindricity of the machined micro holes can be improved by reducing the taper angle of the hole. This paper presents a novel approach for machining holes on brittle material-quartz, using the in-house developed micro abrasive jet machine, wherein the nozzle is given a feed rate equal to the average rate of change of the workpiece thickness. The experiments are conducted to study the effect of this novel approach to the shape of the machined hole by measuring the entrance diameter and exit diameter and hence calculated the taper angle. The obtained experimental results reveals that the taper angle of the machined hole is reduced by approximately 58% using this novel approach and hence achieved the improvement in cylindricity of the machined holes.

An in-process tool wear evaluation approach for ultra-precision fly cutting

Ultra-precision fly cutting (UPFC) is an intermittent cutting process, which is widely used in the fabrication of non-rotational symmetric micro structures with sub-micron form accuracy and nanometric surface roughness. In UPFC, the occurrence of tool wear certainly affects the accuracy of machined micro structures. Aimed at the close relations between tool wear and chip morphologies and the truth that cutting chips are fully formed in a cutting cycle, this research developed a tool wear evaluation approach based on cutting chips. Chip morphology features related to tool failure patterns were identified and then parameterized to predict the tool failure patterns, the surface topography, and surface roughness under the effects of tool failure patterns. Predictions were then verified by experimental results. Research results show that chip morphologies were successfully used to present tool failure pattern, following the well-designed identification procedures, the tool failure patterns are accurately identified. This approach is practical since it can in-process identify tool failure patterns and their effects on surface quality.

Effect of low frequency vibration on micro EDM drilling

A micro hole is a basic feature in micro manufacturing. Micro electrical discharge machining (EDM) is one of the key techniques for machining micro holes in metallic materials. Since debris is accumulated in the discharging gap between the tool electrode and the workpiece, it becomes increasingly very difficult to machine a micro hole as the chosen diameter is progressively decreased or the depth increased. The use of vibration in micro EDM drilling can improve machining efficiency by refreshing dielectric fluids and flushing out the debris from the gap. Although ultrasonic vibration over a few kHz has been introduced in many applications of micro EDM, it is difficult to apply to a workpiece of a very large size or mass. In this study, the effect of very-low-frequency vibration was investigated to improve the efficiency of micro EDM. Low-frequency vibration in the range of 10 to 70 Hz was applied to single-hole machining, to reverse EDM, and to multiple-hole machining. The machining efficiency was investigated while varying the vibration frequency and amplitude.

Development of a Single Pulse Micro EDM System and to Manufacture Micro Spherical Probe Used in Micro CMM

The focus of this research is the development of a single pulse micro EDM system and to manufacture micro spherical probe used in micro CMM. In the single pulse micro EDM system contain unsteady-state multi-degree oscillation circuits to control the transistors’ switches. This configuration is to achieve the adjustment of pulse-off time of the micro-electrical discharge machining system. Investigating the effect of pulse voltages on the critical discharge gaps, the experimental results show that maximum discharge gaps are linearly proportional to the pulse voltages. This tendency serves as the basis for the machine processing parameters. And used of the single pulse micro EDM system to machining micro spherical probe.The micro spherical probe with a diameter smaller than 100 μm, is made by a single pulse micro EDM system with the method of wire electro discharge grinding (WEDG). The current study uses tungsten carbide (WC) as the material for the stylus. Experimental results show that, the micro spherical probe roundness could amount to 2 μm.

Enhancement of performance of wire electrochemical micromachining using a rotary helical electrode

The inherent characteristics of wire electrochemical micromachining (WECMM) enable it to be a feasible alternative to machining micro structures with good surface integrity in difficult-to-machine materials. Efficient electrolyte renewal has been proven to be important to the process stability and material removal rate in the machining of high aspect ratio micro structures. This paper proposes a method of WECMM using a rotary helical electrode to enhance electrolyte refreshment in the machining depth direction gap. Simulations of the flow field indicate that when a helical electrode revolves at a high speed, the electrolyte in the machining gap is stirred drastically, and the helical groove on the electrode surface is conducive to electrolytic flow in the axial direction. In addition, a series of experiments verifies that the maximum electrode feedrate and the slit width uniformity in the depth direction are enhanced by using a rotary helical electrode. Finally, two complex micro structures are successfully produced using a rotary helical electrode at a spindle speed of 20000rpm.

Surface textures on cemented carbide cutting tools by micro EDM assisted with high-frequency vibration

This paper demonstrates the process of micro electro-discharge machining (micro EDM) assisted with high-frequency vibration machining micro holes and linear grooves which are straight or inclined on WC/8 % Co (MA) and WC/15 % TiC/6 %Co (MB) cemented carbide cutting tool rake face or scrap reeling slot. Low-voltage sensing contact is introduced to determine the exact position of holes and grooves. Morphology of textured regions is examined and the elemental chemical composition of close proximity region to a straight hole is identified. Results show that micro holes and linear grooves with high dimension accuracy and exact position are machined as expected by micro EDM assisted with high-frequency vibration. There is no debris accumulating around the cavities. Materials of MA cutting tool adhere on the micro tool electrode slightly, while the dimension of adhesion position becomes constant after 3 μ holes are finished. However, the adhesion does not occur during machining MB cutting tools. The distance of edges of grain refinement regions and areas where elemental chemical composition varies to the contour of the hole is no more than 15 μm.

Tribological behaviors of two micro textured surfaces generated by vibrating milling under boundary lubricated sliding

Surface texture technology is widely used in various friction pairs to obtain good lubrication. However, ever present researches are mainly focused on regular and simple texture shapes such as dimples and grooves. Few works on complex micro texture have been reported due to preparing difficulty. In this paper, two surfaces with complex micro texture, which are micro scale textured (MST) surface and micro furrow textured (MFT) surface, are prepared by ultrasonic vibration-assisted milling (UVAM) method. Also, their tribological behaviors under starved oil lubrication and reciprocating sliding condition are experimentally investigated with a smooth sample as comparison. Experimental results indicate that although the application of ultrasonic vibration leads to the increase of roughness of MST and MFT surfaces, both the two machined micro textures contribute to the improvement of lubricant film strength, and MFT surface has better tribological performance than that of MST surface. As a result, under test conditions, micro texture formed by UVAM method can greatly improve the tribological property of friction surface, especially for its bearing capacity and wear resistance.

Micro grinding with ultra small micro pencil grinding tools using an integrated machine tool

Micro grinding offers a high potential when machining micro structures in hard and brittle materials. In this context, a new machine tool – the nano grinding center – was developed, which allows to manufacture and apply ultra small micro pencil grinding tools without re-clamping. With this new machine tool, the influence of grain size, grain concentration, and process parameters on the material removal mechanisms was investigated during micro grinding of silicon with grinding tool diameters of 40μm and 4μm. Measurements of process forces, surface quality and accuracy were carried out and the results are discussed.