Thinner Recast Layer Research Articles

Surface morphology analysis of AISI-D3 tool steel using rotary tool electric discharge machining process

Electric discharge machining (EDM) is one of the most prominent machining processes, which is used across the world for machining and creating intricate shapes in very hard-to-cut electrically conducting materials. This comprehensive study aims to investigate the surface modification and characterisation of thin AISI-D3 tool steel sheets and provides thorough information about the material characteristics, which are quite vital from the design and reliability point of view. The analysis shows that the average improvement in the final surface finish of the machined surface is close to 12%. In addition, the energy dispersive spectroscopy (EDS) images confirm the presence of 2.1% copper and 25.22% of carbon on the workpiece surface, showing the tool material transfer at the workpiece surface. Moreover, the scanning electron microscope (SEM) images confirm the presence of a thinner recast layer, fewer micro-cracks and very less embedding of tool material on the workpiece surface as compared to the stationary tool process.

Effects of ultrasonic assistance on microhole drilling based on Nd:YAG laser trepanning

The ultrasonic vibration was introduced to assist the Nd:YAG laser trepan drilling for improving drilling quality/performance. Effects of ultrasonic power and pulse energy on geometrical and/or metallurgical quality were deciphered for the ultrasonic-assisted Nd:YAG laser trepanning. The energy dispersive spectroscopy analysis was also carried out to reveal the influence of ultrasonic vibration on the elemental compositions of the areas surrounding the drilled microhole entrance. It was shown that the axial ultrasonic vibration coupled into the Nd:YAG laser trepanning process could effectively improve the hole entrance profile/morphology with less metallurgical defects such as microcracks. Moreover, relatively high ultrasonic power was more beneficial to the improvement of laser trepan drilling quality in terms of smaller hole taper angle, thinner recast layer, and less cracks, etc. However, the oxidation of the microhole sidewall could not be effectively improved by using the ultrasonic assistance.

Effects of bioceramic particles in dielectric of powder-mixed electrical discharge machining on machining and surface characteristics of titanium alloys

In powder-mixed electrical discharge machining (PMEDM), a suspension of powder particles is added to the dielectric to achieve a high surface quality and to improve the material removal rate (MRR). However, for biomedical applications, the machined surface must be nontoxic and also contain bioactive species; these constraints limit the choice of powder material. This study focuses on machining orthopedic-implant materials based on titanium and titanium–tantalum alloys using bioactive hydroxyapatite (HA)-powder suspension as the dielectric. The influence of the powder particles and the work-piece composition on the machining performance was investigated. Employing a suspension dielectric with 5g/L HA caused a smoother surface (Ra 2.1μm) with a thinner recast layer (∼9μm) as compared to using water to machine titanium which has surface roughness of Ra 2.4μm with a recast layer close to 10μm. In addition, the MRR of titanium machined in the HA-powder-suspension dielectric (6.4×10−4gmin−1) was greatly lower than that in water (28.6×10−4gmin−1). However, increasing the HA concentration led to a gradual increase in the MRR, electrode wear rate (EWR), surface roughness, and recast-layer thickness. The MRR, EWR, and the surface roughness of titanium and titanium–tantalum alloys under PMEDM exhibited an inverse relation with respect to the melting temperature and thermal conductivity of the alloy. Furthermore, calcium and phosphorus were incorporated into the recast layer, and their amounts decreased when the discharge current was increased.

The Effects of Pulse on Time and Arc on Time on Surface Quality in Wire-EDM of ASSAB XW-42 and ASSAB 8407 2M Tool Steels

In this study, the effects of cutting parameter on surface quality was investigated experimentally in wire electrical discharge machining (WEDM) process of ASSAB XW-42 and ASSAB 8407 2M tool steels. The surface quality of WEDMachined (WEDMed) was usually characterized by its roughness, recast layer and cracks. The experiments were conducted under different setting of pulse on time and arc on time on. It can be concluded that surface roughness, recast layer thickness and density of microcracks increased proportionally with pulse on time and arc on time. Thin recast layer and low crack density in the surface of ASSAB XW-42 tool steel was due to the low thermal conductivity of work piece material.

Employing severe plastic deformation to the processing of electrical discharge machining electrodes

The tool electrode has a significant role in electrical discharge machining (EDM) performance, as it affects machining efficiency, surface quality and the geometrical accuracy of the machined component. This study presents a new approach for developing a pure copper electrode using severe plastic deformation (SPD) to enhance the machining characteristics during EDM. Equal channel angular pressing (ECAP) is selected because it is the most successful SPD method of processing bulk materials. Finite element analysis, microstructural assessment as well as nanoindentation tests are carried out to determine the behavior of pure copper after one and two ECAP passes. The effectiveness of EDM when using ECAP-treated electrodes is evaluated by introducing new techniques of measuring the volumetric overcut (VOC) and corner sharpness. In addition, tool wear rate (TWR), material removal rate (MRR), electrode wear ratio, surface roughness, surface crack density and the critical crack zone are studied. The results emphasize that an electrode subjected to one pass of ECAP can enhance the workpiece accuracy by decreasing the VOC and increasing corner sharpness by 13 and 66%, respectively. It is also revealed that the nanohardness enhancement following ECAP leads to lower TWR and electrode wear ratio. An investigation of the surface characteristics indicates a thinner recast layer is achieved when using one ECAP pass-treated electrode, which leads to 26% lower surface crack density.

Thinning Process of Recast Layer in Hole Drilling and Trimming by EDM

In order to reduce the recast layer thickness of film cooling holes on turbine blade, a novel thinning process of electrical discharge machining (EDM) is investigated. To avoid the contradiction between holes drilling speed and recast layer of nickel-based superalloy, the EDM holes process consists of two steps, the drilling process for high machining speed and the trimming process for thin recast layer. To measure and evaluate the uneven and inconsistent recast layer thickness of film cooling holes, a mesh partition and multi-point averaged measurement by optical microscope is discussed. Experimental investigation is conducted to determine the EDM drilling and trimming parameters in machining Inconel 738 with 6mm thickness. By changing the discharge polarity in the trimming process, the recast layer thickness is obviously reduced. Over the range of parameters tested, the recast layer thickness can be reduced from 10.472μm to 2.416μm, and the entire process including drilling and trimming could be completed within 20 s. The experimental results show that the hybrid process containing drilling and trimming by EDM is feasible for film cooling holes with thin recast layer thickness.

Increasing the Performance of EDM Process Using Tool Rotation Methodology for Machining AISI D3 Steel

Electric Discharge Machining is one of the most accurate unconventional manufacturing processes used for cutting or creating intricate shapes in very hard or difficult-to-cut, electrically conducting materials. The adoption of tool rotation methodology increases the material removal rate by increasing the spark efficiency and effective debris clearing.The experiments have been performed on AISI-D3 Steel. Results show that the tool rotation phenomenon significantly improves the average MRR and surface finish by 41% and 12% respectively. Moreover, the final surface is more uniform in structure with less number of microcracks and thinner recast layer as compared to the stationary tool EDM.

Parametric Evaluation on Near-Dry Electric Discharge Machining

Near-dry electric discharge machining (EDM) is an eco-friendly process. It does not produce toxic fumes and consequent health hazards. The near-dry EDM generally utilizes a mixture of two phase (liquid and air) dielectric for machining. This investigation reports the influence of four processing parameters, viz. current, flushing pressure, duty factor, and lift on three responses. The responses measured were material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). The work material chosen was high speed steel (HSS). Mathematical models have been proposed herein for evaluation of the effect of processing parameters in near-dry EDM. These models were developed using response surface methodology (RSM). The experimental results reveal that the process parameters taken into consideration were significant for MRR. The TWR was negligible in near-dry EDM. This process gives a finer surface finish with thinner recast layer even at higher discharge energies as compared to conventional EDM.

Current Trends in Electric Discharge Machining Using Micro and Nano Powder Materials- A Review

Powder mixed electric discharge machining (PMEDM) has clearly proven its advantages over EDM without additives. When controlled size and concentration of metal particles are mixed in the dielectric medium of Electrical discharge machining it helps to improve the various machining parameters like increased MRR, reduced surface roughness, reduced tool wear rate and improved topological properties like reduction in microholes, micropores, thin recast layer and improved corrosion resistance of the machined surface. Therefore, PMEDM have attracted the attention of many researchers since last few decade. This paper present a summary of some important research work done on PMEDM by mixing micro and Nano size particle in the dielectric fluid of EDM. Further this review article discuss not only the effect of micro or nano particle size and concentration on the EDM performance but also unfold the other factors like thermal conductivity, electric resistivity and density of micro or nano particles and optimal machine parameters such as peak current, pulse on time andpulse off time which affects the machining performance. From literature review, it has been found that surface finish in PMEDM increases with the decreased particle size and increased powder concentration upto certain limit, but increasing powder concentration beyond the optimal value create short circuit between the tool electrode and workpiece and hence reduces the surface finish. Furthermore micro or nano particles transfer less heat to workpiece by increasing the electrode gap approximately twice as compare to EDM without micro or nano particle, hence improved surface finish and reduced tool wear rate were achieved. Authors have also identified the research gap for further research purpose.

Development of EDM Equipment for Machining Film Cooling Holes

To meet the requirement of precision, machining efficiency and surface quality of film cooling holes, an electrical discharge machining (EDM) equipment was developed with the function of high-accuracy rotation of tool electrode and performances of both high machining efficiency and thin recast layer. The equipment mainly consists of inchworm spindle, pulse power generator with high peak current and control system based on PMAC. Key problems were solved including precision and consistency of holes diameter, compatibility between high peak current and small pulse width and openness of the control system. Performance tests of the equipment show that runout error of the electrode is less than 25 μm, maximum peak current is 50 A while the minimum pulse width being 1μs, positioning accuracy of the control system is less than 2 μm. Machining experiments of vertical and inclined holes verified the feasibility of the designed equipment.

Improvement of Accuracy in Micro-EDM of Tungsten Carbide Using Deionized Water

Tungsten carbide is widely used as molds and dies material due to its superior strength, hardness and wear resistance. However, these characteristics also make it very difficult to be machined. Because the material is removed by spark erosion, micro-EDM has been found to be an effective machining process to machine difficult-to-cut materials such as tungsten carbide. Notwithstanding that micro-EDM using deionized water yields many advantages compared to hydrocarbon oil such as higher removal rate, lower tool wear and thinner recast layer, it has not been widely used due to the poor dimensional accuracy of machined part. This is the result of stray material dissolution caused by the slight conductivity of deionized water. This unanticipated material removal is especially severe for tungsten carbide which is highly susceptible to corrosion. This paper presents an attempt to improve the accuracy of micro-EDM using deionized water by using short voltage pulses. A short pulses generator has been in-house developed for this purpose. The effects of pulse parameters on the stray material dissolution are investigated. It is observed that the stray material dissolution is localized when short voltage pulses are used. As a result, dimensional accuracy of machined parts is significantly enhanced.

Experimental Study to Assess the Effect of Electrode Bottom Profiles while Machining Inconel 718 through EDM Process

Electrical Discharge machining (EDM) is a non-conventional machining process, in general adopted to produce components with complex profiles that are difficult to be achieved through conventional manufacturing processes. Since long, EDM is widely used in industries to machine ‘difficult to machine materials’ like HCHC steel (tool and die material). INCONEL 718 is one of the alloys that have relatively poor machinability in the conventional machining processes, due to its work-hardening nature, retention of high strength at high temperature (700 k) and low thermal conductivity. For Inconel alloy, EDM is a preferred material removal process due to its advantages like reduced machining stresses, lesser work-hardening effects and lesser metallurgical damage. While analysing the possible improvements in the EDM process, it was observed that the bottom surface profile of the electrode was contributing towards many aspects like Material Removal Rate (MRR), Electrode Wear Rate (EWR), surface roughness and surface integrity. Certainly such process improvements would contribute a lot in the shop-floor in terms of productivity and product-quality, while machining Inconel 718 alloy. To understand the effect of the electrode bottom profile and also its extent of influence on machining Inconel alloy, experimental study was carried out through EDM. Electrodes of different bottom profiles were used and the machined surfaces were analysed in terms of recast layer, surface topology, form tolerance and MRR. Electrodes having Convex, Concave and Flat profile at their bottom surface were chosen for the experimental study; electrodes were made of copper rod of 12mm diameter with convex or concave profile at their bottom with three different radii of curvature namely, 6,8 or10mm. The surface roughness of the machined surface was measured and the nature of recast layer formed was evaluated and characterized using scanning electron microscope (SEM). The observations and results of the above experimental study are discussed and analysed in this paper. Nature of the machined surface obtained using the above mentioned electrodes are compared and discussed. It is concluded that the adverse effects caused due to the erosion of flat profile electrodes on the machined surfaces could be overcome by employing convex profile electrodes; concave profile electrodes almost simulate the condition of eroded flat-profile electrode; convex profile electrodes produce machined surfaces of better quality in terms of higher surface finish, thinner recast-layer and closer geometry, in addition to higher MRR compared to flat profile or concave profile electrodes.

Study of Dry EDM with Oxygen-Mixed and Cryogenic Cooling Approaches

Dry electrical discharge machining (EDM) is a technology that has the potential to replace conventional liquid based EDM, owing to its low tool electrode wear, thin recast layer, and environmental friendliness. However, at present major challenges of dry EDM are found in its material removal rate (MRR) and an unsatisfactory surface quality that results from debris reattachment on the EDMed surface. To improve the MRR in dry EDM, two methods are proposed in this work. First, based on an analysis of the oxygen EDM mechanism, a dry EDM approach with an oxygen gas mixture is proposed, and we perform experiments to validate the analysis. Second, dry EDM on cryogenically cooled workpieces is considered, and we describe the accompanying experiments. The experimental results show an increase in the MRR for both the oxygen-mixed EDM and the cryogenically cooled workpiece technique, along with a decrease in the surface roughness value (Ra) for the latter. These results verify the feasibility of the proposed methods in improving dry EDM performance.

Study on Recast Phenomenon in Processing of Micro-Hole with Millisecond Laser

The experiments of micro-hole ablation are conducted firstly on titanium alloy Ti-6Al-4V with Nd: YAG millisecond laser. A significant factor which affects the depth of blind hole is found: the depth of recast material. This paper closely examines the regularity of recast depth varying with laser parameters, discovering that the ratio of recast depth to the entire hole depth decreases as pulse width decreases, and increases as peak power decreases. Verification experiment is conducted on stainless steel 1Cr13, eventually micro-hole with very thin recast layer is drilled when the maximum peak power and the minimum pulse width of the present millisecond laser are used.

UV laser microprocessing and post chemical etching on ultrathin Al 2O 3 ceramic substrate

In this study, an Nd:YVO 4 UV laser was used for microprocessing ultrathin (125 μm) ceramic plates for use as a multi-layer microchip substrate. The effects of the UV laser microprocessing parameters, including laser power density, frequency, laser scanning speed, and pass delay on microprocessing accuracy and quality (kerf width and arithmetic average roughness R a on the kerf sidewall) were investigated by means of a 4 × 4 orthogonal design. The key processing parameters were determined and optimized for small kerf width and minimal R a of the kerf sidewall while retaining high production efficiency. Subsequent chemical etching of the laser processed areas was performed to reduce the kerf surface and kerf sidewall roughness by removing debris and the thin recast layer for the required size precision and post gilding treatment. The results showed that a clean surface and crack-free kerf sidewall with roughness R a of 0.16 μm could be achieved by laser microprocessing and chemical etching.

Improving the fatigue life of electro-discharge-machined SDK11 tool steel via the suppression of surface cracks

The present study performs an experimental investigation to identify the EDM processing parameters which suppress the formation of surface cracks in the machined surface of SKD11 tool steel specimens. In the EDM trials, the specimens are machined using pulse currents of 4 A, 16 A or 32 A with pulse-on durations of either 4 μs or 16 μs. The various specimens are then fatigue tested at loads ranging from 1470 to 2401 N in order to determine their respective fatigue lives. A polished SKD11 specimen is also fatigue tested for comparison purposes. Finally, the fracture surfaces are examined using scanning electron microscopy to examine the crack propagation characteristics. The results show that increasing the pulse current and reducing the pulse-on duration provides an effective means of suppressing the surface cracking phenomenon. Higher values of the pulse current and pulse-on duration are found to increase the average thickness of the recast layer. Overall, the present results show that the four specimens considered in the fatigue test can be ranked in order of reducing fatigue life as follows: (1) the polished specimen, (2) the specimen with a thin recast layer and no surface cracks, (3) the specimen with a thick recast layer and no surface cracks and (4) the specimen with surface cracks.

Laser Generated Crack-Like Features Developed for Assessment of Fatigue Threshold Behavior

Abstract Developing methods to evaluate damage tolerance in high cycle fatigue is an important issue for the propeller industry. Traditional methods to establish threshold stress intensity factors for aluminum and martensitic steel have relied mainly on load shedding through-crack test specimens resulting in a pre-cracking history and the associated closure effects. For threshold determination of real life defects, a surface-crack test method, devoid of pre-cracking and closure issues, is needed. To this end, laser generated crack-like features (LGCLFs) were created and have been used successfully to evaluate the threshold crack growth properties of cracks in 7075-T651 with and without shot peening in axial R = 0.1 loading. For this work, a laser part marking system was used to generate a LGCLF semi-circular in shape, and measuring ∼0.015 in. (0.381 mm) deep by ∼0.030 in. (0.762 mm) long, with a notch height of 0.0007–0.001 in. (17.8–25.4 μm) with a tip radius of 0.000 14 in. (3.5 μm). When evaluated metallographically, these laser notches exhibited a very thin recast layer and a negligible heat affected zone. Specimens produced with these flaws were tested in R=0.1 tension-tension fatigue to produce a stress versus life plot of the data. A NASGRO crack growth model was used to generate stress versus cycle data points for the same geometry over the same stress range with a 7075-T651 material model and a crack growth threshold of 1.35 ksi ⋅(in.)0.5 resulting in very good agreement with the test data. This threshold compares favorably with the small crack threshold of 1.27–1.33 ksi⋅(in.)0.5 produced by da/dN testing performed by NASA at R=0.1 using a compressive pre-cracking method. Testing with samples shot peened prior to generating a LGCLF exhibited significantly higher endurance stresses and failure initiations were not from the LGCLF.

A Study of the Effect of Synchronizing Ultrasonic Vibrations with Pulses in EDM

The paper deals with EDM assisted with ultrasonic vibrations of the electrode. A first part introduces the beneficial effect of ultrasonic vibrations: increased feed rate by a better flushing, particularly for difficult conditions such as finishing with narrow gap: lower damage due to heating (thinner recast layer, increased fatigue life). This is a continuation of the paper introduced at CIRP 1989. A second part shows the results of an experimental investigation of the technique using a synchronization of ultrasonic vibrations and EDM pulses. This allows knowing more about the relationship between the pressure in the bubble and the effect of the discharge. A theoretical approach is proposed to explain this phenomenon.