Effect of ultrasonic-assisted EDM on the surface integrity of cemented tungsten carbide (WC-Co)

This paper studies the effects of tool electrode ultrasonic vibration on some surface integrity properties of cemented tungsten carbide (WC-10%Co) in the electrical discharge machining (EDM) process. Surface integrity concerns surface alterations associated with a manufacturing process, including surface topography, surface metallurgy, and changes of the mechanical and physical properties of the material as well as residual stresses. Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) capabilities, optical microscopy, micro-hardness testing and white light interferometric microscopywere employed to study the surface integrity. This paper studies the topography of the machined surface, the size and amount of cracks on the surface layer, hardness variation in the depth and the composition of the defective layer, when machining with and without ultrasonic vibration of the copper electrode under different machining conditions. SEM, micro-hardness testing results together with surface topography investigation showed ultrasonic-assisted EDM applicability in improving surface integrity.     

Failure analyses of cemented tungsten carbide extrusion die

Abstract

In this study, the failure of a cemented tungsten carbide extrusion die (WC–Co) which was designed for the production of 55 000 components but failed during production of third component has been investigated. The die is used for cold extrusion of auto parts components as sizing die. Sizes achieved by forging process are further refined to required fine tolerance. The component size is required to be controlled within ±20 μm. The investigations revealed that the failure is due to abusive machining of cemented tungsten carbide. Detail studies under different electrical discharge machining conditions have been made to investigate the formation of cracks and their morphology. The major cause of the failure is established as abusive electrical discharge machining conditions with higher pulse current, which lead to micro- to macrocracks at the machining stage. These cracks further enlarged under load conditions when extrusion was done. Based on this study experiments were performed under different machining conditions on the WC–Co material. Optimum parameters were established for machining and accordingly new die was designed and fabricated which is performing very well.     

A Preliminary Study of Chemical Solubility of Ultra-Hard Ceramic AlMgB14 in Titanium: Reconciliation of Model with Experiment

This article investigates the chemical wear behavior of the ultra-hard ceramic AlMgB₁₄ and cemented tungsten carbide for machining aerospace alloys. The chemical interdiffusivity of AlMgB₁₄ against pure Ti and Ti-6Al-4V, in comparison with cemented carbide (WC-6%Co) cutting tool was investigated by means of diffusion couple experiments. The chemical composition profiles of various tool-workpiece combinations were determined by electron probe microanalysis after exposing the couples to 1000°C for 120 h in vacuum. Thermodynamic calculations of the chemical solubility of AlMgB₁₄ show that the experimental diffusion results are in reasonable agreement with the predicted behavior. It is shown that AlMgB₁₄ is significantly less soluble in titanium under static diffusion conditions, and therefore, shows considerable promise as a potential cutting tool for machining Ti alloys.     

Cemented carbide and cermet tooling for film-perforating

The tools used to perforate a particular photographic film started to wear at an unacceptable rate when the film base was changed from cellulose triacetate to polyester (PET). A laboratory investigation was initiated to screen candidate tool materials and identify ones with potential for 10 times life improvement over cemented carbide (WC/10% Co).

The screening tests started with abrasion and corrosion tests on various grades of cemented carbide, cermets and selected ceramics. Concurrent production trials indicated that the laboratory corrosion tests were not correlating with production results. To address this problem, a “nibbler” test was developed which simulates perforating and material removal on a punch after 10⁶ perforations (nibbles) became the screening test metric.

It was determined that abrasion tests do not accurately predict tool material behavior when chemicals are present on or in the materials being perforated. Static corrosion tests do not predict tool response under production conditions. The rubbing of the film on the tool surfaces removes protective films and there can be a significant corrosion component in tool erosion. The nibbler simulates real tool conditions because erosion is produced by actual cutting of coated webs. Nibbler tests in this study indicated that alumina/zirconia resisted film erosion better than cemented carbide, even cemented carbide with PVD coatings. The nibbler tests also indicated that leaving recast layers from electrical discharge machining on cemented carbide greatly increases erosion rates. It should be removed.

Production tests conducted since completion of these laboratory studies suggests that nibbler results correlate with production results. Coated cemented carbides are providing 3 times the service life of uncoated cemented carbides as predicted by the nibbler test.     

激光超声复合切削硬质合金的刀具磨损及其对工件表面质量的影响

基于激光加热辅助切削和超声椭圆振动切削提出了激光超声复合切削加工工艺。采用聚晶立方氮化硼(PCBN)刀具对YG10硬质合金进行了常规切削,超声椭圆振动切削,激光加热辅助切削和激光超声复合切削对比试验。检测了刀具磨损量、刀具磨损形貌、工件表面粗糙度以及工件表面形貌,并通过扫描电镜(SEM)对刀具磨损区域进行了能谱分析,同时研究了激光超声复合切削硬质合金时PCBN刀具的磨损及其对工件表面质量的影响。最后,与常规切削、超声振动切削及激光加热辅助切削进行了对比试验。结果表明:激光超声复合切削时刀具使用寿命显著增加,加工后的工件表面粗糙度平均值分别降低了79%、60%和64%,且工件表面更加平整光滑。激光超声复合切削硬质合金时,PCBN刀具的前刀面磨损表现为平滑且均匀的月牙洼磨损,后刀面磨损表现为较窄的三角形磨损带和较浅的凹坑和划痕;刀具的失效机理主要为黏接磨损、氧化磨损和磨粒磨损的综合作用。     

Process modeling of hybrid machining system consisted of electro discharge machining and end milling

This paper presents a novel hybrid machining process (HMP) that combines cutting action with machining using discharge pulses. Working conditions for a machine tool capable of combining micro-electro discharge machining (EDM) with milling is still an ill-defined problem relying on heuristics because there is insufficient knowledge of the discharge mechanism and the effects of machining parameters. The proposed HMP that combines micro-EDM and milling processes was applied to a steel alloy (AISI 1045) as the workpiece and end mill tungsten carbide as the tool electrode. Test results obtained from a number of experiments showed that the developed HMP yields reasonable machining time and surface roughness. Significant controlling variables for the machining response were identified and ranked using the Taguchi method. Furthermore, the response surface method was used to develop an empirical model based on the correlation between input variables and output responses.     

Fabrication and cutting performance of cemented tungsten carbide micro-cutting tools

We have developed cemented tungsten carbide (CTC) micro-cutting tools of 3 μm diameter by electrical discharge machining (EDM). Microdrilling and micromilling were carried out using the developed tools, and their cutting performance was investigated. Cutting was performed in free-cutting brass plates. Ultrasonic oscillation was employed to lower the cutting resistance. As a result, holes and a slot of 3 μm depth were successfully fabricated using tools made of CTC with 0.6 μm grain size, indicating that successful cutting with 3 μm-diameter tools was accomplished for the first time. Furthermore, CTC with 90 nm grain size was used as a tool material to improve the tool breakage resistance and tool form accuracy. The drilling performance of tools made of this ultrafine-grain-sized CTC was also investigated and found to exhibit a considerably improved average tool life.     

Experimental attempts of sub-micrometer order size machining using micro-EDM

So far, parts larger than several micrometers can be machined by micro-electrical discharge machining (micro-EDM). However, with the growing demands for even smaller parts, sub-micrometer order machining or even nanometer order machining are increasingly required in various industrial areas. In order to meet these requirements, the study on sub-micrometer order manufacturing has become considerably important. In the present study, experimental attempts of sub-micrometer order size machining using micro-EDM was performed, in which the smallest possible size that can be achieved for machined parts was examined, and the factors affecting the manufacturing of sub-micrometer parts were investigated. The results showed that insufficient positioning accuracy, smallest discharge energy and the machined shape error due to the influence of gap control and thermal deformation are not suitable for sub-micrometer machining. Disregarding positioning accuracy and machined shape error, cemented tungsten carbide (WC) and cemented tungsten carbide made of super fine particles (SWC) are relatively better than tungsten (W) from the viewpoint of material structure and influence of residual stress. In particular, SWC is more suitable than WC because both crystal grains size and size of defects among grains are smaller. Setting the polarity of workpiece negative was found to contribute to achieving sub-micrometer machining if the material removal rate is disregarded. Based on these investigation results, sub-micrometer machining using SWC was attempted. The minimum diameter obtained was about 2.8 μm.     

Investigating and removing the re-sticky debris on tungsten carbide in electrical discharge machining

Electrical discharge machining (EDM) is an excellent method to machine tungsten carbide with high hardness and high toughness. However, debris from this material produced by EDM re-sticking on the workpiece surface remarkably affects working efficiency and dimension precision. Therefore, this study investigated the re-sticky phenomenon of tungsten carbide and how to reduce the debris re-sticking on the workpiece surface. In general, the polarity in EDM depended on the different electrical parameters of the machine input and the different materials of the tool electrode. The first item of investigation observed the re-sticky position of the debris to study the effect of different polarities during the EDM process. Next, the tool electrode was set at different conditions without rotation and with a 200 rpm rotational speed to evaluate the rotating effect in EDM. Finally, different lift distances of the electrode and different shapes of electrode with rotation were utilized to investigate the improvement for reducing debris re-sticking on the machining surface. The results showed that only negative polarity in EDM could cause the re-sticky phenomenon on tungsten carbide. On the other hand, debris would notably re-stick on any machining position when the tool electrode was not rotated in EDM. Besides, debris significantly stuck on the center of the working area with rotation of the electrode. Additionally, a larger lift distance of the tool electrode could reduce debris re-sticking on the working surface, but this process would decrease material removal rate in EDM. In the end, a special shaped design of the tool electrode resulted in the re-sticky debris completely vanishing, when the electrode width was 0.6 times the diameter of this cylindrical electrode.     

Evaluation of carbide grades and a new cutting geometry for machining titanium alloys

A new cutting geometry consisting of a high clearance angle (from 10° to 15°) together with a high negative rake angle (from ?10° to ?15°) is proposed for increasing cemented tungsten carbide tool life during the machining of titanium alloys. This geometry would allow the use of a conventional insert (with an included angle of 90°) of any suitable shape (e.g. round, square or triangular) on a modified tool holder. The new geometry is found to yield longer tool life than does a high clearance angle (+15°) alone or a conventional tool with a low negative rake angle (?5°) and a low clearance angle (+5°). Further, the lower cobalt grade (Carboloy grade 999) and finer carbide grain size tools (Carboloy grade 895) are found to yield longer tool life than the higher cobalt grade medium carbide grain size tools (Carboloy grade 883), which are currently the most commonly used grade. A new ceramic tool material, an Si-Al-O-N compound, is found not to be suitable for machining titanium alloys because of rapid wear.     

TURNING STUDIES OF DEEP CRYOGENIC TREATED P-40 TUNGSTEN CARBIDE CUTTING TOOL INSERTS – TECHNICAL COMMUNICATION

In the present work, coated tungsten carbide tool inserts of ISO P-40 grade were subjected to deep cryogenic treatment at ?176°C. Turning studies were conducted on AISI 1040 workpieces using both untreated and deep cryogenic treated tungsten carbide cutting tool inserts. The turning performance was evaluated in terms of flank wear of the cutting tool inserts, main cutting force and surface finish of the machined workpieces. The flank wear of deep cryogenic treated carbide tools was observed to be lower than that of untreated carbide tools in machining of AISI 1040 steel. The cutting force during machining of AISI 1040 steel was lower with the deep cryogenic treated carbide tools when compared with the untreated carbide tools. The surface finish produced on machined AISI 1040 steel workpieces was superior with the deep cryogenic treated carbide tools as compared to the untreated carbide tools.     

Material removal rate and electrode wear ratio study on the powder mixed electrical discharge machining of cobalt-bonded tungsten carbide

In this article, a material removal rate (MRR) and electrode wear ratio (EWR) study on the powder mixed electrical discharge machining (PMEDM) of cobalt-bonded tungsten carbide (WC-Co) has been carried out. This type of cemented tungsten carbide was widely used as moulding material of metal forming, forging, squeeze casting, and high pressure die casting. In the PMEDM process, the aluminum powder particle suspended in the dielectric fluid disperses and makes the discharging energy dispersion uniform; it displays multiple discharging effects within a single input pulse. This study was made only for the finishing stages and has been carried out taking into account the four processing parameters: discharge current, pulse on time, grain size, and concentration of aluminum powder particle for the machinability evaluation of MRR and EWR. The response surface methodology (RSM) has been used to plan and analyze the experiments. The experimental plan adopts the face-centered central composite design (CCD). This study highlights the development of mathematical models for investigating the influence of processing parameters on performance characteristics.     

Suppression of forced vibration due to chip segmentation in ultrasonic elliptical vibration cutting of titanium alloy Ti–6Al–4V

Ultrasonic elliptical vibration cutting of titanium alloy Ti–6Al–4V is investigated in this research. Because products made of Ti–6Al–4V alloy are usually designed for possessing low-rigidity structures or good-quality cut surfaces, machining requirements such as low cutting forces and slow rate of tool wear need to be fulfilled for realization of their precision machining. Therefore, the ultrasonic elliptical vibration cutting is applied as a novel machining method for those products. Machinability of Ti–6Al–4V alloy by the ultrasonic elliptical vibration cutting with cemented carbide tools is examined to figure out suitable cutting conditions for precision machining of Ti–6Al–4V alloy. As experimental results, generated chips, cutting forces, and profiles of cut surfaces are indicated. A forced vibration problem occurred due to the segmented chip formation, which is also well-known in the ordinary non-vibration cutting. Therefore, characteristics of the forced vibration due to the chip segmentation are investigated in this research. Through the experiments, it is found that the frequency and magnitude of the forced vibration have relation with the average uncut chip thickness and cutting width. Especially, it is found that the averaging effect can suppress the forced vibration, i.e. the chip segmentation tends to occur randomly over the large cutting width, and hence the force fluctuations with random phases tend to cancel each other as the cutting width increases relatively against the average uncut chip thickness. Based on the investigations, a new practical strategy to suppress the forced vibration due to chip segmentation is proposed and verified. Using the proposed method significantly decreased cutting forces and good quality of surfaces are obtained when the forced vibration is suppressed compared to the ordinary non-vibration cutting results. Therefore, the results suggest that the precision machining can be realized without sacrificing the machining efficiency by increasing the width of cut and decreasing the average uncut chip thickness.     

Study of the current signal and material removal during ultrasonic-assisted electrochemical discharge machining

Electrochemical discharge machining (ECDM) is a cost-effective machining process used to shape non-conductive materials such as glass and ceramics. The process can overcome poor machinability of hard and brittle materials. Different types of physical phenomena can be added to the ECDM components to improve the machining efficiency. As the main target of this paper, ultrasonic vibration was integrated to the cathode of the ECDM process (UAECDM), which resulted in vibration concentration only to the machining zone. In order to design the experimental configuration, modal analysis was used. Machining speed was the main output of this investigation. Gas film and electric discharge were two main physical phenomena during ECDM. The thickness of gas film, location, and pattern of discharges were determined, experimentally. Also, current signal was a useful tool that could record significant details of involved mechanisms and phenomena during machining. Images of gas film showed that the application of ultrasonic vibration decreased the thickness of gas film by 65%. In addition, the vibration amplitude of 10 μm created the most uniform current signal, which had a considerable effect on the material removal rate (MRR). Results showed that all levels of vibration amplitude increased the machining speed during discharge and hydrodynamic regimes of the machining process.     

Wear Mechanism of Cemented Carbide Tool in High Speed Milling of Stainless Steel

Adhesion of cutting tool and chip often occurs when machining stainless steels with cemented carbide tools. Wear mechanism of cemented carbide tool in high speed milling of stainless steel 0Cr13Ni4 Mo was studied in this work. Machining tests on high speed milling of 0Cr13Ni4 Mo with a cemented carbide tool are conducted. The cutting force and cutting temperature are measured. The wear pattern is recorded and analyzed by high?speed camera, scanning electron microscope(SEM) and energy dispersive X?ray spectroscopy(EDS). It is found that adhesive wear was the dominant wear pattern causing tool failure. The process and microcosmic mechanism of the tool's adhesive wear are analyzed and discussed based on the experimental results. It is shown that adhesive wear of the tool occurs due to the wear of coating, the a nity of elements Fe and Co, and the grinding of workpiece materials to the tool material. The process of adhesive wear includes both microcosmic elements di usion and macroscopic cyclic process of adhe?sion, tearing and fracture.     

Drilling of microholes down to 10 μm in diameter using ultrasonic grinding

Drilling by grinding is useful for fabricating holes in hard and brittle materials with high dimensional accuracy and low machining cost. However, its application to microholes has been limited to those with a diameter on the submillimeter order. The drilling of microholes less than 0.1 mm in diameter by grinding was therefore attempted on crown glass. Cemented tungsten carbide micropins were fabricated by electrical discharge machining and used as micro-grinding tools. They can be employed because the convex parts of discharge craters formed on the tool surfaces serve as cutting edges of abrasive grains of grinding wheels. In order to reduce grinding force and thus prevent tool breakage, ultrasonic grinding was employed with the workpieces ultrasonically oscillated. As a result, microholes down to 10 μm in diameter were successfully drilled. They are the smallest-diameter holes drilled by grinding, to the best of our knowledge. The effect of helical feeding, in which the tool not only rotates around its axis but also moves in planetary motion, on drilling properties was also investigated.     

Analytical and experimental study on the integration of ultrasonically vibrated tool into the micro electro-chemical discharge drilling

Electrochemical discharge machining (ECDM) is a non-traditional machining process which is used to create micro-features on non-conductive materials. Micro holes and micro channels are the most interested features that have been fabricated by researchers. In recent years, some technical augmentations have been added to the ECDM process to achieve a more efficient machining process, but the employment of each augmentation in the most efficient way is not subjected. In this research, ultrasonic vibration is concentrated on the tool tip which directly and continuously effects on the machining zone and avoids global undesirable effects. For this purpose, modal analysis is used to design a special configuration which achieves the maximum amplitude of vibration in the tool tip. Also, an analytical model is presented for both of the electro-chemical discharge machining (ECDM) and ultrasonic assisted electro-chemical discharge machining (UAECDM) to study the effect of ultrasonic vibration on the thickness of gas film. Practical gas film thickness, machining speed, entrance overcut and tapering zone are studied for both of the ECDM and UAECDM to comprehensive understanding the effect of integration of ultrasonic vibration into the traditional ECDM process. Captures of gas film in different condition confirmed that ultrasonic vibration has reduced the thickness of gas film. Same behavior was achieved by employment of the analytical modeling. As a result, numerous small discharges were achieved which increased the material removal rate (MRR) and hole accuracy, simultaneously. Results showed that ultrasonic vibration can increase MRR up to 82%. Also, tapering zone and entrance overcut deviation as accuracy parameters improved 50% and 40%, respectively.     

Study of wear mechanism of hard-alloy tools during machining of refractory alloys

The work “The Mechanism of Wear Process of Cobalt-Carbide” shows the result of studying cemented carbide when machining refractory alloys based on chromium (X65HBΦT) and nickel (XH77TУP). The conducted research has shown that the machining of chromium-based alloy with a more heat-resistant process of the wear of the carbide inserts with or without a nanoscale coating occurs less intensively than for the tool wear process in the machining of Ni alloy It is established that this effect is connected with different crystal structures, phase contents, and properties of the heat-resistant alloys in question.     

Tool vibration in internal turning of hardened steel using cBN tool

The machining of hardened materials with hardness over 45 HRC has been an alternative to grinding since the 1970s, with the commercial availability of cubic boron nitride (cBN) and ceramic tools. However, the low toughness of these types of tool materials makes them very sensitive to damages caused by vibrations, which are critical for operations like internal turning, where the tool resembles a cantilever beam and therefore is susceptible to large deflections. This work aims to contribute to the study of tool performance in internal turning of long holes in hardened AISI 4340 steel in finishing conditions. Different machining conditions, two different tool holders (steel and carbide), and several tool overhangs were tested. The surface finish, acceleration (vibration) signals, and tool wear of cBN inserts were evaluated. The results show that vibration and the material of the tool holder may play a secondary role in the surface finish for stable turning, but the use of carbide tool holders makes the process stable for longer tool overhangs. Moreover, when the cutting becomes unstable, surface roughness is increased severely.     

高强度钢干式铣削替代半精磨的试验研究

采用硬质合金刀片(YW1)和涂层刀片(YB415)进行了高强度钢的干式铣削代替半精磨试验研究。根据试验结果,确定适合加工该型号高强度钢的刀具材料和切削用量。以这两种刀片在不同切削用量条件下的耐用度、加工表面粗糙度和主切削力作为刀具加工性能的评价依据,同时研究了刀片的磨、破损机理和卷、排屑稳定性。试验结果表明:涂层刀片干铣削高强度钢的加工性能优异,工件加工表面质量达到半精磨水平。