Electrical discharge machining of ceramic nanocomposites: sublimation phenomena and adaptive control

Automated Analysis of Pulse Types in High Speed Wire EDM

A study on cryogenically treated molybdenum wire electrode

In present, five-axis numerical control (NC) machining center is used to process blisk, and the technology of plunge-milling and side-milling are widely adopted, which results in lower processing efficiency and high total cost. In the present study, first, a new machining technology of blisk is put forward, which is known as multi-milling, namely, disc-milling is used to remove the large margin of blisk’s channel, plunge-milling can expand the size of groove, further forming the surface of channel, and the corner and angle of the channel can be eliminated by side-milling. Second, with one-stage fan blisk of a certain type aircraft engine as an example, the processing efficiency of three different technologies (multi-milling, plunge-milling+side-milling, and side-milling) are studied by means of UG (Unigraphics NX) software. Third, based on the technology of multi-milling, the specific structure of multi-milling machine tool is designed. Last, the verification test is conducted, test results show that the processing efficiency of blisk can be enhanced drastically, finish cost can be reduced greatly with the multi-milling machine tool, which can give a great push to the development of aviation industry.

Compound efficient and powerful milling machine tool of blisk

Wire electrode is one of the key factors in determining the machining performance of wire electrical discharge machining (WEDM), and developing high-performance wire electrode is an effective method for meeting the ever-increasing requirement of modern manufacturing industries. In this paper, a novel surface microstructure wire electrode (SMWE) is proposed to enhance the performance of WEDM. Experiment data demonstrate that, compared with brass wire electrode and zinc-coated wire electrode, SMWE increases machining efficiency by 23.9–77.8% for Inconel 718 and 14.8–38.6% for Ti6Al4V, and decreases surface roughness by 11–20% for Inconel 718 and 7–10% for Ti6Al4V, respectively. Besides, SMWE can also obtain smoother surface topography, thinner recast layer, and narrower surface cracks. Furthermore, the improvement mechanism of SMWE is revealed from different aspects. It can be found that SMWE can shorten discharge gap breaking downtime, avoid the occurrence of sparks at the same point, and promote more removed debris and heat energy to be brought out. In a word, this proposed SMWE has good popularization value for application in practical industries, and this study provides a new idea for developing high-performance wire electrode.

Investigation on a novel surface microstructure wire electrode for improving machining efficiency and surface quality in WEDM

Surface machined by high-speed wire electrical discharge machining (HS-WEDM) at high energy (average current >8 A) suffers from surface burn and reduced cutting speed increase-rate, a major problem which is investigated in this paper. According to the study, the debris is mainly expelled out of the inter-electrode gap by the liquid medium. When machining at low energy, the gap is full of water-based medium, and the debris is mainly expelled by this medium. However, at high energy the medium in the gap is enormously vaporized and is then reduced due to a thermal load at high energy. Thus, the debris cannot be removed from the gap in time, resulting in its deposition and eventually leading to the surface burn. To overcome this limitation, it is suggested that within a range of discharge energy levels, the erosion products of the HS-WEDM process should be driven by a medium carrier with a higher melting point and vaporization point to ensure that there is sufficient liquid medium in the gap at high energy to carry and expel the debris out of the machining zone. Experiments were conducted by increasing the JR1A (traditionally used dielectric medium) -to-water ratio to increase the content of high-melting-point medium, thus validating the theory. Based on the experimental results, a new type of dielectric medium, JR1H, was formulated to ensure that there is still sufficient liquid medium to expel the debris at large energy machining. A greater threshold of stable cutting speed (more than 330 mm2/min) was achieved with the machining current of 15 A using JR1H, which is a significant breakthrough in higher efficiency HS-WEDM.

Enhanced debris expelling in high-speed wire electrical discharge machining

High-speed wire electrical discharge machining (WEDM-HS) of materials of super-high thickness (more than 1000 mm) is a challenging problem. First, sufficient energy is required to maintain the inter-electrode normal discharge. Next, there must be adequate inter-electrode dielectric fluid. Third, in order to generate a smooth cut surface, it is necessary to suppress the vibration of the wire electrode to reduce vibration lines on the cutting surface. To better understand these challenges, the energy and the flow of the medium between two electrodes were analyzed, allowing the establishment of a relevant model. The results indicated that for super-high-thickness machining, the pulse energy must be adequate to compensate for the energy consumed in the molybdenum wire and inter-electrode working liquid. In addition, the running speed of the wire electrode should be improved to ensure that there is a sufficiently high flow rate of the dielectric fluid. The servo control mode of the existing machine tools and dielectric fluid were improved and then a process experiment was performed. The experimental results show that the process can be carried out efficiently and stably and the workpiece surface can be cut smoothly using the improved working liquid and servo control mode.

Super-high-thickness high-speed wire electrical discharge machining

Effect of no-load rate on recast layer cutting by ultra fine wire-EDM

The electrical resistance of wire electrode increases with the decrease of the wire diameter. It is difficult to use the voltage threshold method to distinguish the spark and short-circuit states according to the discharge voltage, so it cannot meet the requirements of normal machining. In this study, a gap discharge state identification and servo control method based on discharge current are proposed in high-speed reciprocating microwire-EDM. The synchronous pulse can improve the stability of the system by reducing the disturbance of the discharge frequency and deionization. The experimental results show that a high wire speed is beneficial to the introduction of dielectric and the removal of erosion particles. When the target probability is set at 90%, the processing stability is higher. By using Φ 0.08 mm molybdenum wire electrode, the stable cutting of a 1250 height-diameter ratio (the ratio of cutting height to electrode wire diameter) workpiece is realized with an average cutting efficiency of 32.08 mm2/min. This study is a useful exploration of the machining of high height-diameter ratio workpieces by using a microwire electrode in high-speed wire-cut electrical discharge machining (HSWEDM).

Discharge state identification and servo control method of high-speed reciprocating microwire-EDM

This study analyzes the limitations of servo control systems for high-speed wire cut electrical discharge machining (HSWEDM). The discharge gap cannot be adjusted in real time during large energy cutting, as this will prevent interelectrode dielectric liquid from entering the discharge gap steadily, leading to violent vaporization and resulting in surface burning of the workpiece. This study proposes a new servo control system for HSWEDM based on discharge probability detection. The system collects the interelectrode discharge signal by dividing and comparing voltage circuits and then calculating discharge probability in a field-programmable gate array (FPGA), after which the machine tool adjusts feed rate by comparing the actual and initial target discharge probability. Thus, proper and stable discharge gap are ensured, enabling the interelectrode dielectric liquid to remain constant, increasing efficiency and stability, and decreasing surface burning effectively. Experiments prove that a servo control method based on discharge probability detection can increase stable cutting speed to 180 mm2/min and workpiece surfaces show no apparent burning stripes. In addition, the highest cutting speed can be increased to 208 mm2/min.

Hongwei Pan

Papers

Enhanced debris expelling in high-speed wire electrical discharge machining

Super-high-thickness high-speed wire electrical discharge machining

Effect of no-load rate on recast layer cutting by ultra fine wire-EDM

Discharge state identification and servo control method of high-speed reciprocating microwire-EDM

Increasing process efficiency of HSWEDM based on discharge probability detection