Prediction Algorithm for WEDM Arced Path Errors Based on Spark Variable Gap and Nonuniform Spark Distribution Models

Wire electrical discharge machining (WEDM) is a demanding high-precision process for machining of hard-to-machine materials. The main issue is manufacturing errors in shape and radius of small arcs generation. In this paper, a novel model about spark variable gap sizes and nonuniform spark distribution around the wire on arced path machining is first theoretically developed using spark angle domain and WEDM dynamic analysis. Applying spark-force distributed around the wire and resulting wire deflection are estimated by the WEDM conditions influenced by plasma channel specifications, discharge frequency, wire guide clearance, wire tension, and arc radius. Total theoretical arced machining errors including wire deflection and spark gap size variation around the wire interface are calculated based on the proposed model. In addition, machining errors of straight and small arced paths are experimentally analyzed under variation of WEDM influential parameters including discharge frequency, arced path radius (150, 300 and 450 μm), and wire tension through the statistical full factorial. Comparison of the results for different sets of variable parameters shows that the theoretical values of the arced machining errors can be consistent with the experimental one by a coefficient which depends on the machining conditions and the WED machine type. Finally, based on the theoretical and experimental results, a theoretical algorithm and an operational method with mean accuracy of 84.8% are proposed for predicting and compensating the errors of WEDM on the arced paths. Findings of this research can be used in high-accurate WEDM applications and industries.

Development of Numerical Model and Comparison with the Analytical Model for Predicting the Wire Effects in Wire Electric Discharge Grinding

This paper discusses the development of a numerical model and its comparison with the analytical model to predict the wire deflection in WEDG. The movement of wire between upper and lower guides creates vibration during the machining process which can create micro deflection of the wire. The Finite Element Analysis model [FEA] for the wire deflection is analyzed and compared with the analytical model. The deflection of the wire due to the input current may affect the machining of micro parts, which will be used for further research in micro machining and also will help us to choose the parameters such as current, spark gap, wire feed, and the speed of the workpiece during micro machining with WEDG. The FEA results for various forces were compared with the analytical results and found that the developed numerical model results are in good agreement.

Influence of Nozzle Jet Flushing on Wire Breakage in 1st-Cut Wire EDM from Start Hole

In wire EDM process, it is important to smoothly exclude debris and bubbles generated in the working gap for keeping stable performance. Much debris stagnation in the gap would cause frequent occurrence of discharge concentration and secondary discharge, which results in unstable machining performance, such as frequent wire breakage, low removal rate, and low shape accuracy. Therefore, a jet flushing of working fluid using upper and lower jet nozzles has been conventionally applied for excluding the debris and bubbles from the machined kerf. Nevertheless, it is well known that the wire often breaks when the machined kerf length is a few mm from the start hole in 1st-cut wire EDM. The influence of machined kerf length on the flow field, the debris exclusion, and the wire behavier caused with hydrodyanamic force by the jet flushing should be made clear.In this study, variations of flow field in the kerf, the debris accumulation state and the wire deflection caused jet flushing with machined length were analytically investigated by CFD (computational fluid dynamics) and structural analysis when 1st-cut wire EDM was done from a small start hole. Moreover, the effects of machined kerf length on the wire deflection and wire breakage were discussed. Wire breakage frequency experiments showed that wire tended to frequently break at a certain machined kerf length, where the wire deflection rapidly increased and the debris particle residence time in the gap became long.

Methods to Measure Wire Deflection in Wire EDM Machining

It is well kown that the wire electrode is flexible and will lead to a big lag in wire EDM machining, especially in the middle area of the work-piece. Methods to measure the wire deflection when it passes through the work-piece are studied in this paper. It is found that there is discharge spark first at the upper and lower parts of the wire when it cuts to the edge of the work-piece. The discharge spark appears at the middle of the work-piece a few seconds later. Based on this result, a method coined Camera Picture Analysis (CPA) is proposed to estimate the wire deflection. Another method of cross section measurement by the CCD is proposed to make a cross reference with the CPA method. By applying these two methods, the wire deflection models can be established, and used for the corner cut control of wire-cut EDM to improve accuracy of the machined parts.