Study to Improve Drum Shape Error in Rough Cutting of Wire-EDM
Date Issued
2009
Date
2009
Author(s)
Su, Hsin-Cheng
Abstract
Wire electrical discharge machining (Wire-EDM) is an essential material removal process in die and mold making and precision machining. This is because Wire-EDM provides the best alternative or sometimes the only alternative for machining conductive, exotic and high strength and temperature resistive (HSTR) materials with the scope of generating intricate shapes and profiles. However, it usually results in the drum shape along vertical axis (bowing) of the machined part. Several subsequent finishing cuts are needed to remove this inaccurate part so that the required dimensional tolerance is satisfied. A too large bowing will need more finishing cuts, which in turn increases machining time and cost. It also makes process planning of the allowance in advance more difficult. In the most serious case, re-do of the machined part all over again is needed. There have been very few studies on the bowing of the wire-cut machined part so far. The purpose is to find out the reason why the drum shape machined workpiece is formed, and the factors that would affect its magnitude. The effect of the vibration of wire on drum shape error is studied. The experimental results show that the drum shape machined workpiece is formed mainly due to the dielectric fluid flow and debris distribution in the machining gap. There is positive relationship of the location distribution of discharge with drum shape error. Also, the behaviour of the wire vibration observed by high speed camera. The objectives of this thesis are to investigate the relationship between the machining parameters and the characteristic of WEDM. The objectives of this dissertation are to investigate if there are significant parameters affecting barrel shape machined part (drum shape error), and to develop a mathematical model to predict drum shape error. Based on the Taguchi Quality design and the analysis of variance, it is found that comparatively workpiece thickness and ignition on time play more important roles. But statistically there is no significant factor affecting drum shape error. The size of the barrel is the result of cross effect of machining parameters. Based on this finding, the neural network with genetic algorithms to find the optimal operation machined was adopted and a model related the drum shape error and machining parameters was established. Experimental results show that the predicted error is less than 6%. By using this model the amount of drum shape error at rough machining stage can be accurately predicted, and applied for process planning of Wire-EDM. Incorporating the machining settings adjustment principles with the developed model, it is also found that the drum shape error can be reduced from 40μm to around 10μm. Thus, part with less amount of drum shape error and a better straightness 6 μm can be obtained.
Subjects
Wire-EDM
WEDM
discharge location
drum shape error
wire vibration
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-D89522004-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):71317fcd785ab569fdb56c8d2bfd5132