Piercing of High Thickness to Diameter Ratio Holes with Multiple Operations
Date Issued
2011
Date
2011
Author(s)
Chang, Yu-Ming
Abstract
With the ongoing market trend, there is a growing demand on micro products. In the manufacturing process of a micro part, the hole-piercing is commonly involved. Though the hole-piercing process with low thickness to diameter (t/D) ratio has been well-developed, the process for piercing a hole with a high t/D ratio is not yet matured. In addtion, due to the high t/D ratio, the hole usually can not be pierced in one single operation and a multi-operation process is required.
In the present study, piercing of high t/D ratio holes with multiple operations was examined by both the finite element analysis and the experimental approaches. In order to facilitate the finite element analysis in determination of element elimination, the fracture criterion and the critical value for separating the materials were studied first by comparing the experimental phenomenon and the finite element simulation results. Various fracture criteria adopted by the DEFORM software were examined. The tension tests were conducted and the stretches of the specimens to fracture were recorded, comparing with those obtained from the finite element simulations. The comparison indicates that the simulation results with the Normalized Cockcroft & Latham ductile fracture criterion agree well with the experimental data. With the proper ductile fracture criterion used, the piercing mechanism for different t/D ratios was investigated. The effects of process parameters, such as the die clearance, holder force, and
lubrication condition on the piercing force and cutting edge quality were determined.
The multiple operations for piercing a high t/D ratio hole on a S45C sheet were then designed based on the optimum process parameters obtained from the previous study. In order to obtain a smaller punch force and acceptable cutting edge, the number of operations, die clearance and punch shape were optimized according to the finite element analysis. The actual multi-operation hole piercing process was also implemented and the experimental data are compared with those obtained from the finite element results. The efficiency and the accuracy of the analysis model developed in the present study were then validated.
Subjects
hole-piercing
high thickness to diameter (t/D) ratio
ductile fracture criterion
critical fracture value
punch shape design
multiple operations
finite element analysis
experimental validation
Type
thesis
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