A balancing technique for optimal blank part machining

A balancing technique for casting or forging parts to be machined is presented in this paper. It allows an optimal part setup to make sure that no shortage of material (undercut) will occur during machining. Particularly in the heavy part industry, where the resulting casting size and shape may deviate from expectations, the balancing process discovers whether or not the design model is totally enclosed in the actual part to be machined. The balancing process requires a measurement dataset of the blank part to be balanced as well as a computer-assisted design (CAD) solid representation of the design model. A preferential constrained alignment algorithm calculates the proper compensation, or fixture offset, for any type of geometry to eliminate any possible shortage of material if possible, or orient the unavoidable area of missing material for appropriate rework. The alignment is an iterative process involving nonlinear constrained optimization, which forces datapoints to lie outside the nominal model under a specific order of priority. The Simplex method of direct search is used to solve the optimization process at each iteration. Two different artificial objective functions are implemented and compared for the balancing problem, a logarithmic and a least-squares formulation. The technique is applied to the balancing of a wiggle and a hydroelectric turbine blade. Results show that the balancing process under the logarithmic formulation converges faster than with the least-squares expression and is also more appropriate to balance the stock allowance for proper machining of the part.