Optimization of Process Plans by considering Material Handling cost for RMS

Abstract

In global market, responsiveness is the way to be competitive for the enterprises which have the various part families. This can be achieved by the use of CAPP along with advanced optimization techniques. Process planning optimization can be performed on the basis of total production cost of a product. Total production cost consists of material handling cost (MHC), machines and tool usage costs & machine, tool and setup change costs. In literature it is found that MHC is not considered for optimization purposes. According to literature, MHC accounts for 20-50% of total manufacturing cost of a product and by optimization, total manufacturing cost can be reduced 15 to 30%. So, MHC must be considered while optimizing the process plan. In this thesis MHC, along with other costs from literature, has been considered for the process plan optimization. In literature, all the costs are in different ranges and multiplied by different indices to make comparable. In this thesis, the normalization of each cost is recommended for better results. Effect of each cost element is relatively controlled by their corresponding normalized weights, i.e. increasing the effect of any cost results in decreasing the effect of all other costs collectively. Genetic algorithm with edge selection encoding strategy is used to find optimal process plans in MATLAB. The effect of material handling cost vanished by switching off its weight function for benchmarking with previous work. Convergence is performed to select suitable population size, crossover probability, mutation probability and the stopping criteria for recent objective function. Effect of material handling cost is checked by increasing the value of its weight (w6) gradually for first optimized process plan (generated at w6=0). It is observed that material handling cost and total cost increase gradually and sum of all other costs decreases with the rise of w6. A range for the value of w6 is selected where it comprises of near about 20% of the total cost. At this range different process plans are generated and total cost of first optimized process plan is also re-calculated. In case of increasing in the importance of MHE, a new process plan is generated. A comparison of total costs of new process plans with first optimized process plan at the same value of w6 shows that first optimized process plan becomes costly because it was not designed as MHC perspective. It is recommended to add MHC to get optimized result for the cases where the varieties of material handling equipment are available.