Study On Tool Replacement Decision Method For Gear Automatic Production Line Of Gearbox

Tool wear is a ubiquitous objective phenomenon in gear machining. Tool performance degradation due to wear is the main factor which has a significant impact on the quality of gear machining. However, frequent tool replacements will not only increase the tool costs but also cause a large number of production disruptions which affect the efficiency of machine tools of gear machining. In the gear automatic production line of gearbox, frequent tool replacements may further interrupt the production of the whole production line. Therefore, it is necessary to reasonably control the tool replacement of the gear automatic production line of gearbox. Combining the National Major Science and Technology Research Program of China “Gear Automatic Production Line of Gearbox of the Car”, this paper takes the gear automatic production line of gearbox as the research object and uses the machining quality of the workpiece, cutting energy consumption and tool failure as the main factors affecting tool replacement decision-making. This paper investigates the tool replacement decision-making for machine tools in the production line and aims to propose methods for reducing the production cost, improving production efficiency and energy efficiency in the production process.Firstly, the production characteristics and technological process of gear automatic production line of gearbox are introduced. The influences of tool wear on the quality failure probability, cutting energy consumption per workpiece and continuity of production in the production process are analyzed. The problem of decision-making of tool replacement in the gear automatic production line of gearbox is proposed. A research framework of decision-making of tool replacement for machine tools in the gear automatic production line of gearbox is developed. The objectives, influence factors and modeling techniques of tool replacement decision-making are analyzed.Secondly, the periodic tool replacement decision-making for machine tools in the gear automatic production line of gearbox is studied with respect to optimizing the average cost per workpiece in the long run. The cost factors which affect the decision-making of tool replacement are analyzed. A quality failure probability model for the gear production process is proposed based on the Logistic equation. And then the quality loss cost in the gear production process caused by tool wear is estimated. Tool replacement cycle is used as the decision variable, the average cost per workpiece in the long run is selected as the decision objective, and then a periodic tool replacement decision-making model is developed on the basis of renewal reward theorem. The method for solving the decision model is proposed. The characteristics of the optimal solution are analyzed.Thirdly, the periodic tool replacement decision-making for machine tools in the gear automatic production line of gearbox is studied with respect to optimizing the productivity and energy efficiency. Tool wear process is described by a discrete-time and discrete-state Markov chain. Then a model of average productivity in the long run and a model of average energy efficiency in the long run are developed. Basd on the two models, taking tool replacement cycle as the decision variable, a periodic tool replacement decision-making model is developed with respect to optimizing the two objectives of productivity and energy efficiency. The accuracy of the models is verified using the long-run properties of Markov chains. The characteristics of average productivity in the long run and average energy efficiency in the long run with respect to the tool replacement cycle are analyzed.The dynamic decision-making of tool replacement for machine tools in the gear automatic production line of gearbox is studied based on the theory of partially observable Markov decision process(POMDP). According to the basic framework of POMDP and the influences of tool wear on the quality failure probability and cutting energy consumption, the relationship between observations for tool replacement decision-making and the states in the Markov chain of tool wear process is established. The action set is determined for the tool replacement decision-making. The relationship among observations, actions and energy efficiency is investigated and then the immediate reward function about energy efficiency in the decision horizon is proposed. A dynamic decision-making model of tool replacement is developed to maximize the expected total reward over a finite number of horizons. The characteristics of the optimal tool replacement policy and the effect of parameters in the decision model on the optimal policy are analyzed.Finally, combining the tool replacement of the gear automatic production line of gearbox in Chongqing Landai Power Transmission Machinery Limited by Share Ltd., the application of periodic tool replacement decision-making methods are analyzed. The result shows that these methods could be used to improve the production performance.