关键词: 分层实体制造(LOM), 温度场, 实时模拟, 控制方程

Abstract:

Objective: Laminated object manufacturing(LOM) technology stacks layer by layer to produce the required parts. In order to meet the requirements of bonding quality and machining precision of the forming workpiece, the LOM process flow was optimized and improved to solve the influences of the heat affected area on the physical properties of hot melt adhesive in laser cutting process. A mathematical method was used to describe the real-time temperature changes in the laminated hot-pressing process, and the influences of hot-pressing process parameters and temperature field distribution gradient were also discussed so as to provide a reference for ensuring the good adhesion of forming workpiece. Method: Based on the heat transfer theory of wood and the energy conservation equation, the heat transfer control equation of laminar thermal pressure process was established. By simplifying the model through basic assumptions, the three-dimensional unsteady heat conduction problem of laminar thermal pressure process had been simplified to the one-dimensional unsteady heat transfer problem. The forward difference method was used to discretize the governing equation, and MATLAB software was used to simulate the temperature field in the process of laminar hot-pressing. In addition, the temperature distribution curves of different depth layers were analyzed. According to the data obtained from the simulation, the two-dimensional line graph was drawn to explain the influence rule of temperature changing with the number of layers in the hot-pressing process. Results: According to the MATLAB simulation results and the mathematical model of the laminated hot-pressing temperature curve, the influences of hot-pressing plate on the temperature of thin wood layer was decreased with the increase of the number of layers. The temperature of the thin wood layer close to the hot-pressing plate was changed significantly. The reason was that when the hot-pressing plate worked, there was a strong convective heat transferred between the thin wood layer and the hot-pressing plate, which caused the temperature of the thin wood layer to rise. When the number of hot-pressing layers was 15, the temperature of the first thin wood layer close to the hot-pressing plate was 113.07℃. Along the vertical direction of the laminate, the influence of hot pressing on the temperature of the laminate was decreased with the increase of the laminate depth. It was because after leaving the hot-pressing plate, the cold air entered and conducted convective heat exchange with the thin wood layer, which caused the temperature of the thin wood layer to drop rapidly. Therefore, layer 3 temperature was 99.61℃, from layer 1 to layer 3, there was only one layer, and the temperature declined nearly 14.00℃. In the thin wood layer below a certain depth or close to the bottom plate, the temperature change was not obvious, layer 13 temperature was 77.50℃, layer 15 temperature was 75.64℃, from layer 13 to layer 15, there was one layer, the temperature declined less than 2.00℃. Conclusion: In the model, the goodness of fit between the predicted data and the experimental data is high, and the model has a strong guiding role in LOM manufacturing process. The established mathematical model and the innovatively designed working process of the LOM machine tool are related. The program written can be applied to the real-time simulation of the temperature field during the manufacturing process of the solid body. The simulation process of MATLAB can calculate the temperature change history of each point of the model, which is very important to improve the quality of thin wood bonding.

Key words: laminated object manufacturing(LOM), temperature field, real-time simulation, governing equation