导电加热切削有限元模拟及实验研究
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摘要
导电加热切削技术是改善难加工材料切削加工性能,提高表面加工质量、降低刀具耐用度的有效方法。国内外学者已对该加工技术进行了多年研究,但对切削过程具有重要影响的切削力及切削温度研究较少。本文主要研究内容如下：
1.加热电阻。导电加热切削是通过加热电阻对局部切削区材料进行快速加热而发挥作用的,因此研究加热电阻的形成机理、组成结构及经验公式,对分析导电加热切削机理具有重要意义。本文基于电接触理论及导电加热切削特征,提出了切削区加热电阻的三维结构模型。设计正交实验；对加热电阻进行精确检测,建立了加热电阻与切削用量、加热电流的经验公式,该经验公式较好地反映了YT726导电加热切削淬硬GCr15轴承钢时加热电阻的变化规律。
2.导电加热切削的有限元模拟分析。切削过程的模拟仿真在优化实验参数、节约生产成本、提高实验效率等方面具有重要意义。本文首先对导电加热切削过程中的电、力、热耦合情况进行分析,将加热电阻焦耳热效应引起的温升视为工件材料的初始温度,使用与材料硬度相关的AISI52100本构关系描述材料的流动应力,在此基础上利用有限元软件DEFORM模拟切削过程。根据模拟结果,预测了导电加热切削过程中的切削力和切削温度。为了验证有限元模型的准确性,使用相同的实验参数进行切削实验,测量了YT726硬质合金刀具导电加热切削淬硬GCr15轴承钢的切削力。切削力的模拟值与实验值具有一致的变化趋势,且相对误差较小,除去系统误差及测量误差的影响,本文建立的有限元模型是比较准确的。最后,根据切削温度的模拟结果及最佳切削温度守恒定律,优选了导电加热切削的加热电流。
3.导电加热切削尺寸误差分析。导电加热切削提高了切削区温度,改善了难加工材料的切削加工性能,同时也使刀具和工件产生了热变形,影响尺寸精度。本文以细长轴为实验对象,优选了实验参数,对尺寸误差进行实验研究。研究结果表明：导电加热切削细长轴尺寸误差是切削力和切削热耦合的结果。热量使工件产生热变形,影响实际切削深度；但是切削热又会软化工件材料,减小切削力,从而减小工件的变形,这对于减小尺寸误差是有利的。
Electric Hot Machining (EHM) is an efficient method to improve the machinability of difficult-to-cut materials, obtain better surface quality and reduce tool wear. Researchers have studied this cutting technique for many years, however, the study on cutting force and cutting temperature which is significantly important to the mechanism of the EHM, has been paid little attention. So the context in this paper shows as follow:
1. Heating resistance. EHM primarily relies on heating resistance to quickly heat the material in the deformation area, therefore the studies on the generating mechanism, components and empirical equation of the heating resistance are valuable for analysis on the mechanism of the EHM. Based on the electrical contact theory and the characteristics of EHM, a 3D model of heating resistance is established in this paper. And the empirical equation of cutting parameter and heating current to the heating resistance is given by the precious measurements of the heating resistance, which can accurately represent the change law of resistance under certain conditions.
2. FEM simulation of the EHM. The simulation of EHM process is of great significance in the optimization of experimental parameters, the cost saving of prdduction and the incensement of efficiency. This paper seems the exotherm caused by the heating resistance as the initial temperature of the workpiece, uses Umbrello constitutive relation related to the hardness of material to describe the flow stress, and then simulates the EHM process using the FEM software DEFORM. According to the simulation results, this paper predicts the cutting force and cutting temperature in the EHM process. In order to verify the accuracy of the FEM model, this paper measures the cutting force when EHM GCr15 bearing steel of HRC60 with YT726 Carbide cutting tools. The comparison shows that the simulations have well agreed with the experimental results with small relative error, concerned the system error and the measurement error, FEM model built in this paper is accurate. After verifying the accuracy of the FEM model, the optimum heating current can be obtained based on the simulation results of the cutting temperature and the optimum cutting temperature conservation law.
3. Dimensional error in EHM.EHM raises the temperature in cutting zone to improve the machinability of difficult-to-cut materials, meanwhile, high temperature causes distortion of workpiece and tool, affects the dimensional precision. This paper chooses slender shaft as workpiece, optimizes the experimental parameters, and then analyzes the dimensional error. The tests show that dimensional error is caused by both cutting force and cutting temperature. Heat distorts workpiece, affects the actual cutting depth. Meanwhile, heat softens the workpiece, reduces the cutting force, and thus reduces distortion which is beneficial for reduction of dimensional error.
1.加热电阻。导电加热切削是通过加热电阻对局部切削区材料进行快速加热而发挥作用的,因此研究加热电阻的形成机理、组成结构及经验公式,对分析导电加热切削机理具有重要意义。本文基于电接触理论及导电加热切削特征,提出了切削区加热电阻的三维结构模型。设计正交实验；对加热电阻进行精确检测,建立了加热电阻与切削用量、加热电流的经验公式,该经验公式较好地反映了YT726导电加热切削淬硬GCr15轴承钢时加热电阻的变化规律。
2.导电加热切削的有限元模拟分析。切削过程的模拟仿真在优化实验参数、节约生产成本、提高实验效率等方面具有重要意义。本文首先对导电加热切削过程中的电、力、热耦合情况进行分析,将加热电阻焦耳热效应引起的温升视为工件材料的初始温度,使用与材料硬度相关的AISI52100本构关系描述材料的流动应力,在此基础上利用有限元软件DEFORM模拟切削过程。根据模拟结果,预测了导电加热切削过程中的切削力和切削温度。为了验证有限元模型的准确性,使用相同的实验参数进行切削实验,测量了YT726硬质合金刀具导电加热切削淬硬GCr15轴承钢的切削力。切削力的模拟值与实验值具有一致的变化趋势,且相对误差较小,除去系统误差及测量误差的影响,本文建立的有限元模型是比较准确的。最后,根据切削温度的模拟结果及最佳切削温度守恒定律,优选了导电加热切削的加热电流。
3.导电加热切削尺寸误差分析。导电加热切削提高了切削区温度,改善了难加工材料的切削加工性能,同时也使刀具和工件产生了热变形,影响尺寸精度。本文以细长轴为实验对象,优选了实验参数,对尺寸误差进行实验研究。研究结果表明：导电加热切削细长轴尺寸误差是切削力和切削热耦合的结果。热量使工件产生热变形,影响实际切削深度；但是切削热又会软化工件材料,减小切削力,从而减小工件的变形,这对于减小尺寸误差是有利的。
Electric Hot Machining (EHM) is an efficient method to improve the machinability of difficult-to-cut materials, obtain better surface quality and reduce tool wear. Researchers have studied this cutting technique for many years, however, the study on cutting force and cutting temperature which is significantly important to the mechanism of the EHM, has been paid little attention. So the context in this paper shows as follow:
1. Heating resistance. EHM primarily relies on heating resistance to quickly heat the material in the deformation area, therefore the studies on the generating mechanism, components and empirical equation of the heating resistance are valuable for analysis on the mechanism of the EHM. Based on the electrical contact theory and the characteristics of EHM, a 3D model of heating resistance is established in this paper. And the empirical equation of cutting parameter and heating current to the heating resistance is given by the precious measurements of the heating resistance, which can accurately represent the change law of resistance under certain conditions.
2. FEM simulation of the EHM. The simulation of EHM process is of great significance in the optimization of experimental parameters, the cost saving of prdduction and the incensement of efficiency. This paper seems the exotherm caused by the heating resistance as the initial temperature of the workpiece, uses Umbrello constitutive relation related to the hardness of material to describe the flow stress, and then simulates the EHM process using the FEM software DEFORM. According to the simulation results, this paper predicts the cutting force and cutting temperature in the EHM process. In order to verify the accuracy of the FEM model, this paper measures the cutting force when EHM GCr15 bearing steel of HRC60 with YT726 Carbide cutting tools. The comparison shows that the simulations have well agreed with the experimental results with small relative error, concerned the system error and the measurement error, FEM model built in this paper is accurate. After verifying the accuracy of the FEM model, the optimum heating current can be obtained based on the simulation results of the cutting temperature and the optimum cutting temperature conservation law.
3. Dimensional error in EHM.EHM raises the temperature in cutting zone to improve the machinability of difficult-to-cut materials, meanwhile, high temperature causes distortion of workpiece and tool, affects the dimensional precision. This paper chooses slender shaft as workpiece, optimizes the experimental parameters, and then analyzes the dimensional error. The tests show that dimensional error is caused by both cutting force and cutting temperature. Heat distorts workpiece, affects the actual cutting depth. Meanwhile, heat softens the workpiece, reduces the cutting force, and thus reduces distortion which is beneficial for reduction of dimensional error.
引文
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[5]陈定一.难加工材料切削加工的研究与进展[J].机床,1985(10).
[6]孙鹏.淬硬钢导电加热切削技术基础研究[D].大连：大连理工大学,2005.
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[10]叶邦彦,陈文戈.导电加热切削加热电源的研究与应用[J].电加工,1997(4)：11-14.
[11]汤勇,张发英,陈澄洲.断屑器导电加热切削的研究[J].华南理工大学学报(自然科学版),1994,8(4).
[12]罗翔,陈文戈,叶邦彦.微机控制导电加热切削过程的研究[J].机械设计与制造,1998(6)：35-36.
[13]邹春华,赵学智,叶邦彦.导电加热切削模糊控制系统的研究[J].机电工程技,2003,32(2)：99-102.
[14]陈文戈,叶邦彦,周泽华.导电加热切削最佳加热电流的实验研究[J].机械工业师,1999(5)：8-9.
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