放电铣削高效加工技术研究

发布时间：2019-06-22 11:51

【摘要】：在航空航天工业领域,为了保证装备在极端使用环境中的强度、刚度和稳定性,减轻装备的整体重量,降低发射成本,采用了大量的钛合金、镍基高温合金等机械性能优良的难加工材料。为了保证材料组织强度的稳定性,材料的毛坯较大,最终零件与毛胚的重量比一般会低于20%,因此加工中材料去除量很大。难加工材料的加工主要采用切削加工,由于难加工材料自身优越的机械性能,切削加工中普遍存在加工效率低、刀具磨损严重的问题。针对难加工材料加工中存在的上述难题,本文提出采用放电铣削进行钛合金等难加工材料的粗加工,从而达到提高加工效率,降低加工成本的目的,为难加工材料的加工提供新的思路。利用声发射技术,通过检测放电过程中产生的声发射波,研究了不同工作介质中材料蚀除过程的区别,发现空气和煤油中放电时,极间只在放电击穿时产生剧烈的压强变化,而采用水基乳化液作为工作介质时,极间会在放电击穿和放电结束时产生两次剧烈的压强变化,更有利于蚀除材料的排出,使得加工效率更高。通过区分材料的熔化过程和蚀除过程,研究了火花放电过程中材料被熔化和蚀除的过程,并根据检测的声发射波,分析了电弧放电与火花放电的区别,对电弧放电过程中熔化材料的蚀除条件进行了探讨。在现有三轴铣削机床本体的基础上,通过引入大电流脉冲电源、放电检测模块,改进伺服控制系统,设计了放电铣削机床的整体结构。将电弧放电应用到加工中,设计了基于极间平均电压的电极运动伺服控制策略,提高了放电加工的稳定性。通过分析极间放电能量的分配,对加工极性的选择进行了研究,结合实验,检测分析了放电铣削加工中,电极转动和高压冲液对材料蚀除过程的影响。为了改善极间冲液效果,提高蚀除颗粒的排出效率,对放电铣削加工极间工作液流场进行了理论和仿真分析。通过理论分析将冲液区分为有效冲液和辅助冲液,对具有将蚀除颗粒排出放电间隙作用的有效冲液流量的比例进行了研究,仿真分析并通过实验验证了切削厚度和电极直径对极间冲液效果的影响。通过设计中心孔与外侧环孔相配合的分离式电极,改善了极间放电区域的冲液效果,提高了蚀除颗粒的排出效率,降低了电极的制造成本。通过建立放电点温度场模型,研究了流场流速对单次放电工件被熔化深度的影响。为了保证加工后工件的尺寸精度,对放电铣削加工的电极损耗及其补偿进行了研究。通过对比实验,分析了石墨电极的加工优势,研究了电极形状损耗的特点。实验研究了各加工参数对电极损耗率的影响,发现单层切削厚度对电极损耗的影响最为显著,根据实验结果对降低电极损耗率的加工参数进行了优选。将电极损耗划分为侧面损耗和轴向损耗,分别对两种损耗进行了分析,针对侧面损耗,采用调整轨迹重叠率的方法进行了补偿,针对轴向损耗,根据不同的工件形貌,分别设计了具有针对性的电极损耗补偿策略。提出了基于有效放电时间统计的定时对刀与预测补偿相结合的电极轴向损耗补偿策略,提高了复杂工件加工中电极损耗补偿的精度。通过工艺实验研究了放电铣削加工中各加工参数对材料去除率、表面粗糙度和热影响层厚度的影响,检测分析了被加工表面质量的变化。将放电铣削加工与普通成形电火花加工和机械铣削加工的加工效果进行对比,系统分析了放电铣削加工在难加工材料的高效粗加工中的优势。为了保证最终工件的加工质量,引入机械铣削进行精加工,对放电铣削与机械铣削的衔接进行了规划,在同一台机床上先后实现了放电铣削粗加工和机械铣削精加工。将这一加工技术引入到航空航天难加工材料的加工中,能够解决难加工材料加工中加工效率低、加工成本高的难题,在保证加工质量的前提下,实现提高加工效率、降低加工成本的目的。
[Abstract]:In the field of aerospace industry, in order to ensure the strength, rigidity and stability of the equipment in the extreme use environment, the overall weight of the equipment is reduced, the emission cost is reduced, and a large amount of hard processing materials such as titanium alloy, nickel-based high-temperature alloy and the like are adopted. In order to ensure the stability of the strength of the material, the blank of the material is large, and the weight ratio of the final part to the blank is generally lower than 20%, so that the material removal amount in the processing is large. The processing of the difficult-to-be-processed material mainly adopts the cutting processing, and the problem that the machining efficiency is low and the tool wear is serious is common in the cutting processing due to the excellent mechanical property of the difficult-to-be-processed material. In order to solve the above-mentioned problems in the processing of difficult-to-be-processed materials, the rough machining of the difficult-to-be-processed materials such as titanium alloy is proposed in this paper, so as to improve the processing efficiency and reduce the processing cost. by using the acoustic emission technique, the difference of the material etching process in different working media is studied by detecting the acoustic emission wave generated in the discharging process, and when the discharge in the air and the kerosene is found, only a severe pressure change is generated between the electrodes during the discharge breakdown, And when the water-based emulsion is used as the working medium, two severe pressure changes are generated between the electrodes at the end of the discharge breakdown and the discharge, so that the discharge of the corrosion-removing material is more favorable, and the processing efficiency is higher. The process of melting and etching of material in the process of spark discharge is studied by distinguishing the melting process and the etching process of the material, and the difference between the arc discharge and the spark discharge is analyzed according to the detected acoustic emission wave, and the etching conditions of the molten material during the arc discharge are discussed. On the basis of the existing three-axis machine tool body, a large current pulse power supply, a discharge detection module and an improved servo control system are introduced, and the integral structure of the discharge cutting machine is designed. The electrode motion servo control strategy based on the inter-pole average voltage is designed, and the stability of the discharge machining is improved. Through the analysis of the distribution of the discharge energy between the electrodes and the selection of the processing polarity, the influence of the electrode rotation and the high-pressure flushing liquid on the process of material erosion is analyzed and analyzed in combination with the experiment. In order to improve the inter-electrode working fluid effect, the discharge efficiency of the corrosion-removing particles is improved, and the working fluid flow field between the discharge and discharge machining processes is analyzed. The effect of the cutting thickness and the diameter of the electrode on the effect of the inter-electrode flushing is verified by the theoretical analysis, which is the effective flushing liquid and the auxiliary flushing liquid. And the separation type electrode matched with the outer ring hole is designed, so that the flushing effect of the inter-electrode discharge area is improved, the discharge efficiency of the etching and removing particles is improved, and the manufacturing cost of the electrode is reduced. The effect of flow velocity on the melting depth of a single-discharge workpiece was studied by establishing the temperature field model of the discharge point. In order to ensure the dimensional accuracy of the post-processed workpiece, the electrode loss and its compensation are studied. The machining advantage of graphite electrode was analyzed by contrast experiment, and the characteristic of electrode shape loss was studied. The effect of each processing parameter on the loss rate of the electrode is studied in this paper. It is found that the effect of single-layer cutting thickness on the electrode loss is the most significant, and the processing parameters for reducing the loss rate of the electrode are optimized according to the experimental results. the electrode loss is divided into side loss and axial loss, And the corresponding electrode loss compensation strategy is designed respectively. The compensation strategy of the electrode axial loss, which is combined with the timing of the effective discharge time statistics and the prediction compensation, is proposed, and the accuracy of the electrode loss compensation in the processing of complex workpieces is improved. The effects of various processing parameters on the material removal rate, surface roughness and the thickness of the heat-affected layer were studied by the process experiment, and the change of the surface quality of the material to be processed was analyzed. In this paper, the machining effect of the electric discharge machining and the machining of the normal forming electric discharge machining and the mechanical cutting is compared, and the advantages of the discharge machining on the high-efficiency rough machining of the difficult-to-be-processed material are analyzed. In order to ensure the machining quality of the final work piece, the mechanical cutting is introduced to finish machining, and the connection between the discharge and the mechanical cutting is planned. The processing technology is introduced into the processing of the aerospace hard-processing material, and the problem that the processing efficiency is low and the processing cost is high in the processing of the difficult-to-be-processed materials can be solved, and the purpose of improving the processing efficiency and reducing the processing cost is realized under the premise of ensuring the processing quality.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG661;TG54

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