Multi-discharge EDM coring of single crystal SiC ingot by electrostatic induction feeding method

A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved.     

Investigation on the effect of EDM process variables and environments on acoustic emission signals

Abstract

The performance of electrical discharge machining (EDM) primarily depends on the spark quality generated in the inter-electrode gap (IEG) between the tool and workpiece. A method for obtaining accurate information about the spark gap is required to effectively monitor the EDM process. The rise and fall of thermal energy in the discharge zone at a rapid rate during the dielectric breakdown produces high-pressure shock waves. This work explores the suitability of using acoustic emission (AE) generated from these shock waves and the elastic AE waves released on the workpiece due to the induced stress to monitor the performance and spark gap in EDM. The information content of the AE signals acquired at various machining conditions was extracted using AE RMS, spectral energy and peak amplitude. These features were able to well discriminate the machining condition, tool material, workpiece material, flushing pressure, current density, the initial surface roughness of the tool. Additionally, the AE signal features had a good and consistent correlation with the performance parameters, including material removal rate, surface roughness (Ra and Rq) and tool wear. The findings lay the groundwork to develop an effective, non-intrusive in-situ AE-monitoring system for performance and IEG condition in EDM.     

展成式精密电火花加工机床

研制了一种展成式精密电火花加工机床，它含有3个回转机构和4个直线移动机构，工件苡轴，工具电极苡轴和转台均可按需要回转，坐标工作台可作纵向和横向移动，工件头架可作轴向和竖向移动。可设置成多种复合运动方式和相应的结构布局，具有很丰富的加工功能，加工精度能达到微米级并实现电火花镜面加工。     

High-efficiency finishing process for metal mold by large-area electron beam irradiation

A new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high-energy density is irradiated without focusing the beam, and so the EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface instantly. Experimental results show that the surface roughness decreases from 6 μmRz to less than 1 μmRz in just a few minutes under proper machining conditions. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore, the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a possibility to become a high-efficiency finishing process for metal molds.     

Diffusion Bonded EDM Electrode with Micro Holes for Jetting Dielectric Liquid

This paper describes improvement of machining characteristics of electrical discharge machining of deep slots using a tool electrode which has micro holes for jetting dielectric liquid over the working surface. The tool electrode was made by the diffusion bonding of two copper plates, over an interface on which micro grooves for jetting the dielectric fluid were formed using electrolyte jet machining. In conventional machining, it is difficult to drill micro holes at the end of a slim electrode and circulate the dielectric fluid from the other end. Hence a solid tool electrode is used and periodically lifted up during machining to flush debris particles out of the discharge gap. Use of the newly developed tool electrode was found to shorten the processing time and improve machining accuracy significantly compared with the conventional solid tool electrode. Since the holes are micro, the outlet shapes are not replicated onto the bottom surface of the slot machined.     

电火花成形机主轴电极头的流固耦合分析

电火花成形机主轴电极头在回退、直至完全离开工作液的过程中,会受到工作液对其表面产生的阻力作用.研究主轴电极头所受的液体阻力,为主轴支承件的有限元分析和优化设计提供详实可靠的理论依据.     

模糊神经网络在电火花加工机中的应用

从提高系统的加工效率和加工质量角度出发，首先分析了电火花加工过程的特点。并以此分析为基础，提出了在电火花加工过程中，使用模糊神经网络控制技术。利用模糊控制器的特点，结合人工神经元网络的优点，切实校正了某些不完善规则的不利影响，可靠地提高了控制系统的快速响应能力。     

微小电极夹持送进机构设计

设计实现了一种微小电极丝送进机构，使电极丝在随主轴旋转并在轴向高精度的伺服进给控制下，可实现电极丝长距离的送进及损耗自动补偿。其中电极丝的夹紧切换由一个常闭夹丝机构和一个常开夹丝机结构执行，常闭和常开夹丝机构可由电磁或形状记忆合金致动控制。     

从第14届国际电加工学术会议看电火花加工技术的发展趋势

结合第14届国际电加工学术会议和国内外电火花加工技术的最新进展，以一些最新的应用实例系统地综述了电火花加工技术的发展趋势。     

DK7725A型电火花线切割机操作技巧及加工工艺分析

针对DK7725A型高速走丝线切割机床在加工特殊工件时存在的一些问题进行了分析,从工件的装夹,加工参数、加工速度的设置,操作规范的应用,以及降低断丝几率等加工技巧方面进行了详细的讨论,提出了相应的改进措施,从而有利于提高加工质量和加工的稳定性.