Targeted suppression of vibration in deep hole drilling using magneto-rheological fluid damper

Under the concept of precision or targeted vibration suppression, a novel approach is developed to reduce the vibration of drilling tool system in deep-hole drilling process. The concept is to suppress the dominant vibration upon its emergence by variable damping or to force the harmful vibration morph into less harmful by different damper position. A magneto-rheological (MR) fluid damper is designed with adjustable damping capability to counteract emerging vibration. A series of experimental investigations are carried out on the BTA deep hole drilling process. The experimental results show that the adjustable MR damping brings down the vibration in all applications with different suppression effect. A relative optimal suppression can always be found. The suppressed vibration experiences a frequency shift which sheds light on the possible avoidance of matching of unwelcome frequency. Different damper locations have different but consistent suppression results which foresee a possibility of forcing the mode of vibration into less harmful one. A potential precision or targeted suppression of vibration upon its emergence is thus possible.     

EDM turning using a strip electrode

Turning by electrical discharge machining (EDM turning) is an effective method to machine hard-to-cut materials. Generally, a wire-EDM is utilized in EDM turning because it is not concerned with electrode wear. However, wire-EDM turning has a slow machining speed due to its small machining area, and the wire may break due to overheating electrodes. For these reasons, its machining speed must be limited. In this study, a strip-EDM was created in an effort to overcome the problems in the EDM-turning process. This machining method used a conductive strip as an electrode. The strip was fed continuously, like a wire-EDM; therefore electrode wear was not a concern. One advantage of the strip-EDM was that it increased the material removal rate because of its large machining area and non-breaking electrode. In the experiments, machining characteristics were investigated according to machining conditions, and practical machining was carried out via fabrication of complex shapes on a shaft workpiece.     

Process adapted structure optimization of deep hole drilling tools

In order to machine boreholes having a high length-to-diameter ratio, deep hole drilling methods are applied. Especially when drilling ductile materials, the removal of cooling lubricant and chips can be hindered by long chips which block the inside of the chip mouth. In order to increase the volume flow rate of the cooling lubricant and chips, the chip mouth cross-section of a commercially available state-of-the-art BTA (Boring and Trepanning Association) boring tool was analyzed. Structure topology optimization was applied to reduce the drill head material without the drill head losing its stiffness to maximize the chip mouth cross-section. Finally, new drill head design was developed and verified through experimental investigations.     

Ultrasonic deep hole drilling in electrolytic copper ECu 57

At present the machining of highly ductile electrolytic copper ECu 57 with gun drills is carried out at very low feed values, as the material tends to form very long and unfavourable chips. In addition, high frictional forces on the guide rails cause high torsional strain on the gun drill. This paper first reports on the results of ultrasonically assisted deep hole drilling in ECu 57 with tools of 5 mm diameter. The actuator system for exciting axial vibrations in the ultrasonic range is described and experimental results which were obtained from cutting tests are reported. Particular emphasis is put on the improvements compared with the conventional drilling technology without superimposed vibrations. The effect of different input amplitudes is investigated in detail. The performance criteria are drilling moment, surface quality, chip form as well as the surface zone. By optimising the vibration amplitude, cutting speed and feed, the machining result was improved compared with conventional machining, and at the same time the stability of the machining process was simultaneously increased.     

Varying bending eigenfrequencies in BTA deep hole drilling: mechanical modeling using statistical parameter estimation

One serious problem in deep-hole drilling is the formation of a dynamic disturbance called spiralling which causes a multi-lobe shaped distortion of the bore hole cross section. An important factor governing the occurrence of spiralling is the coincidence of a bending eigenfrequency of the boring tool with a multiple of the spindle rotation frequency. This article presents a discrete dynamic model of the tool/boring-bar assembly including a Lanchester-damper and containing free parameters for the unknown stiffness of the tools lateral supports. Furthermore, a method for estimating these parameters by determining the changing eigenfrequencies over the drilling depth from spectrogram data using the maximum likelihood method is proposed. The work presented in this paper is financially supported by the ‘Deutsche Forschungsgemeinschaft (DFG)’ within the ‘Sonderforschungs-bereich (SFB)’ 475. It is conducted in cooperation with Lehrstuhl Computergestützte Statistik, University of Dortmund.     

用块电极轴向进给法电火花磨削微细轴

对电火花磨削微细轴中的关键问题进行了分析，提出并研究了利用块状电极轴向进给磨削微细轴的方法。在自行研制的多功能微细加工装置上，用该方法加工出了直径10μm的微细轴，并用此轴加工出了直径20／μm的微细孔。实验中发现：令伺服响应延时，可改善微细轴的圆度。用此方法得到的微细轴，根部强度高，有利于微细轴的加工和工作。     

A novel method for chip formation analyses in deep hole drilling with small diameters

Recent trends of downsizing and miniaturization of components, e.g. in the automotive industry for the manufacturing of fuel injectors or in the medical industry for the production of bone screws or surgical instruments, increase the importance of mechanical deep hole drilling with small diameters. Unfortunately, there are still some open challenges regarding this process. In addition to the unfavorable ratio of the cutting edge rounding to the achievable feed rates and undeformed chip thicknesses which results in significant mechanical tool loads, the control of the chip formation and the removal constitutes a major difficulty. The slender tool dimensions, especially the small cross sections of the chip flutes, necessitate a favorable chip formation to achieve the required process safety and productivity. Therefore, analyses of the chip formation, when machining difficult-to-cut materials provide the means for an effective process design. This analysis, however, is particularly difficult due to the closed operating zone. Quick-stop devices used for the chip formation analyses so far are limited in the tool diameter respectively the revolution speed. Furthermore the informative value is limited, because a quick-stop test takes a significant time to stop and thus the instantaneous cutting conditions during the tool retraction are altered. To overcome these restrictions, a new method for the analysis of the chip formation in small diameter deep hole drilling is presented in this paper. It is based on the utilization of a high-speed camera and tailored material samples. The experimental set-up and the results of first analyses conducted under minimum quantity lubrication are presented. The chip formation process is analyzed for the single-lip gun drilling of the nickel-based alloy Inconel718 and the bainitic steel 20MnCrMo7.     

深孔筒形件挤压成形有限元分析

深孔筒形件的成形在挤压成形工艺中是一大难点,成形过程中的温度不易控制,使得模具强度降低,成形后的工件容易产生较大的壁厚差.本文在分析深孔筒形件的挤压工艺的基础上,利用非线性有限元软件MSC/Superform对深孔筒形件的挤压全过程进行了模拟,分29、39、82、91、103这5个时间步进行分析,得出挤压过程中的金属流动趋势;并且对成形过程中挤压件的各个部位的温度场进行分析,模拟出实际挤压过程中模具各个部位的温度,另外还得出了各个挤压工步的载荷--行程曲线,以便对模具及各种成形参数进行优化.最后按照模拟的工艺参数进行了试验,得出符合要求的工件.     

电铸与电弧喷涂相结合制造EDM电极

以制造叶片模具电极为例，详细介绍了以叶片原型为母模，通过翻制硅橡胶过渡模、化学镀、电铸和喷涂等工艺手段制造EDM电极的过程。实验证明；电铸与电弧喷涂相结合制造EDM电极，制造周期、成本分别为电铸的25%和10%。     

PLC在深孔钻组合机床控制系统中的应用

本文简要介绍了深孔钻组合机床的控制原理，并给出其PLC控制系统的流程图和梯形图程序设计。     

Fluid structure interaction (FSI) modelling of deep hole twist drilling with internal cutting fluid supply

This paper presents a novel approach for coupling of thermal FE and CFD simulations to predict the temperature distribution in the cutting process. The developed FSI model considers experimentally validated workpiece temperature to simulate the heat convection interactions in drilling operations. This innovative method allows not only for the common analysis of the flow behaviour, but additionally for the detailed investigation of the temperature distribution within the cutting fluid. The simulation provides indications for an insufficient fluid supply of the cutting edge and the results can contribute significantly to the further optimisation of thermally high stressed cutting tools and processes.     

双头深孔钻床控制系统的设计与改造

本文根据双头深孔钻床的工作原理,介绍了用可编程控制器对其工作过程进行自动控制的软、硬件设计方案,并给出了程序控制梯形图及动作说明。     

Automation of centered micro hole drilling using a magnetically levitated table

This paper presents the automation of centered micro hole drilling, using a magnetically levitated table. Centered micro hole drilling, an example of which is nozzle outlet hole drilling, has previously been performed manually by skilled craftsmen. If a micro hole is drilled when the center line of the drill and the center line of the guide hole are not aligned, the misalignment may cause drill breakage. By using a magnetically levitated table, a workpiece can be aligned frictionlessly. When the horizontal support stiffness of the table is set small, by lowering the drill slowly, centering can be performed due to the contact force between the drill tip and the conical surface of the nozzle. Spinning nozzles were used as experimental workpieces, and 0.1–0.5 mm diameter drills were used.     

Tube electrode high-speed electrochemical discharge drilling using low-conductivity salt solution

Film cooling holes are widely used in the aerospace industry, and their fabrication requires high machining speed and accuracy, as well as good surface quality. Tube electrode high-speed electrochemical discharge drilling (TSECDD) is a promising hybrid machining method for the fabrication of film cooling holes in difficult-to-machine superalloys. An electrochemical reaction can occur if a low-conductivity salt solution is used in the drilling. Materials can also be removed at a high speed using electrical discharge machining (EDM). Thus, TSECDD and electrochemical machining (ECM) can be combined into a unique machining process using a low-conductivity salt solution. This machining process achieves both a high machining speed and good surface finish. In this study, the material removal mechanism of TSECDD was studied using a low-conductivity salt solution, and comparisons with high-speed electrical discharge drilling were made. The performance of the process was investigated using salt solutions of various conductivities. The results show that there are different material removal mechanisms in the frontal gap and the lateral gap and that, in the latter, there is a transition from EDM to ECM. Experiments conducted using TSECDD confirm that the use of this process with a low-conductivity salt solution can improve the machining surface and machining efficiency achieved. The results also show that the use of a low-conductivity solution improves the material removal rate, the hole diameter, and the taper angle.     

EDM drilling of ultra-high aspect ratio micro holes with insulated tools

This work presents an innovative method for the Electrical Discharge Drilling of ultra-high aspect ratio (AR > 30) micro holes. It makes use of tools insulated on the sidewall by means of a coating. The concept is to promote the process stability of micro EDM deep drilling by preventing secondary sparks. The performance of standard and customized tools is compared and reviewed against the main criteria of shape quality, tool wear and machining time. Process capabilities are also defined for a given coating. Micro holes within 0.2 mm in diameter and aspect ratio (AR) up to about 120 could be obtained within 1 h. A micro punching die is also realized by combining this strategy with micro wire EDM.     

Optimization of guide pads for the BTA deep hole drilling of high alloyed steels by microfinishing

The boring and trepanning association deep hole drilling of materials with a high tendency to adhesion, such as high alloyed-steels, is characterized by a poor surface quality of the bore hole. Material particles adhere to the guide pads that are positioned on the circumference of the drill head and that are normally responsible for the outstanding workpiece quality. In order to prevent this mechanism the guide pads were coated with an innovative amorphous and tetrahedral bonded (ta-C)-coating. This coating has a reduced friction coefficient of 0.1 against steel and a hardness coefficient of about 7,000 HV. To use the benefits of this ta-C-coating the pre- and the after-treatment of the uncoated carbide substrate and ta-C-coated guide pads are essential. For these process steps a microfinishing process was carried out as an alternative to the conventional treatment by polishing and brushing. The microfinishing of the uncoated guide pads effects a smooth surface that is necessary for an optimum bonding strength of the ta-C-coating at the carbide substrate. Furthermore the chamfer edge in the lead-in-area is rounded which reduces the mechanical load at this specific area during the process. The finishing process of the coated guide pads reduces the coating defects and improves the friction coefficient. Thus, the wear behavior of the guide pads is improved because of the better friction conditions during the drilling process of high alloyed steels.     

Burr formation in short hole drilling with minimum quantity lubrication

Machining with minimum quantity lubrication (MQL) is state of the art. Previous investigations were, however, concerned with tool optimisation and the surface quality of workpieces as well as coating technology. By now the same or partly better machining results than in conventional cutting with flood lubrication can be achieved due to adjusted tool geometries, workpiece materials and coatings. Tests about burr formation in short hole drilling exist for dry cutting or the machining with emulsion. This paper expands these results to the burr formation in machining with MQL.     

Increase of chip removal rate in single-lip deep hole drilling at small diameters by low-frequency vibration support

In order to promote active chip breakage in machining with single-lip drills for drilling deep holes with small diameters, vibration-assistance can be effectively applied. The aim of this work is to investigate the influence of low-frequency and high-amplitude vibration-assistance on the chip formation of age-hardened copper-zirconium for small diameters down to 0.94 mm and L/D-ratios up to 40. The interrelation of vibration and process parameters, like the resulting uncut chip thickness and effective velocity, is described by a kinematic model. The influence of the vibration-assistance on the chipping behavior is investigated by means of FEM-simulation and experimental analyses using a piezo-actuated test setup.     

深部钻探绳索取心孕镶金刚石钻头的关键技术

本文探讨了深部绳索取心钻探钻头的工作特征,在量化分析钻头寿命对钻探效率影响的基础上,集成研究了提高深孔钻头寿命的一些措施,包括提高工作层高度、加强保径、提高保径规的高度、采用金刚石有序排布技术、聚晶与工作层复合技术、粉末石墨装料技术以及采用合理钻进工艺参数等.所获得的结论对提高孕镶绳索取心钻头的效率和使用寿命有积极作用...     

不同电极电火花加工硬质合金的效率研究

通过实验的方式对采用不同电极电火花加工技术加工硬质合金的效率进行了研究。通过调整加工过程中的脉冲宽度和开路电压，变换加工电极，探讨了不同电极材料、开路电压及脉宽加工硬质合金的加工效率的影响.