电镀金刚石钻头钻削碳纤维复合材料研究

碳纤维复合材料钻孔加工时极易产生分层、毛刺、撕裂等缺陷,是典型的难加工材料。针对碳纤维复合材料特点,以电镀金刚石钻头为研究对象,从钻削轴向力、钻孔出口质量等方面分析电镀金刚石钻头钻孔特点,并与硬质合金麻花钻进行对比,得出结论：电镀金刚石钻头钻削碳纤维复合材料时钻削轴向力较小,钻削质量较好,更适合于碳纤维复合材料的加工;钻头转速提高有利于减小钻孔缺陷的产生,钻削轴向力随钻头转速的升高而降低,随钻头直径的增大而增大;最后,通过多元线形回归方法得出电镀金刚石钻头钻削力经验公式。     

夹层结构复合材料钻削试验研究

选用φ12mm高速钢麻花钻,在干切削条件下对夹层结构复合材料进行单因素钻削试验,研究钻削参数的变化对钻削轴向力的影响规律以及出口垫板对分层的影响;选用聚晶金刚石钻头,通过与高速钢麻花钻比较,研究横刃对轴向力以及分层的影响。结果表明:小进给量情况下,选择横刃小的钻头进行钻削,可以提高孔出口的加工质量。     

氧化锆陶瓷微孔钻削加工工艺试验研究

针对氧化锆陶瓷钻削微孔过程中出现的轴向力大和出口崩边严重的问题，使用直径为0.2 mm的金刚石涂层钻头钻削完全烧结的氧化锆陶瓷微孔，通过单因素试验方法，研究主轴转速、进给速度和步进距离对轴向力的影响，在此基础上开展啄钻工艺对比试验，探索变进给啄钻工艺对出口崩边尺寸的影响。结果表明：轴向力大小随着进给速度和步进距离的增加而增大，随着主轴转速的增加先降低后增大；采用变进给啄钻可以有效提高孔出口加工质量。     

进给量对超声振动钻削力的影响研究

在振动钻削加工原理的基础上建立了振动钻削过程中平均钻削力的数学模型,在超声轴向振动钻削试验装置上进行了0Cr17Ni4Cu4Nb不锈钢的普通钻削和振动钻削的钻削力测量试验,通过试验分析了进给量对钻削力和钻头磨损的影响规律。试验结果表明,振动钻削过程中的钻削力明显减小,钻削力曲线更加平缓;振动钻削过程中,随着钻头进给量的增大钻削力逐渐增大,钻头磨损加剧。     

0Cr17Ni4Cu4Nb超声振动钻削的钻削力和切屑研究

针对深小孔钻削过程中存在轴向力和扭矩较大、断屑排屑效果差、刀具易磨损等问题,通过建立轴向振动钻削运动数学模型,分析了超声振动钻削的钻削力和断屑机制。在设计的超声轴向振动钻削试验装置上对0Cr17Ni4Cu4Nb不锈钢材料进行了普通钻削和超声振动钻削深小孔加工试验,对比分析了轴向力、扭矩和切屑形状。实验结果表明:与普通钻削相比,超声振动钻削降低了轴向力和扭矩,获得了良好的断屑和排屑效果,提高了钻削过程的稳定性,延长了刀具的使用寿命。     

TC4钛合金钻削力和钻削温度仿真研究

为了提高TC4钛合金的可钻削性,采用有限元分析软件AdvantEdge建立TC4钛合金铣削加工有限元模型,分析工件和刀具上的温度分布规律,获得了钻削加工过程中钻削参数对钻削力和钻削温度的影响规律。结果表明：钻削TC4钛合金时最高温度出现在切屑上;钻削力随着主轴转速和进给量的增加而增大,随着钻头直径的增大而减小;钻削温度随着主轴转速、进给量和钻头直径的增加而增大。     

钻削参数对碳纤维复合材料孔加工质量的影响

本研究通过单因素试验方法,开展钻削碳纤维复合材料的试验研究。采用KISTALER公司9265B型测力仪测钻削轴向力,并采用撕裂因子评价孔形貌质量,对钻削碳纤维复合材料的过程进行分析,研究不同钻削参数对钻削碳纤维复合材料的轴向力和孔加工质量的影响。试验结果表明:随着进给量的增大,轴向力逐渐增大,孔退钻口撕裂因子呈现先减小再增大的趋势,孔进钻口撕裂因子则呈现逐步小幅增大的趋势。随着转速的增大,轴向力逐步小幅减小,孔退钻口撕裂因子随之减小。并且,进给量对轴向力和孔加工质量的影响远大于转速对轴向力和孔加工质量的影响。在相同条件下,孔进钻口的毛刺、撕裂等缺陷明显少于退钻口的缺陷。     

枪钻低频轴向振动钻孔的有限元分析

为了使枪钻在加工过程中减小钻削力,运用有限元分析软件Deform-3D动态模拟出枪钻钻头低频轴向振动钻削过程。根据枪钻钻头轴向振动钻削的断屑经验公式确定切削参数;建立了加工过程的有限元模型,并动态模拟了轴向振动钻削加工过程和普通加工过程,结合这两种加工过程中刀具所受的轴向力和扭矩变化情况进行了分析;最后将两种加工情况进行对比。结果表明:振动钻削能够显著地降低钻削中产生的轴向力和扭矩,减小钻头的磨损,延长钻头的寿命。     

钎焊金刚石薄壁钻加工工程陶瓷的试验研究

通过用钎焊金刚石薄壁钻加工Al2O3工程陶瓷的钻削试验，测量和分析了在不同加工参数下钻削轴向力和扭矩的变化，并与电镀钻头的加工性能进行了对比。结果表明，用钎焊金刚石薄壁钻加工工程陶瓷材料的设想可行，与电镀钻头相比，钎焊钻头钻削过程更稳定，加工质量更好，尤其在高转速、大进给加工条件下具有明显优势。     

涂层刀具钻削金属基复合材料

为改善金属基复合材料的加工质量,提高加工精度,对表面涂覆金刚石薄层的涂层刀具开展了钻削实验研究。结果表明,与未涂层刀具相比,涂层刀具轴向力小,磨损程度轻,钻孔几何轮廓规则且表面质量好,是钻削加工金属基复合材料的优先首选。     

石英纤维增强陶瓷基复合材料制孔工艺研究

本试验针对目前硬质合金刀具加工石英纤维增强陶瓷基复合材料时存在的刀具磨损严重、加工质量差、效率低下等问题,对比了硬质合金刀具钻孔、PCD刀具钻孔和电镀金刚石套料钻螺旋铣磨制孔的效果,分析了切削力对制孔质量的影响。研究结果表明:纬纱纤维对X向和Y向切削力的影响明显大于经纱纤维,垂直于纬纱纤维方向的切削力较小,平行于纬纱纤维方向的切削力较大;PCD刀具钻孔质量相对较好,刀具磨损不明显,适用于石英纤维增强陶瓷基复合材料的制孔加工。      

A numerical simulator to predict the dynamical behavior of the self-vibratory drilling head

The manufacturing of deep holes has to face problems to evacuate chips, especially for small diameters. Such problems induce frequent tool breakage and poor surface quality. The vibratory drilling enables the chip to be split into small elements thanks to the axial vibrations of the drill, self-maintained by the cutting energy. Thus, chips are easily evacuated from the hole. A specific tool holder with an adapted axial stiffness has been developed in order to investigate this drilling process. The cutting conditions are predetermined in order to lead to axial vibrations with a stable frequency and amplitude. During a period, the amplitude of the vibrations is higher than the feed per revolution, which enables the cutting edges to jump out of the work material. The vibrations are self-maintained and remain stable if some disturbances are absent or very limited such as the friction of the drill against the work material along its margins, the ploughing force induced by the chisel edge, the ploughing force induced by clearance face, etc. The objectives of this paper are (i) to model the dynamical behavior of the self-vibrating drilling head, the cutting and ploughing forces, and the material removal, (ii) to foresee with a numerical simulator the cutting conditions which generate good vibrations, (iii) to validate the numerical simulator with a experimental round of test. This work has also shown that the productivity of the drilling is improved by the use of the vibratory drilling. Deep hole (ratio deep/drill diameter >20) can be drilled with this new technology without any coolant and any retreat cycle with the same quality as a conventional drilling operation.     

The effect of pilot hole on delamination when core drill drilling composite materials

Removal of chips is a serious problem when core drill drilling polymer composites. As the chip is formed it moves to the inner hole of core drill. A hole is pre-drilled to eliminate the thrust caused by the removal chip, thus the threat for delamination is significantly reduced. The diameter of the pre-drilled hole is set equal to the inner hole of core drill. A smaller diameter of pilot hole cannot solve the problem of removal chips, while a larger one tends to cause undesired delamination during pre-drilling. Although valuable efforts have been made for the analysis of drilling-induced delamination, little has been reported on the effect of pilot hole diameter on delamination for core drills. The design of drill tools can be improved using obtained results.     

Design characteristics of new types of drill and evaluation of their performance drilling cast iron—II. Drills with three major cutting edges

This paper describes the performance characteristics of a new type of carbide head twist drill with four flutes, four major cutting edges, and one chisel edge. This drill shows great potential for significantly improving drilling accuracy and productivity. The drill produces holes that are as good as reamed holes. The body and point geometries and the cutting characteristics of the four-flute drill are described, along with the accuracies of hole location, angularity, size and roundness. Cutting forces, drill wear and chip morphology during cast iron drilling are also discussed. The four-flute drill deflects and vibrates much less than two-flute drills, especially in interrupted cutting cases. A patent is pending for this drill.     

Experimental studies on drilling tool load and machining quality of C/SiC composites in rotary ultrasonic machining

Carbon fiber reinforced silicon carbide matrix (C/SiC) composites have great potential in space applications because of their excellent properties such as low density, superior wear resistance and high temperature resistance. However, the use of C/SiC has been hindered seriously because of its poor machining characteristics. With an objective to improve the machining process of C/SiC composites, rotary ultrasonic machining (RUM) and conventional drilling (CD) tests with a diamond core drill were conducted. The effects of ultrasonic vibration on mechanical load and machining quality were studied by comparing the drilling force, torque, quality of holes exit and surface roughness of drilled holes between the two processes. The results showed that the drilling force and torque for RUM were reduced by 23% and 47.6%, respectively of those for CD. In addition, the reduction in drilling force and torque decreased gradually with increasing spindle speed, while they changed slightly with increasing feed rate. Under identical conditions, RUM gave better holes exit than CD. Moreover, because of the lower lamellar brittle fracture and pit originating from carbon fibers fracture, the roughness of surface of drilled holes obtained with RUM was lower than CD and the maximum reduction was 23%.     

Thrust force, torque, and tool wear in drilling the bulk metallic glass

The thrust force, torque, and tool wear in drilling of Zr-based bulk metallic glass (BMG) material are investigated. Drilling the BMG at high speed generates the chip light emission, high tool temperature, and severe tool wear. At low spindle speed, the BMG work-material builds up at the major and margin cutting edges and may break the drill. A range of feasible spindle speed and feed rate for the efficient drilling of BMG without the detrimental chip light emission and cutting edge work-material build-up has been identified in this study. Under the same drilling condition, the WC-Co tool generally requires less thrust force and about the same torque than the high-speed steel tool. The progressive wear of the major and margin cutting edges for BMG drilling is examined. Severe drill wear is associated with the bright BMG chip light emission. Without chip light emission, the drill wear is visible but not severe. This study concluded that precision holes in BMG could be generated with proper selection of tooling and process parameters.     

Nanocrystalline CVD diamond coatings for drilling of WC-Co parts

Drilling of pre-sintered cemented carbide parts is a challenging task due to the high hardness and abrasive nature of the WC grains. This operation is commonly done using uncoated cemented carbide drill bits but the tool life is very limited requiring tool re-sharpening after a few holes. A solution for the improvement of the tool performance is here exploited by the use of nanocrystalline diamond (NCD) films as high abrasion resistant coatings. These coatings were grown in a hot filament chemical vapor deposition (HFCVD) reactor. Filament temperatures in the range of 1940-1980 °C were crucial to obtain highly adherent and very uniform coatings at the cutting edge and on the surfaces of the flutes. The performance of the coated tools was evaluated in through-hole drilling of a pre-sintered cemented carbide showing outstanding cutting efficiency when compared to that of an uncoated tool: maximal 940 mm/min infeed rates (app. 1 s to drill 17 mm) instead of 20 mm/min for the latter; absence of tool wear in contrast to a flank wear of about 50 μm in the uncoated tool after only 4 holes; hole edge integrity even at the highest infeed rates while grain decohesion at the hole edge takes place when using bare drill bits.     

The effect of vibratory drilling on hole quality in polymeric composites

The anisotropy of fiber-reinforced plastics (FRP) affects the chip formation and thrust force during drilling. Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced plastics, which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce good quality holes with high efficiency by conventional drilling method. This research concerning drilling of polymeric composites aims to establish a technology that would ensure minimum defects and longer tool life. Specifically, the authors conceived a new drilling method that imparts a low-frequency, high amplitude vibration to the workpiece in the feed direction during drilling. Using high-speed steel (HSS) drill, a series of vibratory drilling and conventional drilling experiments were conducted on glass fiber-reinforced plastics composites to assess thrust force, flank wear and delamination factor. In addition, the process-status during vibratory drilling was also assessed by monitoring acoustic emission from the workpiece. From the drilling experiments, it was found that vibratory drilling method is a promising machining technique that uses the regeneration effect to produce axial chatter, facilitating chip breaking and reduction in thrust force.     

Minor cutting edge–workpiece interactions in drilling of an advanced nickel-based superalloy

Drilling is one of the key machining operations for manufacturing safety critical components that must comply with strict surface quality standards. The influence of major flank wear of drilling tools on workpiece surface quality has been well established; however, similar information concerning minor cutting edge is currently missing from literature. This paper presents a comprehensive analysis and discussions of the influence of the drill's minor cutting edge to workpiece surface integrity and residual stress distribution for RR1000, a newly developed nickel-based superalloy. These effects are critical to the acceptance of this new material in relation to tool geometry and machining strategies. The thickness of material drag in the hoop direction has been found to be the highest at the top and the least at the bottom of the hole, which is directly related to the contact duration between the minor cutting edge and workpiece surfaces; moreover this difference increased at higher levels of wear of the minor cutting edge. On-line process monitoring techniques have been employed to further understand the material drag phenomena, including feed force, torque and acoustic emission. Compressive axial and tensile hoop stresses at the surface of the holes have been measured as a function of depth and correlated both with metallurgical analysis of drilled surfaces and the process monitoring signals. It was found that the increased material drag associated with a worn tool resulted in compressive hoop surface residual stresses near the entrance hole in correspondence with trends in the processed acoustic emission signal. This work suggests that material drag increases with the duration of the minor cutting edge–workpiece interaction such that plastic deformation is the greatest near the drill entrance holes and that process monitoring of the degree of material drag in hoop direction can be practicable.