Analytical study of maximal tapping torque during forming screw process

Forming screws lead to a bolted assembly forming the threads of the work-piece by displacing material. The automotive industry is one of the largest markets for forming screws, which have been developed in the last ten years. One of the problems facing the designer of bolted assemblies using forming screws is the knowledge of the forming torque during the process.This study proposes an analytical model based on a previous study concerning radial penetration of a rigid acute wedge into a perfectly plastic material. The method uses the slip-line method with a model taking into account the interaction between two consecutive formed threads and enables the mean pressure on the thread flank to be obtained as a function of the formed thread height. From these results and a knowledge of the forming screw end geometry, an analytical method is proposed for the maximum forming torque, the physical phenomena of the displacement of material in the tapping process is illustrated and the significantly influential parameters highlighted. An experimental study seeks to determine the optimal lead hole on the work piece for an M8 screw. This sets limits on the forming torque and conserves a sufficiently well formed thread shape for good stripping resistance. The experimental results are compared favorably with the results of the analytical study in order to validate the forming screw model.     

Experimental study of forming and tightening processes with thread forming screws

Thread forming screws are being increasingly used, particularly in the automobile industry. They are designed to directly assemble two parts by displacing material to form their own thread. This specificity implies knowledge of the screwing torque needed for the thread to be formed in the lower plate of the assembly and of the tightening torque necessary so as to establish the preload in the assembly. The experimental study presented in this paper is divided into two parts.The first concerns the thread forming process and shows the influence of the geometrical parameters of the thread forming screw and of the work-piece, and the influence of the process parameters on the maximum forming torque. A compromise can be proposed for the choice of the lead hole diameter, which is the most important parameter to be considered in order to keep a reasonable forming torque while obtaining threads deep enough to avoid stripping problems.The second part concerns the tightening process. An original experimental device is used to enable an empirical formula to be proposed, based on the ISO standard screw formula giving the tightening torque according to the preload applied inside the assembly.     

Experimental studies of step drills and establishment of empirical equations for the drilling process

Various sizes of step drills were manufactured by a CNC grinder machine and used in the drilling process with different speeds and feed rates to produce single step holes in S1214 free machining steel. The performance of step drills was compared with that of conventional twist drills in the drilling of the free machining steel for the same task. The influences of drill size, feed rate and cutting speed on the performance of step drills were studied. Experimental results show that for better cutting performance, the small diameter should not be less than 60% of the large diameter. Also, most of the changes in the characteristics of the thrust force were influenced by the smaller drill of the step drill. On the other hand, the small diameter part of the step drill only contributed about 30% of the torque. From the experimental results, empirical equations for drilling thrust force and torque have been established for step drills.     

Modeling and tool wear in drilling of CFRP

This paper presents the prediction and evaluation of thrust force in drilling of carbon composite material. In order to extend tool life and improve quality of hole drilling, a better understanding of uncoated and coated tool behaviors is required. This paper describes the development of a phenomenological model between the thrust force, the drilling parameters and the tool wear. The experimental results indicate that the feed rate, the cutting speed and the tool wear are the most significant factors affecting the thrust force. The model can then be used for tool-wear monitoring. The model presented here is verified by experimental tests.     

板状带凸台件的精冲-挤压复合成形分析及工艺设计

总结了半冲孔型、挤压型和模锻型3种典型板状带凸台件的成形类型和特征,并以其中最具代表性的挤压型凸台作为研究对象,分析了板件挤压与正挤压在成形方面的区别,通过分析挤压型凸台成形过程中出现顶部凸起、底部缩孔、根部裂纹和外围凸包4种常见缺陷的原因,进一步提出了相应的解决措施。根据板件挤压凸台成形力的影响因素建立了计算板件挤压凸台成形力的经验公式。给出了在模具尺寸设计时,不同凸台相对高度下的挤压凸台底部孔直径的参考值;指出了凹孔直径即凸模直径越大,则成形力越大,对模具寿命不利。     

The performance of hydrogenated and non-hydrogenated diamond-like carbon tool coatings during the dry drilling of 319 Al

Aluminium alloys, though widely used in the automotive industry, are difficult to machine, particularly by drilling and tapping without the use of metal removal fluids, because of aluminium's strong tendency to adhere to the cutting tool. Tribological tests have revealed that carbon-based tool coatings, such as diamond-like carbon (DLC), promise an improved performance due to their low friction and adhesion. However, the tribological performance of DLC coatings depends on both their hydrogen content and the testing environments. Hence the experimental approach taken in this study was designed to understand the cutting performance of hydrogenated DLC (H-DLC) and non-hydrogenated DLC (NH-DLC) tool coatings during the dry drilling of a 319 Al (Al–6%Si) alloy. An experimental drilling station was built to measure torque and thrust force changes using a cutting speed of 2500 rpm and a feed rate of 0.25 mm/rev. The cutting performance was assessed by measuring the torques and thrust forces generated during the drilling of the first 150 holes or by drill failure—depending on which occurred first. The results indicated that superior cutting performance was achieved, in both torque and thrust force responses, using DLC-coated drills rather than uncoated high-speed steel (HSS) drills. The uncoated HSS drills failed after drilling only 49 holes as a result of excessive aluminium adhesion. At least 150 holes could be drilled using the DLC-coated drills, and both the torque and thrust forces generated during drilling were lower than those with uncoated HSS drills. In addition, a smaller proportion of holes exhibited abrupt increases in torque (at the end of the drilling cycle) during drilling with the DLC-coated drills. Scanning electron microscopy (SEM) investigations showed that the H-DLC drill flutes displayed minimal aluminium clogging—resulting in lower torque. H-DLC coating also diminished metal transfer and buildup edge formation on the drill's flank face and cutting edge. Thus, torque and thrust force measurements, supported by metallographic data, indicated that H-DLC-coated drills provided better dry drilling performance than NH-DLC.     

Mechanistic models of thrust force and torque in step-drilling of Al7075-T651

In the aerospace industry, burr removal is an important and expensive part of the manufacturing process. One approach to minimizing burrs is to lower the thrust force in drilling through suitable modification of the drill geometry such as the use of step drills. This paper focuses on the modeling of thrust force and torque for step drills. A mechanistic model capturing the various material removal mechanisms, i.e. oblique cutting, orthogonal cutting, and indentation, active on different sections of the step drill is developed. Subsequently, a series of experiments is conducted to calibrate and validate the model. The validation results show that the predicted thrust and torque values are in good agreement with measured values, although the torque is slightly underestimated. The validated model was further used to investigate the effects of step drill geometry parameters on the thrust force and torque. The model predictions suggest that the thrust force increases and the torque decreases for larger secondary point angles and inner diameters.     

Friction drilling of cast metals

This study investigates the friction drilling process, a nontraditional hole-making technique, for cast metals. In friction drilling, a rotating conical tool is applied to penetrate work-material and create a bushing in a single step without generating chip. The cast aluminum and magnesium alloys, two materials studied, are brittle compared to the ductile metal workpiece material used in previous friction drilling research. The technical challenge is to generate a cylindrical shaped bushing without significant radial fracture or petal formation. Two ideas of pre-heating the workpiece and high speed friction drilling are proposed. Effects of workpiece temperature, spindle speed, and feed rate on experimentally measured thrust force, torque, and bushing shape were analyzed. The thrust force and torque decreased and the bushing shape was improved with increased workpiece temperature. Varying spindle speed shows mixed results in bushing formation of two different work-materials. The energy, average power, and peak power required for friction drilling were calculated and analyzed to demonstrate quantitatively the benefits of workpiece pre-heating and high spindle speed in friction drilling.     

Drilling of carbon composites using a one shot drill bit. Part I: Five stage representation of drilling and factors affecting maximum force and torque

The thrust force and torque produced during drilling contain important information related to the quality of the hole and the wear of the drill bit [1]. In this paper, the force and torque produced during drilling of carbon fibre using a ‘one shot’ drill bit is investigated. The signals in the time domain were divided into stages and common problems and defects associated with each stage discussed. It is also shown how tool wear and thickness of the workpiece affect the thrust force and torque throughout the drilling process. The findings of this paper are used to develop a mathematical model of the maximum thrust force and torque as described on Part II of this paper and are a valuable reference for future optimisation of drilling carbon composites with a ‘oneshot’ drill bit.     

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.     

电潜螺杆泵传动轴多载荷作用力学特性与疲劳寿命分析

分析电潜螺杆泵举升过程传动轴断轴部位应力分布及疲劳寿命对提高传动机构可靠性和保障电潜螺杆泵连续稳定运行具有重要意义。针对传动轴断轴部位，提出传动轴多载荷作用力学特性分析和疲劳寿命预测方法。数值仿真和现场测试分析结果表明：各载荷单独作用时，销孔应力较大区域沿径向条状分布且应力分布较均匀，内螺纹应力较大区域沿径向自上向下逐渐减弱，且最大应力受扭矩作用最大而受狗腿度产生的弯矩作用最小；各载荷组合作用时，轴向力对销孔和内螺纹应力分布影响最大，且最大应力均小于许用应力而推断两处断轴原因不是超载导致的脆性断裂；内螺纹处疲劳寿命明显小于销孔处疲劳寿命，为传动轴优化设计提供依据。     

Performance evaluation of endrills

This paper evaluates the performance of a relatively new type of drill called an endrill which is a cross between a drill and an endmill. Investigations into the effects of its cutting conditions on the drilling forces, surface finish, drill wear and hole oversize were carried out. It was found that endrills produced better quality holes than conventional twist drills, better surface finish and less oversize of the holes. Hence, with proper feed, speed and flow rate of the pressurized flushing coolant, a good finish of about R_a = 1 μm can be attained without reaming. Thus, the productivity of finished holes can be remarkably improved. Compared to twist drills, lower torque and thrust were observed which yielded improved tool life and reduced power consumption. No “walking phenomenon” was observed when this kind of drill was used and the amount of hole oversize was found to average about 0.7% of the drill diameter as compared to 1.6% when twist drills were used. Finally, general equations for the drill torque and thrust were derived from the experimental results.     

改性氧化铝陶瓷的微孔超声钻磨特性研究

本文研究了改性氧化铝陶瓷的微孔超声钻磨特性，与普通钻磨进行了比较研究，在不同的加工条件下对轴向平均切削力和扭矩进行了定量分析，并对陶瓷表面微结构进行了分析。得出普通钻磨时的轴向平均切削力和平均扭矩均远大于超声钻磨加工时的轴向平均切削力和平均扭矩；当机床主轴转速与发生器输入功率保持不变时，轴向切削力和平均扭矩随着进给量的增大而增大；当保持机床主轴转速不变且进给量比较接近时，在一定的输入功率范围内，轴向平均切削力和平均扭矩随着输入功率(相当于振幅)的增大而增大。超声加工下，磨针磨损较小；超声加工后的孔壁表面光滑。     

基于AdvantEdge的直槽丝锥工艺参数优化

为改善316 L不锈钢材料的攻丝性能,研究以性能指标轴向力、扭矩、温度最低为优化目标,采用单因素试验和全因素试验设计相结合的方法,对影响攻丝性能的直槽丝锥工艺参数(主轴转速、丝锥涂层、切削液种类)进行优化;基于AdvantEdge软件进行攻丝数值模拟,采用熵权分析法确定最佳工艺参数组合,并通过对比试验验证了优化工艺后的...     

Drill wear monitoring using neural networks

The primary objective of this research is to monitor drill wear on-line. In this paper, drill wear monitoring is carried out by measuring the thrust force and torque signals. In order to identify the tool wear conditions based on the signal measured, a neural network, using a cumulative back-propagation algorithm, is adopted. This paper also describes the experimental procedure used and presents the results obtained for establishing the neural network. The inputs to the neural network are the mean values of thrust force and torque, spindle rotational speed, feedrate and drill diameter. The neural network is trained to estimate the average drill wear. It is confirmed experimentally that the tool wear can be accurately estimated by the trained neural network. The accuracy of tool wear estimation using the neural network is superior to that using other regression models.     

滚压参数对螺纹成形影响的实验研究

冷滚压法是加工优质高精螺纹件的一种先进方法,在实际生产加工时通过在数控系统中设置滚丝机的主轴转速、滚丝轮进给速度和精整时间进行加工。本文通过对主轴转速、滚丝轮进给速度和精整时间三因素进行正交实验,分析这三个参数对螺纹外径和加工过程中螺纹温升的影响,得出各因素对这两个指标的影响次序,综合分析外径和温升获得较优滚压参数,为实际生产时合理设置滚压参数提供实验依据。     

Drilling of carbon composites using a one shot drill bit. Part II: empirical modeling of maximum thrust force

In order to extend tool life and improve quality of hole drilling in carbon composite materials, a better understanding of ‘one shot’ hole drilling is required. This paper describes the development of an empirical model of the maximum thrust force and torque produced during drilling of carbon fiber with a ‘one shot’ drill bit. Shaw's simplified equations are adapted in order to accommodate for tool wear and used to predict maximum thrust force and torque in the drilling of carbon composite with a ‘one shot’ drill bit. The mathematical model is dependent on the number of holes drilled previously, the geometry of the drill bit, the feed used and the thickness of the workpiece. The model presented here is verified by extensive experimental data.     

High-throughput drilling of titanium alloys

Experiments of high-throughput drilling of Ti–6Al–4V at 183 m/min cutting speed and 156 mm³/s material removal rate (MRR) using a 4 mm diameter WC–Co spiral point drill were conducted. The tool material and geometry and drilling process parameters, including cutting speed, feed, and fluid supply, were studied to evaluate the effect on drill life, thrust force, torque, energy, and burr formation. The tool wear mechanism, hole surface roughness, and chip light emission and morphology for high-throughput drilling were investigated. Supplying the cutting fluid via through-the-drill holes has proven to be a critical factor for drill life, which can be increased by 10 times compared to that of dry drilling at 183 m/min cutting speed and 0.051 mm/rev feed. Under the same MRR of 156 mm³/s with a doubled feed of 0.102 mm/rev (91 m/min cutting speed), over 200 holes can be drilled. The balance of cutting speed and feed is essential to achieve long drill life and good hole surface roughness. This study demonstrates that, using proper drilling process parameters, spiral point drill geometry, and fine-grained WC–Co tool material, the high-throughput drilling of Ti alloy is technically feasible.     

Modeling of tool wear in drilling by statistical analysis and artificial neural network

The useful life of a cutting tool and its operating conditions largely control the economics of the machining operations. Hence, it is imperative that the condition of the cutting tool, particularly some indication as to when it requires changing, to be monitored. The drilling operation is frequently used as a preliminary step for many operations like boring, reaming and tapping, however, the operation itself is complex and demanding.

Back propagation neural networks were used for detection of drill wear. The neural network consisted of three layers input, hidden and output. Drill size, feed, spindle speed, torque, machining time and thrust force are given as inputs to the ANN and the flank wear was estimated. Drilling experiments with 8 mm drill size were performed by changing the cutting speed and feed at two different levels. The number of neurons in the hidden layer were selected from 1, 2, 3, …, 20. The learning rate was selected as 0.01 and no smoothing factor was used. The estimated values of tool wear were obtained by statistical analysis and by various neural network structures. Comparative analysis has been done between statistical analysis, neural network structures and the actual values of tool wear obtained by experimentation.