Cutting Behaviour Using Variable Feed and Variable Speed when Drilling Stainless Steel with TiN-Coated Carbide Drills

Variable feed and variable speed machining is a significant method for improving the performance of cutting for hard and difficult to machine materials. Tests for optimising tool wear using variable feed and speed for drilling stainless steel using TiN-coated carbide drills are reported. This paper proposes the modelling of the feed and speed variations: f (x) = f _c [1+a sin(2π(x/L) + 3/2π)], ω(x) = ω _c [1+b sin(π(x/L) + 3/2π)], respectively. The results indicate that variable feed machining is superior to constant feed machining with respect to tool life, burr height, and surface roughness. The amplitude of variation of feed, a = 0.8 and the amplitude of variation of speed, b = 0.07, is optimum for maximum tool life. The range of surface roughness from the variable feed and variable speed can be limited from 0.7 μm to 3 μm. The cutting-edge wear and outer corner wear were the dominant mechanisms of the drill wear.     

Tool life evaluation of CFRP drilling with three kinds of drill

Serious tool wear in CFRP drilling is one of the key problems to be solved urgently. Firstly, a suitable indirect evaluation index of tool life is selected according to the literature. The critical delamination force was obtained by blind hole pushing experiment. Then, tool wear experiments were carried out with double point angle drill, stepped drill and reverse edge compound drill to analyze the variation rules of the thrust force, exit burr, exit delamination and tear with tool wear. Threshold values of exit delamination, tearing and critical thrust force were compared with each evaluation index one by one to study the causes of drills failure. The results indicated that the maximum tool wear position was the outer corner. Among the three types drills, the thrust force, delamination factor and burr angle of the reverse edge compound drill are smaller. The double point angle drill fails due to the excessive thrust force, while the stepped drill and the reverse edge compound drill fail due to the hole exit delamination exceeding the threshold. The number of drilled holes of the reverse edge compound drill is 100 % and 25 % higher than that of the double point angle drill and the stepped drill, respectively. Therefore, the reverse edge compound drill is suitable for drilling CFRP.

     

Micro-drilling of Ti–6Al–4V alloy: The effects of cooling/lubricating

This paper presents a series of experimental investigations of the effects of various machining conditions [dry, flooded, minimum quantity lubrication (MQL), and cryogenic] and cutting parameters (cutting speed and feed rate) on thrust force, torque, tool wear, burr formation, and surface roughness in micro-drilling of Ti–6Al–4V alloy. A set of uncoated carbide twist drills with a diameter of 700 μm were used for making holes in the workpiece material. Both machining conditions and cutting parameters were found to influence the thrust force and torque. The thrust force and torque are higher in cryogenic cooling. It was found that the MQL condition produced the highest engagement torque amplitude in comparison to the other coolant–lubrication conditions. The maximum average torque value was obtained in the dry drilling process. There was no substantial effect of various coolant–lubrication conditions on burr height. However, it was observed that the burr height was at a minimum level in cryogenic drilling. Increasing feed rate and decreasing spindle speed increased the entry and exit burr height. The minimum surface roughness values were obtained in the flood cooling condition. In the dry drilling process, increased cutting speed resulted in reduced hardness on the subsurface of the drilled hole. This indicates that the surface and subsurface of the drilled hole were subject to softening in the dry micro-drilling process. The softening at the subsurface of drilled holes under different cooling and lubrication conditions is much smaller compared to the dry micro-drilling process.     

Micro-burr formation and minimization through process control

This paper presents an investigation on micro-burr formation in machining. Micro-cutting is compared with conventional cutting in terms of cutting process characteristic and cutting conditions. In this paper, tungsten–carbide micro-mills were used to cut holes (in a drilling-like process) to investigate top burr formation. The size and type of burr created in stainless steel 304 are studied as a function of machining variables, which are feed, cutting speed and cutting edge radius, to help illuminate the micro-burr formation mechanisms. A series of experiments was conducted to study tool life as a function of cutting conditions. Tool life, here, is defined as the number of holes created before a significant increase in burr height. Based on experimental results, contour charts for predicting burr formation as well as tool life are developed to minimize burr formation and to improve tool life. The model, which includes the effect of feed, cutting speed, and the interaction between the two, predicted the burr height and tool life values with an accuracy of about ±15%.     

Performance of cryogenically treated M35 HSS drills in drilling of austenitic stainless steels

In this study, performance of cryogenically treated M35 high speed steel (HSS) twist drills in drilling of AISI 304 and 316 stainless steels was evaluated in terms of thrust force, surface roughness, tool wear, tool life, and chip formation. To present the differences in tool performance between untreated and treated drills, and machinability between AISI 304 SS and AISI 316 SS, a number of experiments were performed at different combinations of cutting speed, and feed rate. As the results of the conducted experiments, the treated drills showed better performance than untreated drills in terms of thrust force, surface roughness, and tool wear and tool life for both types of stainless steels. Tool lives of treated HSS drills in drilling of AISI 304 SS and AISI 316 SS improved 32% and 14%, respectively, when compared with untreated drills. Experimental results also showed that machinability of AISI 304 SS was harder than the machinability of AISI 316 SS.     

An experimental investigation of the effect of coatings and cutting parameters on the dry drilling performance of aluminium alloys

As a result of the need to automate assembly in the aircraft industry, along with economic and ecological reasons, industry and research institutions have been pushed to develop dry drilling for aluminium alloys to eliminate the need for cooling fluids. The main difficulties in dry drilling are accelerated tool wear due to workpiece material adhesion on the tool and the formation of bigger-sized burrs. This paper describes an experimental research study on machinability in the dry drilling of aluminium alloys and on the potential of the new design of tools and coatings. Dry drilling tests were performed using uncoated drills and two different coatings produced by means of an arc evaporation PVD process. Experiments consisted of machining with a 10-mm diameter three-edged drill to produce 25-mm deep holes. Tool wear evolution and burr size were analysed, as well as the impact of the process parameters on torque, power, feed force and tool temperature.     

Drilling of hybrid aluminium matrix composites

This paper presents the influence of cutting parameters on thrust force, surface finish, and burr formation in drilling Al2219/15SiCp and Al2219/15SiCp-3Gr composites. The composites were fabricated using the liquid metallurgy method. The tools used were commercially available carbide and coated carbide drills. The results revealed that feed rate had a major influence on thrust force, surface roughness, and exit burr formation. Graphitic composites exhibit lesser thrust force, burr height, and higher surface roughness when compared to the other material. The reduced thrust force and burr height is attributed to the solid lubricating property of the graphite particles. The higher surface roughness value for Al2219/15SiCp-3Gr composite is due to the pullout of graphite from the surface. The chips formed when machining graphitic composites are more discontinuous when compared to SiCp reinforced composites and hence advantageous.     

Modeling and analysis of performances in drilling hybrid metal matrix composites using D-optimal design

The present paper deals with the modeling and analysis of machining responses such as the thrust force, surface roughness, burr height, and tool wear in the drilling of hybrid metal matrix composites using carbide, coated carbide, and polycrystalline diamond drills. Experiments are conducted on Al 356 aluminum alloy reinforced with silicon carbide of size 25 μm and mica of size 45 μm. Machining parameters such as spindle speed, feed rate, and weight percent of silicon carbide are chosen as the numerical factors; the drill material is considered as the categorical factor. An experimental plan of a four-factor (three numerical plus one categorical) D-optimal design based on the response surface methodology is employed to carry out the experimental study. The results indicated that the predicted values through the developed model are well in agreement with the experimental results. The results also indicated that the method used is effectively applied for the modeling and analysis of drilling parameters in drilling hybrid metal matrix composites.     

Prediction of burr height formation in blanking processes using neural network

Productivity and quality in sheet metal blanking processes part can be assessed by the burr height of the sheared edge after blanking. This paper combines predictive finite element approach with neural network modelling of the leading blanking parameters in order to predict the burr height of the parts for a variety of blanking conditions.Experiments on circular blanking operation has been performed to verify the validity of the proposed approach.The numerical results obtained by finite element computation including damage and fracture modelling and tool wear effects were utilized to train the developed simulation environment based on back propagation neural network modelling.A trained neural network system was used in predicting burr height of the blanked parts versus tool wear state and punch-die clearance.The comparative study between the results obtained by neural network computation and the experimental ones gives good results.     

Characterization and modeling of burr formation in micro-end milling

Mechanical micromachining is increasingly finding applications in fabrication of components in various fields, such as, biomedical devices, optics, electronics, medicine, communications and avionics. In order to ensure adequate functionality, there are stringent requirements for form and finish in case of biomedical devices like cochlear implants and metallic optics. This necessitates that the post machined surface must be burr free. To address these issues in micromachining, this paper presents results of an experimental study to investigate the influence of main process parameters i.e. speed, feed rate, depth of cut, tool diameter and number of flutes on the formation of the various types of burrs i.e. exit burrs and top burrs produced during micro-end milling operation. The experiments performed using Taguchi method shows that three types of burr formation mechanisms prevail during micro-end milling operations; these are: lateral deformation of material, bending and tearing of the chip. Also, three types of burrs were observed include: Poisson burr, rollover burr in down milling and tear burr in up milling. Further, it is observed that the depth of cut and the tool diameter are the main parameters, which influence the burr height and thickness significantly. However, the speed and the feed rate have small to negligible effect on the burr thickness and height. Besides the experimental analysis, the paper presents an analytical model to predict the burr height for exit burr. The model is built on the geometry of burr formation and the principle of continuity of work at the transition from chip formation to burr formation. Note that prediction of burr height in micro-end milling is extremely challenging due to the complex geometry of material removal and microstructural effects encountered during cutting at that length scales. The model fares well and the prediction errors range between 0.65 and 25%.     

Use of process signals for tool wear progression sensing in drilling small deep holes

Detailed knowledge about the relation between wear progression of a cutting tool and the cutting forces generated is of paramount importance for the development of a tool condition monitoring strategy. This paper discusses the changes in the different process signals with progressing tool wear of small diameter twist drills (D=1.5 mm), when drilling boreholes having a depth of 10 times the diameter in plain carbon steel using MQL. The effect of different wear patterns on the process signals is presented. Furthermore, several features, which evolve over the life of the drills, are identified and extracted from the process signals. Knowledge about the evolution of these features can support the user to determine the final tool life stage, so that the drill can be replaced before the final fracture occurs.     

Analysis of the life of cemented carbide drills with modified surfaces

The performance of cemented carbide cutting tools during machining is influenced not only by the mechanical properties of the coating and substrate but also by the topographies of their surfaces. A tool with good coating and substrate properties but unsuitable topographies may exhibit accelerated wear and, consequently, impaired performance. In this work, drills coated using physical vapor deposition (PVD) were produced with different substrate textures, which in turn generated different coating textures. The surface roughness values of the coated drills were measured together with the residual stress at the interface between substrate and coating. Drilling tests were performed and tool wear was measured during the machining process. Two different tool coatings were studied: TiAlN and TiAlCrSiN. The goal was to study how the characteristics of the substrate and coating (material, surface topography, and residual stress) influence tool life. Tool life experiments were carried out using drilling tests in AISI 1548 steel, which is often used in crankshafts. The primary tool wear mechanism was attrition in all the drills. The main conclusion of this work is that the tool with the lowest roughness and a TiAlCrSiN coating had the best performance in the conditions tested here.     

微铣金属表面微沟槽结构的粗糙度及形貌分析

为了提高和改善微沟槽表面质量,设计了高速微铣削实验,研究了微沟槽底面表面粗糙度和侧壁残留毛刺的变化规律。从理论角度引入了已加工表面的形成机理,建立了微观表面粗糙度理论模型,提出了刀具跳动对侧壁形貌变化影响的规律。利用三轴联动精密微细铣削机床加工微细直沟槽,并选取主轴转速、轴向切深、进给速度、刀具跳动量和材料组织结构为研究因素。采用多因素正交实验和极差分析法,对表面粗糙度值进行数值分析。铝合金,钢和钛合金三类微沟槽底面对应的最佳表面粗糙度值变化范围分别为1.073~1.481 μm,0.485~0.883 μm,0.235~0.267 μm;无刀具跳动钛合金微沟槽壁毛刺的最大高度为7.637 μm,而当刀具存在0.3 μm的径向综合跳动量时对应的微槽壁毛刺的最大高度为21.79 μm。铣削参数对表面粗糙度值的影响按从大到小依次为进给速度、主轴转速、轴向切深,且随着进给速度和轴向切深的增大,表面粗糙度值增大;随着主轴转速的增大,表面粗糙度值先减小后增大;在相同加工条件下,若微圆弧刀刃无磨损,微刀具的跳动量对微直沟槽侧壁表面质量有较大影响。同时,不同金属材料特性也是影响微沟槽表面质量的潜在因素。     

The performance Of DLC-coated and uncoated ultra-fine carbide tools in micromilling of Inconel 718

Coating is an important factor that affects cutting-tool performance. In particular, it directly affects surface quality and burr formation in the micro milling process. After the micromechanical machining process, surface quality is very hard to increase by a second process (grinding, etc.). In addition, in micromechanical machining, the cutting tool needs to have a good resistance to wear, owing to the fact that the cutting process is carried out at high speed. In this study, the machinability of Inconel 718 superalloy was investigated, using a Diamond Like Carbon (DLC) coated tool. The experimental tests were carried out in dry cutting conditions for different feed rates and depth of cuts. It was found that the dominant wear mechanism for all cutting parameters was identified to be abrasive and diffusive wear. Besides, a significantly Built Up Edge (BUE) formation was observed in uncoated tool. The results clearly show that DLC coating significantly decreased BUE. In addition, a smaller cutting force and better surface roughness were obtained with a DLC-coated tool. In conclusion, DLC coating can be used in micro milling of Inconel 718. It reduces the BUE and burr formation, improves surface roughness.     

麻花钻磨损特性的研究

通过对调质合金结构钢的大量钻削试验,研究了麻花钻磨损区的图形特征和磨损机理以及钻头失效与磨损图形参数、钻头切削寿命与钻削速度的关系。结果表明,麻花钻的磨损具有非线性特征,钻头转角和主刀刃及横刃区有两个显著不同的磨损区,随钻削速度的提高,这两个磨损区的特征差异及磨损带宽度之比明显增大。在钻削速度较低、钻头失效时,两个磨损区为较均衡的磨粒磨损和粘结磨损;钻削速度较高时,转角区剧烈的粘结磨损和氧化磨损使钻头加快失效,而主刀刃及横刃上的磨损却很小。受此影响,麻花钻的磨钝标准、耐用度问题较为复杂,钻头的寿命（Ｔ）－速度（Ｖ）曲线的泰勒特性范围很窄。     

涂层钻头加工不锈钢磨损机理研究

研究了TiN、TiAlN、TiCN三种高速钢涂层专用麻花钻头钻削加工1Cr18NigTi奥氏体不锈钢时的刀具寿命以及刀具表面涂层的磨损特性。通过研究刀具寿命以及对刀具前刀面涂层磨损形态和元素成分的变化规律，揭示了三种涂层钻头的磨损机理。结果表明：在中低速、湿切削的情况下，TiCN涂层要优于TiAlN涂层，明显优于TiN涂层；TiCN涂层高速钢专用钻头较TiAlN、TiN涂层高速钢专用钻头更加适合不锈钢的钻削加工。研究结果对提高不锈钢钻削加工效率与加工质量具有重要意义。     

Modeling and optimization of burr height in drilling of Al-7075 using Taguchi method and response surface methodology

This investigation presents the use of Taguchi and response surface methodologies for minimizing the burr height and the surface roughness in drilling Al-7075. The Taguchi method, a powerful tool to design optimization for quality, is used to find optimal cutting parameters. Response surface methodology is useful for modeling and analyzing engineering problems. The purpose of this paper was to investigate the influence of cutting parameters, such as cutting speed and feed rate, and point angle on burr height and surface roughness produced when drilling Al-7075. A plan of experiments, based on L₂₇ Taguchi design method, was performed drilling with cutting parameters in Al-7075. All tests were run without coolant at cutting speeds of 4, 12, and 20 m/min and feed rates of 0.1, 0.2, and 0.3 mm/rev and point angle of 90^°, 118°, and 135°. The orthogonal array, signal-to-noise ratio, and analysis of variance (ANOVA) were employed to investigate the optimal drilling parameters of Al-7075. From the analysis of means and ANOVA, the optimal combination levels and the significant drilling parameters on burr height and surface roughness were obtained. The optimization results showed that the combination of low cutting speed, low feed rate, and high point angle is necessary to minimize burr height. The best results of the surface roughness were obtained at lower cutting speed and feed rates while at higher point angle. The predicted values and measured values are quite close to each other; therefore, this result indicates that the developed models can be effectively used to predict the burr height and the surface roughness on drilling of Al-7075.     

Drilling of hybrid Al-5%SiCp-5%B4Cp metal matrix composites

Hybrid metal matrix composites consist of at least three constituents—a metal or an alloy matrix and two reinforcements in various forms, bonded together at the atomic level in the composite. Despite their higher specific properties (properties/unit weight) of strength and stiffness, the nonhomogeneous and anisotropic nature combined with the abrasive reinforcements render their machining difficult. The work piece may get damaged and the cutting tools experience high wear rates, which may lead to an uneconomical production process or even make the process impossible. This work reports on the drilling of Al-5%SiC_p-5%B₄C_p hybrid composite with high-speed steel (HSS), not expensive PCD, or carbide drills in an attempt to explore the viability of the process. Drilling of Al-5%SiC-5%B₄C composites with HSS drills is possible with lower speed and feed combination. The cutting conditions for minimized tool wear and improved surface finish are identified. Characterization of tool wear and surface integrity are also carried out.     

A comparative study of material phase effects on micro-machinability of multiphase materials

In the mechanical micro-machining of multiphase materials, the cutting process is undertaken at a length scale where material heterogeneity has to be considered. This has led to increasing interest in optimising the process parameters for micro-machining of such materials. In this study the micro-machinability of two steels, a predominantly ferrite material (AISI 1005) and a near-balanced ferrite/pearlite microstructure (AISI 1045) was studied. Workpiece sample deformation properties were characterised by nano-indentation testing. Additionally, metallographic grain size evaluation was undertaken for the workpiece microstructures. Surface roughness, workpiece microstructure and burr size for micro-machined parts as well as tool wear were examined over a range of feed rates. The results suggest that for micro-machined parts, differential elastic recovery between phases leads to higher surface roughness when the surface quality of micro-machined multiphase phase material is compared to that of single phase material. On the other hand, for single phase predominantly ferritic materials, reducing burr size and tool wear are major challenges. Thus, the paper elucidates on material property effects on surface and workpiece edge quality during micro-milling.     

ROTARY ULTRASONIC MACHINING OF CARBON FIBER-REINFORCED POLYMER: FEASIBILITY STUDY

Carbon fiber-reinforced polymer (CFRP) has been widely used in aircraft components, automotive parts, and sporting goods. Hole machining is the most frequently employed operation of secondary machining for fiber-reinforced composites. However, challenges (delamination, splintering, burr, short tool life, low machining precision, and low surface quality) still remain for their widespread applications. Rotary ultrasonic machining (RUM) is a non-conventional machining process that has been used to drill holes in composite materials. However, it has not been used to drill this type of CFRP. In this article, RUM is introduced into drilling holes in this type of CFRP for the first time. The feasibility to machine carbon fiber-reinforced epoxy using RUM is investigated experimentally. Chips, edge chipping, surface roughness, tool wear, and thrust force were measured. Effects of RUM process variables (rotation speed, vibration amplitude, and feedrate) on thrust force and surface roughness were studied. Results showed that RUM could be used to drill holes in CFRP with high productivity and low tool wear. A better surface was produced by higher rotation speed and lower feed rate.