HOLE QUALITY IN DEEP HOLE DRILLING

Deep hole drilling represents the most economical method of hole producing with length-to-diameter ratios ≥5. The objective of this study was to ascertain the effect of machining parameters on hole quality produced by the deep hole machining process and to develop a better understanding of the effect of these process parameters on the hole quality. Such an understanding can provide insight into the quality control problems of the holes when the process parameters are adjusted to obtain certain characteristics. This study deals with the experimental results obtained during boring trepanning association (BTA) drilling on medium carbon steel (AISI 1060). The surface roughness, out-of-roundness, and hole size are influenced by cutting speed and feed rate of the deep hole drilling.     

A STOCHASTIC CHARACTERIZATION OF THE MACHINE TOOL WORKPIECE SYSTEM IN BTA DEEP HOLE MACHINING Part II: Response Analysis and Evaluation of the Tool Tip Motion

In this paper, the solutions to the stochastic differential equations, which mathematically represent the machine tool work-piece system in BTA deep hole machining are presented. The solutions to the parametric stochastic differential equations have been obtained using the well known averaging technique. The non-parametric inhomogeneous equations have been solved using the Fokker-Planck equation. Based on these solutions, the true motion of the tool tip has been described using the maximum, average and minimum deviation curves. These curves predict that helical grooves will be formed on the workpiece and such helical grooves were observed on the workpieces. Also, the maximum, average and minimum values of deviation of the tool tip which is a measure of the roundness error are established. Based on these results an upper bound for the roundness error as a function of depth of hole is derived. The measurement of roundness of the specimens reveals that the experimental values be in the zone predicted by the theory in a finite region. So it can be speculated that the resultant force system is not completely balanced at the pads.     

An analytical tim6 domain evaluation of the cutting forces in BTA deep hole machining using the thin shear plane model

This paper presents an analytical approach to describe the cutting forces in 1ST A deep hole machining processes in the time domain. The method takes into account the effect of different machining conditions. Since the cutting velocities employed in BTA deep hole machining process are relatively high, and since small chips are produced due to the presence of tool chip breakers, the analysis is developed on the basis of the thin shear plane model.

The cutting velocity is a linear function of radius and the rake angle. Cutting is different in the two regions of the cutting tool, so the total cutting force acting on the cutting tool is determined by integrating the force on a small incremental thickness of the cutting tool. This approach, to predict the value of the cutting forces without resorting to any empirical techniques, clearly illustrates the effect of various system parameters on the machining process.

The resultant force system on a new BTA cutting tool consists of an axial force and torque. But with the increase in the number of holes bored, not only does the cutting profile deteriorate, but the wear pads do too. The resultant force system will then consist of three force components and a torque, due to the fact that the forces are not balanced at the wear pads. Under such conditions, the cutting force equations derived in the latter half of the paper, coupled with the properties of the randomly varying component, can be used as the forcing function on the machine tool to evaluate not only the response but also the regions of stability and instability during the machining.     

Cutting force and hole quality analysis in micro-drilling of CFRP

Micro-drilling in carbon fiber reinforced plastic (CFRP) composite material is challenging because this material machining is difficult due to anisotropic, abrasive and non-homogeneous properties and also downscaling of cutting process parameters affect the cutting forces and micro-drilled hole quality extensively. In this work, experimental results based statistical analysis is applied to investigate feed and cutting speed effect on cutting force components and hole quality. Analysis of variance based regression equation is used to predict cutting forces and hole quality and their trend are described by response surface methodology. Results show that roundness error and delamination factor have similar trends to those of radial forces and thrust force, respectively. Non-linear trends of cutting forces and hole quality errors are observed during downscaling of the micro-drill feed value. Optimization results show that cutting forces and hole quality errors are minimum at a feed value which is almost equal to the tool edge radius rather than at the lowest feed value. Therefore, the presented results clearly show the influences of size effects on cutting forces and hole quality parameters in micro-drilling of CFRP composite material.     

An experimental investigation for the stochastic modelling of the resultant force system in BTA deep hole machining

This paper presents the measurement and a statistical analysis of the resultant force system, consisting of an axial force and torque, in BTA deep hole machining. The measurements were performed using a specially designed two-component piezoelectric dynamometer and adopting the rotating cutting tool-stationary workpiece procedure. The dynamometer was calibrated for static and dynamic outputs and techniques were employed for increasing the measuring accuracy and reducing the cross-interference by obtaining the elements of the system transfer function. Experiments were carried out to measure the mean values and the dynamic fluctuations of the axial force and torque. The recorded data was processed and analysed to establish all major statistical properties of the axial force and torque. Results show that the dynamic fluctuations of the axial force and torque in BTA deep hole machining can be represented by a stationary wideband process with a gaussian density distribution function. Such a mathematical model is essential for evaluating the dynamic response of the machine-workpiece system as well as the true motion of the cutting tool tip, and to establish the reliability of the machining process.     

基于多源融合理论的机床圆度误差测量不确定度评定

圆度误差是评价机床加工精度的重要指标.为实现机床圆度误差测量不确定度的评定,对基于球杆仪测量的机床圆度误差的贡献因素及不确定度评定方法进行研究.首先,采用最小二乘法(least sqaure method,LSM)对圆度误差进行评定.然后,基于黑箱理论提出了多源融合误差测量不确定度评定方法.接着,根据球杆仪测量机床圆度...     

Mechanical micro-drilling of nimonic 80A superalloy using uncoated and TiAlN-coated micro-drills

Micro-drilling is a complex mechanical machining process. Micro-drilling experiences an early tool damage which is a major drawback for nickel-based superalloy. This paper examines the wear condition on the micro-tool cutting edge, surface roughness of machined holes, and hole diameter analysis in micro-drilling of Nimonic 80A, using two types of micro-drills (uncoated and TiAlN coated) with 0.79?mm diameter. Micro-drilling tests, using cutting speed (V_c), feed rate (f_z), and the micro-drill diameter as experimental parameters were carried out to bring out the best optimized machining conditions in micro-drilling of Nimonic 80A. Wear on the tool cutting edge and burr height occurring at the entrance of drilled holes were measured at constant period to give the lastingness of micro-drill. Quality of holes were analyzed in terms of surface roughness inside the hole and the hole diameter after every five drilled holes. The result obtained from the above analysis showed that TiAlN-coated micro-drill performs way better than the uncoated micro-drill in terms of wear, surface roughness, hole quality, and burr. Thus, the above performed study gives the knowledge to select micro-tool for machining of Nimonic 80A which could be useful in the aerospace industry.     

High-accuracy turning with slender boring bars

The paper presents the theoretical background for new approaches for achieving high accuracy in finish turning with slender tools.The approaches are developed especially for high-accuracy turning with vibrationsdamped boring bars with a length-to-diameter ratio up to14.The approaches are based on established force models of turning operations and utilize a three-pass scheme where the deflection of the boring bar is calculated and compensated for in the final passes.Very good results are achieved in practical machining tests for a great variation of cutting conditions.Experiments show that the typical diameter error is 0.01 mm,even in situation where the tool deflection is 0.3 mm.     

Experimental Investigation into the Hole Quality in Ultrasonic Machining of WC-Co Composite

This study has focused on the evaluation of the influence of different input variables (cobalt content, thickness of workpiece, tool profile, tool material, size of abrasive grains, and power rating) on the hole quality (dimensional and form accuracy) obtained in ultrasonic machining of WC-Co composite material. Taguchi's approach has been employed for planning the experiments and optimization of the experimental results. Three measures of hole quality (hole oversize, out of roundness, and conicity) have been investigated under controlled experimental conditions. The experimental results showed that abrasive grit size and power rating were most influential for the hole quality. Hole quality has been found to be improved at higher cobalt content, whereas it is found to be degraded with the use of coarse grit size.     

Surface characteristics of titanium with rotary EDM

Experimental investigations have been carried out on electro-discharge machining of titanium in respect of surface finish, out-of-roundness and overcut using rotating copper-tungsten tool electrode. An attempt has also been made to compare the results with stationary electrode. It is concluded that rotation of electrode improves out-of-roundness, surface roughness, overcut and out-of-roundness increase with increase of current with both rotating and stationary electrodes.     

喷油器体深孔直线度加工工艺参数优化

深孔直线度误差严重影响着高压共轨喷油器体的性能。为研究不同的加工工艺参数对喷油器体深孔直线度的影响规律,根据单因素试验方法,利用枪钻对喷油器体深孔进行加工试验,采用线结构光视觉测量技术与最小二乘法测量深孔直线度,分析切削速度、进给速度和切削液压力对喷油器体深孔直线度的影响规律。结果表明：随着切削速度的增大,直线度先减小后增大,当切削速度为6 200 r/min时,直线度最小;当进给速度较小时,直线度较小,随着进给速度的增大,直线度总体呈现波动上升的趋势;当切削液压力较低时,直线度较大,直线度随着切削液压力的增大而减小,当切削液压力值达到8 MPa后,直线度随切削液压力的增大而增大。基于三因素三水平的正交试验,对试验结果进行极差和方差分析,获得最佳加工工艺参数组合：切削速度为6 200 r/min、进给速度为50 mm/min、切削液压力为8 MPa,并对该参数组合进行试验验证。研究结果对减小深孔加工直线度,提高喷油器体加工质量和系统喷油性能的稳定性具有重要的参考价值。     

Experimental and computational analysis of the coolant distribution considering the viscosity of the cutting fluid during machining with helical deep hole drills

An experimental analysis regarding the distribution of the cutting fluid is very difficult due to the inaccessibility of the contact zone within the bore hole. Therefore, suitable simulation models are necessary to evaluate new tool designs and optimize drilling processes. In this paper the coolant distribution during helical deep hole drilling is analyzed with high-speed microscopy. Micro particles are added to the cutting fluid circuit by a developed high-pressure mixing vessel. After the evaluation of suitable particle size, particle concentration and coolant pressure, a computational fluid dynamics (CFD) simulation is validated with the experimental results. The comparison shows a very good model quality with a marginal difference for the flow velocity of 1.57% between simulation and experiment. The simulation considers the kinematic viscosity of the fluid. The results show that the fluid velocity in the chip flutes is low compared to the fluid velocity at the exit of the coolant channels of the tool and drops even further between the guide chamfers. The flow velocity and the flow pressure directly at the cutting edge decrease to such an extent that the fluid cannot generate a sufficient cooling or lubrication. With the CFD simulation a deeper understanding of the behavior and interactions of the cutting fluid is achieved. Based on these results further research activities to improve the coolant supply can be carried out with great potential to evaluate new tool geometries and optimize the machining process.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00383-w     

Mechanism of material removal in the magnetic abrasive process and the accuracy of machining

In this paper, we focus on the magnetic abrasive process as a sizing process and present a theory which explains the out-of-roundness error phenomenon based on force analysis of the material removal mechanism. The theory is independent of the size and material of the workpiece and the design of the magnetic abrasive machine tool. The theory results are verified experimentally. The limiting accuracy of the magnetic abrasive process, the machining time required to achieve specified accuracy of the workpiece, and the material removal rate are determined.     

电流变技术在抑制深孔切削颤振中的应用

针对深孔加工中出现的切削颤振问题,利用电流变液的电流变效应,设计一套基于流动和剪切混合工作模式的电流变减振器。通过对深孔切削系统的动力学模型的建立和分析,得到系统的运动微分方程。利用MATLAB/Sinmulink对动力学模型进行仿真分析并进行实验验证,结果表明电流变减振器能够减小颤振的振幅,且在不同电场强度下具有不同的减振效果。因此通过控制电流变减振器的电场强度可以有效地抑制深孔机床中切削颤振的发生。     

CRYOGENIC MACHINING OF KEVLAR COMPOSITES

Previous attempts to machine Kevlar aramid fibre reinforced plastics (KFRP) with conventional cutting tools have proven to be extremely difficult. This has somewhat restricted the material's usage, often negating the advantages of its high strength to weight ratio and fatigue tolerance. The present paper describes a novel technique of machining KFRP under cryogenic conditions with remarkable results compared to those obtained at ambient temperatures. The investigation carried out with turning operation shows dramatic improvement of the tool performance and surface quality. The effects of various machining parameters such as workpiece temperature, cutting speed and tool geometry on the machinability of KFRP are presented and analyzed. It appears that care is necessary to judge the tool life as the typical tool wear growth and surface finish or cutting force may produce contradictory results. It is also suggested that, for KFRP, surface finish of the machined workpiece is a very good criterion to determine the tool life. To aid the understanding of the machining mechanics, a microscopic investigation of the cutting zone while actually machining a testpiece at ambient and cryogenic temperatures is also reported.     

Characteristics of array holes with large aspect ratio in aluminum-based cast alloy

Array holes were obtained by machining methods or nontraditional machining methods, and casting process was rarely used in the preparation of array holes. In this experiment, stainless steel thin rods coated with alcohol group graphite paint were chosen as cores to prepare array holes on aluminum-based cast alloys, and the roughness and roundness of holes were analyzed. The results show that array holes cast with 2?mm pitch of holes, 0.54?mm diameters, and large aspect ratio of 100 were obtained. The roundness and roughness of holes were influenced by consumption of carbon element from surface of hole core and wettability between molten metal and hole core surface; the lower roughness and the better roundness could be acquired under these experimental conditions. And roughness of holes (R_a) was about 6.3?µm, which is close to that obtained by machining, and the value of hole shape factor (K, characterizing the roundness of the hole) was above 0.7; the shape of the hole approached a circular shape.     

New algorithm to minimise kinematic tool path errors around 5-axis machining singular points

The singular points of a given 5-axis CNC machine could be found in the domain of the joint variables of the machine. In the neighbourhood of a singular point, even for a small change of the tooltip position, an enormous change of axis displacements of the machine is often required. This causes a large deviation between the real cutting path and the desired tool path, and the machining surface could be destroyed. This paper provides with an analytical scheme for identifying singular configuration of 5-axis CNC machines. In particular, an efficient and robust algorithm is proposed to compute the cutter path across the neighbourhood of the singular points identified such that the computed cutter path tracks the desired tool path within a controllable error. Numerical examples and real cutting parts are carried out and discussed to show the effectiveness and the efficiency of the presented method.     

Investigating the Machinability of AISI 420 Stainless Steel Using Factorial Design

This work aims at studying the machining characteristics of high-strength materials using carbide cutting tool inserts at different cutting conditions. This is an essential step in building up an accurate machining information system. The tested material is high-strength stainless steel of the AISI 420 type. Machining tests were carried out using orthogonal cutting conducted to investigate the machining characteristics for high-strength stainless steel AISI 420 at different cutting conditions and tool rake angles. This assessment is achieved by investigating the effect of cutting parameters (cutting speed, feed, depth of cut, and tool geometry) on cutting forces, specific cutting energy, shear angle, coefficient of friction, shear stress, shear strain, and shear strain rate. Empirical equations and a correlation for the behavior of each of the output responses were investigated as a function of the independent variables. Main effect and interaction plot were presented for the most influential factors affecting the main cutting force and the power consumed.     

An experimental investigation as to the effect of cutting parameters on roundness error and surface roughness in cylindrical grinding

This paper presents the results of an experimental investigation as to the effects of grinding parameters on roundness error and surface roughness in cylindrical grinding. Many variables including the wheel materials, wheel loading and dressing, workpiece metallurgy, work drive mechanisms, work holding methods, coolant types, feeds and speeds, machine stiffness and age, surface conditions, centre conditions, floor vibrations all influence the quality of ground parts. However, the composite sum of these grinding parameters creates static and dynamic forces. It is obvious that the roundness error and surface roughness are created by many parameters, but in this study, only the effects of the depth of cut, work speed and feed rate which create the grinding forces in cylindrical grinding are investigated. The grinding experiments were planned according to the principles of orthogonal arrays (OAs), developed by Taguchi, and were performed so as to understand the effects of these parameters on roundness error and surface roughness. The experimental data was analysed by using statistical tools: the percent contribution from an analysis of variance (ANOVA) and the correlation between machining parameters with roundness error (R) and also surface roughness (Ra). Roundness was found to be the most related with the cutting speed, grinding force and depth of cut, while surface roughness is related to feed rate and work speed.     

A simple method for estimating the roundness of minimum zone circle

With the rapid development of micromachining technology, the feature size of object parts becomes smaller whilst the required tolerance accuracy becomes higher. The geometry of these micro-parts must be critically verified at sub-micrometer or even nanometer accuracy in three dimensions to guarantee machining quality, such as the cylindrical parts. Therefore, the method for estimating roundness error plays an increasingly important role in machining. This paper focuses on the roundness estimation based on the minimum zone circle method in a Cartesian coordinate system. An asymptotic search method is also proposed to obtain the coordinates of the concentric centre of the minimum zone circle model and to calculate the roundness error. Comparison and simulation experiments are also conducted to test the performance of the proposed method. The results demonstrate that the proposed method is effective, reliable and can meet the requirements for roundness estimation.