PREDICTION AND EXPERIMENTAL ANALYSIS OF CUTTING FORCES DURING MACHINING OF PRECISION EXTERNAL THREADS

External thread cutting is a complex 3-D process in which the cutting conditions vary over the thread cutter profile. It is accepted as a mature; however, heavily experience based technology and there are few academic work published. Determining the cutting forces during machining is crucial to explain formation of the surface layer, residual stresses, selection of the most appropriate machine tool and optimizing the process. This investigation is an attempt to predict thread cutting forces by dividing the thread chip into three parts, one thread root and two side faces. Variation of the cutting parameters including the shear angle, mean cutting temperature and friction force on the flank face of the tool along the thread tool root and sides are determined. In the thread root and sides, chip compression ratios for the V-shaped single piece and separately cut chip zones are measured and cutting forces are calculated and compared for precision metric thread cutting on a SAE 4340 steel bar.     

RESEARCH ON SUPERPLASTICITY IN SiCp/2024Al AND SiCp/8090Al-Li COMPOSITES

0 INTRODUCTIONAs we know, metal matrix comPOsites (MMCs)are one kinds of advanced materials. Comparing withmetal materials, they show higher specific properties.Because MMCs have a 1ot of special properties, theyare more idea1 structure materials for aviation, spacenavigation industry and automobile industry.Theywill be used widely in the soon future.Aluminum-matrix comPOsites have attracted considerable acade-mic and industrial attention.With aluminum matrixcomposites reinforced wit…     

复杂曲面五坐标加工中主曲率匹配法的刃形误差

主曲率匹配法是精密加工中一种较先进的算法,但在应用到圆环面刀具上时做了一些简化。对其中切削刃的简化所带来的误差进行了研究,建立了圆环面刀实际切削刃的数学表达式,提出了刃形误差的概念,推导出了误差表达式,并对若干关键参数的影响进行了定量研究。分析指出刃形误差是一种宽带误差,它对最大允许加工带宽有一定的限制,在实际应用主曲率匹配法时必须进行校验才能保证加工精度。     

EFFECT OF CRYSTALLOGRAPHIC ORIENTATION ON CUTTING FORCES AND SURFACE FINISH IN DUCTILE CUTTING OF KDP CRYSTALS

In order to investigate the influence of material anisotropy in ductile cutting of Potassium Dihydrogen Phosphate (KDP) crystals, experiments of face cutting of (001) plane of KDP crystals are carried out by using an ultra-precision lathe with a single point diamond tool. The cutting forces, surface finish, and surface roughness in all crystallographic orientations of the machined surface are measured, and a power spectrum analysis method is used to reveal the cutting force patterns. The experimental results show that the cutting forces and surface roughness vary greatly with different crystallographic orientations of KDP crystal, and that amplitude variation of cutting forces and surface finish is closely related with the cutting parameter of the maximum undeformed chip thickness. With the maximum undeformed chip thickness below 30 nm, the amplitude variation of cutting force and surface finish is minimized, and a super-smooth surface with consistent surface finish in all the crystallographic orientations can be achieved. The surface roughness is 2.698 nm (Ra) measured by Atomic Force Microscope (AFM). These findings provide criteria for achieving a large-scale KDP crystal with consistent super-smooth surface using ductile cutting technology.     

PENETRATION ABILITY OF ABRASIVE WATERJETS IN CUTTING OF ALUMINUM-SILICON CARBIDE PARTICULATE METAL MATRIX COMPOSITES

This article presents a set of studies performed on aluminum-silicon carbide particulate metal matrix composites prepared by adding 5, 10, 15 and 20% of SiC in aluminum alloy and processed with abrasive water jets that are formed with garnet and silicon carbide abrasives of 80 mesh size. These studies are essentially meant to assess the penetration ability of abrasive water jets on different compositions of Al-SiC _p MMCs produced by stir casting method. Abrasive waterjet cutting experiments were conducted on trapezoidal shaped specimens of different composites as well on the constituent materials i.e., 100% aluminum alloy and 100% SiC specimens by varying water pressure, jet traverse speed and abrasive mass flow rate, each at three different levels. The percentage contribution of individual and combined effects of process parameters on penetration ability was analyzed by means of analysis of variance. Contribution of waterjet pressure and traverse speed on jet penetration in these meaterials are found to be more than abrasive flow rate. Among the interaction effects, waterjet pressure and jet traverse speed combinations contribute more to jet penetration. The results presented in this study can be used to build statistical models that can predict the depth of penetration of jet in different MMCs. This study also highlights the need to choose suitable abrasive mass flow rates and jet traverse speeds for effective processing of MMCs with abrasive water jets.     

OPTIMAL MQL AND CUTTING CONDITIONS DETERMINATION FOR DESIRED SURFACE ROUGHNESS IN TURNING OF BRASS USING GENETIC ALGORITHMS

The evolving concept of minimum quantity of lubrication (MQL) in machining is considered as one of the solutions to reduce the amount of lubricant to address the environmental, economical and ecological issues. This paper investigates the influence of cutting speed, feed rate and different amount of MQL on machining performance during turning of brass using K10 cemented carbide tool. The experiments have been planned as per Taguchi's orthogonal array and the second order surface roughness model in terms of machining parameters was developed using response surface methodology (RSM). The parametric analysis has been carried out to analyze the interaction effects of process parameters on surface roughness. The optimization is then carried out with genetic algorithms (GA) using surface roughness model for the selection of optimal MQL and cutting conditions. The GA program gives the minimum values of surface roughness and the corresponding optimal machining parameters.     

基于遗传算法的超精密切削表面粗糙度预测模型参数辨识及切削用量优化

建立易于分析各切削用量对粗糙度影响关系的表面粗糙度预测模型和最优的切削用量组合,是超精密切削加工技术的不断发展的需要。针对最小二乘法和传统优化方法的不足,提出了将遗传算法用于超精密切削表面粗糙度预测模型的参数辨识,并用于求解最优切削用量,给出了金刚石刀具超精密切削铝合金的表面粗糙度预测数学模型和切削用量优化结果,进行了遗传算法和常规优化算法的比较,结果表明遗传算法较最小二乘法和传统的优化方法更适合于粗糙度预测模型的参数辨识及保证切削用量的最优。     

Performance enhancement of cryogenic machining and its effect on tool wear during turning of Al-Ticp composites

The current research is to focus on developing a liquid nitrogen diffusion system to optimize the usage of liquid nitrogen and maximizing cooling and lubrication capability by effective penetration. An atomized liquid nitrogen spray system was developed to diffuse liquid nitrogen effectively at a low flow rate (10–12 L/h) and as a high velocity (8–50 m/s) droplet jet to the machining zone. Using coated carbide tool with varying tool geometry (rake angle, approach angle, and nose radius), an investigation was performed to study the role of atomized liquid nitrogen spray-assisted machining, on performance of tool and surface quality of the machined workpiece during turning of Al-TiCp composite. To analyze the performance of liquid nitrogen spray-assisted machining, various experiments were conducted. The results obtained from the experiments reveal that the effective use of atomized liquid nitrogen spray machining is a feasible alternative to dry, wet, and cryogenically chilled argon gas. This technique significantly reduces heat generation in machining zone. The study also emphasizes the influence of tool geometry on the machinability of Al-TiCp metal matrix composites.     

SURFACE INTEGRITY CHARACTERIZATION AND PREDICTION IN MACHINING OF HARDENED AND DIFFICULT-TO-MACHINE ALLOYS: A STATE-OF-ART RESEARCH REVIEW AND ANALYSIS

This paper presents a review of the state-of-art research on surface integrity characterization, especially the characteristics of residual stresses produced in machining of hardened steels, titanium and nickel-based superalloys using the geometrically defined tools. The interrelationships among residual stresses, microstructures, and tool-wear have been discussed. Current research on residual stress modeling and simulation using finite element method has been critically assessed. Also, the rationale for developing multi-scale simulation models for predicting residual stresses in machining has been presented. At the end, possible future work has been proposed.     

高速铣削SiC_p/Al复合材料表面形貌功率谱密度研究

为了研究切削参数对高速铣削SiCp/Al复合材料表面微观形貌的影响,本文采用不同切削参数进行了高速铣削实验,利用Talyscan150型表面粗糙度测试仪对加工表面进行测量,对获得的表面数据进行功率谱密度(PSD)分析。结果表明:高速铣削SiC颗粒增强铝基复合材料时,进给量与铣削深度对功率谱密度影响不大,切削速度是主要影响因素,并且随着切削速度的增大,功率谱密度值降低,表面质量提高。加工表面的主要空间波长成分能够反映加工工艺条件对加工表面形貌的影响。     

Effect of machining parameters on the milling process of 2.5D C/SiC ceramic matrix composites

Abstract

The C/SiC ceramic matrix composites are widely used for high-value components in the nuclear, aerospace and aircraft industries. The cutting mechanism of machining C/SiC ceramic matrix composites is one of the most challenging problems in composites application. Therefore, the effects of machining parameters on the machinability of milling 2.5D C/SiC ceramic matrix composites is are investigated in this article. The related milling experiments has been carried out based on the C/SiC ceramic matrix composites fixed in two different machining directions. For two different machining directions, the influences of spindle speed, feed rate and depth of cut on cutting forces and surface roughness are studied, and the chip formation mechanism is discussed further. It can be seen from the experiment results that the measured cutting forces of the machining direction B are greater than those of the in machining direction A under the same machining conditions. The machining parameters, which include spindle speed, feed rate, depth of cut and machining direction, have an important influence on the cutting force and surface roughness. This research provides an important guidance for improving the machining efficiency, controlling and optimizing the machined surface quality of C/SiC ceramic matrix composites in the milling process.     

MODELING AND OPTIMIZATION OF PROCESS PARAMETERS FOR DELAMINATION IN DRILLING GLASS FIBER REINFORCED PLASTIC (GFRP) COMPOSITES

Glass fiber-reinforced composite materials are used in varieties of applications due to their excellent properties. Drilling is an indispensable process for this kind of materials. Delamination due to drilling is an important concern and is to be reduced. In the present work, drilling tests were carried out on computer numeric control (CNC) drilling machine. The parameters considered for the drilling investigations were spindle speed, feed rate and diameter of the drill bits. Multiple regression analysis is used for the modeling of process parameters in drilling of GFRP composites. Taguchi's S/N ratio analysis and desirability-based approach are used for the optimization of process parameters for studying the delamination in drilling of GFRP composites. The results revealed that the factor feed rate and drill diameter are the most influential parameters which affects the delamination in drilling of GFRP composites. The interaction between the parameters also affects the delamination in drilling of GFRP composites.