DUCTILE-REGIME MACHINING OF PARTICLE-REINFORCED METAL MATRIX COMPOSITES

This paper presents research results on ultraprecision machining of metal matrix composite (MMC) composed of aluminum matrix and either SiC or A1₂ 0₃ particles. Ductile-regime machining of both SiC and aluminum was evaluated to improve the surface integrity of the composite. Both polycrystal-line diamond (PCD) and single crystalline diamond (SCD) tools were used to ultraprecision machine the composites at a depth of cut ranging from 0 to 1μm using a taper cut. The feedrate was normalized to the tool nose radius. A model is proposed to calculate the critical depth of cut for MMCs reinforced with either A1₂0₃ or SiC. The critical depths of cut were found to be 1 p.m and 0.2 u.m for MMCs reinforced with A1₂ 0 or SiC₃, respectively. Both depth of cut and crystallographic direction of the ceramic particles are the sufficient conditions for ductile-regime machining. Although both tools produce similar surface finish, a SCD tool removed the MMC as chips while a PCD tool simply smeared the surface. A diffusion-abrasion mechanism was suspected to cause the surprising wear of the SCD tools when machining the aluminum/SiC composite.     

OPTIMAL MACHINING CONDITIONS FOR TURNING OF PARTICULATE METAL MATRIX COMPOSITES USING TAGUCHI AND RESPONSE SURFACE METHODOLOGIES

The present investigation focuses on the influence of machining parameters on the surface finish obtained in turning of LM25 Al/SiC particulate composites. The experiments are conducted based on Taguchi's experimental design technique. In this work, the effect of machining parameters on the surface roughness is evaluated and optimum machining conditions for maximizing the metal removal rate and minimizing the surface roughness are determined using response surface methodology. A second-order response surface model for the surface roughness is developed to predict the surface roughness. The predicted values and measured values are fairly close to each other, which indicates that the developed model can be effectively used to predict the surface roughness on the machining of Al/SiC-MMC composites with 95% confidence intervals within the ranges of parameters studied.     

OPTIMAL MACHINING CONDITIONS FOR TURNING OF PARTICULATE METAL MATRIX COMPOSITES USING TAGUCHI AND RESPONSE SURFACE METHODOLOGIES

The present investigation focuses on the influence of machining parameters on the surface finish obtained in turning of LM25 Al/SiC particulate composites. The experiments are conducted based on Taguchi's experimental design technique. In this work, the effect of machining parameters on the surface roughness is evaluated and optimum machining conditions for maximizing the metal removal rate and minimizing the surface roughness are determined using response surface methodology. A second-order response surface model for the surface roughness is developed to predict the surface roughness. The predicted values and measured values are fairly close to each other, which indicates that the developed model can be effectively used to predict the surface roughness on the machining of Al/SiC-MMC composites with 95% confidence intervals within the ranges of parameters studied.     

金属基复合材料的超塑性研究

本文研究了粉末冶金法制造SiCp/LY12复合材料的超塑性7测定了等温热反拆挤压态SiCp/LY127SC/LY12复合材料的位伸、压缩m值,分析了工艺参数对超塑性的影响,确定了超塑成形工艺参数,并初步分析了SiCp/LY127SC/LY12复合材料的显微结构和超塑性的关系。     

MACHINING OF FIBER-REINFORCED COMPOSITES

Abstract

Since the introduction of glass fiber-reinforced polymer composites in the early 1940s, composite materials development was driven by the needs of space, defense, and aircraft industries where performance rather than cost was the prime consideration. At the beginning, conventional machining techniques were adopted to machine glass fiber-reinforced composites for convenience as well as to keep the capital costs down. This was followed by significant advancements in tool materials and tooling design. With the development of new and more challenging metal-matrix and ceramic-matrix composites, conventional manufacturing processes proved to be inadequate or even inappropriate to process them. Need and opportunity, therefore, exists for alternate nontraditional machining operations, such as laser machining, water jet (WJ) and abrasive water jet (AWJ) cutting, electrical discharge machining, ultrasonic-assisted machining, and electrochemical spark machining. When composites become more popular and are used in large volume in the civilian sector, such as auto and other consumer industries, material and processing costs will be the driving factors. A high degree of automation for the mass manufacturing of composite parts will be required to bring the costs down and compete with other materials. Advancements in the nontraditional machining processes offer an opportunity to process these materials economically, thus realizing the full potential of the composite materials. This paper gives a broad overview on the various issues involved in machining (conventional and nonconventional) of fiber-reinforced composites. The field of composites, in general, and machining of composites, in particular, are so broad that it would not be possible to do justice by discussing each aspect of composite material machining without ending up with a voluminous document. This review, therefore has to be limited to a few aspects of composite materials and their machining techniques. It may also be pointed out that in this review certain areas are dealt more in-depth than others. Personal preferences and availability of material in the open literature are some of the reasons for this nonuniformity in coverage. Also, some areas are more actively pursued than others. An attempt is made to highlight some of the issues and opportunities in the area of machining of composites.     

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.     

ON THE QUALITY OF MACHINED SURFACE REGION WHEN TURNING Al/SiC METAL MATRIX COMPOSITES

The effect of tool nose wear land length and the reinforcement volume fraction of SiC on the quality of the machined surface region were investigated using a finish turning operation. Turning operations were carried out at the same cutting speed, feed rate and depth of cut and under dry cutting condition. Al/SiC work materials containing 20% and 30% SiC reinforcement particles were used in both hot-rolled and heat-treated conditions. Surface and subsurface of the machined samples were examined using a scanning electron microscope. Residual stress distribution of the surface region was determined using a modified deflection-etching technique. Surface damage in the form of short and long grooves parallel to the direction of cutting, cavities, micro-cracks and fractured areas were observed for all the material conditions used in this experiment. These damages were attributed to the presence of hard particles of SiC and severe plastic deformation of the surface region. Peak residual stress values were higher for the heat-treated samples as compared with hot-rolled condition. This was attributed to the high radial or thrust forces that were brought about by the high tool nose wear land lengths for the heat-treated samples.     

偏轴剪切载荷下单向纤维增强金属基复合材料弹粘塑性响应

提出一种可以描述单向纤维复合材料多轴弹粘塑性行为的细力学模型。详细考究了纤维取向,纤维体积含量及应变率对单向上Ｂ／Ａｌ复合材料总体剪切弹粘塑性行为的影响。     

MACHINING OF CORTICAL BONE: SIMULATIONS OF CHIP FORMATION MECHANICS USING METAL MACHINING MODELS

This paper investigates chip formation in the machining of cortical bone and the application of isotropic elastic-plastic material models with a pressure dependent yield stress and a strain path dependent failure strain law to finite element calculations to predict observed behaviour. It is shown that a range of models can be created that result in segmented chip formations and a range of specific cutting forces similar to those observed experimentally. Results from the simulations provide an explanation for differences in the ratio of thrust to cutting forces observed between previous experimental studies, namely that the cutting tools used may have had different edge sharpness or degree of damage induced by the material removal process. Measurements of edge profiles from one of these studies support that explanation and emphasize the importance of tool toughness in maintaining efficient cutting of bone.     

MODELING THE PHYSICS OF METAL CUTTING IN HIGH-SPEED MACHINING

ABSTRACT

Physical modeling of metal cutting was carried out to provide an understanding and prediction of machining process details. The models are based on finite element analysis (FEA), using a Lagrangian formulation with explicit dynamics. Requirements for material constitutive models are discussed in the context of high-speed machining. Model results address metal cutting characteristics such as segmented chip formation, dynamic cutting forces, unconstrained plastic flow of material during chip formation, and thermomechanical environments of the work-piece and the cutting tool. Examples are presented for aerospace aluminum and titanium alloys. The results are suited for analysis of key process issues of cutting tool performance, including tool geometry, tool sharpness, workpiece material buildup, and tool wear.     

MODELING THE PHYSICS OF METAL CUTTING IN HIGH-SPEED MACHINING

Physical modeling of metal cutting was carried out to provide an understanding and prediction of machining process details. The models are based on finite element analysis (FEA), using a Lagrangian formulation with explicit dynamics. Requirements for material constitutive models are discussed in the context of high-speed machining. Model results address metal cutting characteristics such as segmented chip formation, dynamic cutting forces, unconstrained plastic flow of material during chip formation, and thermomechanical environments of the work-piece and the cutting tool. Examples are presented for aerospace aluminum and titanium alloys. The results are suited for analysis of key process issues of cutting tool performance, including tool geometry, tool sharpness, workpiece material buildup, and tool wear.     

绿色切削加工技术的研究

通过分析湿式加工方法所带来的环境危害阐述绿色切削加工的意义,研究绿色切削加工的机理及关键技术,包括高速干切削的特点,低温风冷却切削、绿色刀具的表面摩擦学设计和切削几何特性的设计技术等。     

MACHINING STUDIES OF UD-FRP COMPOSITES PART 2: FINITE ELEMENT ANALYSIS

A number of parameters and an exhaustive material development and experimental procedure to determine the response variables like cutting forces, surface damage restricts the expensive experimental research. In this context, Finite Element Method (FEM) analysis can be used as a tool for the prediction of the various machining responses. A finite element analysis of the orthogonal machining of Uni-directional Glass Fiber Reinforced Plastic (UD-GFRP) laminates is presented in this study to understand the complex relation between fiber orientation, tool geometry, depth of cut on cutting forces and sub-surface damage.     

EXPERIMENTAL STUDIES AND MODELING OF HEAT GENERATION IN METAL MACHINING

Heat generation in the cutting zones due to plastic deformation and friction in the cutting region governs insert wear, tensile residual stresses on the machined component surface and may give rise to undesired tolerances and short component life. Therefore, it is crucial that the heat generation is kept under control during metal cutting. In this study an analytical model for prediction of heat generation in the primary and secondary deformation zones is compared with results from finite element simulations and temperature measurements using IR-CCD camera. The used cutting data are altered to study the temperature influence from tool geometry and feed when machining stainless steel SANMAC316L and low carbon steel AISI 1045.     

MACHINING STUDIES OF UD-FRP COMPOSITES PART 2: FINITE ELEMENT ANALYSIS

ABSTRACT

A number of parameters and an exhaustive material development and experimental procedure to determine the response variables like cutting forces, surface damage restricts the expensive experimental research. In this context, Finite Element Method (FEM) analysis can be used as a tool for the prediction of the various machining responses. A finite element analysis of the orthogonal machining of Uni-directional Glass Fiber Reinforced Plastic (UD-GFRP) laminates is presented in this study to understand the complex relation between fiber orientation, tool geometry, depth of cut on cutting forces and sub-surface damage.     

MATERIAL PROPERTY NEEDS IN MODELING METAL MACHINING

ABSTRACT

Different laws of how flow stress varies with strain, strain rate, and temperature, from different authors, are reviewed and compared for their predictions of behavior in the primary and secondary shear conditions of metal machining. Despite differences in their structure, the laws give similar numerical values of flow stress in primary shear conditions, but show large differences in secondary shear. Friction laws are also discussed. There is a need to develop secondary shear yield and friction laws.     

MATERIAL PROPERTY NEEDS IN MODELING METAL MACHINING

Different laws of how flow stress varies with strain, strain rate, and temperature, from different authors, are reviewed and compared for their predictions of behavior in the primary and secondary shear conditions of metal machining. Despite differences in their structure, the laws give similar numerical values of flow stress in primary shear conditions, but show large differences in secondary shear. Friction laws are also discussed. There is a need to develop secondary shear yield and friction laws.     

THEORETICAL PREDICTION OF TOOL-CHIP CONTACT LENGTH IN ORTHOGONAL METAL MACHINING BY COMPUTER SIMULATION

A method for determination of tool-chip contact length is theoretically presented in orthogonal metal machining. By using computer simulation and based on the analyses of the elastro-plastic deformation with lagrangian finite element method in the deformation zone, the accumulated representative length of the low layer, the tool-chip contact length of the chip contacting the tool rake are calculated, experimental studies are also carried out with 0.2% carbon steel. It is shown that the tool-chip contact lengths obtained from computer simulation have a good agreement with those of measured values.     

增强体颗粒失效对SiCp/Al复合材料屈服强度的影响

采用Eshelby等效夹杂理论,分析SiCp/Al复合材料受载时作用在SiC颗粒上的应力.假设SiC颗粒失效符合Weibull统计分布,在综合考虑复合材料各种强化机制的基础上,引入颗粒失效对材料屈服强度的影响,建立SiCp/Al复合材料的屈服强度模型.结果表明,该模型预测的屈服强度与相应的实验结果吻合较好.同时模型显示在屈服状态下,颗粒直径较小时,复合材料的颗粒失效以界面脱粘为主,而随着粒度的增大,颗粒的断裂分数迅速增大,颗粒失效则转变为由颗粒断裂和界面脱粘共同控制.