A.K. Balaji

Performance-Based Predictive Models and Optimization Methods for Turning Operations and Applications: Part 2—Assessment of Chip Forms/Chip Breakability

Abstract This paper presents recent developments in chip control research and provides major applications in tuming operations involving the use of complex grooved tool inserts. On the basis of the basic chip morphology presented by Nakayama (1984) , four major parameters contributing to complex 3-D chip curl are identified: chip back-flow, chip up-curl, chip side-flow, and chip side-curl. A summary of past research in each of these four categories is presented as well as a description of an attempt to combine these parameters into one readily measured variable. An analysis of cyclic chip formation is then presented with experimental evidence from high-speed filming of the chip curling and breaking processes. The most commonly known “chip chart” technique is then described. The paper concludes with details of an attempt to develop a computer-aided process planning system incorporating a predictive capability for chip breakability in turning operations.

Machining Performance and Health Effects of Cutting Fluid Application in Drilling of A390.0 Cast Aluminum Alloy

Environmental issues in machining have led to a push to curtail the use of cutting fluids. However, cutting fluid effects on part quality, process planning, and operator exposure to aerosols need to be first studied. The effects of cutting fluid application on hole accuracy and mist generation have been studied for blind-hole drilling of A390.0 aluminum alloy. Different cutting fluid types and application modes were tested under varying conditions of cutting speed, feed, and hole depth. The cooling and chip-transporting ability of cutting fluids was found to have the maximum effect on dimensional accuracy. Dry cutting yielded holes with the least accuracy, while mist lubrication was found to give superior dimensional accuracy to dry cutting but had the worst aerosol concentration. Flooding with synthetic cutting fluid gave the best overall results.

Progressive tool-wear mechanisms and their effects on chip-curl/chip-form in machining with grooved tools: an extended application of the equivalent toolface (ET) model

Abstract Chip-form/chip-breakability and tool-wear/tool-life are two important aspects commonly considered in evaluating the performance of a machining process. The advent of new grooved tools with complex chip-groove geometry has required a better understanding of the curling behavior of the chip for effective curling and breaking of the chip. This paper presents a methodology for modeling chip-curl in machining with progressively worn grooved tools from measured cutting forces by using the equivalent toolface (ET) model. The ET is an imaginary flat toolface formed by effective inclination and rake angles to represent a grooved tool. This is achieved by iteratively changing the effective angles to match the flat-faced forces, calculated from a predictive cutting force model, with the measured grooved tool forces. The variation of the ET orientations resulting from the combinations of the effective angles shows a good correlation with the chip-curl ratio (ratio of up-curl to side-curl calculated from the twist angle), defined to indicate the curling pattern of chip. In this paper, this methodology is extended to correlate chip curling when machining with progressive tool-wear mechanisms in grooved tools. Experiments have been performed to measure the cutting forces at varying stages of progressive tool-wear, and chips are collected for a range of cutting conditions. The anticipated chip-curl/chip-forms and the associated dominant tool-wear patterns from the use of the predictive ET model are correlated well with the experimental observations.

Performance-Based Predictive Models and Optimization Methods for Turning Operations and Applications: Part 3—Optimum Cutting Conditions and Selection of Cutting Tools

This paper presents a summary of recent developments in developing performance-based machining optimization methodologies for turning operations. Four major machining performance measures (cutting force, tool wear/tool life, chip form/chip breakability, and surface roughness) are considered in the present work, which involves the development and integration of hybrid models for single and multi-pass turning operations with and without the effects of progressive tool wear. Nonlinear programming techniques were used for single-pass operations, while a genetic algorithms approach was adopted for multi-pass operations. This methodology offers the selection of optimum cutting conditions and cutting tools for turning with complex grooved tools.

AN ‘EFFECTIVE CUTTING TOOL THERMAL CONDUCTIVITY’ BASED MODEL FOR TOOL–CHIP CONTACT IN MACHINING WITH MULTI-LAYER COATED CUTTING TOOLS

This paper presents a new modeling approach, based on Oxleys predictive model, for predicting the tool–chip contact in 2-D machining of plain carbon steels with advanced, multi-layer coated cutting tools. Oxleys original predictive model is capable of predicting machining parameters for a wide variety of plain carbon steels, however, the tool material properties and their effects are neglected in the analysis. In the present work, the effect of the tool material, more particularly, the effect of multiple coating layers and the individual coating thicknesses on the tool–chip contact length in orthogonal machining is incorporated. The results from the model predict the tool–chip contact length with respect to major cutting parameters such as feed and rake angle, work material parameters such as the carbon content in the steel, and varying thicknesses and combinations of coating layers. This model enables more precise cutting tool selection by predicting the relative tribological impact (in terms of tool–chip contact length) for a variety of multi-layer coated tools.

Force decomposition model for tool-wear in turning with grooved cutting tools

The lack of a satisfactory methodology to predict the tool-wear progression/tool-life in a machining operation with a grooved tool necessitates development of quantitative predictive models for tool-wear. This paper presents a new methodology for decomposing and distributing the resultant force generated in machining with a grooved tool within the three major tool-wear regions: edge region, secondary-face region, and groove backwall region. By measuring the edge force from the experiments, the forces acting on the other two major wear regions can be found from the kinematics of the 3-D chip-flow and the geometry of the tool insert. The Coulomb coefficient of friction is assumed only at the groove backwall region. The effect of chip side-flow is considered by measuring the chip side-flow angle from experiments using high speed filming techniques. With the new methodology, the decomposed forces acting on the wear regions can be related to the dominant wear modes of a grooved tool. The new methodology implicitly includes the influencing parameters on tool-wear, including cutting conditions, tool geometry and chip-groove geometry, since changes in these parameters are reflected in the cutting forces. This force decomposition method offers a new approach for predicting the cutting tool-wear analytically using the measured cutting forces.

Performance-Based Predictive Models and Optimization Methods for Turning Operations and Applications: Part 1—Tool Wear/Tool Life in Turning with Coated Grooved Tools

Abstract Tool wear/tool life is an important aspect commonly considered in evaluating the performance of a machining process. The advent of new grooved tools with complex chip-groove geometry has required a better understanding of their effects on tool wear/tool life. This paper presents an overview of research at the University of Kentucky on extensions to the conventional tool wear and tool life methodologies when machining with grooved tool inserts resulting from the more complex wear features observed and the more subtle failure criteria applied. The influence of cutting conditions including the cutting speed, feed and depth of cut on the tool life was studied experimentally using tools with chip-groove geometries and different tool coatings. It was shown that the slope and intercept of the log-log plot of tool life versus feed, for example, change considerably for different chip-groove geometries or different tool coatings. An empirical tool-life equation to consider the effects of these parameters was proposed. The approach described required that 11 tool wear/tool life tests be conducted for every tool insert. In a comparison between predicted and experimental tests involving 200 production trials, this approach predicted tool life within 24% of the results encountered, while tool-life estimations using conventional approaches yielded results that gave an error of more than 300%. Furthermore, an ‘equivalent toolface (ET)’ model was developed to correlate progressive tool wear to changes in chip formation with corresponding predictability of the dominant wear modes in turning with grooved cutting tools.

On a Process Modeling Framework for Sustainable Manufacturing: A Machining Perspective

Sustainability and economic factors are increasingly pushing industry towards environmentally friendly manufacturing methods. However, the implications of processing level changes, which are being introduced at a significant rate, for overall, environmental impact need better characterization. In the first half of this paper, a simplified framework for enhancing sustainability in manufacturing, by enabling rapid assessment of approximate life-cycle implications of competing process-level alternatives, is introduced. This framework relies on developing or enhancing manufacturing process models in such a way that a superior quantitative evaluation of the environmental and economic impacts of decisions made in manufacturing process planning can be established. In the second half of this paper, the specific case of metal machining is presented. In machining the maximum attention has been directed towards reducing the traditional profligate use of metalworking fluids. Consequently, a significant quantity of research work has been directed towards developing dry and near-dry, or Minimal Quantity Lubrication (MQL), machining techniques. A review of available literature shows that several outcomes of these techniques for product life-cycle assessment need to be addressed — i.e., some environmental tradeoffs are often involved in their implementation. Avenues for further research in sustainable machining, including some ideas for advancing dry and near-dry machining without resorting to chemical action for extreme-pressure lubrication, are also presented.Copyright

A MACHINING PERFORMANCE STUDY IN DRY CONTOUR TURNING OF ALUMINUM ALLOYS WITH FLAT-FACED AND GROOVED DIAMOND TOOLS

This paper presents the results from an experimental study of dry contour turning operations on aluminum alloys (6061B and 2011-T3) using PCD flat-faced and diamond coated grooved tools. The machining performance is assessed on the basis of cutting forces, chip flow, chip-form and surface roughness observed during contour turning operations. The constantly varying cutting conditions (especially effective depth of cut due to varying geometry of the contour surface) and effective tool geometry cause a wide fluctuation in cutting forces and the ensuing chip flow. The chip flow angle is measured along the contour geometry using high-speed filming techniques and these results are compared with predicted chip flow values from the measured experimental cutting forces (which are measured along the entire contour geometry). The resultant surface roughness at different locations along the contour profile is measured and correlated with the chip flow and chip-form variations. Machining performance issues specifically relevant to dry contour turning of aluminum (such as problems due to poor chip flow and the resultant poor surface roughness) are studied and the effectiveness of selective work–tool (both tool material and tool geometry) pairs is illustrated.

Tribological and Thermal Effects of Cutting Fluid Application in Machining With Coated and Grooved Cutting Tools

The use of Cutting Fluids (CFs) in machining operations is being increasingly questioned in recent years for environmental and economic reasons, leading to efforts in promoting dry, as well as minimal quantity of lubricant (MQL), machining. However, the tribological effectiveness and thermal aspects of CF action at modern cutting conditions, which not only involve relatively high cutting speeds but also advanced tool coatings and chip-breaking geometric features, need better understanding. This paper presents an experimental investigation into the effects of different CF application methods on various machining performance measures while cutting with commercially available flat-faced, as well as grooved, uncoated and coated cemented tungsten carbide tools. CF effects under dry, flood, and MQL conditions, were gauged through their influence on cutting forces, tool temperatures, tool-chip interfacial contact, and chip morphology during machining of AISI 1045 steel. The results show new trends on the individual cooling and lubricating effects of CF application methods, and the effects of their interactions with the tool coatings and the presence/absence of chip-breaking grooves.Copyright