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Hard Turning and the Machine Tool
Daniel P. Soroka
Hardinge Inc.
One Hardinge Drive
Elmira, NY 14902
Abstract: This paper describes how the machine tool characteristics such as dynamic stiffness relate to the total operation in terms of part quality, tool life and the economics of the application. Current and future development activities are targeted toward improvements in the machine tool dynamic stiffness as well as in the process area for methods to control white layer formation.
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Surface Quality and Tool Wear in Interrupted Hard Turning of 1137 Steel Shafts
Radu Pavel*, Keith Sinram**, Dana Combs***, Michael Deis***, Ioan Marinescu*
* University of Toledo, MIME Department, Nitschke Hall 4005, MS312, Toledo, OH 43606
** Spicer Driveshaft Division, Dana Corporation, P.O. Box 955, Toledo, OH 43697-0955
*** Advanced Technology Resource Group, Dana Co., Technical Resource Park, 8000 Yankee Rd.,
Ottawa Lake, MI 49267
Abstract: This paper was published in the Proceedings of the American Society for Precision Engineering 2002 Annual Meeting. It presents the results of an experimental study of hard turning of a spline shaft made of 1137 steel hardened to 47 - 50 HRC. The goal was to obtain a similar or better surface finish as in case of grinding for the external interrupted surface (OD turning) defined by ten splines. Two types of cutting tools were first analyzed from the viewpoint of tool wear and surface roughness. The wear of the cutting inserts was evaluated and recorded using optical and SEM microscopy. After choosing the most suitable insert for interrupted cutting, a mathematical model for average roughness prediction was determined using Response Surface Methodology. The response variable was the average surface roughness, Ra, and it was investigated as a function of the cutting regime (feed, cutting speed, and depth of cut) for a given geometry of the cutting tool. The workpieces used for wear trials were also analyzed from the viewpoint of superficial layer transformations, pre-eminently occurrence of white layer.
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White Paper: Wear Trends of PCBN Cutting Tools in Hard Turning
Ty G. Dawson and Dr. Thomas R. Kurfess
The George Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, Georgia, USA 30332-0450
Abstract: Hard turning is a developing technology that offers many potential benefits compared to grinding, which remains the standard finishing process for critical hardened steel surfaces. To increase the implementation of this technology, questions about the ability of this process to produce surfaces that meet surface finish and integrity requirements must be answered. Additionally, the economics of the process must be justified, which requires a better understanding of tool wear patterns and life predictions. An ongoing comparative study of wear rates and tool lives under varying cutting parameters is presented here. To date, the study has consisted of seventeen different machining conditions with four different cutting tool materials. Tool life results agree with previous research in this area, indicating that polycrystalline cubic boron nitride (PCBN) tools with low CBN content have improved lives resulting from the benefits of the ceramic binders compared to the cobalt binder typically used for higher CBN content tools. More interesting is a resulting trend in flank wear patterns that could currently help to predict tool life under certain cutting conditions. Further work is being done to understand the wear process in an attempt to model this relationship for a larger range of conditions.
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Machining Hardened Steel With Ceramic-Coated and Uncoated CBN Cutting Tools
Ty G. Dawson
Thomas R. Kurfess
The George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, Georgia
Abstract: As part of a continuing study of tool wear in hard turning, five different cutting tool materials were selected for full tool life tests at a range of reasonable cutting conditions. The tools were ceramic-coated and uncoated polycrystalline cubic boron nitride (CBN). Previous results have indicated that low CBN content tools perform better than high CBN content tools. The low CBN content tools have a moderate CBN percentage combined with ceramic binder materials and are designed for finish machining of hardened steels, making these tools the focus of this study. Additionally, new low CBN content tools that have TiN and TiAlN coatings were tested. The coatings are advertised to insulate the CBN substrate and improve tool life, which held true for most conditions, although significant chipping was initially observed on the crater scars of these tools. A new tool geometry design was also tested, which had a wiper on the nose radius of the tool that allowed improved surface finish without sacrificing productivity or tool life substantially.
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Tool Life, Wear Rates, and Surface Quality in Hard Turning
Ty G. Dawson and Thomas R. Kurfess
The George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, Georgia
Abstract: An on-going comparative study of wear rates and tool lives under varying cutting parameters is presented in this paper, along with results indicating the abilities and limitations of the hard turning process to produce finished surfaces with acceptable roughness and integrity. To date, the study has consisted of thirteen combinations of machining conditions. The tests were performed with four different cutting tool materials supplied by two manufacturers. Tool life results agree with previous research in this area, indicating that low content CBN tools have improved lives resulting from the increased bonding strength of the ceramic binders compared to the cobalt binder typically used for higher CBN content tools. More interesting is a resulting trend in flank wear patterns that could help to predict tool life under certain cutting conditions. Further work is being done to understand the wear process in an attempt to model this relationship for a larger range of conditions. Surface quality limitations are also presented, in terms of limited achievable surface roughness due to increased plowing action at low feeds. Microstructural changes on machined surfaces are then discussed, with an explanation given for the ability to produce surfaces free of white layer, even when cutting with worn cutting tools.
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An Investigation of Tool Wear and Surface Quality in Hard Turning
Ty G. Dawson
Thomas R. Kurfess
The George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0405
Abstract: This paper discusses experimental results of turning experiments on 52100 steel hardened to 58-62 HRC. A set of five different cutting conditions was selected to machine with five polycrystalline cubic boron nitride (PCBN) cutting tools for the life of each tool. The objective was to determine the effect of the cutting parameters on tool wear, changes in tool geometry, and resultant workpiece surface quality.
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Machining Hardened Steel With Polycrystalline Cubic Boron Nitride Cutting Tools
A Dissertation Presented to The Academic Faculty
By Ty Grant Dawson
In Partial Fulfillment Of the Requirements for the Degree
Doctor of Philosophy in Mechanical Engineering
Georgia Institute of Technology
June 14, 2002
Summary: Machining hardened steels has become an important manufacturing process, particularly in the automotive and bearing industries. Abrasive processes such as grinding have typically been required to machine hardened steels, but advances in machine tools and cutting materials have allowed hard turning on modern lathes to become a realistic replacement for many grinding applications. There are many advantages of hard turning, such as increased flexibility, decreased cycle times, reductions in machine tool costs, and elimination of environmentally hazardous cutting fluids. Despite these advantages, implementation of hard turning remains relatively low, primarily due to concerns about the quality of hard turned surfaces and a lack of understanding about the wear behavior of polycrystalline cubic boron nitride (PCBN) cutting tools.
Because PCBN tools are expensive, excessive tool wear can eliminate the economic advantage of hard turning. To address this concern, this research investigated the effects of changing process conditions on wear behavior when turning hardened AISI 52100 steel (62 HRC) with both ceramic-coated and uncoated PCBN cutting tools. Traditional techniques of characterizing tool condition (optical and scanning electron microscopy) provide important information about tool wear, but are generally restricted to qualitative analysis. For a quantitative study of wear, a white light interferometer was used to obtain three-dimensional images of the wear scar on cutting tools. Data from these measurements allow quantification of flank wear, crater wear, and tool life, andempirical wear models describe the behavior well. Using three-dimensional wear data, a new technique was developed to determine the volumetric wear loss in the crater and flank regions by localizing the interferometer data to a model of the tool, then integrating deviations between the localized data and the model. This allows a quantitative comparison of the two wear modes, which cause changes in cutting forces and surface quality over the lives of tools.
Dimensional accuracy and high quality surfaces are also required if hard turning is to replace any grinding process. A primary concern in hard turning is the generation of undesirable changes to the surface microstructure and the formation of tensile residual stresses. Additionally, surface roughness must be comparable to grinding if hard turned surfaces are to be accepted. The results of this work indicate that proper selection of machining conditions yields acceptable dimensional accuracy and surface quality, and allows adequate tool life for most applications.
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Cutting Forces Modeling Considering the Effect of Tool Thermal Property—Application to CBN Hard Turning
Accepted for publication as a full paper in International Journal of Machine Tool and Manufacture Technology
Yong Huang, Research Assistant
Steven Y. Liang, Professor
George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0405, USA
Abstract: Force modeling in metal cutting is important for a multitude of purposes, including thermal analysis, tool life estimation, chatter prediction, and tool condition monitoring. Numerous approaches have been proposed to model metal cutting forces with various degrees of success. In addition to the effect of workpiece materials, cutting parameters, and process configurations, cutting tool thermal properties can also contribute to the level of cutting forces. For example, a difference has been observed for cutting forces between the use of high and low CBN content tools under identical cutting conditions. Unfortunately, among documented approaches, the effect of tool thermal property on cutting forces has not been addressed systemically and analytically. To model the effect of tool thermal property on cutting forces, this study modifies Oxley’s predictive machining theory by analytically modeling the thermal behaviors of the primary and the secondary heat sources. Furthermore, to generalize the modeling approach, a modified Johnson-Cook equation is applied in the modified Oxley’s approach to represent the workpiece material property as a function of strain, strain rate, and temperature. The model prediction is compared to the published experimental process data of hard turning AISI H13 steel (52 HRc) using either low CBN content or high CBN content tools. The proposed model and finite element method both predict lower thrust and tangential cutting forces and higher tool-chip interface temperature when the lower CBN content tool is used, but the model predicts a temperature higher than that of the finite element method.
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Force Modeling in Shallow cuts with Large Negative Rake Angle and Large Nose Radius Tools—Application to Hard Turning
Accepted for publication as a full paper in International Journal of Advanced Manufacturing
Yong Huang, Research Assistant
Steven Y. Liang, Professor
George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0405, USA
Abstract: In finish turning, the applied feedrate and depth of cut are generally very small. In some particular cases, such as the finishing of hardened steels, feedrate and depth of cut are much smaller than tool nose radius. If the tool with large tool nose radius and large negative rake angle is used in finish turning, the ploughing effect is pronounced and needs to be carefully addressed. Unfortunately, the ploughing effect has not yet been systematically considered in force modeling in shallow cuts with large negative rake angle and large nose radius tools in 3-D oblique cutting. In this study, in order to model the forces in such shallow cuts, first the chip formation forces are predicted by transforming the 3-D cutting geometry into an equivalent 2-D cutting geometry, then the ploughing effect mechanistic model is proposed to calculate the total 2-D cutting forces. Finally, the 3-D cutting forces are estimated by a geometric transformation. The proposed approach is verified in the turning of hardened 52100 steel, in which cutting condition is typified as shallow cuts with negative rake angle and large nose radius tools. Here the workpiece material property of hardened 52100 steel is represented by the Johnson-Cook equation, which is determined from machining tests. The comparison between experimental results and model predictions is presented.
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Minimum Quantity Lubrication in Finish Hard Turning
To appear in HNICEM ‘03
Ronan Autret, Graduate Research Assistant
Steven Y. Liang, Professor
George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0405
Abstract: Metal cutting fluids changes the performance of machining operations because of their lubrication, cooling, and chip flushing functions. Typically, in the machining of hardened steel materials, no cutting fluid is applied in the interest of low cutting forces and low environmental impacts. Minimum quantity lubrication (MQL) presents itself as a viable alternative for hard machining with respect to tool wear, heat dissertation, and machined surface quality. This study compares the mechanical performance of minimum quantity lubrication to completely dry lubrication for the turning of hardened bearing-grade steel materials based on experimental measurement of cutting forces, tool temperature, white layer depth, and part finish. The results indicate that the use of minimum quantity lubrication leads to reduced surface roughness, delayed tool flank wear, and lower cutting temperature, while also having a minimal effect on the cutting forces.
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Hard Turning and the Machine Tool
