Copyright (c) 2009 All rights reserved. http://works.bepress.com/dwaldorf Recent documents in Daniel J. Waldorf en-us Wed, 07 Oct 2009 10:25:36 PDT 3600 http://works.bepress.com/dwaldorf/12 http://works.bepress.com/dwaldorf/12 Tue, 12 May 2009 17:01:10 PDT An analytical comparison is made between two basic models of the flow of workpiece material around the edge of an orthogonal cutting tool during steady-state metal removal. Each has been the basis for assumptions in previous studies which attempt to model the machining process, but no direct comparison had been made to determine which, if either, is an appropriate model. One model assumes that a separation point exists on the rounded cutting edge while the other includes a stable build-up adhered to the edge and assumes a separation point at the outer extreme of the build-up. Theories of elastic-plastic deformation are employed to develop force predictions based on each model, and experiments are performed on 6061-T6 aluminum alloy to evaluate modeling success. The experiments utilize unusually large cutting edge radii to isolate the edge component of the total cutting forces. Results suggest that a material separation point on the tool itself does not exist and that the model that includes a stable build-up works better to describe the experimental observations. Daniel J. Waldorf Articles http://works.bepress.com/dwaldorf/13 http://works.bepress.com/dwaldorf/13 Tue, 12 May 2009 17:01:10 PDT Under normal machining conditions, the cutting forces are primarily due to the bulk shearing of the workpiece material in a narrow zone called the shear zone. However, under finishing conditions, when the uncut chip thickness is of the order of the cutting edge radius, a ploughing component of the forces becomes significant as compared to the shear forces. Predicting forces under these conditions requires an estimate of ploughing. A slip-line field is developed to model the ploughing components of the cutting force. The field is based on other slip-line fields developed for a rigid wedge sliding on a half-space and for negative rake angle orthogonal cutting. It incorporates the observed phenomena of a small stable build-up of material adhered to the edge and a raised prow of material formed ahead of the edge. The model shows how ploughing forces are related to cutter edge radius--a larger edge causing larger ploughing forces. A series of experiments were run on 6061-T6 aluminum using tools with different edge radii--including some exaggerated in size--and different levels of uncut chip thickness. Resulting force measurements match well to predictions using the proposed slip-line field. The results show great promise for understanding and quantifying the effects of edge radius and worn tool on cutting forces. Daniel J. Waldorf Articles http://works.bepress.com/dwaldorf/14 http://works.bepress.com/dwaldorf/14 Tue, 12 May 2009 17:00:51 PDT This study examines the performance of a new class of wear-resistant but economical cutting tools produced by varying the binder composition of standard cemented carbide composites. By replacing some or all of the cobalt binder with rhenium and nickel-based superalloy, a stronger composite tool results, potentially capable of machining heat-resistant superalloys at significantly higher cutting speeds. Sample tools with alternative binder were produced and compared to standard tools bound with cobalt only. Turning experiments on Inconel 718 were run to evaluate wear resistance and tool life for several grades. The experimentation also examined the effects of varying the relative proportions of each binder constituent as well as the overall binder percentage in the composite. Results show a clear advantage of the alternative binder tools as evidenced by a 150% increase in tool life or the equivalent of an 18% increase in cutting speed. Although increasing amounts of rhenium in the binder show a positive effect on performance, the effects of superalloy and overall binder % are inconclusive. Daniel J. Waldorf Conference Proceedings http://works.bepress.com/dwaldorf/11 http://works.bepress.com/dwaldorf/11 Tue, 12 May 2009 12:03:29 PDT This paper aims to provide experimental data in support of a modified theoretical model for quantifying the effect of cutting tool edge geometry on machining forces. A previously published slip-line model is simplified and extended to the case of turning. Several sets of machining experiments were run with custom-fabricated cutting inserts of varying edge hone radius and chamfer geometry. Cutting forces were measured using a dynamometer during cutting. Results show that varying edge geometry can have a major effect on cutting forces. The developed model effectively captures the edge phenomenon and its effect on cutting forces and also offers a glimpse of how the edge geometry can affect dynamic process damping. Daniel Waldorf Articles http://works.bepress.com/dwaldorf/9 http://works.bepress.com/dwaldorf/9 Tue, 12 May 2009 12:03:28 PDT Solder paste masks or stencils are an integral part of the manufacturing process for surface mount PCBs. This study examines the feasibility of a process for rapid creation of a solder paste stencil using thermoplastic material. CNC laser cutting of the stencil geometry is replacing traditional use of chemical etching on metal sheets to produce stencils. Laser cutting has been used to improve process speed, accuracy, and cost. This research attempts to continue to simplify and reduce costs in the stencil making process by proposing as the stencil material a common thermoplastic that can be cut easily and quickly using a low-power rapid-prototyping laser process. The effects of several variables on the success of the process are experimentally tested to determine a feasible solution. Various solder pastes and solder material characteristics are studied for their effect on the new material. Stencil dimensions, including thickness and aperture characteristics, are examined. Several key process factors are also varied in the tests to determine recommendations for settings such as print direction, alignment procedures, squeegee pressure and attack angle, print speed, and stencil release method. Subjective evaluation is also made of important qualities of the paste in reaction to the new material, including paste roll and consistency, paste volume, adherence, and instances of cold slumping. The resulting process is demonstrated by producing plastic stencils on a rapid prototyping laser housed in the Cal Poly laboratories. Cost, cycle time, and performance characteristics of the plastic stencil are estimated. Christopher K. Wong Conference Proceedings http://works.bepress.com/dwaldorf/10 http://works.bepress.com/dwaldorf/10 Tue, 12 May 2009 12:03:28 PDT A strategy is developed for identifying cutting tool wear on a face mill by automatically recognizing wear patterns in the cutting force signal. The strategy uses a mechanistic model development to predict forces on a lathe under conditions of wear and extends that model to account for the multiple inserts of a face mill. The extended wear model is then verified through experimentation over the life of the inserts. The predicted force signals are employed to train linear discriminant functions to identify the wear state of the process in a manner suitable for on-line application. Daniel Waldorf Articles http://works.bepress.com/dwaldorf/8 http://works.bepress.com/dwaldorf/8 Tue, 12 May 2009 12:03:27 PDT A Recent Society of Manufacturing Engineers (SME) grant received by Manufacturing Engineering Program at Cal Poly has provided funds to strengthen its curricular focus on supply chain management, flexibility, business skills, quality, and process controls. New courses and laboratories are developed in electronics manufacturing, information technology, and supply chain management. A functioning supply chain environment has been developed to provide vertical integration among several courses. A software tool being developed in-house integrates the activities of the students who play the roles of customers and suppliers. Details of the various components of this comprehensive project are presented in this paper. Daniel Waldorf Articles http://works.bepress.com/dwaldorf/6 http://works.bepress.com/dwaldorf/6 Tue, 12 May 2009 12:03:26 PDT A 10-week course was designed with funding from the Society of Manufacturing Engineers (SME) and input from industry representatives, to offer upper division engineering students a course on advanced automation. The objective was to provide engineering students theoretical and hands-on practical experience with automation technologies that will be of prime importance over the next decade: data acquisition and instrumentation, machine vision and motion control. This paper describes the machine vision portion of that class. It describes important concepts, hands-on equipment, and labs developed for this course, as well as examples of student projects from Spring Quarter, 2004. The course and laboratory materials were evaluated for learning effectiveness and technical content, which are included in this paper. Jose Macedo Articles http://works.bepress.com/dwaldorf/4 http://works.bepress.com/dwaldorf/4 Tue, 12 May 2009 12:03:25 PDT Recent work in modeling of the ploughing mechanism in basic metal machining may provide a means of estimating the additional forces to be expected when cutting with a worn tool. The results predict the rubbing stresses due to the finite radius of an unworn tool edge. Since an unworn tool can be thought of as a worn tool with a wear land width VB = 0, these stresses can make up part of a strategy for predicting the additional forces incurred by a worn tool. This paper develops a wear model by proposing a technique for utilizing the stresses predicted by the ploughing model to estimate the stresses on the flank based on both elastic contact and plastic flow at the flank. Orthogonal cutting experiments with worn tools were performed to test the approach. Predictions for these tests, as well as for previously published results, are presented and show great promise for achieving a reliable wear-force prediction strategy. Daniel Waldorf Articles http://works.bepress.com/dwaldorf/5 http://works.bepress.com/dwaldorf/5 Tue, 12 May 2009 12:03:25 PDT The concept of an effective orthogonal cutting edge in turning is considered. The orientation of this edge in the radial-longitudinal plane, as commonly modeled through an effective lead angle, is studied. The methods of effective lead angle prediction used in numerous previously developed force models are plagued with large errors over ranges of process inputs, in particular feed rate and depth of cut. Four previously developed methods of effective lead angle prediction are reviewed and compared to a new method presented here. This new method accounts for the size effect as introduced through the variation in chip thickness along the cutting edge, especially along the tool nose region. The difference in the new method is that the effect of continuous chip thickness variation along the cutting edge is included when evaluating the specific machining energies rather than using an average chip thickness, which has been used in the other methods. Therefore, the differential normal and friction force components acting on the rake face are functions of chip thickness through both the elemental chip load and the specific energies. Their directions are characterized by the orientations of the rake face and edge. By numerically integrating the differential force components modeled in this fashion, a significant improvement in effective lead angle prediction accuracy is realized. This improved accuracy is verified using experimental data obtained for 1018 steel and 304 stainless steel at varying levels of feed rate, depth of cut, cutting speed, nose radius and tool lead angle. William J. Endres Articles