Showing papers in "Journal of Engineering for Industry in 1989"

A Mathematical Approach to Automatic Configuration of Machining Fixtures: Analysis and Synthesis

Abstract: A mathematical theory for automatic configuration of machining fixtures for prismatic parts is developed. The following functions of fixtures are analyzed: deterministic workpiece location, clamping stability, and total restraint. The synthesis of fixtures includes the determination of locating and clamping points son workpiece surface and the determination of clamping forces. The theory deals with the general case of 3-dimensional parts, polygon support, and multiple machining operations

Tool Wear Detection Using Time Series Analysis of Acoustic Emission

Abstract: :This paper discusses th.e monitoring of cutting tool wear based on time series analysis of acoustic emission signals. In cutting operations, acoustic emission provides useful information concerning the tool wear condition because of the fundamental dif­ ferences between its source mechanisms in the rubbing friction on the wear land and the dislocation action in the shear zones. In this study, a signal processing scheme is developed which uses an autoregressive time-series to model the acoustic emission generated during cutting. The modeling scheme is implemented with a stochastic gradient algorithm to update the model parameters adaptively and is thus a suitable candidate for in-process sensing applications. This technique encodes the acoustic emission signal features into a time varying model parameter vector. Ex­ periments indicate that the parameter vector ignores the change of cutting param­ eters, but shows a strong sensitivity to the progress of cutting tool wear. This result suggests that tool wear detection can be achieved by monitoring the evolution of the model parameter vector during machining processes.

Grinding mechanisms and strength degradation for ceramics

Abstract: This paper presents a critical review and evaluation of knowledge of the grinding mechanisms for ceramic materials and their influence on the finished surface and mechanical properties. Two main research approaches are identified: a machining approach and an indentation fracture mechanics approach. The machining approach has typically involved measurement of the grinding forces and specific energy coupled with microscopic observations of the surface morphology and grinding detritus. Any proposed mechanisms of abrasive-workpiece interaction must be consistent with the magnitude of the specific energy and its dependence on the grinding conditions. The indentation fracture mechanics approach assumes that the damage produced by grinding can be modeled by the idealized flow system produced by a sharp indentor. Indentation of a ceramic body is considered to involve elastic/plastic deformation with two principal crack systems propagating from the indentation site; lateral cracks which lead to material removal and radial/median cracks which cause strength degradation. Each of these approaches provides insight into grinding behavior and strength degradation, but each has its shortcomings.

Model Reference Adaptive Force Control in Milling

Abstract: This paper describes the design and implementation of a Model Reference Adaptive Controller (MRAC) for force control in milling. First, previous work in this area is discussed. Results from previous work on the performance of fixed gain process controllers is summarized. The design of an MRAC for force control in milling is described, including a discussion of the implementation issues of noise and com­ putational speed. The adaptive controller was found to perform more satisfactorily than fixed gain controllers, but is difficult to implement and tune, primarily because of the unmodeled dynamics or measurement noise resulting from runout on the mill­ ing cutter. In this problem there was sufficient separation between the noise and the signal frequency that the noise could be filtered. However, the addition of the filter added additional dynamics to the system which reduced the overall performance from that expected from digital simulations. Increasing labor costs and the increasing need for machined parts with high precision, complex geometries has caused a dramatic increase in the number of Numerically Controlled (NC) and Computer Numerically Controlled (CNC) machine tools being used in production. These NC and CNC machine tools have greatly reduced operator input, resulting in signifi­ cant improvements in productivity. However, it has been demonstrated that further improvements can be made by on­ line manipulation of the programmer specified feedrates [1]. This can be done by implementing a process controller which uses some measure of the process (typically cutting force) to adjust the feedrate. The use of such process controllers has resulted in substantial improvements in productivity [2]; however, they have introduced some serious new problems resulting from variations inherent in the cutting process. For­ tunately, these problems can be reduced or eliminated by using ideas from adaptive control theory in the controller design. The purpose of the research reported in this paper is to ex­ amine the application of a model reference adaptive force con­ troller to the milling process. This paper is organized as follows: in the next section previous work is discussed, in­ cluding the development of a process model and a discussion of the effects of process parameter variations on the perform­ ance of fixed gain process controllers. A subsequent section describes the design of a model reference adaptive controller (MRAC) for milling. The implementation of the MRAC, and experimental results are then presented and discussed. Finally, the research is summarized, major conclusions are drawn, and topics for future research are indicated. Previous Research •«. This section discusses the literature pertinent to the applica­ tion of adaptive control to milling. Before a detailed discus­ sion of the literature can be presented, a point of terminology must be clarified.

On-Line Detection of Localized Defects in Bearings by Pattern Recognition Analysis

Abstract: A pattern recognition analysis scheme was developed for investigating vibration signals of bearings. Two normalized and dimensionless features are extracted by short-time signal processing techniques. Employing these two features, two linear discriminant functions have been established to detect defects on the outer race and rollers of bearings, respectively. Results of fault detection/diagnosis, based on the experimental data of imposed bearing defects, indicated the technique to be 14 percent better in the rate of success for the detection of defects than the best among the state-of-the-art

On-Line Monitoring of Tool and Cutting Conditions in Milling

Abstract: This paper is concerned with on-line monitoring of tool and cutting conditions in a milling operation. Key features of the cutting force signal are extracted from the force signal pattern over one spindle revolution. The proposed monitoring scheme combines these features to differentiate tool breakage from variations in cutting conditions. Experimental results are presented to support the proposed monitoring scheme.

An Investigation of the End Milling Process Under Varying Machining Conditions

Abstract: Varying machining conditions are encountered in adaptively controlled machining situations where operating conditions such as the feedrate and spindle speed are adjusted continuously to achieve desired objectives. Proper design, of constraint-type adaptive control systems in particular, requires models of the milling process mechanics since the milling process is usually part of the feedback loop. The adequacy of available models of milling process mechanics is evaluated here experimentally for many cases of varying machining conditions, including changing axial and radial depths of cut and feedrate. Startup transients in the force as the cutter engages the workpiece are also investigated. The significance of dynamic effects in the milling process and of effects such as runout, for constraint-type adaptive control system design, is then evaluated.

A fast algorithm for on-line machining process modeling and adaptive control

Abstract: A fast, on-line algorithm for machining process modeling and control is proposed. The modeling is accomplished via a new recursive estimator that offers good ac­ curacy at a minimal computational load. Its Fast Kalman-type version, that further reduces its computational complexity, is also presented. The adaptive controller, which is based on on-line identification and closed-loop pole assignment, is characterized by a low computational load and no need for a priori process informa­ tion. The analytical results are supplemented by numerical simulations, where the proposed scheme is used for the control of a turning operation and shown to offer very good performance under noisy conditions and suddenly changing machining dynamics.

Scallop Removal in Die Milling by Tertiary Cutter Motion

Abstract: The feasibility of a newly proposed method for the removal of cutter marks in die finishing operations has been investigated. The method is based on the superposition of a tertiary motion onto the conventional cutter motions. Path equations that consider motion and geometric variables have been derived and used as a basis for the development of a computer simulation model for generating three-dimensional surface representations. It has been shown that the tertiary motion results in a considerable reduction in the volume of the material in the scallops or blend marks left on the surface.

Investigation of Heat Transfer and Simulation of Metal Flow in Hot Upsetting

Abstract: The author wishes to thank National Science Foundation for its grant to the Engineering Research Center for Net Shape Manufacturing at The Ohio State University and Drs. T. Altan and S. L. semiatin for their useful suggestions and encouragement during the course of this work. Also, he wishes to thank Mrs. Harriet W. Dana and Mr. G. Shen for typing the manuscript and Mr. W. Wu fot valuable discussion.

Shaping Silicon Nitride With a Carbon Dioxide Laser by Overlapping Multiple Grooves

Abstract: On etudie la possibilite de faconner des ceramiques de Si 3 N 4 par recouvrement de rainures multiples produites par un faisceau laser au CO 2 fonctionnant en continu. On examine l'influence des parametres experimentaux, on discute d'une strategie pour le faconnage au laser et on presente une evaluation economique

Design and Manufacturing Analyses for Integrated CAD/CAM of Cams

Abstract: The design analysis begins with the lift schedule specified either by analytical functions or by discrete data points which are transformed to an analytical form by cubic spline interpolation. The required cam contour and its curvature at each point on the cam periphery are then derived. Machining of the required cam shape is analyzed for NC jig grinding, CNC grinding, and rocker grinding