Showing papers in "Journal of Engineering for Industry in 1991"

Automatic Disassembly and Total Ordering in Three Dimensions

Abstract: Generating a sequence of motions for removing components in a three-dimensional assembly, one at a time, is considered—the robot motion being strictly translational. We map the boundary representation of a given assembly to a tree structure called Disassembly Tree (DT). Traversing the DT in pre- and post-order yields a minimal sequence of operations for disassembly and assembly, respectively. In this paper, an assembly is classified by the logical complexity of its DT (an ordered graph whose nodes are components of the given assembly) and by the geometric complexity of the nodes in DT (in terms of the number of motions needed to remove a single component). Next, whether a component can be removed in one motion is described as a predicate. This predicate is then used in an algorithm for constructing the DT. For a class of assemblies that exhibit total ordering, the algorithm decides whether each component can be removed in a single motion, by constructing a DT in O(N log N) time, on the average, where N is the total number of mating faces in the assembly.

Optimization factors in abrasive-waterjet machining

Abstract: Machining applications such as cutting, milling, and turning are considered along with sample data. The effects of different AWJ parameters on both the functional performance of the AWJ system components and the material removal process are discussed

Fixture planning with friction

Abstract: A fixture planning module is being developed as part of a computational system for concurrent product and process design. The module employs symbolic and numerical analyses at different levels of detail, from fast geometric checks to more time consuming force and friction analyses, depending on the completeness of the machining plan. In this paper we focus on the approaches used for analyzing fixture kinematics and clamping forces, including the analysis of friction. Since many fixture arrangements rely on friction to hold a part, the ability to reason about friction is an important component of fixture planning. Limit surfaces in force/moment space are introduced as a convenient formalism to check whether parts will slip and to help in specifying clamping forces.

Command Generation for Three-Axis CNC Machining

Abstract: This paper investigates the command generation for three-axis CNC machining. In the integration of CAD and CAM, it is necessary to relate machine tool dynamics and control in a CAM process to the geometrical data in a CAD model. The data stored in a CAD model is usually static in nature and represented by unitless parameters. Yet, in machine tool motion and control, the data should be transformed into a time dependent domain. In this paper, the geometrical properties of a cutter path, including position, tangent, curvature and torsion are analytically related to the motion dynamics of a machine tool including feedrate, acceleration, jerk and driving force. The information about feedrate, acceleration and driving force is needed for command generation. Jerk analysis can be used for cutting quality analysis.

Experimental Investigations into Traveling Wire Electrochemical Spark Machining (TW-ECSM) of Composites

Abstract: Experiments are carried out on glass-epoxy and kevlar-epoxy composites, using sodium hydroxide (NaOH) as electrolyte. The wire and the workpiece were kept in physical contact with each other by the use of a gravity feed mechanism. The effects of voltage and concentration of the electrolyte on material removal rate, average diametral overcut, tool wear rate, and wire erosion ratio are reported

Stick-Slip Vibration of Drill Strings

Abstract: The stick-slip vibration is introduced as a new mechanism to explain the large amplitude torsional oscillation of the drill strings in oil and gas well drillings. A record of field data is identified and simulated according to the new mechanism. The analytical results derived from the numerical simulation agree with the field data with 95.6 percent accuracy. The physical phenomenon of the stick-slip vibration of drill string is explained by initiating a phase trace in the phase plane. The beating phenomenon in drilling is interpreted in terms of stick-slip vibration. The effects of viscous damping, rotary speed and natural frequency on the stick-slip vibration are discussed

Localization of 3-D Objects Having Complex Sculptured Surfaces Using Tactile Sensing and Surface Description

Abstract: The presented method determines position and orientation of an object by minimizing the sum of the squared distances of the measurement points from the surface of the object with respect to the parameters of transformation. Tactile sensing by Coordinate Measurement Machine (CMM) has been used as the means of measurement

A Transfer Function Description of Sheet Metal Forming for Process Control

Abstract: Three-dimensional forming of sheet metal parts is typically accomplished using one or two shaped tools (die) that impart the necessary complex curvature and induce sufficient in-plane strain for part strength and shape stability. This research proposes a method of applying closed-loop process control concepts to sheet forming in a manner that automatically converges upon the appropriate tooling design. The problem of controlling complex deformation is reduced to a system identification problem where the die-part transformation is developed as a spatial frequency domain transfer function. This transfer function is simply the ratio of the measured change in spatial frequency content of the part and the die. It is then shown that such a transfer function can be used to implement closed-loop process control via rapid die redesign. Axisymmetric forming experiments are presented that establish the appropriateness of the linear transfer function description (via a test of superposition) and demonstrate the convergence properties of the proposed control method

Effect of Machining Processes on the Fatigue Strength of Hardened AISI 4340 Steel

Abstract: The effect of two finishing processes, namely, cutting and grinding, on the fatigue strength of hardened AISI 4340 steel was investigated. Three sets of flat tensile specimens were prepared by first machining into the general shape of the fatigue specimen standard, then they were hardened to HRC 54. The final grinding was carefully performed on one set of specimens. Two sets of specimens were fly cut to obtain a surface finish comparable to the ground surface. The residual stress distribution, surface structure, and surface profiles were determined. Fatigue testing was accomplished on these specimens in tension under load control. All the residual stress patterns were compressive, but the residual stress created by fly cutting reached a much deeper layer than that created by grinding. Fly cutting also produced a surface with a higher fatigue strength than the grinding did.

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Building Layered Models to Support Engineering Decision Making: A Machine Learning Approach

Abstract: This paper presents a new model building methodology which, given a detailed mechanistic model of a task, can optimally produce a set of models with layered abstraction according to the user’s specified modeling objectives. These layered models can be used to evaluate decisions made at different levels of abstraction during a typical problem-solving process such as engineering design and planning. In our research, the model building process is viewed as a learning activity and inductive machine learning techniques from AI are combined with traditional optimization methods to form our prototype model building system called AIMS (Adaptive and Interactive Modeling System). The layered analysis models built by AIMS offer several distinctive advantages over those traditional analysis models which can only provide evaluations at very detailed stages of decision making. These advantages include: early evaluation to avoid costly iterations, fast execution for interactive applications, more comprehensibility for human inspection, and deep roots in domain physics for higher accuracy. Case study results of building layered models for a process design task of an intermittent cutting process are presented as a demonstration of the potential use of our system. We also explain this model building research in the context of the knowledge processing technology as a new foundation for advanced engineering automation.

Analysis of Fluid Flow Under a Grinding Wheel

Abstract: Fluid flow under a grinding wheel is modeled using a perturbation scheme. In this initial effort to understand the flow characteristics, we concentrate on the case of a smooth wheel with slight clearance between the wheel and workpiece. The solution at lowest order is that given by standard lubrication theory. Higher-order terms correct for inertial and two-dimensional effects. Experimental and analytical pressure profiles are compared to test the validity of the model. Lubrication theory provides good agreement with low Reynolds number flows; the perturbation scheme provides reasonable agreement with moderate Reynolds number flows but fails at high Reynolds numbers. Results from experiments demonstrate that the ignored upstream and downstream conditions significantly affect the flow characteristics, implying that only a model based on the fully two- (or three-) dimensional Navier-Stokes equations will accurately predict the flow. We make one comparison between an experiment with a grinding wheel and the model incorporating a one-dimensional sinusoidal roughness term. For this case, lubrication theory surprisingly provides good agreement with experiment.

A Boundary Element Method Analysis of the Thermal Aspects of Metal Cutting Processes

Abstract: In this paper, the b oundary e lement m ethod (BEM) approach is used to analyze the thermal aspects of steady state metal cutting processes. Particular attention is paid to modeling of the boundary conditions at the tool-chip and the chip-workpiece interfaces. Since the velocities in each of the regions are different, the heat transfer within the tool, the chip, and the workpiece are first calculated separately. A complete model for heat transfer during steady state turning is then obtained by matching the boundary conditions across the primary and the secondary shear zones. An exact expression for matching is developed to avoid any iterations. The temperature fields within the workpiece, the chip, and the tool for various processing conditions are obtained and presented. The numerical results obtained by the BEM are also compared to Jaeger solutions and existing FEM results reported in the literature. The BEM is found to be efficient and robust for this class of steady state conduction-convection problems.

Experimental Techniques for Bearing Impedance Measurement

Abstract: The dynamic characteristics of rotating machinery are almost always influenced by the impedances of the machine bearings (including the bearing supports) and it is particularly important to know of their likely values at the design stage when predicting machine critical speeds, unbalance response, and stability. In many instances the vital data may be obtained from theory which must be confirmed by experimental measurement beforehand, or alternatively the data may be obtained directly from experimental measurement when the appropriate bearing has already been manufactured. The experimental techniques available for use in the measurement of bearing impedances are varied, both in their experimental procedure and in the theoretical treatment of the data that is gathered. The aim of this paper is to provide a concise account of these techniques, and to discuss the potential advantages and disadvantages of each approach. In this document, the procedures described are classified in terms of the type of experimental measuring equipment required. These vary from the simplest of test rigs, which provide only a static load in one direction and where impedances can be evaluated by hand calculation, to sophisticated apparatus capable of providing static and dynamic loads in several directions and which require computer software to extract the bearing impedances from the measured data. The type of experimental procedure selected by the rotor dynamicist will depend upon the experimental facilities available, on the time available to carry out the testing, and on the required reliability of results. Each of these considerations is discussed for each procedure described. It is concluded that measurements made using multifrequency test signals provide more reliable data, although all measurement methods yield coefficient values which agree with theoretical predictions to within about 20 percent in general, and all methods have a significant scatter of results associated with their use.