Prismatic Workpieces Research Articles

Development of Friction-Assisted Extrusion Process for Producing Thin Metal Strips.

A new concept of "friction-assisted extrusion" to produce a thin metal strip is proposed. In the process, a rectangular prismatic workpiece inserted into the container is compressed by a punch against an anvil, and the anvil is forced to move horizontally. A thin strip can be extruded through the gap by the high friction force over the anvil surface. Very thin strips of aluminium and copper up to about 50 μm in thickness could be formed up to the extrusion ratio R = 200 with a considerably low punch pressure ratio p/2k=1∼2(p : punch pressure, k : yield shear stress), which agreed with the theoretical value estimated by the upper bound method.

Predicting Machine Low-Frequency Domain Errors by Finite Information Mapping Using Artificial Neural Network

Currently, it is difficult or even impossible to check the dimensional accuracy of a prismatic workpiece when it is in the process of automatic machining operations. This research presents an artificial neural network based methodology for predicting low-frequency domain errors of computer numerical controlled machining centers. This research provides the information needed for real-time, in-process machining dimensional accuracy assessment and feedback control for error compensation. Analytical and neural network approaches are employed in parallel to solve this problem. A multiple-sensor system is incorporated with the model for real-time data acquisition. The results demonstrate that neural network based methodology is not only capable to predict the errors of entire workpiece but also able to delivers a fast and excellent reference for on-line error compensation.

A CAPP System for Automatic Tool Selection in Drilling Operations

Abstract The paper presents the process planning of prismatic workpieces which are usually manufactured in a machining centre. The main interest has been laid on an automatic tool selection based on the information of tools used previously in similar manufacturing operations. A Computer Aided Process Planning System for Machining Centre Operations has been developed.

Optimization Methods Applied to Selecting Support Positions in Fixture Design

This paper proposes optimization techniques to assist in the design and evaluation of fixtures for holding prismatic workpieces. This formulation of the fixturing design problem takes into account deflection of the workpiece subjected to assembly or machining loads. Using the minimization of the workpiece deflection at selected points as the design criterion, the design problem is determining the positions of the fixture supports. The Finite Element Method is used for calculating deflections that are the basis for the design objective function, and the Broyden-Fletcher-Goldfarb-Shanno optimization algorithm is used to determine the fixture support positions. In this paper the proposed objective function is developed and the method is illustrated with three numerical examples.

Geometric adaptive straightness control system for the peripheral end milling process with large error sources

An off-line Geometric Adaptive Control (GAC) scheme is proposed to compensate for machining straightness errors due to the machine tool's inaccuracy and those arising as a result of the metal cutting process during the finish peripheral end milling process. In the milling process, the workpiece travels along the guideway while the spindle system remains fixed. The scheme is based on the exponential smoothing of post-process measurements of relative machining errors due to the tool and bed deflections. Without a priori knowledge of the variations of the cutting parameters, the time-varying parameters are estimated by an Exponentially Weighted Recursive Least Squares (EWRLS) method. This method is able to incorporate a straightedge which is not necessarily accurate to identify the guideway errors. To reduce the drift of the cutting parameters, a single parameter adaptation method is introduced. Experimental results show that the location error is controlled within the range of the fixing error of the milling bed on the guideway. Further, the waviness error is reduced to less than 10 μm in the machining of a 508-mm long prismatic workpiece regardless of the machining conditions.

Knowledge-Based Process Planning System for Prismatic Workpieces in a CAD/CAM-Environment

The present paper will introduce by way of extract an approach for the planning of new designed prismatic workpieces. Hereby graphic interactive treatment of CAD-model data, transformation of CAD-data into the object basis of an expert system, as well as the determination of operations and sequencing the process are closer looked at. The approach will be based on the structuring of workpieces into logical units and geometrical elements, as well as on the description of processes by means of process units. Optimizing sequenced processes will be based upon a task related prestructuring of the problem and determination and solving of Importance matrices.

Locating Point Synthesis in Fixture Design

A method for selecting and positioning locating points in fixture design is proposed. The types of fixture applications considered are for prismatic workpieces that use the 3-2-1 locating principle as the general structure of the fixture. The design synthesis problem uses six rules based on machining practice to select the secondary and tertiary locating datums for a workpiece stored in a boundary representation solid modeler. Once these edges are selected, kinematic rules are used to determine the position of the locating points so as to allow accessibility when loading and unloading a workpiece. Examples are given to illustrate this method, as well as the positioning of support points on the primary datum plane.

Pattern Recognition and Process Planning Prismatic Workpieces by Knowledge Based Approach

FEXCAPP. a feature oriented and knowledge based generative type CAPP system is presented in the paper. For the CAD/CAPP integration, a feature recognition module based on Directed Edge Data Structure and Attributed Adjacency Graph concepts are utilized. From this features, tool approach direction, tool radius and machining sequence are determined by tree search algorithm. ROHULUS and OPS5 are used as a geometric modeller and an inference engine. And an axiomatic approach is utilized to include the tolerance and machine's precision information in determining the cutting conditions. Finally. for CAP/CAM integration. NC codes are automatically generated from the process sequence file and transmitted to the NC milling machine through RS-232C.

The analysis of equilateral grip of a prismatic and convex workpiece

Certain facets of the gripping problem in robotics are discussed. A gripper with a single degree of freedom is considered, which consists of three equal-length fingers. The set of workpieces under consideration are modeled by prismatic and convex polyhedra. This leads to a planar-geometric formulation. The computational geometric problem of inscribing, in a given convex polygon, an equilateral triangle that is locally minimal, is addressed. Feasibility and the (computational) geometric construction of the solution are emphasized. >

Forecasting compensatory control (FCC) of machining flatness

Forecasting Compensatory Control (FCC) was implemented to improve the flatness of three dimensional prismatic workpieces in an end-milling operation. The basic logic of the strategy is based on inprocess error measurement, stochastic modelling, and prediction and compensation of the cutting errors. The proposed FCC system consisted of a newly developed laser-based in-process flatness error measurement system, a hydraulic positioning servo system, and a digital microcomputer control system. Through the application of the FCC system to on-line cutting experiments, the workpiece flatness error was reduced by up to 80% during machining.

The H-Pallet concept and its possibilities-new solutions of prismatic workpiece handling in the close range of machinery

The current situation on the market concerning industrial products has a great influence on production techniques, i.e. the development is concerned more with smaller batches than mass production of similar items. The reason for this is that competition requires the satisfaction of growing customer requirements. In addition, the life of product lines is getting shorter with an expanding field of products. Therefore the trends in machine tool design are directed towards flexible automated production. For the manufacturing of axially symmetrical parts ‘flexible manufacturing cells’ consisting of lathes and robots have been created. For prismatic workpieces, stations with automated clamping and pallet changers now exist which also improve the prospects for flexible production systems.

Technology for the control of quality in automated manufacturing

This paper reviews the present status of technology for the quality assurance of products produced by flexible automation parts-manufacturing. Two examples of practical systems that represent typical products (rotational and prismatic work-pieces) are described with particular emphasis on control functions relevant to product quality

Measurement of Internal Threads in a Multi-Coordinate Measuring Device

In the use of a computer-controlled measuring centre for the quality assurance in flexible production systems, the flexibility in comparison with conventional multi-coordinate measuring devices has been increased by increasing the scope of possible measurements to an extent that largely all measurement jobs involved in prismatic workpieces can be solved by this system. A survey revealed that there is also a need for testing internal threads; it also showed that there is a number of typical types of defects which occur very frequently in the manufacturing of internal threads, where these defects restrict the operability of the threads involved. To detect defects caused in manufacturing and to test whether the thread parameters lie within the permissible limits, a program has been prepared that permits an automatic test sequence. In contrast to the inspection by attributes using thread plug gauges, this approach permits statements as to the dimensions to be made at a justifiable amount of measurement and, thus, a correction of the errors. The development for the measuring centre makes it possible to reduce the extent of material flow in the production system, since the need for additional measuring devices may be obviated.