A simple upper-bound strip technique has been devised as a development of the upper-bound element technique for the prediction of the spread in flat-tool indentation. A kinematically admissible velocity field for three-dimensional deformation is proposed. From the derived velocity field the upper-bound load and the deformed configuration are determined by optimizing some parameters. The theoretical estimates of forging load and deformed configuration are found to be in good agreement with experimental results and with rigid-plastic finite-element method results published in the literature. This technique can therefore be incorporated into forging-die CAD software for simulating and predicting the metal flow in cavities, which is mainly done by FEM and which until now has been a time-consuming process.
A stability analysis of the cutting process of a solid cylindrical rotating workpiece clamped by a four-jaw chuck with balanced pressure at the jaws has been carried out. The net reaction balancing the cutting force is found to consist of an infinite number of force components oscillating at frequencies 4ω, 8ω, 12ω, …, etc., where ω is the angular speed of rotation of the workpiece, and a stationary force term 2F0 where F0 is the static balancing force impressed along each jaw-line. The stationary force term tends to give a uniform depth of cut. However the harmonic force terms tend to spoil the uniformity in the depth of cut. It is predicted that under the resonant condition of the fourth-harmonic force, the minimum depth of cut will occur at the mid positions between two jaws and the maximum at the jaw-positions. Chatter vibration of the system will be observed at angular spindle speeds approaching ω0/4, ω0/8, ω0/12, …, etc., where ω0 is the angular natural frequency of the system. A stability chart has been drawn to suggest the safe operating regions.
This paper describes an integrated approach to the design and manufacture of cylindrical type objects with complex curvature. The modules in this system include the scanning of the object, its surface description and subsequent modification, the tool path generation, and the NC machining of the object. The operation of each module is illustrated in a case study involving the design and manufacture of a shoe last for orthopedic footwear.
The advent of CAD/CAM system, robotics simulator and off-line programming tools has provided a significance contribution to advanced manufacturing technology. A natural progression would be to integrate these computer aided tools with a robotics workcell within a flexible manufacturing system, FMS. Such an integrated approach is currently developed within GINTIC for the assembly of modular fixtures in its intelligent flexible manufacturing system, IFMS for the machining of complex shape components. This paper describes the configuration and development of this system. The functions associated with each modules within the integrated robotics off-line programming system will be also elaborated.
The efficiency of empirical studies aimed at establishing the cause-and-effect relationships between the manipulable parameters of a manufacturing process and the resultant measurable process behavior can be greatly enhanced by the appropriate application of experimental design methodologies. Some techniques of selecting suitable experimental parameter settings in the face of certain special process characteristics and operational constraints are discussed in this paper with particular reference to fractional factorial designs.
Although the elevated-temperature drawing of wire has been employed in industry for a number of years, the process has not been investigated systematically and many facets of the process are not yet understood. Generally, exploration of the mechanics of wire drawing has been confined to cold working, for which the effects of strain-rate and temperature on the flow stress can be neglected: it is believed that no attention has been paid to the mechanics of wire drawing at elevated temperatures.
This paper presents the strategy of combined workholding and workhandling to reduce machine setup time using a three degrees-of-freedom (DOF) in-parallel actuated manipulator. The manipulator is characterized by its short-arm rigidity, high force-to-weight ratio and relatively simple inverse kinematics. It has two orientation freedoms to adapt to a complex surface and a translation freedom for clamping actuation. Unlike workhandling which requires the robotic arm to have the ability to follow a path in three dimensions at specified accuracy and speed, workholding requires the part and the manipulator to be over-constrained. The reactions result in time-varying, path-dependent and load-dependent Coulomb friction and stiction, which have significant influences in joint motion. To investigate the effects of the nonlinearities on the joint motion control, a prototype manipulator has been built. A digital tracking control algorithm under the influences of the nonlinearities was experimentally evaluated.
The prime objective of the presently reported work is to assess the accuracy of the finite-element modelling of three-dimensional metal-forming processes, where the block-compression process has been chosen for experimental substantiation of the results of the theoretical model. A three-dimensional rigid-plastic finite-element approach has been used to simulate the metal flow during compression and the results of calculations of the strain distribution are compared with the strains measured during the compression of lead samples. Discrepancies between the calculations and the measurements are discussed in the paper and their sources are analyzed. The conclusion is drawn that the experimental verification of the results of the three-dimensional rigid-plastic finite-element method shows the high accuracy of the latter and confirms its ability to simulate metal-forming processes.
This paper proposes a model for the growth of flank wear in milling. It incorporates the predominant mechanisms of wear which are abrasion and diffusion and also accounts for thermal fatigue and the effect of the number of teeth. The results obtained are compared to actual data and are shown to be in good agreement.
Tool wear measurements are a significant factor in the operation of an automation machine tool installation. This paper reports four methods for detection of tool wear: cutting force, chip direction, temperature rise and acoustic emission signal. The simple combined measurement method will be used to indicate ceramic tool wear or breakage. Ceramic inserts on a lathe single point cutting were used in the tests at high cutting speed. The true root-mean-square, RMS, of the acoustic emission signal measured at the base of the insert is shown to be the most sensitive to tool wear.
The pressing of metal alloys in the mashy state is one of the latest technologies in the forming of metallic products. During the plastic working of the material in this condition, the deformation resistance is much lower than in conventional hot working. Moreover, the liquid component in the alloys alters the mechanism of plastic deformation as well as the pattern of metal flow, which allows high strains to be applied in a single die-impression: the process is therefore of importance in industrial practice. The present paper is a continuation of an earlier study of the plastic working of materials in the mashy state and is concerned with the possible application of this technique to the manufacture of forgings of complex shape in a single technological operation.
The establishment of a Military Academy (which later became the Royal Military Academy, R.M.A.) in 1741 at Woolwich, near London, for training officers for the artillery and engineering arms of Britain's army, continued without massive changes for about one and a half centuries. During that period a succession of men - as Professors - were appointed to the mathematics Chair in the Academy and a few others in neighbouring subjects, and fulfilled theier duties mainly through research - principally in studying in its early formative years the subject of internal and external ballistics - by textbook-writing, and by sustaining interest and answering a national need for their professed subject. At this time the English universities failed to perceive or even neglected what today is thought of as their proper duty. As little is known about these men, collectively, by the present-day cognoscenti of applied mechanics and mathematics, this paper endeavours to outline their scientific contributions, describes the background, mainly humble, from which they came and aspects of the institution to which some of them gave their whole working life.
In this paper, a detector to measure the chucking force of the collet chuck holders used in machining centers has been developed, and various kinds of chucks are tested. The chucking pressure distribution is corresponding to the deformation of chuck's bore and the mean chucking pressure has a good agreement with the estimated value from the maximum chucking torque.
In this paper, a framework for automated mechanical assembly planning is discussed. The paper addresses three major issues: conceptual assembly design representation, assemblability analysis, and assembly plan generation. The objective of the study is to develop an effective way to model and plan for the assembly of a product. It is hoped that noty assembly planning can be automated, but also the feedback provided by the planning system can help to improve the design from a manufacturing point of view. Since the feasibility of automating the assembly plan generation depends on whether the assembly design is represented in a complete, unambiguous, and easy to use form, the design representation is the first issue addressed. In order to ensure the "manufacturability" of an assembly, the assemblability of the design must be analyzed at the early design stage. This analysis can be viewed as a rough planning. It provides the designer a quick feedback, thus the design can be changed before it is finalized. Before the actual assembly can be conducted, a detailed assembly plan must be prepared. Such an assembly plan is used for shop scheduling, and sometimes assembly system design.
This paper deals with the development of MPSEL, a system for the selection of machining parameters in a job shop. An overview for the role of this research within the manufacturing system has been provided. The factors and procedures used in the selection of machines, tools, fluids, tool angles, and in the analysis of the compatibility between operations and work materials has been outlined. The methods used for data acquisition and control of inference engine have been described. The necessity of integrating expert systems with algorithms for efficient decision making has been emphasized.
This paper describes the phases involved in developing several PC-based computer aids for sheet-metal work. A blank layout program was first developed, followed by flat patterning and design considerations of progressive dies. An attempt is made to link the programs together to form a useful package for the design of progressive dies. The program incorporates a number of expert design rules and provides an automated solution for progressive-die layout with the following features: automated blank layout, punch-shape determination and optimisation to take advantage of standard commercial punches; automated staging of the punches considering punch interference and minimum die-opening separation; die plate configuration, etc. This software provides a good aid to progressive die design and, since it is PC-based, it is within the reach of many small tool and die shops.
Burnishing, a plastic deformation process, is becoming more popular as a finishing process. Experimental work based on 34factorial design has been carried out on a vertical machining centre to establish the effects of ball-burnishing parameters on the surface roughness of AISI 1045 specimens. Analyses of the results by the analysis-of-variance technique and the F-test show that the ball material, the lubricant, the feed and the depth of penetration, have significant effects on the surface roughness. A pre-machined surface roughness of 4 μm (Rtm) can be finished to about 0.772 μm.
Utilizing inertial energy storage the homopolar generator (HPG) is capable of delivering multimegawatt, megampere current pulses into resistive or inductive loads with high efficiency. (1) Such HPG's have been used for many years as power supplies for research in pulsed processing of metal alloy components and systems. Most of these processes rely on extremely rapid thermal excursions in the workpiece(s) caused by resistive heating during the current pulse. A new application of pulsed HPG's that carries great promise is homopolar pulse consolidation (HPC) of powder metal alloys or components.(2) In HPC, powder metal constituents are loaded into a thermally and electrically insulated die, then precompacted to an initial pressure. the “rams” of the compaction press are also the electrodes for homopolar discharge current. While in single residency, the powder compact is heated uniformly by HPG discharge current, sintering occurs, and consolidation is accomplished by hydraulic control of the consolidation press. The process is completed in approximately one sec, with unaided cooling to room temperature on the order of 100 sec, depending on compact mass. Microstructural control is closely tied to beginning particle size and distribution. Traditionally unsinterable alloys have been consolidated using HPC. Novel intermetallic alloys and phases have been produced. Cermets and other composites can be produced, as long as the continuous matrix is conductive. New tooling designs allow for controlled atmospheres, near-net shapes, and automated manufacturing.
In this investigation, a comparison is made between the flow stress as evaluated through the torsion test with that as evaluated through the compression test, for the prediction of the peak pressure in the extrusion of commercial purity titanium. Room temperature, ring- and solid-compression tests and torsion tests were carried out at nominal strain rates ranging from 0.05 to 32s−1 to evaluate the flow stress. Cold extrusion tests were also carried out on the same material, using MoS2 as the lubricant, to determine the actual peak extrusion pressure for various reductions, for two extrusion processes; namely solid forward and hollow forward extrusion. The peak extrusion pressures observed were compared with those predicted using the flow-stress data evaluated through the compression and the torsion tests, the results showing that the torsion-test data affords a closer prediction.
This paper discusses the development of an expert system based on axis orientation of the parts in a three dimensional system. For any part fed to a machine cell, the material handling planning system presents the part to the assembly robot in the desired orientation. Group Technology classification and coding method is used for part identification, as well as for the feeding mechanism design.
