Showing papers on "Machining published in 1990"

Intelligent Manufacturing Systems

Abstract: Introduction - flexible machining and assembly systems components of knowledge-based systems machine learning design of mechanical parts and mechanisms process planning. KBSES - a knowledge-based system for equipment selection group technology - models and algorithms. KBGT - a knowledge-based system for group technology models and algorithms for machine layout. KBML - knowledge-based system for machine layout aggregate scheduling of machining and assembly systems scheduling models and algorithms. KBSS - a knowledge-based system for scheduling in automated manufacturing.

Ductile‐Regime Machining of Germanium and Silicon

Abstract: Precision machining of germanium and silicon was studied using single-point diamond turning. Special attention was directed to the so-called ductile regime wherein optical quality surface finishes can be machined directly on brittle materials. A novel interrupted-cutting test and a new model of the machining process were used to measure a critical-depth parameter experimentally. This parameter governs the transition from plastic flow to fracture along the tool nose. The critical-depth parameter can be used to provide physical insight into the effect of various machining parameters such as tool rake angle or tool clearnace angle. Because of a complex interplay between tool geometry, machining parameters, and material response, a large fraction of material removal occurs by fracture even when ductile-regime conditions are achieved.

Machining of Titanium and its Alloys—a Review:

Abstract: Even though a new generation of tool materials is now available which is revolutionizing machinability of a large number of work materials, the machining of titanium continues to be a problem. In t...

Micro electro-discharge machining and its applications

Abstract: A micro electro-discharge machining (MEDM) technology is presented It allows machining of micro holes and shafts as small as 5 mu m in diameter with a best surface roughness of 01 mu m R/sub max/ and of roundness of 05 mu m, as well as a variety of complex shapes of equivalent accuracy In the MEDM, machining for silicon with 10-100 Omega -cm resistivity is possible; machining up to a depth of 10 times the electrode diameter is easy, and the electrode wear is small A prototype microair turbine of 22 mm external diameter, which is able to rotate at a speed of approximately 1000 rpm, is discussed >

A micro-positioning tool post using a piezoelectric actuator for diamond turning machines

Abstract: A micro-positioning tool post ‘Piezo tool servo’ has been developed for high-resolution tool servo systems for ultra-precision diamond turning machines. It was designed by using a wire-cut parallel spring mechanism, a PZT stack actuator and a capacitance gauge. To eliminate the non-linearities in the PZT actuator and to improve the stiffness and response, two types of closed-loop controller were applied to the tool post, and compared. Both controllers were effective in obtaining flat frequency characteristics, resolution, static stiffness and static stability. The actual resolution of depth-of-cut control was determined by a cutting test on an aluminium alloy.

Production management system

Abstract: A production management system controls a production line having a plurality of assembling/machining stations including pieces of production equipment such as nut runners. The production management system includes a computer for supplying control information to control the pieces of production equipment, a first information network for transmitting the control information from the computer to the assembling/machining stations, and a second information network for transmitting information indicating results of operation in the assembling/machining stations to downstream assembling/machining stations to allow defective portions of workpieces to be repaired in the subsequent assembling/machining stations. The first information network comprises a plurality of separate networks associated respectively with divided portions of the production line.

A Comparison of Statistical and AI Approaches to the Selection of Process Parameters in Intelligent Machining

Abstract: This paper presents an approach for the selection of a set of process parameters for use in machining control. The approach is aimed at providing a range of parameters within which machining operations can be optimized. Because of the complexity and somewhat unpredictable nature of the machining process, this approach combines process modelling with rule-based techniques. Modelling correlates process state variables such as surface roughness or chip merit mark to process parameters such as feed rate, cutting speed, and tool rake angle. The modelling techniques considered in this paper include multiple regression analysis, group method of data handling (GMDH), and neural network. A rule-based module determines the final operational range of control parameters based on user information and modelling predictions. The different modelling techniques have been evaluated using data from orthogonal cutting.

NC milling tool path generation for arbitrary pockets defined by sculptered surfaces

Abstract: In machining die cavities or mechanical parts, it is often necessary to remove material within a given boundary. Although this pocket cutting capability is implemented in many numerical control packages, most of them can handle only convex shaped pockets bounded by curves of limited types and numbers. A procedure has been developed to machine a pocket with a convex or concave free surface bounded by lines, circular arcs and free curves. The cutter location data are computed directly with better computational efficiency than normal, without using an iterative method.

Automatic 3D machining feature extraction from 3D CSG solid input

Abstract: A method for automatically extracting the machining features from 3D CSG solid input is proposed. The method involves converting a part's CSG tree representation into its equivalent DSG tree representation and then identifying the types of machinable features from the DSG tree. A DSG tree is a special case of CSG tree in which all geometric operations are of ‘difference’ type. The method is proposed for recognizing prismatic part features and its outputs contain feature attributes and possible tooling entrance faces, etc. Computer simulation is provided to illustrate the proposed method.

A molecular dynamics model of the orthogonal cutting process

Abstract: Material removal, as found in the cutting and grinding processes, is important in many areas of fabrication technology. Examples include high-speed machining by single point turning, surface milling and drilling. An idealized model that contains the essential physics of these processes is the two-dimensional orthogonal cutting geometry. Following the work of Shaw, an attempt is made to obtain a fundamental understanding of the commonly observed phenomena in the chip forming process: the atomistic mechanisms of plastic deformation within the primary shear zone and the observed shear angle ({phi}); the resultant energy flow from the tool doing work; the stress, strain and material flow fields; the morphology of the chip (smooth, segmented, crystalline or amorphous); the role of different depths of cut (t), rake angles ({alpha}), and clearance angles ({theta}); and the role of the tool tip radius, roughness (friction), and wear. The molecular dynamics computer simulation method is an ideal tool for the study of the atomistic mechanisms of these deformation processes. Simulations are performed for a model of copper at room temperature using 10{sup 3}--10{sup 6} atoms, depths of cut in the range l--50nm. and cutting speeds of 1--2500 meters per second (m/s). These simulations are strictly two dimensionalmore » (plane strain). Here, focus is on the chip forming process, the atomistic mechanisms of plastic deformation, the flow of energy into the chip and workpiece, and the material flow and stress fields for the orthogonal geometry ({alpha} = 0), sharp tools, and shallow depths of cut (t {approx} 5 nm). 5 refs., 3 figs.« less

The Effects of Variable Speed Cutting on Vibration Control in Face Milling

Abstract: This paper discusses the use of variable speed cutting for vibration control in the face milling process. Both simulation and experimental results show that the self-excited vibrations that can occur during constant speed cutting, and hence put limitation on the possible size of cut, can be suppressed by continuously varying the spindle speed. Through both analytical and experimental studies, the shape of variable speed trajectory has been examined, in terms of both the trackability by the spindle servo system and performance in terms of vibration suppression. It was found that a sinusoidal wave because of its acceleration and jerk characteristics can be tracked more precisely than some other periodic waves. The dynamic face milling force model was used to study the effects of speed trajectory parameters, namely, the frequency and amplitude. The results, in general, show the method to be fairly robust to the specific nature of the machining situation in terms of both processing conditions and system dynamics. Speed trajectory design was, however, shown to be somewhat dependent upon the nominal cutting speed and dominant frequencies of the system.

Electrical discharge machining of carbon fibre composite materials

Abstract: An investigation has been made into the feasibility of using Electrical Discharge Machining (EDM) as a means of machining carbon fibre composite materials. Machining was preformed at various currents, pulse durations and with different tool materials and polarities. There exists an optimum material removal rate with peak current and the pulse-on time. However, electrical discharge machining of carbon fibre composite materials should be done at low current density as high current density would cause the epoxy resin to smear over the surface leading to reduced material removal rate and rapid deterioration of the EDM surface. It is found that copper electrodes perform better than graphite electrodes in terms of tool wear, and tools with positive polarity give higher material removal rate and lower tool wear ratio.

Investigations into machining of composites

Abstract: Fibre reinforced plastics (FRP) have an important place in the field of engineering materials. Initially, the main emphasis in research was on the development of materials. Currently, however, more attention is being paid to the industrial production of FRP products. Normally, conventional methods for machining of these materials are used, but reports have indicated poor performance of these conventional types of cutting tools during machining of FRP. In this paper, a new approach using electrochemical spark machining (ECSM) for cutting and drilling holes in composites is proposed. The feasibility of using ECSM for machining FRP was first ascertained. Then a parametric study of the process was performed by planning the experiments using a ‘design of experiments’ concept as well as a ‘one variable at a time’ approach. Kevlar-fibre-epoxy and glass-fibre-epoxy composites as work materials, copper as the tool material and an aqueous solution of NaCl as electrolyte were used. It is concluded that ECSM is a viable solution for cutting FRP. However, for achieving the desired accuracy, surface finish and economics of the process, the machining parameters need to be optimized.

Wear mechanisms of ceramic cutting tools when machining ferrous and non-ferrous alloys

Abstract: Three ceramic cutting tool grades CC 670 (based on alumina and silicon carbide whiskers) and CC 680 (based on silicon nitride) were used for the evaluation of tool life and wear mechanisms when machining a heat-resistant alloy, Inconel 718. Tool life for both grades was determined by flank wear and depth-of-cut (DOC) notch wear except at high feed rates. Flank wear was determined by chemical interaction with the workpiece material for both cutting tool materials tested. DOC notch wear was mainly determined by seizure and pull-out of tool material fragments. Comparative tests were also performed on steel SS 2541 (similar to AISI 4340) with grade CC 670 where both flank and crater wear were found to limit tool life. The main reason for the rather good wear resistance of silicon carbide reinforced alumina in Inconel 718 in contrast to its behaviour in steel was the formation of magnesia-based protective coatings.

Method and apparatus for polishing optical elements

Abstract: An apparatus for controlling the machining of optical elements is disclosed. The apparatus comprises the thus measured value of radius curvature with the measured value of radius curvature of previously polished lens, means for determining curvature correcting value by comparing the thus obtained curvature variation value with a previously set allowed value of radius curvature, means for determining correcting value of machining conditions during the swinging motion based on the thus determined curvature correcting value, and means for adjusting the machining conditions in accordance with the correcting value of machining conditions.

Cutting tool form compensaton system and method

Abstract: A compensation system for a computer-controlled machining apparatus having a controller and including a cutting tool and a workpiece holder which are movable relative to one another along a preprogrammed path during a machining operation utilizes a camera and a vision computer for gathering information at a preselected stage of a machining operation relating to the actual shape and size of the cutting edge of the cutting tool and for altering the preprogrammed path in accordance with detected variations between the actual size and shape of the cutting edge and an assumed size and shape of the cutting edge. The camera obtains an image of the cutting tool against a background so that the cutting tool and background possess contrasting light intensities, and the vision computer utilizes the contrasting light intensities of the image to locate points therein which correspond to points along the actual cutting edge. Following a series of computations involving the determining of a tool center from the points identified along the tool edge, the results of the computations are fed to the controller where the preprogrammed path is altered as aforedescribed.