Showing papers on "Machining published in 1991"

Laser Machining: Theory and Practice

Abstract: Contents: Overview of Machining Processes.- Lasers for Machining.- Basics of Laser Machining.- Heat Transfer and Fluid Mechanics for Laser Machining.- Laser Machining Analysis.- Laser Machining Applications.

Ductile-regime machining model for diamond turning of brittle materials

Abstract: A new machining model has been developed for single point diamond turning of brittle materials. Experiments using the interrupted cutting method allow model parameters to be determined that provide a quantitative method for determining the machinability of a material with respect to the rake angle, tool nose radius and machining environment. The model uses two parameters, the critical depth of cut and the subsurface damage depth, to characterize the ductile-regime material removal process. Also included in the model is a parameter used to set a process limit defined as the maximum feed rate. Machining experiments have verified the model, and allow for determination of optimum machining conditions.

On the Computational Geometry of Pocket Machining

Abstract: I Introduction.- 2 Survey of contour-parallel Milling.- 3 Survey of direction-parallel milling.- 4 Preliminaries.- 5 Computing Voronoi diagrams.- 6 Implementation issues.- 7 The concept of monotonous areas.- 8 Generating the tool path.- 9 Constructing the mesh.- 10 Generating the tool path.

The prediction of cutting force in ball-end milling

Abstract: Due to the development of CNC machining centers and automatic programming software, the ball-end milling have become the most widely used machining process for sculptured surfaces. In this study, the ball-end milling process has been analysed, and its cutting force model has been developed to predict the instantaneous cutting force on given machining conditions. The development of the model is based on the analysis of cutting geometry of the ball-end mill with plane rake faces. A cutting edge of the ball-end mill was considered as a series of infinitesimal elements, and the geometry of a cutting edge element was analysed to calculate the necessary parameters for its oblique cutting process assuming that each cutting edge was straight. The oblique cutting process in the small cutting edge element has been analysed as an orthogonal cutting process in the plane containing the cutting velocity and chip flow vectors. And with the orthogonal cutting data obtained from end turning tests on thin-walled tubes over wide range of cutting and tooling conditions, the cutting forces of ball-end milling could be predicted using the model. The predicted cutting forces have shown a fairly good agreement with test results in various machining modes.

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

Computer-Aided Process Planning

Abstract: 1. Basic Concepts of Process Planning. Introduction. Manufacturing processes and process planning. Composition of machining processes. Requirements for process planning. Basic information for process planning. Economics of process planning. Chapter summary. 2. Machining Accuracy. Concept of machining accuracy. Methods for obtaining required dimensional accuracy. Factors causing machining errors. Methods for determining machining accuracy. Surface quality. Methods for machining accuracy improvement. 3. Technological References and Dimension Calculation. Need for referencing. Principle of coincidence of references. Selection of locating references. Selection of operational references. Recalculation of dimensions. 4. Process Routing Planning.Tasks involved in process routing planning. Analysis of part drawings. Selection of machining methods. Division of machining stages. Concentration and differentiation of operations. Arrangement of heat-treatment operations. Arrangement of auxiliary operations. 5. Machining Operation Design. Tasks involved in machining operation design. Selection of machine tools and tooling. Determination of machining allowances. Determination of operational dimensions and tolerances. Selection of machining conditions. Estimation of time standards. Process plan documentation. 6. Group Technology. Introduction to group technology. Classification and coding. Production flow analysis. Fuzzy-set based PF formation. 7. Computer-Aided Process Planning Systems. Evolution of computer-aided process planning. Variant or generative? 8. Process Planning Algorithms. Issues in process planning. Process planning knowledge. Operation selection. Intermediate surface determination. Application of methodology to CAPP. Determination of optimal intermediate surface specifications. Operation sequencing. 9. Knowledge-Based Process Planning. Knowledge-based systems. Languages and tools for knowledge-based expert systems. Important issues regarding knowledge-based system projects. Knowledge-based systems and process planning. Knowledge acquisition for process planning. 10. Assembly Process Planning. Introduction to assembly planning. Fundamentals of assembly. Data and knowledge processing for assembly planning. Planning for mechanical assembly. Index.

Machine parameter selection for turning with constraints: an analytical approach based on geometric programming

Abstract: This paper describes the design and development of an analytical tool for the selection of machine parameters in turning. The problem is to determine values for machine speed and feed that minimize the total cost of machining; specifically the costs associated with machining time and cutting tool wear. Geometric programming is used as the basic methodology, and the solution approach for the selection of machine parameters is based on an analysis of the complementary slackness conditions and realistic machining conditions. The quality of the solution is illustrated on several examples and compared to solutions obtained by some optimization methods proposed in the literature. In general, our technique is simple and straightforward and indicates how sensitive the solution is to the machine power consumed and surface finish attained.

NC machining with G-buffer method

Abstract: The G-buffer method is applied to NC machining. A total NC system is created that consists of all essential functions, such as tool path generation, path verification, and feed rate control. Moreover, any combination of object surface and tool shape is acceptable. By utilizing G-buffers created from a parallel projection, the required NC functions are realized as image processing operations. This ensures that the NC software is independent from surface description. Conventional rendering software can be used to make the G-buffers. Any surface can be milled if it can be rendered by parallel projection. Tool shape changes can be easily handled by changing the image processing filters. 3D examples of geometric surfaces, mesh data, and volume data are milled with this method, and the results show that the method is very effective.

The fatigue performance of machined surfaces

Abstract: It is well known that surface condition has a strong effect on fatigue life, and that most surfaces produced by conventional manufacturing operations such as machining and forging have poorer fatigue behaviour than polished surfaces commonly used for laboratory specimens. As yet, there are no reliable quantitative models to predict the behaviour of such surfaces; the problem is a multi-parameter one, involving surface roughness, surface microstructure and residual stress. High-cycle fatigue data was obtained for En19 steel, using four types of machined surface, produced by: polishing, grinding, milling and shaping. Residual stress was eliminated by heat treatment. Fatigue limit data were plotted as a function of roughness parameters using Kitagawa-type diagrams, and compared to simple notch-based and crack-based models. It was found that, whilst both theories tended to be overly conservative, fracture mechanics approaches are useful for relatively low roughness, when the surfaces can be modelled as a series of short cracks. For higher roughness a notch-based approach is appropriate.

Valve and micropump incorporating said valve

Abstract: A valve is formed by machining a silicon wafer 18 bonded to a glass wafer 2. This machining forms a membrane 44 and a sealing ring. Part of the surface of the membrane 44 and optionally the sealing ring are oxidized in order to impart a mechanical pre-tension to the membrane holding the valve in a closed position. Further etching 52 may be carried out in a manner such that in the absence of the aforesaid pre-tension the valve is in the open position at rest.

Fibre orientation and mechanical behaviour in reinforced thermoplastic injection mouldings

Abstract: Process variables, fibre orientation distribution and mechanical properties were inter-related for injection-moulded short-glass fibre-reinforced polypropylene and polyamide and long-glass fibre-reinforced polyamide. The properties of the reinforced grades were also contrasted with those of the base polymer. A rectangular mould with triple pin-edge gates on the same side to facilitate a single melt flow-front or double flow-front advancing adjacently, was employed. Mouldings were evaluated for fibre orientation distribution, and tensile, dynamic mechanical and fracture properties. The relative magnitudes of the shell and the core fibre-orientation persuasions depended on the melt and the mould temperatures, and the injection ram speed. An increase in G c, K c, ultimate tensile strength (UTS) and elastic moduli values and a decrease in tan δ values were observed with fibre reinforcement. The properties showed marked sensitivity to the position of the specimens in the moulding because of the associated variations in the fibre orientation. The prediction of UTS based on a rule of mixture relationship for strength and the Halpin-Tsai equations for elastic moduli had limited success. The predictions were improved by employing measured data representative of regions of high fibre orientation, e.g. knit-line. The estimation was weakened in the material systems containing significant production-induced voids. An inference of the fracture toughness values was that the composites contained flows of the order of 0.2 mm in size, which is conceivable, either as voids or as defects introduced in the machining of the specimens.

Physically vapor deposited coatings on tools: performance and wear phenomena

Abstract: Coatings produced by physical vapor deposition (PVD) enhance the performance of tools for a broad variety of production processes. In addition to TiN, nowadays (Ti, Al)N and Ti(C,N) coated tools are available. This gives the opportunity to compare the performance of different coatings under identical machining conditions and to evaluate causes and phenomena of wear. TiN, (Ti,Al)N and Ti(C,N) coatings on high speed steel (HSS) show different performances in milling and turning of heat treated steel. The thermal and frictional properties of the coating materials affect the structure, the thickness and the flow of the chips, the contact area on the rake face and the tool life. Model tests show the influence of internal cooling and the thermal conductivity of coated HSS inserts. TiN and (Ti,Zr)N PVD coatings on cemented carbides were examined in interrupted turning and in milling of heat treated steel. Experimental results show a significant influence of typical time-temperature cycles of PVD and chemical vapor deposition (CVD) coating processes on the physical data and on the performance of the substrates. PVD coatings increase tool life, especially towards lower cutting speeds into ranges which cannot be applied with CVD coatings. The reason for this is the superior toughness of the PVD coated carbide. The combination of tough, micrograin carbide and PVD coating even enables broaching of case hardened sliding gears at a cutting speed of 66 m min −1 .

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