Showing papers on "Machining published in 1993"

Effect of Tool Edge Geometry on Energy Dissipation in Ultraprecision Machining

Abstract: Summary An experimental study of the effect of single crystal diamond tool edge geometry on the resulting cutting and thrust forces and specific energy in the ultraprecision orthogonal flycutting of Te-Cu was made. The effects of both the nominal rake angle and tool edge profile were investigated over uncut chip thicknesses from 20μm down to 10 nm. Characterization of the tool edge was performed with the use of atomic force microscopy. Both the nominal rake angle and tool edge profile were found to have significant effects on he resulting forces and energies.

Chip Formation in the Machining of Hardened Steel

Abstract: With the availability of polycrystalline cubic boron nitride (PCBN) it is possible to machine very hard gears, etc. at speeds of (60–150 m/min = 200–500 fpm). When this is done using PCBN tools in face milling, Chip formation is of a cyclic saw toothed type. This type of chip formation is reviewed in relation to other types of cylic and noncyclic chip formation. The root cause of high frequency, saw toothed chip formation is found to be periodic gross shear fracture extending from the free surface of the chip toward the tool tip and not adiabatic shear as commonly believed.

Cutter-location data optimization in 5-axis surface machining

Abstract: A method of generating ‘optimal’ cutter-location data for 5-axis NC contour milling from given cutter-contact data is presented in the paper. The cutter-location data-optimization problem is formulated as a 2D constrained minimization problem. The cutter orientation angles consisting of the tilt angle α and yaw angle β are used as decision variables. An analytic expression for approximate cusp heights is derived as a function of α, β (for a given path interval) to be used as a measure of optimality. The proposed optimization scheme has been successfully applied in the 5-axis face milling of large marine propellers.

Real-time Compensation for Time-variant Volumetric Errors on a Machining Center

Abstract: An error compensation system has been developed to enhance the time-variant volumetric accuracy of a 3-axis machining center by correcting the existing machine errors through sensing, metrology, and computer control techniques. A general methodology has been developed to synthesize both the geometric and thermal errors of machines into a time-variant volumetric error model. Instead of the well-known 21 geometric error components, 32 machine linkage errors are formulated as a 4D error field including the space domain and the time domain. Different types of models are proposed for different kinds of thermal error components. A compen­ sation controller based on an IBM/PC has been linked with a CNC controller to compensate for machine errors in real time. This scheme has been implemented on a horizontal machining center and has been shown, using metrology instruments, to improve the machine accuracy by an order of magnitude. A cut workpiece in­ spected using a coordinate measuring machine (CMM) has also shown that di­ mension errors have been reduced from 92.4 fim to 18.9 \x,m in a dimension of 404 x 310 mm2 and the depth difference of milled surf aces has been reduced from 196 fim to 8 fim.

Laser machining of ceramic cores

Abstract: A method is disclosed for producing a hollow airfoil, specifically, a blade or vane for a gas turbine engine, which is formed with a complex interior for cooling purposes. Broadly, the method comprises the steps of molding a green ceramic core having outer surfaces generally contoured to produce the intended interior surfaces of the completed airfoil, heating the green ceramic core to a sufficient extent to produce a fired core, and operating on the fired core with a laser to modify the characteristics of the fired core. Use of the laser enables the formation of detailed features having a transverse dimension less than approximately 0.020 inches. Specific operations may include labeling, trimming, cutting, drilling either by punching or trepanning, etching or milling, and glazing or strengthening. In another embodiment of the invention, a layer is produced on the core surface having a very high surface energy to promote the flow of the casting alloy around the core within the mold.

Control of Machining Processes

Abstract: This paper reviews the important recent research contributions for control of machining processes (e.g., turning, milling, drilling, and grinding). The major research accomplihsments are reviewed from the perspective of a hierarchical control system structure which considers servo, process, and supervisory control levels. The use and benefits ad advanced control methods (e.g., optimal control, adaptive control) are highlighted and illustrated with examples from research work conducted by the authors

Determination of optimal cutting conditions using design of experiments and optimization techniques

Abstract: In process planning or NC part programming, optimal cutting conditions are to be determined using reliable mathematical models representing the machining conditions of a particular work-tool combination. The development of such mathematical models requires detailed planning and proper analysis of experiments. In this paper, the mathematical models for TiN-coated carbide tools and Rochling T4 medium carbon steel were developed based on the design and analysis of machining experiments. The models developed were then used in the formulation of objective and constraint functions for the optimization of a multipass turning operation with such work-tool combinations.

A study on the influence of workpiece properties in ultrasonic machining

Abstract: In ultrasonic machining (USM), brittle materials are machined by repeated impacts on the workpiece through a medium of abrasive slurry. Material removal rates are influenced by the various process parameters including the properties of the workpiece material. In this investigation, the influence of fracture toughness and hardness of workpiece materials are studied and reported. Fracture toughness is found to be an important parameter. Experiments are conducted with both conventional and rotary USM modes. Machining performance in the rotary mode is found to be much superior to the conventional mode. The results of static, sliding and rolling indentation tests reported by other investigators are used for explaining the importance of the fracture toughness.

Experimental and finite element predictions of residual stresses due to orthogonal metal cutting

Abstract: The development and implementation of a finite element method for the simulation of plane-strain orthogonal metal cutting processes with continuous chip formation are presented. Experimental procedures for orthogonal metal cutting and measurement of distributions of residual stresses using the X-ray diffraction method are also presented. A four-node, eight degree-of-freedom, quadrilateral plane-strain finite element is formulated. The effects of elasticity, viscoplasticity, temperature, friction, strain-rate and large strain are included in this formulation. Some special techniques for the finite element simulation of metal cutting processes, such as element separation and mesh rezoning, are used to enhance the computational accuracy and efficiency. The orthogonal metal cutting experiment is set-up on a shaper, and the distributions of residual stresses of the annealed 1020 carbon steel sample are measured using the X-ray diffraction method. Under nominally the same cutting conditions as the experiment, the cutting processes are also simulated using the finite element method. Comparisons of the experimental and finite element results for the distributions of residual stresses indicate a fairly reasonable level of agreement. The versatility of the present finite element simulation method allows for displaying detailed results and knowledge generated by orthogonal metal cutting processes, such as the distribution of temperature, yield stress, effective stress, plastic strain, plastic strain-rate, hydrostatic stress, deformed configuration, etc. Such knowledge is useful to provide physical insights into the process as well as to better design the process for machining parts with improved performance.

Laser machining apparatus and method

Abstract: A method and apparatus for detecting the machining status of a laser beam machining device, having a multi-mirror resonator for generating a machining beam, which utilizes the secondary light generated by the machining operation and returned from the workpiece surface into the resonator for control of the machining operation. The oscillator and accompanying components, such as beam dividing mirrors and splitters, are operative to separate the secondary light from the laser beam within the resonator and direct the two beams separately to detectors located outside of the resonator. Alternatively, the secondary light and laser beam may be directed to the outside together where they are separated by an integrating sphere for detection.

Nearly arc-length parameterized quintic-spline interpolation for precision machining

Abstract: The paper presents a method of interpolating a set of discrete data points to form a composite quintic spline for application in precision machining. Precision machining requires tight machining tolerance, i.e. the preselected data points on the original curve are approximately evenly distributed according to a small total curvature between two consecutive data points. With this restriction, the resultant composite quintic splines, in comparison with cubic splines, are closer to being arc-length parameterized. The quintic splines are also likely to have shapes that are close to those of the original curves with no unwanted high-order oscillations. Curves with these properties should be useful for reverse engineering and online motion-command generation for precision machining.

Development of an Intelligent Machining Center Incorporating Active Compensation for Thermal Distortion

Abstract: An intelligent machining center that employs thermal actuators to actively compensate for thermal deformation has been designed, constructed and tested. The machining center also incorporates an intelligent controller, force and deformation sensors and fail-safe mechanism to protect against catastrophic failure of the system. Both matrix control techniques and neural network approaches to the control of the thermal deformation of the machine structure have been tested. In both cases, the measured maximum thermal deformation was controlled to a level of 10 micrometers, approximately 1/3 the level of the uncontrolled machine.

Method and apparatus for machining a workpiece

Abstract: An apparatus machines a workpiece by a rotating cutting tool having at least one coolant channel extended toward the free end thereof with high-pressure coolant jetting onto the free end of the cutting tool. The coolant has sufficient pressure and flow rate to remove the heat and the chips generated during the machining. The cutting tool is fed in a path suitable for each machining operation with the cutting edges being advanced into the workpiece in a reverse direction to the feed direction. The apparatus can machine a workpiece of a material having high hardness and high toughness.