Showing papers on "Machining published in 1981"

On the Mechanics of Chip Segmentation In Machining

Abstract: The mechanics of chip segmentation, during machining of a cold rolled steel has been investigated from a phenomenological point of view using a high speed movie camera and an explosive quick stop device. The latter was used for obtaining chip root samples at various stages of segmentation for subsequent examination in the Optical and Scanning Electron Microscope (SEM). The chip segmentation process is found to arise as a result of instabilities in the cutting process and is further augmented by the dynamic response of part of the machine tool structure. This process involves a slow forward movement of the plastic boundary in the primary shear zone forming a ramp on the free surface of the chip followed by a rapid return of the plastic boundary back towards the tool forming a step on the chip segment as a result of partial fracture at the free surface. This process is characterized by large strains, low shear angles that oscillate cyclically and stick-slip friction on the rake face. The instability in the cutting process is proposed to be due to the negative stress—strain characteristics of certain materials at large strains, as Walker and Shaw [1] proposed, involving void formation around second phase particles, their propagation into microcracks in the primary shear zone and coalescence of these cracks leading to partial fracture. Evidence for this has been obtained in this investigation.

Machine Tool Vibration

Abstract: In the machining of optical components truth-to-form and surface finish are of critical importance and the adverse effects of vibration must be avoided if satisfactory work is to be produced. This paper discusses the two basic types of vibration encountered in the use of machine tools - forced vibration and chatter, and the ways in which they can affect finished workpieces. Some of the techniques available for investigating and solving vibration problems on machine tools are described and some of the design principles to be considered in reducing the susceptibility of machine tools to vibration are discussed.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

System and method of precision machining

Abstract: A system and method are disclosed for automatically machining a work piece to precise selectively determined dimensions under computer numerical control. A movable probe is calibrated against position reference surfaces and is then used to calibrate the position of a fixed probe. The latter serves as a position reference for calibrating the cutting edge of one or more cutting tools. All calibrations are performed under closed loop control. Appropriate tool position offsets are automatically determined from deviations between the programmed and the actual probe and tool positions and are entered into numerical control means to modify the programmed machining operation. After machining has been initiated, probing of the work piece occurs at least once before the final cut is taken and the appropriate tool position offsets are determined and entered to assure that the dimensions of the finished surface will conform to the desired selectively determined dimensions. Any dimensional deviations which are shown to exist upon probing of the finished surface, are indicated together with the allowable machining tolerances for each dimension.

Effect of Machining Damage on the Strength of a Glass-Ceramic

Abstract: A study has been made of the strength characteristics of machined glass-ceramic surfaces using an indentation flaw technique. The strength is found to decline or increase with progressive removal of the machining damage layer by a polishing procedure, depending on whether the indentation is made after or before the polishing. The results are interpreted in terms of a residual compressive stress in the initial machined surface. It is argued that failure to allow for the contribution of this stress in the fracture mechanics description of flaw growth could lead to significant errors in the evaluation of crack propagation parameters.

Method and device for detecting tool abnormality in machine tools

Abstract: Method and device for detecting tool abnormality in machine tools in which a threshold value is determined based on the condition of a tool in machining and tool abnormality is detected by comparing data successively obtained from the tool during machining with the threshold value. The threshold value is determined by computing the tool condition data in machining for a period when an externally provided switch is on and stored in a memory of the device when the switch turns off. The application of this invention to numerical controlled machine tools is also disclosed in which a plurality of threshold values are determined according to machining conditions in each machining process and tool abnormality is detected by comparing tool condition data during machining with one of the threshold values corresponding to the condition of the machining.

Machining systems and control systems therefor

Abstract: A machining system includes machine tools each capable of performing, in a working area thereof, machining on a workpiece carried on a pallet, a pallet magazine including movable stations each capable of carrying and conveying a pallet and having pallet change positions each associated with each of the machine tools, pallet changers each associated with each of the machine tools and each capable of transferring a pallet between the working area of the associated machine tool and the associated pallet change position, numerical control devices each associated with each of the machine tools and each capable of storing part programs and of controlling the associated machine tool, and a system controller comprising first memory for storing, in relation to each of schedule numbers indicating order of machining, an indicium of a pallet carrying a workpiece to be machined in the related order and an indicium of a part program to be used for machining the related pallet, and second memory for storing, in relation to an indicium of each of the pallets, and indicium of the movable station carrying the related pallet.

Cutting tool retreat and return for workpiece protection upon abnormality occurrence in a preprogrammed machine tool

Abstract: A numerically controlled (NC) machine tool has apparatus for automatically positioning and feeding a cutting tool to follow a programmably predetermined path. Sensing devices are provided to detect when the cutting tool suffers an abnormality, such as becoming dull or chipped. The feed devices of the NC machine tool are then commanded, by an arithmetic unit having a memory and by an NC command generating unit, to automatically retreat the cutting tool. It retreats, without interference with the workpiece, to a first position, parametrically determined by the shape and size of the workpiece, cutting tool data for the abnormality, completion and tool exchange positions, and by the nature of the machining operation. This retreat location is a position at which the cutting tool may be replaced. After replacement of the cutting tool, the cutting tool is automatically returned, via the first position, to a second position from which the machining is resumed. The second position is determined by the arithmetic means to provide for repeated machining of a portion of the surface of the workpiece leading to the position at which the abnormality was sensed.

Analysis of Electro Discharge Machining of Cemented Carbides

Abstract: Summary The difficulties of correlating Electrical Discharge Machining (EDM) process parameters with the surface integrity aspects of machined cemented carbides have been recognized. These difficulties arise not only because of complex and random nature of spark phenomenon but also due to the complex composition and structure of the cemented carbide materials. This paper analyzes the surface profiles of spark eroded cemented carbide workpieces in the light of a recently introduced Data Dependent Systems approach to EDM. The parameters of a model obtained from such an analysis are shown to render fairly accurate values of technological factors such as material removal rate, surface roughness and electrode wear. Various grades of Kennametal cemented carbides are machined with conditions recommended by the CIRP's Scientific Technical Committee E. The application of a thermal model based on the Data Dependent Systems approach to predict material removal rate in this case is demonstrated. The possibility of relating the length of cracks with the machining parameters and material properties using such a thermal model is discussed.

Pulse laser pretreated machining

Abstract: An improved laser-assisted machining process has special application to difficult-to-machine materials such as the titanium alloys and high temperature superalloys. A layer of material to be removed by a cutting tool is made weaker by drilling a series of holes using a pulse laser beam ahead of the cutting process so that the tool removes the rest of the weaker material with relative ease. There is a decrease of cutting forces, breakage of the chip to a manageable size, and reduced tool wear.

Pointed heat-generating device for molds of injection molding machines

Abstract: This invention relates to a pointed heat-generating device for molds of injection molding machines. It comprises a metal casing, a pointed projectile heat-generating means fixed with the metal casing, and a gate formed at the pointed heat-generating means and communicated to a cavity of the molds, characterized in that a heat-generating wire is penetrated wholly into a passage which is bored in a non-processed cylindrical material and an alloy portion is formed in an inert gas between an end of the heat-generating wire and the non-processed cylindrical material, thereby the alloy portion being formed as a pointed part of the heat-generating means by machining.

Process for machining a worm-type workpiece with a worm-type tool

Abstract: A process for dressing a single or multiple-grooved worm or threaded workpiece by a single or multiple-grooved worm or threaded dressing tool includes the turning of the workpiece and tool with the dressing tool in a comb-type contact with the workpiece. By using an additional axial relative movement between the dressing tool and the workpiece, determined by the radial positioning and return movements, the contact points are displaced such that the desired grinding profile is produced on the workpiece. Since the entire surface area of the instantaneous contact points is significantly smaller than the entire profile area of the workpiece, the cutting forces which occur are relatively small, so that high dressing speeds can be obtained. It is also possible to make various flank corrections on the workpiece. The apparatus for carrying out the process is also disclosed.

Electric discharge machining device

Abstract: PURPOSE:To obtain desired peak current value in an electric discharge machining even in the case of a finishing process where the electric discharge current pulse width is extremely short by improving the first transition of the electric discharge current with a compensating current and shortening the last transition period. CONSTITUTION:A low impedance circuit 14 for high frequency is provided in parallel to a machining pulse transmission circuits 10 and 11 to improve the first transition and the last transition delay of the electric discharge current wave figure due to the high frequency impedance in the circuits 10 and 11, a coaxial cable (the circuit 14) constituting a low impedance circuit for high frequency consisting of a machining gap 3 to a D.C. power source 4 and a current limiting resistor 6 via a capacitor 15. When a switching element 6 for the control is turned on by a signal from a control part 7 the voltage is applied to the gap 3 to start the electric discharge. Thus, desired peak current value can be obtained even when the discharge pulse width is extremely short.

The effect of lead on the friction and machining of brass

Abstract: Experiments have been carried out on two αβ-brass alloys of similar zinc content, one containing 2·9% lead and the other being lead free. The experiments were of three types: (i) metal-cutting experiments, (ii) sliding friction experiments and (iii) mechanical-property measurements. The effect of lead was found to be very marked in all three cases. In metal machining, the lead addition caused the rake-face friction force to be reduced by a factor of about 5. Similarly, the coefficient of friction in sliding experiments, using an unlubricated steel hall, was reduced from 0·62 without lead to 0·32 with lead. Chip fracture was found to occur at larger depths of cut when machining the leaded alloy. This feature is related to a large reduction in ductility when lead is present. In a torsion test the shear strain to fracture was reduced by a factor of approximately 3 and a similar reduction was found for the fracture energy in a three-point notched bend test. The results of tensile tests showed that th...

Comparative studies of ecm, edm and ecam

Abstract: The characteristics of electrochemical and electrodischarge machining are compared with electrochemical arc machining, a process which relies on electrical discharge in electrolytes to effect metal removal. Since little is known about the nature of this process, investigations of sparks in dielectrics and electrolytes are reviewed. Some relevant applications of edm and ecm are then discussed, and comparisons drawn with the new process

Electrical contact probe and method of manufacturing

Abstract: A simplified and more economical manufacturing method for the contact head of a spring contact probe is disclosed. Only two passes of a machining tool across the axis of the contact head on orthogonal axes produces a center pyramid contact point, two pairs of surrounding chisel points, and two pairs of contact points in the spaces between the chisel points formed from metal remaining after the two machining passes.

Process for manufacturing thin unitary hollow metal bodies

Abstract: A process for forming hollow bodies of metal materials, particularly of aluminum alloys, based on a suitable combination of mechanical operations comprising deep drawing, stretching, tapering and tool machining, whereby it is possible to obtain essentially cylindrical one-piece metal bodies with a concave dished bottom and a dome-shaped head provided with a beaded opening. The unitary bodies are characterized in that the cylinder walls are very thin, highly strain-hardened and endowed with high mechanical properties, permitting a remarkable reduction in the metal material amount used in the aforesaid enbloc bodies, destined for being used chiefly as pressure containers, for example for aerosol.

Multiple pipe element electrode assembly EDM method and apparatus

Abstract: A multiplicity of conductive pipe elements are arranged in parallel with one another in mutually insulating relationship and are secured together in a cup to form a multiple electrode assembly. The assembly is advanced into a workpiece in the machining feed direction and additionally is displaced relative to the workpiece by a Z-axis motor in a plane orthogonal to the machining feed direction by X-axis and Y-axis motors a distance slightly in excess of the uniform spacing (Gx,Gy) between the pipe electrodes along each of two mutually orthogonal axes in the plane. The additional displacement may be effected alternatively by vibrating the pipe elements transversely to the axes thereof with an amplitude essentially equal to the said distance. For further machining of the same workpiece, a proportion of the pipe elements may be released from the securely held state and individually advanced and/or retracted with rates of movement determining the shapes of the final machined contour. The power supply comprises an AC-DC-HF-DC Pulse inverter having multiple output terminals respectively connected to the multiple pipe elements. Machining liquid is pumped to and from the machining gaps via the pipe elements.

Electrospark machining device

Abstract: PURPOSE:To prevent an accident from occurring, by a method wherein an actual machining feed distance based on instructions from a numerical controller is compared with a distance to be machined which is obtainable through a counted value of a dischrge pulse effective from the machining point of view, through the result of which progress of the machining is controlled. CONSTITUTION:A computing circuit 23 computing a machined distance on the assumption that it has been machined according to a machining feed instruction pulse from a numerical controller 19 is provided, in a device machining a work 10 clamped on a movable table 3 in a Y axis direction with an appropriate device by electric discharge to be generated between the work 10 and a wire electrode 11 under supply of a machining liquid. In addition to the above, a computing circuit 22 computing an actual machining feed distance according to an output pulse from each of motor driving circuits 20, 21 is provided. Whether output pulses from both computing circuits 23, 22 are generated at a fixed ratio or not is inspected by a comparison circuit 24 so that an alarm output circuit 25 is made to operate when a ratio between both distances is exceeded a fixed allowable value.