Showing papers in "Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology in 1986"

A general methodology for machine tool accuracy enhancement by error compensation

Abstract: A general methodology for increasing the accuracy of machine tools by compensating for the inherent systematic errors is described. This methodology in

Automatic laser tracking interferometer system for robot metrology

Abstract: There is a growing worldwide effort to develop internationally accepted procedures and terminology for the measurement and description of robot performance. One of the most difficult problemss is that of determining the positional accuracy of an industrial robot throughout its large work zone. The concept of a 3 d laser tracking interferometer system is described in this paper and preliminary results obtained from a two-dimensional version of the system are presented. The full 3 d system is currently being constructed.

Plasma channel growth and the resolidified layer in edm

Abstract: An analysis for the computation of the plasma channel size, is presented as a function of pulse-on duration in edm . It has been shown that accounting for the effects of the plasma growth leads to marked improvement in analytical results obtained. The paper also suggests a method for evaluating the thickness of the resolidified layer in edm machined workpieces. The analytical values of the resolidified layer thickness agree well with published experimental data.

Micro-electrodischarge machining using water as a working fluid—I: micro-hole drilling

Abstract: Micro-electrodischarge machining ( medm ) using water as a working fluid is systematically studied to find its characteristics. As a result, the unique advantages of high removal rate, low electrode wear and consequently higher working efficiency, without formation of carbonaceous materials are found under optimum experimental conditions, as compared with the case when kerosene is used. This was achieved by the choice of suitable combinations of electrode and workpiece materials and electrode polarity. Use of a tungsten electrode with straight polarity is exceedingly good with respect to high removal rate and low electrode wear. This makes it possible to obtain a non-tapered straight micro-hole around 0.1 mm in diameter with a certain anticipative working gap. The advantageous properties of this machining method are effectively utilized to drill deep micro-holes with a ratio of depth to diameter of the order of 10–17 as in the case of 2.9 mm depth and 0.17 mm diameter, which is superior to the limits achievable with both electrodischarge drilling ( edd ) using kerosene and mechanical drilling with a micro-drill.

In-proces sensors for surface roughness and their applications

Abstract: Potential non-contact optical methods for in-process surface roughness measurement are described, including reflected light position detection, focu

A comparison of different algorithms for circularity evaluation

Abstract: The measurement and evaluation of circularity of cylindrical components is very important for the majority of cylindrical workpieces used in precision engineering. Further, since the measurement and evaluation of cylindricity is more complex and time consuming, only circularity is evaluated for most applications. The evaluation of circularity from a circularity graph and/or from digital data requires a suitable algorithm. The most commonly used criterion for this has been the least squares criterion, though it is known that this does not necessarily give the best solution. Hence, an attempt has been made in this paper to propose different algorithms and compare them. The algorithms considered are based on the methods of least squares, intuition, general second-degree equation for a circle, best-fit ellipse and simplex search. A comparison of these methods is presented.

The development of an electrodischarge machine for micro-hole boring

Abstract: This paper describes an electrodischarge machine † for micro-hole boring capable of improved accuracy and performance in boring precision small diameter holes in components such as ink jet nozzles for printers, electron gun apertures for graphic displays, micro-connectors for high-speed computers, and optical components for telecommunications Micro-energy discharging permits machining of 15–300 μm diameter micro-holes with a roundness accuracy of 05 μm or better and a surface roughness less than 01 μm No bending stress is applied to the tool electrode, therefore high precision machining of cylindrical surfaces, machining with very thin side-walls, and machining of overlapping multiple-holes are all possible, regardless of the hardness of any electrically conductive material Tool electrodes of any diameter are machinable using reversed-polarity electric discharge and are replaceable in the same way as conventional drills Travel of the tool electrode is controlled automatically by microprocessor, thus eliminating the need for a skilled operator

The significance of surface topography in engineering

Abstract: All machining processes leave characteristic topographic features on the surfaces of components. This paper reviews a wide range of examples in which the surface topography of a component has been found to bear a significant effect on its function. Problems in manufacture which are related to surface roughness requirements are also disccused.

Analysis of taper produced in side zone during ecd

Abstract: The full capabilities of electrochemical machining ( ecm ) have not been utilized in production, mainly due to some inherent problems associated with tool design For example, the side wall generated during electrochemical drilling ( ecd ) of a cylindrical hole is tapered To study the effect of process parameters on the taper produced during ecd , experiments were performed using brass as cathode, low alloy steel forgings and castings as anode and aqueous solution of NaCl as electrolyte From the analysis of the results, some useful conclusions have been derived that would be helpful in controlling the taper produced by bare tool, bare bit tool or coated tool

Multi-objective optimization of the ecm process

Abstract: Optimization of process parameters is helpful in efficient working of the process and, hence, in lowering the cost of machining. Optimization of ECM process parameters has been achieved by considering only one objective at a time from metal removal rate, geometrical accuracy, and total process cost. From a practical point of view, a solution of the ecm problem satisfying all three objectives simultaneously is highly desirable. In the proposed model, a multi-objective problem involving the ecm process is formulated producing highly nonlinearized equations. These are then linearized by regression analysis and converted into a goal programming format. Finally, the problem is solved by the partitioning algorithm. It is concluded that the tool, or cathode, remains safe at the optimal values of design variables obtained in the examples discussed. The optimal value of voltage when metal removal rate is the only objective, is found to be higher than the case when the geometrical accuracy requirement is also to be satisfied.

High-speed test of thermal effects for a machine-tool structure based on modal analysis

Abstract: A new test method has been developed to evaluate the temperature rise of machine-tool structures. In this method, which uses short period data obtained during a warm-up run, the machine-tool structure is modelled by the finite element method (FEM) and is analysed in terms of the eigenvalues of the thermal equation. Characteristic temperature rise curves for the structure are obtained, which have variable parameters. The values of these depend upon the strength of heat sources. Then, by determining the parameters such that the characteristic temperature rise curves fit those obtained during a warm-up run, it is possible to identify the strength of the heat sources, and thus the values of temperature rise for any point in the structure. Experiments have been carried out which verify the effectiveness of the method.

A new method for determining geometric accuracy in the axis of movement of machine tools

Abstract: Measurements of geometric accuracy in machine tools, especially of errors in moving machine parts against their theoretical axes, are taken by means of displacement pick-ups moving along a reference standard1,2, such as a cylindrical test specimen. This procedure is impeded by physical form errors in the standards, especially for heavy machines, as well as by adjustment errors in the standards against the machine part to be measured. These disadvantages can be avoided by using a non-material standard like a laser beam with a four quadrant photodiode as sensor and a special analysis of the measurement data.

Roughness form and waviness measurement by means of light-scattering

Abstract: This paper deals with a non-contact, optical measuring method which unites the assessment of roughness form and waviness in one single instrument. The

Factors affecting component measurement on coordinate measuring machines

Abstract: It can often be difficult to find a complete relationship between the specified performance of a coordinate measuring machine ( cmm ) (see Fig 1) and actual results obtained, because of unexplained differences between them. This report explain one method of identifying these differences and discusses some sources of error which may give rise to them.

Chemical machining as a precision material removal process

Abstract: The adaptation of a photochemical machining process to replace a precision machining operation is presented An ultrasonically activated photoresist was used to establish the cutting boundary, and an etchant was used as a cutting tool to remove material from the workpiece This precision material removal process proved to be highly effective when compared to more conventional precision machining techniques

Fabrication of fine apertures in metal foils by photoelectrochemical milling

Abstract: The potential of a photofabrication process involving photolithography and electrochemical milling has been established for the production of accurate holes in a range of sheet materials (10–500 μm thick), including molybdenum, platinum, Pt-10Rh, sterling silver, carat gold and silver- and palladium-based alloys. Based on scanning electron microscopy, the new technique shows its unique capability of producing high quality components in materials which were hitherto considered to be difficult or impossible to fabricate. Furthermore, the technique does not involve the use of any highly toxic or aggressive chemicals; a non-passivating neutral solution of sodium chloride is used as the electrolyte. Details of the type, concentration and application of the electrolyte are discussed. The technique appears to be potentially attractive to the manufacturers of fine apertures and similar intricate shapes of industrial components and jewellery items.

A high precision straight-motion system

Abstract: In this system, a steel block is completely floated by air pads mounted on a mechanical sliding table When the table moves, the vertical and horizontal positions and the pitch, roll and yaw angles of the block change because of the misalignment of the sliding table These changes are detected against references by optical and electronic devices and the positions and angels of the block controlled by changing the supply pressure to each pad Straight-edge masters and a laser straightness interferometer are used as the references for vertical and horizontal straightnesses, and autocollimators are used to detect the change in pitch and yaw angle attitudes As a reference to the roll angle attitude, the two straight-edge masters are used The working length of the system is 1 m The positional errors of the block motion with respect to the references are less than 01 and 04 μm and the angular changes are less than 02 s of arc

Factors affecting the machining accuracy of a chucked workpiece

Abstract: A deviation in shape called ‘out-of-roundness’ is commonly observed in machined workpieces held by three-jaw chucks in turning operations. This out-of-roundness is due mainly to the variation in the stiffness of the workpiece-chuck-spindle system; the stiffness being higher when the cutting force is acting against a jaw and lower when acting along a jaw. This variation in stiffness of the workpiece-chuck-spindle system, termed here ‘directional orientation’, also leads to the generation of a type of parametric vibration. An attempt has been made to get rid of this effect of directional orientation by optimizing the contact between the jaw face and workpiece. Cutting tests were conducted on tapered testpeices with full contact between the jaws and the testpiece. Various contact chord lengths and spindle speeds were used. Measurements of out-of-roundness, limiting depth of cut and radial cutting force were made for analysis. Results show that where the deviation in shape of the testpiece has a three-pronged profile, and the peak at the third multiple is significant in the frequency spectrum of the radial cutting force, a contact chord length equal to the radius of the testpiece gives the optimized clamping condition.

Accuracy of work-pieces produced by one-pass creep feed grinding

Abstract: Work-piece profile and dimensional errors are caused by the following three major factors: elastic deflection between wheel and work-piece, wheel wear, and thermal deformation of work-piece. This paper aims to clarify comprehensively and quantitatively the effect of these factors on the accuracy of a work-piece produced by one-pass creep feed grinding ( cfg ). Among these factors, the effect of the thermal deformation of the work-piece has not been well understood because of the inherent difficulty in predicting the temperature distribution of the work-piece. In the present study, the work-piece temperature distribution is analysed by a three-dimensional finite element method ( fem ) where the cooling effect of the coolant is measured and the energy transfering as heat into the work-piece is timated by Jaeger's moving heat theory extended to include the cooling effect. From this, the thermal deformation of the work-piece is estimated by Jaeger's moving heat theory extended to include the cooling effect. From this, the thermal deformation of the work-piece is also predicted by fem .

An investigation into the assessment of surface finish by microwave reflection

Abstract: Non-contact methods are ideal for in-process monitoring of surface finish. In this context, the application of microwave reflection for the assessment of roughness assumes significance. It is well known that surface roughness affects the reflection of microwaves, and the energy loss in their transmission is considerably influenced by the finish of the wave guides. Experimental investigations were conducted with a sweep oscillator and reflectometer to find the feasibility of this technique in monitoring the roughness of manufactured surfaces. A number of surface specimens produced with different machining operations were measured for the return loss, and these compared with the normal roughness values. This paper deals with the experiments conducted and results obtained in these investigations.

Evaluation of conditional multiple concentric circular arcs

Abstract: Measurement and evaluation of circularity of cylindrical components is well established using roundness measuring instruments, but when circular track Problems of this and more complex nature have been faced while evaluating the tool-changer arm-holder tracks of NC machines. Since no methods are avail

Analysis of surface finish in milling by power spectral density measurement

Abstract: The power spectral densities ( psd ) of surface profiles of milled steel samples have been determined by analogue measurement techniques, ie by a spectral analyser. The recorded psd curves indicate the presence in the surface profiles of some periodic components. Increase of cutting speed during milling causes the spectral density values to decrease. By psd measurement it was possible: to distinguish between surface profiles with the same R a value, but milled under different cutting conditions; and to detect axial run-out of the milling cutter, which results in waviness of machined surfaces.

Automatic restart control system for electrochemical machining

Abstract: This paper describes the development of a microprocessor-based automatic restart control system ( arcs ) capable of eliminating flaws caused by restarts during the electrochemical machining ( ecm ) process. This makes ecm a viable cost-effective technique for producing precision parts previously handled by conventional methods.