Yoshiyuki Uno

Electrode Jump Motion in Linear Motor Equipped Die-Sinking EDM

The effects of electrode jump parameters on machining speed and depth were experimentally investigated in linear motor equipped electrical discharge machining. A new definition named Machining speed break point is introduced, theoretically calculated from a proposed electrode jump and debris exclusion model, and compared with the experimental results. Additionally, an algorithm is developed to calculate the accumulation of debris in machining gap. The algorithm showed that the debris concentration in gap rises suddenly before the machining speed break point.

High Performance Slicing Method of Monocrystalline Silicon Ingot by Wire EDM

In this study, the slicing of silicon ingot by wire EDM is discussed, and the machining properties are experimentally investigated. Also, the accuracy of sliced wafer and the contamination on the machined surface are evaluated. Experimental results made it clear that the accuracy of wafer by this slicing method is almost the same as that by the conventional methods, and even higher slicing speeds are possible when multi type wire EDM slicing can be realized. Additionally, the contamination due to the adhesion and diffusion of wire electrode material into the sliced surface can be reduced by wire EDM under the condition of low current and long discharge duration. Therefore, wire EDM has a high potential as a new slicing method for monocrystalline silicon ingot.

Deformation characteristics of plastics in YAG laser forming

Plastic material can be also bent by laser forming in the same way as metal material, and larger bending angle can be obtained as compared to metal material. However, its deformatio nmechanism has not been yet clarified. Therefore, in this study, the machining characteristics and the deformation mechanism of plastic in YAG laser forming were made clear by experimental and numerical analysis. Small temperature gradient was obtained by thermal analysis in laser forming of high density polyethylene. The plastic material could be bent due to high viscoelasticity in spite of small temperature gradient. Specimen was first bent by the temperature gradient in thickness direction in a few seconds after the laser irradiation. Then, the temperature of specimen became almost the same in thickness direction, and the temperature gradient appeared only in side direction. Therefore, the deformation of specimen was occurred by the contraction of specimen in side direction and the effect of initial shape, which was deformed by the temperature gradient just after the laser irradiation. Besides, it was clarified that small thermal conductivity of plastic material lead to low cooling speed. Therefore, sufficient cooling time is necessary in order to control the deformation accurately, since the temperature of specimen should be kept equal before every laser irradiation.

Precision micro cutting of thin steel plate with newly designed laval nozzle by pulsed YAG laser

This paper deals with laser cutting of thin steel plate by pulsed YAG laser using newly designed Laval nozzle. The assist gas flow spouted from the Laval nozzle dose not have Mach Shock Disk in free jet, and its straightness is superior to a traditional convergent nozzle. Therefore, the pressure on workpiece increases, and the dross height can be reduced remarkably even under low supply gas pressure condition. Thus, the consumption of flow quantity of assist gas can be reduced, when the dross height is equal. Besides, color change by excessive oxidation due to the heat conduction from dross is smaller at the back side of workpiece around the kerf, since Laval nozzle can remove melted material more effectively compared to a convergent nozzle. However, the supplied gas pressure should be carefully set, since Laval nozzle has many unstable regions, where the pressure on workpiece changes periodically. The dross height dose not increase or almost equal in the case of Laval nozzle, when the gap distance between the nozzle tip and the workpiece surface is changed from 1mm to 2mm. Because the assist gas flow from Laval nozzle has an excellent straightness and the pressure on workpiece does not reduce drastically. Moreover, it was made clear that Laval nozzle designed for the special condition can reduce the dross more effectively and decrease the unstable region.This paper deals with laser cutting of thin steel plate by pulsed YAG laser using newly designed Laval nozzle. The assist gas flow spouted from the Laval nozzle dose not have Mach Shock Disk in free jet, and its straightness is superior to a traditional convergent nozzle. Therefore, the pressure on workpiece increases, and the dross height can be reduced remarkably even under low supply gas pressure condition. Thus, the consumption of flow quantity of assist gas can be reduced, when the dross height is equal. Besides, color change by excessive oxidation due to the heat conduction from dross is smaller at the back side of workpiece around the kerf, since Laval nozzle can remove melted material more effectively compared to a convergent nozzle. However, the supplied gas pressure should be carefully set, since Laval nozzle has many unstable regions, where the pressure on workpiece changes periodically. The dross height dose not increase or almost equal in the case of Laval nozzle, when the gap distance betwee...

High Efficiency Electrical Discharge Machining with Graphite Electrode

High speed cutting of metal mold by machining center has recently been developed, and it has gradually taken the place of EDM, since the machining efficiency of EDM process is smaller than that of cutting one. From this point of view, higher efficiency EDM is greatly expected to be realized. However, EDMs ability has never been sufficiently displayed, since the machining condition is usually set to avoid the unstable machining. In general, excessive stagnation of debris between the electrode and workpiece leads to an occurrence of arc phenomenon and a generation of heat resolved carbon. Therefore, the exclusion of debris from the working gap is very important for stable machining. It has conventionally been carried out with absorbing or flushing of dielectric fluid through the holes drilled in the electrode or the workpiece, or jumping motion of the electrode. However, these methods have disadvantages such as the time necessary to machine holes or the low machining efficiency.In this study, a new excluding method of debris using the rapid flow due to evaporation of dielectric fluid is proposed, and the EDM characteristics of this method are experimentally discussed. As a result, it was made clear that higher efficiency EDM can be attained by this method and that debris can be smoothly removed when the discharge current is large, the gap is narrow and the pulse interval time is short as far as the machining is stable.

Study on Dross Generation in Fine Machining with Pulsed YAG Laser

YAG laser has actively been used for precision micro machining, since it has become possible to get stable and high quality beam and the spot diameter can be focused less than 100 micrometers. High energy beam machining with YAG laser or CO2 laser is heat energy machinig accompanied with heating, fusion, evaporation processes, therefore the adhesions of spatter and dross to base material lead to the deterioration of machining integrity. In this paper, the dross generation mechanism in precision micro cutting of thin plate with pulsed YAG laser is experimentally investigated.Main conclusions obtained are as follows:(1) In a single pulse machining, the spatter scatters on the base material surface at irradiation side and the dross sticks around the hole at exit side.(2) Oxygen assist gas makes the mobility of melting material increase, which leads to the decrease of the adhesion of dross.(3) The height of dross is greatly affected by the beam overlap rate, and it takes maximum when the beam overlap rate is about 93%.(4) The dropout phenomenon of dross is occurred when the beam overlap rate is more than 96%.(5) The generation of dross is restrained by shortening the gap distance between the nozzle of assist gas and the workpiece.

Fundamental study on form grinding. (3rd report). V-profile groove grinding of fine ceramics.

V-profile groove grinding process of fine ceramics with a formed metal-bond diamond wheel is experimentally investigated, analyzing initial profile of formed wheel, wheel wear, stock removal, grinding force, number of cutting edges on working wheel surface and so on, comparing with those in grinding metals with WA vitrified-bond wheel. Main results obtained are as follows : (1) Initial profile of formed metal-bond diamond wheel is expressed by an isosceles triangle whose top is rounded like that of WA wheel, but the tip radius of diamond wheel is much larger than that of WA wheel. (2) The number of cutting edges on working wheel surface is approximately constant and is not affected by different positions along wheel width and different angles of formed wheel, which is different from that in WA wheel. (3) The ratio of wheel wear to grinding length in steady wear region is decided only by initial cutting depth and is not affected by different positions along wheel width and different angles of formed wheel.

A quantitative analysis of grinding process of partially stabilized zirconia.

In order to describe quantitatively the grinding process of partially stabilized zirconia (PSZ) with metal bonded diamond wheel, the analytical method established for metal grinding is applied to the grinding process of fine ceramics, and the theoretical values are compared to the experimental values. It is made clear that the plunge grinding process of PSZ with metal bonded diamond wheel can be represented by five independent characteristic parameters such as the size generation acceleration, the wheel wear rate, the grinding system stiffness, the contact stiffness and the cutting stiffness. By the characteristic parameters, variations of the grinding force, the stock removal, the residual stock through a grinding cycle and the grinding cycle time can be predicted.

Fundamental study on form grinding. (2nd report). Grinding process of V-profile groove.

Grinding process of V-profile groove with a formed wheel is experimentally investigated, analyzing initial profile of formed wheel, wheel wear, stock removal, number of cutting edges on working wheel surface, bonding strength of a cutting edge and so on. Main results obtained in this paper are as follows : (1) Initial profile of formed wheel is different from ideal one at tip zone of V-profile. (2) The number of cutting edges increases with increasing depth from wheel surface, increasing distance from the center of wheel width and larger formed angle of wheel. (3) The bonding strength of a cutting edge increases with an increase of formed angle of wheel. (4) The ratio of wheel wear to grinding length is decided only by real cutting depth and is not affected by grinding length and different positions along wheel width. (5) The generated groove angle as compared with formed angle of wheel becomes larger with an increase of grinding length because of wheel wear.

Cylindrical plunge grinding process of sialon.

Cylindrical plunge grinding process and surface generation process of Sialon are experimentally investigated with bronze bond diamond wheel, analyzing grinding force, surface roughness, wheel wear, ground surface and so on. Main conclusions obtained in this study are as follows : (1) In a cylindrical plunge grinding process of Sialon with bronze bond diamond wheel, there are three distinct grinding processes such as spark-in, steady and spark-out. (2) Ground surface is formed by plastic deformation as well as brittle fracture in grinding Sialon. (3) Diamond grain primarily wears in attrition. (4) Grinding force increases with an increase of setting depth of cut, while surface roughness is hardly influenced by setting depth of cut.