Electrodeless electrolytic dressing grinding method and apparatus

Abstract: A semi-conductive grindstone (10) comprising grains and a semi-conductive bonding part to fix the grains is prepared, a voltage is applied between the grindstone and the conductive workpiece (1), an conductive grinding fluid is supplied between them, the grindstone is contacted to the workpiece, the bonding part of the grindstone is subjected to electrolytic dressing in the contact point, and the workpiece is simultaneously ground by using the grindstone. A semi-conductive bonding part is preferably composed of metal powder and an insulating resin. Consequently, application is possible to peculiar grindstone such as ball-nose grindstone, grinding process of the workpiece is simultaneously possible with dressing of the working surface of the grindstone by electrolytic dressing, and thus, long time grinding is also possible maintaining high efficiency and high preciseness.

Description: The present invention relates to an electrodeless electrolytic dressing grinding method and apparatus capable of grinding of a workpiece and dressing the working surface of a grindstone simultaneously, in accordance with the preamble of claims 1 and 3. Such a method and an apparatus is already known from prior art document JP 8257912 A, showing a grindstone, wherein a voltage is applied between the grindstone and a workpiece by a voltage supplying means. The workpiece and the grindstone are merged in a fluid. The grindstone is composed of abrasive grain and a conductive resin matrix. For example, there are following problems in finishing process of a mold having a free form surface: low degree of freedoms of shape in copy process with a grindstone, necessary correction of the grindstone. Besides, profile process with a straight grindstone restricts the profiling shape due to the low degree of freedom of the diameter and the tip radius of the grindstone and a process machine itself. Further, the problems of a blade-like (thin blade) grindstone are that a working surface like a point causes a rough finished surface, and process preciseness is lowered by deflection of the grindstone. Therefore, it is most suitable for finishing process of the mold by using a so-called ball-nose grindstone of which tip is round. However, finishing process of a free surface using the ball-nose grindstone causes lowering of grinding efficiency after a short time and requires frequent dressing of the grindstone in offline. It is because that in-process dressing of the grindstone is impossible. This causes problems that are time consuming and difficult to reset the position of the grindstone resulting in low preciseness produced. On the other hand, electrolytic in-process dressing grinding (hereafter, ELID grinding) was developed and published by the present applicants as a grinding means to achieve high efficient and ultra-precise mirror surface grinding that has been considered as impossible by conventional grinding art. In the ELID grinding, conductive bonding part of a metal bond grindstone is dissolved by electrolytic dressing, therefore dressing and grinding are done simultaneously. The present grinding method allows efficient mirror finish for an ultra-hard material by using a metal bond grindstone having fine grains and has a characteristic capable of achieving high efficiency and ultra-preciseness. However, the ELID grinding requires in-process electrolytic step for the grindstone and therefore, a space for installation of electrodes other than a working part is essential. Thus, such grindstone as the ball-nose grindstone having a small working surface of the grindstone and a peculiar shape has a problem to be difficult of installing electrodes near the working surface of the grindstone. In order to solve these problems, the applicants of the present invention previously created "an electrolytic interval dressing grinding method" and submitted an application (Japanese Patent Gazette No. 1992-115867). In this method, as diagrammatically shown in Fig. 1, an electrode 3 is installed with a gap from the objective grinding material 1 (workpiece), an conductive grindstone 2, to which a voltage has been applied, is repeatedly moved between the workpiece 1 and the electrode 3, and a conductive grinding fluid is supplied between the conductive grindstone 2 and the workpiece 1 to carry out alternately electrolytic dressing and grinding process. However, it is a problem that grinding by this method is inefficient and application to a peculiar grindstone such as the ball-nose grindstone is difficult, because of requiring alternation of electrolytic dressing and grinding process. Further, the applicants of the present invention created "an electrolytic dressing method and apparatus using an electrode contacting to a semiconductor" and submitted an application (Japanese Patent Gazette No. 1994-170732). In this means, as diagrammatically shown in Fig. 2, an conductive grinding fluid is supplied to a gap between the conductive grindstone 2 having a contact surface to the workpiece 1 and the electrode 3 made of a semiconductor material and contacted to the working surface, a voltage is applied between the grindstone 2 and the electrode 3, and the grindstone 2 is subjected to dressing by electrolysis. For reference, 4, 5, and 6 represent a brush, an electric power source, and a nozzle. The electrode 3 consisting of a semiconductor material allows electrolytic dressing of the grindstone by direct contact to the contacting surface (working surface) of the grindstone 2. This means also has a problem that application to a peculiar grindstone such as the ball-nose grindstone is difficult. The present invention has been created to solve said various problems. The purpose of the present invention is to provide grinding method and apparatus to allow applying to a peculiar grindstone such as the ball-nose grindstone, grinding process simultaneously dressing the working surface of the grindstone by electrolytic dressing, and thus, long time grinding maintaining high efficiency and high preciseness, wherein at the same time the sparking problem between the grindstone and the workpiece can be prevented. This object is met by the features of claims 1 and 3. According to the method and apparatus of present invention, sparks generated between the semi-conductive bonding part and the workpiece can be prevented, the bonding part of the grindstone is subjected to electrolytic dressing in the contact point to dress the grindstone by contacting directly the semi-conductive grindstone (10), that is composed of grains and the semi-conductive bonding part to fix grains, to the workpiece having electrical conductivity, applying a voltage between them by a voltage applying means (12). Therefore, the workpiece can be simultaneously ground for process in the condition of contacting the grindstone to the workpiece as it is. According to the preferred embodiment of the present invention, the semi-conductive bonding part is composed of mixture of metal powder such as copper powder and an insulating resin such as phenol resin. The semi-conductive bonding part can be set to have an electric resistance, that allows smooth electrolytic dressing operation without generating sparks, by changing mixing proportion (for example, 7:3) of metal powder and the insulating resin based on the component. It is preferable that the semi-conductive grindstone (10) is a ball-nose grindstone. Applying the method and apparatus of present invention by using the ball-nose grindstone allows finishing process of a mold, etc. having a free surface by grinding continuously maintaining high efficiency and high preciseness for a long time. Other purposes and benefit characteristics of present invention are known from the following description with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagrammatic view of a prior art by the applicants of the present invention. Fig. 2 is another diagrammatic view of a prior art by the applicants of the present invention. Fig. 3 is a structural diagrammatic view of an electrodeless electrolytic dressing grinding apparatus. Fig. 4 is a diagrammatic view of a semi-conductive bonding part. Fig. 5 is a structural diagrammatic view of another electrodeless electrolytic dressing grinding apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Herewith, the preferred embodiment of the present invention will be described with reference to the drawings. The same symbol is given to a common part in respective figures to omit a duplicate description. Fig. 3 is a structural diagrammatic view of an electrodeless electrolytic dressing grinding apparatus of the present invention. In this figure, the electrodeless electrolytic dressing grinding apparatus of the present invention has the semi-conductive grindstone (10), a voltage applying means (12), and a supplying means (14) of grinding fluid. In the mode for carrying out the claimed invention, the semi-conductive grindstone (10) is the ball-nose grindstone and comprises the shank 10a of the grindstone made of a metal with a high electric conductivity and the hemispheric grindstone part 10b installed in the tip (the bottom of the figure) thereof. The shank 10a of the grindstone is driven in high speed by a driving means around the center of core of the shank, and controlled in Z direction (top and bottom directions) according to numeric control. The grindstone part 10b of the semi-conductive grindstone 10 is composed of grains such as diamond or CBN and the semi-conductive bonding part to fix the grains. In addition, the semi-conductive bonding part is a mixture made of conductive metal powder and the insulating resin, and for example, formed by mixing and melting metal powder and the insulating resin. Copper powder is, for example, preferable for metal powder and other metal powder is also usable. A phenolic resin is, for example, preferable for the insulating resin and other insulating resins are also usable. The proportion of metal powder and the insulating resin is determined to obtain an appropriate electric resistance, prevent sparking phenomenon positioning of the resin between the workpiece, and operate an appropriate electrolytic dressing. The proportion of copper powder and the phenolic resin in combination of them is preferably around 7:3. The voltage applying means 12 comprises an electric power source 12a, a brush 12b, and an electric line 12c connecting a workpiece 1, the shank 10a of the grindstone, and the electric power source, and applies a voltage between the grindstone 10 and the workpiece 1. The electric power source 12a is preferably ELID power source of constant current capable of supplying pulsed direct current voltage. The brush 12b, in this embodiment, directly contacts to the outer surface of the shank 10a of the grindstone and applies a plus voltage to the grindstone 10 and minus voltage to the workpiece 1. The workpiece 1 is installed in X-Y table 17 that sandwich the insulator 16, and controlled in horizontal directions according to numeric control. The supplying means 14 of grinding fluid has a nozzle 14a aligned toward the contact part of the grindstone unit 10 with the workpiece 1 and a grinding fluid supplying line 14b to supply conductive grinding fluid to the nozzle 14a, and supplies conductive grinding fluid to the contact part of the grindstone 10 (specifically, the grindstone unit 10b) with the workpiece 1. According to the method for electrodeless electrolytic dressing grinding of the present invention using the electrodeless electrolytic dressing grinding apparatus, a voltage is applied between the semi-conductive grindstone 10 and the workpiece 1, and the conductive grinding fluid is supplied between the grindstone and the workpiece, the grindstone 10 (the grindstone unit 10b) with the workpiece 1 for grinding process the workpiece 1 by the grindstone 10. According to these steps, sparks generating between the semi-conductive bonding part and the workpiece 1 can be prevented and the bonding part of the grindstone can be subjected to electrolytic dressing in the contact point to dress the grindstone, because the semi-conductive grindstone 10 is composed of grains and the semi-conductive bonding part to fix grains. Therefore, the workpiece can be ground for process in the condition of contacting the grindstone 10 to the workpiece 1, as it is, simultaneously with dressing. Fig. 4 is a diagrammatic view of a semi-conductive bonding part. As shown in this figure, the semi-conductive bonding part comprising the semi-conductive grindstone 10 is, as described before, a mixture made of conductive metal powder (shown with ) and the insulating resin (shown with ○), and for example, formed by mixing and melting metal powder and the insulating resin. Therefore, sparking phenomenon is prevented by presence of the resin between metal powder and the workpiece on the basis of that the semi-conductive bonding part is located between the workpiece 1 and an conductive member such as the shank 10a of the grindstone and the semi-conductive bonding part has an appropriate electric resistance, and appropriate electrolytic dressing occurs under the presence of the conductive grinding fluid keeping direct contact of the grindstone 10b with the workpiece 1. Therefore, for example, applying the method and apparatus of the present invention by using the ball-nose grindstone allows finishing process of a mold, etc. having a free form surface by grinding continuously maintaining high efficiency and high preciseness for a long time. Fig. 5 is a structural diagrammatic view of another electrodeless electrolytic crossing grinding apparatus of the present invention. In this figure, the electrodeless electrolytic dressing grinding apparatus of the present invention has the semi-conductive grindstone 10, the voltage applying means 12, and the supplying means 14 of grinding fluid. In the mode for carrying out the claimed invention, the semi-conductive grindstone 10 is the grindstone with a very small diameter and composed of the shank 10a of the grindstone made of a metal with a high electric conductivity and the cylindrical grindstone unit 10b installed in the tip (the left-hand of the figure) thereof. The shank 10a of the grindstone is rotated in a high speed by a driving means, not shown in a figure, around the center of core of the shank, and controlled in X direction (left and right directions) and Z direction (top and bottom directions) according to numeric control. The conductive workpiece 1 has a cylinder having an innernal diameter somewhat larger than that of the cylindrical grindstone unit 10b and installed in a rotating table 17 over the electric supplying body 18 and insulation 16. The voltage applying means 12 apply a voltage between an electric power source 12a, a brush 12b, electric supplying body 18, and an electric line 12c connecting electrically the shank 10a to the electric power source, and applied a voltage between the grindstone 10 and the workpiece 1. Other components are same as those of the mode for carrying out the claimed invention shown in Fig. 3. According to the present constitution, the present invention can be applied even when there is no space for installation of electrodes because of almost no difference between the innernal diameter of the workpiece 1 and the external diameter of the grindstone 10. Embodiments The condition of the surface of a grindstone and working surface was observed and measured after surface process of a steel piece (SKD11) for a mold by using the electrodeless electrolytic dressing grinding apparatus aforementioned. Table 1 and Table 2 shows the outline of the specification of apparatus used and the condition of the process carried out, respectively. Grinding machine NC vertical milling machine Grinding grindstone Metal-resin-bond Mounted grindstone Size D20-R10 metal: resin= 7:3 ELID power source ELID power source of constant current Grinding fluid AFG-M Diluted with tap water in 50 times Mesh size of grindstone #80 #200 Rotation speed of grindstone (rpm) 1000 1000 Feed speed of X axis (mm/min) 200-400 200 Y axis depth of cut (µm) 10-20 5-15 Open-circuit voltage (V) 20-60 20 Peak current (A) 5-10 5 On/Off time (µsec) 2 2 Initially, electrodeless electrolytic process was carried out by using a #80 grindstone. Some sparks are generated between the grindstone and the workpiece under the electrolytic conditions of 60V - 10A. Sparks occurred causes a damage on the surface of the grindstone and the surface of the workpiece and therefore a good worked surface was not produced. A film particular in the ELID grinding under the electrolytic condition of 20V - 6A was formed on the surface of the grindstone to allow good grinding surface like a mirror surface. Subsequently, a feeding speed and a depth of cut were adjusted to increase process efficiency. An excessive feeding speed cause chattering and therefore about 200 mm/min produced a good worked surface. On the other hand, the depth of cut of 20 µm caused wear-down of the dressed surface, insufficient dressing by electrolytic dressing, and finally a result of loading. By the depth of cut of 16 µm or under, grinding surface having like a mirror surface is obtained to allow good processing. In process using a #200 grindstone, a comparative test was conducted in absence and presence of electrification. In electrified process (the present invention), the depth of cut of 10 µm caused a little wear of the dressed surface, however, around 5 µm allowed stable mirror finish processing. In the absence of electrification (conventional art), process was started in dressed condition. The depth of cut of 5 µm caused loading after a short time and the grindstone was worn and deformed. From aforementioned embodiment, it has been confirmed that the electrodeless electrolytic dressing grinding method and apparatus of the present invention provide a good worked surface to accomplish stable process by selecting optimal electrolytic conditions and process conditions according to the size of grains. As stated before, the electrodeless electrolytic dressing grinding method and apparatus of the present invention have the following excellent effects: applicability to a peculiar grindstone such as ball-nose grindstone, possible grinding process of the workpiece simultaneously with dressing of the working surface of the grindstone by electrolytic dressing, and thus, long time grinding maintaining high efficiency and high preciseness. The present invention has been described in conjunction with the preferred embodiment. The embodiment described herewith is to be considered in all respects as illustrative and not restrictive.

Claims: An electrodeless electrolytic dressing grinding method comprising the step of: preparing a grindstone (10), applying a voltage between the grindstone and the conductive workpiece (1), supplying conductive grinding fluid between them, contacting the grindstone to the workpiece, dressing the bonding part of the grindstone of the contact point by electrolytic dressing, and simultaneously grinding the workpiece by the grindstone, characterized in that the grindstone (10) is a semi-conductive grindstone (10) comprising grains and semi-conductive bonding part to fix the grains is prepared. An electrodeless electrolytic dressing grinding method according to claim 1, characterized by said semi-conductive bonding part is composed of a mixture of metal powder and an insulating resin. An electrodeless electrolytic dressing grinding apparatus comprising; a grindstone (10), a voltage applying means (12) for applying a voltage between the grindstone and the conductive workpiece (1), and a supplying means (14) of grinding fluid for supplying conductive grinding fluid between the grindstone and the workpiece, whereby contacting the grindstone to the workpiece, dressing the bonding part of the grindstone of the contact point by electrolytic dressing, and simultaneously grinding the workpiece by the grindstone, characterized in that the grindstone is semi-conductive and comprises grains and a semi-conductive bonding part to fix the grains. An electrodeless electrolytic dressing grinding apparatus according to claim 3 characterized by said semi-conductive bonding part consisting of metal powder and an insulating resin. An electrodeless electrolytic dressing grinding apparatus according to any one of claims 3 or 4, characterized by said semi-conductive grindstone (10) is a ball-nose grindstone.

Inventors: OHMORI HITOSHI, OHMORI, HITOSHI
Applicants: RIKAGAKU KENKYUSHO, THE INSTITUTE OF PHYSICAL & CHEMICAL RESEARCH
Application year: 1999
Main classification: B24B53
IPC codes: B24B53, B24B19