JPH01188266A - Electrolytic dressing for electric conductive grindstone and device thereof - Google Patents

Abstract

PURPOSE:To obtain a mirror surface and a flat surface at high speed and with high precision by applying a voltage onto an electric conductive grindstone and dressing said electric conductive grindstone through electrolytic decomposition. CONSTITUTION:During the grinding work for a workpiece (e.g., silicone wafer) 13, a weakly electric conductive liquid (coolant liquid) 16 is supplied between an electric conductive grindstone 10 and the workpiece 13 by a liquid feeding means. A voltage is applied between the grindstone 10 and the weakly electric conductive liquid 16 by an electric power source device 12. The grindstone 10 is dressed by the electrolytic effect due to the application, and the workpiece 13 is ground to a mirror surface and a flat surface.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a dressing method and device for a grinding wheel used for grinding in the field of machining, and particularly relates to a dressing method and device for a grinding wheel used for grinding in the field of machining, and particularly for dressing a grinding wheel having conductivity such as a cast iron fiber bonded diamond grinding wheel. The present invention relates to a method and apparatus for electrolytically dressing a conductive grindstone, in which the grindstone is dressed by electrolytic effect.

(Prior art and its problems) Cast iron fiber bond diamond grinding wheel (hereinafter referred to as CI F
It is called B-D whetstone: Ca5t Iron Fib
erBonded-Diamond) is a type of fiber-reinforced composite material made by mixing diamond abrasive grains and carbonyl iron powder into a base material of cast iron fibers and molding and sintering them. Research has been conducted to realize high (removal) efficient grinding of materials.

The basic grinding action of the conventional grinding wheel, which is called the so-called "koubure-type" grinding wheel, is different from that of a cutting machine where a constant cutting edge grinds until the end. During machining, the abrasive grains and binder are pulverized, new cutting edges and holes are constantly generated, and the workpiece material is removed. However, the above-mentioned CIFB-D grindstone is a typical so-called blind type, and because of the diamond abrasive grains and its strong bond material, the above-mentioned self-growth effect of the abrasive grain cutting edge and pores does not occur. Further, even if a dressing method using a WA stick grindstone made of aluminum oxide abrasive grains is used, there is a problem in that a sufficient protrusion amount of the abrasive grains, which is a main condition for grinding, cannot be obtained. Therefore, recently, a spark dressing method has been developed that combines dressing and grinding, in which the sparks generated when forcibly grinding difficult-to-cut materials remove the bond material of the main grindstone as well as the work material. However, in actual production lines, there is no grinding process that simply requires a high removal amount, and there are still few processing machines that have the rigidity and output to withstand strong grinding forces. Applied research to processes was desired.

The present inventors have developed a C
We conducted repeated research with the aim of applying the IFB-D whetstone, and focused on the fact that a good glossy surface cannot be obtained if the abrasive grains of the whetstone are insufficiently protruded, and various studies were conducted on conventional dressing methods. Ta. In particular, the smaller the abrasive grains are made to obtain a good mirror surface, the more difficult it becomes to dress the CI FB-D grindstone, and if you carelessly perform mechanical dressing using a conventional WA stick grindstone,
There was a problem in that fine abrasive grains were dropped before sufficient abrasive grain protrusion was obtained. In addition, we applied the slurry dressing method to the main whetstone by grinding while supplying free abrasive grains, and discovered that by applying the electric discharge grinding method, it was possible to obtain a glossy surface that could not be obtained conventionally. By combining a fine abrasive CI FB-D grindstone and an electrolytic dressing method during the grinding process, good mirror polishing of silicon wafers was achieved. (Means for solving the problem) The present invention , a conductive grindstone is interposed with a weakly conductive liquid during the grinding process of a workpiece, a voltage is applied between the grindstone and the liquid, and the electrolytic effect therebetween causes the grindstone to be dressed, i.e. It is characterized by obtaining an appropriate amount of abrasive grain protrusion from the grinding wheel. In particular, at the start of grinding, strong electrolytic dressing is performed to obtain sufficient abrasive grain protrusion.
Furthermore, during grinding, when grinding debris clogs between abrasive grains and the surface becomes smooth, weak electrolytic dressing is applied.

As a specific configuration, a supply means for supplying a weakly conductive liquid to the contact surface of the conductive grindstone with the workpiece, or adjusting the liquid level of a liquid tank such as grinding fluid, is used to connect the grindstone to the workpiece. This can be achieved by an electrolytic dressing device comprising a means for interposing the liquid on the contact surface of the electrode, and a power supply device for applying a voltage between the conductive grindstone and the weakly conductive liquid.

(Function) The abrasive grain protrusion formation process and grinding action by the electrolytic dressing method of the present invention will be described in detail below.

FIG. 5A is a schematic diagram showing the cross-sectional shape of the CI FB-D grindstone before use, in which diamond abrasive grains are appropriately distributed in the cast iron fibers, bond material, and pores. In general, a grindstone before use has a rough uneven surface and a runout of the axis, so it is necessary to perform truing according to the purpose of processing.

FIG. 5B is a schematic diagram showing the cross-sectional shape of a CIFB-D grindstone that has been subjected to truing and dressing by WA stick grindstone grinding. As mentioned at the beginning, this whetstone does not crush the abrasive grains like conventional whetstones, so the 5B
As shown in the figure, although the surface is smoothed, there are no cutting edges or holes formed by abrasive grains.

Therefore, when you start grinding with this surface condition, initially,
Grinding is possible by protruding some diamond abrasive grains, but within a short time, bond material and cast iron fibers other than the abrasive grains come into contact with the workpiece due to abrasion reduction and clogging of the abrasive grains. As a result, clean grinding cannot be performed.

Contrary to electroplating, an electrolytic polishing technique is known in which the surface of the workpiece is dissolved and metal is deposited on the cathode when an electric current is applied to the workpiece in an electrolytic solution using the workpiece as an anode. The CI FB-D grinding wheel contains cast iron fibers and iron powder, so it is electrically conductive, and the coolant (grinding fluid) is weakly conductive, so when electricity is passed between the grinding wheel and the coolant from a power source, an electrolytic effect occurs. The metal part on the surface of the whetstone melts, and non-conductive diamond abrasive grains protrude.

FIG. 4A shows a first process of the invention, in which CIFB
FIG. 5 is a schematic diagram showing a cross-sectional shape of the -D grindstone obtained by dressing the surface state shown in FIG. 5B by a strong electrolytic effect.

The conductive metal part is dissolved by electrolysis, while the non-conductive diamond abrasive grains remain as they are, providing a protrusion that allows for grinding. The desired abrasive grain protrusion amount can be set by the applied voltage of the power supply device, current, time, conductivity of the grinding fluid, etc.

The grinding action of the CIFB-D grinding wheel of the present invention on the workpiece is slightly different from conventional grinding by grinding abrasive grains, and the diamond abrasive grains in this grinding wheel act to a high degree as cutting edges, resulting in an action close to cutting. This is to remove the workpiece. Therefore, the abrasive grains are worn away while removing the workpiece.

FIG. 4B shows the second process of the present invention, and is a schematic diagram in which the amount of abrasive grain protrusion decreases during the grinding process, and grinding debris accumulates between the abrasive grains, causing clogging. In this process, as the grinding process progresses, grinding debris is removed by a weak electrolytic effect, and dressing can be performed automatically during actual processing without stopping the operation until the grinding process is completed. In addition, even if the second process is performed for an extremely long period of time and all the abrasive grains that were acting as cutting edges are worn out, if the first process is performed again, new abrasive grains can be created in a short time. Since the abrasive layer can be made to protrude, the entire abrasive grain layer of the whetstone can be used effectively without reducing production efficiency.

Grindstones that can be electrolytically dressed include not only metal bonded grindstones such as CI FB-D grindstones, but also non-metallic grindstones that can be applied by mixing metal powder or the like to impart conductivity.

(Effects of the invention) The present invention enables silicon, which was conventionally considered to be difficult to process, to
In addition to hard brittle materials such as ferrite and ceramics, cemented carbide, various steel materials, and magnetic metal materials, conductive CI FB-D and CIFB-CBN (when grinding iron-based materials) grinding wheels, etc. By sequentially performing a dressing effect using strong electrolysis and electrolytic grinding processing using relatively weak electrolysis, it has become possible to obtain extremely good mirror and smooth surfaces that were previously unobtainable with high efficiency and high speed. Ta. Moreover, it can be applied to abrasive processing other than grinding such as super finishing, honing, and lapping, and can perform not only mirror finishing but also heavy grinding, and can easily achieve high removal efficiency.

This electrolytic dressing method for conductive grinding wheels can be performed unattended, at high speed, and with high precision by controlling the electrolytic conditions, making conventional mechanical dressing unnecessary. Dressing of the grindstone becomes easy, and furthermore, dressing can be performed regardless of the shape of the grindstone, so the invention has high flexibility. As for the electrolyte, even a commercially available water-soluble grinding fluid diluted with tap water has weak conductivity, so it is not only economical as it does not require special additives, but also eliminates the risk of corrosion of the machine due to the electrolyte. do not have.

The structure of the electrolytic dressing device does not require major modification, as it can be combined with existing processing machines and parts can be attached like an accessory. The electrolytic power supply device can also be applied to electrical discharge truing, and after electrical discharge truing on the machine, it can immediately shift from electrolytic dressing to electrolytic grinding, eliminating complicated labor at each processing stage, and improving machined surface roughness and grinding resistance. Equipped with equipment that measures the resistivity and temperature of the grinding fluid, the resistivity of the workpiece, etc. in-process, it is possible to constantly control the optimum abrasive grain protrusion amount and achieve semi-automation of the grinding process.

As described above, the present invention is applicable to fields such as grinding and polishing, regardless of the type and shape of the grinding wheel as long as it is conductive, and can be performed semi-automatically in-process. This method is highly efficient, has a long life, is economical, and has a wide range of applications.

(Example) The table below shows the specifications of the grinding system used to carry out the present invention.

In this example, a precision rotary surface grinder with a fineness of CIFB-
A D grindstone (#4000) was attached, and an existing wire-cut power source was used to generate electrolysis. The grinding machine is
In addition to using static pressure bearings for both the grinding wheel shaft and table rotation shaft, it has high rigidity as it is an experimental machine, and the coolant (grinding fluid) is released from the center of the magnet shaft, which has a great effect in reducing clogging of the grinding wheel. . In addition, the power supply has an applied voltage, a maximum current value,
Frequency can be set arbitrarily. Furthermore, improvements have been made to the coolant tank, power supply brush, etc. used for electrolytic grinding, and commercially available coolants are used without mixing any special electrolyte.

FIG. 1 is a block diagram of an apparatus for carrying out the electrolytic dressing method of the present invention. The figure shows the main parts of a precision rotary surface grinder 1) and an electrolytic power supply 12. In the figure, silicon 13 as a work material is fixed in a water tank 15 on a rotary table 14, and is ground with a CIFB-D grindstone 10 while submerged in a coolant liquid 16.

The positive (+) electrode (positive voltage) of the power supply device 12 is connected to the power supply brush 17 applied to the outer periphery of the grinding wheel 10, and the negative (-) electrode (negative voltage) is connected to the copper wire 18 suspended in the coolant liquid 16. There is. That is, by using the coolant itself as a negative (-) electrode, electrolysis is constantly generated. Before processing, use the WA stick whetstone (#80° #400) with the CI FB-D whetstone (
Truing and dressing were performed by grinding with #4000), and then silicon was ground under various electrolytic conditions and grinding conditions. Moreover, the surface roughness after grinding was measured using a reference length of 2.5 mm.

FIG. 2 is a graph showing the effect of electrolytic dressing according to the first process of the present invention. In advance, CIF
The BD grindstone was a WA stick grindstone that had undergone truing, etc., and was used for electrolytic grinding of silicon. The graph shows the change in electrolytically ground surface roughness depending on the grinding distance of 1000 mm for four cases where the feed rate is constant at 107 mm/min and the maximum current value is 100, 120, and 140.160 A, respectively. As is clear from the figure, the surface roughness improves with the electrolytic grinding distance in all cases, and when the maximum current value is 140 and 160 A, the grinding distance is 700 A.
It can be seen that Rmaxo, 1-0.21) m is achieved at mm or more, and dressing of the C I FB-D grindstone by the electrolytic effect is effective.

Next, following the dressing effect described above, a second process of the present invention is performed in which grinding is performed while applying electrolysis. Figure 3 is a graph showing the electrolytic grinding characteristics, where the maximum current value was maintained at 16OA and the grinding distance was 1000m.
m, the feed speed is 359, 202, 10, respectively.
The processing speed was set at 7.76.44 mm/min. From the same figure, the surface roughness of electrolytic grinding is 359
Rmaxo even at mm/min, the ground surface of 4μm persists, and at low speed feed of 44mm/min, Rmaxo,
06 A mirror surface of 0.08 μm was achieved. In the figure, the maximum current value is 16OA, but electrolytic grinding using a CIFB-D grindstone can achieve the same surface roughness even if the current value is lowered to about IOA.

As described above, the present invention was able to achieve an extremely good mirror surface by sequentially performing the electrolytic dressing effect and the electrolytic grinding process. Furthermore, the ground surface obtained by this method exhibits a surface texture due to almost perfect plastic flow even if the workpiece material is a brittle material, and has a mirror surface. This mirror surface had almost no brittle fractures, and it was confirmed that there were few cranks remaining on the surface layer.

The inventors of the present invention obtained very good results with ferrite and alumina in addition to the silicon used in the above examples, and the results are shown in the table below.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an apparatus for carrying out the electrolytic dressing method of the present invention, Fig. 2 is a graph showing the effect of the electrolytic dressing of the present invention, and Fig. 3 is a graph showing the electrolytic grinding characteristics of the present invention. , 4th A
The figure is a schematic diagram of a cross section of a grinding wheel showing the abrasive grains protruding from the magnet surface due to the electrolytic dressing effect of the present invention. Figure 4B is a diagram showing the removal of clogging due to the dressing effect during the electrolytic grinding process of the present invention. Fig. 5A is a schematic diagram showing the cross-sectional shape of the CI FB-D grindstone before use. Fig. 5B is a schematic diagram of the cross-sectional shape of the CI FB-D grindstone after truing and dressing with a WA stick grindstone. It is a diagram. (Explanation of symbols) 1) Main parts of precision rotary surface grinder,
12...Power supply device, 13...Silicon work material, 14...Rotary table, 15...
・Coolant tank, 16... Coolant liquid, 17... Power supply brush, 18... Copper wire. Figure 4A Electrolytic Tresching (Flocess 1) Figure 4B Electrolytic Inflow Dressing (Flocess 2) Figure 5A Beginner (Before Truing) Figure 5B Trueing Acquisition Procedure Amendment (Method) Director of the Patent Office Kunio Ogawa 1. Indication of the case 1986 Patent Application No. 12305 3. Person making the amendment Relationship with the case Applicant name (679) RIKEN 4. Agent

Claims (6)

[Claims] (1) An electrolytic dressing method for a conductive grindstone, which comprises applying a voltage to the conductive grindstone and dressing the grindstone by electrolysis. (2) When starting to use the conductive grindstone, perform the dressing at a relatively high speed, and after the grindstone surface is flattened,
The electrolytic dressing method according to claim 1, wherein the dressing is performed at a relatively low speed. (3) The electrolytic dressing method according to claim (1), wherein the conductive grindstone comprises abrasive grains and metal bonds. (4) Claim No. 1, characterized in that the conductive grindstone is made of a non-metal bond containing a grindstone and metal particles.
) The electrolytic dressing method described in section ). (5) The electrolytic dressing method according to claim (1), wherein the dressing is performed during grinding of the workpiece. (6) A conductive grindstone, a liquid supply means for supplying a weakly conductive liquid to the contact surface of the conductive grindstone with the workpiece, and a power supply device that applies a voltage between the conductive grindstone and the weakly conductive liquid. An electrolytic dressing device for conductive grinding wheels.