JP2838314B2 - Electrolytic interval dressing grinding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the field of mirror grinding, and more particularly, to the mirror surface of the inner surface of a small-diameter cylinder to which electrolytic in-process dressing grinding (hereinafter referred to as ELID) is applied. The present invention relates to an electrolytic interval dressing grinding method suitable for grinding.

(Prior Art) Conventionally, as shown in FIG. 5 using a cast iron fiber bond diamond / cubic boron nitride grindstone (hereinafter collectively referred to as CIFB grindstone and individually referred to as CIFB-D / CBN grindstone). Internal grinding is performed. In the figure, a cylindrical workpiece 51 attached to a rotating chuck 50 has a shaft-mounted CIFB.
The cut is given by abutting the grindstone 52, and a mirror surface is created by feeding the grindstone. However, in this method, clogging due to chips is easily generated, and the single-stone dresser 53 is used every one to several passes. Dressing is performed to ensure normal removal action, and the surface roughness is improved to obtain a glossy surface. However, abrasive grains of about several tens of microns are the limit, and a grindstone composed of abrasive grains on the order of microns has not been applied. Therefore,
This method is not suitable for creating a high-precision mirror surface.

Therefore, the present inventors have developed a mirror surface grinding method by the ELID method using a CIFB grinding wheel (Japanese Patent Laid-Open No. 1-188266), and further applied an internal mirror surface grinding method as shown in FIG. Proposed [Park, Omori, Takahashi, Nakagawa: Scientific Lectures and Proceedings of the 1989 Autumn Meeting of the Japan Society of Precision Engineering, p899-p900]. In FIG. 4, a cylindrical work material 41 attached to a rotating chuck 40 is fed with a cut CIFB grindstone 42 having a notch in contact therewith to create a mirror surface. At this time, a feeding electrode (+) 43 is provided in contact with the shaft portion 46 of the grinding stone which has been trued in advance, and an ELID electrode (-) 44 is provided in proximity to the grinding stone portion. The abrasive grinding fluid (coolant) 45 is flowed and interposed, a voltage is applied between the two electrodes, and the cast iron fiber bond is eluted by weak electrolysis to ensure the projection of micron-order diamond or boron nitride abrasive grains. This realizes mirror grinding. By a method in which the grinding wheel 42 and the electrode 44 are integrated and driven, to obtain a surface roughness of a maximum roughness Rmax = 60 nm and a center line average roughness Ra = 8 nm in a cylindrical inner diameter of 45 mm to 70 mm and a length of 30 mm to 70 mm. Was completed.

(Problems to be Solved by the Invention) The above method can realize a desired stable internal mirror surface grinding, but has a disadvantage that the inner diameter that can be processed is limited due to the relationship between the grinding wheel diameter and the size of the ELID electrode. there were. Therefore, the mirror grinding of the inner surface of the small-diameter cylinder could not be performed.

An object of the present invention is to provide an interval dressing grinding method in which electrolytic dressing and grinding are alternately performed for the purpose of mirror grinding of the inner surface of a cylinder having high-precision surface roughness, particularly the inner surface of a small-diameter cylinder.

(Means for Solving the Problems) The above-mentioned problem is solved by providing an electrode at an axial distance from an end face of a cylindrical work material, and repeatedly driving a conductive grindstone between the work material and the electrode. In addition, the present invention can be solved by an interval dressing grinding method characterized in that a conductive grinding fluid is interposed between the conductive whetstone to which a voltage is applied and the electrode, and electrolytic dressing and grinding are alternately performed.

(Operation) FIGS. 3A, 3B, and 3C are front cross-sectional views illustrating a grinding path of internal grinding using an interval dressing grinding method. In FIG. 3A, the rotating chuck
The ELID electrode (-) 34 is fixed at a distance in the axial direction from the end surface of the cylindrical portion of the cylindrical work material 31 attached to 30.
First, the CIFB with shaft that the power supply electrode (+) 33 contacts before processing
The grindstone 32 is stopped at the position of the ELID electrode 34, a coolant 35 is flowed, and electricity is supplied to the CIFB grindstone to perform initial electropolishing. In the next FIG. 3B, a constant cut is given and traverse grinding is performed to the bottom of the cylinder. Then, the electrode is returned to the original position. The interval electrolytic dressing is performed in the state shown in FIG. 3C, and thereafter, the steps shown in FIGS. 3B and 3C are repeatedly performed while giving a cut. Here, the potential remains applied. In other words, the present invention provides a CIFB grinding wheel with a cylindrical work material,
This is a method in which electrolytic dressing and grinding are alternately performed while repeatedly driving between the end face of the cylindrical portion of the work material and an ELID electrode provided at an interval in the axial direction.
Since the ID electrode is arranged outside the workpiece and the interval dressing is performed, the inner surface of the cylinder having the inner diameter substantially equal to the outer diameter of the CIFB grinding wheel can be mirror-polished.

In addition, the present invention can be applied to the ELID method according to requirements such as a case where a processing shape of a work material is special or a case where an ELID electrode hinders a processing step.

(Example) Hereinafter, an example of the present invention will be described in detail.

FIG. 1 is a conceptual diagram in which the electrolytic interval dressing grinding of the present invention is applied to internal mirror surface grinding using a dedicated electrode. In the figure, a work material 11 is mounted on a rotating chuck 10 of a turning center processing machine, and a CIFB grinding wheel with a shaft is mounted on a chuck (not shown) capable of reciprocatingly driving the work material.
Attach 12 The power supply electrode 13 is brought into contact with the shaft of the whetstone with a shaft. The ELID electrode for electrolytic dressing 14 is supported by a support member 15 and an insulating member 16 fixedly attached to a part of a grinding machine, and has a coolant supply hole on an electrode surface facing the grindstone. The water-soluble coolant diluted with tap water is supplied from the coolant supply port 17 to the gap between the grindstone and the electrode through the supply hole. A terminal 18 is provided on the electrode and connected to an ELID power supply. Grinding is performed by rotating the grindstone in a direction opposite to the rotating direction of the work material, and cutting and feeding.

CIFB grinding wheels are available in CIFB-D or CIFB-
A CBN grinding wheel was selected and truing was performed in advance using a # 100 carborundum (C) grinding wheel. First, after the initial dressing (FIG. 3A) was performed for about 10 to 15 minutes by electrolytic dressing, the inner mirror surface was ground, and the conditions of interval dressing, the influence on the work material, the surface roughness of the machined surface, and the like were examined. The table below shows the specifications of the experimental system that attempted ELID internal mirror grinding for various materials.

As a first example, a hard and brittle material was selected, and internal mirror polishing was performed on a cemented carbide (WC), silicon carbide (SiC), and alumina (Al ₂ O ₃ ) using a # 4000CIFB-D grindstone.
The inner diameters are all φ30 mm. Use an electrode that is large enough to cover about one-third of the circumference of the grinding wheel.
The axial distance between the end face of the workpiece and the electrode is about 10 mm. The processing conditions are: grinding wheel peripheral speed vt283m / min, work peripheral speed vw
Under the conditions of 10 m / min, whetstone feed F130 mm / min, depth of cut d4 μm (per diameter), stable processing was possible at Rmax = 52 nm and Ra = 7 nm without concern for interval dress timing.

FIG. 2 shows the relationship between the dressing current and the number of times of processing (pass), which is an index for the electrolysis conditions and feed rates, which are parameters for determining the conditions of the interval dress. The figure shows
It shows the difference in the change in the current value Ir required for electrolytic dressing from the initial dress to the number of intervals when the peak current Ip of the ELID power supply is set under two conditions of α = 24 A and β = 12 A. . Under the condition α, the maximum current did not fluctuate every time, but under the condition β, the maximum current tended to increase gradually, indicating that a shortage of dressing would occur. That is, the condition α
In this case, the protrusion of the abrasive grains in each interval dressing is sufficiently ensured, and the ratio of the eluted bond to the nonconductive film is naturally large, so that the grinding stone (+) and the ELID electrode (-)
The fact that the conductivity between them is suppressed to some extent leads to the phenomenon that the maximum current value of the actual current Ir is constant. However, under the condition β, the amount of abrasive grains projected in each interval dressing is small, and naturally the amount of the bond material eluted is small.Therefore, the ratio of the nonconductive film remaining on the grinding wheel surface is small, and the conductivity between the grinding wheel and the electrode is The non-conductive film thickness, which is an insulator, increases as the friction decreases during processing. The difference in the electrode interval dressing efficiency under each of these conditions appears as a change in the actual current. The condition α was close to the optimum in the present apparatus and the present embodiment.

In the case of silicon carbide, stable mirror finishing was performed with the same tendency as that of a cemented carbide, but in the case of alumina, the actual current Ir was required to be twice the α condition due to brittle grinding dust. Therefore, in the case of alumina, the voltage was raised from about 60 V under the condition α to about 90 V to further improve the electrolytic interval dressing efficiency.

As a second embodiment, the inner surface mirror processing of various steel materials is
Performed using a 4000CIFB-CBN grinding wheel. Other grinding conditions are the same as in the first embodiment. In the case of a steel material, the grinding dust has the same electrolytic properties as in the case of cemented carbide, and good results were obtained by setting the interval dress condition to be equal to the electrolytic dressing condition α in FIG. In addition, it was found that setting of the same dressing strength as that of alumina was necessary for processing of the S15C material having low hardness.

The following table shows the measurement results of the average machined surface roughness of the various work materials obtained by carrying out the present invention.

According to the table, although there is a slight difference in the surface finish between the hard and brittle materials, Rmax = 52 nm for the cemented carbide
And good surface roughness were obtained. For silicon carbide, Rmax =
The value was 105 nm, but this is a value based on pores generated from uneven sintering of the applied material, and is not essential due to this processing. For steel materials, the quenched material is Rmax = 60
Mirror finishing was possible around nm, and the same finishing effect was confirmed.
It was found that the characteristics of the raw material (S15C) and cast iron (FC25) were similar to those of silicon carbide.

Further, in addition to the above-mentioned inner mirror surface processing of the inner diameter φ30 mm, as a result of processing the inner diameter φ12 mm, the lower the hardness and the smaller the diameter, the more the surface roughness tends to be deteriorated.

From the above results, according to the present invention, a surface having a good mirror surface and a roughness accuracy of nanometer order was able to be realized particularly in a hard and brittle material.

(Effect of the Invention) According to the present invention, the ELID electrode is installed outside the work material,
Grinding and electrolytic dressing for protruding abrasive grains are alternately performed by repeatedly driving the CIFB grinding wheel. Since the ELID electrode is always in close proximity to the grindstone and does not need to be installed in the same body, it has become possible to grind a minute diameter inner surface, which was extremely difficult in the past; Moreover,
Stable precision machining could be performed without impairing the machining efficiency, and further, the loss of the grindstone due to the wear amount of the dresser and excess (excessive) dressing, which were problems in the prior art, could be eliminated.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a processing example according to the present invention, FIG. 2 is a graph showing a relationship between processing time (number of times) and dress current according to the present invention, and FIGS. 3A to 3C are inner surfaces according to the present invention. FIG. 4 is a front cross-sectional view showing a grinding path of a grinding process. FIG. 4 is a front cross-sectional view showing a mirror inner surface grinding process using a conventional ELID method. FIG. 5 is a front sectional view showing a conventional CIFB grinding wheel. It is a front sectional view. (Explanation of reference numerals) 10,30,40,50 …… Rotating chuck, 11,31,41,51 …… Work material, 12,32,42,52 …… CIFBD grinding wheel with shaft, 13,33,43… … Power supply electrode, 14,34,44 …… ELID electrode, 15 …… Support member, 16 …… Insulation member, 17 …… Coolant supply port, 18 …… Terminal, 35,45 …… Coolant, 46 …… Shaft Part, 47, 47 ', 54 ... coolant nozzle, 53 ... dresser.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-35869 (JP, A) JP-A-3-251352 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B24B 53/00

Claims (1)

(57) [Claims] An electrode is provided at an axial distance from an end surface of a cylindrical work material, and a conductive grindstone is repeatedly driven between the work material and the electrode. An interval dressing grinding method characterized in that a conductive grinding fluid is interposed between a conductive grindstone and the electrode, and electrolytic dressing and grinding are alternately performed.