VITRIFIED-BOND SUPERABRASIVE WHEEL

Abstract

 There is provided a vitrified bond super-abrasive grinding wheel having a super-abrasive grain layer, wherein the super-abrasive grain layer 6 includes a super-abrasive grain 3, a pore 5 and a vitrified bond 2, and in the super-abrasive grain layer 6, an area ratio of a coarse vitrified bond grain having an area of 30 µm² or larger is 10% or less.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a vitrified bond super-abrasive grinding wheel. The present application claims the priority based on Japanese Patent Application No. 2022-048144 filed on March 24, 2022. The entire contents of the description in this Japanese patent application are incorporated herein by reference.

BACKGROUND ART

[0002] Conventionally, a vitrified bond super-abrasive grinding wheel is disclosed in, for example, Japanese Patent Laying-Open No. 2014-61585 (PTL 1).

CITATION LIST

PATENT LITERATURE

[0003] PTL 1: Japanese Patent Laying-Open No. 2014-61585

SUMMARY OF INVENTION

[0004] A vitrified bond super-abrasive grinding wheel according to the present disclosure has a super-abrasive grain layer, wherein the super-abrasive grain layer includes a super-abrasive grain, a pore and a vitrified bond, and in the super-abrasive grain layer, an area ratio of a coarse vitrified bond grain having an area of 30 µm² or larger is 10% or less.

BRIEF DESCRIPTION OF DRAWINGS

[0005] 

Fig. 1 is an enlarged view of a part of a cut surface of a super-abrasive grain layer 6 of a vitrified bond super-abrasive grinding wheel according to the present disclosure.

Fig. 2 is a schematic view of a sintered compact obtained in a manufacturing process described in an Example.

Fig. 3 is a photograph of one field of view (80 µm × 62 µm) of a sample in which Si constituting a vitrified bond is colored.

DESCRIPTION OF EMBODIMENTS

[Problem to be Solved by the Present Disclosure]

[0006] A conventional vitrified super-abrasive grinding wheel has the problem of being likely to wear.

[0007] A conventional vitrified super-abrasive grinding wheel has the problem of a high wear rate.

[0008] The present inventors have earnestly studied to reduce the wear rate, and as a result, have found that a correlation can be seen between an area of coarse vitrified bond grains having an area of 30 µm² or larger and a wear rate of a vitrified super-abrasive grinding wheel in a super-abrasive grain layer constituting the vitrified super-abrasive grinding wheel.

[0009] The present disclosure made based on such findings is directed to a vitrified bond super-abrasive grinding wheel having a super-abrasive grain layer, wherein the super-abrasive grain layer includes a super-abrasive grain, a pore and a vitrified bond, these are dispersed in the super-abrasive grain layer, and in the super-abrasive grain layer, an area ratio of a coarse vitrified bond grain having an area of 30 µm² or larger is 10% or less.

[0010] In the vitrified bond super-abrasive grinding wheel configured as described above, the area of the coarse vitrified bond grain is small. Therefore, wear starting from the coarse vitrified bond grain can be prevented and the wear rate can be reduced.

[0011] Fig. 1 is an enlarged view of a part of a cut surface of a super-abrasive grain layer 6 of a vitrified bond super-abrasive grinding wheel according to the present disclosure. As shown in Fig. 1, the vitrified bond super-abrasive grinding wheel is a vitrified bond super-abrasive grinding wheel having a super-abrasive grain layer 6 including super-abrasive grains 3 bonded by vitrified bonds 2, and super-abrasive grain layer 6 includes pores 5, vitrified bonds 2, and Al₂O₃ 4 constituting fillers. Super-abrasive grain layer 6 preferably includes 50 to 70% by volume of pores 5. Super-abrasive grain layer 6 preferably includes 5 to 20% by volume of vitrified bonds 2. Super-abrasive grain layer 6 preferably includes 5 to 30% by volume of Al₂O₃ 4 constituting the fillers.

[0012] Super-abrasive grain layer 6 more preferably includes 55 to 70% by volume of pores 5, 5 to 15% by volume of vitrified bonds 2, and 10 to 30% by volume of Al₂O₃ 4. Super-abrasive grain layer 6 does not need to include Al₂O₃ 4.

[0013] Furthermore, super-abrasive grain layer 6 most preferably includes 55 to 70% by volume of pores 5, 5 to 15% by volume of vitrified bonds 2, and 10 to 25% by volume of Al₂O₃ 4.

[0014] Since the % by volume of each of super-abrasive grains 3, pores 5, vitrified bonds 2, and Al₂O₃ 4 can be changed widely, it is possible to select the specifications of the grinding wheel that are most suited to the type of workpiece, a grinding condition, the type of grinder and the like.

[0015] Particularly when a cup-shaped grinding wheel (e.g., type 6A2 or the like defined in JIS B4131) is used to perform surface grinding processing on a workpiece with a rotary table-type vertical-axis surface grinder, it is possible to select the specifications of the grinding wheel that can maintain good grinding performance for a long time even when a contact area between super-abrasive grain layer 6 and the workpiece is large.

[0016] A vitrified bond having a known composition can be applied to the present disclosure. For example, a vitrified bond having the following composition can be applied.

[0017] SiO₂: 30 to 50% by mass; Al₂O₃: 2 to 10% by mass; B₂O₃: 40 to 60% by mass; RO (RO is at least one type of oxide selected from CaO, MgO and BaO): 1 to 10% by mass; R₂O (R₂O is at least one type of oxide selected from Li₂O, Na₂O and K₂O): 2 to 5% by mass

[0018] A vitrified bond other than the above-described vitrified bond can also be applied to the present disclosure.

[0019] Al₂O₃ 4 is, for example, α-Al₂O₃. By applying α-Al₂O₃, a wafer made of silicon, sapphire, monocrystalline SiC, GaN or the like can be ground with a high degree of accuracy and efficiency.

[0020] By adding α-Al₂O₃ to super-abrasive grain layer 6, a degree of concentration of the super-abrasive grains can be reduced without reducing the mechanical strength of super-abrasive grain layer 6. As a result, even in the case of a wafer made of a difficult-to-grind material, the grinding resistance can be reduced during grinding processing, and thus, stable grinding performance can be maintained for a long time.

[0021] An average grain size of Al₂O₃ 4 is, for example, 200% or less of an average grain size of super-abrasive grains 3.

(Example)

[0022] The provided vitrified bond super-abrasive grinding wheel has the super-abrasive grain layer having good dispersibility of glass. In order to manufacture this, diamond abrasive grains, a vitrified bond including glass, a pore forming material, a filler, a binder, and ceramics balls were blended in various compositions, to obtain mixed powders. The mixed powders were mixed at a certain rotation speed (15 to 150 rpm) for 10 hours in the case of Sample Nos. 1 and 2 and for 120 hours or longer in the case of Sample Nos. 3 to 5, and were dried and pulverized, to obtain prescribed granulated powders. Then, the granulated powders were molded into chip-shaped compacts using a press, and binder removal processing was performed in the air atmosphere, and subsequently, firing was performed at the temperature of 750°C in the air atmosphere. As a result, sintered compacts of the super-abrasive grain layer having various compositions were obtained. Analysis results of the compositions of these sintered compacts are shown below.

[Table 1]

Sample No.	Composition (% by volume)
	Vitrified bond	Filler	Pore	Diamond
1	7.1	19.6	59.3	14.0
2	7.1	19.6	59.3	14.0
3	7.1	19.6	59.3	14.0
4	7.1	19.6	59.3	14.0
5	7.1	19.6	59.3	14.0

[0023] A method for specifying each component is a method by a combustion test and ICP atomic emission spectroscopy. Each of the sintered compacts is crushed into powder and combusted at 1000°C. An amount of decrease in mass before and after combustion is converted as an amount of decrease in diamond abrasive grains. The remaining powder is dissolved in a basic solution, and thereafter, the concentrations of Al, Si and the like obtained by ICP atomic emission spectroscopy are regarded as the concentrations of Al₂O₃, SiO₂ and the like and the masses thereof are calculated. The % by mass is obtained from each of the calculated masses, and the % by volume is obtained from a volume calculated at a known density. The compositions of the sintered compacts are specified by the above-described method.

[0024] The main component of the vitrified bond is SiO₂.

[0025] Fig. 2 is a schematic view of the sintered compact obtained in the manufacturing process described in the Example. For Sample Nos. 1 to 5, a sample having a dimension of 7 mm × 5 mm × 3 mm was cut out from each of a front surface 101, an upper surface 102 and a rear surface 103 of a sintered compact 100. Crosssection polisher (CP) processing and carbon coating were performed on one part of each sample. CROSSSECTION POLISHER IB-19530 manufactured by JEOL Ltd. was used as the CP processing device.

[0026] Under the following measurement conditions, scanning electron microscope (SEM) measurement and energy dispersive X-ray spectroscopy (EDX) measurement were performed on the CP-processed surface of each sample. This is for coloring the Si element with the EDX to make glass in the structure visible. A tabletop microscope "Miniscope TM3030" manufactured by Hitachi High-Technologies Corporation was used as the SEM device. An energy dispersive X-ray analyzer "Quantax70" manufactured by BRUKER was used as the EDX device. The SEM measurement conditions were an accelerating voltage of 15 kV and a measurement magnification of 2000x. The EDX measurement conditions were an accelerating voltage of 15 kV and a capturing time of 200 seconds.

[0027] As a result, eight images (80 µm × 62 µm) in each of which Si was colored were obtained for each of the three samples of front surface 101, upper surface 102 and rear surface 103.

[0028] The obtained 24 images were put into image analysis software (MultiImage Tool manufactured by SYSTEM IN FRONTIER INC.) and subjected to automatic binarization in accordance with the commands shown in Table 2.

[Table 2]

No.	Command	Target image	Processing
1	input: file	EDX image	capture EDX image
2	input: file	backscattered electron image	capture backscattered electron image
3	conversion: trimming	EDX image	cut image into prescribed dimension
			conditions: L = 0, T = 0, R = 0, B = 23
4	filter: median	EDX image	denoise with Filter = 3 × 3
5	conversion: binarization	EDX image	binarize with threshold values R = 86, G = 11, B = 11
6	mask: labeling	EDX image	label binarized region
7	conversion: trimming	backscattered electron image	cut image into prescribed dimension
			conditions: L = 0, T = 0, R = 0, B = 23
8	conversion: binarization	backscattered electron image	binarize with threshold values R = 100, G = 100, B = 100
9	mask: labeling	backscattered electron image	label binarized region
10	mask: label removal	backscattered electron image	binarize region other than inside of pore
11	operation: duplication	EDX image, backscattered electron image	binarize glass portion other than inside of pore
12	output: file	EDX image, backscattered electron image	output numerical data such as area of binarized region, and images

[0029] As a result, numerical data about the distribution of a region including Si (glass) and a region not including Si, and the size of each region was obtained.

[0030] A plurality of pieces of glass are present in a scattered manner in a field of view. A region mapped with the EDX is defined as a glass area. This glass area refers to a total area of the plurality of pieces of glass (vitrified bond grains) present in a scattered manner. Furthermore, glass having an area of 30 µm² or larger in one piece of glass is defined as a coarse vitrified bond grain and a total area thereof is calculated.

[0031] Using Microsoft Excel, a coarse glass area ratio (a ratio of glass having an area of 30 µm² or larger) was calculated in accordance with the following calculation equation:

A = a total sum of areas of vitrified bond grains having an area of 30 µm² or larger in the 24 images

B = a total sum of areas of vitrified bond grains in the 24 images.

[0032] The coarse glass area ratios in the three samples were calculated and an average value thereof was calculated. Furthermore, the Vickers hardness of each sample was calculated. Results are shown in Table 3.

[Table 3]

Sample No.	Area ratio of coarse vitrified bond grains (%)	Hardness (HRC)	Wear rate (%)			Load current value (A)
			Average	Maximum	Minimum	Average	Maximum	Minimum
1	16.8	30	120.8	180.5	76.4	2.1	2.2	1.9
2	10.3	42	101.1	150.0	53.9	2.4	2.6	2.0
3	2.9	61	37.9	71.4	18.2	2.5	2.6	2.3
4	2.0	57	40.5	60.0	19.2	2.4	2.5	2.2
5	2.1	62	38.7	72.2	17.3	2.5	2.6	2.3

[0033] Fig. 3 is a photograph of one field of view (80 µm × 62 µm) of the sample in which Si constituting the vitrified bond is colored. In the field of view of the super-abrasive grain layer, a region 201 corresponds to the coarse vitrified bond grain having an area of 30 µm² or larger. A vacancy 202 is shown in black color in the photograph. In this field of view 200, one piece of coarse glass is observed. In Fig. 3, a region of a non-coarse vitrified bond grain is also specified. Region 201 constituting the coarse vitrified bond grain includes super-abrasive grain 3 and Al₂O₃ 4, in addition to vitrified bond 2 shown in Fig. 1.

[0034] The chip of the sintered compact was bonded to a core made of aluminum alloy by using an adhesive, and thereafter, truing and dressing were performed using a conventional grindstone, to complete a vitrified bond diamond wheel for each of Sample Nos. 1 to 5.

[0035] The wheel was a segment-shaped cup wheel (JIS B4131 6A7S type) having an outer diameter of 250 mm and including a super-abrasive grain layer having a width of 3 mm.

[0036] The wheel was dressed using a vertical-axis rotary surface grinding machine, and thereafter, 16 surfaces of eight SiC wafers (materials to be ground) each having a diameter of 4 inches (10.16 cm) were continuously processed. In addition, the grinding resistance (the load current and the normal resistance) and the wear rate of the abrasive grain layer during processing were measured and evaluated with the change or average value during continuous processing.

[0037] Grinding machine: HRG300 manufactured by TOKYO SEIMITSU CO., LTD.

Workpiece: 4-inch SiC (a plane having a crystal plane orientation of (0001) is ground, and thereafter, a plane having a crystal plane orientation of (000-1) is ground)

Spindle rotation speed (min^-1): 2000

Workpiece rotation speed (min^-1): 301

Feed speed (µm/sec): 0.4

Removal (µm): 10

Spark Out (a time period for which the grindstone is rotated at the end of grinding processing, without down feed) (sec): 10

[0038] The wear rate was calculated in accordance with the following equation:

Wear rate = amount of change in height of super-abrasive grain layer/amount of change in thickness of workpiece × 100 (%).

[0039] Results are shown in Table 3.

[0040] It was confirmed from these results that the area ratio of the coarse glass needs to be 10% or less.

[0041] It is understood that when the area ratio of the coarse glass is 10% or less, the wear rate is extremely low, which results in a long-life vitrified bond super-abrasive grinding wheel that is less likely to wear.

[0042] Furthermore, in each of Sample Nos. 3 to 5, the load current value is within a permissible range, and thus, it is understood that the grinding performance does not deteriorate.

[0043] It should be understood that the embodiment and example disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

[0044] 1 vitrified bond super-abrasive grinding wheel; 2 vitrified bond; 3 super-abrasive grains; 4 Al₂O₃; 5 pore; 6 super-abrasive grain layer; 100 sintered compact; 101 front surface; 102 upper surface; 103 rear surface; 200 field of view; 201 region; 202 vacancy.

Claims

1. A vitrified bond super-abrasive grinding wheel having a super-abrasive grain layer, wherein

the super-abrasive grain layer includes a super-abrasive grain, a pore and a vitrified bond, and

in the super-abrasive grain layer, an area ratio of a coarse vitrified bond grain having an area of 30 µm² or larger is 10% or less.

2. The vitrified bond super-abrasive grinding wheel according to claim 1, wherein
the super-abrasive grain layer further includes a filler, and includes 5% by volume or more and 20% by volume or less of the vitrified bond, and 50% by volume or more and 70% by volume or less of the pore, with the remainder being the super-abrasive grain and the filler.

Drawing