JP2017170554A - Vitrified grindstone for low pressure lapping for lapping machine and polishing method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vitrified grindstone for a lapping machine capable of achieving an enhanced polishing efficiency in a polishing condition with a low rotation speed and a low pressure using bonded-abrasive grindstone with small-grain-sized abrasives.SOLUTION: A vitrified grindstone comprises: composite abrasives incorporating hard abrasives and soft abrasives both with respective grain diameters not greater than 10 μm bonded with a low-melting-point and low-shrinkable vitrified bond which is melted at a temperature equal to or lower than 900°C to be thermally decomposed. A binder phase with the vitrified bond has a porous structure, porosity of 55% or greater in a volume ratio of the grindstone. A surface to be press-contacted with a work-piece to be polished has numerous fine pores 7, 8 open to the outside.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a low-pressure processed vitrified grindstone employed in a lapping machine (planar grinder), and more particularly to a grindstone capable of efficiently performing high-precision polishing and a polishing method using the grindstone.

  For processing of brittle materials such as semiconductor substrates, ceramics mechanisms, and functional parts, a lapping machine is used, and free abrasive machining is performed by pouring free abrasive grains between the surface plate and the workpiece (workpiece). However, since the loose abrasive machining has problems relating to machining efficiency, environmental conservation, machining accuracy, etc., it is considered to replace it with machining using a fixed abrasive grindstone.

  As the fixed abrasive grindstone, for example, those described in Patent Documents 1 to 3 below are known. The fixed abrasive grindstone disclosed in Patent Document 1 is a vitrified grindstone in which abrasive grains are bonded with a vitrified bond containing a reactive sintering agent made of carbonate and a flux made of metal fluoride.

  Regarding the vitrified grindstone of Patent Document 1, a grindstone using an abrasive grain having an abrasive grain size of 4 to 8 μm (2500 mesh), a grindstone using an abrasive grain having an abrasive grain diameter of 2 to 4 μm (4000 mesh), and a maximum porosity. A 54.5% whetstone is listed in the examples.

  The grindstone of Patent Document 2 is configured by forming fan-shaped segments by arranging fan-shaped grindstone pieces curved in a radial direction along a circle concentric with the center of rotation of the surface plate, and arranging the segments radially on the surface of the surface plate. The polishing scraps and falling abrasive grains dispersed in the coolant used during polishing are efficiently discharged to the outside.

  In addition, the grindstone of Patent Literature 3 (a lapping plate for a lapping machine) has a fan-shaped belt-shaped grindstone piece that is bent between the grindstone pieces adjacent in the radial direction and between the grindstone pieces adjacent in the circumferential direction and has a groove and a diameter that are continuous in the circumferential direction. The supply of the polishing liquid to the polishing portion is improved by bonding to the surface of the annular carrier so as to form a groove extending linearly in the direction.

JP2015-112665A JP 2009-233846 A JP 2005-238413 A

  For example, when trying to process a thin workpiece with high accuracy without warping or scratching on a lapping machine that uses a fixed abrasive wheel, the wheel rotation speed, workpiece rotation speed, and workpiece pressing pressure against the wheel are compared to normal polishing. Extremely low processing is required.

For example, the grinding wheel revolutions per minute (speed) is 40 to 100 rotate, the workpiece rotation speed (rotation speed) 20-50 rotation, the workpiece pressing pressure against the grindstone told ^50g / cm ^{2 ~500g} / cm 2 Processing under conditions that reduce sharpness is forced.

  The conventional fixed abrasive grindstone that can cope with such conditions is limited to # 2000 (2000 mesh, abrasive grain size of 5 to 10 μm, average grain size of 8 μm).

  However, with the # 2000 grindstone, the processed surface is rough and large wrinkles are likely to occur, which increases the burden of the final finishing polishing process and makes the processing time very long.

  Therefore, from the viewpoint of reducing the burden of the final polishing process, it is desired to perform a process aiming at a mirror surface as much as possible using a grindstone using finer abrasive grains (a grindstone having a larger number than # 2000). However, in the lapping process, the sharpness tends to decrease as the grain size of the grindstone becomes finer, and the polishing efficiency deteriorates.

  Existing fixed abrasive wheels can be used for roughing on lapping machines. However, when finishing with a fine abrasive grain, sharpness decreases, so-called machining allowance (polishing depth) decreases. The wrinkles generated by processing cannot be removed, and the processed surface becomes rough. Or if it processes until it cuts off a wrinkle, processing time will inevitably become long.

  Nevertheless, in the processing aiming at the mirror surface (processing for increasing the surface roughness of the processed surface), a grindstone having a fine grain size is required.

  There is no product that satisfactorily meets the demand for efficiently performing high-precision polishing (lapping) under the conditions of low rotational speed and low pressurization using the fine grinding stone.

  For example, the grindstone of Patent Document 2 prevents clogging of the grindstone surface (processed surface) by positively discharging abrasive scraps and falling abrasive grains dispersed in the coolant to the outside by high-speed rotation of the grindstone.

  As a result, the reduction in sharpness is suppressed, but it is rather in terms of improving the polishing efficiency that the polishing debris and falling abrasive grains dispersed in the coolant in the polishing process under conditions of low rotational speed and low pressure are discharged to the outside. The inventors obtained knowledge that would have an adverse effect.

  The suggestion regarding this knowledge is not found in Patent Documents 1 and 3 as well as Patent Document 2.

  Based on the above knowledge, various devices for improving the polishing efficiency in the polishing process under the conditions of the low rotational speed and the low pressure by the fixed abrasive grindstone having a small abrasive particle diameter are sought and as shown in the above-mentioned Patent Document 1. It was found that a vitrified grindstone with the following ingenuity was effective.

  An object of the present invention is to provide a devised vitrified grindstone for a lapping machine and a polishing method using the same to obtain a high surface roughness processed surface.

  The low-pressure machined vitrified grinding wheel for lapping machine of this invention is a low melting point / low shrinkage melting point and thermal decomposition temperature of 900 ° C. or less, which is a composite abrasive composed of hard abrasive grains and soft abrasive grains each having a grain size of 10 μm or less. A grindstone bonded with a porous vitrified bond, wherein the bonded phase of the vitrified bond has a porous structure, and the porosity in the volume ratio of the grindstone is 55% or more, and is pressed against the workpiece to be processed. There are innumerable fine pores open to the outside on the surface.

  The pores are small-size pores and medium-size pores, or small-size pores, medium-size pores, and large-size pores, and can take in abrasive grains that are crushed and dropped during use of the grindstone.

  The size of the pores is about the size close to the particle size of the hard abrasive grains used for the small size pores, and about 10 to 20 times the particle size of the hard abrasive grains for the medium size pores and the large size pores. Apply.

  For example, in the case of a # 8000 grindstone, small pores are about 1 to 3 μm and medium size pores are about 20 μm.

  The size of the pores varies depending on the size of the abrasive grains used (the grindstone count). The size of the pores becomes smaller as the grindstone using the abrasive grains having a smaller particle diameter (the grindstone having a larger count).

This grindstone satisfies the relationship shown in Table 1 with respect to grindstone particle size and grindstone hardness (grindstone bond degree) under the following test conditions.

  The hard abrasive grains of the composite abrasive grains are diamond abrasive grains or cubic boron nitride (CBN) abrasive grains. The soft abrasive grains are abrasive grains selected from cerium oxide, silica, barium sulfate, and zirconium oxide.

  The volume ratio of the hard abrasive grains to the soft abrasive grains is preferably 70 to 95% hard abrasive grains and 5 to 30% soft abrasive grains.

  The low melting point / low shrinkage vitrified bond includes those disclosed in Patent Document 1, for example, a reactive sintering agent composed of at least one of zinc carbonate and magnesium carbonate, and lithium fluoride as a flux of metal fluoride. This is preferable because it can cause micro-dropping of abrasive grains bonded with a low pressure.

The hard abrasive grains of the composite abrasive are, for example, alumina (Al ₂ O ₃ ), sapphire (Al ₂ O ₃ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), zirconia (ZrO ₂ ), nitriding. Aluminum (AlN), silicon (Si), quartz / quartz (SiO ₂ ), cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ), carbide, PCD (diamond sintered body), PCB (boron sintered body) Diamond abrasive grains are used for polishing brittle materials such as glass, and cubic boron nitride abrasive grains are used for polishing iron-based materials.

  Furthermore, the soft abrasive grains, in order to exhibit the effect of assisting the processing by the mechanochemical reaction and the effect of improving the surface roughness, take into account the material to be processed, and the aforementioned cerium oxide, silica, barium sulfate, zirconium oxide Use properly.

  The grindstone hardness is changed according to the grain size of the abrasive grains used. As the abrasive grains become finer, the number of abrasive grains increases dramatically even at the same concentration level, and the cutting load acting on each abrasive grain decreases. Accordingly, the hardness of the grindstone is lowered as the abrasive grains used become finer. This makes it easy for the abrasive grains on the surface of the grindstone to be crushed and dropped even at a low pressing load.

As the form of the grindstone, those listed in 1) to 3) below are preferable.
1) Radiation in which a trapezoidal grindstone segment divided into a plurality of pieces in the radial direction is attached to the surface of the lapping surface plate with a gap (separation distance) of 2 mm or less between adjacent grindstone segments or in a state of no gap. Placement type.
2) A lattice-shaped type in which a square grindstone segment is attached to a lapping surface plate in a lattice shape with a gap of 2 mm or less between adjacent grindstone segments or without a gap.
3) A honeycomb shape type in which hexagonal grindstone segments are affixed to a lapping surface plate in a honeycomb shape with a gap of 2 mm or less between adjacent grindstone segments as in the above.

  The above-mentioned forms 1) to 3) are suitable for a large-sized grindstone having a diameter exceeding 300 mm (some of which have an outer diameter of φ1210 mm).

The grindstone of the present invention is preferably used under the conditions of grinding wheel rotation speed: 100 rpm or more, more preferably 100 to 200 rpm, workpiece rotation speed: 30 to 50 rpm, grinding stone pressing pressure against the workpiece: 100 to 1000 g / cm ² , and machining fluid supply. .

The processing fluid in this processing uses water in consideration of environmental aspects in order to facilitate cleaning in the subsequent process, but an additive may be added. As the additive, for example, a synthetic type water-soluble cutting fluid obtained by adding ethylene glycol can be used.
The supply amount of the working fluid is preferably 20 ml / min or less. More preferably, it is 3-10 ml / min.

  The present invention employs a polishing method for processing a hard brittle material under the above conditions using a vitrified grindstone and a lapping machine that employ diamond abrasive grains as the hard abrasive grains, and CBN abrasive grains as the hard abrasive grains. A polishing method for processing a ferrous material under the above conditions using a vitrified grindstone and a lapping machine is also provided.

  A grindstone using a vitrified bond as a binder for abrasive grains is excellent in dressing properties but also has a strong abrasive grain supporting force, and does not lose its shape during use. Therefore, it is possible to perform high-precision machining without sagging of the workpiece end face, which is a problem in polishing using loose abrasive grains.

  The vitrified grindstone of the present invention is hardened by vitrified bonds to increase the porosity, and the smaller the grain size of the grits used, the smaller the grindstone hardness. Abrasive grains are crushed and dropped.

  As the abrasive grains used become finer, the number of abrasive grains per unit volume increases dramatically even at the same concentration, and the actual load received by one abrasive grain decreases. For this reason, the hardness of the grindstone is reduced as the size becomes finer, the abrasive grains used are finer, and even when the grinding stone pressing pressure against the workpiece is low, the abrasive grains are slightly dropped.

  In addition, since the porosity is large, there are innumerable open pores on the surface of the grindstone, and the released pores are crushed and dropped to take in abrasive grains mixed in the working fluid (this can be water) Hold.

  As a result, processing with a sharpness in a form in which processing with a fixed abrasive wheel and processing with semi-fixed abrasive particles taken in and held in open pores are combined is advanced, and a grindstone with a fine abrasive grain size is used. In addition, it is possible to efficiently perform polishing under conditions of low rotational speed and low pressure.

  A grindstone with a trapezoidal, square, or hexagonal grindstone segment affixed to a lapping plate is superior in biting to the workpiece compared to a single flat grindstone. It leads to efficiency improvement.

  According to the polishing method of the present invention, high-precision polishing can be performed because processing is performed under the conditions of low rotation speed and low pressure using a grindstone having a fine abrasive grain size. In particular, according to the method in which the supply amount of the machining fluid is limited to a range of 20 ml / min or less, outflow of the dropped abrasive grains from the processed surface is suppressed, and the dropped abrasive grains are in the pores on the surface of the grindstone. It is easy to hold, the processing efficiency by the semi-fixed abrasive grains is increased, and the processing time is shortened.

(A) is a top view which shows an example of the low-pressure process vitrified grindstone for lapping machines of this invention, (B) is a perspective view which shows a part of the grindstone. (A) is a top view which shows the modification of the vitrified grindstone of FIG. 1, (B) is a perspective view which shows a part of the grindstone. (A) is a top view which shows the other example of the low pressure processing vitrified grindstone for lapping machines of this invention, (B) is a perspective view which shows a part of the grindstone. (A) is a top view which shows the modification of the vitrified grindstone of FIG. 3, (B) is a perspective view which shows a part of the grindstone. (A) is a top view which shows the further another example of the low-pressure process vitrified whetstone for lapping machines of this invention, (B) is a perspective view which shows a part of the whetstone. (A) is a top view which shows the modification of the vitrified grindstone of FIG. 5, (B) is a perspective view which shows a part of the grindstone. It is a side view which shows an example of the grinding | polishing processing method of this invention. It is an image figure at the time of use of the cross section of the low pressure processing vitrified grindstone for lapping machines of this invention.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a low-pressure machining vitrified grindstone for a lapping machine and a polishing method using the same according to the present invention will be described below with reference to FIGS.

  1A and 1B, FIG. 6A and FIG. 6B are all specific examples of the low-pressure processed vitrified grindstone 1, and FIG. 1A represents the entire grindstone. A top view and (B) are perspective views showing a part of each grindstone. The low-pressure machining vitrified grindstone 1 shown in each figure includes a lapping surface plate 2 and a grindstone 3.

  The low-pressure machined vitrified grindstone 1 of FIG. 1 is a radial arrangement type, and a trapezoidal grindstone segment 3A divided into a plurality of pieces in the radial direction is brought into close contact with the surface of the lapping surface plate 2 with adjacent grindstone segments closely spaced. It is pasted radially. The grindstone segments 3A may be arranged in three or more rows in the radial direction.

  The low-pressure machined vitrified grindstone 1 in FIG. 2 is a modification of the radial arrangement type in FIG. 1, and a trapezoid grindstone segment 3 </ b> A divided in a radial direction on the surface of the lapping plate 2 is adjacent to the grindstone segment. A gap g of 2 mm or less is provided between them in a radial manner.

  The low-pressure machining vitrified grindstone 1 of FIGS. 3 and 4 is a lattice-shaped type, and a plurality of small-sized square grindstone segments 3B are brought into close contact with each other as shown in FIG. 3 or adjacent as shown in FIG. A gap g of 2 mm or less is provided between the matching square grindstone segments 3B.

  The low-pressure processed vitrified grindstone 1 of FIGS. 5 and 6 is a honeycomb-shaped type, and small-sized hexagonal (it is regular hexagonal in the figure) grindstone segments 3C are brought into close contact with each other as shown in FIG. As shown in FIG. 6, a gap g of 2 mm or less is pasted between the adjacent square grindstone segments 3 </ b> C.

  The grindstone segments 3A, 3B, and 3C are composed of composite abrasive grains in which hard abrasive grains 5 and soft abrasive grains 4 (see FIG. 8) each having a grain size of 10 μm or less are combined with a melting point and a thermal decomposition temperature of 900 ° C. or less (implemented). The product used in the example is 850 ° C. or lower) and is bonded with a low melting point / low shrinkage vitrified bond.

  As shown in FIG. 8, the binder phase 6 by vitrified bond has a porous structure in which a large number of medium-sized pores 7 and small-sized pores 8 are scattered (including large-sized pores depending on the grindstone particle size). Thus, the porosity in the volume ratio of the grindstone 3 or the grindstone segments 3A, 3B, 3C is 55% or more. Further, the grindstone hardness satisfies the relationship shown in Table 1 above.

  The size of the medium size pores 7 and the large size pores (not shown) is about 10 to 20 times the particle size of the hard abrasive grains 5.

  Further, the size of the small-sized pores 8 is close to the particle diameter of the hard abrasive grains 5 (there are not only larger particles than the hard abrasive grains 5 but also small ones). These pores are partly on the surface of the grindstone that presses against the workpiece, whereby the surface of the grindstone has innumerable fine open pores (concave portions).

  The hard abrasive grains 5 are diamond abrasive grains or CBN abrasive grains, and abrasive grains having a particle diameter of 5 to 10 [mu] m (# 2000, 2000 mesh) to 2 to 4 [mu] m (# 4000, 4000 mesh) for roughing polishing. Is suitable. The roughing process is performed under conditions of a machining allowance of 20 μm or more to ensure a processed surface roughness of 0.1 μmRa or less.

  In addition, abrasive grains having a particle size of 0 to 2 μm (# 8000, 8000 mesh) to a particle size of 0 to 0.1 μm (# 120,000, 120,000 mesh) are suitable for polishing finishing. A mirror surface of 0.01 μmRa or less is secured by processing to 10 μm.

  The soft abrasive grains 4 are cerium oxide, silica, barium sulfate, zirconium oxide, and the like, and those having a particle diameter of 0.05 to 0.1 μm are used for the example grindstones.

  Further, as the low melting point / low shrinkage vitrified bond of the binder, one containing a reactive sintering agent made of zinc carbonate or magnesium carbonate and lithium fluoride is used.

Polishing with a lapping machine using such a grindstone is: grinding wheel rotation speed: 100 rpm or more, more preferably 100 to 200 rpm, workpiece rotation speed: 30 to 50 rpm, grinding wheel pressing pressure against the workpiece: 100 to 1000 g / cm ² , machining fluid Supply amount: 1 ml / min or more and 20 ml / min (the value converted to 1 cm ² of the surface area of the grindstone is 0.02 ml) or less, more preferably 3 to 10 ml / min (0.003 to 0.01 ml / cm ² ). It meets the conditions.
The conversion value of the surface area of 1 cm ² of the grindstone here is a value obtained for a trial grindstone having an outer diameter of φ380 mm and an inner diameter of φ140 mm (the same applies hereinafter).

  The processing situation is shown in FIG. In FIG. 1, 1 is a low-pressure machining vitrified grindstone with a grindstone 3 affixed on a lap surface plate 2, W is a workpiece (workpiece), 9 is a holder plate with a workpiece W affixed, 10 is a workpiece via the holder plate 9 A rotary pressurizing body for applying a pressing pressure and a rotational force to W, 11 is a rotary table of a lapping machine equipped with a grindstone.

  The work W is attached to the holder plate 9 using wax.

  As described above, the dropping supply amount of the working fluid is set to 20 ml / min or less. This is smaller than the supply amount in general polishing processing. The supply amount of the machining fluid is optimal so that the dynamic pressure effect of water can be obtained at the minimum because the amount of abrasive grains that have fallen off and mixed into the machining fluid does not flow out of the machining portion.

For performance evaluation, grinding wheels A to F of Examples having the compositions shown in Table 1 and grinding wheels A, B, and C of comparative examples were prepared. The abrasive used for each grindstone is a composite abrasive having the composition shown in Table 2, that is, a hard abrasive (diamond abrasive) by volume ratio of about 90% and a soft abrasive (SiO ₂ abrasive) of about 10%. is there.

In both Examples and Comparative Examples, diamond abrasive grains having a grain size of 0 to 2 μm (8000 mesh) were used, and soft abrasive grains of SiO ₂ having an average grain diameter of 0.05 μm were used.

  In order to confirm the influence of concentration (concentration), a high concentration product with a concentration of 110 (Example A), a medium concentration product with Examples 82 and 57 (Examples D and E), and a low concentration of 12 A concentration product (Example F) was also prepared.

Table 3 shows the compositions of the binders of Examples and Comparative Examples.

  The binder ratio with respect to 1 part by mass of the unit abrasive grains of the prototype sample is 0.25 parts by weight for Example A and Comparative Example A, 0.3 parts by weight for Example B and Comparative Example B, and Examples C to F. Comparative Example C is 0.4 parts by weight.

  Each prototype sample was uniformly mixed with abrasive grains and a binder, then compression molded into a predetermined shape and a predetermined size, and fired after drying.

  The firing temperature was kept at a maximum firing temperature of 770 ° C. for 4 hours for Examples A to C, and kept at a maximum firing temperature of 720 ° C. for 3 hours for Comparative Examples A to C.

  The hardness of the prototype wheel obtained, the structure in volume ratio%, and the degree of concentration are shown in Table 2 above.

  The wheel hardness in Table 2 is a value measured by a method of pressing a steel ball indenter having a diameter of 3.175 mm with a standard load of 29.4 N and a test load of 196 N using a Rockwell superficial hardness tester. expressed.

  Next, a low-pressure machined vitrified grindstone for a lapping machine having the shape shown in FIGS. 1 to 6 was prototyped using the prototype grindstone. The prototype has a grindstone outer diameter: φ380 mm and an inner diameter: φ140 mm. Table 4 shows the size and the number of used grindstone segments in this prototype grindstone.

  An actual cutting test was conducted using the low pressure machining vitrified grinding wheel for lapping machines of Examples A to F and Comparative Examples A, B, and C in Table 2. The form of the grindstone used is 1-9 in Table 4.

In this test, tap water was used as the processing liquid. The dripping supply amount of the tap water which is the processing liquid is 1 ml / min (0.001 ml / cm ² ), 2 ml / min (0.002 ml / cm ² ), 3 ml / min (0.003 ml / cm ² ), 6 ml. / Min (0.006 ml / cm ² ), 10 ml / min (0.01 ml / cm ² ), 20 ml / min (0.02 ml / cm ² ), 60 ml / min (0.06 ml / cm ² ), 100 ml / min ( 8 levels of 0.1 ml / cm ² ).

According to the supply amount of 20 ml / min or less out of these eight supply amounts, diamond abrasive grains or soft abrasive silica (SiO ₂ ) that have fallen off from the fixed abrasive grains in the lapping process are processed. It mixes with the liquid (water) and stays between the grindstone and the workpiece, and functions effectively as loose abrasive grains and semi-fixed abrasive grains taken into fine open pores.

  In the actual cutting test, a sapphire substrate having a diameter of 4 inches was processed, and the C surface of the substrate was polished. The C surface of the sapphire substrate was pre-processed under the following conditions, and the C surface was unified to a surface roughness of 0.7 μm Ra (center line average roughness).

-Pre-processing-
Polishing with a vitrified grindstone of the concentration 140 using diamond abrasive grains having an abrasive grain size of 22 to 36 μm (600 mesh).

  For processing for the actual cutting test, a Trinity-Y lapping machine EJW-380I-1ALD / CMP manufactured by Nippon Engis was used.

  The dimensions of the low-pressure processed vitrified grindstone used in the test are an outer diameter: φ380 mm, an inner diameter φ: 140 mm, and a thickness of 5 mm.

  The processing conditions were four levels of grinding wheel rotation speed 50 rpm, 100 rpm, 150 rpm, and 200 rpm.

  Moreover, the number of rotations of the work was set to three levels of 10 rpm, 30 rpm, and 50 rpm. The upper limit of the possible workpiece rotation speed of the lapping apparatus used for machining is 60 rpm, and since there is concern about the stability of machining at 60 rpm, the workpiece rotation speed in this test was set to 50 rpm.

  Table 5 shows combinations of the samples having the compositions shown in Tables 2 and 3, the grindstone forms shown in Table 4, the grindstone rotation speed, the work rotation speed, the actual load of machining, and the supply amount of the machining fluid.

  The working fluid used tap water. The evaluation results of this processing test are also shown in Table 5. The evaluation was performed by measuring the processing rate (removing allowance T per minute), the grinding wheel wear amount W, the finishing ratio (T / W), and the finished surface roughness, and comparing the obtained data.

From the test results in Table 5,
-Effect of binder-
When Examples 1, 3, 18, 32 and Comparative Examples 1 to 4 having the same amount of binder and only different bond type are compared with Comparative Examples 1 to 4, the grindstone of the Example has a large allowance although the amount of wear is not significantly different from that of the Comparative Example. Is improved by 40 to 60%, and the finished surface roughness is also improved. From this, the effectiveness of the invention grinding wheel can be confirmed.

-Influence of concentration of grinding wheel (concentration)-
From the comparison between Example 19 and Examples 33 to 35 in which the influence of the degree of concentration was observed, the grindstone of Example 33 in which the proportion of hard abrasive grains (diamond abrasive grains) was 70% and the degree of concentration was as low as 82 was measured. Compared to the grindstone of Example 19, the machining allowance is reduced by about 20%, while the grindstone wear amount is slightly better.

  Further, Example 35, which has an extremely low concentration level of 13, is in a state where it is not cut and worn, and does not function at all as a high-efficiency processing grindstone.

  From these facts, it can be inferred that 70% or more of the content ratio of hard abrasive grains (diamond abrasive grains) in the fixed abrasive grindstone is required.

  Conversely, a 100% hard abrasive grain (diamond abrasive grain) with zero soft abrasive content is excellent in abrasion resistance, but the machining allowance is reduced, and the surface roughness of the processed surface is Although it is a little worse, it has been found in past tests that wrinkles are generated on the processed surface of the workpiece. From this, it is considered that 70 to 95% of the hard abrasive grains are effective.

-Effect of grinding wheel rotation speed-
From the test results of Examples 2 to 5, as the number of grindstone rotations per unit time is increased (the rotation speed is increased), the machining allowance increases without deteriorating the grindstone wear amount and the finished surface roughness. . In Example 2 where the rotational speed of the grindstone is as low as 50 rpm, the machining allowance is extremely small and the finished surface roughness is not good.

  On the other hand, Examples 4, 19, 23, 25 to 27 and 29 with a grinding wheel revolution number of 150 rpm per unit time and Examples 5, 20, 24 and 30 with a grinding wheel revolution number of 200 rpm have a large machining allowance. The finished surface roughness is also good.

  The grinding wheel rotation speed in the test was limited to 200 rpm for the lapping machine, so machining at higher rotation speeds was not possible. However, the machining allowance and finished surface roughness were higher (high rotation speed). It can be easily guessed that the better results will be obtained by processing with (3).

  By the way, in polishing processing using loose abrasive grains, a grinding wheel rotational speed of 50 to 100 rpm is usually used, and processing at a grinding wheel rotational speed exceeding 100 rpm is clearly different from a general processing method.

-Influence of workpiece rotation speed-
From the test results of Examples 3, 6 and 7 in which the workpiece rotation speed was varied, the grinding wheel wear amount increased as the rotation speed per unit time of the workpiece increased (the rotation speed increased), but the machining allowance increased. The finished surface roughness of the machined surface is improved.

  According to the experimental results, the work rotation speed: 50 rpm gives the best result, and Example 6 having a low rotation speed of 10 rpm has an extremely small machining allowance and poor finished surface roughness.

  In addition, since the rotation speed of the workpiece is 60 rpm in the case of the lapping machine used, the upper limit in the test was set to 50 rpm at which stable performance is exhibited. Since the flatness of the processed workpiece surface deteriorates as the workpiece rotates at a higher speed (becomes a concave surface), the upper limit of the workpiece rotation speed is considered to be about 50 rpm, which is the same as the processing using loose abrasive grains. It is done.

-Effect of processing pressure (actual load)-
From the test results of Examples 3 and 8 to 11 with different actual loads, the allowance increases as the actual load is increased, and the allowance is maximized in Example 11 with an actual load of 1000 g / cm ² . However, the grinding wheel wear increases as the actual load increases. Therefore, the processing pressure at a fixed abrasive grinding wheel 300g ^/ cm ² ~1000g ^/ cm 2 C., considering the grindstone wear ^{amount, 300g / cm 2 ~500g / cm} 2 is better.

Processing pressure which is usually employed in free-abrasive machining ^is a ^{50g / cm 2 ~200g / cm 2} , machining with fixed abrasive grinding wheel is desirable to high working pressures. However, in a lapping process in which thin workpieces are often processed, it is not practical to apply an actual load of 500 g / cm ² or more due to problems such as workpiece warpage and carrier rotation.

-Effect of dripping supply amount of machining fluid-
From the test results of Example 3 and Examples 12 to 17 in which the dropping supply amount of the working fluid (in the example is water) is different, the allowance is large at a supply amount of 3 ml / min to 10 ml / min, and 6 ml / min. The allowance is the largest in the supply amount (Example 3).

  On the other hand, the finished surface roughness of Example 13 with the supply amount of 3 ml / min is most excellent. The influence of the supply amount of the machining fluid is remarkable, and the test result shows that the effective supply amount is 3 ml / min to 10 ml / min.

  If the amount of the processing fluid supplied is small, the fallen abrasive grains are less likely to be discharged from the polishing unit, but at the same time, the fallen abrasive grains cannot move freely. Connected.

  Further, if the amount of processing liquid supplied is too large, the dropped abrasive grains are discharged to the outside of the lapping machine and cannot function as loose abrasive grains or semi-fixed abrasive grains, so that the machining allowance is reduced.

  The amount of grinding wheel wear is reduced by removing the falling abrasive grains to the outside, and the grinding stones are suppressed from being scraped by the falling abrasive grains. However, if high-efficiency machining is targeted, increase the machining allowance. Need to prioritize.

-Effect of wheel shape and gap size between wheel segments-
In contrast to Examples 3 to 5 in which the trapezoidal grindstone segment was affixed to the lapping surface without any gaps, Examples 18 to 20 in which gaps were provided between the trapezoidal grindstone segments were slightly increased in machining allowance and grinding wheel wear amount under the same processing conditions. The improvement is seen.

  Regarding Examples 22 to 24 using the square grindstone segments, in the case of Example 23 where the grindstone rotational speed was 150 rpm, an increase in machining allowance was observed, whereas in Example 24 where the grindstone rotational speed was 200 rpm, the machining allowance was increased. The rotational speed of the grinding wheel is reduced to the same level as the machining allowance of Example 22 at 100 rpm. In each of Examples 22 to 24, the grinding wheel wear amount is 3.0 to 4.0 μm, which is relatively small.

  In Examples 28 to 31 using the hexagonal grindstone segment, no increase in the machining allowance is observed, but the grindstone wear amount is suppressed to 4.0 μm or less.

If the grindstone segment is a trapezoid, square, or hexagonal shape, the wheel wear amount will be reduced if the grindstone segment shape is 2 mm, but the machining allowance will be reduced. To do.
This is because the finely crushed abrasive grains and the dropped abrasive grains are discharged to the outside of the lapping machine and do not stay on the surface of the grindstone.

When a hexagonal grindstone segment is used in the structure in which a gap is provided between the grindstone segments, both the machining allowance and the grindstone wear amount are reduced as compared with those using other shape grindstone segments.
This is because the crushed or fallen abrasive grains are easily discharged to the outside of the grindstone along the groove, and the retention between the grindstone and the work is reduced and the function as free abrasive grains or semi-fixed abrasive grains is not exhibited. .

  It is presumed that this reduced the damage caused by the falling abrasive grains on the grindstone, which was a factor for improving wear resistance (decreasing the amount of wear on the grindstone).

  A grindstone that uses a trapezoidal grindstone segment or a square grindstone segment with a gap between the grindstone segments is rotating, so that the falling abrasive grains are suppressed from flowing out straight toward the outer periphery of the grindstone, Thereby, it becomes easy to stay between a grindstone and a workpiece | work, this enters into the open pore of a grindstone surface, and functions as a semi-fixation abrasive grain. It is thought that this works effectively and the allowance increases.

  In addition, since the wear amount of the grindstone is smaller when the grindstone segment is pasted with a gap than when the grindstone is pasted without any gap, some of the fallen abrasive grains can be externally damaged without damaging the grindstone. Seems to have been discharged.

  This can also be seen from the fact that Example 27 with a gap of 2 mm promoted this tendency, and compared with Example 23, the machining allowance was reduced and the grinding wheel wear amount was improved.

  For those with a gap between the grindstone segments, Examples 28 to 30 using a hexagonal grindstone segment and Examples 22 to 24 using a square grindstone segment are those at 150 rpm than at 100 rpm. However, the allowance has increased, while the allowance has decreased. This is presumably because the higher the rotation speed, the higher the tendency that the dropped abrasive grains are discharged to the outside through the groove between the segments. The tendency of the falling abrasive grains to be discharged to the outside is larger in the grindstone using the hexagonal grindstone segment than in the grindstone using the square grindstone segment.

  The grindstone using the trapezoidal grindstone segment is significantly different in the case of the same grindstone rotational speed with respect to the machining allowance, as compared with Examples 3 to 5 in which the gap between segments is 0 and Examples 18 to 20 in which the gap is 1 mm. There is no, and the machining allowance increases as the rotational speed of the grindstone increases.

  On the other hand, in the case of a grindstone using this trapezoidal grindstone segment, the wear amount of the grindstone tends to decrease by 20 to 30% when the gap between the segments is 1 mm as compared with the case where the gap is zero.

  This is because, for a grindstone using a trapezoidal grindstone segment, even if a gap between the segments is provided, most of the finely crushed abrasive grains and dropped abrasive grains are not discharged to the outside and remain between the grindstone and the workpiece. It can be inferred that the fine stones enter the fine open pores on the grindstone surface and are functioning effectively as semi-fixed abrasive grains.

  As can be seen from the results of Example 21, even though the grindstone uses a trapezoidal grindstone segment, when the gap between the segments is 2 mm, the tendency of the crushed and dropped abrasive grains to be discharged to the outside increases. Although the wear amount of the grinding wheel is reduced and the wear resistance is improved, the machining allowance is reduced, which is disadvantageous in terms of high efficiency machining.

  According to the test results of Examples 23, 25, and 26 in which the gap between the grindstone segments was set to 1 mm and the supply amount of the machining fluid was changed, the abrasive particles that were crushed and dropped when the supply amount of the machining fluid was small (Example 25) However, it cannot move freely between the grindstone and the workpiece, cannot enter the open pores on the grindstone surface, and it becomes difficult to function as a semi-fixed abrasive grain, so that the machining allowance is slightly reduced.

  However, the grinding wheel wear amount and the finished surface roughness of the workpiece surface are not significantly different from those of Examples 23 and 26 in which the machining fluid supply amount is large, and it can be said that the machining fluid supply amount 2 m1 / min is also in a practical range.

If the working fluid supply amount is too large, even if there is no gap between the grindstone segments, the crushed and dropped abrasive grains are discharged to the outside, the sharpness is lowered, and the machining allowance is reduced. Accordingly, the drop supply amount of the working fluid is preferably 1 to 20 ml / min (0.002 to 0.02 ml / cm ² ), and ^{2 to} 10 ml / min (0.003 to 0.01 ml / cm ² ). Better.

DESCRIPTION OF SYMBOLS 1 Low-pressure processing vitrified whetstone 2 Lapping surface 3 Whetstone 3A Trapezoid grindstone segment 3B Square grindstone segment 3C Hexagon grindstone segment 4 Soft abrasive 5 Hard abrasive 6 Bonding phase 7 Medium size pore 8 Small size pore 9 Holder plate 10 Rotation Pressurized body 11 Rotary table g Gap

Claims (8)

  A grindstone obtained by bonding composite abrasive grains, each of which has a particle diameter of 10 μm or less, and a combination of soft abrasive grains with a low melting point and low shrinkage vitrified bond having a melting point and a thermal decomposition temperature of 900 ° C. or less, The bonded phase by vitrified bond has a porous structure, and the porosity in the volume ratio of the grindstone is 55% or more, and countless fine pores opened to the outside on the surface pressed against the workpiece to be processed Low-pressure machining vitrified grinding wheel for lapping machines.   2. The low-pressure machined vitrified grindstone for a lapping machine according to claim 1, wherein the pores are a mixture of medium-sized pores of about 20 μm and small-sized pores of about 1 to 3 μm. The low-pressure processed vitrified grindstone for a lapping machine according to claim 1 or 2, which satisfies the relationship shown in the following table for the grindstone particle size and the grindstone hardness under the following test conditions.

  The hard abrasive grains of the composite abrasive grains are diamond abrasive grains or cubic boron nitride abrasive grains, and the soft abrasive grains are abrasive grains selected from cerium oxide, silica, barium sulfate, and zirconium oxide, and the hard abrasive grains thereof The low-pressure processed vitrified grindstone for a lapping machine according to any one of claims 1 to 3, wherein the ratio of the volume ratio of the soft abrasive grains to the soft abrasive grains is 70 to 95% hard abrasive grains and 5 to 30% soft abrasive grains.   Affix a trapezoidal stone segment, square stone segment, or hexagonal stone segment divided into multiple pieces in the radial direction to the surface of the lapping surface plate with a gap of 2 mm or less between adjacent grinding stone segments or with no gap between them. The low-pressure-processed vitrified grindstone for a lapping machine according to any one of claims 1 to 4, which is configured. Using the low-pressure processed vitrified grindstone for lapping machines according to any one of claims 1 to 5, wherein diamond grits are used as the hard abrasive grains, the grindstone rotation speed: 100 rpm or more, the work rotation speed: 30-50 rpm, A grinding method for grinding the surface of a work made of a hard brittle material under conditions of a grinding stone pressing pressure: 100 to 1000 g / cm ² and a processing liquid supply amount: 1 ml / min to 20 ml / min. Using the low-pressure machining vitrified grindstone for a lapping machine according to any one of claims 1 to 5, wherein CBN abrasive grains are used as the hard abrasive grains, the grindstone rotation speed: 100 rpm or more, the work rotation speed: 30-50 rpm, Grinding method for grinding the surface of a workpiece made of an iron-based material under the conditions of a grinding stone pressing pressure: 100 to 1000 g / cm ² and a working fluid supply amount: 1 ml / min to 20 ml / min.   The polishing method according to claim 6 or 7, wherein the polishing is performed with the grindstone rotation speed set to 100 to 200 rpm and the processing liquid supply amount set to 3 to 10 ml / min.

Images