JP2013046960A - Resin bond grinding wheel suitable for grinding processing of hard material such as nitride-added cermet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grinding wheel capable of machining a nitride-added cermet and cemented carbide with a high grinding ratio.SOLUTION: A diamond resin bond grinding wheel is configured such that mixed abrasive grains are used which contain a main component of abrasive powder composed of two kinds of diamond and DLC, and in which a ratio containing the diamond is 25% to 45% (55% to 75% in DLC ratio), and a grinding condition is set by which grinding heat produced during grinding does not become excessive, so that DLC to be preferentially lost is optimized to efficiently expose diamond abrasive grains of a sharp cutting edge.

Description

  The present invention relates to a resin-bonded diamond grindstone that can grind a workpiece having a low grinding ratio under a generally adopted grinding condition, such as nitrogen-added cermet, at a high grinding ratio.

  Among the wear-resistant tools and cutting tools, particularly in applications requiring high adhesion wear resistance, nitrogen-added cermets, that is, Ti (C, N) -XC-Ni-Co and TiC-TiN-XC-Ni-Co Cermet is used. Here, the C / N atomic ratio is usually 3/7 to 9/1, X is a metal element such as Mo, W, Ta, Nb, Zr, V, and Cr, and the total amount is 0 to 45 mass% in terms of carbide XC. The weight ratio of the binding metals Ni and Co is 0/100 to 100/0, and the total amount is 0.1 to 35 mass%. Here, nitride XN may be used instead of carbide XC.

  In order to process the nitrogen-added cermet sintered body into a wear-resistant tool or cutting tool having a predetermined dimension, a grinding method using a diamond grindstone is generally used. With a conventional cermet grindstone, for example, the shape is φ200 mm × 10 mm, and using a surface grinding machine EPG52 manufactured by Nagase Integrex Co., Ltd., the grindstone peripheral speed is 1500 m / min, the left and right feed speed is 12 m / min, the front and rear feed speed is 150 mm / min, Grinding ratio, ie (grinding removal volume) / (grinding wheel), when a 1mm grinding is performed on a φ60mm disc-shaped nitrogen-added cermet (hardness 91.0HRA) with a depth of 10 μm and a coolant supply rate of 60 L / min The wear volume is about 16.

  Since the grinding ratio when cutting WC-Co cemented carbide (hardness 88.0HRA) under the same conditions is about 780, the grinding ratio of nitrogen-added cermet is about 1/49 compared to cemented carbide. There is extremely low. This result indicates that the wear rate of the abrasive layer of the grindstone is about 49 times greater in the nitrogen-added cermet than in the cemented carbide.

  This is because (1) the carbonitride phase (Ti (C, N) and XC in the nitrogen-added cermet (Ti, X) (C, N). Unlike WC as a component, it is generally a non-stoichiometric compound, that is, the (C + N) / Ti atomic ratio and the (C + N) / (Ti + X) atomic ratio are both 1 or less, and the crystal lattice point of C or N is a vacancy. Therefore, when the diffusion of atoms becomes active due to the temperature rise based on the grinding heat generated in the grinding process, it is easy to absorb C atoms in the abrasive grains.

  (2) When C atoms are absorbed, the friction surface of the abrasive grains wears and becomes smooth (Non-Patent Document 1), that is, “smooth wear” occurs.

  (3) By smoothing the abrasive grains, the frictional resistance between the abrasive grains and the cermet is increased, the temperature of the friction surface is further increased, and absorption of C atoms, that is, smooth wear becomes more and more remarkable. Oxidation and graphitization of the grains occur, and the frictional resistance increases further.

  (4) When such excessive smooth wear occurs and the frictional resistance exceeds the abrasive gripping force of the bond material, the abrasive grains fall off from the grindstone bond layer, and in some cases, seizure occurs between the bond layer and the cermet. It is generally considered that the falling abrasive grains rub against (co-rubb with) the remaining abrasive grains, resulting in further smooth wear and dropping of the remaining abrasive grains and wear.

  In order to avoid this, conventional diamond wheels for nitrogen-added cermets are gripped by a resin bond layer with a medium hardness using a highly friable diamond abrasive powder before excessive smooth wear occurs. Since grinding is performed by repeatedly causing early breakage and dropping of the abrasive grains so that a new cutting edge of the abrasive grains is always generated, the wear rate of the abrasive grains is high, that is, the grinding ratio is low.

  In order to confirm the “smooth wear” described in the above paragraph 0006, the present inventors also first ground a nitrogen-added cermet (hardness 91.0HRA) sintered body with a commercially available diamond wheel for nitrogen-added cermet. The abrasive wear state of the grindstone after the grinding power increased considerably from the initial stage was investigated. As a result, most of the abrasive grains exhibited a smooth wear surface.

The reason for this is that the present inventors reacted Ti (C, N) carbonitride phase or TiN nitride phase in nitrogen-added cermet and these with added carbide (XC) such as Mo ₂ C and WC. The resulting (Ti, X) (C, N) carbonitride solid solution phase (generally present around (Ti, X) (C, N) grains. That is, the hard phase particles have a core portion of (Ti, X) ( (C, N), the outer peripheral portion becomes a (Ti, X) (C, N) carbonitride solid solution phase, indicating a so-called core / rim structure), but not directly absorbing C atoms from diamond or DLC, It was thought that diamond and DLC were graphitized and mainly absorbed C atoms of the graphite. In Non-Patent Document 1, the cause is the interfacial reaction between diamond and the carbonitride phase or nitride phase.

  Next, the appearance of particles of five types of commercially available resin particles for resin-bonded diamond whetstones (referred to as A, B, C, D, and E) (if there is a coating layer, only the coating layer is treated with acid) The diamond ratio (DLC ratio) was examined in detail. FIG. 1 shows the appearance of three types of abrasive grains A, C, and E as an example. When observing each of these abrasive grains in detail, the surface of the abrasive grains of any abrasive powder is not necessarily limited to the multi-faceted state peculiar to diamond, but includes many irregularities. Their ratio varies depending on the type of abrasive powder. The aim of this is to make the surface of the abrasive grains uneven, and to ensure adhesion with the bond material of the grindstone.

  Because of the surface shape, the inventors of the present invention do not include abrasive grains consisting of perfect diamond, but also include some diamond-like carbon (also referred to as amorphous carbon, hereinafter referred to as DLC), the ratio of which I felt the possibility of different depending on the type of grain. Therefore, the above-mentioned commercially available resin-bonded diamond abrasive powders 5 types by using a scanning laser Raman microscope RAMAN-11 manufactured by Nanophoton Co., Ltd. (If there is a coating layer, only the coating layer is removed by treatment with acid) Was subjected to Raman analysis (surface analysis).

Image is obtained by the Raman scattered light obtained by the Raman spectrometry In this method, diamond peak (Raman shift 1330 cm ^-1) in green, when the DLC peaks (Raman shift 1450 cm ^-1) displayed in yellow to red, The abrasive grains in the scanned range are displayed in different colors. And it was clarified that each ratio can be found by measuring the number of pixels of both types. The results are as shown in Table 1, and it was found that each abrasive grain contains a considerable amount of DLC, and that the DLC content varies depending on the type of abrasive grains.

  In order to estimate the stability of these diamonds and DLC against temperature rise due to frictional heat during grinding, the diamond abrasive powder and DLC film were heated in the atmosphere (heating temperature up to 1400 ° C in the former and 600 ° C in the latter. Changes due to the heating time of 30 minutes were examined. The reason why the DLC film was used here was that a powder with 100% DLC could not be found.

  The results are shown in FIG. 2 and FIG. From this, it can be seen that diamond burns and disappears at about 810 ° C. to 980 ° C., and that the DLC film burns and disappears at a much lower temperature of about 300 ° C. to 400 ° C. Since these are atmospheric results, they show oxidation, but it is presumed that both diamond and DLC are carbonized (graphitized) on the friction surface where little oxygen is supplied during grinding (wet, ie, using a coolant).

  From this fact, the inventors of the present invention understand that the carbonitride particles such as Ti (C, N) absorb carbon of the abrasive grains because the carbonitride particles such as Ti (C, N) as described above. Non-stoichiometric compound, that is, (C + N) / Ti atomic ratio and (C + N) / (Ti + X) are 1 or less and are compounds that easily absorb C. Even if it is applied, the temperature of the friction surface between the abrasive grains and the cermet to be ground rises due to grinding heat, and mainly DLC in the abrasive grains is carbonized and converted to graphite (that is, to the carbon in the state before being synthesized). (Return) After that, the idea that carbonitride particles mainly absorb C atoms of DLC-derived graphite preferentially was obtained.

  This is because the bonding force between C atoms and C atoms is graphite <DLC <diamond. Here, since the frictional heat generated on the friction surface (cutting surface) between the abrasive grains and the work material is not instantaneously removed by the cooling liquid in the vicinity of the friction surface, the inventors of the present invention have the C atom in the vicinity of the friction surface. It is believed that the temperature will rise to a temperature at which sufficient diffusion occurs.

  From the above, it is known that the grinding of nitrogen-added cermet must be performed under grinding conditions in which grinding heat is difficult to generate in order to suppress wear of abrasive grains. Further, if the grinding conditions are set so that the grinding heat does not become excessive, DLC in the abrasive grains is mainly graphitized, and this is absorbed by carbonitride particles such as Ti (C, N) of cermet (1) charcoal. Atom vacancies in nitride particles can be eliminated, thereby suppressing C atom absorption from diamond and (2) DLC of abrasive grains disappears preferentially, so that sharp cutting edges are formed on the abrasive grain surface. The idea is that the diamond part of the steel can be exposed, so that the original performance of the abrasive grains can be extracted and grinding can be performed efficiently. This is the first finding.

  The grinding heat is caused by heat generation due to friction between the abrasive grains and the material to be ground and heat generation due to chip deformation. The calorific value per unit time of both should be reduced if the grinding wheel peripheral speed is lowered. Therefore, it is presumed that smoothing due to abrasive wear decreases when the grindstone peripheral speed is lowered.

  In order to confirm this, a resin bond grindstone φ200 mm × 10 mm using abrasive powder C and a surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd., left / right feed rate 12 m / min, front / rear feed rate 150 mm / min, cutting The grinding wheel peripheral speed exerted on the abrasive wear state of the grinding wheel surface when grinding a 1 mm diameter disk-shaped nitrogen-added cermet (hardness: 91.0HRA) of φ60 mm at 10 μm and a coolant supply amount of 60 L / min. The influence was investigated and FIG. 4 was obtained (the “smoothing rate” in the figure is described later).

  As expected, the smooth wear surface decreased as the wheel peripheral speed decreased. Further, as shown in the figure, the grinding ratio was remarkably increased as the grinding wheel peripheral speed was lowered. Here, the present inventors color-coded the surface that was worn and smoothed and the surface that was not worn and smooth on the magnified observation photograph (250 times) of the abrasive grains on the surface of the grindstone, and determined the respective areas as pixels. Thus, the ratio of the area of the wear smooth surface to the sum of the areas of both types (that is, the cross-sectional area of the abrasive grains on the observation surface) is defined as “smoothing rate”. FIG. 5 shows a schematic diagram and a calculation formula thereof.

  FIG. 6 shows the influence of the grinding wheel peripheral speed on the grinding ratio and the smoothing rate. From this figure, it can be seen that when the grinding wheel peripheral speed is lowered, the smoothing rate is reduced and the grinding ratio is drastically improved. In other words, compared to the conventional 1500 m / min grinding wheel speed, it reaches about 94 times (1509/16 from the measured values shown in Table 2 below, although it cannot be read from the figure alone) at 800 m / min. That is, the above-mentioned first knowledge of the present inventors that “by setting the grinding conditions under which the grinding heat does not become excessive, the original performance of the abrasive grains can be extracted and can be efficiently ground” has been proved.

Even when the grinding wheel peripheral speed is slowed, when the cutting depth and table feed speed are increased, or when the nitrogen content of the cermet is increased, the hard phase particle size is further atomized (hardness HRA is increased). In this case, the amount of generated grinding heat is increased, and the wear form and smoothness of the grindstone are changed. Therefore, the grinding ratio tends to decrease from the value shown in FIG. However, when the grinding removal volume is 28.3 cm ³ , a high grinding ratio can be obtained as long as the aforementioned smoothness of the abrasive grains is less than 70%. Therefore, it has been found that the grinding may be performed under the condition that the abrasive grain smoothing rate of the grindstone surface when the nitrogen-added cermet is ground is less than 70%. This is the second finding.

  By the way, it is known that when the peripheral speed of the grindstone is lowered, the stress in the tangential direction of the abrasive grains increases, and the abrasive grains easily fall off from the grindstone bond layer (resin). FIG. 7 shows the result of the investigation, and a resin bond grindstone φ200 mm × 10 mm using an abrasive powder E with less irregularities on the abrasive grain surface than the abrasive powder C, and using a surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd. Grinding wheel peripheral speed 800 m / min, left / right feed speed 12 m / min, front / rear feed speed 150 mm / min, depth of cut 10 μm, coolant supply rate 60 L / min. 0HRA) The grindstone surface after 1 mm grinding of the sintered body is shown.

  In this case, the grinding ratio is 72, which is significantly lower than 1509 in the case of the abrasive powder C. The cause of this was found by observation of the wear state that the abrasive powder E was frequently dropped. That is, it has been found that the uneven shape of the abrasive grain surface is important.

  Next, it was investigated whether or not the grinding ratio was improved to prevent dropping. In order to prevent the dropout, the surface of the abrasive grains may be uneven under the same bond material. FIG. 8 is a result of investigating it, and using a surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd. with a resin bond grindstone φ200 mm × 10 mm using an abrasive powder A having more surface irregularities than the abrasive powder C, Grinding wheel peripheral speed 800m / min, left / right feed speed 12m / min, front / rear feed speed 150mm / min, depth of cut 10μm, coolant supply amount 60L / min, φ60mm disk-shaped nitrogen addition cermet (hardness 91.0HRA) The grindstone surface after grinding 1mm of a sintered compact is shown.

  In this case, the grinding ratio is 98, which is significantly lower than 1509 in the case of the abrasive powder C. As apparent from the comparison of the state of the abrasive grains in FIGS. 7 and 8 above, the abrasive powder E has less falling off of the abrasive grains than the abrasive powder A, but is severely worn. This can be considered that the abrasive powder A has many irregularities, that is, too much DLC, so that the diamond to be used as a cutting edge becomes too small, and the strength and hardness of the abrasive grains are significantly reduced. It was judged that both of these acted synergistically and the abrasive wear resistance was insufficient.

  For these reasons, the uneven shape on the abrasive grain surface, that is, the DLC ratio or the diamond ratio is extremely important, but those ratios of the abrasive powders A to E are as shown in Table 1 above. Table 2 shows the relationship between both ratios and the grinding ratio.

  From this, as already described in FIG. 6, the abrasive powder C reaches about 94 (1509/16) times at 800 m / min compared with the conventional 1500 m / min. When the abrasive powders B, C, and D are used and the grinding wheel peripheral speed is set to 900 and 800 m / min, the grinding ratio is 910 to 1700. In the case of the abrasive powders A and E, the grinding wheel peripheral speed is 800 m / min. The grinding ratios are 98 and 72, which are extremely small. Under the same 800 m / min grinding wheel peripheral speed, the grinding stone of abrasive powder C is about 15 times (1509/98) and about 21 (1509/72) times that of grinding stones A and E, respectively. Become.

  From this, it is clear that the abrasive powders B, C and D have a significantly higher grinding ratio than the abrasive powders A and E. Therefore, in order to increase the grinding ratio, it was found that the diamond ratio of the abrasive grains is appropriately in the range of 25% to 45% (DLC ratio in the range of 75% to 55%). Even in grinding of a cemented carbide (hardness 88.0 HRA), when the grinding wheel peripheral speed is 800 m / min, the abrasive powder is about 29 times (3938/136) in E with respect to E. In the case of the same abrasive powder C in the cemented carbide, the peripheral speed of the grinding wheel is increased to about 5 times (3938/780) at 800 m / min compared to the conventional 1500 m / min. Even with hard alloys, it is clear that the grinding ratio increases when the grinding wheel peripheral speed is decreased.

  That is, when the diamond ratio of the abrasive grains is less than 25%, the abrasive wear amount increases excessively even under conditions where the grinding wheel peripheral speed is low so that excessive grinding heat is not easily generated, and the grinding ratio deteriorates. On the other hand, when the diamond ratio is 55% or more, the abrasive grains fall off from the bond layer under a condition that the grinding wheel peripheral speed is low so that excessive grinding heat is hardly generated, and the grinding ratio is deteriorated. Therefore, the range of 25% to 45% is appropriate for the proportion of diamond in the abrasive grains. This is the third finding. That is, the grinding ratio can be increased by selecting the abrasive powder and decreasing the grinding wheel peripheral speed.

  The resin bond that holds the abrasive grains may be a resin-based hard bond that can hold the abrasive grains satisfying claim 1. The above-mentioned abrasive grain size is the result of # 140 (average diameter is about 108 μm), but if the abrasive powder is in the size range having grinding power, development of a grinding wheel with excellent grinding ability based on the same principle. It is possible to search for grinding conditions.

  In addition, some abrasive grains are coated with Ni, Ti, Cu, Al, etc. However, even when these are used, since the wear surface of the abrasive grains in actual grinding is peeled off, the type of coating material should be changed. It was confirmed that the present invention was applied (useful) regardless of the case.

In the diamond grinding wheel for grinding, whose bond material is mainly resin, the proportion of diamond is 25% to 45% by surface analysis using a scanning laser Raman microscope RAMAN-11 manufactured by Nanophoton Co., Ltd. (the proportion of DLC is 55% to 75%) ) using the resin bonded grinding wheel using abrasive powder, grinding nitrogen added cermet (the hardness 91.0HRA) at 28.3 cm ³ grinding and smoothing rate of the grinding wheel surface if is less than 70% conditions By doing so, the grinding ratio can be about 94 times (1509) of the conventional value (16). Further, the WC-Co cemented carbide (hardness 88.0HRA) can be ground at about 29 times (3938) the conventional grinding ratio (136).

Satoshi Suzuki, Hidekage Matsubara, Hiroshi Hayashi, Yasuo Sato: Powder and Powder Metallurgy, 30 (1983), p. 235.

It is the external appearance of diamond abrasive powder for resin bonds. Effect of heating temperature on diamond weight (atmosphere: air, time: 30 min). It is the result measured about the diamond abrasive grain considered to have the highest crystallinity. Diamond-like carbon (DLC) Influence of heating temperature on the film thickness (atmosphere: air, time: 30 min). It is the influence of the grindstone peripheral speed on the wear state of the abrasive grains after grinding the nitrogen-added cermet with a resin bond grindstone. Grinding wheel: Resin bond grindstone φ200 mm × 10 mm, using abrasive powder C Processing equipment: Surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd. Processing conditions: Left / right feed rate 12 m / min, front / rear feed rate 150 mm / min, depth of cut 10 μm, coolant supply 60L / min, total cutting depth 1mm Workpiece: φ60mm disk-shaped nitrogen-added cermet (hardness 91.0HRA) sintered body It is a formula for calculating the smoothing rate. S _Fn is the smooth wear surface of the abrasive grains S _NFn is the non-smooth area of the abrasive grains S _0n is S _Fn + S _NFn It is the influence of the grinding wheel peripheral speed on the grinding ratio and the smoothing rate of the abrasive grains. Grinding wheel: Resin bond grindstone φ200 mm × 10 mm, using abrasive powder C Processing equipment: Surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd. Processing conditions: Left / right feed rate 12 m / min, front / rear feed rate 150 mm / min, depth of cut 10 μm, coolant supply 60L / min, total cutting depth 1mm Workpiece: φ60mm disk-shaped nitrogen-added cermet (hardness 91.0HRA) sintered body It is a worn state of abrasive grains after the nitrogen-added cermet is ground with a resin bond grindstone. Grinding wheel: Resin bond grindstone φ200 mm × 10 mm, using abrasive powder E Processing equipment: Surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd. Processing conditions: grinding wheel peripheral speed 800 m / min, left-right feed speed 12 m / min, front-rear feed speed 150 mm / min , Cutting 10 μm, coolant supply amount 60 L / min, total cutting amount 1 mm Workpiece: φ60 mm disk-shaped nitrogen-added cermet (hardness 91.0 HRA) sintered body It is a worn state of abrasive grains after the nitrogen-added cermet is ground with a resin bond grindstone. Grinding wheel: Resin bond grindstone φ200 mm × 10 mm, using abrasive powder A Processing equipment: Surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd. Processing conditions: grinding wheel peripheral speed 800 m / min, left-right feed speed 12 m / min, front-rear feed speed 150 mm / min , Cutting 10 μm, coolant supply amount 60 L / min, total cutting amount 1 mm Workpiece: φ60 mm disk-shaped nitrogen-added cermet (hardness 91.0 HRA) sintered body

As a result of grinding under the following conditions 1 to 6, Table 2 was obtained.
1. Grinding equipment related surface grinder EPG52 manufactured by Nagase Integrex Co., Ltd.
Wheel size φ200mm × 10mm
Table left / right speed 12m / min
Table longitudinal speed 150mm / min
Cutting depth 10μm / pass
Coolant supply amount 60L / min
Total depth of cut 1mm
2. Smoothing rate The surface of the grindstone is magnified, and the wear-smoothed surface and the non-smoothed and non-smoothed surface are color-coded, and each area is read with a pixel. The ratio of the area of the wear smooth surface to (that is, the abrasive grain cross-sectional area on the observation surface) is defined as the smoothing rate.
3. Material to be ground φ60 × 10mm
4). The abrasive _{Ti (C, N) -Mo 2} C-WC-Ni cermet hardness 91.0HRA
5. Material to be ground WC-Co Cemented Carbide Hardness 88.0HRA

Claims (1)

  The main component of the abrasive powder consists of two types of diamond and diamond-like carbon (DLC), the ratio of which is a surface analysis by a scanning laser Raman microscope RAMAN-11 manufactured by Nanophoton Co., Ltd. (with a coating layer such as Ni) Is 25% to 45% of diamond (and therefore DLC is 75% to 55%) in the case where only the coating layer is removed by treatment with acid or the like, and the grinding heat generated during grinding is excessive. A diamond resin bond grindstone that optimizes DLC that disappears preferentially by setting the grinding conditions that do not become necessary, so that diamonds with sharp cutting edges are efficiently exposed.