JPS6351823B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grinding method for grinding a cylindrical inner surface using a rotating grindstone.

In small-diameter internal grinding processing in which a cylindrical inner surface with a diameter of about 10-odd millimeters is ground using a rotary grindstone, a rotary grindstone 1 is used to support and rotate the inner surface of the cylindrical surface, as illustrated in the attached Fig. 1. The support shaft 2 is elastically bent and pressed against the cylindrical inner surface 3 to be ground, and for this reason, the spindle 4, which supports and rotates the rotation support shaft 2, is pressed against the inner surface 3 of the cylinder to be ground. The rotational axis 5 is set to be inclined by a certain swing angle α with respect to the central axis 6 of the cylindrical inner surface 3 to be ground. In a mass production line that continuously produces a large number of articles of the same shape through small-diameter internal grinding using this method, several grinding conditions and grindstone specifications are taken into account in order to satisfy a predetermined processing accuracy. Once the angle α is determined, it is common to continue processing a large number of articles while keeping the swing angle constant.

However, if grinding is continued on a large number of objects while keeping the swing angle constant, as the number of grinding increases, the entrance diameter and back diameter of the ground cylindrical inner surface will change as the number of grinding increases, as shown in Fig. 2. The diameter difference between the two diameters gradually increases, and the shape of the ground cylindrical inner surface becomes tapered from the gradually increasing entrance side toward the back side. This is because as the number of grinding processes increases, the rotary whetstone is used with successive dressings, but as the grinding and dressing are repeated, the diameter of the whetstone gradually decreases. This is due to the fact that the pressing force per unit area when pressed against the shaped inner surface gradually increases, the grinding resistance decreases, and the amount of elastic deflection of the rotary support shaft 2 decreases. Therefore, in conventional small-diameter internal grinding, the operator is required to interrupt the machining process and correct the swing angle α every time the taper reaches a number of machining operations that pose a risk of exceeding the allowable limit. ing. However, such correction work is a major obstacle in fully automating this type of processing work. To solve this problem, it is of course possible to incorporate an automatic correction mechanism into the grinding machine that operates to rotate the entire spindle unit and reduce the swing angle little by little every time a predetermined number of machining is reached. solutions are very expensive.

The present invention addresses the above-mentioned problems in small-diameter internal grinding, and by modifying the feeding process in which the rotary support shaft of the rotary grindstone is sent in the cutting direction, the same grinding process can be achieved regardless of changes in the diameter of the rotary grindstone. The present invention proposes a method for properly grinding a cylindrical inner surface continuously at a swing angle so that the taper is always 0.More specifically, the present invention provides a method for carrying out grinding while feeding the rotary support shaft in the cutting direction. Transition from the cut-in grinding step to a spark-out step in which the feeding of the rotary support shaft in the cut direction is stopped and grinding is performed while driving the rotary grindstone in the cut direction only by the return force of the elastic deflection of the rotary support shaft. It is proposed that the time point be made variable and, more specifically, be brought closer to the end point of grinding as the diameter of the rotary grindstone decreases.

As mentioned above, in the grinding method in which the cylindrical inner surface is ground with a rotary grindstone while the rotary support shaft is elastically bent, the grinding process is called depth-of-cut grinding, in which grinding is performed while the rotary support shaft is being fed in the cutting direction. process, and a spark-out process in which the rotating support shaft stops feeding in the cutting direction and grinding is performed while driving the rotary grindstone in the cutting direction only by the return force of the elastic deflection of the rotating support shaft. It is common practice. This is illustrated with reference to FIG. 3 as follows.

Figure 3 is a graph showing the depth of cut in which the rotary support shaft of the rotary grindstone is sent in the cutting direction during grinding, and the corresponding depth of cut in which the rotary grindstone actually moves in the cutting direction, versus time. It is. In the figure, the part indicated by solid line a is rapid traverse in which the rotating grindstone is rapidly sent to the machined surface of the workpiece in the early stage of grinding, and contact between the rotating grindstone and the cylindrical inner surface to be ground has not yet occurred. Not yet. The solid line b in the figure indicates the rough polishing stage, which is divided into a first stage up to Q ₀ and a second stage from Q ₀ to Q ₁ . In the first stage, the force pressing the rotary grindstone against the cylindrical inner surface to be ground is still relatively small, so there is almost no elastic deflection of the rotary support shaft, and the depth of cut of the rotary support shaft is reduced. and the depth of cut of the rotary grindstone are almost the same. Q ₀ to Q ₁ show how the depth of cut of the rotary support shaft increases with time in the second stage of rough grinding, while the broken line b' shows the depth of cut of the rotary grindstone in the second stage of rough grinding. shows an aspect in which the amount increases over time. At this stage, the elastic deflection of the rotary support shaft increases, so that the cutting amount of the rotary grindstone becomes smaller than the amount by which the rotary support shaft is actually sent in the cutting direction. At this stage, the diameter of the ground cylindrical inner surface is usually constantly monitored by an in-process gauge, and when the depth of cut of the rotary wheel reaches a predetermined P ₁ , the grinding process begins with rough grinding. Switched to Seiken. The depth of cut of the rotary support shaft at this switching point is _Q1 .

The solid line c shows how the depth of cut of the rotary support shaft increases with time during fine-honing, and the broken line c' shows how the rotary grindstone actually moves in the direction of the cut when the rotary support shaft is sent in the direction of the cut as shown in the solid line c. This shows how it is done. As fine grinding progresses in this way, when the in-process gauge detects that the actual depth of cut has reached _P2 , the grinding machine stops feeding the rotary support shaft in the direction of the cut, and from now on A spark-out process is carried out in which grinding is performed while the rotary grindstone is driven in the cutting direction only by the return force of the elastic deflection of the rotary support shaft. In the figure, the solid line d shows how the feed amount of the rotary support shaft changes over time during the spark-out process, and of course this remains at a constant amount, which is the depth of cut _Q2 at the end of fine polishing. During this spark-out period, the depth of cut of the rotary grindstone further increases from _P2 as shown by the broken line d', and when it is confirmed by the in-process gauge that the depth of cut has reached the target value _P3 , The grinding process is finished.

In such conventional grinding methods, the spark-out starting point is set at a point where the spark-out depth of cut ε is set to a predetermined value, that is, the depth of cut is smaller than the final target value _P3 by a predetermined amount ε. ₂ .

The present inventors investigated the relationship between the depth of cut or machining allowance caused by such spark-out and the cylindricity of the cylindrical inner surface finally obtained by grinding, and as a result, as illustrated in FIG. It was found that as the out-cutting allowance increases, the cylindricity gradually decreases. Here, cylindricity is the difference between the entrance diameter and the back diameter of the cylindrical inner surface to be ground, and a positive value of cylindricity means that the entrance diameter is larger than the back diameter, and the cylindrical inner surface is closer to the entrance. On the other hand, if the cylindricity is negative, it means that the ground inner surface of the cylindrical shape is tapered and opens toward the back of the inlet.

The present inventors effectively utilize this relationship between spark-out machining allowance and cylindricity, and shift the spark-out starting point to compensate for the decrease in cylindricity caused by the decrease in the diameter of the rotary grinding wheel. The Company intends to compensate for such damages.

FIG. 5 illustrates how to shift the sparkout initiation point as the diameter of the wheel decreases in accordance with the present invention. 4 is a diagram corresponding to an enlarged view of a portion S in FIG. 3. FIG. When several objects are further ground from the grinding state shown in Fig. 3 and the diameter of the rotary grindstone is reduced by a predetermined amount, the transition point from fine grinding to spark out is P ₂ , Q ₂ is delayed from the point in time to the point corresponding to P ₂ ′ and Q ₂ ′.
In this case, the sparkout follows the course shown by the broken line d'' from the depth of cut corresponding to P ₂ ′ and reaches the predetermined final depth of cut at the time P ₃ ′, but the machining distance ε′ due to the sparkout is is smaller than the value ε.If the spark-out machining allowance is reduced from ε to ε' in this way, the cylindricity increases correspondingly, and the amount of increase increases the cylindricity due to the decrease in the diameter of the rotary grinding wheel. is set exactly equal to the amount of decrease in
The cylindricity of the ground cylindrical inner surface is kept constant, and if the setting is made to set the value to 0 from the beginning, the cylindricity will always be 0 regardless of the decrease in the diameter of the rotating grindstone. Grinding to a true cylindrical inner surface can be performed.

FIG. 6 is a schematic diagram showing one embodiment of an apparatus for carrying out the grinding method according to the present invention. The amount by which the diameter of the rotary grindstone is reduced is determined by the number of times the article having a cylindrical inner surface is processed by the rotary grindstone and the number of times the rotary grindstone is dressed. In this case, when the number of dressings has a certain relationship with the number of processes on the article, the amount of reduction in the diameter of the rotary grindstone can be determined based only on the number of processes. Therefore, in the apparatus shown in FIG. 6, a machining number counter 10 and a dressing number counter 1 are used as information sources for providing the diameter of the rotary grindstone or its reduction amount.
1 is used, and the information on the number of processing and the number of dressings from these counters and the diameter of the cylindrical inner surface 3 or the grinding process provided by the in-process gauge 12 that measures, for example, the inlet diameter of the cylindrical inner surface 3 to be ground. Information regarding the depth of cut in the cut is supplied to the control device 13. Based on this information, the control device 13 determines the transition point at which the grinding process is shifted from the polishing process to the spark-out process, and supplies the output signal to the cutting feed device 14 to control its operation.

Thus, according to the present invention, as the diameter of the rotary grindstone decreases, or as the number of times the article is processed by the grinding wheel increases, or in addition to that, as the number of dressings of the rotary grindstone increases. In this way, the transition point from the depth-of-cut grinding process in which the rotational support shaft of the rotary grindstone is actively moved in the cutting direction to the spark-out process, which is performed by stopping the rotational support shaft in the cutting direction, is brought closer to the end of grinding. By the simple method of shifting the rotary grindstone, the cylindrical inner surface to be ground can be ground to a surface with zero cylindricity, that is, a surface having a correct cylindrical shape, regardless of the reduction or decrease in the diameter of the rotary grindstone.

In the embodiment described above, the transition point P ₂
continuously as the diameter of the whetstone decreases, or as the number of items processed by the whetstone increases, or as the number of dressings of the whetstone increases. Although it has been explained that the transition point is moved, of course, such movement of the transition point may be performed discontinuously (or intermittently) in several stages.

Furthermore, by utilizing the correlation between the spark-out machining allowance and the cylindricity shown in FIG. 4, it is possible to correct changes in the swing angle α that occur during continuous machining due to thermal changes or the like. Furthermore, even if the cylindricity changes due to changes in the type of grindstone or the rigidity of the grindstone, it is possible to guarantee high accuracy in cylindricity by changing the spark-out machining allowance.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing how small-diameter internal grinding is performed, and Figure 2 is an example of how taper-like errors occur on the cylindrical inner surface to be ground as the number of machining increases in small-diameter internal grinding. Graph, Figure 3 is a graph illustrating the relationship between the depth of cut and time in the grinding process including the depth of cut grinding process and the spark-out process, Figure 4 is a graph illustrating the relationship between spark-out machining allowance and cylindricity. FIG. 5 is a diagram illustrating a mode in which the transition point from the notch grinding process to the spark-out process is shifted according to the present invention;
FIG. 6, which is a diagram corresponding to part S in the figure, is a schematic diagram illustrating the configuration of an apparatus for carrying out the grinding method according to the present invention. 1 - Rotating grindstone, 2 - Rotating support shaft, 3 - Cylindrical inner surface, 4 - Spindle, 10 - Machining number counter, 1
1 - Dress number counter, 12 - In-process gauge, 13 - Control device, 14 - Cut feeding device.

Claims (1)

[Claims] 1. A grinding method in which a cylindrical inner surface is ground with a rotary grindstone in a state where the rotation support shaft of the rotary grindstone is elastically bent, such as in small-diameter internal grinding, and the rotation support shaft is supported and The rotation axis is set to be inclined at a predetermined torsion angle with respect to the center axis of the cylindrical inner surface, and the rotation is performed through a cut grinding process in which grinding is carried out while feeding the rotation support shaft in the cutting direction. Variable is the transition point to a spark-out step in which feeding of the support shaft in the cutting direction is stopped and grinding is performed while driving the rotary grindstone in the cutting direction only by the return force of the elastic deflection of the rotary support shaft; A method characterized in that the transition point is brought closer to the end point of grinding as the diameter of the rotary grindstone decreases, and the spark-out process time is reduced as the diameter of the rotary grindstone decreases.