Method and device for grinding metal annular member

Abstract

Provided is a grinding method capable of preventing variation in the outer diameter of a processed object 1 at the completion of grinding regardless of change in the amount of elastic deformation of the processed object 1 based on the change in the cutting ability of a grindstone 4. The outer diameter D of the processed object 1 during grinding is measured by gauge heads 5 in process. Plural target values D.sub.i that differ from each other are set for the outer diameter D of the processed object 1, and first threshold values are set for the rate of change of the outer diameter D of the processed object for each of these target values D.sub.i. Spark out is started when the outer diameter D of the processed object 1 becomes equal to a target value D.sub.i and the absolute value of the rate of change v is greater than a first threshold value that corresponds to the target value D.sub.i.

Claims

1. A method for grinding a metal annular member, comprising a step of grinding a circumferential surface of a metal annular processed object using a rotating grindstone while measuring a dimension in a radial direction of the processed object in process, the grinding comprising a rough grinding, a finish grinding, and a spark out in order, wherein a condition for starting the spark out is determined based on a rate of change of the dimension in the radial direction of the processed object, and wherein a first threshold value for the rate of change of the dimension in the radial direction of the processed object is determined for each of a plurality of different preset target values for the dimension in the radial direction of the processed object, and when the dimension in the radial direction of the processed object becomes one target value of the plurality of different preset target values, the spark out starts under a condition that an absolute value of the rate of change of the dimension in the radial direction of the processed object becomes greater than the first threshold value that corresponds to the one target value.

2. The method for grinding a metal annular member according to claim 1, wherein a condition for ending the spark out is determined based on the rate of change of the dimension in the radial direction of the processed object, and the spark out ends when an absolute value of the rate of change of the dimension in the radial direction of the processed object becomes less than a second preset threshold value.

3. A device for grinding a metal annular member, comprising: a means for supporting and fastening a metal annular processed object and rotating the processed object; a means for positioning the processed object in a radial direction; a rotating grindstone grinding a circumferential surface of the processed object; a sensor measuring an outer diameter of the processed object; and a controller controlling a rotation of the rotating grindstone based on a measurement result measured by the sensor; wherein when using the rotating grindstone to perform grinding of the circumferential surface of the processed object, the grinding comprising a rough grinding, a finish grinding and a spark out in order, while measuring a dimension in the radial direction of the processed object, the controller determines a timing for starting the spark out based on a rate of change of the dimension in the radial direction of the processed object, and wherein, when the dimension in the radial direction of the processed object becomes one target value of a plurality of different preset target values for the dimension in the radial direction of the processed object, the controller compares an absolute value of the rate of change of the dimension in the radial direction of the processed object with one of first threshold values for the rate of change of the dimension in the radial direction of the processed object that are determined for each of the plurality of different preset target values for the dimension in the radial direction of the processed object, the one first threshold value corresponding to one of the target values at a particular time, and starts the spark out under a condition that the absolute value of the rate of change of the dimension in the radial direction of the processed object is greater than the one first threshold value corresponding to the one target value at the particular time.

4. The device for grinding a metal annular member according to claim 3, wherein the controller determines at least one of a timing for starting the spark out or a timing for ending the spark out based on the rate of change of the dimension in the radial direction of the processed object, and the controller ends the spark out when the absolute value of the rate of change of the dimension in the radial direction of the processed object becomes less than a second preset threshold value.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A shows a side view illustrating the state of performing grinding of a processed object by an example of a grinding device to which the present invention is applied; and FIG. 1B shows an end view as seen from the right in FIG. 1A of the state illustrated in FIG. 1A.

(2) FIG. 2 shows a graph illustrating an example of change in the outer diameter of a processed object during grinding in an example of an embodiment of the present invention.

(3) FIG. 3 shows a flowchart that illustrates the processing for determining the timing for the start of spark out in this example.

(4) FIG. 4 shows a flowchart that illustrates the processing for determining the timing for the end of spark out in this example.

(5) FIG. 5 shows a view that corresponds to an enlarged view of section X in FIG. 2.

(6) FIG. 6 shows a graph illustrating an example of the feed amount of a grindstone, the outer diameter D of a processed object, and the change in the rate of change v of the outer diameter D during grinding in this example.

(7) FIG. 7A shows a side view illustrating the state before the grindstone is pressed against a processed object that is supported by a grinding device of conventional technology; and FIG. 7B shows a side view exaggeratedly illustrating the state when the grindstone is pressed against a processed object.

(8) FIG. 8 shows a graph illustrating an example of the change in the outer diameter of a processed object due to grinding in conventional technology.

MODES FOR CARRYING OUT INVENTION

(9) FIG. 1A to FIG. 6 illustrate an example of an embodiment of the present invention. A feature of this example is that, by suitably setting the timing at which spark out begins (change from finish grinding to spark out) and ends in the grinding process, the outer diameter D of a processed object (work) 1 is suppressed from varying in the completed state of processing, and the time required for grinding is prevented from becoming unnecessarily long regardless of change in the amount of elastic deformation of the processed object 1 due to a change in the cutting ability of the grindstone 4. The grinding device of this example is basically the same as the construction of a conventional grinding device and comprises: a rotating drive shaft (not illustrated in the figure) that supports and secures a processed object and causes that processed object to rotate; a backing plate 2 that is fastened to the tip end of this rotating drive shaft and magnetically affixes an annular processed object (work) 1 to the end surface thereof; two shoes 3 that position the processed object 1 in the radial direction; a rotating grindstone 4 that grinds the outer-circumferential surface of the processed object 1; a sensor (not illustrated in the figure) that comprises at least two gauge heads 5 and measures the outer diameter D of the processed object 1; and a controller (not illustrated in the figure) that controls the rotation of the rotating grindstone 4 based on the measurement results measured by the sensor. As a means for supporting, securing and rotating the processed object 1, it is possible to use a combination of a rotating drive shaft, and a known chuck device such as a mechanical chuck or magnetic chuck that can be attached to the rotating drive shaft, and that can support and secure the processed object 1 on the rotating drive shaft. Moreover, as a means for positioning the processed object 1 in the radial direction, it is also possible to use rollers and the like, or use a combination of an arbitrary number of rollers and shoes. As a sensor for measuring the outer diameter D of the processed object 1, it is possible to use a contact displacement sensor that uses contacts as the gauge heads 5, or it is possible to use a non-contact sensor that uses laser lights as the gauge heads 5.

(10) The method of grinding in this example, including the method of grinding a processed object 1 using a grindstone 4, is the same as the basic processing in the conventional method. In other words, in the grinding process of this example, the outer-circumferential surface of the processed object 1 is grinded using a rotating grindstone 4 while measuring the dimension in the radial direction of the processed object 1 in process, and the grinding process is performed on the outer-circumferential surface of the processed object 1 in the order: a rough grinding, a finish grinding and a spark out. More specifically, the outer diameter D of the processed object 1 can be measured in process by two gauge heads 5, and the controller switches from the rough grinding to the finish grinding when the outer diameter D of the processed object 1 that is measured by the gauge heads 5 reaches a specified value.

(11) A feature of the controller in this example is that the controller determines both the start and end of spark out based on the rate of change v (m/s), which is the amount of change per unit time of the outer diameter D of the processed object 1 that is measured by the gauge heads 5. More specifically, in order for the controller to determine the timing of the start of spark out (timing at which grinding is switched from the finish grinding to the spark out), plural (for example, 5 to 6) target values D.sub.i are set in advance for the outer diameter D of the processed object 1. When the number of target values is 5, the value i is a natural number that is no less than 1 and no greater than 5 (1i5), and the target values D.sub.i are set so that D.sub.1>D.sub.2> . . . >D.sub.5. Furthermore, first threshold values v.sub.i are set for the rate of change of the outer diameter D of the processed object 1 for each of these target values D.sub.i. Target values D.sub.i and first threshold values v.sub.i such as these are found by testing or calculation in advance according to the shape and material of the processed object 1. In other words, the target values D.sub.i and the first threshold values v.sub.i change according to the shape and material of the processed object 1.

(12) The method by which the controller determines the timing for starting spark out based on the rate of change v of the outer diameter D of the processed object 1 will be explained with reference to the flowchart in FIG. 3. The work illustrated in this flowchart is executed by the controller from the start of finish grinding to the start of spark out, or until the end of grinding when suitable timing for starting spark out cannot be determined.

(13) First, in step 1, the controller determines whether or not the outer diameter D of the processed object 1 that is measured by the gauge heads 5 at that instant is the same as the target value D.sub.i (whether or not the outer diameter D is within a specified range with the target value D.sub.i being the center value). The initial value of the value i is taken to be 1 (i=1). When the outer diameter D is not equal to the target value D.sub.i (DD.sub.i), processing advances to step 2, and the controller determines whether or not the outer diameter D is less than the target value D.sub.i (D<D.sub.i). In step 2, when the outer diameter D is equal to or greater than the target value D.sub.i (DD.sub.i) (however, the case in step 1 in which these values are the same (D=D.sub.i) is excluded), finish grinding continues, and after a specified amount of time, processing returns to step 1. When the outer diameter D is less than the target value D.sub.i (D<D.sub.i), processing advances to step 3, and the value i is increased by 1, after which processing advances to step 4. In step 2 and step 3, when the outer diameter D is less than the target value D.sub.i (D<D.sub.i), the outer diameter does not become equal to the target value D.sub.i even when finish grinding is continued after that, so this work is a process for making the target value D.sub.i that is used for comparison with the outer diameter D a value D.sub.i+1, which is value that is one step smaller.

(14) In step 4, the controller determines whether or not the value i is equal to or less than the number (total number) n of target values D.sub.i. When the value i is greater than the number n of target values D.sub.i (i>n), processing advances to step 5, grinding of the processed object 1 ends and since suitable timing for starting spark out could not be determined, the controller issues a warning from a display such as a buzzer or warning light. When the value i is equal to or less than the number n of target values D.sub.i (in), then after a specified amount of time has elapsed, processing returns to step 1. In other words, step 4 and step 5 are performed in the procedure from step 1 to step 6 described later, and when suitable timing for staring spark out could not be determined by comparing the outer diameter D of the processed object 1 with the minimum target value D.sub.n of the target values D.sub.i, this procedure becomes a procedure for ending grinding in error (exception process).

(15) On the other hand, in step 1, when the outer diameter D is the same as the target value D.sub.i (D=D.sub.i), processing advances to step 6, and the controller determines whether or not the absolute value of the rate of change v of the outer diameter D of the processed object 1 at that instant is greater than the first threshold value v.sub.i that corresponds to the target value Di. When the absolute value of the rate of change v is greater than the first threshold value v.sub.i (|v|>v.sub.i), processing advances to step 7, the controller starts spark out (the feed speed of the grindstone 4 is made 0) and ends the procedure for determined the timing for starting spark out. When the absolute value of the rate of change v is equal to or less than the first threshold value v.sub.i (|v|v.sub.i), processing advances to the procedure from step 3 to step 4, after which the controller performs processing according to the procedure described above.

(16) After spark out has started, the controller determines the timing for ending spark out according to the procedure illustrated in FIG. 4. The work illustrated in the flowchart in FIG. 4 is executed by the controller from after the start of spark out until spark out ends. First, in step 8, the controller determines whether or not the absolute value of the rate of change v is less than a second preset threshold value v.sub.f that was set in advance at specified periods of time (fixed time). Then, when the absolute value of the rate of change v becomes less than the second threshold value v.sub.f (|v|<v.sub.f), processing advances to step 9, and the controller ends spark out. On the other hand, when the absolute value of the rate of change v is equal to or greater than the second threshold value v.sub.f (|v|v.sub.f), spark out continues without ending, and after a specified amount of time elapses, processing returns to step 8. The second threshold value v.sub.f is found by experimentation or calculation in advance. When it is particularly necessary to keep the tolerances of dimensions small (for example, 1 m or less), then after spark out has ended, it is also possible to perform step-feed grinding of the processed object 1 in which the feed speed of the grindstone 4 and the cutting amount of grindstone 4 are very small in order to make the outer diameter D of the processed object equal to the target dimension.

(17) With the method for grinding a metal annular member of the present invention, even when variation occurs in the amount of elastic deformation of the processed object 1 based on the change in the cutting ability of the grindstone 4, it is possible to prevent the outer diameter of the processed object 1 at the end of spark out from varying, and it is possible to prevent the time required for grinding from become unnecessarily long. In other words, in this example, in order to determine the timing for starting and ending spark out, the rate of change v, which is the amount of change per unit time of the outer diameter D of the processed object 1, is used. That is, the timing for starting and ending spark out can be determined by taking into consideration the amount of elastic deformation of the processed object. Here, the reason that the timing for starting spark out can be determined while taking into consideration the elastic deformation of the processed object 1 will be explained with reference to FIG. 2 and FIG. 5. FIG. 2 and FIG. 5 illustrate the change in the outer diameter D of the processed object 1 that is measured in process by gauge heads 5 when the amount of elastic deformation of the processed object 1 due to pressing by the grindstone 4 became large due to degradation of the cutting ability of the grindstone 4 (solid line a), and when the amount of elastic deformation of the processed object 1 is small before degradation of the cutting ability of the grindstone 4 (dashed line b).

(18) In FIG. 2, in order to clarify that the time required for performing spark out from finish grinding changes according to the differences in the amount of elastic deformation of the processed object 1, switching from rough grinding to finish grinding is illustrated such that the timing is the same for when the amount of elastic deformation of the processed object 1 is large and small. Actually, switching from rough grinding to finish grinding is performed when the outer diameter D of the processed object 1 becomes a specified value, so the timing of this switching changes according to the change in the cutting ability of the grindstone 4. The larger the amount of elastic deformation of the processed object 1 is during rough grinding as the cutting ability degrades, the larger the amount that the processed object 1 is elastically restored during spark out becomes, and the amount of grinding in spark out increases. Therefore, the larger the elastic deformation of the processed object 1 is, in order to decreasing the amount of grinding by finish grinding, it is necessary to end finish grinding earlier and switching from finish grinding to spark out earlier (spark out is started when the outer diameter D of the processed object 1 is large).

(19) As can be clearly seen from FIG. 2 and FIG. 5, during finish grinding, when the outer diameter D is the same (for example D=D.sub.i), the amount of elastic deformation of the processed object 1 in rough grinding is large, and the rate of change v.sub.a1 when the amount that the processed object 1 is elastically restored is large is greater than the rate of change v.sub.b1 when the amount that the processed object 1 is elastically restored is small (v.sub.a1>v.sub.b1). Therefore, the first threshold value v.sub.1 that corresponds to the target value D.sub.1 is regulated so as to be less than the rate of change v.sub.a1 when the amount of elastic deformation of the processed object 1 is large, and so as to be equal to or greater than the rate of change v.sub.b1 when the amount of elastic deformation of the processed object 1 is small (v.sub.b1v.sub.1<v.sub.a1). Moreover, the first threshold value v.sub.2 that corresponds to the target value D.sub.2 that is smaller than the target value D.sub.1 is regulated so as to be less than the rate of change v.sub.b2 at the time when the outer diameter D of the processed object 1 is the same as the target value D.sub.2 (v.sub.2<v.sub.b2) in case that the amount of elastic deformation of the processed object 1 is small. By regulating the target values D.sub.i and the first threshold values v.sub.i in this way, the condition (v.sub.a1>v.sub.1) for starting spark out in step 6 is satisfied when the outer diameter D of the processed object 1 becomes the same as the target value D.sub.1 (D=D.sub.1) by finish grinding, so spark out starts.

(20) On the other hand, when the amount of elastic deformation of the processed object 1 is small, the condition (v.sub.b1v.sub.1) in step 6 is not satisfied (in the case of switching to spark out as is, the outer diameter of the processed object 1 would be larger than the target dimension), so spark out cannot be started and finish grinding continues. As finish grinding is further performed, the outer diameter D becomes small, and when the outer diameter D becomes the same as the target value D.sub.2 (D=D.sub.2), the condition (v.sub.b2v.sub.2) in step 6 is satisfied, so spark out starts. In this way, plural target values D.sub.i are set for the outer diameter D, and by setting first threshold values v.sub.i for each of the target values D.sub.i so that the smaller the values of the target values D.sub.i become, the first threshold values v.sub.i that correspond to the target values D.sub.i become small, and it is possible to determine the timing for starting spark out (switching from finish grinding to spark out) while taking into consideration the amount of elastic deformation of the processed object 1.

(21) On the other hand, in determining the end of spark out in this example, spark out ends when the rate of change v becomes less than the second threshold value v.sub.f (practically becomes 0 except in the case of measurement error) regardless of the change in the size of the amount of elastic deformation due to degradation of the cutting ability of the grindstone 4. The rate of change v practically becomes 0 when the elastic deformation of the processed object 1 is released, and the outer-circumferential surface of the processed object becomes smooth. Therefore, when the cutting ability of the grindstone 4 is good and the amount of elastic deformation is small, the time that is required for elastic deformation of the processed object to be released is short, so it is possible to end spark out earlier. However, when the cutting ability of the grindstone 4 is bad, and the amount of elastic deformation is large, the time required for releasing the elastic deformation of the processed object 1 becomes long, and the time for performing spark out can be sufficiently maintained. In this way, in this example, it is possible to determine suitable timing for ending spark out regardless of change in the size of elastic deformation. Therefore, in this example, it is possible to prevent variation in the outer diameter of the processed object 1 at the completion of grinding regardless of change in the amount of elastic deformation of the process object 1 due to change in the cutting ability of the grindstone 4, and it is possible to prevent the time required for grinding from becoming unnecessarily long.

INDUSTRIAL APPLICABILITY

(22) The method and device for grinding a metal annular member of the present invention can be applied not only in the case of performing grinding of the outer-circumferential surface of a metal annular processed object, but can also be applied in the case of grinding the inner-circumferential surface.

EXPLANATION OF REFERENCE NUMBERS

(23) 1 Processed object 2 Backing plate 3 Shoe 4 Grindstone 5 Measurement gauge