JP2012115987A - Grinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of reduction in quality such as a dimensional error and surface roughness of a ground surface of a machined workpiece caused by thermal deformation of the workpiece.SOLUTION: A grinder includes dimensional error minimization grinding function parts 26 and 27 estimating a thermal deformation amount of a workpiece W accompanying a time lapse after spark-out after accurate grinding is started and controlling relative displacement while considering the thermal deformation amount after the spark-out is started. The grinder includes a surface roughness improving grinding function part 28 estimating a thermal contraction amount and thermal contraction speed of the workpiece W during machining accompanying the time lapse after spark-out after accurate grinding is started, then displacing a grinding wheel 10 relatively to the workpiece W so that the workpiece W may be cut in by the grinding wheel at a minute cut-in speed relevant to a change of thermal contraction speed by an amount relevant to the change of the thermal contraction amount for a fixed time in the spark-out process and then executing spark-out in a state that relative displacement is stopped till the real dimension of the workpiece W is a target dimension.

Description

The present invention relates to a grinding machine provided with a workpiece support rotating means for supporting a workpiece and rotating it around a specific center line, and a grinding wheel that is rotated around a grinding wheel axis and is relatively displaced in the workpiece rotation radial direction with respect to the workpiece.

As a grinding machine provided with a sizing device for measuring the outer diameter of a portion to be ground during workpiece grinding, for example, those shown in Patent Documents 1 to 3 exist.

In direct sizing grinding on this type of grinding machine, grinding is performed while measuring the workpiece dimensions with a sizing device, and the outer diameter of the workpiece becomes the target dimension based on the dimensional information output from the sizing device. Stop grinding at the point. In direct sizing grinding performed in this way, even if the measurement error of the sizing device is zero, a dimensional error may appear in the workpiece after processing. Recent research has revealed that this is due to thermal expansion and contraction caused by temperature changes in the workpiece.

That is, the workpiece at the end of grinding is expanded by grinding heat. When the workpiece is removed from the grinding machine and the outer diameter is measured, the workpiece is cooled and contracted. Accordingly, the workpiece outer diameter as a result of the measurement differs between the measurement during the grinding cycle by the sizing device and the post measurement after the completion of grinding.

At this time, if the heat shrinkage of each workpiece is constant, there will be no variation in the workpiece outer diameter of the multiple workpieces that have been ground, but in actual grinding, the sharpness of the grinding wheel will change in relation to the elapsed grinding time. For this reason, the temperature of the workpiece at the end of grinding differs between workpieces, the amount of thermal shrinkage of the workpiece is not constant, and the workpiece outer diameter varies.

In addition, when entering the spark-out process, which is the final stage of workpiece grinding by the grinding machine, the cutting feed of the wheel head is stopped, the heat generation effect is greatly reduced, and the accumulated heat of the workpiece is removed by the grinding fluid, so that the workpiece is removed. Begins heat shrinking. In this spark-out process, the grinding wheel responds to the deformation by elastic restoring deformation of the workpiece, which is elastically bent and deformed by the grinding back force of the grinding wheel, on the surface of the workpiece separated from the grinding wheel at a speed corresponding to the heat shrinkage. Grinding is performed by improving the surface roughness while generating the outer diameter dimension of the workpiece during the contact while being held in contact with force (or a secondary amount). At this time, if the thermal contraction is abruptly performed, the dimension generation of the workpiece is completed in a short time, and there is a situation in which the surface roughness improvement process that proceeds along with the dimension generation is not sufficiently performed.

On the other hand, an AE sensor that detects an acoustic emission signal (vibration wave or sound wave in an ultrasonic region having a frequency of, for example, about 100 kHz to 1000 kHz) is already known. For example, as disclosed in Patent Document 4, grinding is performed. It is used to detect the contact start time of a grindstone and a workpiece.

JP-A-6-79621 JP-A-6-335858 Japanese Patent Laid-Open No. 7-1000076 Japanese Patent Laid-Open No. 10-244464

In the process of confirming the characteristics of the AE sensor on the grinding machine by experiments, the inventors have performed grinding if there is no change in the system system of the grinding machine, that is, if there is no change in the shape and dimensions of the workpiece and the processing conditions. I came to know the fact that the AE sensor fixed on the board accurately generates an output proportional to the grinding resistance during grinding of the workpiece (which may be the main grinding force or the grinding back component force). is there. As a result, the grinding resistance generated between the grinding wheel and the workpiece during grinding can be detected with high accuracy.

In addition, the present inventors have found that there is a proportional relationship between the amount of thermal deformation of the workpiece and the main component force of grinding unless the shape, dimensions, and processing conditions of the workpiece change during grinding on the grinding machine. It was confirmed.

Furthermore, during grinding on the grinder, the change in the amount of thermal deformation of the workpiece over time when the grinding wheel is separated from the workpiece immediately before the end of the fine grinding and the amount of thermal deformation of the workpiece during the spark-out process It was confirmed that changes over time can be identified substantially. However, in both cases, the condition is that the work is rotated at the same rotational speed by the work support rotating means, and the grinding fluid is poured into the work in the same flow condition.

The present invention was devised based on these findings. That is, due to thermal deformation of the workpiece during grinding, the dimensional accuracy of the workpiece grinding position and the surface roughness of the surface to be ground are degraded. It is an object of the present invention to provide a grinding machine that can perform high-precision and high-quality machining by preventing this.

In order to achieve the above object, the grinding machine of the present invention includes a workpiece support rotating means for supporting a workpiece and rotating it around a specific center line, and a grinding wheel that is rotated around a grinding wheel axis and is relatively displaced in the workpiece rotation radial direction. In a grinding machine equipped with the above, the grinding wheel is separated from the workpiece while the workpiece is rotated and the grinding fluid is continuously poured, and the outer diameter of the workpiece is continuously measured over time under the separated state. The thermal deformation amount detection function unit for acquiring the relationship between the elapsed time and the thermal deformation amount of the workpiece, and the time position estimated by the acquired relationship at each time position after the spark-out start point A surface roughness-improving grinding function unit is provided that relatively displaces the grinding wheel so as to cut into the work by a cutting amount smaller than the thermal deformation amount for a predetermined time.

Further, after the fixed time has elapsed, after the relative displacement is stopped, the outer diameter of the workpiece measured at each time position is combined with the thermal deformation amount at each time position estimated from the acquired relationship. When the actual dimension of the workpiece obtained in this way reaches the target dimension, the retreat start of the grinding wheel is controlled.

On the other hand, by relatively displacing the grinding wheel so as to cut into the work by the small cutting amount, the outer diameter of the work measured at each time position and the thermal deformation at each time position estimated from the acquired relationship When the actual dimension of the workpiece obtained by combining the quantity reaches the target dimension, the grinding wheel starts to retract.

According to the present invention described above, a very small cutting speed (specifically, the workpiece can be sharply improved so that the surface roughness of the surface to be ground of the workpiece can be drastically improved with respect to the workpiece during the spark-out process). Can be sent in a size that can be ignored in terms of machining accuracy), and the quality of the surface roughness can be dramatically improved.

In addition, after cutting for a certain period of time at a very small cutting speed, the grinding wheel is stopped and the grinding wheel is stopped until the target dimension is taken into account, taking into account the amount of thermal deformation of the workpiece. It is also possible to execute grinding so that the actual dimension, which is the dimension after convergence, becomes the target dimension accurately.

On the other hand, even during cutting at a very small cutting speed, the actual dimension, which is the dimension after the thermal deformation of the workpiece has converged, is accurately set to the target dimension, and then the spark-out with the relative displacement stopped is performed. Since the actual dimension is monitored so as to become the target dimension, when this is reached, the grinding wheel can be retracted.

An embodiment of a grinding machine according to the present invention will be described with reference to FIGS.
FIG. 1 shows a general CNC grinder used for grinding cylindrical bodies and cams, 1 is a bed, 2 is a workpiece provided on the bed 1 so as to be movable in the left-right direction (Z-axis direction). A support table 3 is a grindstone table provided on the bed 1 so as to be movable in the front-rear direction (X-axis direction).

4 is a servo motor for feeding the work support table 2 provided in the same body as the bed 1, and feeds and moves the work support table 2 in the Z-axis direction via a screw feed mechanism (not shown). Reference numeral 5 denotes a servomotor for feeding the grinding wheel base 3 provided in the same body as the bed 1, and feeds and moves the grinding wheel base 3 in the X-axis direction via a screw feeding mechanism (not shown).

On the work support table 2, work support rotating means including a headstock 6 and a tailstock 7 are formed. 8 is a servo motor for driving the spindle 9 provided on the spindle head 6, 10 is a grinding wheel fixed to the grinding wheel shaft 11 on the grinding wheel base 3, and 12 is a motor for rotating the grinding wheel shaft 11. . The spindle stock 6 is provided with a spindle center 13 a and a screw turning 13 arranged concentrically with the spindle 9, and the tailstock 7 is provided with a centering center 14 arranged concentrically with the spindle 9. At this time, a right spindle stock can be provided instead of the tailstock 7, and a member similar to the spindle center 13 a can be provided concentrically with the spindle 9 so as to be capable of synchronous rotation. A sizing device 15 is provided on the work support table 2 to measure the diameter of the work w during grinding. The sizing device 15 is provided with a contact that is in contact with the peripheral surface of the workpiece w.

In FIG. 2, reference numeral 16 denotes an AE sensor as a grinding resistance detecting means, which is fixedly embedded in the vicinity of the grinding wheel 10 at the center of the grinding wheel shaft 11. An output portion of the AE sensor 16 is electrically coupled to a transmission portion 17 fixed to the shaft end of the grindstone shaft 11 on the side opposite to the grindstone. Reference numeral 18 denotes a receiving unit that receives a signal transmitted from the transmitting unit 17 in a non-contact state, and is fixed to a support piece 20 that is fixed to the bearing 19 that rotatably supports the grindstone shaft 11. The receiving unit 18 is electrically coupled to a numerical controller 21 for controlling each unit. Reference numeral 22 denotes a grindstone cover that covers the outer periphery of the grinding wheel 10.

The configuration around the AE sensor 16 can be modified as shown in FIG. 3. In this example, the AE sensor 16 is fixedly embedded in the shaft end of the grindstone shaft 11 on the grindstone side. The AE sensor 16 is covered with the grindstone shaft 11 so as to cover the AE sensor 16, and the receiving unit 18 is secured to the grindstone cover 22 via a support piece 20. Parts corresponding to the respective parts in FIG.

When using the CNC grinder described above, a program for causing the computer incorporated in the numerical controller 21 to perform automatic grinding is stored. Then, the workpiece w is positioned between the spindle center 13a and the tailstock center 14, and each end of the work w is fixedly gripped by the spindle center 13a and the tailstock center 14. At this time, the center of the workpiece w coincides with the center of rotation of the main shaft 9. Thereafter, each part is brought into an operating state, and automatic grinding is started.

The operation of each part in this automatic grinding will be described in order.
First, the motor 12 is rotated, and the grinding wheel 10 is rotationally driven. Further, the servo motor 4 is rotated as necessary, and the work support table 2 is moved in the Z-axis direction. As a result, the workpiece w is moved together with the headstock 6 and the like, and the workpiece w to be ground is brought into a state facing the grinding wheel 10 in the X-axis direction. Subsequently, as shown in FIG. 4, the grindstone platform 3 is positioned at a coordinate position p <b> 1 that is a reference position specified in advance by a program on the machine coordinates in the X-axis direction.

Thereafter, the high-speed forward function unit 23 incorporated in the numerical controller 21 operates as follows.
That is, the AE sensor 16 is activated before the grinding wheel 10 is advanced. At this time, since the grinding wheel 10 is not in contact with the workpiece w, the grinding wheel 10 is idling and grinding air. Therefore, since the AE sensor 16 has a grinding resistance of the grinding wheel 10 (the ratio of the grinding resistance and the principal grinding force qs is constant if the grinding conditions are the same, the grinding principal component force qs may be used. qs is one of the component forces of the grinding resistance acting on the grinding point and refers to the force in the tangential direction of the grinding wheel perpendicular to the radial direction of the grinding wheel passing through the grinding point. The zero output is transmitted to the numerical controller 21 via the transmitter 17 and the receiver 18.

As the zero output is confirmed by the numerical control device 21, the grinding wheel base feed control means 24 incorporated in the numerical control device 21 increases at a specific speed Vk so as to bring the grinding wheel base 3 closer to the workpiece w as shown in FIG. Move forward. Even during this high speed advance, the AE sensor 16 continues to generate an output to detect the grinding resistance, and the numerical controller 21 samples this output at a relatively short time interval Δt, and immediately calculates the grinding resistance at each sampling time point. Detect.

When the grinding resistance specified in this way exceeds a preset specific value, the grindstone feed control means 24 has a cutting speed (grinding stone feed speed) at the time of rough grinding in which the cutting speed of the grinding wheel 10 is determined in advance. The forward speed of the grindstone table 3 is reduced so as to match Vp1.

That is, for example, when plunge cut grinding is performed as shown in FIG. 5A, the wheel head feed is reduced to the coarse feed speed, and when traverse cut grinding is performed as shown in FIG. By setting the feed amount in the X-axis direction of the grindstone table 3 when switching the feed direction of the table 2 to a size corresponding to the coarse grinding, the grindstone table feed speed becomes the coarse feed speed.

After the operation of the high-speed forward function as described above is performed, as shown in FIG. 4, after performing rough grinding or medium roughening, back-off is executed as necessary, and finally spark out is executed. . It is also possible to grind at the grinding wheel feed rate at the time of rough grinding by using the rough grinding as the rough grinding stage instead of dividing it into rough grinding and middle grinding. In FIG. 4, Vp11 is the wheel head feed speed at the time of medium roughing, and Vp2 is the wheel head feed speed at the time of fine grinding.

The numerical control device 21 includes a thermal deformation amount detection function unit 25, a dimension error minimizing grinding function unit 26 for the first workpiece w, a dimension error minimizing grinding function unit 27 for the second and subsequent workpieces w, and The surface roughness improving grinding function unit 28 is incorporated. Next, the operation of each functional unit will be described.

<Thermal deformation detection function unit 25>
First, the operation of the thermal deformation amount detection function unit 25 will be described with reference to FIGS.
That is, as shown in step (1) of FIG. 6, for example, the workpiece w is cut under the grinding conditions as shown in FIG. Force data corresponding to the grinding back component force may be acquired by measurement with the AE sensor 16, and then the process proceeds to step (2) in FIG. The grinding wheel 10 is moved away from the workpiece w by rapid retreat. In this state, the operation of continuing to pour the grinding fluid as before is maintained while rotating the workpiece w.

On the other hand, as shown in step (3) of FIG. 6, the dimension signal data output from the sizing device 15 that measures the outer diameter of the part to be ground of the workpiece w from the time immediately after the rapid retraction of the grindstone table 3. The thermal deformation amount dθw of the work w specified by is detected at a minute time interval Δt. If the detection is continued until, for example, a time of 60 seconds or more elapses, the thermal deformation amount data, which is data about the change in the thermal deformation amount dθw obtained with the passage of time, is as shown in FIG. It will be a thing. In step (4) of FIG. 6, the amount of thermal deformation dθw at each detection time is set to a determination interval n of an appropriate specific length.
Repeat the averaging at Δt.

Next, in step (5) of FIG. 6, it is determined whether this averaging process has been repeated until a predetermined measurement time Tk, and when it has been repeated, the process proceeds to step (6) of FIG.

As judged from FIG. 7A, the thermal deformation amount dθw converges to dθk in about 60 seconds from the time point immediately after the rapid retreat of the grinding wheel head in step (2) of FIG. 6, but from the viewpoint of grinding efficiency, You cannot wait for this long convergence. Therefore, in the step (6) of FIG. 6, the figure after the time Tk is used by using the thermal deformation amount data detected until the time Tk (about 10 seconds) which is a relatively short waiting time in FIG. 7B. Extrapolation estimation data that is equivalent to that obtained by averaging the thermal deformation amount dθw at each detection time point in FIG. 7A by step (3) in FIG. 6 is created. The extrapolation estimation data created in this way is as shown by the curve after time Tk in FIG. Here, the relationship between the thermal deformation amount dθw and the elapsed time T from the time of rapid retreat of the grinding wheel head is expressed by the following equation, that is, dθw = f (T).

Finally, the process proceeds to step (7) in FIG. 6. In this step (7), the curve shown in FIG. 7 (b) is turned upside down as shown in FIG. On the other hand, the actual thermal deformation amount that occurs, that is, the calculated value d′ θw of the thermal deformation amount is determined.

This determination is performed as follows.
That is, the relationship between the actual thermal deformation amount d′ θw and the passage of time T after the grindstone table 3 has rapidly retracted is as shown in FIG. 7C, that is, d′ θw = dθk−f. It is represented by (T). Judging from the shape of the curve representing the actual thermal deformation amount d′ θw in FIG. 7C, it is clearly an exponential function.

Therefore, it is assumed that the following equation (s1) is established.
d′ θw = dθk−f (T) = dθk · αT
... (s1)
However, 0 <α <1.
From the formula (s1), the following formula, that is, f (T) = dθk (1−αT) is obtained.

From this equation, the following equation (s2) representing the amount of thermal deformation dθw during measurement in FIG. 7B is obtained.
dθw = f (T) = dθk (1−αT) (s2)

It has already been confirmed experimentally that this equation fits exactly in the actual case.
Therefore, the thermal deformation amount detection function unit 25 uses the equation (s2) to set the values (constants) of α and dθk in the equation (s2) as 0 <T <Tk in FIG. It is calculated by the method of least squares based on the curve obtained from the already measured thermal deformation amount dθw of the region.

The change process of the thermal deformation amount d′ θw thus determined is a change process in a state in which the grinding wheel base 3 is rapidly retracted and the grinding wheel 10 is separated from the work w, but the grinding wheel 10 is actually used as the work w. This is almost the same as the process of changing the amount of thermal deformation d′ θw when grinding in the spark-out process. The reason is considered that the grinding resistance (grinding main component qs) is rapidly attenuated during the spark-out process and hardly affects the change in the amount of thermal deformation.

<Dimension Error Minimizing Grinding Function Unit 26 for Minimizing the Dimensional Error of the First Work w>
Next, the operation of the dimension error minimizing grinding function section 26 will be described with reference to FIGS.
This functional unit 26 is for grinding the workpiece w after the thermal deformation amount is measured by the previous thermal deformation amount detection function unit 25 so as to minimize the dimensional error. The dimensional error minimizing grinding is executed based on the measured thermal deformation amount d′ θw of the section 25.

The function representing the calculated value d′ θw of the thermal deformation amount with respect to time T after the grindstone table 3 is rapidly retracted is as shown in the above equation (s1), and the changing process of the calculated value d′ θw is shown in FIG. It is shown in (a).

Immediately after the operation of the function 26 is started, as shown in step (1) of FIG. 9, the regrind start time Tg and the plunge speed Vps at that time are automatically set using the function of the above formula (s1). To decide. Specifically, in FIG. 8A, for example, the function d′ θw = dθk−f (T) = dθk · αT is used, and the plunge speed related to the magnitude of the calculated thermal deformation amount d′ θw. The regrind start time Tg in the Vps determination process is specified to an arbitrary appropriate size, and the plunge speed Vps is determined from this Tg. Here, the re-grinding start time Tg is obtained by adding various calculation times to the thermal deformation amount measuring time Tk in FIG. 7, and the grinding wheel at the position when the time T is zero starts the infeed movement at the plunge speed Vps. The grinding wheel moving time from when the workpiece is touched to the workpiece w is added.

In step (2) in FIG. 9, the re-cut time t is counted from the actual regrind start time (= Tg) at which the grinding wheel 10 actually contacts the work w again and starts grinding the work w. To start. At the same time, in step (3) of FIG. 9, measurement of the outer diameter R of the part to be ground of the workpiece w is started by a signal output from the sizing device 15 (may be measured before that).

In step (4) of FIG. 9, the calculation value d′ θw of the thermal deformation amount is calculated.
The calculated value d′ θw is an expression described in FIG.
d′ θw = dθk−f (Tg + t) = dθk
.Alpha.Tg + t (s3)
Is calculated by Here, Tg is an actual grinding start time.

The workpiece w is rotating at an appropriate speed from the time point of rapid retraction of the grinding wheel head (time point of T = 0) by the thermal deformation amount detection function unit 25 to the time point of re-cutting (time point of T = Tg) in FIG. In addition, since the grinding fluid is poured under a certain condition, the amount of thermal deformation d′ θw is the time after the wheel head retreats so as to pass on the curve shown in FIG. 8A corresponding to the above formula (s1). Decrease with respect to T. Accordingly, it is possible to match both times so that the position of Tg on the time T-axis shown in FIG. 8A becomes t = 0 on the re-cut time t-axis in FIG. 8A. This is a necessary and sufficient condition for calculating the amount of thermal deformation with respect to the cutting time t without error. For this reason, the above equation (s3) is obtained by replacing “T” in the equation in FIG. 7, that is, d′ θw = dθk−f (T) with “Tg + t”. From this equation (s3), the changing process of the thermal deformation amount d′ θw of the workpiece w in the re-cutting process is quantitatively estimated.

In step (5) of FIG. 9, the actual dimension Rr is added from the calculated thermal deformation amount d′ θw and the sizing device signal R as shown in the following equation (s4).
Rr = R + d′ θw (s4)
By using this formula (s4), the cutting position of the grinding wheel 10 in consideration of the dimension (actual dimension Rr) of the workpiece w with the thermal deformation amount d′ θw converged, that is, the thermal deformation amount d′ θw, is quantitatively determined. Inferred with high accuracy.

Next, the comparison between the target dimension Rk and the actual dimension Rr is repeated in step (6) of FIG. 9, and when Rr> Rk is satisfied, that is, the re-cut time t is t1 in FIG. 8B. At the time, the process proceeds to step (7) in FIG. 9, where a grinding wheel base retreat signal is transmitted. After that, as shown in FIG. 8B, the sizing device signal R increases, but the actual dimension Rr considering the amount of thermal deformation remains constant, and in a state where the workpiece w is cooled, The diameter of the portion to be ground matches the target value Rk.

<Dimension Error Minimizing Grinding Function Unit 27 for Minimizing Dimensional Error of Second and Later Work w>
Next, the operation of the dimensional error minimizing grinding function unit 27 for the i-th workpiece w, which is the second and subsequent ones, will be described with reference to FIGS.
First, the precondition of this function, that is, the relationship between the thermal deformation amount dθk and the grinding resistance (may be the grinding main component force qs or the grinding back component force) will be described.

FIG. 10 shows the main grinding force qs (measured in step (1) in FIG. 6) when the wheel head 3 is rapidly retracted in step (2) in FIG. 6 and the thermal deformation amount dθk of the workpiece w at that time. This shows the relationship with (see (a) of FIG. 7). As is apparent from FIG. 10, even if the plunge speed Vp and the speed ratio Kv (= work w peripheral speed / grinding wheel peripheral speed) are changed over a wide range, there is a difference between the thermal deformation amount dθk and the grinding principal component force qs. A proportional relationship exists. Here, the central data (qs (1), dθk (1)) in FIG. 10 indicates the principal grinding force qs (1) and the amount of thermal deformation dθk at the spark-out start point of the first workpiece w. (1). In this case, by measuring the grinding resistance qs (i) at the spark-out start point of the i-th workpiece w, the thermal deformation amount dθk (i) at that time can be quantitatively estimated by the following equation (s5). Become.

dθk (i) = dθk (1) · qs (i) / qs (1) (s5)
This expression (s5) means that the thermal deformation amount dθk at the spark-out start point increases in proportion to the grinding resistance as compared with the first workpiece w. It is different from the actual change process.
That is, the actual change process of the thermal deformation amount d′ θw is as shown in FIG.
In FIG. 12A, the thermal deformation amount d′ θw at the spark-out starting point increases as the plunge speed Vp in the incision grinding process increases. However, as shown in FIG. It is not a form expanded in the direction. FIG. 12B shows a diagram in which the curves showing the thermal deformation amount d′ θw of only the spark-out process of FIG. 12A are moved in parallel to the horizontal direction (time axis) and overlapped. All overlap one curve.
The fact is that each curve showing the thermal deformation amount d′ θw only in the spark-out process of FIG. 12A is expressed by the equation dθk (1) · ατ, and the curved shape does not change, and the spark-out It means that the starting point will be the one moved.

This condition is satisfied only when the workpiece w having the same material, shape and dimensions is ground with the same grinding wheel 10, and is not satisfied when the dimension of the workpiece w, the grinding machine, or the like is changed. However, it is considered that the change of the plunge speed Vp and the speed ratio Kv in the processing conditions can be sufficiently handled.

Under such a premise, the calculated value d′ θw (i) of the thermal deformation amount of the i-th workpiece w in the spark-out process is estimated as follows. That is, the calculated value d′ θw (1) of the thermal deformation amount in the spark-out process is the spark instead of the time T in the equation (s1) in the operation of the thermal deformation amount detection function unit 25 for the first workpiece w. It is given by the following equation (s6) using the out time τ.
d′ θw (1) = dθk (1) · ατ (s6)

Since the shape of the curve representing the equation (s7) does not change, the thermal deformation amount dθk (i) at the i-th spark-out start point given by the following equation (s7) is the same as that in the equation (s5).
dθk (i) = dθk (1) · qs (i) / qs (1)
... (s7)

Now consider qs (i)> qs (1). When the value of this dθk (i) is determined on the equation (s6), the amount of thermal deformation d′ θw with the passage of time from the point where the spark-out start point has moved to the left by τk (i) as shown in FIG. It can be seen that (i) changes.
Mathematically, the solution of τk (i) (<0) is a value of τ such that the left side of the equation (s6) is dθk (1) · qs (i) / qs (1), and the following equation (s8) It is represented by
τk (i) = logα (qs (i) / qs (1))
... (s8)

From the above, the calculated value d′ θw (i) of the amount of thermal deformation in the i-th spark-out process to be obtained after all goes to the right in the curve of FIG. 13A so that τk (i) is the origin. The translated function is expressed by the following equation (s9).
d′ θw (i) = dθk (1) · ατ + τk (i)
(S9)
This equation (s9) becomes the curve of FIG. This completes the formulation of the dimensional error minimizing grinding function.

Since the above formulation was considered as qs (i)> qs (1), the thermal deformation amount d′ θw (i) at the spark-out start point of the i-th workpiece w can be understood by substituting τ = 0. Starting from ατk (i), since τk (i) <0, the amount of thermal deformation at the starting point is certainly large.
Conversely, when qs (i) <qs (1), the equations are satisfied as they are, and the analysis result is τk (i)> 0. Therefore, the amount of thermal deformation d′ θw ( i) will definitely be smaller.

FIG. 14 shows an operation flow of the dimension error minimizing grinding function unit 27 for the i-th workpiece after the second one, which will be described next. First, in step (1) of FIG. 14, the grinding resistance at the spark-out start point (may be the grinding main component force qs (i) or the grinding back component force) is measured by the AE sensor 16. Next, in step (2) of FIG. 14, the thermal deformation amount dθk (i) at the spark-out start point is calculated from this measured value by equation (s7), and further, in step (3) of FIG. (S9) is used to determine the curve of the amount of thermal deformation d′ θw (i), whereby the amount of thermal deformation d′ θw (i) of the workpiece w over time after the start of spark-out is estimated. finished.

In step (4) of FIG. 14, the thermal deformation amount d ′ is calculated from the calculated thermal deformation amount d′ θw (i) and the dimension R of the portion to be ground of the workpiece w being ground specified from the output of the sizing device 15. The actual dimension Rr of the workpiece when 'θw (i) is converged is calculated by the following equation (s10).
Rr = R + d'θw (i) (s10)
By using this equation (s10), when the thermal deformation amount d′ θw (i) is converged, the actual dimension Rr which is the outer diameter of the portion to be ground of the workpiece w, that is, the thermal deformation amount d ′. The dimension of the workpiece w considering θw (i) is estimated quantitatively and accurately as shown by a curve in FIG.

Next, the comparison between the target dimension Rk and the actual dimension Rr is repeated in step (5) of FIG. 14, and when Rr> Rk, that is, when the re-cut time becomes τ1 in FIG. Then, the process proceeds to step (6) of FIG. 14 where a whetstone stand backward signal is transmitted. Thereafter, as shown in FIG. 15, the outer diameter R of the portion to be ground of the workpiece w specified from the output of the sizing device 15 increases, but the thermal deformation amount d′ θw (i) converges. The actual dimension Rr, which is the outer diameter of the part to be ground of the workpiece w at that time, remains constant, and the outer diameter of the part to be ground of the workpiece w matches the target value Rk.

A grinding machine equipped with the above-described thermal deformation amount detection function unit 25, the first workpiece w dimension error minimizing grinding function unit 26, and the second and subsequent workpiece w dimension error minimizing grinding function unit 27 is used. When many workpieces of the same type (same shape and size) are ground repeatedly, the operation flow shown in FIG. 16 is preferably executed.

In FIG. 16, the operation flow by the thermal deformation amount detection function unit is performed in steps (1) to (4). At this time, in step (1), the grinding resistance (grinding main component qs) immediately before the end of the fine polishing is measured by the output of the AE sensor 16. In step (2), the grindstone base 3 is rapidly retracted by about 20 μm at the end of the fine polishing to separate the grinding grindstone 10 from the workpiece w. In step (3), the thermal deformation amount dθw of the workpiece w is detected by the output of the sizing device 15 under the condition that the rotation of the workpiece w and the supply of the grinding fluid to the workpiece w are maintained in the same manner as in the fine grinding process. . In step (4), as shown in FIG. 7, data such as the calculated value d′ θw (1) of the thermal deformation amount is obtained. In step (5), grinding of the first workpiece w is automatically executed by the operation of the dimensional error minimizing grinding function unit 26 of the first workpiece w.

Next, the process proceeds to step (6), where the roughing and fine polishing of the second workpiece is performed. When the fine polishing is completed, the grinding wheel table 3 is stopped to move back and the feed is stopped and sparked out. Is started. In this spark-out process, automatic grinding of the second workpiece by the operation of the dimension error minimizing grinding function unit 27 of the second and subsequent (i-th) workpiece w is performed in steps (7) to (11). Run as shown. At this time, in step (7), the grinding resistance (grinding main component qs) immediately before the end of the fine polishing (just before the start of spark-out) is measured by the AE sensor. In step (8), the amount of thermal deformation d′ θw (i) in the spark-out process is estimated. In step (9), a shift process is performed in which the thermal deformation amount d′ θw (i) is added to the signal position R of the sizing device. In this state, as shown in step (10), when the spark-out is executed and it is detected by the sizing device that the workpiece w has reached the target dimension Rk, the process proceeds to step (11) and the machining is completed. .

Next, the process proceeds to step (6), and grinding of the third workpiece is executed in steps (6) to (11), and thereafter steps (6) to (11) are repeated for each workpiece.

<Surface roughness improving grinding function part 28>
Next, the operation of the surface roughness improving grinding function unit 28 will be described with reference to FIGS.
In the general spark-out process, the feed movement of the grindstone table 3 is stopped. Unlike this, the grindstone table 3 is not stopped in the spark-out process, and it is fed at an extremely fine cutting speed, so that the surface roughness plays. It has been confirmed by the inventor and the like that a practical improvement is possible.

Specifically, for example, by changing the grinding fluid flow rate Q so as to decrease from the time when the grindstone table 3 is rapidly retracted in step (2) of FIG. 6, in the spark-out process of the workpiece w as shown in FIG. The thermal deformation rate of becomes small. In FIG. 17, the lower curve shows the relationship between the spark-out time τ and the thermal deformation amount dθw of the workpiece when the flow rate Q of the grinding fluid is 15 L / min in the spark-out process in which the feed of the grindstone table 3 is zero. The upper curve shows the relationship between the spark-out time τ and the thermal deformation amount dθw of the workpiece when the flow rate Q of the grinding fluid is 3 L / min in the spark-out process in which the feed of the grindstone table 3 is stopped. ing.

If the grinding wheel base 3 is fed at a very fine cutting speed under the condition that the flow rate Q of the grinding fluid is not changed by the difference between the two curves in FIG. 17, the surface roughness of the workpiece to be ground is dramatically improved. This has already been confirmed by the inventors' experiments, and FIG. 18 shows the results of the experiments compared with those under other processing conditions.

FIG. 18A illustrates the uneven state in the range of the length of the surface to be ground of 0.8 mm, and the right half range in this figure shows a case where general spark-out grinding is performed for 2.5 seconds. There are many steps where the difference in height is significantly greater than 2 μm, while the left half range is obtained when ultra-fine cutting speed grinding is performed for 2.5 seconds. In other words, there are no stepped portions where the height difference exceeds 2 μm, and there are many stepped portions significantly lower than this.

Further, FIG. 18B shows a curve showing the relationship between the very small cutting time t and the surface roughness Ry when the very small cutting speed grinding is performed, and a general grindstone table is stopped. When spark-out grinding is performed and the grinding fluid flow rate Q is 15 L / min, a curve indicating the relationship between the spark-out time τ and the surface roughness Ry, and a general spark in which the grindstone table 3 is stopped A curve showing the relationship between the spark-out time τ and the surface roughness Ry when performing thermal deformation rate control grinding in the state where the grinding fluid flow rate Q is reduced to 3 L / min when out grinding is performed. It is shown.

Here, the surface roughness improving grinding function unit 28 aims at the effect of improving the surface roughness by the above-described extremely small cutting speed grinding.
The requirement necessary to effectively realize the improvement function of the surface roughness improvement grinding function section 28 is how much cutting amount is fed in how long.

The processing conditions in the case of the ultra-fine cutting speed grinding shown in FIG. 18 are such that the thermal deformation amount (thermal shrinkage amount) dθw (i) of the workpiece w shown in FIG. 19 calculated by the above equation (s2) is reduced in the vertical direction. The grindstone table 3 is fed with respect to the extremely fine cutting time τ by the amount of the amount. Here, dθw (i) means the amount of thermal deformation dθw of the i-th workpiece w. The reason for adopting such feeding is that it has already been confirmed that it is effective for improving the surface roughness.

In order to carry out such ultra-fine cutting speed grinding after the start of spark-out, the amount of thermal contraction dθw (i) of the workpiece w and the thermal contraction speed with the passage of time τ after the start of spark-out has been estimated. In this case, the thermal contraction amount dθw (i) corresponds to the thermal deformation amount dθw of the workpiece w in the spark-out process for the first workpiece w described in the operation of the thermal deformation amount detection function unit 25. To do. Therefore, as described above, the heat shrinkage dθw (i) and the heat shrinkage rate are expressed by the constants α and dθk in the equation (s2), that is, dθw = f (T) = dθk (1−αT). It is determined so as to meet the processing conditions of grinding, and is estimated by the determined equation (s2) of these constants.

The curve of the amount of heat shrinkage (heat deformation amount) dθw (i) in FIG. 19 corresponds to the curve of the heat deformation amount dθw in FIG.

The extremely small cutting amount du, which is the feed amount of the grindstone table 3 in the extremely small cutting speed grinding of the i-th workpiece, is proportional to the thermal deformation amount (thermal shrinkage amount) dθw (i) of the workpiece w (<1 ) Multiplied by k · dθw (i), and its change with the passage of time after the start of spark-out is as shown in FIG. The extremely fine cutting speed grinding specified in this way is executed until a predetermined time τg (for example, 2.5 seconds) elapses after the spark-out starts.

As described above, it is possible to realize a surface roughness improving function by making a very small cut in the spark-out grinding process. In order to perform high-precision grinding of the workpiece w by the surface roughness improving grinding function unit, the inherent function of the surface roughness improving grinding function unit and the dimension error minimizing grinding of the previous dimension error minimizing grinding function unit The functions must be advanced simultaneously, and the operation flow in this case will be described with reference to FIG.

In FIG. 20, steps (0-1) and (0-2) are the same as most processes in the operation flow of the thermal deformation amount detection function unit 25 described above. Here, the first (i = 1) Grinding resistance (grinding principal component force qs (1)) immediately before finishing the work w is measured, and data on the amount of thermal deformation dθw (1) is acquired. Steps (1), (2), (3), (4), (5), and (6) are the same as the processes on the operational flow of the dimensional error minimizing grinding function unit 27 of the i-th workpiece w. At this time, in step (1), the grinding resistance (grinding principal component force qs (i) at the start of spark-out of the i-th workpiece w is measured, and in step (2), the spark-out start time is calculated according to equation (s7). The thermal deformation amount dθk (i) is calculated, and in step (3), the curve of the thermal deformation amount d′ θw (i) is determined by the equations (s8) and (s9), and the thermal deformation amount (heat (Shrinkage amount) dθw (i) The thermal deformation amount (thermal shrinkage amount) dθw (i) is inferred from the equation (s1), and the equation dθw (i) = dθk (i) −d′θw (i) Thus, the heat deformation amount (heat shrinkage amount) dθw (i) and the heat shrinkage rate in the spark-out process of the i-th workpiece w are predicted, and step (3-1) is calculated. ) (3-2) and (5-1) indicate processing unique to the surface roughness improving grinding function section 28. Is.

After step (3), the process proceeds to step (3-1). Here, a proportional coefficient k and an extremely small cutting time τg are determined as standard set values. These set values may be experimentally valid values fixedly set in advance, or the surface roughness measurement by the operator is performed in a post process, and the measurement results are fed back to obtain a proportional constant k And the very small cutting time τg may be appropriately changed according to the measurement result. In the latter case, a neural network may be used.

Next, the process proceeds to step (3-2). Here, based on the thermal deformation amount (heat shrinkage amount) dθw (i) estimated in step (3), a very small cutting amount du of the grindstone table 3 is calculated. Execute grinding by the cutting depth (very small cutting speed grinding).

Next, the process proceeds to step (5) through step (4). In step (5), it is determined whether or not the actual dimension Rr exceeds the target dimension Rk. When it does not exceed, it moves to step (5-1), and when it exceeds, it moves to step (6).

In step (5-1), it is determined whether or not the very small cutting time (which is a subordinate concept of the spark-out time) τ exceeds the set time τg. When not exceeding, the process returns to step (3-2), and when exceeding, the feeding of the grinding wheel base 3 is stopped and the process proceeds to step (4). Thereafter, the feeding of the grinding wheel base 3 is stopped. As long as the actual dimension Rr does not exceed the target dimension Rk in step (5), the process proceeds to step (5-1). In this case, the micro cut time τ is naturally set to the set time τg. Is repeated, and the process of returning to step (4) is repeated while the feed of the grindstone table 3 is stopped.

Thus, the spark-out grinding proceeds. Thereafter, when it is determined in step (5) that the actual dimension Rr exceeds the target dimension Rk, the process proceeds to step (6), and the grindstone table 3 moves backward. Thus, the workpiece is separated from the workpiece w and the grinding is finished. Other operations are performed in accordance with the above-described operations.

In the operation flow of FIG. 20, the actual dimension Rr exceeds the target dimension Rk in step (5) before it is determined in step (5-1) that the micro cut time τ exceeds the set time τg. May occur. That is, it is possible that the actual dimension Rr exceeds the target dimension Rk and the grinding is finished at the stage where the function of the surface roughness improving grinding function unit 28 is not performed to the extent that the purpose is achieved. Such a situation must be avoided. For this purpose, the value of the set time τg required to achieve the purpose of the surface roughness improving grinding function section and the spark-out (minimum dimensional error) when the grindstone table 3 is stopped. It is necessary to adjust to some extent the period during which the combined grinding function portions 26 and 27 are to be executed. In order to perform efficient grinding while maintaining the surface roughness with high quality, it is preferable that the period of the spark-out in which the grindstone is stopped is as short as possible. If it is difficult to secure an appropriate set time τg, the grinding allowance in the spark-out process may be slightly increased.

In order to quantitatively improve the surface roughness improvement function of this surface roughness improvement grinding function part in a more stable state, it is necessary that the surface roughness of the workpiece w has been improved to some extent during the fine grinding process. In order to realize this, for example, an appropriate grinding resistance and a grinding continuation time with this grinding resistance are experimentally confirmed in advance, and the numerical controller is used under the confirmed conditions. Let's perform the fine study.

When a grinding machine having the surface roughness improving grinding function section 28 as described above is used to grind many workpieces w of the same type (same shape and size) repeatedly, the operation flow shown in FIG. Should be executed automatically.

In FIG. 21, the first workpiece is actuated by some functions of the thermal deformation amount detection function unit 25 in steps (1) to (3). Each of these steps (1) to (3) is the same as (1) to (3) in FIG. 16, and in this step (3), the thermal deformation amount dθw of the workpiece w is specified. In step (4), the amount of thermal deformation dθw is equivalent to the amount of thermal contraction of the workpiece w, and the data of the thermal contraction amount dθw or the thermal contraction speed is obtained.

Thereafter, the process proceeds to step 5 where the grindstone table 3 is fed. In step (6), the grinding resistance (grinding main component qs (i = 1)) at the start of spark-out is measured by the AE sensor. In step (7), a thermal deformation amount (thermal shrinkage amount) dθk (i = 1) at the start of spark-out is calculated from the measured value qs (i = 1) of the main grinding force, and this calculated value is used. The thermal deformation amount (thermal shrinkage amount) d′ θw (i = 1) of the workpiece w in the spark-out process is specified, and the thermal deformation amount (thermal shrinkage amount) dθw (i = 1) in FIG. 19 corresponding thereto is specified. To decide. As a result, the amount of heat deformation (heat shrinkage amount) dθw (i = 1) and the heat deformation rate in the spark-out process were estimated. Next, in step (8), an extremely small cutting amount du in the spark-out process is determined, and extremely small cutting speed grinding is executed. When the sizing device 15 detects that the workpiece has reached the target dimension, the machining of the first workpiece is completed.

Thereafter, the process proceeds to step (5) again, and the operations from steps (5) to (9) are executed for the second workpiece. At this time, in step (6), the grinding resistance (grinding main component qs (i = 2)) at the start of spark-out is measured by the AE sensor. In step (7), the amount of thermal deformation (heat shrinkage amount) dθk (i = 2) at the start of spark-out is calculated from the measured value qs (i = 2) of the main grinding force using equation (s7). From the calculated values, using equations (s8) and (s9), the thermal deformation amount (thermal contraction amount) d′ θw (i = 2) of the workpiece w in the spark-out process is specified, and FIG. The amount of heat deformation (heat shrinkage) dθw (i = 2) is determined according to the above description. As a result, the amount of heat deformation (heat shrinkage amount) dθw (i = 2) and the heat deformation rate in the spark-out process were estimated. Next, in step (8), an extremely small cutting amount du in the spark-out process is determined from the thermal deformation amount (thermal shrinkage amount) dθw (i = 2), and extremely small cutting speed grinding is executed. Then, when the sizing device 15 detects that the workpiece has reached the target dimension, the machining of the second workpiece is completed.
Thereafter, steps (5) to (9) are repeated for each workpiece w.

It is a top view which shows the CNC grinder used by this invention. It is sectional drawing which shows the structure around the grindstone axis | shaft of the said grinding machine. It is a figure which shows the modification of the said grinding wheel shaft periphery. It is a figure which shows the standard grinding process performed with the said grinding machine. The grinding process by the said grinding machine is shown, A is explanatory drawing of plunge cut grinding, B is explanatory drawing of traverse cut grinding. It is a figure which shows the operation | movement flow of a thermal deformation amount detection function part. It is a figure which shows the curve etc. of the data obtained by the action | operation of a thermal deformation amount detection function part. Regarding data when the first workpiece is ground by the dimension error minimizing grinding function part, (a) is a diagram showing a curve of a change process of the calculated value d′ θw of the thermal deformation amount, and (b) is an actual figure. It is a figure which shows the curve of the change process of the dimension Rr. It is a figure which shows the operation | movement flow of the dimension error minimization grinding function part at the time of grinding the 1st workpiece | work. It is a figure which shows the relationship between the grinding main component force qs just before a spark out, and the amount of thermal deformation d (theta) k. The data which concerns on the dimension error minimization grinding function part are shown, (a) is a figure which shows the change process of the grinding principal component force qs, (b) relates to the incorrect estimation about the calculated value d'θw of the amount of thermal deformation. It is a figure which shows a curve. It is explanatory drawing which shows the change process of actual thermal deformation amount d '(theta) w. A curve or the like related to the calculated value d′ θw of the thermal deformation amount is shown, (a) is a diagram showing a curve for estimating the calculated value d′ θw (i) of the i-th workpiece, and (b) is i pieces. It is a figure which shows the curve which concerns on the said calculated value d '(theta) (i) of the workpiece | work of an eye. It is a figure which shows the operation | movement flow of the dimension error minimization grinding function part at the time of grinding an i-th workpiece | work. It is a figure which shows the change process of the dimension R specified from the output signal of the sizing apparatus in the action | operation of the dimension error minimization grinding function part, the change process of the actual dimension Rr of the i-th workpiece | work, etc. It is a figure which shows an example of the operation | movement flow in the case of grinding many workpieces of the same kind repeatedly. It is a figure which shows the change process of the thermal deformation amount d (theta) w in the spark-out process of a workpiece | work. It is a figure which shows the surface roughness of the workpiece | work in very minute cutting speed grinding and other types of grinding. It is explanatory drawing about determination of the very small cutting amount. It is a figure which shows the operation | movement flow of a surface roughness improvement grinding function. It is a figure which shows an example of the operation | movement flow in the case of grinding many workpieces of the same kind repeatedly.

6 Headstock (work support rotation means)
7 Tailstock (work support means)
9 Spindle (work support rotation means)
10 Grinding wheel 11 Grinding wheel shaft 13a Spindle center (work support means)
14 Tailstock center (work support means)
16 Grinding resistance detection means (AE sensor)
25 Thermal deformation amount detection function unit 26 Dimensional error minimizing grinding function unit 27 Dimensional error minimizing grinding function unit 28 Surface roughness improving grinding function unit τg Set time (time data)
dθw Thermal deformation (thermal shrinkage)
d′ θw Thermal deformation qs Grinding principal component force Rk Target dimension Rr Actual dimension w Workpiece

Claims (3)

In a grinding machine comprising a workpiece support rotating means for supporting a workpiece and rotating around a specific center line, and a grinding wheel rotated around a grinding wheel axis and relatively displaced in the workpiece rotation radial direction with respect to the workpiece,
The grinding wheel is separated from the workpiece while the workpiece is rotated and the grinding fluid is continuously poured, and the outer diameter of the workpiece is continuously measured over time under the separated state, and the elapsed time and thermal deformation of the workpiece. A thermal deformation amount detection function unit for acquiring a relationship between the amount;
Relative displacement of the grinding wheel so as to cut into the workpiece for a certain period of time by a cutting amount smaller than the amount of thermal deformation at the time position estimated from the acquired relationship at each time position after the spark out start point. A grinding machine comprising a surface roughness improving grinding function section.
In a grinding machine comprising a workpiece support rotating means for supporting a workpiece and rotating around a specific center line, and a grinding wheel rotated around a grinding wheel axis and relatively displaced in the workpiece rotation radial direction with respect to the workpiece,
The grinding wheel is separated from the workpiece while the workpiece is rotated and the grinding fluid is continuously poured, and the outer diameter of the workpiece is continuously measured over time under the separated state, and the elapsed time and thermal deformation of the workpiece. A thermal deformation amount detection function unit for acquiring a relationship between the amount;
Relative displacement of the grinding wheel so as to cut into the workpiece for a certain period of time by a cutting amount smaller than the amount of thermal deformation at the time position estimated from the acquired relationship at each time position after the spark out start point. After that, after the relative displacement is stopped, the workpiece obtained by combining the outer diameter of the workpiece measured at each time position and the thermal deformation amount at each time position estimated from the acquired relationship A grinding machine comprising a surface roughness improving grinding function unit for controlling the start of retreat of the grinding wheel when the actual dimension of the grinding wheel becomes a target dimension.
In a grinding machine comprising a workpiece support rotating means for supporting a workpiece and rotating around a specific center line, and a grinding wheel rotated around a grinding wheel axis and relatively displaced in the workpiece rotation radial direction with respect to the workpiece,
The grinding wheel is separated from the workpiece while the workpiece is rotated and the grinding fluid is continuously poured, and the outer diameter of the workpiece is continuously measured over time under the separated state, and the elapsed time and thermal deformation of the workpiece. A thermal deformation amount detection function unit for acquiring a relationship between the amount;
At each time position after the spark-out start point, the grinding wheel is relatively displaced so as to cut into the workpiece by a cutting amount smaller than the thermal deformation amount at the time position estimated from the acquired relationship. When the actual dimension of the workpiece obtained by combining the outer diameter of the workpiece measured in step 1 and the amount of thermal deformation at each time position estimated from the acquired relationship becomes the target dimension, the grinding wheel starts to retract. A grinding machine comprising a surface roughness improving grinding function section to be controlled.