JPH0448584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling the dimensions of a workpiece in grinding.

(Conventional technology and its issues) Conventionally, the dimensions of the workpiece being machined were continuously measured using an in-process gauge, the measurement data was input into a control mechanism, and the grinding wheel was used to cut the workpiece until it reached the pre-specified dimension. In automatic grinding machines equipped with automatic sizing devices that automatically control grinding operations, size control is performed by taking into account a certain amount of expansion of the workpiece due to grinding heat during grinding.

This will be explained based on FIG. This figure is a diagram showing the relationship between a typical conventional grinding cycle (gauge machining cycle with gear eliminator) and grinding power. Rapid feed, rough cutting feed,
is the finishing feed of the cut, is the spark-out of the cut,
○A is the cutting start point, ○B is the power atmosphere level hold point, ○C is the gear eliminator detection point (grinding start point), ○D is the rough grinding feed completion point, ○E is the finishing point The grinding completion point, ○ is the grinding completion point, and ○ is the cutting retreat point.

In Figure 1, the upper half is the grinding cutting cycle diagram;
The lower half shows the grinding power diagram. For example, the total power during rough grinding defined by the grinding start point ○C and the rough grinding feed completion point ○D is the area divided between these points between the horizontal axis and the grinding power diagram ( Grinding power area)
corresponds to Conventionally, size control has been carried out by assuming that this grinding power area is constant and allowing for a constant amount of expansion of the workpiece.

However, in reality, the area of the rough grinding power is affected by factors such as the sharpness of the grinding wheel, and if this changes, the power height (PH) will vary even if grinding is performed with a certain cutting cycle, and the area of the rough grinding power will vary depending on each workpiece. As a result, the workpiece temperature varies greatly when rough grinding is completed. For details, see (a) Changes in the grinding power of the grinding wheel shaft drive motor after resharpening depending on the degree of wear of the dressing diamond (b) Changes in the grinding power when the grinding wheel diameter changes from small to large (c) Amount of grinding wheel correction Variations in grinding power due to variations in (dress correction amount) (d) Variations in grinding power due to variations in re-sharpening speed (dress lead) (e) Variations in heat generation due to differences in grinding allowance (f) Grinding cutting speed (g) Fluctuations in grinding power due to variations in grinding power (g) Fluctuations in grinding power due to clogging of the grinding wheel surface, spillage, etc. Due to causes such as (i) to (g) above, variations in workpiece temperature at the time of finishing grinding occur. As a result, variations occurred in the final finished dimensions of the workpiece, resulting in machining defects.

To prevent this, rough grinding and fine grinding are
It is necessary to repeat the grinding process several times or to extend the spark-out period after rough grinding to provide a cooling period, but this causes other problems such as an increase in the number of steps and a longer cycle time.

On the other hand, in order to estimate the amount of thermal expansion of the workpiece more accurately, a method has been proposed in which the amount of thermal expansion of the workpiece is estimated based on the grinding time (Japanese Patent Laid-Open No. 52-135492
issue). However, when estimating the amount of thermal expansion based only on the grinding time, an increase in the amount of heat generated due to deterioration of the sharpness of the grindstone is not taken into account. Therefore, if the feed of the grindstone remains the same as before deterioration, even if the grinding time remains the same, the amount of heat accumulated in the workpiece will increase more than usual, resulting in a larger amount of thermal expansion than usual. This increased amount cannot be estimated from the grinding time.

(Means for Solving the Problems) In view of the above-mentioned problems of the prior art, this invention aims to improve and eliminate the problems, and controls the rough grinding power to a constant level by controlling the feeding speed of the grinding wheel relative to the workpiece. We discovered that it is possible to calculate the expansion amount of the workpiece due to grinding heat according to the level of the rough grinding power from the grinding time during rough grinding, and that we can feed this expansion amount of the workpiece to the in-process gauge to correct the atmosphere point. This is what I did.

Note that the relationship between the amount of thermal expansion of the workpiece and the grinding time is explained by the following equation.

Fn: Grinding force in the normal direction of the grinding wheel Ft: Grinding force in the tangential direction of the grinding wheel U: Grinding wheel peripheral speed μ: Coefficient of friction between grinding wheel and workpiece given that, Ft:μ・Fn Because it is, Grinding power (PH) is PH=Ft・U=μ・Fn・U It can be expressed as

The amount of heat q that flows into the workpiece per unit time is calculated as follows: q∝μ・Fn・U∝PH During grinding, assuming that the amount of heat removed from the workpiece by the grinding fluid is proportional to q and that the grinding wheel peripheral speed U is constant. The total amount of heat Q that flows into the workpiece can be expressed as Q∝PH・PT, where PT is the machining time.

The amount of thermal expansion △d in the diametrical direction of the workpiece is, if the original diameter is D, △d=ν・D・Q/(k・W) ∝K・PH・PT Where, ν: Linear expansion of the workpiece rate, k: specific heat of the workpiece, W: weight of the workpiece, K: constant of proportionality.

From the above equation, it can be seen that the amount of thermal expansion of the workpiece due to grinding heat can be calculated from the grinding time (PT) during rough grinding according to a certain level of rough grinding power (PH). Note that the proportionality constant K can be determined by calculation, but can also be determined from experimental results using sample workpieces.

(Example) The present invention will be explained below with reference to the drawings.

A workpiece size control method according to the present invention will be explained based on FIG. 3. The figure is a grinding power diagram, where the horizontal axis shows time, and the vertical axis shows the power (grinding power) of the grinding wheel shaft drive motor 4, and the power atmosphere level hold point,
is the grinding start point, is the gauge atmosphere correction power level, is the peak power control level, is the coarse grinding completion gauge signal point, is the finishing feed completion gauge signal point, and is the grinding completion gauge signal point.

When the cycle is started, the grindstone 1 is first rapidly fed into the cut to the point where the rapid feeding is completed. At this point, the power of the grindstone shaft drive motor 4 is held to the power point, and the cutting is switched to rapid feed. Then, when the grindstone 1 reaches the grinding start point, it is switched to the incision grinding feed and starts rough grinding. When the power of the grindstone shaft drive motor 4 increases and passes the gauge atmosphere correction level, that is, PH ₁ , the integration of the power width (time) Pt is started. The power of the grinding wheel shaft drive motor 4 is at the peak power control level,
That is, when the power increases to PH ₂ , the rough grinding feed is made slower than usual to lower the power, and when the power decreases to the gauge atmosphere correction level PH ₁ , the power is returned to the normal coarse grinding feed and the power is increased.

In this way, while maintaining the rough grinding power constant, the dimension measurement section 10 corrects the atmosphere point, for example, changes the finished dimension to the larger side, until the coarse grinding feed is completed at every predetermined power width (time) Pt. The shifting correction is repeated PT/Pt=n times.

Even when the sharpness of the grindstone deteriorates, the amount of thermal expansion of the workpiece increases in proportion to the increase in the grinding power area, but the power of the grindstone shaft drive motor 4 is corrected by reducing the feed speed of the grindstone 1 relatively significantly. (In this case, correct the power height by lowering it to between PH ₁ and PH ₂ ) to maintain it at a constant level, and increase the amount of atmosphere point correction by increasing the power width accordingly. This prevents the work from being finished with negative dimensions.

After the point where the rough grinding feed is completed, the grinding wheel 1 is fed to finish the cut, sparks out, and the cut is retreated.

Next, a control block for carrying out the work size control method shown in FIG. 3 will be explained based on FIG. 2.

As shown in the figure, a grindstone 1 is supported by a grindstone stand 3 slidably provided on a machine bed 2 and driven by a drive motor 4, and a feed drive section is controlled by a feed drive control signal A from a control section 5. 6 gives a cutting motion. When the drive motor 4 starts, it outputs a grindstone shaft drive motor power signal B, and this signal B is sent to the measuring device calculation unit 8 via the grinding power measurement unit 7.
It is also input to the control section 5. Measuring device calculation section 8
is configured to calculate the amount of thermal expansion of the workpiece due to the grinding power area between Pt from the grinding time Pt, repeat this calculation n times, and calculate the amount of thermal expansion between the machining times PT. .

On the other hand, a support device (not shown) that supports the workpiece 9 has a dimension measuring section (in-process gauge) 10, and this dimension measuring section 10 measures the dimensions of the workpiece 9 during grinding and outputs a dimension signal C. It is input to the control section 5 via the measuring device calculation section 8. Further, the correction signal D output from the measuring device calculating section 8 is input to the dimension measuring section 10, and the atmosphere point of the dimension measuring section 10 is automatically corrected.

(Effects of the Invention) As explained above, according to the present invention, the rough grinding power is controlled to a constant level by controlling the feed rate of the grinding wheel, and the grinding time during rough grinding is adjusted according to the level of the rough grinding power. The amount of expansion of the workpiece due to grinding heat is calculated, and the amount of expansion of the workpiece is fed back to the in-process gauge to perform atmospheric point correction.The finished size of the workpiece can be adjusted without being affected by deterioration of the grinding wheel cutting quality. In addition, it is possible to eliminate the inconveniences such as the increase in the grinding process due to the conventional repeated two-time grinding and the lengthening of the cycle time due to the setting of the cooling period.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the correspondence between typical conventional grinding cycles and grinding power, Fig. 2 is a control block diagram of a specific device for this invention, and Fig. 3 is based on the control method of this invention. It is a grinding power diagram. 1... Grindstone, 4... Drive motor, 6... Feed drive unit,
10...Dimension measurement section (in-process gauge).

Claims (1)

[Claims] 1. In the grinding process in which the dimensions of the workpiece being machined are measured with an in-process gauge and finished to the specified dimensions, the rough grinding power (PH) is kept constant by controlling the feed rate of the grindstone relative to the workpiece. The amount of expansion of the workpiece due to the grinding heat is calculated from the grinding time (PT) during rough grinding according to the level of the rough grinding power (PH), and the amount of expansion of the workpiece is fed back to the in-process gauge. A method for controlling the dimensions of a workpiece in grinding processing, which is characterized by correcting the atmospheric point. 2. A workpiece size control method in grinding according to claim 1, characterized in that the above-mentioned atmosphere point correction is repeatedly performed at certain fixed time intervals (Pt).