JPH0117829B2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application This invention is used to cut workpieces to predetermined dimensions in so-called aus cutting, in which steel machine parts are cut in a supercooled austenite state during the quenching and cooling process. This relates to a dimensional control method for finishing.

B. Prior Art Generally, it is known that dimensional changes as shown in FIG. 1 occur during the quenching heat treatment process of steel. In other words, an item with dimension A initially expands to B due to thermal expansion due to quenching heating, and by rapid cooling from point B, thermal contraction occurs from B → C → D and the dimension changes to point M _s . Then, by further cooling from the M _s point to room temperature, transformation expansion of martensite occurs, and the dimensions expand from D to E again.
Finally, the A dimension becomes the E dimension.

Therefore, when machining general steel machine parts, the amount of expansion due to quenching heat treatment (in Figure 1) is determined in advance, and the target machining dimensions are set taking into account the amount of expansion, and the desired finished dimensions are obtained by quenching heat treatment. (Target dimensions for grinding considering the machining allowance for grinding).

On the other hand, M _s
Since cutting is performed in a temperature range C that is higher than the M _s point near the point, the target machining dimensions were set taking into account the contraction and expansion between the points. Therefore, in aus cutting, while it is important to control the dimensions during cutting, it is also very important to control the temperature of the workpiece during cutting.

However, in order to strictly control the temperature of the work to be oascutted (the work taken out from the quenching furnace), the temperature of the quenching furnace must be strictly controlled. In addition, expensive quenching furnace equipment with a highly accurate temperature control function is required. Moreover, in actual operation, the workpiece temperature during cutting is
There are problems such as variations in the quenching heat treatment conditions and a drop in temperature during transportation to the machining machine after the heat treatment, making it difficult to always maintain a constant temperature.

C. Purpose of the Invention Therefore, the purpose of the present invention is to solve the problem that, in aus cutting in which cutting is performed in the supercooled austenite state during the quenching and cooling process, even if the workpiece temperature changes during cutting, the final finished dimension (first Point E in the figure) can be controlled to be constant at all times.

D. Structure of the invention This invention relates to cutting processing (auscutting).
For this purpose, the temperature of the workpiece mounted on the lathe is measured before cutting starts, and the temperature difference from the temperature preset as the workpiece temperature when performing aus cutting (hereinafter referred to as reference temperature) is determined. The temperature difference is calculated and converted into the amount of dimensional change due to heat treatment transformation of the workpiece, especially the amount of shrinkage, and feedback correction of the tool position (target machining dimension of the workpiece to be cut) is performed based on the amount of dimensional change. It is. This invention was based on the results of various experiments, and it was found that dimensional shrinkage occurred almost linearly during cooling to the M _s point after the completion of aus cutting, and that martensite decreased during cooling to room temperature. This is based on experimental results showing that the amount of expansion is constant due to transformation.

E. Example A workpiece made of high carbon chromium bearing steel (SUJ3) and made into a hollow cylindrical shape is used.
After uniformly heating this to a quenching temperature of 850℃ for 1 hour,
After rapidly cooling in oil at 200°C and holding for about 3 minutes, it was taken out from the oil and quickly chucked on a lathe to perform cutting on the outer diameter surface. At this time, the workpiece was removed from the lathe chuck and cooled in air until it reached room temperature, and the temperature and dimensional changes of the workpiece were measured, as shown in Figure 2. After the cutting was completed (220℃).
It was revealed that dimensional shrinkage occurred almost linearly during air cooling from 100 to about 160 M _s point, and that during cooling to room temperature quantitative expansion occurred due to martensitic transformation. As a result, from Fig. 2, the shrinkage rate per unit temperature (dimensional change rate △l/l・℃ per 1°C) from the end of aus cutting to the M _s point → [heat of supercooled austenite] The contraction rate] is found to be approximately 2.2×10 ^-5 , and the expansion rate (△l/l) from the M _s point to room temperature is found to be 4.1×10 ^-3 , so the target dimension for aus cutting (l) and the room temperature The relationship between the final finished dimension (L) that has been cooled down to the temperature at which the aus cutting starts (T) is expressed by equation (1).

L=l+△l=l+l{4.1×10 ^-3 −(T-160)
×2.2×10 ^-5 } =l {1+4.1×10 ^-3 −(T-160)×2.2×10 ^-5 }
...(1) Based on the above results, we have come to the conclusion that the following method is effective when considering a method that can always control the final finished dimensions to be constant even when the workpiece temperature fluctuates during cutting. In other words, after checking the workpiece after quenching heat treatment, the workpiece temperature is measured, and the shrinkage dimension amount corresponding to the temperature difference with respect to the reference temperature is fed back to the NC processing machine as a tool correction value. Figure 3 is a flowchart of this method. It is. At that time, the thermal contraction coefficient of the supercooled austenite obtained above was used as the temperature-dimensional conversion coefficient for each tool.
2.2×10 ^-5 is used.

Regarding the above, a more specific experimental example will be shown.

With the above control method, the inner ring work of deep groove ball bearings is No. 1.
- Continuously conducted cutting experiments for No. 14. The cutting conditions in this experiment were as follows, and the cutting tool layout was as shown in FIG.

Cutting speed: V = 200 m/min Feed amount: f = 0.2 mm/rev Depth of cut: T = 1.5 mm (forged rolling product finished by cutting once to specified dimensions) Tool used: 12.7 mmφ round black ceramic tool rake angle −6゜−9゜−8.5゜ Also, the correction coefficient per unit temperature of each cutting part is
The target dimensions for processing the workpiece are outer diameter 135.5mm and inner diameter 99.5mm.
mm, and the width is 47.2 mm, it is determined as follows based on the dimensional change curve after the completion of aus cutting shown in Fig. 2.

Outer diameter: 135.5×2.2×10 ^-5 ≒3.0×10 ^-3 Inner diameter: 99.5×2.2×10 ^-5 ≒2.2×10 ^-3 Width: 47.2×2.2×10 ^-5 ≒1.1×10 ^-3 Above Once the correction coefficient per unit temperature of each cutting part is determined, the amount of dimensional change due to heat treatment transformation (shrinkage dimensional amount) corresponding to the temperature difference between the workpiece temperature at the start of cutting and the aus cutting reference temperature is used as the tool correction value. Convert it using the NC temperature correction device and convert it into
Feedback is performed in the NC processing machine control section to avoid being affected by changes in workpiece temperature at the start of aus cutting.

The heat treatment conditions were as follows: After being held at 850°C for 1 hour in an electric furnace, quenching was performed using a quenching cooling device. In order to clarify the effect of temperature compensation and the effect of cutting compensation, No. 1.2 was heated at a quenching temperature of 200℃ for 3.5 minutes so that the cutting start temperature changed greatly.
No.3.4 at 180℃ for 4 minutes, No.5 to No.14 at 180℃
The cooling conditions were varied by holding at ℃ for 3.5 minutes (the work temperature at the start of aus cutting was varied).

As a result, it was revealed that even when the cutting start temperature fluctuates by about 30°C as shown in FIG. 5, the effect of the corrective cutting according to the present invention makes it possible to control the final finished size to a nearly constant size.

F. Effects of the Invention According to the present invention, even if the temperature of the workpiece at the start of cutting fluctuates, the final finished dimensions can always be controlled to a constant dimension, and therefore, it is extremely useful as a method for machining precision parts made of tough steel. .

[Brief explanation of drawings]

Fig. 1 is a thermal expansion/contraction curve diagram of steel, Fig. 2 is a dimensional change curve diagram after the completion of aus cutting, Fig. 3 is a flowchart of the workpiece dimension control method of this invention, and Fig. 4 is a cutting tool. Layout diagram, 5th
The figure is a graph showing cutting start temperature and dimensional measurement results.

Claims (1)

[Claims] 1 In aus cutting, in which cutting is performed in the supercooled austenite state during the quenching and cooling process, the workpiece temperature before cutting is measured, the temperature difference with respect to the reference temperature is calculated and converted into the amount of dimensional change due to heat treatment transformation, and the tool position is calculated. A workpiece dimension control method characterized by performing feedback correction as a correction amount.