In the gray cast iron cutting force measurement test, the different installation position of the turning tool and the sticking position of the strain gauge will lead to the difference in the ratio of the cutting force of gray cast iron to the electrical signal. In order to avoid the impact of this difference on the test results, the test device needs to be calibrated before the test to determine the relationship curve between the cutting force of gray cast iron and the electrical signal, that is, the calibration curve.

Fig. 1 is a schematic diagram of Z-direction turning force calibration. Before calibration, first stick the strain gauge on the qb-07 double parallel octagonal ring dynamometer. After the qb-07 double parallel octagonal ring dynamometer is connected with the strain gauge, fix it on the ordinary lathe, adjust and fix the position of the machine clamping tool, then remove the original ordinary machine clamping tool head and replace it with the self-made calibration tool head, A steel ball is fixed at the tool tip of the tool head for calibration, and the ball center position of the steel ball must coincide with the tool tip of the machine clamp tool head, so as to accurately calibrate the cutting force of gray cast iron. Taking the calibration of Z-direction gray cast iron cutting force as an example, when calibrating, place a force measuring ring vertically on the steel ball (as shown in Figure 2), apply a series of vertically downward fixed Z-direction forces to the calibration cutter head through the force measuring ring, and the strain on the cutter head is measured by the strain gauge connected with the octagonal ring and displayed on the computer connected with it, By setting the cutting force of gray cast iron and the obtained strain value, the proportional relationship between the cutting force of gray cast iron and the electrical signal of strain gauge can be determined, and the calibration curve can be drawn.

The test calibration curve is shown in Figure 3. The calibration curve of gray cast iron cutting force in the three directions takes the force read out by the force measuring ring as the ordinate axis and the strain read out by the strain gauge as the abscissa axis, and draws the calibration curve with origin. After the calibration in the three directions is completed, install the tool holder for gray cast iron cutting and the gray cast iron cutting sample on the lathe to start the gray cast iron cutting test.

As can be seen from Figure 3, none of the three calibration curves passed through the origin of the coordinate axis, because there was some loading force when pasting the strain gauge on the octagonal ring, and there was also an initial loading force when fixing the octagonal ring on the machine tool, but the strain tester was cleared after the octagonal ring and the tool were completely fixed, which was reflected in the calibration curve when the strain was zero, The loading force is not zero. Once the octagonal ring is fixed on the machine tool, it will not be disassembled during the cutting force test of gray cast iron, so this initial loading force can be completely ignored.