Application of Mandrel Method in Processing and Inspection of Eccentric Gear

The eccentric gear is one of the key parts of the heavy-duty mechanical press. In the main transmission system of the heavy-duty press, the eccentric gear, the connecting rod, the guide post, and the slider constitute a crank-slider mechanism, which converts the rotary motion of the eccentric gear into a sliding motion. The linear reciprocating movement of the block realizes the punching function of a heavy mechanical press. The manufacturing accuracy of the eccentric gear directly affects the movement accuracy of the slider of the mechanical press, so it is particularly important to solve the processing problem of the eccentric gear.

1 Mandrel method processing instructions

The mandrels are two slender shafts of the same size designed to facilitate the processing of eccentric gears. They need to be quenched and refined to ensure their size and shape accuracy. After the eccentric gear tooth surface processing is completed, take the reference tooth as the center, move the same number of teeth on both sides to adsorb the mandrel in the tooth groove through the magnetic meter seat, and find the lowest point of the two mandrels through the dial indicator, so that The lowest point coincides, so as to achieve the centering of the eccentric gear tooth profile, so as to facilitate the subsequent feature processing.

2 Process analysis

2.1 Difficulties in processing technology

Figure 1 shows the outline drawing of the eccentric gear. The outer circle of the center of the eccentric body is not concentric with the addendum circle and the center of the hole. One piece of eccentric gear tooth top center, hole center, and eccentric body center must be on the same straight line, and the other eccentric gear tooth groove center, hole center, eccentric body center must be on the same straight line, unequal tolerances are equal Is 0.05.

Figure 1 Outline drawing of eccentric gear

The main feature of this part is eccentricity. Because the gear outer circle, end face, center hole and eccentric outer circle surface of this part require high position accuracy (the surface roughness requirements are also very high), and the eccentric distance must be guaranteed, so the clamping Processing is more difficult.

2.2 Machining process

The machining process is as follows: welding heat treatment spray brushing → ultrasonic inspection → marking → car outer circle, inner hole, end face → marking to find the highest point of the eccentric outer circle of the blank → hobbing → gear grinding → milling the datum of the eccentric part → Eccentric part of turning → milling keyway → inspection → fitter process → assembly.

2.3 Machining process of milling the eccentric part datum

The benchmark for milling the eccentric part is the most critical machining process. The qualification of the machining accuracy directly determines the qualification of the part. Therefore, the specific machining steps and various factors that may affect the machining accuracy must be fully considered before the process is processed. factor. Such as the guarantee of the machining accuracy of tooling, the elimination of machine tool errors, and the stability of machining tools. In this process, the eccentric gear is machined on the gantry milling machine using the mandrel method.

2.3.1 Clamping of the workpiece

As shown in Figure 2, two eccentric gears of the same platform are laid flat on the worktable of the gantry milling machine in the same direction, and contour pads are placed under the eccentric gears. When placing, try to make the eccentric part and the axis of the center hole and the reference tooth The centers are on the same line. With the reference tooth as the center, count the same arbitrary number of teeth on both sides, and the mandrel is adsorbed in the tooth groove through the magnetic table holder.

Figure 2 Workpiece clamping and alignment

2.3.2 Alignment of the workpiece

Firstly, after aligning the side generatrix of the center hole, press the workpiece slightly, and then pull the lowest point of the mandrel on the spindle of the machine tool, so that the lowest point of the mandrel is on the same straight line. If the value of the observation table is not equal, fasten it in the T-slot through the L-shaped pressure plate, and fine-tune the tooth surface of the eccentric gear at the top of the L-shaped pressure plate by the screw until the dial indicator value does not change. At this time, the eccentricity is explained. The left and right sides of the gear centered on the reference tooth have been adjusted to ensure that the center of the tooth tip, the center of the hole, and the center of the eccentric body are connected on the same straight line. Then the workpiece is pressed tightly, and the center hole is checked. After the clamping and alignment is completed, the next step of processing is started.

2.3.3 Milling eccentric datum

After installing the cutter head on the spindle of the machine tool, first align the center of the center hole, and then offset the eccentric distance to the eccentric part to determine the center of the eccentric part, and mill the datum on the upper end of the eccentric part for subsequent lathe processing and alignment. Because the eccentric datum is milled by the same distance to the same side of the machine tool, the influence of the machine gap can be eliminated, so as to ensure that the eccentric distances of the two pieces of the same machine are equal. This processing method is simple and efficient, and the measurement error is small, the level of requirements for the operator is reduced, and the processing requirements of the two eccentric gears on the same set can be relatively easily guaranteed.

2.4 Processing precautions

When processing, you need to pay attention to the following:

①As the normal process flow of parts processing, before using the above method to process parts, it is necessary to mark the blank and align the line according to the line, and the marking must be accurate and serious. After finding the highest point of the eccentric outer circle part of the blank on the lathe, click this line. Before hobbing, be sure to press this line as the hobbing center to ensure the subsequent turning allowance of the eccentric part.

②Because the eccentric gear is welded by dissimilar steel, after the stress is removed from the welding, the gear hobbing must pay attention to the release of the stress during the hobbing, to prevent the stress deformation from causing insufficient grinding allowance, which will affect the reference tooth profile of the mandrel adsorption. Precision.

3 Check critical dimensions

After the processing is completed, the key dimensions of the eccentric gear need to be inspected on the three coordinates to verify the rationality of the processing method. Similarly, the tolerance of the line connecting the center of the tooth tip, the center of the hole, and the center of the eccentric body on the same straight line is detected by the spindle method. As shown in Figure 3.

Figure 3 Critical dimension inspection

The eccentricity of two eccentric gears on the same platform and the tolerance of the center of the tooth groove, the center of the hole, and the center of the eccentric body on the same straight line through the three-coordinate detection are in line with the requirements of the drawing, thus verifying the eccentricity of the mandrel method. The rationality of gears.

4 Conclusion

This article mainly studies the application of the mandrel method in the processing and inspection of eccentric gears, and introduces the processing process and precautions of the method in detail. The eccentric gear processed in accordance with the above process flow is proved by inspection and full-load test of the press to fully meet the requirements of production and processing.

This method provides an effective guarantee for the accuracy of the heavy-duty press, reduces the rework caused by processing errors in the past, saves processing and assembly time, and improves the company's economic benefits.