Drilling skills on arc surface

As shown in Figure 1, the material of this part is aluminum alloy 2A12, the shape is arc, there are 4 M5 threads on the arc surface, need to drill 4-φ4.2 threaded bottom hole, the axis of the hole is perpendicular to the arc surface . How to process these 4 holes quickly and conveniently, and ensure the position accuracy is a processing problem.

1. Process analysis

To process this part, there are 3 methods to analyze according to the general process plan: one is fitter marking, marking out the position of the hole, and drilling according to the marking position. However, because the drilling position of the part is a circular arc surface, it is difficult to ensure the accuracy of the machining position of the hole and the quality of the part. The second is to use advanced processing equipment-five-axis CNC machine tool processing, this method is simple and easy to operate. However, our company's five-axis processing equipment is limited, and the processing cost is high, which is not the best processing solution. The third is self-made tooling, using simple tooling fixture, processing on ordinary boring machine. This method is not only low cost, fast processing, but also can ensure the processing accuracy very well, so it is a better choice.

2. Tooling design

According to production experience, the parts are circular arc surfaces with irregular shapes. There are two options for fixture design.

(1) Option 1 is to match the clamp body to the inner surface of the part. The clamp structure is shown in Figure 2. It is mainly composed of the clamp body 1, the fixed sleeve 2, and the compression screw 3. The wire cutting process clamps the specific outer surface and the inner surface of the part. Cooperate. The compression screw compresses the parts through the fixing sleeve.

(2) Scheme 2 The clamp body is matched with the outer arc surface of the part. The clamp structure is shown in Figure 3. The clamp is mainly composed of the clamp body 1, the compression screw 2, the limit plate 3, and the fixed screw 4. The internal diameter of the CNC lathe machining fixture φ32 is in contact with the arc surface R16 of the part, and the fit gap between the two is not more than 0.02mm to ensure the position accuracy of the machining hole. Use the limit plate 3 to position the parts, and lock the parts with a compression screw.

Through the actual processing of parts, the parts processed by the fixture in Scheme 1, the product fit is not good, the position of the threaded hole is deviated, and the gap between the parts is too large, which affects the quality of the product. Scheme 2 The design of the fixture is consistent with the assembly relationship when the parts are used. The processed parts have higher precision, accurate positioning, high matching accuracy, and good product quality. And it is easy to assemble and disassemble parts, which is convenient and quick. Based on this, option 2 fixture is selected. The clamp is made of stainless steel material, which can reduce the error caused by tool wear and ensure the accuracy of the parts, and the processing of batches of parts is very fast.

When processing the clamps, pay attention to ensure that the coaxiality of the outer circle of the left chuck and the inner hole of the right part of the clamp is 0.01mm, to ensure the position accuracy of the end face E of the specific positioning part of the clamp, and to ensure the limit plate The symmetry accuracy is good.

3. How to use

Install the fixture on the machine tool, as shown in Figure 3, first install the clamp body 1 on the self-centering chuck. Surface A is the fixture positioning and fixing surface, which is close to the end surface of the chuck. Fix the dial indicator on the main shaft of the machine tool, use the dial indicator to align the clamp specific axis B with a runout not greater than 0.02mm, and then find the clamp specific end face C to ensure that the perpendicularity between the end face C and the axis B is not greater than 0.02mm, and clamp it. Install the parts, the end face of the part is positioned close to the E surface of the clamp, the position of the part is restricted by the limit plates 4 on both sides, and the two compression screws 2 are tightened to fix the part.

When processing, correct the two sides of the workpiece to determine the processing angle position. The boring machine uses the position relationship between the clamp design and the part, enters the drilling coordinates, and the drill drills through the guide hole on the clamp. After the processing is completed, loosen it. Tighten the screw, take out the parts, project the inspection of the position accuracy of the first hole, and batch process after qualified.

4. Conclusion

It is proved by batch processing that the fixture has simple design structure, convenient manufacturing, quick clamping of parts, flexible adjustment, high production efficiency, and reusable use. The machining process is safe and reliable, and the machining accuracy of the parts can be guaranteed. It is very suitable for mass production and can be used as a reference for similar parts.