Rolling process of thin-walled rotating body

1. Analysis of the Rolling Process for Thin-Walled Rotating Parts

In a research project conducted by the company's head office research institute, the product components included thin-walled rotary shell parts such as housings and cylinders (see Figures 1 and 2). These parts are challenging to process due to their thin walls and complex shapes.

Figure 1: Housing

Figure 2: Cylinder

The closing section of these parts is particularly difficult when cut, making it hard to maintain quality. Additionally, the cylinder’s length exceeds one meter, which further complicates the manufacturing process. As a result, the team decided to use thin-walled pipes instead. Since this was a research and trial production stage with a small batch size and an unfinished design, using a pressure-forming mold was not feasible. There were no precedents for designing large-scale drop molds, and the cost and time required would have been too high. Therefore, the research institute engineers and craftsmen opted for a test processing approach using a horizontal lathe with a roller. Roller rolling is a technique where a rolling tool applies pressure to a thin-walled part, causing it to deform and take the desired shape. The main challenges in this process included: - Large differences in external dimensions between the two housing parts. - Uncertainty in pre-cutting length due to dimensional changes during rolling. - Difficulty in determining the mandrel size due to unpredictable material rebound. - A tight timeline, with only less than a month available for testing and production.

2. Rolling Process Method for Thin-Walled Rotating Parts

After extensive brainstorming and careful planning, the following steps were established for the rolling process: **Step 1:** Preliminary design and machining of the rolling positioning mandrel based on the internal dimensions from the product drawings. **Step 2:** Cutting the raw material according to the preliminary calculated blank length. **Step 3:** Conducting process tests on the lathe. After several rolling operations, the final positioning mandrel (as shown in Figures 3 and 4) and the pre-processing part length were determined (the housing was 124mm, and the cylinder was 1,145–1,150mm).

Figure 3: Spinning Shell Mandrel

Figure 4: Spinning Cylinder Mandrel

For the rolling of the shell, the spindle speed was set at 710 r/min, feed rate at 0.3 mm/r, and rolling depth between 0.2–3 mm. After 8–10 passes, the feed rate was reduced to 0.12–0.15 mm/r to reach the final dimensions. The roller used is shown in Figure 5.

Figure 5: Roller Wheel

For the cylinder, the spindle speed was 160 r/min. During the initial closing phase, the material was pulled out by 4–5 mm to locate the spindle, then another 2 mm to close the mouth. After 4–5 cycles, the bottom was flattened, and the mouth diameter was adjusted to be less than 2 mm from the specified size. Then, a single mold was used to screw into the tailstock of the lathe, shaping the bottom as shown in Figure 2. Finally, the bottom hole was machined to match the design. When clamping the workpiece, a suitable jacket was used to prevent surface damage or deformation.

3. Conclusion of the Rolling Process for Thin-Walled Rotating Parts

Within less than a month, the research and production tasks for both the housing and cylinder parts were successfully completed, meeting all design requirements. Although some adjustments are still needed for optimal performance, this process set a new precedent for rolling thin-walled shells using a roller. It fulfilled the needs of the research and ensured smooth progress in both development and production, achieving the expected design outcome.

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