Cold rolling thread and turning thread large-diameter superposition processing technology
To ensure the thread size in the cold rolling process is accurate and stable, higher precision requirements are placed on the diameter of the raw material. As a result, most blanks that need to be cold-rolled must be precisely turned or ground. Otherwise, the rolled thread may have poor accuracy and unstable quality, making the cold rolling process difficult to control. In some cases, this can even lead to broken rollers, reducing the lifespan of both tools and machine equipment. The use of cold rolling combined with turning thread large-diameter superposition processing technology offers an effective solution to these issues.
Figure 1: Hollow thin-walled parts to be rolled
**1. Process Principles and Features**
The principle of the large-diameter superposition machining process involves using a mandrel to support the inner hole of a hollow workpiece instead of relying on traditional guide supports during thread rolling. A wide-blade plane forming turning tool is installed below the workpiece, allowing for the removal of excess metal that exceeds the required diameter during the rolling process. This technique combines the advantages of both cold rolling and turning, resulting in a more accurate and stable thread diameter.
This method enhances the process by integrating the turning of the large diameter into the rolling operation. By adjusting the position of the turning tool during the rolling process, the dimensional accuracy of the blank does not need to be as strict as in conventional methods. Instead, the blank only needs to undergo rough machining before rolling, with a small increase in diameter (0–0.3 mm). This reduces the need for extensive finishing processes, lowers manufacturing difficulty, and cuts energy consumption and costs.
For example, in the case of hollow thin-walled parts with shoulders, the original blank diameter requirement was d0 = 25.95–0.06 mm. After applying the superposition process, the actual process size became d0' = 26.23–0.28 mm. The key features of this process include:
- High accuracy and stability in the large diameter of the thread.
- Trapezoidal thread crest close to the theoretical profile.
- Reduced precision requirements for the blank diameter before rolling.
- Lower finishing workload, reduced manufacturing complexity, and cost savings.
- Expanded adjustment range for standard rolling machines, improving efficiency and enabling multi-tasking.
**2. Process Equipment**
Figure 2 shows the schematic of the large-diameter superposition processing device used for hollow thin-walled parts with shoulders.
1. Rolling wheel
2. Square head eccentric shaft
3. Upper support frame
4. Support mandrel
5. Thread large-diameter tool
6. Tool holder body
7. Adjustment screw
8. Tool fastening screw
The device is retrofitted onto a standard thread rolling machine. Its structure is simple, easy to modify, and requires minimal effort. The basic design of the thread rolling mechanism remains unchanged, consisting of a fixed roller and a movable roller. The fixed roller rotates, while the movable roller moves along the axis to feed or retract the workpiece.
The upper support system includes a mandrel, support frame, eccentric shaft, and bearings. The mandrel is mounted in two single-row tapered roller bearings, ensuring smooth rotation. It supports the hollow thin-walled part, determining its center height and axial position.
The turning device consists of a tool holder body, a flat turning tool, and adjustment screws. It is installed at the base of the original support guide plate. The distance between the tool and the workpiece centerline can be adjusted to achieve the desired thread diameter.
**3. Operation Points**
Before starting the process, select the appropriate rolling wheels, supporting mandrel, flat turning tool, and measuring instruments based on the workpiece dimensions and processing requirements. Install them correctly according to the machine’s specifications.
Next, set the rolling parameters such as feed rate, spindle speed, and rolling cycle. Start the machine and check if all components are operating properly. Once everything is ready, mount the workpiece on the mandrel when the center distance between the two rollers is at its maximum.
During the automatic cycle, the movable roller feeds the workpiece toward the fixed roller while the support frame swings. The large-diameter turning tool removes excess material as the thread is formed. After reaching the preset time, the roller retracts, and the operator can remove the workpiece for inspection.
If the thread size and quality meet the standards, continue processing. If any issues arise, adjust the machine accordingly and repeat the process until the desired results are achieved. Once the part meets all requirements, the process can run automatically without further intervention.
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