Cold rolling thread and turning thread large-diameter superposition processing technology
In order to ensure the accuracy and stability of thread size during the cold rolling process, higher precision is required for the diameter of the raw material. Therefore, most of the blanks that need to be cold-rolled must undergo precise turning or grinding. Otherwise, the rolled thread will have poor dimensional accuracy, unstable quality, and the cold rolling process becomes difficult to control. In some cases, the rollers may even be damaged, reducing the lifespan of the tools and machine equipment. The use of cold rolling combined with a large-diameter superposition machining technique can effectively address these challenges.
Figure 1 shows hollow thin-walled parts that are 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 a traditional support guide. A wide-blade plane forming turning tool is installed beneath the workpiece, allowing it to remove excess metal that exceeds standard dimensions during the rolling process. This ensures that the thread crest is formed accurately while maintaining the correct diameter. This method is known as "large-diameter superposition machining."
Compared to conventional methods, this process allows for greater flexibility in controlling the thread diameter by adjusting the position of the turning tool during rolling. As a result, the dimensional requirements for the blank before rolling are less strict, reducing the need for finishing processes and lowering manufacturing costs. For example, in the case of a hollow thin-walled part shown in Figure 1, the required blank diameter was originally d0 = 25.95–0.06 mm, but after applying the superposition technique, it became d0’ = 26.23–0.28 mm.
This process offers several advantages: improved accuracy and stability of the thread diameter, a trapezoidal thread crest close to the theoretical profile, reduced precision requirements for the blank, lower energy consumption, and increased processing efficiency. It also expands the adjustment range of ordinary rolling machines, enabling one-machine operation and improving productivity.
**2. Process Equipment**
Figure 2 illustrates the schematic of a large-diameter superposition machining device 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 installed on a standard thread rolling machine. Its structure is simple and easy to modify, requiring minimal effort. The original rolling mechanism remains intact, consisting of a fixed roller and an active roller. The fixed roller rotates, while the active roller moves along the axis to feed 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. The support frame is adjusted via the square head eccentric shaft, allowing for precise center height adjustments.
The turning device, located at the base of the original support guide plate, consists of a tool holder, turning tool, and adjustment screws. By adjusting the position of the tool, the distance from the cutting edge to the workpiece centerline can be controlled, thus regulating the thread diameter. This enables accurate and consistent results.
**3. Operational Points**
Before starting the process, select the appropriate rolling wheel, mandrel, turning tool, and measuring instruments based on the workpiece specifications. Install them correctly according to the machine's adjustment requirements. Choose suitable rolling parameters such as feed speed, spindle speed, and cycle time.
Once everything is set, mount the workpiece on the mandrel and start the machine. Check for normal operation and enter the automatic cycle. During the rolling process, the active roller feeds the workpiece, rolls the thread, and simultaneously performs the large-diameter turning. After reaching the preset time, the roller returns to its original position.
At this point, the operator can remove the part, inspect the thread size and quality, and make necessary adjustments if any issues are found. Once the dimensions are stable and meet the requirements, the machine can continue the automatic cycle. This method ensures consistent, high-quality results with improved efficiency and reduced tool wear.
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