Sheet metal parts and products are ubiquitous in industry and everyday life and are widely recognized as one of the fundamental processing categories.
There are four main sheet metal processing techniques: punching (shearing), bending (rolling), welding and surface treatment.
In addition to these techniques, riveting technology is also an important method for connecting sheet metal parts.
Riveting involves using specialized equipment and dies to apply force and compress or embed the riveted parts into the workpiece, ensuring it remains secure and upright. This process is illustrated in Figure 1.
Fig.1 Riveted parts of communication equipment
Common riveting techniques include radial riveting and rotary riveting. In this section we will discuss some important precautions and key points for the production control of radial riveting, which is commonly used in our factory (see Fig. 2).
Fig. 2 Radial riveting equipment and riveting process
Selection of riveting processes and precautions
(1) The size of the bottom riveting hole should be designed in strict accordance with the manuals of general or special equipment, standard parts, and should comprehensively consider the material, thickness, model and strength requirements of the base material and riveting parts.
When machining the bottom hole, blanking or laser cutting is commonly used as a pre-processing method. Table 1 compares the two molding and laser cutting processes.
Table 1 Two laser molding and cutting processes
| Pre-process | Die blank | Laser cut |
| Bottom hole size | Good accuracy and consistency | The stability of hole shape and size is slightly poor |
| Substrate change | The cutting strip is not smooth | There are hardness changes in and around the hole wall |
| Another attention | The burr surface is convex and the smooth surface collapses | Lead, splash and other strange matters |
For parts with high quality requirements and large production batches, it is recommended to customize the die, consider the riveting direction, and prioritize the stamping process to create the bottom riveting hole.
If the previous process involves bending, it is necessary to consider whether the lower rivet hole is located on the (upper) bending line.
In this situation, a pre-processing step involves creating a small hole, followed by bending and stretching, and then creating the small hole to the designed size through drilling or reaming.
(2) When selecting the riveting process, it is essential to consider the throat depth of the actual equipment, the shape of the upper and lower supports and other conditions to confirm whether it can be carried out successfully.
In addition, it is generally recommended to arrange the riveting process after the surface treatment process (such as electroplating, chemical oxidation, spraying, etc.).
If riveting is performed before surface treatment, it can often lead to the problems listed in Table 2.
Table 2 possible problems caused by different surface treatments
| Process | Can cause problems |
| Carbon Steel Electroplating | The zinc layer of stainless steel rivets is peeling off, the thread is not smooth, the electroplating solution is stored, and corrosion is slow under working conditions |
| Chemical oxidation of aluminum | The diameter of the bottom hole increases, the rivets loosen and the strength decreases |
| Surface spraying | Increase the amount of coating that escapes, and it is easy to cause bad threaded rivets |
(3) For certain specialized products, such as base materials with a thickness of ≤ 1.5 mm or products with high-pressure riveting strength requirements, welding reinforcement may be required after pressure riveting.
In cases where welding reinforcement is required, it is recommended not to select galvanized parts for pressure riveting as this may have an adverse impact on the welding reinforcement process.
Precautions for riveting operation
The general requirements for the riveting process to work are:
- Select appropriate pressure parameters (refer to the riveting pressure listed in the equipment or standard parts manual and take care to ensure correct unit conversion without errors).
- Select appropriate upper and lower molds.
- Select the correct riveting parts.
- Use tools and accessories reasonably.
- Observe necessary safety precautions.
Furthermore, in our factory's actual production, we would like to share the following three operational guidelines.
(1) Operators typically evaluate the tightness of a rivet by observing whether there is a gap between the riveted parts and the substrate or whether there are steps in the riveting position after countersunk riveting. This 100% self-inspection operation is necessary. Furthermore, the surface hardness of the material, from galvanized plates to stainless steel plates and low carbon steel, decreases in turn. Therefore, in actual processing, the pressure parameters must be adjusted in advance according to the riveting materials. To rivet parts with a risk of falling, the technical requirements for welding and spot reinforcement must be communicated to the customer in advance.
(2) Riveting operations should be completed in one go to eliminate the need for two rounds of riveting and to reduce the repair of dropped riveted parts, especially for parts with high material surface hardness. Flower teeth and base materials of riveted parts are damaged after repair. If it is necessary to repair original parts, welding reinforcement must be carried out after riveting.
(3) For technical inspection after riveting, inspectors must have the basic ability to check the breaking torque and, if possible, the breaking impulse force. The first article inspection and technical sampling inspection of the riveting process cannot be replaced by the operator's self-inspection, so this work must be implemented.
Other precautions for the riveting process
(1) It is important to pay attention to whether the riveting position interferes with adjacent bend edges (lines), outer edges or weld beads, as this can affect both the quality of the riveting and the appearance of the assembly. See Table 3 for common riveting interference problems.
Table 3 Common Riveting Interference Problems
| Type | Example | Proposal |
| Freeboard Distance |
|
L1 Value Reference Manual |
| Distance from bend edge |
|
L1 ≥ radius of curvature and L1 ≥ radius of the riveter's riveting head |
| Near the weld bead | Be sure to check for any interference between the riveted parts and the upper and lower dies. If there is interference, the dies may need to be repaired to prevent air gaps. |
(2) When there are several types of riveting pattern parts and similar parts in the same component, it is recommended to avoid operating them all on the same machine to avoid mixing and misuse of the riveting parts. Furthermore, when there are many parts riveted to the same specification in a component, the riveting sequence must be standardized to avoid lost rivets.
(3) During the riveting process, if the operator needs to leave his post for any reason, such as eating or changing, the work table must be cleaned to ensure that the processed and unprocessed parts are not mixed.
(4) If there is a hole close to the riveting position, it is important to confirm whether the hole has been extruded or deformed after riveting. For pressure riveted bolts and nuts, a thread gauge should be used to detect the through end and the end end after pressure riveting.
Conclusion
The above content summarizes the experience gained in handling common problems and operations during the riveting process in sheet metal production and processing.
It is worth noting that some factories have partially achieved automation of automatic feeding and riveting mechanisms. This automation solution is beneficial to avoid human errors to a large extent. However, the degree of automation implemented varies due to factors such as cost, technology, product variety, type and batch size.
Whether you choose manual operation, semi-automatic or fully automatic production scheme, the information presented above can be useful in your production process.
