Sheet metal parts and products are ubiquitous in both industry and daily life, and are widely recognized as one of the fundamental processing categories.
There are four primary sheet metal processing techniques: punching (shearing), folding (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 tooling dies to apply force and compress or embed the riveted parts into the workpiece, ensuring that it remains secure and vertical. 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
Process selection and precautions of riveting
(1) The size of the riveting bottom 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 processes of die blanking and laser cutting.
Table 1 Two processes of die blanking and laser cutting
| Pre-process | Die blanking | Laser cutting |
| Bottom hole size | Good accuracy and consistency | The stability of the hole shape and size is slightly poor |
| Substrate change | The blanking tear band is not smooth | There are hardness changes on and around the hole wall |
| Other attention | The burr surface is convex and the smooth surface collapses | Lead, splash and other foreign 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 riveting bottom hole.
If the previous process involves bending, it is necessary to consider whether the riveting bottom hole is located on the bending line (upper).
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 form of upper and lower supports, and other conditions to confirm whether it can be carried out successfully.
Furthermore, it is generally recommended to arrange the riveting process after the surface treatment process (such as electroplating, chemical oxidation, spraying, etc.).
If riveting is carried out before surface treatment, it can often lead to issues listed in Table 2.
Table 2 possible problems caused by different surface treatments
| Process | May cause problems |
| Carbon steel electroplating | The zinc layer of stainless steel rivets is peeling, the thread is not smooth, the electroplating solution is stored, and the corrosion is slow under working conditions |
| Aluminum chemical oxidation | The hole diameter of the bottom hole becomes larger, the rivets become loose and the strength decreases |
| Surface spraying | Increase the amount of escaping coating, and it is easy to lead to poor threaded rivets |
(3) For certain specialized products, such as base materials with a thickness ≤ 1.5mm or products with high pressure riveting strength requirements, welding reinforcement may be necessary after pressure riveting.
In cases where welding reinforcement is required, it is recommended not to select galvanized parts for pressure riveting, as this can have an adverse impact on the welding reinforcement process.
Precautions for riveting operation
The general requirements for the operation of the riveting process 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 error).
- Select appropriate upper and lower molds.
- Select correct riveting parts.
- Reasonably use tooling and fixtures.
- Observe necessary safety precautions.
Additionally, in the actual production of our factory, we would like to share the following three operational guidelines.
(1) Operators typically judge the firmness of a rivet by observing whether there is a gap between the riveted parts and the substrate or whether there are steps at the riveting position after countersunk riveting. This 100% self-inspection operation is necessary. Additionally, the hardness of the material surface, from galvanized plates to stainless steel and low-carbon steel plates, decreases in turn. Thus, in actual processing, pressure parameters should be adjusted in advance according to the riveting materials. For riveting parts with a risk of falling off, technical requirements for welding and spot reinforcement should be communicated with the customer beforehand.
(2) Riveting operations must be completed in one go to eliminate the need for two rounds of riveting and to reduce the repair of fallen riveted parts, especially for parts with high material surface hardness. The flower teeth and base materials of riveted parts are damaged after repair. If original parts must be repaired, welding reinforcement must be carried out after riveting.
(3) For technical inspection after riveting, inspectors must have the basic ability to spot-check the breaking torque and, if possible, the breaking push-off force. The first article inspection and technical sampling inspection of the riveting process cannot be replaced by an 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 bending edges (lines), outer edges, or weld beads, as this can affect both the quality of the riveting and the appearance of the assembly. Please refer to Table 3 for common riveting interference problems.
Table 3 Common interference problems of riveting
| Type | Example | Proposal |
| Distance from the free edge |
 | L1 value reference manual |
| Distance from bend edge |
 | L1 ≥ bending radius and L1 ≥ riveting head radius of riveter |
| Close to the weld bead | Be sure to check for any interference between the riveting parts and the upper and lower dies. If there is interference, the dies may need to be repaired to prevent any air gaps. |
(2) When there are multiple types of riveting standard parts and similar parts on the same component, it is recommended to avoid operating them all on the same machine to prevent mixing and misuse of the riveting parts. Additionally, when there are many riveting parts of the same specification on a component, the riveting sequence should be standardized to prevent missed rivets.
(3) During the riveting process, if the operator needs to leave their post for any reason, such as for eating or shift handover, the worktable must be cleared to ensure that processed and unprocessed parts are not mixed.
(4) If there is a hole near the riveting position, it is important to confirm whether the hole is extruded or deformed after riveting. For pressure-riveted screws and nuts, a thread gauge should be used to detect the through end and stop end after pressure riveting.
Conclusion
The above content summarizes the experience gained from handling common issues and operations during the riveting process in sheet metal production and processing.
It is worth noting that some factories have partially achieved the automation of automatic feeding mechanisms and riveting. This automation solution is beneficial in avoiding human errors to a great extent. However, the degree of automation implemented varies due to factors such as cost, technology, product variety, type, and batch size.
Whether you opt for manual operation, semi-automatic or fully automatic production scheme, the information presented above can be useful in your production process.
