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Sheet Metal Riveting: Process Selection And Precautions

As one of the basic processing categories, sheet metal parts and products can be seen everywhere in industry and daily life, and have been well known.

The four processes of sheet metal processing include punching (shearing), folding (rolling), welding and surface treatment.

As a kind of connection method, riveting technology also plays an important role in the processing of sheet metal parts.

Riveting is to use special equipment and special tooling die to exert force on the press riveted parts to completely compress or embed them into the workpiece, so as to ensure its firmness and verticality, as shown in Fig. 1.

Riveted parts of Westinghouse communication equipment

Fig. 1 Riveted parts of communication equipment

Common riveting includes radial riveting and rotary riveting. Here, some precautions and key points of production control are discussed for the radial riveting (i.e. ordinary riveting of common parts) process commonly used in our factory (Fig. 2).

Radial riveting equipment and riveting process

Fig. 2 Radial riveting equipment and riveting process

Process selection and precautions of riveting

(1) The size of the riveting bottom hole shall be designed in strict accordance with the manual of general or special equipment and standard parts, and comprehensively considering the material, thickness, model and strength requirements of base material, riveting parts, etc.

When actually machining the bottom hole, the pre-process of blanking or laser cutting is usually used. Table 1 compares the two processes of die blanking and laser cutting.

Table 1 Two processes of die blanking and laser cutting

Pre-processDie blankingLaser cutting
Bottom hole sizeGood accuracy and consistencyThe stability of hole shape and size is slightly poor
Substrate changeThe blanking tear band is not smoothThere are hardness changes on and around the hole wall
Other attentionThe burr surface is convex and the smooth surface collapsesLead, splash and other foreign matters

For parts with high-quality requirements and large batch, it is recommended to customize the die, consider the riveting direction, and give priority to the stamping process to make the riveting bottom hole.

If the previous process involves bending, it is necessary to consider whether the riveting bottom hole is in the bending line (upper). In this case, it is necessary to pre-process the small hole, bend and stretch, and then process the small hole to the design size through drilling or reaming.

(2) When selecting the riveting process, it must refer to the throat depth of the actual equipment, the form of upper and lower supports and other conditions to confirm whether it can be operated.

In addition, generally, the riveting process shall be arranged after the surface treatment process (such as electroplating, chemical oxidation, spraying, etc.). If you riveting before surface treatment, you will usually encounter the problems in Table 2.

Table 2 possible problems caused by different surface treatments

ProcessMay cause problems
Carbon steel electroplatingThe 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 oxidationThe hole diameter of the bottom hole becomes larger, the rivets become loose and the strength decreases
Surface sprayingIncrease the amount of escaping coating, and it is easy to lead to poor threaded rivets

(3) For some special products, such as base material thickness ≤ 1.5mm or high requirements for pressure riveting strength, welding reinforcement needs to be added after pressure riveting.

If the welding reinforcement process is required, it is recommended not to select galvanized parts for pressure riveting parts, so as to reduce the adverse impact on welding reinforcement.

Precautions for riveting operation

The general requirements for the operation of the riveting process are:

  • Select appropriate pressure parameters (refer to the riveting pressure in the equipment or standard parts manual, and pay attention to the unit conversion without error);
  • Select appropriate upper and lower molds;
  • Select correct riveting parts;
  • Reasonably use tooling and fixtures;
  • And safety precautions.

In addition, in the actual production of the factory, I would like to share the following three operation guidelines.

(1) Operators usually judge whether the riveting is firm by observing whether there is a gap between the riveting parts and the part substrate, or whether there are steps at the riveting position after the countersunk riveting parts. This 100% self-inspection operation is necessary.

In addition, the hardness of the material surface, galvanized plate, stainless steel plate and low-carbon steel plate are reduced in turn.

Therefore, in the actual processing, the pressure parameters can be adjusted in advance according to the riveting materials.

For the riveting parts with the risk of falling off, the technical requirements for welding and spot reinforcement shall be communicated with the customer in advance.

(2) The riveting operation must be completed at one time to eliminate two times of riveting and reduce the repair of falling riveted parts, especially the parts with high material surface hardness.

The flower teeth and base materials of riveted parts are damaged after repair. If the original parts have to be repaired, welding reinforcement must be carried out after riveting.

(3) For the technical inspection after riveting, it shall have the basic detection ability of spot-checking the breaking torque, and if possible, spot-checking the breaking push-off force at the same time.

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) Pay attention to whether the riveting position interferes with the adjacent bending edge (line), outer edge, or weld bead, thus affecting the riveting quality or assembly appearance. See Table 3 for common riveting interference problems.

Table 3 Common interference problems of riveting

TypeExampleProposal
Distance from the free edge

Common interference problems of riveting

L1 value reference manual
Distance from bend edge

Common interference problems of riveting

L1 ≥ bending radius and L1 ≥ riveting head radius of riveter
Close to the weld beadPay attention to whether the riveting parts and the upper and lower dies interfere. If there is die interference, it can be realized by repairing the die to avoid air.

(2) When there are many kinds of riveting standard parts and similar parts on the same part, try not to arrange them all to operate on the same machine to avoid mixing and misuse of riveting parts;

At the same time, when there are a large number of riveting parts of the same specification on the parts, the riveting sequence shall be standardized in the operation to prevent missing riveting.

(3) In the process of riveting, if the operator leaves his post, such as eating and shift handover, the worktable must be “empty” to ensure that the processed parts and unprocessed parts are not mixed.

(4) If there is a hole near the riveting position, confirm whether the hole is extruded and deformed after riveting;

For pressure riveted screws and nuts, use thread gauge to detect the through the end and stop end after pressure riveting.

Conclusion

The above is the experience accumulated in the actual common problems and operation of the riveting process in sheet metal production and processing.

In fact, in some factories, the automation of automatic feeding mechanisms and riveting has been partially realized.

Through the automation solution, human errors can be avoided to a great extent. However, the application degree of automation is different.

Factors such as cost, technology and product variety, type and batch greatly affect the realization of the automation scheme of the riveting process.

Whether it is manual operation, semi-automatic or fully automatic production scheme, I hope some of the contents summarized above can play a role in your production.

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