Five major joining processes for sheet metal

1. Flanging and riveting

Flange riveting is a classic mechanical fastening process. The process is to first punch out the "sprouting" (i.e., the ring-cylindrical protrusion formed by stretching outward) from one workpiece, and pre-match it with the via hole or salad hole (tapered counterbore) of the other workpiece, and then use a round punch to flange the peripheral wall of the "sprouting" outward so that it is pressed tightly against the board surface of the other workpiece, thereby achieving a non-detachable connection between the two workpieces.

The advantages of this process are high connection strength and high efficiency, and the sprouting and counterboring holes themselves have positioning functions and are easy to assemble. The core elements are to control the height, outer diameter and wall thickness of the buds, and to ensure that the flange is fully opened to avoid loosening of the riveting due to insufficient flanging or breakage.

This process is widely used, for example, it can often be seen in the production of car seat brackets, wiper arms and other components.

2. Tox riveting (no rivet connection)

Tox riveting, a rivet-free cold forming technology, also known as rivet-less connection, is an innovative cold connection technology. It doesn't require any additional fasteners. It only uses a special convex-concave mold to force the connected plates to produce plastic flow at the connection point and inlay each other in one stamping process, forming a connection point with neither edges nor burrs.

Its biggest advantage is that there is no thermal deformation during the cold connection process, and it can completely protect the coating or paint layer on the surface of the workpiece without damaging its corrosion resistance. At the same time, it has the advantages of wide riveting range, high dynamic fatigue strength (higher than resistance spot welding) and low operating cost. 

However, its static strength is usually lower than that of self-piercing riveting (SPR) and other processes, so it is currently mainly used in non-load-bearing parts such as car doors and hoods.

4. Resistance spot welding

Resistance spot welding is a type of fusion welding and is a traditional process with extremely high strength in sheet metal connections. The principle is to use the positive and negative electrodes of the welding device to short-circuit the workpiece to be welded, and instantly generate high current, which melts the metal at the contact point to form a nugget, and the connection is realized after cooling.

It has many advantages such as good connection performance, high structural rigidity, good integrity and sealing (easy to ensure air tightness and water tightness), and easy automation. In automobile body-in-white manufacturing, the spot welding automation rate is extremely high, and the single-station welding speed can reach 0.8 seconds/point.

However, due to the high temperature generated during welding, it may cause damage to plates with decorative surfaces (such as elevator car door panels), and there are thermal deformation problems, so its application in some specific fields is limited.

5. Screw connection

Screw connections are the most common and flexible detachable connection method. It mainly generates pre-tightening force through the screwing of threads to compress the connected parts. Common forms include self-tapping screws directly driven into the plate, tapping first and then tightening the screws, or used in conjunction with rivet studs/nuts, etc.

Its biggest advantage is that it can be disassembled and assembled repeatedly for easy maintenance and adjustment. In fields such as electronics, the assembly time of a single piece using cross-recessed pan head screws can be as short as 0.5 seconds, which is very efficient.