Mechanical joining – also called joining by forming – has become interesting for the automotive industry due to the request to reduce fuel consumption and thereby emissions.
In order to reduce weight on the car body, the usage of lightweight materials in the body-in-white application has increased. This includes aluminium, high-strength steel alloys, polymers, and composites. Here the different type of mechanical joining becomes important.
All mechanical joining methods are cold forming techniques. One general benefit for all mechanical joining methods is the mobility of the material after joining. At the same time mechanical joining offers an impressive strength.
Mechanical joining is divided up into two main groups:
- Without fastener
- With fastener (riveting)
Advantages of mechanical joining
- No thermal structural transformation of work pieces
- Numerous choice of material of rivets, sizes, forms etc.
- High strength capacity
- Mobility of material after joining
- Easy to control quality
- Good environmental behavior – no emission or polution
Disadvantages of mechanical joining
- Can be difficult or impossible to repair joints
- Many rivets are patented and may mean higher cost
Riveting is the general term for joining with rivets / fasteners. You can find many types of riveting where we have described some of them below.
The principle of riveting is to join two or more plates mechanically by a joint. The joint is placed in a hole in the plates and forced mechanically to deform and thereby lock the plates.
Self-piercing riveting (SPR)
The principle is that it fastens together two or more sheets of material mechanically with a self-piercing rivet. The rivet pierces the top sheet and the joining is achieved when the rivets pierces the bottom sheet partially, deforms the material into the die, and thereby forms a mechanical interlock. Often a layer of adhesive is used to keep the sheets in place while riveting.
Advantages of the self-piercing riveting method
- Working with un-weldable material or material that is very difficult to weld
- Working with dissimilar materials
- When protective coatings need as little damage as possible
Disadvantages of the self-piercing method
- The result doesn’t give a perfectly flush surface
- Attention in design needs to be on the possibility of corrosion due to the possible accumulation of water or moisture in the gaps between rivet and sheets
The challenges working with Self-piercing riveting (SPR) method
- To find the best suitable rivet in form, size, and material
- To obtain the correct level of penetration of the rivet
- To obtain the perfect level of penetration of the rivet
- To predict the static and dynamic behavior
The blind riveting method is very often used in aircraft industry, shipping, but also in the electronics industry. Some call the rivets “blind rivets” others “hollow rivets”.
Advantages of Blind Riveting
- Very fast to install
- Can be installed from single side
Disadvatanges of Blind Riveting
- The tail shows on the back
The joint is created by the deformation of the die-side and thereby locking the rivet by filling the ring grove.
The joint is produced at the clinched point directly out of the sheet material components – meaning without fastener. The clinching method can be used for lightweight sheet materials such as low-density metals, and nonmetals. Conventional clinching can be used for joining metal–metal combinations. Some metal–non-metal pairs can only be connected by hybrid clinching or modified clinching.
When talking about clinching you divide them up into “round” and “square” clinching.
Clinch riveting is a combination of the clinch process and the riveting.