Resistance projection welding
Resistance projection welding (short form: projection welding) is a variant of resistance pressure welding (order number 23 according to EN ISO 4063). A welded connection is created by means of an electric current and a force that is supplied to the workpieces by mostly flat, large-area electrodes .
Process description
The current concentration at the welding point is achieved by embossed bosses in the sheets to be joined or by the shape of the parts to be joined. Depending on the projection and electrode arrangement, there are different variants of projection welding. During welding, the projections are largely deformed back by the electrode force and heating as a result of the current flow. This reshaping is usually not complete, the remaining surface deformation on the workpiece part with the embossed boss being retained. The protrusion, which is formed back during welding, forms a connection in the form of a lens.
The heat generation depends on the resistance ratios at the joint and the square of the current flowing. The contact resistance and the material resistance of the joining partners involved contribute significantly to the formation of the weld nugget. The contact resistance between the parts to be joined is influenced by the projection geometry, the contact pressure and the surface condition of the workpieces. The electrodes are usually cooled during welding. Clean surfaces of the work pieces and working surfaces of the electrodes are important for the consistent quality.
Welding parameters
The lens is surrounded by a heat affected zone. The structure of the material in the heat affected zone is changed by the action of heat. The welding parameters influence the size of the welded joint and the structure of the heat-affected zone and thus the quality of the joint.
The setting parameters are the welding current, the welding current time and the electrode force. Since the contact resistance between the parts to be joined is influenced by the projection geometry, the projection geometry must also be evaluated as a setting parameter. The so-called attachment and repositioning, the electrical operating behavior of the welding machine and the type and form of current are important for the formation of the connection .
Electrode force
The electrode force influences the contact resistance. The force required depends on the geometric shape of the boss, the material thickness and the material strength. Excessive electrode force and a hard placement of the electrodes can cause impermissible deformation of the protrusions even before the start of the welding process.
Welding current
The level of the welding current determines the level of Joule heat generated . The amperage goes into the square of the heat generation. Therefore fluctuations in the current are clearly noticeable. The current intensity is to be selected depending on the formation of the projection, the material thickness and composition, the surface and the number of projections to be welded at the same time.
Welding current time
The welding current time is very short compared to that of resistance spot welding.
The following table shows examples of welding parameters (projection geometry group A according to EN 28167).
| Sheet thickness (in mm) |
Hump diameter (in mm) |
Electrode force (in kN) |
Welding current (in kA) |
Welding current time (in ms) |
|---|---|---|---|---|
| ≤ 0.5 | 1.6 | 0.4 | 4.0 | 60 |
| 0.5 <t ≤ 0.63 | 2.0 | 0.6 | 4.2 | 80 |
| 0.63 <t ≤ 1.0 | 2.5 | 0.8 | 4.5 | 80 |
| 1.0 <t ≤ 1.6 | 3.2 | 1.3 | 6.3 | 100 |
| 1.6 <t ≤ 2.5 | 4.0 | 2.0 | 8.0 | 140 |
| 2.5 <t ≤ 3.0 | 5.0 | 3.6 | 12.0 | 280 |
Welding equipment
The known welding devices for resistance welding are used for projection welding . Differences result from the electrode shapes and the fastenings for the electrode systems.
credentials
- ↑ DIN 1910-100: 2008-02 Welding and related processes - Terms - Part 100: Metal welding processes with additions to DIN EN 14610: 2005.
- ↑ a b DIN EN ISO 4063: 2011-03 Welding and related processes - List of processes and serial numbers.
- ↑ EN ISO 16432: 2007 Resistance welding - Process for projection welding of low-alloy steels with or without a metallic coating.
- ↑ DVS - German Association for Welding and Allied Processes : Projection Welding of Steel DVS Merkblatt 2905, 2001.
- ↑ a b EN 28167: 1992: "Bump for resistance welding"