Welding by point
or welding by bossing.

Ce process allows continuous or discontinuous assemblages to be made by overlay, for welding by wheel in that the location of current and effort on the welding area is not obtained by the electrodes, due to the geometry of the welding parts themselves.

The figure below gives three typical examples of bump assembly or bringing back:

  • Welding two sheets flat, one of the sheets has previously received by stamping a number of bumps that will be used to locate current and effort
  • Welding a bridle on a plate, all over the periphery; welding is continuous and waterproof and is carried out by merging the sling provided for this purpose
  • Continuous welding by wheel on surfaces that are always degreased suitable for lengths, such as forging coils.
  • Welding by approximation with tongs made of bits that pinch sheets that allow welding

In all cases, the current is brought to the two welding parts using copper blocks that are also used to apply the welding effort. These copper blocks have shapes adapted to those of the parts, widely sized, they are little stressed and little affected by wear.

The 2-piece welding operation has a global character: a single machine cycle is sufficient to perform all the welds planned for the assembly of the 2 parts positioned and maintained by the copper blocks which thus become real welding tools.https://deltam

Cases of screw welding, nuts, gougeons, by bossing

It is possible to weld screws of nuts on a sheet metal, for this it requires a fairly powerful machine, and specific nuts and screws that have on the underside in principle 3 bosses at 180o

Welding principle

  • The welding intensity rated I in kA: This is the intensity of the welding current given in kiloampers (kA), it is regulated by the sequence, which must include a tore of measurement, according to which it more or less opens the thyristors by the trigger current. Too weak the weld is not good, too loud the point is burned. Be careful because I act squared (see Joule’s formula).
  • The maintenance time (or forging on some machines): This is the time given to cool the welding point, no current passes but the machine this keeping closed under pressure.

It is said of Forge when the machine allows to get an effort between the upper electrodes during this time. Too short to the limit the parts can separate, too long it penalizes productivity.
Order of magnitude of parameters (welding of two 1 mm steel plates with electrodes 6 mm in diameter): F – 270 daN, I – 10 kA, welding time – 10 – (periods), berthing time according to the machine, maintenance time – 10.

Note: To improve the quality of a weld, one must first increase I according to the capacity of the machine, if not increase the welding time with an impact on productivity, or decrease (inversely proportional) the welding effort to the limit possible of the control of the projections.

Welding by bits

The bits are 2 blocks parts, rounded, chanfreinated as the case to allow the assembly of wire in diameter from 0.5 to 10mm.

The materials to be expected
for electrode and bits

The material par excellence is DELTA 600 but the thickness, coating and the search for less wear is guided by harder materials like DELTA 700, DELTA 701, DELTA 800 or Tungsten/Copper alloys with ratios of 75/25-80/20 etc.
The contact parts can also be chosen harder to reduce wear and increase productivity and in this case they are directed towards two-material electrodes.
In any case, there is no material input therefore the electrode part crossing and mechanical approximation of the parts to be welded allows a mooring of the metals in presence, for a perfect weld and avoiding of course the bonding.

Choose a welding process:
The cost of investment

The cost of the investment will be an important point to consider. You have to have a market large enough to deal with investments such as energy-intensive equipment.
With this technology, you won’t have to choose between quality level or performance: these two criteria are well met. High-density processes are used only in industries where the level of quality or production must be at its highest.
Example: in the nuclear industry, fuel capsules are welded with this process.

The quality of the weld

The automation of welding is interesting because thanks to the programming of welding equipment we can not only increase the efficiency, but also control the quality of the weld according to the desired result.

This does not detract from the need for the experienced welder because it is he who must validate the result of the welding after developing the welding process. Unlike manual welding with a wand, welding results are perfectly controllable and quickly profitable.

The milkman

The slag is a kind of “crust” that can form with certain welding processes that use little or no protective gas. This slag will have to be removed after the weld has cooled. Of course, this is an additional operation that needs to be taken into account, but in terms of quality, this milkman has an advantage in terms of the quality of the weld.

In fact: the slag allows the weld to cool slowly, unlike some soda welding processes. As a result, less deformations or stresses are obtained inside the welded metal. These constraints are often difficult to quantify.
The following welding processes create a slag: submerged bow welding and electrode welding (stick).

In conclusion

Point welding is fast


oint welding gives extremely fast results. Due to extreme heat, it adheres 2 pieces of metal quickly, evenly and efficiently. Since this process is relatively fast, it does not tend to distort either of the 2 pieces of metal (for example in car body panels, where this process is often used).

Point welding is cheaper

Welding saves production costs. It is much more cost effective welding point. It lends itself well to the production of the assembly line. Robotic use can be incorporated during the point welding process.

Welding is more energy efficientEcri

Write by Philippe Herrmann, managing director of DELTA METAL based in Munster in Alsace