Technology and equipment for spot welding of automotive high strength steels.

Technology and equipment for spot welding
of automotive high strength steels.

Nowadays there are two main subjects which determine development and production for all automotive industry. With increasing fuel cost, there is a strong demand in the automotive industry for decreasing the weight of a vehicle to improve its efficiency and reduce CO2 emission. But when reducing vehicle weight, the structural performance needs to be maintained to achieve modern safety requirements. Transformation-induced plasticity (TRIP) steels belong to the class of high strength steels (HSS) that have an ability to absorb more energy during a crash due to the delayed transformation of retained austenite (RA) to martensite upon deformation. But there are some problems with spot welding of those types of steel:

1) Formation of brittle martensite structures during the welding process.

2) Low welding lobe.

3) Defects inside a weld spot and a heat affected zone.

During the research some experiments were made and estabilished that it is necessary to change the welding technology compared to Mild steel:

1) Increase the electrode force by 20% or more depending on yield strength.

2) Increase weld time when appropriate.

If these changes are not sufficient, then try these additional changes:

1) Try a multi-pulse welding schedule (several pulses or post heating).

2) Larger tip diameter and/or change the type of electrode.

3) Increase minimum weld size.

To achieve the desired quality of weld joints some modifications of welding equipment should be made:

1) Increase welding force by upgrading pneumatic operating cylinder or replacing it with hydro cylinder.

2) Ann an inverter power supply with feedback circuit and a support of multi-pulse schedule to control heat dissipation and cooling speed.

There also was made an experiment to establish the influence of surface contamination with grease, which may burn during the welding process and increase carbon content inside the weld.

Дата добавления: 2015-11-04