Process Introduction of Projection Welding Machine for High Strength Hot Formed Steel Plate Nut

1.Preamble：
Due to the ultra-high strength and high mechanical safety of high-strength hot-formed steel plates, it is increasingly used in the automotive industry, and the use parts are concentrated in the front/rear bumper frame, A-pillar/B-pillar, There are nuts and bolts on these key parts such as the central passage and the front and rear door anti-collision plates that need projection welding; the nut projection welding machine is the first choice for projection welding of body parts because of its short welding time, small heat-affected zone, and high efficiency. Resistance welding equipment is also used for the welding of high-strength hot-formed steel plates and nuts and bolts.

2. Case analysis:
Example 1: Suzhou Anjia is used for projection welding of A-pillar nuts of a certain car model. The plate is BTR165H hot-formed steel with a thickness of 1.8MM; the nuts are M10 projection welding flange nuts and three-section crescent bosses; welding requirements: torque 130N.M, push-off force 8KN, no damage to the thread, no obvious damage to the appearance;
2.1 Welding machine: The model is Anjia DR-30000J, which adopts mountain-shaped electrodes to press vertically;

2.2 Welding specification adjustment:
2.2.1 In the adjustment of conventional resistance welding process parameters, three basic elements: welding time, welding current, and welding pressure are indispensable, while there is no welding time adjustment item for capacitor energy storage welding machines, welding current It is also reflected by the charging voltage, so the adjustment of the energy storage welding machine specification is mainly to match the welding pressure and the charging voltage. In special cases, an additional tempering voltage will be added to refine the grain;
2．2．2Difficulties that need to be overcome when adjusting the projection welding process of high-strength thermoformed steel nuts in this case: 1. The setting of welding pressure. Lower, higher pressure will lead to premature crushing of the bumps, so it is best to use a saddle-shaped pressure curve for the welding pressure. In practical situations, the stepped second-stage pressure is more common, which can ensure that the bumps will not be crushed prematurely. 2. The charging voltage setting, too high charging voltage will generate excessive heat during welding, and the nut metal will be extruded and splashed, which will cause Two situations are caused, one is that the spatter leads to a reduction in the fusion joint area (overburning), and the nut push-off force decreases, and the other is that the thread plug gauge cannot pass through; the lower charging voltage will lead to insufficient welding depth, and the nut push-off force is not up to standard and Welding;
3．2．3 Process specification adjustment method, when adjusting two welding elements (charging voltage and welding pressure), it is necessary to adjust and match the other value based on one of them, and two adjustments cannot be made at the same time; experience should be taken into account here , there are similar parameters of nut projection welding that can be used as a reference, which can effectively reduce the number of adjustments, but the welding of high-strength thermoformed plates requires greater current and pressure, which can be used from the test data of the same specification on ordinary materials. The starting point is adjusted, and the best value is found through trial welding and laboratory verification; when it is necessary to pay attention, it should be increased by 3-5% on the basis of trial welding data during mass production to meet the lower limit of fluctuations caused by other reasons for the product ;
2．3 Welding parameter confirmation：

3．4Workpiece push-off force and destruction test：

3．Electrode Part Process Supplement：
3．1 Due to the huge welding pressure and very high peak current during projection welding of high-strength hot-forming steel plates, the requirements for electrode materials are very high during welding, which requires high softening temperature, high conductivity and high hardness. Dispersed copper (aluminum oxide copper) has these advantages (softening temperature up to 950°), and has become the most suitable electrode material for projection welding of high-strength hot-formed steel sheets;
3．2 Commonly used materials for locating pins are bakelite, ceramics, KCF, etc. In recent years, European and American car companies have used silicon nitride as locating pins for projection welding of high-strength thermoformed steel plates because of their longer service life (200,000 times) and insulation Good effect, high hardness and other characteristics make it a new favorite material for projection welding locating pins, but because of its high price, it is not widely used at present, but this is the direction of locating pins in the future.
3．3 During projection welding of high-strength hot-formed steel plates, due to its physical characteristics and the use of hard-standard welding, the probability of metal extrusion is relatively high. The method of blowing air from the lower electrode can effectively improve it, and blow air to the welding area with a larger air pressure during welding. , can rapidly oxidize and burn the extruded metal, greatly reduce the adhesion of the extruded metal, and ensure the qualified thread.
4．Epilogue
Through the test on the high-strength hot-formed steel plate projection weldment, under the condition of using Anjia capacitor energy storage welding machine and reasonable process, the technical requirements can be met after welding, and even far higher than the technical requirements. There is no doubt that the capacitor energy storage welding The machine is one of the ideal projection welding equipment for high-strength hot-formed steel plate projection welding, and it has brought a major breakthrough in welding technology to the welding industry! It brings spring to the industry’s high-strength hot-formed steel plate nut projection welding!