Stainless steel is a new type of environmentally friendly material. With its characteristics of corrosion resistance and formability, it has been widely used in the field of auto parts.
In the automotive industry, due to the stainless steel raw material (steel plate), the car bodies must all be connected by welding. Therefore, laser welding plays a very important role in the application of stainless steel in the automotive industry.
Due to the influence of many factors, stainless plates have deformation problems and are difficult to control, which will greatly affect the application of stainless plates in the automotive industry. So, what is the countermeasure?
Overview of Laser Welding Stainless Plates
Laser welding mainly refers to a welding method that uses laser energy as a heat source to melt and connect workpieces. In the process of laser welding, the laser irradiates the surface of the material to be welded and affects it. A part of it is reflected, and the rest is absorbed into the material to complete the welding target.
In short, the process of laser welding is to use a high-power laser beam focused by the optical system to irradiate the surface of the material to be welded, and then make full use of the material to absorb light energy for heating and other treatments. Finally, the welding joint is formed by cooling. A kind of melting welding process. Under normal circumstances, laser welding is mainly divided into thermal conductivity welding and deep penetration welding.
The hazards of welding deformation and the main factors affecting welding deformation
The main factors affecting welding deformation are welding current, pulse width, and frequency. As the welding current increases, the width of the weld seam also increases, and phenomena such as splashes gradually appear, resulting in oxidation and deformation of the weld seam surface, accompanied by roughness; the increase in pulse width increases the strength of the welded joint. When the pulse width reaches a certain level the heat conduction energy consumption on the surface of the material also increases.
The evaporation causes the liquid to splash out of the molten pool, resulting in a smaller cross-sectional area of the solder joint, which affects the strength of the joint; the influence of the welding frequency on the welding deformation of the stainless steel plate is closely related to the thickness of the steel plate.
For example, for a 0.5mm stainless steel plate, when the frequency reaches 2Hz, the overlap rate of the weld is higher; when the frequency reaches 5Hz, the weld is burned seriously, the heat-affected zone is wider, and deformation occurs. It can be seen that it is imperative to strengthen the effective control of welding deformation.
Effective Countermeasures to Avoid Laser Welding Distortion
Controlling deformation is a systematic project. The best strategy is to optimize every link of welding.
Countermeasure 1: Use Rigid Fixation and Reasonable Fixtures
This is the most direct and effective method. Use strong external constraints to counteract the internal stress generated by welding.
Use special welding fixtures: Design special fixtures with uniform clamping force and firm clamping according to the shape of the workpiece. The fixture should have sufficient rigidity and will not deform under the clamping force.
Increase clamping points: For large-sized thin plates, multiple clamping points should be evenly distributed along both sides of the weld to prevent the plate from warping between two points.
Copper pressing plate/pad: Copper has excellent thermal conductivity. Using copper pressing blocks or pads on the fixture can help quickly take away excess heat near the weld, reduce the heat-affected zone, and thus reduce deformation.
Countermeasure 2: Optimize Welding Process Parameters
Reasonable process parameters aim to use ” as little heat input as possible to complete high-quality penetration”.
Increase welding speed: Increase welding speed as much as possible while ensuring full penetration. The faster the speed, the less heat input per unit length, and the smaller the deformation.
Accurately control laser power: Avoid using power far exceeding the required power. Excessive power will unnecessarily increase the heat-affected zone.
Use pulse waveforms: For heat-sensitive thin plates, use pulsed lasers with high peak power and short pulse width to melt the metal instantly while reducing the conduction of heat to the parent material.
Adjust defocus: Appropriate positive defocus can obtain a larger spot and lower power density, which helps to form a wider and smoother weld, and sometimes helps to improve stress distribution.
Countermeasure 3: Optimize Weld Design and Welding Sequence
Through clever arrangements, the stresses generated can offset each other.
Reduce weld cross-sectional area: Under the premise of meeting strength requirements, try to reduce the size of the weld (such as groove angle). The smaller the weld, the less metal is filled and the smaller the shrinkage.
Use symmetrical welding: For symmetrical structures, use double-sided symmetrical welding so that the deformation stresses generated on both sides can offset each other.
Segmented step-back welding method: Divide a long weld into several sections, and use a jump-type or welding method from the middle to both ends to make the heat and stress distribution more uniform and avoid stress accumulation in a single direction.
Countermeasure 4: Ensure Excellent Assembly Gap
Excessive gap is a common cause of increased deformation.
Precise assembly: Ensure that the assembly gap before welding is uniform and as small as possible. An excessive gap will force you to use more filler wire or a slower speed to fill, which means greater heat input.
Spot welding fixation: Before formal welding, firm spot welding positioning along the weld can effectively prevent gap changes caused by heat during welding.
Countermeasure 5: Choose High-Quality Raw Materials
An often overlooked but crucial factor is the material itself.
Plate with good flatness: If the stainless steel plate used has internal stress or poor flatness, the heat of welding will become the “last straw that breaks the camel’s back”, releasing and aggravating these original deformations.
Uniform thickness: Plates with uniform thickness can ensure the consistency of heat absorption and conduction during welding, and it is easier to obtain stable welding results.
In Conclusion
As an effective welding technology, laser welding technology plays an active role in improving welding quality. However, due to the influence of factors such as laser current, laser welding of stainless plates has problems such as deformation. In this regard, welders can take the orthogonal experiment method to obtain the best process parameters of different thickness steel plates, combine the parameters to perform welding work, and continuously improve the welding quality, to minimize the occurrence of steel plate deformation.