Application of fiber laser welding robot and its quality control

click：12372022-05-04 12:24:51　

The large number of fiber laser welding robots currently used in the automotive industry shows that the laser welding technology has matured. However, the laser welding technology is more complicated than the traditional welding technology, and the quality control link is different from the traditional welding quality control. Therefore, strengthening the quality control has important significance for the development of laser welding.

The most basic characteristics of lasers are: monochromaticity, directionality, and correlation. These unique properties coupled with the resulting high brightness and ultra-short pulses make it very suitable for welding. The application of laser welding technology in the manufacturing field from pulse to continuous, from low power to high power, from thin plates to thick parts, from simple single welds to complex shapes, has gradually become a mature modern processing technology.

Application of fiber laser welding robot technology in automotive industry

Laser welding is divided into pulse laser welding and continuous laser welding. In continuous welding, it can be divided into heat conduction welding and deep penetration welding. With the development of laser output power, especially the emergence of high-power lasers, laser deep penetration technology has been rapidly developed at home and abroad. The maximum welding aspect ratio has reached 12: 1, and the laser welding materials have also been changed from generally low. Carbon steel has developed to today's welding of galvanized sheet, aluminum sheet, titanium sheet, copper sheet and ceramic materials. The laser welding speed has also reached tens of meters per minute. Laser welding technology has become increasingly mature and is widely used in production lines. Such as roof welding, high-speed tailor welding of automobile floor and structural parts (including door body), and has achieved great economic and social benefits.

Advantages and disadvantages of automotive laser welding "laser" can concentrate a very large amount of energy at a small point of action. This has many advantages over traditional welding and fusion welding processes:

Processing accuracy has doubled. Laser welds can react in the high temperature zone due to heat. Due to the relatively narrow width of the laser weld, these smaller high-temperature regions also make the accompanying thermal deformation very small.

The power and size of the laser focus can be dynamically adjusted according to the processing requirements, and the processing process can be monitored in real time, realizing various application possibilities.

When using a solid-state laser, the laser can be transported flexibly without manipulation. In this way, the energy source and processing equipment can be separated from the space without difficulty.

The laser beam does not cause any wear and can work stably for a long time.

Accounted for relevant data statistics, in developed European and American industrial countries, 50% to 70% of auto parts are completed by laser processing. Among them, mainly laser welding and laser cutting, laser welding has become a standard process in the automotive industry. Laser welding of body panels can weld metal plates of different thicknesses and with different surface coatings, and then punch them. The panel structure thus made can achieve the most reasonable metal combination. Since it is rarely deformed, secondary processing is also saved. Laser welding has accelerated the process of replacing cast parts with stamped body parts. Using laser welding can reduce the overlap width and some strengthening components, and can also reduce the volume of the body structure itself. The weight of this body alone can be reduced by about 50kg. In addition, laser welding technology can ensure that the welding point connection reaches the joint level, effectively improving the rigidity and collision safety of the vehicle body, and effectively reducing the noise in the car.

It is required that the assembly accuracy of the weldment is high, and the position of the beam on the workpiece cannot be significantly shifted. This is due to the small spot size and narrow weld seam after laser focusing. If the workpiece assembly accuracy or beam positioning accuracy does not meet the requirements, welding defects can easily be caused. The cost of lasers and related systems is high, and the one-time investment is large.

Process technology for laser processing

To make laser welding work, reliable coordination between its various functional groups and the safe operation and proper maintenance of the equipment are essential. The following four technologies are the pillars of modern processing technology. Their reliable functional connections and their comprehensive grasp are necessary for the safe and reliable introduction of laser processing technology.

Types of quality defects in automotive laser welding

Due to the complexity of automotive laser welding process and many influencing factors, when the processing quality declines, it cannot be explained with a general reason. The beginning and end of a laser weld seam are generally considered to be the most critical part. The following are some typical defects of laser welding of car body-in-white:

Pores: The diameter of normal pores (larger than tiny pores) does not exceed 1.0mm.

Micropores / voids: When the diameter of pores is less than 0.2mm, it is a micropore; when the diameter of pores is greater than 1.0mm, it is called a void.

Fusion Weld: There is no solder in the weld, and the weld looks like a laser weld.

Poor solder connection: The electrode is not connected on the side of the workpiece. Where the welds are connected, the welds appear to "scatter."

One-sided connection of solder: The solder is connected to only one side.

Sausage phenomenon: The processed parts are not connected, and the solder is stretched and accumulated at the weld seam.

Irregular weld: Collapse or protrusion of the weld.

Scaly accumulation: The surface of the weld is not smooth and appears rough.

Weld Beginning / End Weld Issue: Welding will be underfilled or overfilled on the edges of the workpiece, or unmelted electrode residue will be found on the track.

Factors Influencing Automotive Laser Welding Quality

Possible reasons or sources of quality defects in body-in-white production:

1) Reasons for laser equipment:

Dirty protective glass lenses or aging arc lamps in the laser will reduce the power of the laser.

The focus position of the laser is incorrect. When the diameter of the laser focal point is too small, too much laser energy is concentrated on the welding rod, so that the solder becomes too hot, while the side of the workpiece is not heated enough, so that the solder does not easily flow to the Going in the gap. When the diameter of the laser focus is too large, the laser energy is not concentrated and the welding is not fast.

2) Reason for electrode:

Wrong electrode preheating temperature.

The alloy composition of the electrode material is changed (this may not meet the processing requirements).

The speed of the electrode guidance is not constant or does not match the speed of the laser equipment processing head.

3) Reasons for other auxiliary equipment:

Leakage of gas molecules due to solidification of the melt.

Fluctuation due to incorrect feed speed given by the program or robot speed.

4) Clearance size:

The gap size between the welded parts exceeds the requirements of the laser equipment.

Quality Control of Automotive Laser Welding

1) Equipment maintenance:

Among the quality defects and influencing factors of automobile laser welding, it is mentioned that most of the quality defects are caused by equipment failures, so daily equipment maintenance and repair are particularly important. The following summarizes several requirements for laser equipment maintenance:

Protect the glass lens every day and replace the damaged lens in time.

Every day, we need to clean the welding spatter residue of the fixture and tighten the fixing bolts of the fixture.

Check the arc lamp in the laser every week and replace the aging arc lamp in time.

Some auxiliary equipment such as robots, wire feeding mechanisms, etc. require some daily maintenance.

2) Dimensional accuracy requirements for welding workpieces:

Laser welding also requires very high assembly accuracy. For example, the workpiece assembly accuracy or beam positioning accuracy cannot meet the requirements, which can easily cause welding defects. Therefore, good and accurate clamping technology is the guarantee of laser welding. The joint gap between the welded parts in ordinary welding is required to be about 2mm, and the ideal situation for laser welding is that the smaller the gap, the better. Usually, the gap between the parts to be welded is controlled by 0.2mm in the body-in-white production.

3) Quality control of body size:

Based on on-site body-in-white laser welding quality control experience, it is necessary to set up a size group to monitor key dimensions that affect laser welding quality. The size group consists of the measurement part, production part, quality assurance part, and model part. Group members hold regular size meetings to discuss and resolve any dimensional deviations. The measurement part needs to measure the key dimensions every day and provide corresponding reports. The production part needs timely feedback information, the quality assurance part judges the quality problems generated, and cooperates with the same board part to develop a solution.