3 Advantages of Using Pulsed Laser Welding to Repair Molds

3 Advantages of Using Pulsed Laser Welding to Repair Molds

Pulsed laser welding technology reduces the overall repair time of the mold while maintaining high metal hardness compared to tungsten extremely inert gas protection (TIG) welding.

Tungsten extremely inert gas protection (TIG) welding is generally done before manual finishing or CNC processing is completed, and is a traditional method for dealing with wear or damage to mold surfaces. However, pulsed laser welding technology, which has been widely used in the German industry for decades, is gradually being used as a mold repair and other welding applications.

The welding machine emits a laser beam at a pulse of 5 to 10 ms, melts the master material of the work piece placed on the welder and fills the solder wire, and then re-cures the melting pool before the next pulse is emitted. This process has high peak power compared to continuous TIG and other welding operations, but transmits very little heat to the original material. In fact, most work pieces cool down as soon as the welding process is completed.

Mr. Blair Learn is President of Alpha Laser-US, North American Distributor of Alpha Laser, Germany. The company mainly produces aluminium-doped aluminum garnets, as well as fiber laser welding, cladding and hardening equipment. Mr. Blair Learn says that while pulsed laser welding is currently not as fast as TIG welding, it has three main advantages:

1. Pulse laser welding shortens the overall service time.

A slow heating process is required before welding large mold components with TIG. After welding, the cooling process is also time-consuming to prevent the master material from cracking. However, the heating and cooling processes add up to several hours, resulting in delays in manual bending or CNC processing during repair. When using pulsed laser welding equipment, the work parts do not need to be controlled for heating and cooling because the heat transfer is reduced. In addition, in the welding process, there is no need to remove the mold, there is no need to cut off the power of the press, this situation often occurs in the process of large mold processing. The reason is that the pulsed laser welding machine is different from TIG welding and does not require ground wire to be connected to the mold. Laser welding processes also allow precise welding of tiny details and areas without accidentally touching adjacent features or surfaces. Laser welding uses fine wires with a diameter of 0.003inch, which shortens subsequent processing times.

2. Pulse laser welding minimizes the effect on the hardness of the work piece.

TIG welding produces a deeper thermal impact zone (HAZ) than pulsed laser welding. The thermal impact zone is the part between the molten metal and the unaffected wood below it. This part undergoes adverse changes during smelting, resulting in the growth of the grain structure and the softening of the metal. The depth of the thermal impact zone with TIG welding can reach 0.15inch, while the standard range of pulse laser welding is 0.008 to 0.012inch. The larger the thermal impact zone of TIG welding, the greater the reduction in metal hardness in that area. With the TIG welding process, the material hardness value in the thermal impact zone decreased by 15 to 22 HRC points, while the pulse laser welding was only 2 to 4 points. If this damage occurs on a molded component, it can result in a shorter service life. As a result, modules repaired by TIG welding may then need to be heat treated.

3. The results of pulse laser welding are more repeatable.

Manual TIG welding is more artistic than pulsed laser welding. Depending on the skill level of the TIG welder, the welding bead path may include the weld peak and the weld valley. In contrast, with pulsed laser welding, the accuracy of the start and stop operating positions can be improved, while the high degree of consistency of the welds formed by deposition is higher. Pulsed laser welders, such as alpha Laser mobile Alflak and ALP welders for mold repair, come with their own cross-line microscopes to ensure that the operator can pinpoint the laser beam. In addition, only 4 parameters, i.e. voltage, frequency, pulse time and point-of-light diameter (laser beam diameter), need to be adjusted for each job.

These welders support manual, semi-automatic, or full CNC modes. In general, however, the full CNC mode is used for production operations, not mold repair. In semi-automatic mode, the operator can lock any or all axes during laser operation, allowing them to rotate at a set speed and weld at straight lines or at complex angles, a simple process. Pulse laser welding machine, in the spot welding, accuracy can be as small as 0.004inch, and the miniature TIG device welding point size can only reach 0.04inch.

Mr. Blair Learn adds that advances in technology have also made pulsed laser welders more powerful. First, it's more powerful. In 2010, the maximum power of a laser welding machine with a zirconium-aluminum garnet pulsed laser reached 200W (aluminium-aluminum garnet lasers were used for mold repair at a higher frequency than fiber lasers). Since then, Alpha Laser and other manufacturers have developed 300W models. Alpha Laser also introduced the 500W model. He says the 500W model is soldered twice as fast as the 300W model and can be further increased in metal deposition with a larger diameter filled wire. The maximum fill wire diameter for the 300W model is usually 0.025inch, while the maximum diameter for the 500W fill wire is 0.0625inch.

Second, increased mobility. The self-pushing Alflak model is equipped with a continuous track like a tank. Mr. Blair Learn says this combination makes it easy to move welding units from one location to another, benefiting even large factories that produce large molds, tools or parts that move on track. These are the company's largest laser models, with an arm extension length of nearly 5 inch. The laser head can be rotated back up or down for easy access to a variety of work features.