Red Copper Welding Process Analysis

Red copper is one of the earliest metals used by humans. It has many excellent properties and functions, good electrical and thermal conductivity, excellent plasticity, easy to heat and cold pressure processing, and makes great contributions to the development of human society. With the continuous development of science and technology, red copper has created more new uses. Among the non-ferrous metals consumed by Chinese industries, red copper ranks second place, behind aluminum, widely used in construction, electrical, machinery manufacturing, and defense industries.

Laser welding has the advantages of high energy density, small amount of molten metal, narrow heat affected zone, high welding quality and production efficiency. It can greatly improve the welding efficiency and welding quality of red copper, so it is chosen by more and more industries. However, due to the low absorption rate of the fiber laser by the highly reflective material, the processing difficulty is also greater, and also has higher requirements of the laser source.

Problems of red copper welding:

(1) Difficult fusion and variability: Due to large thermal conductivity of red copper (around 350W/MK), the heat transfer rate is very fast during welding processing, which makes it difficult to fuse the red copper and the filler together, and the heat affected zone of the welding parts is large. Because of the large linear expansion coefficient of red copper, if the fixture is not clamped in place during welding, it will cause obvious deformation of the workpiece.

(2) Micro porosity: Pores will occur during red copper welding, especially during deep penetration welding. The generation of pores is mainly caused by 2 conditions, one is the diffusive pores directly produced by the dissolution of hydrogen in the red copper, and the other is the reaction pores caused by the redox reaction.

Solution:
The absorption rate of red copper for infrared laser is about 5% at room temperature, and the absorption rate can reach about 20% after heating to near the melting point. In order to realize the laser deep penetration welding of red copper, the laser power density must be increased.


Applicable laser:

When Maxphotonics single module 3000W fiber laser (35um) is equipped with a welding head with lens collimation and focus ratio of 100:200, the output laser power density is as high as 3120KW/mm², which is 50% higher than the power density of the same power 50um core diameter laser (the power density of the same power 50um core diameter laser is only 2000KW/mm²), and equipped with the swing welding head, it will stir the molten pool with the laser beam and expand the keyhole in deep penetration welding, which is beneficial to gas overflow, making the welding process more stable, less spattering, and fewer micro pores after welding.


Application 1: Red copper cable lug welding

In the past, cable lugs were generally processed in the form of soldering and hydraulic pressure, but these methods were not strong and conductive, could not meet the needs of demanding industries. However, laser processing has become a better processing method choice due to its high efficiency, no consumables, and strong electrical conductivity.

Welding skills:
(1) The angle of the welding head is tilted during welding process, prevent long term back reflection light from damaging the laser.
(2) The power of the laser must reach the absorption value of the material (red copper) to prevent laser from being reflected.
(3) The energy density ratio of the small core diameter of the laser is more concentrated, and it is easy to reach the absorption value of the material (red copper).
(4) Swing welding can improve surface quality.

Application Industry: Electric Power

Application 2: Red copper sheet welding

The 0.3mm red copper overlap welding requires that the welding surface be smooth and flat, no explosive spots and bumps on the welding surface, and the back surface cannot be affected by heat. The tensile force after welding is required to reach more than 200N without deformation. Laser welding has excellent characteristics such as high energy density, high welding efficiency, small heat affected zone, and high degree of automation. It is suitable for welding thin red copper sheets.

Welding skills:
Use ring segment welding to increase tensile force, control deformation, fast low swing and high density, control bottom not to weld through, and small spacing to control surface flatness.

Application industry: instrumentation, aerospace

 Front side                                                              Back side

Application 3: Red copper water cooling pipe welding

Welding 0.8mm wall thickness flat water cooling pipe to the red copper structural parts. The welding method is fillet welding, which requires good sealing performance after welding, and the weld seam does not crack when twisted by 90 degrees.

Welding skills:
Due to the spatial relationship of the structural parts, the angle of the incident laser is limited, and the angle between the optical path and the copper tube should be maintained at 45 degrees as much as possible, and it should not be too inclined.

Application industry: air conditioning, construction

Application 4: Red copper water cooling block welding

Water cooling block 2mm red copper and 0.5mm red copper are spliced for sealing welding, welding surface is required to be smooth and flat, without blast spots, and withstand pressure of 0.8Mpa after welding.

Welding skills:
(1) The angle of the welding head is tilted during welding process, prevent long term back reflection light from damaging the laser.
(2) The power of the laser must reach the absorption value of the material (red copper) to prevent laser from being reflected.
(3) The energy density ratio of the small core diameter of the laser is more concentrated, and it is easy to reach the absorption value of the material (red copper).
(4) Swing welding can improve surface quality.

Application industry: refrigeration equipment, electronic equipment