Laser welding and cutting of aluminium

LASER BEAM WELDING OF (ALUMINUM)

Introduction

Aluminum is a rapidly growing material and has found many new applications as an engineering material.

Growth is taking place mainly in the transport sector cars, buses, trains and marine vessels.

Joining is a key technology in many cases and especially welding of aluminum, which is shown by the growing interest in aluminum welding.

Weight savings of 40-60% are often mentioned in many cases, reducing fuel consumption in transport vehicles.

The Process

Laser beam welding (LBW) is a process that melts and joins metals by heating them with a laser beam.

Power

Lasers are available in sizes up to 25 kilowatts power output.

Lasers in the size range 3 Kw to 10Kw are usually adequate for the aluminum sheet thicknesses automotive applications.

The power absorption changes dramatically at times, producing an unstable process with poor penetration control and a rough bead surface.

Advantages of laser welding: deep welds(high penetration) at high welding speeds(the

welding speed can be too high to give the weld metal sufficient time to mix well before solidification).

a narrow heat-affected zone. little distortion of the workpiece. precise heat input. narrow weld bead minimal thermal distortion. High productivity. The laser beam, unlike other fusion processes, can be

projected in air with no loss in power, and no vacuum chamber is needed.

AA6061 butt welded joint

Problems and Solutions to Laser Welding Aluminum Hot Cracking or Weld Solidification Cracking.This complication occurs because of:• solidification stresses on the microstructure. • aluminum’s high thermal expansion and conductivity.• Weld metal solidification cracking was observed with

increasing the welding speed to 4 m/min in the case of AA6061 alloy as shown in Figure.

Problems and Solutions to Laser Welding Aluminum

Solution:

1-Adding filler material.

Solution:

2-backing strip

The effect of composition on the solidification cracking sensitivity of several aluminum alloys:

 

Problems and Solutions to Laser Welding Aluminum The Presence of Hydrogen:Hydrogen is abundant, especially in manufacturing

environments, and its solubility in molten aluminum can lead to gross porosity.

Water, lubricants, and air all contain the element, and although it readily dissolves into molten aluminum, it has virtually no solubility in solid aluminum.

As a result, hydrogen in the molten weld pool is either trapped in the weld as pores, or it outgases, which causes blowholes upon solidification.

Problems and Solutions to Laser Welding Aluminum The Presence of Hydrogen:Fortunately, some simple preventive measures can be

taken to prevent hydrogen-related issues from occurring.

1. Keep materials clean and dry, including the filler wire or foil.

2. Avoid temperature differentials (e.g., storage to production area) that can cause condensation on the parts or filler material.

3. Clean weld joints and remove porous oxides when needed.

4. Use a shielding gas.

Problems and Solutions to Laser Welding Aluminum Porosity and Blowholes:• These issues also can be caused by volatile alloying

elements such as zinc, magnesium, and lithium. • These elements vaporize, escape through the

keyhole, and pull molten material along with them, leaving weld voids and spatter in their wake.

• It is believed that porosity formation was mainly attributed to:

1. insufficient surface cleaning of base metal prior to welding.

2. insufficient shielding.

Problems and Solutions to Laser Welding Aluminum Porosity and Blowholes:

Problems and Solutions to Laser Welding Aluminum Porosity and Blowholes:The solution:• large focused spot size or tandem focus spot. • enough time (e.g., reduced weld speed) for the

vapors to exhaust without causing damage• Reduced by careful mechanical and chemical

cleaning of base metal prior to welding and by increasing the flow rate of shielding gas to 25 l/min.

Problems and Solutions to Laser Welding Aluminum• METAL EVAPORATION: • Al–Mg alloys are solution strengthened by alloying with Mg, Mg loss can result in

substantial reduction in the tensile strength of the weld metal.

Problems and Solutions to Laser Welding Aluminum Reflectivity:• The very high reflectivity of a laser beam by the

metal surface is a well-known problem in LBW .• As much as about 95% of the CO2 beam power can

be reflected by a polished metal surface.SolutionSurface modifications such as roughening, oxidizing,

and coating can reduce reflectivity significantly.

Problems and Solutions to Laser Welding Aluminum Reflectivity:• Once keyholing is established, absorption is high because

the beam is trapped inside the hole by internal reflection• Since the shorter-wavelength solid-state lasers, like disk

and fiber, have a higher absorption into aluminum, they must be the best laser for all applications.

• For thicknesses up to about 4 or 5 mm, the 1-micron wavelength of the solid-state laser is preferred; however, when material thickness is 6 mm or more, the CO2 laser (10.6-micron wavelength) is the best choice.

Welding joint Mechanical Properties

Mechanical Properties

• The effect on hardness:

Mechanical Properties

• Tensile elongation of welded joints :• AA6061-T (heat treated stable)

Mechanical Properties

• Tensile strength of welded joints:• B: Base metal - W0: As-welded - WT: Heat treated

Laser cutting of aluminum

Laser cutting:

• Cutting of aluminum:

• Plasma and laser cutting are - along with mechanical cutting - the most effective methods for cutting aluminum.

• Laser cutting of aluminum is suitable for thicknesses of up to around 8 mm. The advantages are even edges and a high cutting speed. A CO2 laser is normally used, with an output of between 1.5 and 4 kW.

Laser cutting:

• Choice of gas

• When cutting aluminum:• (Oxygen or Nitrogen can be used as a cutting gas)• Clean cutting surfaces by (high pressure of gas)

• For cutting AL-alloys use N2 for cutting pure-AL O2

Laser cutting:

• The role of cutting gas1-The gas transports the molten material away from the cut edge.2-Sometimes the gas reacts with the metal that is being cut.3-The additional heat being created contributes to increasing the cutting speed.4-The gas cools the cut edge, which helps to reduce the surface area affected by the heat generated by the Cutting.

•5-The gas prevents steam and particles contaminating the nozzle.

Laser cutting:

• Cutting qualityCompared to plasma cutting , laser cutting can give more:1-even edges. 2-a smaller cutting width.3-fewer thermal effects on the material in use.

Laser cutting:

• Problems in laser cutting aluminum:• Unlike standard-grade or carbon steel, aluminum is light-

reflective and heat-conductive metals, so it can be difficult to fabricate them using a laser cutting process

• A possible solution:• Use of a higher power setting coupled with compressed gas

technology.• Using gases in conjunction with cutting operations is fairly

common.