Welding Aluminum is more challenging than the other metals due to its specific properties. Only fusion welding process is appropriate for this material, due to its thermal conductivity, which is about 209W/m K and its low melting point, which is approximately. MIG, TIG, Electron Beam and Laser are some of the fusion welding procedures, which generate intense heat in relatively small area in order to melt the material in desired portion. The amount of the applied heat must be controlled very precisely. Manual welding procedures quality and control such as MIG and TIG is completely depending on heat sinking and operator skill.
Aluminum does not change its appearance when it reaches its melting point, thus welding which requires visual judgement will be unreliable. On the other hand, automated systems such as Electron Beam and Laser, which are managed and controlled completely with computers, are often superior in accuracy and quality compared to manual methods.
Laser welding for aluminum is one of the most popular and common welding methods of this material. This procedure offers great pace of work and clean welds. The process penetration can rich 0.25 inches and the heat-affected area will be minimized.
Common Challenges of Welding Aluminum
Oxidation
It is natural to have oxide film on the working surface of aluminum during welding process. The problem is the melting point of the oxidase aluminum, which is almost 3 times greater than the pure material. This can cause contamination in the process and lead to porosity issues. This film must be removed by chemical or mechanical methods.
Hydrocarbon Contamination
Hydrocarbon contamination often happens during preparation and storage of the material. This surely cause issues when welding. Prior to welding process, aluminum parts are formed, sawed, sheared and machined regularly. Complete removal of any lubricant used in such fabrication operations is necessary in order to avoid low quality result.
Preparation for Laser Welding of Aluminum
Before starting the procedure, a pre-welding preparation is required. Amount of the preparation depends on the condition of the aluminum parts, which need to be processed. Cleanliness of the machine and storage conditions are the main factors. The sheets must be completely clean in order to avoid oxide films and hydrocarbon contamination. This can be achieved by using stainless steel wire brushes or by utilizing chemical cleaning methods with immersions in corrosive solutions and water. If there are hydrocarbon residue on the surface, it can be removed with acetone or alcohol based solvents. Using chlorinated solvents for this purpose is not allowed due to their toxic gases.
Another important factor, which needs accurate preparation, is the joints fabrication. Aluminum is softer than the most metals, thus special care in assembly and machining must be taken. Avoiding any machining method that can leave smeared or ground surface is essential. Utilizing post cutting the joint edge can overcome this problem. Grinding process is also not recommended. In many cases, a course disk can be helpful through the procedure. Blowing off the debris must be done with a nitrogen or argon gas bottles.
Laser welding of aluminum requires a precise joint for maintaining acceptable mismatch and gap. For placing the laser beam accurately, a good fixture is required. This is done with utilizing different types of joints such as butt joint, lap joint and fillet joint.
Types of Lasers for Welding Aluminum
There are four main laser types, which are suitable for welding aluminum products such as ACM panels, long boards and sidings. These types are CO2, Fiber, which is often Ytterbium, Disk and YAG, which stands for Yttrium-Aluminum-Garnet. All of these methods and technologies are able to produce high quality welding and choosing the right system is depending on operational costs, rather than the quality. However, each method has its unique characteristics, which can make some of them more preferable for different applications, alloy combinations and joint configurations.
Operations for Laser Welding of Aluminum
Depending on the application, there are different types of operations used for the purpose. Followings are two of the most common methods used in industry.
Pulsed Welding With Laser
In this method of welding, the beam is switched on and off at a very high pace which is 10-1000 HZ. Thus, the energy is applied to the aluminum in separate bursts. Each pulse creates a small melted area and with slight movement of the piece, series of overlapping welds produce continuous bread. These melted areas start to cool very quickly, thus the amount of heat in the surroundings is minimized. This method is the best way to weld an aluminum material when low thermal input is needed. This is due to the high thermal conductivity of the material.
Continuous Wave Laser Welding
This method is often mentioned as keyhole welding due to its deep penetrating ability. In this operating system, a steady beam is applied to the aluminum product. This laser is generally feed at speed of 25-100 inches per minute in order to prevent overheating of the parts. Due to the constant rate of applied heat, this method is approvable for more crack sensitive alloys.
