How does laser deposition welding work?

March 18, 2024

Laser deposition welding is a complex process that requires a lot of preparation before turning on the laser.

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Here are some of the key steps involved in the process.
Step 1 – Surface Preparation
Metal billets and ingots have protective surface coatings. These coatings are usually oils used to prevent rust, metal plating, or oxides (in the case of aluminum).
You need to remove unwanted compounds and impurities from the metal and roughen the surface—a rougher surface results in better metal adhesion during welding. The tiny bumps and cavities on the surface provide excellent anchor points for the molten filler metal to adhere to.
Step 2 – Filler Metal Delivery
The filler metal, usually a fine metal powder, flows from an air nozzle with an inert gas (nitrogen or argon). Inert gases prevent oxidation, blow away unwanted surface impurities, and keep welds clean and slag-free.

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Making fine and consistent metal powders is an expensive process. Creating the metal powder typically requires more effort than laser deposition welding itself.
Therefore, many laser deposition machines use thin metal wires instead. The wire can be fed manually or automatically via a motor and roller system near the laser head.
It should be noted that when welding, the filler metal can be the same as the workpiece, while the surface coating can be different.
Step 3 – Local laser heating
A precise CNC system directs a high-power laser beam to the desired location. The laser melts the workpiece surface and incoming filler metal in less than a second.
The laser beam inputs a fixed amount of energy into the workpiece, and the energy deposition area is controlled by the wattage of the laser source and the spot diameter. The laser spot diameter is the size of the contact point between the laser and the workpiece.
A larger spot size means the energy is more spread out and the longer it takes to melt the surface. The smaller spot diameter means all the laser energy is concentrated on a tiny spot, reducing melting time.

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Smaller spot size means greater accuracy and faster welding times. It also minimizes material deformation because the heat is concentrated at one point and no excess heat is radiated to the surrounding environment.
Step 4 – Layering and Multiple Passes
Laser metal deposition (LMD) is not limited to welding, it is also often used to create components from scratch. After the initial laser pass, the laser head goes through another round and deposits a new layer of material on top of the first layer. Repeat this process until you reach the desired height.
For additive manufacturing, layers continue until the complete part is built. In contrast, welding only requires one or two layers.
Layer thickness and number of layers help control the amount of metal deposited.
Step 5 – Cooling and Solidification
Because the heat is localized, the welded area also cools relatively quickly, almost immediately after the laser leaves the spot.
The LMD process involves depositing energy directly into a small spot on the workpiece. Smaller contact points mean energy is used more efficiently, so the laser can move faster.
A faster laser means less total energy and heat deposited into the workpiece. Less heat deposited means faster cooling. Rapid cooling brings the additional side effect of better microstructure.
7 Advantages of Laser Deposition Welding
Laser metal deposition (LMD) is the accumulation of many years of research on additive manufacturing technology. Every aspect of laser metal deposition is designed with one goal in mind—the improvement of traditional processes.
Here are some of the biggest benefits laser deposition welding brings to modern manufacturing processes.
1. Faster welding time
The high-power laser melts the workpiece quickly, and the CNC controller quickly moves the laser head from one point to another, resulting in incredibly fast welding times.
Automatic table feeding enables continuous welding without any stops during the process. Computer-controlled welding also minimizes errors, saving more time on the production floor.
Managing and optimizing various process laser metal deposition parameters improves welding efficiency and reduces production time.
2. Greater precision and control
Almost every laser metal deposition machine is automated and computer-controlled, except for a few handheld models. High precision and control enable more complex welds at faster speeds.
Few experienced welders can match the accuracy and precision of automated laser welding machines.
3. Higher quality welds
The fine powder particles of the filler material fill gaps more efficiently, resulting in a stronger weld. Since everything is pre-measured and controlled by a computer, the amount of metal deposited is exactly what is needed, meaning the molten pool remains consistent throughout the process.
Additionally, internal jets are used to prevent slag formation and metal oxidation and to blow away small fragments of vaporized metal.
4. Zero distortion of heat source
Traditional welding processes introduce large amounts of unwanted heat to the base material. A small amount of heat is transferred to the solder joint, and the remainder seeps into the surrounding environment, causing the metal to deform (warp).
Laser metal deposition is an extremely precise process in which the laser beam melts only a small portion of the workpiece and nothing more. The process is so efficient that it is often used for full-surface welds because there is no need to worry about material distortion.
Surface welding is the process of coating one material with another material (or materials) to improve surface finish and wear resistance.
5. Wider material compatibility
Welding becomes more difficult as you move to higher quality and rarer materials. The traditional process is suitable for common materials such as iron, copper, stainless steel, and even aluminum alloys. But there are special cases to deal with involving tough metals like tungsten, volatile metals like magnesium, and soft metals like gold.
Laser metal deposition supports a wide variety of metals, alloys, and even some ceramics. Using LMD you can weld the following materials.
Nickel alloy
Tungsten carbide
magnesium alloy
cast iron
Aluminum alloy
Cobalt-based alloy
Titanium alloy
6. Reduce material waste
Laser welding minimizes material waste. Metal powder is fed into the workpiece at a controlled feed rate to avoid over/under deposition. Unlike traditional welding which uses a filler rod, laser deposition welding uses continuous wire and powder particles.
Use only the required amount of filler and reserve the rest for the next weld.
7. Reduce post-processing work
Since laser metal deposition produces cleaner welds, often, you don't even need to perform any post-processing. There is no need to wire brush the workpiece, grind away excess puddles, or straighten deformations during welding.
Reducing post-processing can save a lot of time on the production floor and significantly increase productivity.