Laser Welding - Welding Mastermind

Laser welding and TIG welding are two different methods used to join two materials--often metals--together. While both welding strategies are effective, they each offer their own share of advantages and disadvantages. What is the difference between laser welding and TIG welding? The following are some of the key differences between laser welding and TIG welding: FeaturesLaser WeldingTIG WeldingFusing ProcessUses concentrated beams of light to melt seams together. Uses a combination of heat created from an electric arc and a filler metal to melt and bond seams together. Oxygen ShieldSeparate nozzle on the laser directs carbon dioxide to the weld site.Shield in the form of inert gas, most often argon. Filler MaterialNot required for laser welding.Thin filler metals commonly used. The best welding method for your project will depend on a number of factors, including material type and your welding goals. What is Laser Welding? Light Amplification by Stimulated Emission of Radiation, or laser welding, is “a process used to join metals or thermoplastics together using a laser beam to form a weld.” (Source: TWI-Global) How it Works Laser welding involves focusing an amplified, highly-concentrated beam of light on each material’s seams to the point of melting. This melting process around the seams allows the two surfaces to fuse into a joint within seconds. The weld is protected with the use of a process gas or cutting gas; the gas usually takes the form of carbon dioxide and is directed at the weld location via a separate nozzle on the laser to prevent oxygen exposure. Types of Lasers There are multiple types of lasers used in laser welding: gas lasers, solid-state lasers, and fiber lasers are the most common. Gas Lasers - Gas lasers use a combination of gases--such as helium and nitrogen, or carbon dioxide--to produce the concentrated light. To do so, they use a low-current, high-voltage power source to “excite” the gas mixture. Gas lasers are often used in keyhole welding modes for automotive projects, such as car bodies and transmission components. Solid-State Lasers - Solid-state lasers are commonly used for welds involving glasses and yttrium aluminum garnet (YAG) materials. They can produce large spot welds, in addition to deep spot and seam welds. Fiber Lasers - Fiber lasers are versatile in that they can be used for both thin and thick material welds. They are low-cost compared to other laser types but still produce quality spot welds. Modes of Laser Welding Laser welding can be done in two different modes: heat conduction welding and keyhole welding. Heat Conduction Welding This method involves heating the metal surface past its melting point, but not so much that it begins to vaporize. The result is a very smooth and clean-looking weld. Heat conduction welding is more common for weld projects that do not require a high weld strength. (Heat conduction welding uses a low power laser, typically under 500W.) Keyhole Welding In this method, the laser beam heats up the metal to the point of vaporization on the contact surface, digging deep down into the metal. This results in a “keyhole,” where the metal maintains a plasma-like state with temperatures above 10,000K. (Keyhole welding requires a high powered laser over 105W per millimeter squared.) The mode that is chosen will depend on the power density across the beam that hits the workpiece. This factor will also affect how the laser beam will interact with the material it is welding. (Source: Interesting Engineering) Continuous-Wave & Pulsed Laser Welding With laser welding, you also have the option of using continuous-wave lasers or pulsed lasers. Continuous-Wave Lasers Continuous-wave (CW) lasers produce a constant, uninterrupted beam of concentrated light. They are usually fiber lasers that use active diodes to output strong laser light. CW lasers are often used for deep penetration welds and to fuse materials more sensitive to cracking, such as high-carbon stainless steel. CW lasers are also recommended for non-heat-sensitive materials and high volume production projects. Pulsed Lasers Just as the name suggests, pulsed lasers produce a series of short bursts of light energy at a specific width and frequency. A seam with pulsed lasers is created by overlapping spot welds. Because energy is stored before its release throughout the duration of this method, pulsed lasers are capable of reaching high peak powers, resulting in the creation of fast, durable spot welds. Pulsed lasers are often recommended for use with heat-sensitive, reflective, or thin materials. Weld Joints There are four different types of weld joints that can be created with laser welds: Butt Welds - Formed by welding the ends of two parts together. Filler Lap Welds - Also known as a tee joint, filler lap welds involve creating a “T” with the two surfaces and joining them with a triangular-shaped weld. Overlap Welds - Created by placing one section over another. Edge Flange Welds - Formed by welding the edges of two materials together. Uses for Laser Welding The process of laser welding can be used on a variety of materials, including: Carbon Steels (Note: It can be difficult to weld steels higher in carbon; to minimize the chances of cracking, make sure you preheat the material before welding.)High-Strength, Low Alloy Steels AluminumStainless Steel (Note: Stainless steel is one of the most common materials used with laser welding, but avoid stainless steel that contains sulfur and phosphor. This steel has a lower melting point, making it more likely to crack and experience porosity problems after welding. Low carbon stainless steel usually works best.)Titanium ThermoplasticsPrecious Materials Because laser welding can be used with any thin or thick material that has a high heat conductivity, it is often used in the following industries: Aerospace EngineeringMedicalAutomotiveFine JewelryElectronics What is TIG Welding? Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding, is “a strategy that involves using a tungsten electrode to heat the metal that is being welded.” (Source: Welding School) During this process, an inert gas, such as argon, is used to help shield the weld from oxygen contamination. How it Works The welder creates an arc between the base metal and non-consumable tungsten electrode. Where the arc and base metal meet, a molten weld pool forms. Thin filler metal is carefully fed into the pool, where it begins to melt. A shielding inert gas helps protect the tungsten electrode and pool from oxygen contamination. The result of the TIG welding process is a slag-free weld that has the same corrosion resistance properties as the original metal. (Source: Welding School) Modes of TIG Welding The “modes” of TIG welding are classified by how the power supply in the TIG welding machine creates an electric arc between the electrodes and materials. There are two main modes of TIG welding: direct current and alternating current. Direct Current Direct current, or DC, describes the flow of electricity moving a constant direction and/or having a voltage with a consistent polarity, either positive or negative. An example of direct current is the current in batteries. You can also find direct currents in low voltage devices such as remote controls or cell phones. Negative Polarity - When it comes to welding, an electrode-negative direct current or straight current offers faster deposition rates because the electrode allows for faster melt-ff. Positive Polarity - On the other hand, an electrode-positive direct current results in deeper penetration. Direct current TIG welding is commonly used for all metals except for magnetic types such as aluminum and magnesium alloys. This is because it cannot produce the high-intensity heat necessary to overcome the magnetic forces. If a magnetic field happens to be present in the area in which the direct current weld is being performed, it may interact with the welding current; this results in the welding arc deflecting from the weld path, significantly reducing the quality of the weld. In general, direct current is the preferred mode of welding for many reasons: It results in a smoother weld due to the consistent linear direction of the current.Direct current can maintain a stable arc, being easier to control and more reliable than alternating current. Welding machinery that uses direct currents are usually less expensive and more user-friendly.Direct current welds thinner metals much better than alternating current. Direct current TIG welding is best used for the following types of welds: Hard FacingOverhead or Vertical WeldingHeavy Deposit Build UpsSingle Carbon BrazingStainless Steel WeldingTap Cutting However, there are a few disadvantages to using direct current TIG welding over an alternating current, too: There is a greater potential for the arc blowing out due to a magnetic field presence. Direct currents cannot be supplied from electrical grids, so they require a transformer to change the current from alternating current to standard current for use. The transformer itself can be quite expensive. Alternating Current Alternating current, or AC, describes electricity that constantly switches direction; this results in a voltage that periodically reverses in polarity. You can expect to find alternating currents in the electrical outlets in your home or high-voltage devices such as household appliances. An alternating current changes its polarity at 60 hertz, at least 120 times per second. In TIG welding, this reversed polarity allows for deep penetration welds. In addition, since the current and the magnetic field of the arc frequently switches direction in only a second, there is no net deflection of the arc. Alternating current TIG welding can be used to weld magnetic metals--such as aluminum and magnesium alloys--which cannot be done with direct current welding. This is because the changing current is not affected by magnetism like its counterpart mode. The arc for an alternating current remains stable and is much easier to control for the welder. This mode of TIG welding is ideal for the following types of welds: Downhand Heavy PlateFast FillAluminum Welding with High FrequencyMachinery RepairsSeam Welding in Shipbuilding The only drawback to using alternating current TIG welding is that the quality of the weld is not nearly as smooth as direct current welding, primarily due to its continuous change in polarity. It is likely that you will see more spatter in an alternating current weld. Styles of Arc Starting There are three styles of arc starting used in TIG welding: scratch start, lift start, and HF start. Scratch Start - Scratch start is an older starting technique that is usually used with a transformer type of welding machine. Lift Start - This start is more common with inverter welding machines. When the tungsten is gently touched on the weld surface and lifted off, the control circuit senses this and quickly ignites the arc after lift-off. HF Start - This start allows arc creation without the need to touch the weld surface with the tungsten. This can be an important feature if there is any risk of tungsten contamination in the weld. Gas Delivery TIG welding requires the use of inert gas shielding in order to produce an uncontaminated weld, so the right method of introducing the gas to the weld is necessary. Some TIG welding machines automate this process, while others require you to activate the gas shield manually. More in-depth TIG welding machines will have a built-in gas valve that will automatically be turned on when the trigger for the torch is pressed. Such machines will typically allow you the ability to set a timer for pre-gas and post-gas emission--pre-gas to clear the area of oxygen before beginning the weld, and post-gas to help cooling after the weld--in addition to maintaining gas shielding during active welding. Less sophisticated welding machines may not have a built-in gas valve and will require the use of a torch that does have a built-in, manually operated valve. Weld Joints There are a variety of weld joints that can be created with TIG welding, some of the most common being: Tee Joint Welds - Also referred to as “Filler Lap” or “Fillet” welds. These welds are used to create a triangular weld between two surfaces joined at a right angle. Corner Welds - Involves welding two pieces of material together in the shape of an “L.Butt Welds - Joins the ends of two parts together. Uses for TIG Welding TIG welding is used for welding many types of metals, including: High-Carbon SteelStainless SteelBronzeNickel AlloysChromeBrass Copper Magnesium AluminumGold Due to the wide number of metals it can be applied to, the TIG welding process is often used in a range of industries, such as: Aerospace EngineeringAutomotiveConstructionPetroleum TIG welding can also be used for everyday applications, such as repairs or even large art structures. Similarities & Differences Between Laser Welding & TIG Welding Some of the key similarities and differences between laser welding and TIG welding are as follows: FeaturesLaser WeldingTIG WeldingFusing ProcessUses concentrated beams of light to melt seams together. Uses a combination of heat created from an electric arc and a filler metal to melt and bond seams together. Oxygen ShieldSeparate nozzle on the laser directs carbon dioxide to the weld site.Shield in the form of inert gas, most often argon but sometimes helium. Filler MaterialNot required for laser welding.Thin filler metals commonly used. Gap BridgingNarrow fusion zone, lack of filler metal results in poor gap bridging. Wide fusion zone, use of filler metal allows for good gap bridging.Residual Stress & DistortionLow heat input per unit length results in low residual stress and distortion.High heat input per unit length results in high residual stress and distortion.Common UsesIndustrial applications.Personal or common applications.Key AdvantagesCan weld a variety of thin and thick metals, precision and accuracy makes it easy to overcome complicated joins, creates clean and strong welds. More control over the welding process, inexpensive equipment, can join materials that do not have a good fit or have gaps. Key DisadvantagesExpensive investment and high maintenance costs, not ideal for reactive materials in which cracks may occur, difficult to join surfaces with gaps. Requires a high level of experience and dexterity, transfer of heat can lead to distortion and weaker welds, more susceptible to contaminants.EfficiencyHigh welding speeds and productivity.Low welding speeds and productivity. Cracking PropensityFormation of brittle phases.High chance of solidification cracking. Cooling RateFast cooling rate; material ready to handle nearly immediately after the laser weld process. Slow cooling rate. Overall EffectivenessProduces clean, high-quality welds for a range of materials.Results in clean, high-quality welds for a range of materials. (Source: ResearchGate) Which Welding Method is Better? Both laser welding and TIG welding seem to produce similar quality results at face value, but which welding method is best for your project? The following are some of the advantages and disadvantages of both weld strategies: Laser Welding As you’ll find with all types of welding, laser welding offers its own advantages and disadvantages. Pros Because laser welding uses a concentrated heat source, it can be performed at high welding speeds in thin materials.Laser welding can create narrow, deep welds between square-edged sections of thicker materials. The welding process can be automated with a CAD or CAM setup, while TIG welding requires the process to be done manually. It can handle complicated joins as well as dissimilar materials. Laser welding also allows you to access difficult areas better. Laser welding is ideal for detailed work because it offers accurate and precise targeting.Its precision means that there is less scrap produced. Results in very high-quality welds due to the weld being more narrow and having an ideal depth-width ratio. The heated area around the weld does not spread to the surrounding material. Due to its fast cooling, the weld can be handled almost immediately after the process is completed. There are little deformation and shrinkage in the materials being welded. Equipment is portable. Cons Initial laser welding set-ups can be a more costly investment. Laser welding devices have high maintenance costs. Not ideal for use with reactive materials. Fast cooling rate may lead to cracking in certain metals. It is more difficult to overcome gaps. Setting up an automated laser welding system requires proper alignment and regular maintenance. (Source: Interesting Engineering) TIG Welding TIG welding also has advantages and disadvantages. Pros TIG welding can be used for many metals in comparison to other types of welding processes. TIG welding is also very versatile; it can be used on thin and thick metals. Welders have more control over the welding process. Ideal for detailed welding projects. TIG welding produces precise, clean results. This process does not result in sparks, smoke, or fumes. Equipment is less expensive compared to laser welding. Due to the use of filler material, it is easier for the welder to overcome gaps between two surfaces that do not have a good fit. TIG welding’s slow cooling rate means there is less of a chance for cracking in certain metals. Cons TIG welding requires a high level of hand-eye coordination and focus for the perfect weld. In addition, creating a successful TIG weld requires more experience and skill compared to laser welding. TIG welding can be a more time-consuming process. Heat can be transferred to the surrounding metal, leading to distortion or a change in the metal structure. This can result in weaker welds. TIG welds are more susceptible to contaminants.Machinery is not as easily portable compared to laser welding equipment. Not recommended for use in vertical or overhead positions due to the liquid pool that forms around the weld. (Source: Welding School) Laser-Hybrid Welding If you are not sure as to which welding method is right for your project, you could also consider using a combination of both laser and arc welding, or laser-hybrid welding. Laser-hybrid welding is a welding process that combines the keyhole method of laser welding with the gap tolerance of arc welding (i.e., TIG). How Laser-Hybrid Welding Works In laser-hybrid welding, the laser beam and the electrical arc operate simultaneously in one area and will influence each other in different ways, depending on the kind of arc or laser process being used. With metals, the laser beam is focused on the surface of the material to heat it to the point of vaporization. The arc helps heat the metal, allowing it to reach this vaporization temperature faster. The result is a vapor cavity or keyhole. The TIG torch is then used to bridge the gap between the two parts, sealing it with thin filler wire. Uses for Laser-Hybrid Welding Laser-hybrid welds work well with thick, metal materials to often form butt joint or T-joint welds, including: High-Performance Carbon & AlloysStainless Steel Laser-hybrid welding is commonly used in heavy industrial applications, such as: Construction Machinery and VehiclesAdvanced StructuresEnergy Industry - Gas pipelines, utility towers, storage tanks, and other energy components. Automotive Industry - Truck productionRail Vehicle ManufacturingShipbuildingAerospace Applications Advantages of Laser-Hybrid Welding Ideal for very thick materials.Laser-hybrid welding can create deep, penetrating joints in the weld. Hybrid welding can be a faster process compared to laser and TIG welding on their own. It produces a higher seam quality. The combination of laser and TIG welding methods improve the weld’s tolerance to joint fit-up.The combination reduces the chances of cracking, internal porosity, and thermal distortion.The process can be automated, like traditional laser welding. It can be a more stable process compared to individual welding methods. This is because it offers the welder more control over the weld quality and properties with the arc welding consumables and gas mixtures involved. It significantly reduces fabrication costs for large industries. Disadvantages of Laser-Hybrid Welding It is not fit for common welding applications; it is usually ideal for heavy industry welding. Advanced training and skills are needed to operate a laser-hybrid device due to its difficulty in use. The initial investment can be very expensive. There are numerous parameters to consider when combining laser welding with TIG welding since they each can be performed in different modes (the laser beam and electrical arc will influence each other in different ways, depending on their modes). Therefore, welders will need to carefully study both laser and TIG welding in order to determine the best combination of modes for each project. The wrong combination can result in a bad weld. Essentially, depending on the application, with laser-hybrid welding, it is possible for you to reap the benefits of both laser and TIG welding.