GTAW produces a very narrow, focused arc with good directional control and real-time amperage control, thereby reducing the chances for problems commonly associated with welding thin materials, such as burn-through or warping. The process, when completed properly, can also reduce instances of cracking and porosity - the entrapment of gas in a weldment - that can cause costly downtime for rework. These same benefits hold true whether you are welding on aluminum, mild steel or stainless steel.
Following are answers to 10 frequently asked questions that can help you increase your success when welding on thinner pieces of these materials - and help you gain greater productivity at the same time.
1. What is the best power source for welding thin stainless steel?Both a standard DC power source and an inverter-based machine will provide good results, but an inverter power source offers the benefit of reliable low amperage, high-frequency arc starts and a narrow, focused arc to lessen burn-through on these materials. Set either type of machine on straight polarity (DCEN, or direct current electrode negative). Also, consider a power source with pulsing capabilities, particularly if you will be welding stainless steel frequently. These machines can switch the current between a high peak amperage and a lower background amperage at regular intervals to help reduce distortion by effectively lowering the average amperage level. They also offer greater control of the weld penetration profile.
2. Can I use the same power source for welding thin aluminum?You need a power source with AC capabilities to weld aluminum. An AC/DC inverter provides the best high frequency arc starts and directional arc control, as well as the capability (via the balance control) to clean the oxide layer on the surface. It also initiates an arc quickly at low beginning amperages, which helps minimize heat input into the material and reduce the heat-affected zone (HAZ) - the area adjacent the weld deposit that could be potentially affected by heat from welding. It also reduces the probability of burn-through. For optimal performance, consider adding a remote current control, as it will allow you to adjust and manage the heat input more readily.
3. What are the recommended parameters for welding thin materials?As a general rule, use 1 amp for every .001-inch of material you are GTA welding. For example, when welding materials 1/4 inch, you should weld at approximately 200 to 250 amps. When you are welding aluminum, you can adjust the amount of oxide cleaning and the width of the arc. Experience will guide your judgment, but an AC balance of 70-75 percent electrode negative (EN) and 120 Hz of AC frequency is a good starting point. Those settings should be able to accommodate for the surface oxide layer and provide a smooth, stable arc with good directional control.
4. How important is part fit-up when welding thin materials?Very. To minimize heat input when GTA welding thin materials, it is important that the materials fit as closely together in the joint to be welded as possible. Having gaps requires additional filler metal to fill the space and more heat to melt it, which leads to a greater likelihood of burn-through or warping. If necessary, you can place small tack welds along the joint to keep the materials in place or you can clamp them together. You also may consider fixturing with or without a back purge of argon. The greater mass from the fixture helps pull heat from the weld, giving you greater weld puddle control and minimizing the heat concentration in the thinner material.
5. What type of torch is best for welding thin materials?For welding 1/4-inch and thinner materials, a 150- to 300-amp GTAW torch is sufficient. An air-cooled model is less expensive than a water-cooled torch and does not require a separate cooler, which makes it more portable. These torches do, however, tend to be larger and heavier so they are a little more difficult to maneuver. If you have a power source with a water cooler (either integrated or separate), you can use a water-cooled torch. This style has a smaller handle and body, is lighter weight and offers greater access into joints with restricted access.
6. Are there any recommendations for the torch angle?Yes. The GTAW torch should be positioned nearly perpendicular to the weld joint. The most common technique is to tilt the torch back about 15 degrees and push the weld puddle along the joint. Doing so produces a symmetrically round weld puddle that concentrates the heat. As when welding any type of material, finding a comfortable position is key in obtaining a quality weld when working with thin materials. Determine for yourself the manner in which you can gain the most control of the GTAW torch. Some people prefer to hold the torch like a pencil, for example. Position your body so you can see the weld joint and the tip of the tungsten, keeping it approximately 1/8 inch away from the base material. Doing so helps keep the arc length consistent and prevent arc wandering that could increase heat input. It also helps you maintain good gas coverage and allows visibility to the weld puddle so that you can better control your travel speeds.
7. What impact does travel speed have when welding thin materials?A steady travel speed is critical when welding thin materials. Too slow of a travel speed can cause heat to build up in the base metal or cause a wide weld bead. A good technique is to push the torch forward, moving it so that the weld puddle is slightly ahead of the torch and always visible. Proceed and add filler metal at a pace that allows you to create a weld that is approximately equal to the base metal thickness. This pace helps ensure consistent weld width and penetration, providing a greater opportunity to create the appropriate-sized, quality weld bead.
8. What is a gas lens and how can it help when welding thin materials?A gas lens is a component that can replace the collet body in a GTAW torch. It is typically made of brass or copper and contains layered mesh stainless steel screens. The purpose of a gas lens is two-fold. First, it provides better shielding gas coverage and distributes it around the tungsten and weld puddle more evenly than a GTAW torch without a gas lens, and without having to increase the gas flow rate, which may ultimately disturb the arc. This greater shielding gas coverage helps protect against pinholes and/or porosity, particularly at the start of the weld. Secondly, gas lenses allow you to extend your tungsten further to gain greater access to restricted joints.
9. What type of tungsten should I use when welding thin materials?As a general rule, a pointed 2 percent ceriated tungsten is a good choice for welding materials 1/4 inch and thinner, as it provides good arc starts at the low amperages needed when welding these materials. It also maintains a stable arc when welding in both AC and DC, making it versatile for welding on aluminum, stainless steel or mild steel. Select a tungsten diameter that can handle the welding amperage. A 3/32-inch diameter is the most common for 1/4-inch material, but you should use a smaller diameter for very thin metals, as it produces a smaller arc cone and more consistent starts at low amperages. If you plan to weld mostly stainless steel, you may consider using 1.5 percent lanthanated tungsten, as it provides good low-current DC arc starts.
10. What is the best way to prepare my tungsten?When welding on thin materials, grind your tungsten lengthwise to a point. Do not grind around the tungsten, as it creates ridges that the arc will follow, essentially making it wander and increasing the heat input on the base material (see Figure 1). Ideally, use a dedicated tungsten grinder for the job. These grinders are designed to grind the tungsten evenly and can help you better gain consistent arc performance. If you do not have access to a grinder, use a 250 grit or finer grinding wheel and designate it for this purpose only. Using the grinding wheel for any other purpose can contaminate it and cause the tungsten to pick up debris that could cause arc instability or weld defects.
While there are many precautions to take when GTA welding thinner materials, particularly those 1/4-inch and thinner, starting with these basics can improve your chances of success. They can also help you minimize weld defects, reduce instances of burn-through and increase your productivity. Remember, too, if you encounter troubles when welding thinner materials, you can always contact a trusted welding distributor or equipment manufacturer for help.