A purged gas chamber offers extreme protection, but is expensive in terms of cost and the shielding gas required to purge it , potentially cumbersome to weld in and does not always accommodate large work pieces. It is also more time-intensive. Pay close attention to your weld procedures as they may dictate the purity levels and dew point of that argon. Some applications may even require Helium, however, may be allowed as a backing gas as it provides the same general protection as argon. Argon is recommended as the primary ingredient in the shielding gas as it provides greater arc stability, greater density, is less expensive and more readily available.
Two components that you may not generally use in other TIG welding applications that are critical to the shielding process are a gas lens and a trailing shield. A gas lens replaces the standard collet body and improves the flow and coverage of the shielding gas around the tungsten, the arc and the weld pool.
Trailing shields can either be purchased or fabricated to match specific joint configurations and provide a continuous secondary shielding gas source to ensure the weld puddle and heat affected zone stay protected until each drops below the to degree window. Use a clean, non-porous plastic hose to transport all shielding gasses as rubber absorbs oxygen that could contaminate the weld. Some welders will also use oversized cups to achieve additional coverage surrounding the weld, but this is only necessary within practical means.
As such, a transformer- or inverter-based welding power source with DC capabilities will suffice. AC welding capabilities are not necessary unless you are regularly using the power source to weld other alloys as well.
A few key considerations:. Either an air- or water-cooled torch will suffice in this application, dependent on factors such as accessibility to the joint and welding amperage. Water-cooled torches are smaller and offer greater comfort and joint accessibility, but come in at a higher price point along with the need to purchase or add a cooling device.
Air-cooled torches are a bit larger, but cost less and are likely suitable for the majority of titanium welding applications. According to AWS D Filler metal is typically matched directly to the base metal, although there are some instances where a variation is used to achieve desired mechanical properties, such as using a filler metal with lower strength to improve ductility. Filler metal selection should always be dictated by the weld process. While your success will depend largely on your preparation, there are a few important pointers to keep in mind when welding titanium tube and pipe:.
Upon completion, titanium will tell you if it is an acceptable weld or not by its color. Colors ranging from silver to straw to brown are typically acceptable. As you get into blues, greens, grays and eventually to white, these welds are unacceptable. Step back and examine each step of your process to determine where contamination is entering the weld. Eliminating that variable should help you get the colors you are looking for. If contamination is present, the weld joint will have to be completely cut away and started anew — there is no quick fix for a contaminated titanium weld.
With these tips and resources, you should be on your way to making a successful weld on titanium tube and pipe. Always consult your weld procedures to guide you and, when in doubt — clean.
American Welding Society. AWS D To activate your FREE subscription today, simply select which newsletter s you would like to receive and complete the form below. Miller respects your privacy concerns. Read our privacy policy for more information. Because different welding processes respond differently and create different levels of color on titanium, the guidelines used in context with the weld process can help welders quickly recognize and easily identify weld problems.
The detailed but clear provisions in the AWS D1. The guideline is a one-stop shop for the proper design engineering, welding, and inspection of titanium welded components. The AWS Titanium Welding Committee welcomes new members to participate in the process of updating the code with additional test data and to bring new ideas and developments into the document.
A common question when welding titanium is, How important is the discoloration of the weld surface? Figure 3 The new gunner protection kit, designed by the Armament Research, Development, and Engineering Center at Picatinny Arsenal, also uses titanium components.
Weld color can be an indicator of an unacceptable weld, but everyone involved in titanium fabrication—designers, engineers, welders, fabricators, and inspectors—should keep in mind that discoloration should be used as part of the decision-making process and not the sole factor in weld acceptance.
The chart below shows a range of colors that may develop when titanium is exposed to atmospheric conditions at elevated temperatures. The color change is an indication of the thickness of the surface oxide rutile that develops and, thus, an indicator of the degree of weld contamination that may have occurred. With minimal or no oxidization, the surface color will be silver or light straw, while in severe cases of oxidation, loose, flaky white or gray deposits form.
If a contract specifically requires evaluation of weld color, the AWS D1. The code specifies the inspection requirements, qualifications, and responsibilities for individuals evaluating welds and provides detailed color acceptance criteria in the form of Table 5. When discoloration is found in a weld, the welding team should examine the welding equipment, filler wire, and work environment to understand the cause.
For example, a contaminated tungsten welding electrode is evidence that the quality of the primary shield gas has been compromised in the welding torch lines, whereas contamination at the end of the filler wire could be an example of a poor wire manipulation technique.
Ineffective shielding can lead to discoloration of the weld as indicated in the chart below. Possible causes of ineffective shielding are the location of the welding area, such as near a door or vent where the air current flowing across the weld can cause the inert gas shield to fail to some degree.
It is imperative to perform welding in an area free from drafts to prevent hot weld metal from being exposed to atmospheric oxygen and nitrogen if bright, shiny silver welds with minimal contamination are required.
GMAW produces a titanium vapor in the weld arc that deposits onto the cooler weld surface as finely divided titanium particles. Because of the reactive nature of titanium, these particles will combust spontaneously upon exposure to atmospheric oxygen once outside the protective weld gas shield. The nature of the resulting black deposit on the weld makes it difficult for inspectors to use color guidance charts as a reference for visual inspection of weld color.
It is therefore very important that every manufacturer establish and approve welding inspection procedures applicable to the specific welding processes adopted. Interested parties can contact the AWS to learn how to get involved. Stephen Luckowski is chief, prototype manufacturing team, Building , Picatinny Arsenal, NJ , , stephen. Figure 5 The color of a titanium weld can indicate the amount of weld contamination present in the weld. Source: The Welding Institute. Read more from this issue.
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Not yet registered? Sign up. Our Sites. Categories Additive Manufacturing. Aluminum Welding. Assembly and Joining. Automation and Robotics. Argon's density is greater than air, so it tends to flow over the surface of a part in the same way water does. Where eddies occur, air can become mixed with the argon cover gas and create swirl patterns. What really separates titanium welding from most other types of GTAW is the need for an argon cover on the weld's back side. Wherever the titanium is heated, brittle alpha-case can form.
For very complex parts with interior passages or parts that require a lot of welding repairs, glove boxes may offer an economical answer. For parts too large to fit through the glove box, special flexible polyethylene plastic bags, complete with attached gloves, can be used. Use a purge monitor to see when the bag contains clean-enough argon, strike an arc, and weld away.
Working in airtight gloves, especially for extended periods, can be hot, but doing so is part of the challenge of working with titanium. The end of the weld is equally important. The titanium is hot, and the protective argon flow is still needed until the metal has cooled below about degrees F.
Color can be your best indicator of sufficient argon use. Some discoloration may occur beyond the HAZ and, depending on the criticalness of the weld, may be acceptable. Be certain to contain the titanium dust from grinding operations. Titanium flake and powder are used in fireworks and should not be allowed to accumulate. Many times the white sparkling effect in aerial shells or pyrotechnic fountains comes from the burning reaction of titanium. The reaction can be similar to the thermite welding reaction if mixed dust is allowed to react.
While fireworks are fun on the Fourth of July, an unexpected release of this kind of energy can be hazardous. Waterfall filters can be effective in controlling titanium dust. Why use GTAW for welding titanium and not gas metal arc welding?
Many times, it's easier to adjust the temperature of the weld pool, ensure there is just enough metal to prevent undercuts, or add a filler metal that is not the same as the base metal or metals with GTAW. By adding the metal separately from the electrode maintaining the weld pool, you have more options and more control.
High-purity argon; clean work areas free of combustible grinding debris; the white-glove treatment after thorough cleaning; well-designed and -maintained purges on both sides of the part to distribute the argon evenly; and the technique of holding the torch in place until the metal has cooled below degrees F should produce a clean, silver-colored titanium weld every time. Midwest City, OK Email David Hass. View the Digital Edition. This magazine has served the welding community in North America well for more than 20 years.
Enjoy full access to the digital edition of STAMPING Journal , which serves the metal stamping market with the latest technology advancements, best practices, and industry news. Enjoy full access to the digital edition of The Additive Report to learn how to use additive manufacturing technology to increase operational efficiency and improve the bottom line.
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