Everything To Know About Drawn Arc Stud Welding

The Basics Of Drawn Arc Stud Welding

Drawn arc stud welding is a process by which a metal stud is joined to a metal workpiece by heating both parts with an arc. It permits strong, one-sided welds on base metals with thicknesses starting at 0.048″ (1.2 mm) and produces welds in as little as 0.06 seconds. During the process, the stud is loaded into the stud weld tool chuck, and a ferrule is placed over the end. Then, the weld tool is placed against the work position. When the trigger is pressed, the DC power supply sends a signal that energizes the weld tool’s internal lift mechanism lifting the stud, drawing the pilot arc. A key factor that differentiates stud welding from other fastening processes is that the fastener is attached to the workpiece without marring the other side. This method provides highly reliable fastening for a wide variety of applications and allows almost any size or configuration of a metal stud to be welded quickly to a workpiece while providing maximum weld penetration and reliability.

Drawn arc stud welding provides excellent welding success under a broad range of conditions. It produces a full cross-sectional weld, forming a bond that is stronger than the surrounding metal. This section examines its quality, productivity, and cost advantages, including improved weld strength; aesthetic appeal; ample design freedom, faster, easier manufacturing with fewer steps, labor savings, and fabrication savings. A weld produced by the drawn arc process offers a variety of benefits, including high structural integrity, excellent productivity, leak resistance, and corrosion resistance, as well as creating a joint that is less susceptible to loosening from noise and vibration.

Benefits Of Using Drawn Arc Stud Welding Products

Size And Penetration

When dealing with diameters ranging from 1/4 inches to 1 inch, drawn arc stud welding is an excellent process to use (there are exceptions, but they require a more specialized setup.) For rugged or critical applications, most designers, manufacturers and weld engineers want excellent penetration.

When compared to typical wire or stick welding, which ranges from 100- 300 and 200- 600 amps, respectively, drawn arc welding begins at 400. With a range that easily goes to 2,000 amps, drawn arc brings a lot of power to the table. The energy from drawn arc welding means excellent penetration into the base material. Penetrations of 1/8 - 1/4 inch are not uncommon with this process, making designers, manufacturers and weld engineers alike satisfied. More importantly, your customers on the final end are pleased because they have a high-quality finished product.

Low Installation Costs

When considering a fastening solution, it is important to consider overall total costs. This breaks down into three factors:

• Speed: The process of drawn arc stud welding is fast. When production times are important, then drawn arc stud welding is a reliable choice, with arc times ranging from .250 to 1.25 seconds.
• Fewer Manufacturing Steps: Drawn arc stud welding eliminates punching, drilling, tapping and riveting. With special techniques, it permits welding on painted surfaces, eliminating the need for pre-grinding and recoating, as well.
• Labor Savings: Labor costs are dramatically reduced with drawn arc stud welding because through-hole preparation is eliminated, allowing a single worker to complete the process.

Single Sided Fastening Process

The single-sided fastening process is important in several scenarios, such as:

• Difficult Accessibility To Reverse Side: If the reverse side is difficult to reach, as in the case of a large item such as earth-moving equipment, a building, or a bridge.
• Leak Proof Fastening: If the application requires leak-proof fastening. If applying this process to a liquid-filled container, like transformers, or welding on ships and tankers, this is a critical benefit to drawn arc welding.
• Added Security: Because of the single-sided nature of stud welding, it is excellent in tamper-proof applications because there is no visible fastener to remove or destroy, making this an excellent security factor.
• Aesthetics: Since the fastener is not seen from the appearance side; it is often chosen with aesthetics in mind when manufacturers want to showcase their product.

As you can see, drawn arc stud welding is an appropriate practice where heavy-duty materials are necessary. The durability, cost-effectiveness and speed of application all make this a reliable and preferred fastening method.

When To Use Drawn Arc Stud Welding

There are many different applications that use drawn arc stud welding. In general, this is the equipment and the process used for ¼-inch to 1-inch diameter studs. These studs are fast to install, vibration resistant, and strong and durable. The process of arc stud welding includes the use of a ceramic ferrule against the workpiece and around the stud. This ferrule is removed after the stud welding process.

Industrial Applications

For example drawn arc welding is most commonly used in:

Construction & Bridges

This includes embedded plates in precast concrete construction and when composite construction is used in the decks of steel buildings and bridges.

Construction & Agriculture Equipment

Weld studs are often used in the manufacturing of all types of equipment where vibration and heavy-duty operation are a factor. Threaded weld studs and tapped weld stud bosses are used to mount items to the structure, as well as to route cables and hoses. Stud welding can also be used in the manufacturing of hydraulic cylinders used on such equipment.

Electrical

Power distribution systems, electrical enclosures, and switchgear all benefit from drawn arc stud welding. Many of these applications require a leak proof joint. Stud welding fills that need perfectly.

Shipbuilding

Drawn arc welding is used widely in shipbuilding; specialized alloys such as Inconel and HY80 are often specified to boost corrosion resistance or to maintain hull integrity.

What To Know About Drawn Arc Systems

There are three main components in today’s drawn arc stud welding equipment:

Power Source

Today’s power sources (excluding doors and storage compartments) typically only have a few mechanical components:

• Cooling Fans
• Contactors
• Switches/buttons/knobs

Cabling

There are four main cables involved with stud welding systems:

• Incoming Power: provides electrical power to the stud welding system.
• Weld Cable: carries the welding current from the power source to the stud gun.
• Ground Cable: carries the welding current from work back to the power source.
• Control Cable: carries the trigger and lift signals from the power source to the stud gun.

Stud Gun

This part of the system holds the fastener to be welded, automatically strikes the arc, and is critical to the success of the weld.

These components have various maintenance needs. The arc stud welding power source, since it has few mechanical components, rarely needs maintenance. Recommended maintenance would be to blow out the inside of the power source annually. Dust and dirt can be drawn into a power source and land on electronic components. This dust and dirt trap heat in the components. Heat causes the majority of problems with power sources. By blowing out the dust annually, it is not unusual to get 20 years of life from a stud welding power source. Some power sources have demand fans; this is a fan that only operates when internal components are hot enough to require it. Other power sources have fans that run all the time. Power sources that have fans that run all the time will require more frequent cleanings as they draw in more dirt and dust. It is also a good idea to locate power sources away from grinding and other debris-generating operations.

The cables can quickly be visually inspected. While simple to maintain, they are critical in the success of the drawn arc stud welding process. If any cuts are noticed, or any bare cable or fraying is evident, then the cable should be replaced. Each operator should quickly inspect his/her own cable set up to ensure safe operation. Exposed incoming, weld, or ground cables can be life-threatening. The best policy is to replace those cables immediately. Control cable damage is a common source of stud weld system failure. Replacing the control cable at the first sign of damage will ensure maximum system uptime.

Finally, the stud Gun is the system component that should receive the most frequent maintenance. The gun is primarily mechanical. Those mechanical systems and the ease and speed at which they move are critical to the success of the weld joint. Too often, tools (guns) are not maintained and components bind or drag and cause poor welds. For heavy users (500,000 studs/year), a quarterly tear-down clean, inspect and replace maintenance program is recommended. For normal use (250,000 studs/year), tear down every six months is recommended, and for lighter users, annual tear down is recommended.

If these simple maintenance steps are followed, your stud weld system will operate reliably for many, many years.

Rules Of Thumb For Success In Drawn Arc Stud Welding

There are several questions surrounding how to properly set up a drawn arc stud weld machine. Where does one start? What is the proper setup? That said, there are several rules of thumb that can help a welder get to the right setup values.

There are two pieces of stud welding equipment to set up, and each area has two important parameters that need to be dialed in specific to the weld stud being used:

1. The Gun (stud welding tool)

• Lift
• Plunge

2. The Power Supply

• Time
• Current

Now it’s important to look at each parameter, starting with the gun. For the welding gun, there typically are acceptable parameters based on the type of welding being done.

For general industrial purposes, the following parameters provide good starting values:

Industrial Settings

• Lift: 3/32in (.093in/2.5mm) | Plunge 1/8in (.125in/3mm)

For construction uses, such as buildings and bridges, the values change a bit:

Construction Settings

• Bare Beam: Lift 1/8in (.125in/3mm) | Plunge 1/4in (.25in/6mm)
• Through Deck: Lift 1/8in (.125in/3mm) | Plunge 3/8in (.37in/9.5mm)

The second parameter involves the power supply. The following rules of thumb are helpful:

Amperage

• Use 100 amps of current for every 1/16in of diameter. For example: ¾ stud = 12/16 so 12 x 100 = 1200 amps

Time

• Use the decimal equivalent of the stud diameter (in inches) as the time. For example: ¾ stud = .750 inches -- Use .750 seconds as the time

For steel with higher carbon content, such as A36, use 10% greater settings for both time and current.

While these rules of thumb will get you close to the proper settings, it is ultimately up to the operator to tweak the parameters to the ideal settings for your project.

Welding Aluminum With The Drawn Arc Process

Drawn arc welding aluminum studs is challenging, although it can be done. Compared to steel and its alloys, aluminum has a narrower tolerance for setup and weld parameters. Once you find acceptable parameters, even small drifts of those parameters can cause the process to fail.

Like aluminum CD stud welding, the material must be adequately prepared and cleaned. Oxides and oils can interfere with successful aluminum stud welding. Cleaning the surface with a stainless steel brush will remove the oxide layer. After brushing, wiping down with a non-VOC cleaner is recommended.

Using drawn arc with aluminum weld studs requires a shielding gas. The most commonly used is 100% Argon (Ar). However, Ar/Helium (He) mixes (25% to 75% He) and 100% pure He can also be used. He has greater arc ionization energy as well as thermal conductivity. This results in more significant heat at the weld zone benefiting aluminum stud welding. In most facilities performing welding, Ar is readily available, and He is not, so most users settle for 100% Ar. If you find yourself having trouble with 100% Ar remember that an Ar/He mix is an available option.

It is also critical that the correct accessories are used for stud welding Aluminum. The most successful aluminum stud welding uses ceramic ferrules as well as shielding gas. There are specialized foot pieces that distribute the shielding gas as well as hold the ceramic ferrule around the aluminum weld stud. Image Industries has the necessary accessories to meet your aluminum arc welding applications. Another consideration is the stud tip design. Aluminum studs should have an extra “tip” on the end. This small-sized extra tip burns away rapidly. Once the tip has burned away, the arc length is effectively longer than it would have been otherwise. The longer arc length creates a higher voltage at the weld, which increases the heat in the weld zone.

The final appearance of a drawn arc welded stud will not be as aesthetically pleasing as a steel stud weld. Also, the visual indicators common to steel stud welding do not apply. The flash ring around the base of an aluminum stud is not a good indicator of weld quality. The best way to verify quality welds is to bend test or torque test pre-production samples. Once optimum parameters have been determined, it is recommended that periodic in-process checks be performed to ensure that the weld quality is maintained.

Speak With Image Industries About Drawn Arc Stud Welding Products

As you can see, drawn arc stud welding is an appropriate practice where heavy-duty materials are necessary. The durability, cost effectiveness and speed of application, all make this a reliable and preferred fastening method. At Image Industries, our customers know that when it comes to stud welding, we are the company of choice for equipment, service and insight.