MIG

Metal Inert Gas (MIG) Welding: An arc is struck between a consumable electrode and the sheet metal to be welded. The consumable electrode is in the form of continuous filler metal. An inert gas surrounds the arc and shields it from the ambient to prevent oxidation.

Carbon steels, low alloy steels, stainless steels, most aluminum alloys, zinc based copper alloys can be welded using this process.

Tungsten Inert Gas (TIG) Welding: An arc is truck between a tungsten electrode (non-consumable) and the sheet metal to be welded. An inert gas shields the arc from the ambient to prevent oxidation. A filler material is optional

Carbon steels, low alloy steels, stainless steels, most aluminum alloys, zinc based copper alloys can be welded using this process. TIG is quite suitable for welding dissimilar materials, but usual cautions of galvanic corrosion still apply.

The TIG process is a slower process compared to the MIG process, but the quality of weld is cosmetically better. There is no weld spatter, and the quality of welds is higher than MIG welding.

Oxy Acetylene Gas Welding: Acetylene or some combustible gas is combined with Oxygen and the flame heats the sheet metal to be welded. A filler metal rod supplies the molten metal for the joint.

This method is readily available, but the heat can cause distortion in sheet metal. Due to this, this method is being displaced by other methods such as MIG and TIG welding.


Types of Weld Joints
• Butt, T, corner, lap, and T joints are the common types of joints used in sheet metal welding. These can all be used with MIG and TIG welding.
• Corner joints are used frequently in sheet metal cabinet construction.


Wire Mesh Welding Lines
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• Types of welds are often confused with the types of joints. The basic types of welds are fillet, square, and grooved.


Material Thickness and Weld Strength
• MIG welding can be done for thicknesses ranging from 0.5 mm to 6.3 mm (0.020 to 0.250 in). TIG can be used for thicknesses as low as 0.125 mm (0.005 in).
• Weld strength can be upto the strength of the underlying material. To improve overall system robustness it is better to increase material thickness rather than over specifying the weld.


Manufacturing Considerations
• The surface to be welded needs to be clean and degreased and any foreign debris should be removed. In the case of hot-rolled steel or aluminum, wire brushing may need to be done to remove scales and oxides, for the highest quality welds.
• Weld distortion occurs whenever a weld is done. This can be minimized by spacing the weld tacks at least 50 mm (2 in) apart. Welding distortion can also be minimized by fixturing (and clamping) while welding as well as heat sinking.
• Parts should be designed with features that are self-locating with respect to mating parts. This removes the need for dedicated fixtures and its costs. Fixtures also introduce additional tolerances due to deflections imposed on the parts by the clamping pressure. Fixtures can also slow down production due to fact that parts have to be placed in the fixture and clamps (if any) that need to be activated.
• Welds locations should be located with operator access in mind. If it is not accessible to a weld electrode, it is not weldable. Thus, in designs that involve sections such as channels, boxes access of electrodes needs to be considered.
• Tolerancing of welded parts is usually generous. This allows the parts to be welded without too much elaborate fixturing or secondary processing such as grinding. If tight tolerancing is desired, it is best achieved by self-locating features on the mating parts.


Cosmetics Considerations
• MIG welding causes a lot of spatter that needs to be sanded or filed, if cosmetically objectionable. Thus, it is best to avoid MIG welding on exterior surfaces if cosmetics are important. TIG welding is better suited for no spatter welding, even though it is more expensive.
• The parts that are to be welded need to fit well with each other without too large a gap. This is particularly important in fusion welding, where no filler material is used. If too large a gap is used, then excessive shrinkage will take place.


Finish Considerations
• Parts that need painting will require surface preparation in the form of sanding and grinding. The cost of this preparation needs to be considered in the total cost.
• Parts that need to be electroplated should have seams that do not overlap, and not have corners or edges where the plating solutions can be trapped, leading to corrosion in the long term.

A Guide to Aluminum Welding

A Guide to Aluminum Welding
Reprinted courtesy of Welding Design and Fabrication magazine.

Follow the rules of thumb offered here for selecting welding equipment, preparing base materials, applying proper technique, and visually inspecting weldments to ensure high-quality gas-metal-and gas tungsten-arc welds on aluminum alloys.
Even for those experienced in welding steels, welding aluminum alloys can present quite a challenge. Higher thermal conductivity and low melting point of aluminum alloys can easily lead to burnthrough unless welders follow prescribed procedures. Also, feeding aluminum welding wire during gas-metal-arc-welding (GMAW) presents a challenge because the wire is softer than steel, has a lower column strength, and tends to tangle at the drive roll.

To overcome these challenges, operators need to follow the rules of thumb and equipment-selection guidelines offered here...

Gas-metal-arc-welding:
Base-metal preparation: To weld aluminum, operators must take care to clean the base material and remove any aluminum oxide and hydrocarbon contamination from oils or cutting solvents. Aluminum oxide on the surface of the material melts at 3,700 F while the base-material aluminum underneath will melt at 1,200 F. Therefore, leaving any oxide on the surface of the base material will inhibit penetration of the filler metal into the workpiece.
To remove aluminum oxides, use a stainless-steel bristle wire brush or solvents and etching solutions. When using a stainless-steel brush, brush only in one direction. Take care to not brush too roughly: rough brushing can further imbed the oxides in the work piece. Also, use the brush only on aluminum work-don't clean aluminum with a brush that's been used on stainless or carbon steel. When using chemical etching solutions, make sure to remove them from the work before welding.
To minimize the risk of hydrocarbons from oils or cutting solvents entering the weld, remove them with a degreaser. Check that the degreaser does not contain any hydrocarbons.

Preheating: Preheating the aluminum workpiece can help avoid weld cracking. Preheating temperature should not exceed 230 F-use a temperature indicator to prevent overheating. In addition, placing tack welds at the beginning and end of the area to be welded will aid in the preheating effort. Welders should also preheat a thick piece of aluminum when welding it to a thin piece; if cold lapping occurs, try using run-on and run-off tabs.

The push technique: With aluminum, pushing the gun away from the weld puddle rather than pulling it will result in better cleaning action, reduced weld contamination, and improved shielding-gas coverage.

Travel speed: Aluminum welding needs to be performed "hot and fast." Unlike steel, the high thermal conductivity of aluminum dictates use of hotter amperage and voltage settings and higher weld-travel speeds. If travel speed is too slow, the welder risks excessive burnthrough, particularly on thin-gage aluminum sheet.

Shielding Gas: Argon, due to its good cleaning action and penetration profile, is the most common shielding gas used when welding aluminum. Welding 5XXX-series aluminum alloys, a shielding-gas mixture combining argon with helium - 75 percent helium maximum - will minimize the formation of magnesium oxide.

Welding wire: Select an aluminum filler wire that has a melting temperature similar to the base material. The more the operator can narrow-down the melting range of the metal, the easier it will be to weld the alloy. Obtain wire that is 3/64- or 1/16- inch diameter. The larger the wire diameter, the easier it feeds. To weld thin-gage material, an 0.035-inch diameter wire combined with a pulsed-welding procedure at a low wire-feed speed - 100 to 300 in./min - works well.

Convex-shaped welds: In aluminum welding, crater cracking causes most failures. Cracking results from the high rate of thermal expansion of aluminum and the considerable contractions that occur as welds cool. The risk of cracking is greatest with concave craters, since the surface of the crater contracts and tears as it cools. Therefore, welders should build-up craters to form a convex or mound shape. As the weld cools, the convex shape of the crater will compensate for contraction forces.

Power-source selection: When selecting a power source for GMAW of aluminum, first consider the method of transfer -spray-arc or pulse.
Constant-current (cc) and constant-voltage (cv) machines can be used for spray-arc welding. Spray-arc takes a tiny stream of molten metal and sprays it across the arc from the electrode wire to the base material. For thick aluminum that requires welding current in excess of 350 A, cc produces optimum results.
Pulse transfer is usually performed with an inverter power supply. Newer power supplies contain built-in pulsing procedures based on and filler-wire type and diameter. During pulsed GMAW, a droplet of filler metal transfers from the electrode to the workpiece during each pulse of current. This process produces positive droplet transfer and results in less spatter and faster follow speeds than does spray-transfer welding. Using the pulsed GMAW process on aluminum also better-controls heat input, easing out-of-position welding and allowing the operator to weld on thin-gage material at low wire-feed speeds and currents.

Wire feeder: The preferred method for feeding soft aluminum wire long distances is the push-pull method, which employs an enclosed wire-feed cabinet to protect the wire from the environment. A constant-torque variable-speed motor in the wire-feed cabinet helps push and guide the wire through the gun at a constant force and speed. A high-torque motor in the welding gun pulls the wire through and keeps wire-feed speed and arc length consistent.
In some shops, welders use the same wire feeders to deliver steel and aluminum wire. In this case, the use of plastic or Teflon liners will help ensure smooth, consistent aluminum-wire feeding. For guide tubes, use chisel-type outgoing and plastic incoming tubes to support the wire as close to the drive rolls as possible to prevent the wire from tangling. When welding, keep the gun cable as straight as possible to minimize wire-feed resistance. Check for proper alignment between drive rolls and guide tubes to prevent aluminum shaving.
Use drive rolls designed for aluminum. Set drive-roll tension to deliver an even wire-feed rate. Excessive tension will deform the wire and cause rough and erratic feeding; too-little tension results in uneven feeding. Both conditions can lead to an unstable arc and weld porosity.

Welding guns: Use a separate gun liner for welding aluminum. To prevent wire chaffing, try to restrain both ends of the liner to eliminate gaps between the liner and the gas diffuser on the gun.
Change liners often to minimize the potential for the abrasive aluminum oxide to cause wire-feeding problems.
Use a contact tip approximately 0.015 inch larger than the diameter of the filler metal being used - as the tip heats, it will expand into an oval shape and possibly restrict wire feeding. Generally, when a welding current exceeds 200 A use a water-cooled gun to minimize heat buildup and reduce wire-feeding difficulties.

MATERIALS FAILURE ANALYSIS

MATERIALS FAILURE ANALYSIS

Our materials engineers and metallurgists provide independent expert opinions regarding weld or material failure analysis. Forensic investigation of your product failure is accomplished by analyzing and testing materials and welds. Root cause analysis of your weld or material failure can be identified by our failure analysis experts. Features of our product failure analysis capabilities include:

Weld failure analysis Analysis conducted by registered professional engineers Failure mode identification Broad failure analysis experience Fracture evaluations Root cause analysis determination Photographic documentation

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Electron Beam Welding

Electron Beam Welding

Electron Beam Welding (EBW) is a fusion joining process that produces a weld by impinging a beam of high energy electrons to heat the weld joint. Electrons are elementary atomic particles characterized by a negative charge and an extremely small mass. Raising electrons to a high energy state by accelerating them to roughly 30 to 70 percent of the speed of light provides the energy to heat the weld.

An EBW gun functions similarly to a TV picture tube. The major difference is that a TV picture tube continuously scans the surface of a luminescent screen using a low intensity electron beam to produce a picture. An EBW gun uses a high intensity electron beam to target a weld joint. The weld joint converts the electron beam to the heat input required to make a fusion weld.

The electron beam is always generated in a high vacuum. The use of specially designed orifices separating a series of chambers at various levels of vacuum permits welding in medium and nonvacuum conditions. Although, high vacuum welding will provide maximum purity and high depth to width ratio welds.

EBW Benefits Single pass welding of thick joints Hermetic seals of components retaining a vacuum Low distortion Low contamination in vacuum Weld zone is narrow Heat affected zone is narrow Dissimilar metal welds of some metals Uses no filler metal EBW Limitations High equipment cost Work chamber size constraints Time delay when welding in vacuum High weld preparation costs X-rays produced during welding Rapid solidification rates can cause cracking in some materials

Common EBW Concerns

We can help optimize your welding process variables. Evaluate your current welding parameters and techniques. Help eliminate common welding problems and discontinuities such as those listed below:

EBW Problems and Discontinuities

• Undercutting

• Porosity

• Cracking

• Underfill

• Lack of fusion

• Shrinkage voids

• Missed joints

Robotic Welding

Robotic Welding
There are two popular types of industrial welding robots. The two are articulating robots and rectilinear robots. Robotics control the movement of a rotating wrist in space. A description of some of these welding robots are described below:

Rectilinear robots move in line in any of three axes (X, Y, Z). In addition to linear movement of the robot along axes there is a wrist attached to the robot to allow rotational movement. This creates a robotic working zone that is box shaped.

Articulating robots employ arms and rotating joints. These robots move like a human arm with a rotating wrist at the end. This creates an irregularly shaped robotic working zone.


There are many factors that need to be considered when setting up a robotic welding facility. Robotic welding needs to be engineered differently than manual welding. Some of the consideration for a robotic welding facility are listed below:

* Accuracy and repeatability
* Number of axes
* Reliability
* Fixtures
* Programming
* Seam tracking systems



* Maintenance
* Controls
* Weld monitors
* Arc welding equipment
* Positioners
* Part transfer

A robotic welding system may perform more repeat ably than a manual welder because of the monotony of the task. However, robots may necessitate regular recalibration or reprogramming.

Robots should have the number of axes necessary to permit the proper range of motion. The robot arm should be able to approach the work from multiple angles.

Robotic welding systems are able to operate continuously, provided appropriate maintenance procedures are adhered to. Continuous production line interruptions can be minimized with proper robotic system design. Planning for the following contingencies needs to be completed:

* Rapid substitution of the inoperable robots.
* Installing backup robots in the production line
* Redistributing the welding of broken robots to functioning robots close by

Stick Welding

Stick Welding

Shielded Metal Arc Welding (SMAW) is frequently referred to as stick or covered electrode welding. Stick welding is among the most widely used welding processes. The flux covering the electrode melts during welding. This forms the gas and slag to shield the arc and molten weld pool. The slag must be chipped off the weld bead after welding. The flux also provides a method of adding scavengers, deoxidizers, and alloying elements to the weld metal.

Stick Welding Benefits Equipment used is simple, inexpensive, and portable Electrode provides and regulates its own flux Lower sensitivity to wind and drafts than gas shielded welding processes All position capability Common Stick Welding Concerns We can help optimize your welding process variables. Evaluate your current welding parameters and techniques. Help eliminate common welding problems and discontinuities such as those listed below: Weld Discontinuities Undercut Incomplete fusion Porosity Slag Inclusions Cracks Stick Welding Problems Arc Blow Arc Stability Excessive spatter Incorrect weld profile Rough surface Porosity

MIG Welding

MIG Welding Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding. MIG welding is a commonly used high deposition rate welding process. Wire is continuously fed from a spool. MIG welding is therefore referred to as a semiautomatic welding process.

MIG Welding Benefits All position capability Higher deposition rates than SMAW Less operator skill required Long welds can be made without starts and stops Minimal post weld cleaning is required MIG Welding Shielding Gas The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool. There are three primary metal transfer modes: Spray transfer (MP3 Audio) Globular transfer (MP3 Audio) Short circuiting transfer (MP3 Audio) The primary shielding gasses used are: Argon Argon - 1 to 5% Oxygen Argon - 3 to 25% CO2 Argon/Helium CO2 is also used in its pure form in some MIG welding processes. However, in some applications the presence of CO2 in the shielding gas may adversely affect the mechanical properties of the weld.

Common MIG Welding Concerns

We can help optimize your MIG welding process variables. Evaluate your current welding parameters and techniques. Help eliminate common welding problems and discontinuities such as those listed below:

Weld Discontinuities Undercutting Excessive melt-through Incomplete fusion Incomplete joint penetration Porosity Weld metal cracks Heat affected zone cracks

MIG Welding Problems

• Heavily oxidized weld deposit
• Irregular wire feed
• Burnback
• Porosity
• Unstable arc
• Difficult arc starting