Is it possible to weld cast alloy

Postweld heat treatment, even if limited to aging alone, will restore some of their properties if the proper filler alloy has been used in welding. Aluminum forms an oxide layer on the surface, which can contaminate the weld. An AC power source switches the polarity of the arc between positive and negative.

When the polarity of the arc is positive, current flows from the work surface towards the electrode producing a cleaning effect that blasts the oxide away from the surface. When the arc switches back to negative, energy flows from the electrode to the work surface producing heat that melts the metal.

By increasing or decreasing the duration of the positive or negative phase of the AC cycle, the cleaning and welding characteristics of the arc can be modified. Some TIG welders have a "squarewave" control feature that allows the electrode negative EN portion of the AC cycle to be increased up to 90 percent.

By increasing the negative phase the AC cycle provides greater heat penetration, faster welding and narrows the weld bead.

It also allows the use of a smaller diameter tungsten electrode to more precisely direct the heat in a confined area. Reducing the negative phase of the cycle produces greater cleaning action to remove heavier oxidation, and reduces heat penetration when welding thin castings. These advances largely resulted from using "inverter-based" power sources, which permit controlling the arc in ways never before possible, i. There are no hard rules about setting balance control, but the typical error involves over-balancing the cycle.

Too much cleaning action electrode positive or EP causes excess heat build-up on the tungsten. This creates a very large ball on the end of the tungsten electrode. Subsequently, the arc loses stability and the operator loses the ability to control the direction of the arc and the weld puddle.

Arc starts begin to degrade as well. On the other hand, too much electrode negative results in too much penetration and a scummy weld puddle.

If the puddle looks like it has black pepper flakes floating on it, add more cleaning action EP to remove oxides and other impurities. Inverter-based welders let operators adjust the welding output frequency from 20 to Hz. Conventional welders have a fixed output of 60 Hz.

Decreasing frequency produces a broader arc cone, which widens the weld bead profile and better removes impurities from the surface of the metal. It also transfers the maximum amount of energy to the work piece, which speeds up applications requiring heavy metal deposition as when filling a large crack or void in a casting.

Increasing frequency produces a tight, focused arc cone. This narrows the weld bead, which helps when welding in tight spots. The operator can direct the arc precisely at the crack and not have the arc dance from side to side. And, very importantly, operators can use a pointed tungsten, which further improves arc control and bead shape. A good starting point for general welding, would be 80 to Hz. These frequencies will be comfortable to work with, increase control of the arc direction and boost travel speed.

For a fillet weld application with full penetration in the weld without putting too much amperage in the metal, increase the frequency to to Hz. For build-up work, start at 60 Hz and adjust lower from there. Independent amperage control of the EN and EP portions of the AC cycle, allows the operator to direct more or less energy into the work piece, as well as take heat off the tungsten. For example, when welding a thick piece of aluminum, the operator can put amps of EN into the work and only 60 amps of EP into the tungsten.

This provides faster travel speeds, faster feed of filler rods, deeper penetration, and the potential to eliminate preheating. Some companies have cut production time by up to two-thirds using this technology. Independently increasing EN amperage while maintaining or reducing EP amperage also provides the following: narrows the arc cone, nearly eliminating the etched zone at the toes of welds With the new technology directing heat into the work, not the tungsten, straight Argon alone may suffice.

Independently increasing EP amperage while maintaining or reducing EN amperage produces a wider arc cone, wider bead and shallower penetration. No strict guidelines for setting independent EN and EP current values have been established because it is such new technology.

Start with practice pieces and experiment to find the values that work best for a particular application. Frequency control is another area where advances have been made.

The AC arc in a traditional, rectifier-based TIG welder is prone to stumbling, wandering and outages, all of which lead to poorer weld quality. These symptoms usually occur during the EN to EP transition because the welder does not have enough voltage to drive through the zero amp range and then reestablish the arc at the electrode, or because the welder cannot transition through the zero amp range quickly enough.

To improve arc starts and arc stability, a traditional GTAW machine superimposes high frequency HF on the AC sine wave to form a path for the arc to follow as it crosses the zero amp range. As a result, one control switch on the front panel typically lets the operator select between "HF off," "HF start only" or "HF continuous. As a result, HF interferes with electronics such as that used in CNC machines, computers and other electronically controlled equipment that may be in the shop.

An inverter eliminates the need for continuous high frequency to maintain the arc, as well as and the cost of purchasing a separate high-frequency module. It can also minimize or even eliminate the need for HF on start-up. View the Digital Edition.

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Tube and Pipe Production. I am definitely going to try that. A: amperage was set to either and I used a foot pedal. I would guess I was at about for the thick section and amps for the thinner areas.

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