Feb. 06, 2024
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DC welding is a welding process that uses a direct current electrical supply to produce an electric arc between the welding electrode and the metal workpiece. This arc produces heat that melts the metal and creates a weld.
DC welding is commonly used for welding ferrous metals such as mild steel, cast iron, and stainless steel, as well as some non-ferrous metals such as aluminum and copper alloys. It is widely used in a variety of industries, including construction, shipbuilding, automotive, and aerospace.
One of the key advantages of DC welding is that it allows for precise control of the welding parameters, such as voltage, amperage, and electrode position, which results in high-quality welds with minimal defects. This makes it suitable for a wide range of welding applications, from general fabrication to critical structural welding.
In addition, DC welding is often preferred for its ability to produce smooth, uniform beads with minimal spatter, which helps to reduce cleanup time and increase overall efficiency. The DC welding process also produces a stable arc that is easy to control, making it ideal for welding in tight spaces or on thin materials.
There are two main types of DC welding: DC electrode negative (DCEN) and DC electrode positive (DCEP). In DCEN welding, the electrode is negatively charged and the workpiece is positively charged, while in DCEP welding, the electrode is positively charged and the workpiece is negatively charged.
DCEN welding is often used for welding thin materials, as it produces a more stable and focused arc that helps to reduce the risk of burn-through. On the other hand, DCEP welding is more commonly used for welding thicker materials, as it produces a hotter and more penetrating arc that is better suited for penetrating into the base metal.
DC welding is also used in a variety of specialized welding applications, including stick welding, tungsten inert gas (TIG) welding, and metal inert gas (MIG) welding. In stick welding, a welding electrode is held in the welder's hand and used to produce the electric arc. In TIG welding, a tungsten electrode is used to produce the arc, and the welder uses a separate filler rod to add metal to the weld joint. MIG welding uses a continuously fed wire electrode to produce the arc and add metal to the weld joint.
In conclusion, DC welding is a versatile and reliable welding process that is widely used in a variety of industries due to its precise control, efficient operation, and high-quality results. Whether used for general fabrication or specialized welding applications, DC welding is an essential tool for welding professionals and metal workers. For more information, please contact us. We will provide professional answers.
TIG-200P-AC/DC AC Aluminum TIG Welder
The TIG-200P-ACDC TIG Welder with Pulse offers the versatility to meet the needs of both hobbyists and professional welders, and is especially suitable for welding aluminum using AC TIG and Pulsed AC TIG welding modes.
This is a 200A welder that requires accessories such as an electrode positioning system, arc voltage control, oscillator, and seam tracking device. This welder is used for welding in both semi-automatic and automatic versions. The materials used in tungsten rods are argon gas and filling wire. Argon was used as shielding gas.
It features a range of pulse functions for high performance including 200 amp AC (starting current 10 to 200) or DC TIG welding and a viscous function
Digital Indicator: Displays actual and preset amperage, improving accuracy and repeatability of the welding process
Equipped with AC square wave TIG welding, AC pulse TIG welding, DC pulse TIG welding, DC pulse TIG welding and rods.
This digitally designed AC/DC TIG welding machine uses the most advanced inverter technology.
The machine is capable of using AC or DC welding. You can choose DC welding to weld carbon steel, stainless steel, copper, and many other metals. At the same time, it can be switched to AC welding for welding aluminum and aluminum alloys.
When welding in this mode the TIG welding torch is connected to the positive output of the welding inverter and the work return cable to the negative output.
When the arc is established the current flows in the circuit and the heat distribution in the arc is around 33% in the negative side of the arc (the work piece) and 67% in the positive side of the arc (the welding torch).
This means the electrode is subjected to the highest heat levels and therefore must be much larger than with DCEN mode even when the current is relatively low to prevent the electrode overheating or melting. The work piece is subjected to the lower heat level so the weld penetration will be shallow.
This method of connection is often referred to as reverse polarity.
Also, with this mode the effects of magnetic forces can lead to instability and a phenomenon known as arc blow where the arc can wander between the materials to be welded. This can also happen in the DCEN mode but is more prevalent in the DCEP mode.
It may be questioned what use is this mode when welding. The reason is that some non ferrous materials such as aluminium on normal exposure to atmosphere form an oxide on the surface.This oxide is created due to the reaction of oxygen in the air and the material similar to rust on steel. However this oxide is very hard and has a higher melting point than the actual base material and therefore must be removed before welding can be carried out.
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The oxide may be removed by grinding, brushing or some chemical cleaning but as soon as the cleaning process ceases the oxide begins to form again. Therefore, ideally it would be cleaned during welding. This effect happens when the current flows in the DCEP mode when the electron flow will break down and remove the oxide. It could therefore be assumed that DCEP would be the ideal mode for welding these materials with this type of oxide coating. Unfortunately because of the exposure of the electrode to the high heat levels in this mode the electrodes size would have to be large and arc penetration would be low.
The solution for these types of materials would be the deep penetrating arc of DCEN mode plus the cleaning of DCEP mode. To obtain these benefits AC welding mode is used.
When welding in AC mode the current supplied by the welding inverter operates with either positive and negative elements or half cycles. This means current flows one way and then the other at different times so the term alternating current is used. The combination of one positive element and one negative element is termed one cycle.
The number of times a cycle is completed within one second is referred to as the frequency. In the UK the frequency of alternating current supplied by the mains network is 50 cycles per second and is denoted as 50 Hertz (Hz)
This would mean that the current changes 100 times each second. The number of cycles per second (frequency) in a standard machine is dictated by the mains frequency which in the UK is 50Hz.
It is worth noting that as frequency increases magnetic effects increase and items such as transformers become increasingly more efficient. Also increasing the frequency of the welding current stiffens the arc, improves arc stability and leads to a more controllable welding condition.
However, this is theoretical as when welding in the TIG mode there are other influences on the arc.
The AC sine wave can be affected by the oxide coating of some materials which acts as a rectifier restricting the electron flow. This is known as arc rectification and its effect causes the positive half cycle to be clipped off or distorted. The effect for the weld zone is erratic arc conditions, lack of cleaning action and possible tungsten damage.
Arc rectification of the positive half cycle
The Sine Wave
The sinusoidal wave consists of the positive element building up to its maximum from zero before falling back to zero (often referred to as the hill).
As it crosses zero and the current changes direction towards its maximum negative value before then rising to zero (often referred to as the valley) one cycle is completed.
Many of the older style TIG welders were only sine wave type machines. With the development of modern welding inverters with increasingly more sophisticated electronics came development on control and shaping of the AC waveform used for welding.
The Square Wave
With the development of AC/DC TIG welding inverters to include more electronics a generation of square wave machines was developed. Due to these electronic controls the cross over from positive to negative and vice versa can be made almost in an instant which leads to more effective current in each half cycle due to a longer period at maximum.
The effective use of the magnetic field energy stored creates waveforms which are very near square. The controls of the first electronic power sources allowed the control of a ‘square wave’. The system would allow control of the positive (cleaning) and negative (penetration) half cycles.
The balance condition would be equal + positive and negative half cycles giving a stable weld condition.
The problems that can be encountered are that once cleaning has occurred in less than the positive half cycle time then some of the positive half cycle is not productive and can also increase potential damage to the electrode due to overheating. However, this type of machine would also have a balance control which allowed the time of the positive half cycle to varied within the cycle time.
Maximum Penetration
This can be achieved by placing the control to a position which will enable more time to be spent in the negative half cycle with respect to the positive half cycle. This will allow for higher current to be used with smaller electrodes as more
of the heat is in the positive (work). The increase in heat also results in deeper penetration when welding at the same travel speed as the balanced condition.
A reduced heat affected zone and less distortion due to the narrower arc.
Maximum Cleaning
This can be achieved by placing the control to a position which will enable more time to be spent in the positive half cycle with respect to the negative half cycle. This will allow for very active cleaning current to be used. It should be noted that there is an optimum cleaning time after which more cleaning will not occur and the potential of damage to the electrode is greater. The effect on the arc is to provide a wider clean weld pool with shallow penetration.
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