Unit: Gas Metal Arc Welding




НазваниеUnit: Gas Metal Arc Welding
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Дата конвертации09.10.2012
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Slide # 25: Transformer

  • The transformer in a power supply is a step-down transformer that takes high-voltage, low-amperage AC input supplied from power companies and changes it to low-voltage, high-amperage AC welding current.

  • For example, your input power may be 230 volts on a 50-amp branch circuit. This voltage is much too high and the amperage is much too low for welding applications. The transformer takes this condition and reverses it to a much lower voltage, in the range of 13-45 volts (most applications 15-35 volts) and increases the amperage to a much higher level appropriate for welding.

Slide # 26: Reactor

  • From the transformer, the electricity goes to a control that stabilizes and adjusts the welding current. This is called the reactor.

  • The reactor can be a tap reactor that selects amperage ranges to weld with. A tap reactor “taps” into segments of the secondary of the transformer and provides step control. This is the least expensive means of controlling welding output.

  • Another reactor is a moveable iron reactor. This is generally done by keeping the windings in the transformer stationary, and moving a piece of iron between the windings to control amperage. A moveable iron reactor provides continuous step-less control of amperage.

  • A saturable reactor or Silicon Controlled Rectifier (SCR) can also be used and also provides a continuous step-less control for more precise control of welding output. An SCR is an electrical control that uses a low voltage, low amperage, DC circuit to change the effective magnetic characteristics of the reactor core.

  • In a power supply that delivers only AC to the arc, these are the internal electrical components of the power supply. We now need to discuss how we convert AC to DC, which is the current primarily used in arc welding.

Slide # 27: Bridge Rectifier

  • In power supplies that deliver DC and/or AC current to the arc, there needs to be a device that changes this now low-voltage, high-amperage AC into DC.

  • This device is called a rectifier. A rectifier converts AC to DC. They are very efficient and very reliable.

  • A rectifier is a device that allows current to flow in only one direction.

  • If we remember the path that AC takes, it takes one of a sine wave path. This represents one cycle in which current flows in one direction for ½ of the cycle and stops at the zero line, then reverses it’s direction of flow for the other ½ cycle. This cycle repeats itself over and over again at a frequency of 60 Hz or 60 times a second in the United States.

  • A rectifier does not allow current to reverse itself. It only allows current to flow in one direction. In essence, it directs current in the same direction rather that allowing it to change direction. This is called direct current of DC. The direction of current flow determines whether the polarity is DC+ or DC-.

Slide # 28: Inductance Coil

  • We often call the current coming out of a rectifier “choppy” or rippled DC. In other words, the path of current is not as smooth as it could be and therefore, the arc characteristics are not as smooth as they could be.

  • A device is placed inside power supplies to correct this problem. This device is called an inductance coil, which is sometimes called a choke or stabilizer. The main function of the choke is to smooth out the rectified rippled DC and therefore, smoothes out the DC arc characteristics.

  • RLC circuits share the responsibility for smoothing the arc. When inductance is added, energy is drawn from the stored energy in the RLC circuit.

Slide # 29: Basic Transformer - Summary



  • To review the components of a transformer designed power supply, we have the following taking place:

  • Power companies supply a high-voltage, low-amperage AC current to our shops and homes. This is the input power supplied to the welding power source.

  • This high-voltage, low-amperage AC enters the transformer where it is converted to a low-voltage, high –amperage AC suitable for welding.

  • A reactor is a device that allows control of the welding amperage and comes in many forms such as tap selectors, moveable irons, and SCR type controlled machines.

  • If the power supply delivers AC only to the welding arc, this completes the majority of the electrical components.

  • However, if the power supply also delivers DC, a rectifier is added to allow current to only flow in one direction, literally changing AC to DC.

  • Finally, an inductance coil or choke filters out this rippled DC and a smooth DC is delivered to the welding arc.

Slide # 30: Basic Electricity

Video

  • Basic Electricity Video

Slide # 31: Gas Metal Arc Welding

Inverter Technology

  • GMAW title slide for Inverter Technology.

Slide # 32: Inverter Technology



  • The state-of-the-art AC and/or DC transformer power source is an inverter. There are several advantages of inverters over traditional transformer designed power supplies, which will be discussed later. There are also a few concerns or limitations of inverters that will also be discussed.

  • The design of an inverter is more complex than that of a traditional power supply with more components and electrical circuitry. The illustration is a block diagram depicting the 6 main components of an inverter.

Slide # 33: Rectifier



  • The input power coming in to the inverter power supply is again, alternating current or AC as produced by power companies. It is of high-voltage and low-amperage, and is not suited for welding. The frequency is 60 Hz in the United States and 50 Hz in many foreign countries.

  • In an inverter based power supply, this input power is immediately passed through a rectifier. Remember that a rectifier is a device that only allows current to flow in one direction, and in essence changes AC to DC.

  • This DC is rippled or not smooth and is still high-voltage and low-amperage, which is not suitable for welding.

Slide # 34: Filter


  • This rippled DC is next passed through a filter to smooth it out. This has the same effect as the choke or inductance coil in the basic transformer designed machine.

  • This power is still of high-voltage and low-amperage and is not suitable for welding as of yet.

Slide # 35: IGBT

  • The next component of an inverter is a device that identifies and distinguishes an inverter from a basic transformer designed machine.

  • This component is a high-speed switching device and can come in many forms that include Field Effect Transistors (FETs), Insulated Gate Bipolar Transistors (IGBTs), and Darlington switches.

  • An IGBT requires an incoming DC signal. The IGBTs elevate the frequency to levels such as 20,000 Hz as found in all Lincoln Electric inverters.

  • They supply pulsed DC current to the main transformer primary windings. Each switch board feeds current to a separate, oppositely wound primary winding of the main transformer. The reverse direction of current flow through the main transformer primaries and the offset timing of the IGBT switch boards induce an AC square wave output signal at the secondary of the main transformer.

Slide # 36: IGBT - Insulated Gate Bipolar Transistor

  • The IGBT or high-speed switch is what makes an inverter what it is and what it does.

  • The DC coming out of a IGBT is at 20,000 Hz but is still high-voltage and low-amperage, and not suitable for welding yet.

  • You might be asking yourself, “What is the advantage of an elevated frequency?” This will be discussed later.

Slide # 37: Iron at 200,000 Cycles

  • As seen on this illustration, transformers operating at higher frequencies are lighter and more efficient.

  • Inverters are a fraction of the size of a transformer-based machine, which makes them excellent choices for portable or maintenance welding machine.

  • Due to the fact that the transformers are more efficient in an inverter, and heat losses are at a minimum, the size of the transformer is much smaller cooling fans are much smaller, and power consumption is less.

  • This concept is not a new one. As seen on the slide, this theory was discovered back in 1911.

Slide # 38: Iron at 200,000 Cycles

  • This chart, again, from 1911, shows how efficiency greatly increases in a transformer as the frequency of operation increases. It also shows how the size of the transformer decreases accordingly.

Slide # 39: Transformer

  • Going back to the remaining components of an of an inverter, from the IGBTs, the rest of the inverter greatly resembles that of a basic transformer machine.

  • From the IGBT, we have AC at 20,000 Hz, at high-voltage, low-amperage.

  • This is passed through a step-down transformer to change this AC to low-voltage and high-amperage at 20,000 Hz.

  • Due to the efficiency of the process attained through high frequency, transformers are very small and compact when compared to basic machines.

Slide # 40: Rectifier

  • The next component is a rectifier. A rectifier only allows current to flow in one direction (changes AC to DC).

  • The DC that comes out of the rectifier is rippled or not as smooth as it can be. It is also of low-voltage and high-amperage.

Slide # 41: Choke

  • From the rectifier, the rippled DC goes to the choke (or inductance coil) that smoothes out the DC at low-voltage and high-amperage so that it is suitable for welding.

  • The DC is extremely smooth and smoother than that of a standard transformer, due to the elevated frequency used in an inverter.

Slide # 42: Inverter Technology - Summary

  • This completes the internal components of an inverter from input power to extremely smooth DC welding current.

Slide # 43: Inverter Technology - Benefits


  • The following slide highlights the major advantages of an inverter based power supply.

Slide # 44: Inverter Technology

Video

  • Inverter Technology Video

Slide # 45: Gas Metal Arc Welding

Chopper Technology

  • GMAW title slide for Chopper Technology.

Slide # 46: Chopper Technology



  • One type of state-of-the-art DC power source is a chopper. There are several advantages of choppers over traditional transformer designed power supplies, which will be discussed later. There are also a few concerns or limitations of choppers that will also be discussed.

  • Chopper Technology is a trademark of the Lincoln Electric Company.

  • The design of a chopper is more complex than that of a traditional power supply with more components and electrical circuitry. The illustration is a block diagram depicting the 6 main components of a chopper machine.

Slide # 47: Transformer

  • The input power coming in to the chopper power supply is again, AC as produced by power companies. It is of high-voltage and low-amperage, and is not suited for welding. The frequency is 60 Hz in the United States and 50 Hz in many foreign countries.

  • The transformer transforms the high-voltage and low-amperage into low-voltage and high-amperage which is more suitable for welding.

  • Chopper technology is not limited to static machines. It can also be found in Lincoln Electric's engine drive line. The AC sent to the rectifier in this case comes from a three-phase alternator.

Slide # 48: Rectifier



  • In a chopper based power supply, this input power is immediately passed through a transformer and then sent to a rectifier. Remember that a rectifier is a device that only allows current to flow in one direction, and in essence changes AC to DC.

  • This DC is rippled or not smooth and is not suitable for welding.

Slide # 49: Filter


  • This rippled DC is next passed through a filter (capacitor) to smooth it out. This has the same effect as the choke or inductance coil in the basic transformer designed machine.

Slide # 50: IGBT

  • The next component of a chopper is a device that identifies and distinguishes a chopper from a basic transformer designed machine.

  • This component is a high-speed switching device and can come in many forms that include, IGBTs, and Darlington switches.

  • An IGBT requires an incoming DC signal. The IGBTs elevate the frequency to levels such as 20,000 Hz as found in all Lincoln Electric choppers. The difference between an inverter power source and a chopper power source is that in an inverter, the IGBTs are placed before the primaries of the main transformer while in a chopper they are placed after the secondaries of the main transformer.

Slide # 51: IGBT - Insulated Gate Bipolar Transistor

  • The IGBT or high-speed switch is what makes an inverter what it is and what it does.

  • The DC coming out of an IGBT is at 20,000 Hz. It differs from an Inverter because the DC coming out of the IGBT is now low-voltage and high-amperage.

  • You might be asking yourself, “What is the advantage of an elevated frequency?” This will be discussed later.

Slide # 52: Inductor and Diode

  • From the IGBT, the rippled DC goes to the inductor and diode assembly where current is shared between these units and the IGBT. It acts to smooth out the DC at low-voltage and high-amperage so that it is suitable for welding.

  • The DC is extremely smooth and smoother than that of a standard transformer, due to the elevated frequency used in a chopper.
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