Welding tips from Kemppi
15/10/2012 - Welding tips from Kemppi Welding Machines.
Before starting a new welding job, the operating condition of the welding equipment should be inspected. The connections of the power cable, gas tube, grounding cable and welding gun must be checked. It must also be ensured that one is using the right shielding gas type and that the gas output works. The type and diameter of the filler material wire must be checked. Additionally, the appropriate fixing of the wire reel in the wire feeder must be ensured.
After this one must review the feed rolls of the wire feeder engine and make sure that the wire guides and feed rolls are suitable for the filler material and wire diameter used.
The welding gun must be detached from the wire feeder, making sure that the gun’s liner is of correct size and type are correct. The gas nozzle must be detached from the gun and any splashes must be cleaned from it. The condition and size of the contact tip must be checked. Additionally, the gas disperser and contact tip holder must be cleaned.
One can check the shielding gas flow with a rotameter at the end of the welding gun. If the wire is already in the gun, the pressure adjustment screw of the wire feeder engine needs to be detached to prevent the wire from moving, after which one should press the gun trigger and measure the gas flow. The easiest way for checking the flow of the shielding gas is the GAS TEST function, if one is available in the wire feeder. This function only activates the gas flow to the welding gun but does not activate wire feeding.
Welding angle and torch movement (Picture A)
When welding with solid wires or metal-cored wires, the gun is usually moved in pushing angle, with the exception of downward welding and welding of particularly thin sheet metals. In symmetric fillet welding, aim the welding gun has a 45-degree angle to the corner of the fillet and perpendicular to the groove in butt joints.
When welding with flux-cored wires, move the welding gun in pulling angle to prevent the slag generated by the wire from mixing with the molten weld. The arc pressure will keep the slag behind the molten weld. Certain directional welds, such as upward welding, are an exception to this. In this case the welding gun is moved with the handle behind the direction of movement, and earth’s gravity ensures that the slag will not rise above the molten weld.
Welding torch speed (Picture B)
The correct speed of the welding torch is an important factor for successful welding. The speed of motion affects the shape, penetration, heat input and effective throat thickness of the weld. The effective throat thickness refers to the shortest distance from the base of the weld to the surface of the weld.
If the speed of motion is too slow, the molten weld may roll in front of the arc and make the molten weld pool difficult to manage. An excessively high speed, on the other hand, may result in too small penetration and effective throat thickness.
The recommended speed may be provided in the welding instructions. It is, however, difficult to estimate the speed during welding. One way to determine the speed is to weld approximately 10 cm and time it with a clock. This allows for determining the speed as centimetres per minute.
When using high wire feed speeds, it may be difficult to start the welding. A so-called creep start feature has been designed to make the beginning of welding easier.
The creep start feature starts feeding the wire at a low speed and does not attain the pre-set value until the wire touches the work piece and the arc ignites. The creep start adjustment is done in the welding machine’s control panel, if needed.
Hot start and soft start
When welding materials with good thermal conductivity, such as aluminium, it is easy to generate faults in the weld in the beginning. Using the so-called hot-start feature can decrease these. When using the hot-start feature, the welding power momentarily increases at the beginning of the welding to a level above the preset welding power. The power and duration of a hot start can usually be adjusted in the machine’s control panel.
When doing butt welding of sheet metal, the so-called soft-start feature may be useful, as it helps keep the edges of the sheets intact. A soft start is the opposite of hot start. The welding power is momentarily lower than the preset welding power during the start-up of the welding. The power and duration of a soft start can also usually be adjusted.
Adjusting welding parameters
The wire feed speed and the welding current are connected to each other. When increasing or decreasing the wire feed speed, the welding current follows. The arc voltage must be in correct relation to the wire feed speed and the welding current to produce stable welding. Sometimes it may, however, be very difficult to decide which value to change and in which direction to attain a good welding result.
The arc voltage is too low in relation to the wire feed speed, if:
- the sound of the arc is loud;
- there is a lot of spatters;
- the weld is more narrow and the cap is higher.
The arc voltage is too high in relation to the wire feed speed, if:
- the sound of the arc is soft
- the arc is long
- the weld is wider and lower
- the drop size of the filler material is large;
- the risk of undercuts is increased.
There are a number of tables and guides that will assist in producing good welding results. There are also welding machines that automatically determine the correct arc voltage for the wire speed and welding current. Even in those machines, one may need to make adjustments to the arc voltage, as there may be differences between the filler material wires of different manufacturers.
With power sources equipped with stepped voltage adjustment it may not be possible to adjust the voltage to the exact correct figure in relation to the wire speed. In such cases, one can do the fine-tuning by increasing or decreasing the speed of the wire feed.
Common tips for enhancing welding work
There are simple ways for enhancing the welding work. With manually done work stages planned in an appropriate way and designed ergonomically, individual production may experience higher productivity increases than mechanisation would attain.
Pay attention to the working position. The most efficient position to do welding is downhand. In downhand welding, the work piece is placed on a level so that welding can be done in a natural position. Devices intended for turning the work piece should be utilised so that the work piece position allows for an ergonomic welding position.
Downhand welding is efficient
Choosing the right welding process also plays an important role in work productivity. Any productivity increase attained by changing the welding process should be carefully investigated, even if changing the process could require additional investments.
Correct choice of welding parameters affects the efficiency of the welding work and also extra labour expenses. For example, the time spent removing spatters decreases the productivity of welding work. One can reduce the generation of splashes with pulse welding, for example.
For more tips, news and articles please visit Kemppi Welding.
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