Post-Processing of weld seams

There is several reasons for post-processing of weld seams. Work piece can set a mechanical, hygienic, or appearance requirements for the weld seams, so the post-treatment is necessary.

With post-processing you can improve the corrosion resistance of the weld seam by removing impurities from the surface caused by welding, oxide, and surface below prone to corrosion.

So what kind of abbrasives should be used? Use high quality abrasives because they are more durable and cost-effective. High quality abrasives delivers real productivity benefits across your

operation without the premature dulling associated with traditional abrasives.

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Welding Tips: Checking the equipment before starting the welding

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

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

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.

Creep start

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 preset 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.

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.

Text source: Kemppi

MIG/MAG welding: Principles and Applications

Welding: Principles and Applications is a good book about welding that we recommend.

MIG/MAG welding: General

In MIG/MAG welding, an arc is created with the power supply through the welding gun between the welding wire being fed and the work piece. The arc fuses the material being welded and the welding wire, thus creating the weld. The wire feeder continuously feeds welding wire through the welding gun throughout the welding process. The welding gun also provides shielding gas to the weld.

The MIG and MAG welding methods differ from each other in that MIG (metal inert gas) welding uses an inert shielding gas, which does not participate in the welding process, while MAG (metal active gas) welding employs an active shielding gas that participates in the welding process.

Usually the shielding gas contains active carbon dioxide or oxygen, and therefore MAG welding is by far more common than MIG welding. In fact, the term MIG welding is often accidentally used in connection with MAG welding.

Text source: Kemppi

Why do we need different welding methods?

Welding methods can be classified by the method used in producing the welding heat and the way the filler material is fed into the weld. The welding method used is selected based on the materials to be welded and the material thickness, the required production efficiency and the desired visual quality of the weld.

The most commonly used welding methods are MIG/MAG welding, TIG welding and manual metal arc welding. The oldest, most known and still fairly common process is manual metal arc welding, which is commonly used in installation workplaces and outdoor sites that demand good reachability.

The slower TIG welding method allows for producing extremely fine welding results, and therefore it is used in welds that will be seen or that require particular accuracy.

MIG/MAG welding is a versatile welding method, in which the filler material need not be separately fed into the molten weld. Instead, the wire runs through the welding gun surrounded by the shielding gas straight into the molten weld.

There are also other welding methods suitable for special needs, such as laser, plasma, spot, submerged arc, ultrasound and friction welding.

Text source: Kemppi

TIG-Welding: Efficient welding

TIG welding is usually used when the welding quality requirements are high or the material thickness is particularly low. In this case, the production of the weld material is often low and the welding speed does not grow to a large figure. TIG welding can, however, be enhanced in a variety of ways.

The melting power can be increased by integrating the wire feeder into the torch or by moving from cold wire technique to hot wire technique. The production of the weld material may increase by up to 200% when moving to hot wire welding. In the cold wire technique, the melting of the filler material commits part of the effect of the arc and reduces the production of the weld material. In the hot wire process, however, the filler material wire is heated with a separate power source and the production of the weld material increases.

Using activating paste improves welding speed and increases the penetration. When activating PATIG paste is spread on the weld spot, the area of the arc becomes smaller and the density of the current in the anode point increases by 150% to 200%. The paste is comprised of a powder and binding acetone that can be spread with a brush or as a spray. The applications include sheet wheels, pressurised containers and material thicknesses 3–12 mm (I groove with one burn).

The selection of the shielding gas can affect the fusing and penetration of the basic material. The most commonly used shielding gas in TIG welding is Argon. Its benefits are its low price and good shielding effect combined with the ignitability of the arc. Its weakness is its poor thermal conductivity and the subsequent potential problems in the smooth fusing of the weld. The fusing can be improved by adding 5–25% hydrogen to the shielding gas. This will also reduce the area of the arc and increase the penetration.

Using helium as the shielding gas allows for good merging of the filler with the basic material and produces good penetration. However, its weakness is in the poor ignitability of the arc. This can be improved by using a mixture of helium and argon.

TIG-welding: Processes

AC/DC

TIG welding methods are classified according to the welding current to DC TIG and AC TIG for direct current and alternating current, respectively. TIG welding power sources are suitable for both current types (AC/DC) or for only DC welding.

DC welding is typically used in welding a variety of metals. Alternating current must, however, be used in aluminium welding.

If current mixed of both direct and alternating current is used in TIG welding, the method is called MIX TIG welding. It is a particularly useful method when welding aluminium materials of different thicknesses together.

Pulsed TIG

In Pulse TIG welding, the power source pulses the welding current, which reduces the heat effect affecting the material being welded. This is useful particularly when welding thin materials in which the TIG heat input is great. Pulse welding also improves the manageability of the molten weld pool and the penetration.

The Kemppi Mastertig MLS welding machines, for example, allow for using the so-called synergic pulse TIG feature in which the pulse parameters are programmed in the machine and the user only needs to adjust the welding current.

Text source: Kemppi

TIG-welding: Technique

TIG welding is used in sites where the appearance, quality and cleanness of the weld are important. This presents special requirements for the accuracy of the welding job. Additionally, TIG welding is more demanding because there are more issues to control in this welding technique than in the other techniques. In TIG welding, the torch is moved with one arm while the other feeds the filler material to the molten weld. A TIG welder must, therefore, accurately control both arms and one cannot be used for supporting the torch as in MIG/MAG welding.

These special requirements make TIG welding more difficult particularly in the beginning. However, the arms will soon adjust to the paths of motion required in welding and TIG welding becomes routine. Yet, demanding TIG welding is usually done by a welder who specialises in TIG welding.

TIG welding is done with a pushing torch motion. The filler can be fed into the weld either drop by drop or continuously, keeping the filler wire constantly in the molten weld.

Text source: Kemppi

TIG-Welding: Equipments

TIG welding equipment comprises a power source, grounding cable, welding torch and shielding gas bottle or gas network connection. The machine may also contain a liquid cooling unit. A wire feeder is not required as the filler material is manually fed.

Text source: Kemppi

TIG-Welding: Applications

The most important applications for TIG welding are pipeline and pipe welding. It is, however, used in many industries, such as aviation and aerospace and sheet metal industries when welding particularly thin materials and special materials such as titanium. TIG welding is suitable for both manual and mechanised welding as well as for using welding robots.

Text source: Kemppi

TIG-Welding: General

In TIG welding (Tungsten inert gas), the welding arc is formed between a non-consumable tungsten electrode and the work piece. The shielding gas is an inert gas that does not affect the welding process per se. Usually the shielding gas is argon and it protects not only the molten weld but also the electrode in the torch from oxygenation.

A filler material may not be necessary in TIG welding. The pieces can be fused also by melting the groove together. If a filler is used, it is fed into the molten weld manually and not through the weld torch as in MIG/MAG welding. Therefore, the TIG welding torch has a completely different structure than a MIG/MAG torch.

Various TIG welding methods include, for example, the DC TIG welding method that uses direct current, AC TIG welding that utilises alternating current, and pulse TIG.

Text source: Kemppi

Mig Welding Uphill Technique