13th Week Unanswered Terms
1-Effects of Welding Speed at Welding: The effect of increasing the welding speed for the same current and voltage is to reduce the heat input. The welding speed does not influence the electromagnetic force and the arc pressure because they are dependent on the current. The weld speed increase produces a decrease in the weld cross section area, and consequently penetration depth (D) and weld width (W) also decrease, but the D/W ratio has a weak dependence on travel speed . These results suggest that the travel speed does not influence the mechanisms involved in the weld pool formation, it only influences the volume of melted material. Normal welding speeds are from 100 to 500 mm/min depending on current, material type and plate thickness.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.33)
2- Filler Metals for Welding: Filler metals are generally used for plate thickness above 2 mm, having chemical composition similar to that of the parent material. Filler metal diameter is between 1.6 and 3.2 mm and in automatic systems is normally added cold from a roll or a coil.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.34)
3-Electrode Diameter for Welding: Chemical composition of the electrodes is similar to that of the materials being welded. Most usual electrode diameters are 0.8, 1, 1.2 and 1.6 mm. Electrodes of lower diameter are used for thin materials. Electrodes of 1.2 and 1.6 mm diameters are utilized in welding thicker materials and need higher currents, which produce larger weld pools. Electrodes of 1.6 mm diameter are not recommended for positional applications.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.43)
4-Welding Gases for Laser Welding: In laser welding two gases are commonly needed, the assisting gas to remove plasma, which is injected laterally, and a coaxial shielding gas to prevent atmospheric contamination. A root gas is also needed in keyhole welds where all the material thickness is melted. Helium and mixtures of argon and helium are used as welding gases. Argon shields the weld metal and helium is required to control the plasma formation in CO2 laser welding. If Nd:YAGs are used for welding, the plasma formation is not an aspect of major concern and argon is the recommended welding gas. Small additions of oxygen, hydrogen or CO2 can be used depending on material and process to increase productivity further. Helium, argon or mixtures of these gases are used for most materials, including reactive metals such as titanium or zirconium. For reactive materials the shielded area must be increased, because they are sensitive to air contamination down to low temperatures (400 ºC). Nitrogen can also be used for welding stainless steels in less demanding applications.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.52)
5-Welding Force for Resistance Spot Welding: The increase of the welding force reduces contact resistance because, in first analysis, it promotes the increase of contact area, due to deformation of surface asperities and eventually the rupture of surface oxide films. Electrode clamping forces must be high, particularly when welding low resistivity metals in order to reduce the proportion of heat generated in the interface electrode/workpiece.Electrode force must be increased with increasing current, unless part of the melted material of the nugget can be expelled. Other factors such as bad fit and lack of mechanical support contributes for the material expulsion. Distance of the weld to the edge of the sheets should be larger than 1.5 D, where D is the weld diameter. Excessively high forces are also undesirable because they can cause large surface indentation of the work-pieces and damage of the electrodes.Electrode clamping force increases with increasing thickness and strength of the work-pieces. Forces between 1000 and 15,000 N are usual for plate thicknesses up to 3 mm, though values of 20,000 N can be used in steel sheets 6 mm thick.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.60)
6-Non-consumable Electrodes: Non-consumable electrodes are composed of pure tungsten or of tungsten alloys.Pure tungsten electrodes can be used with DC but are more sensitive to contamination, have lower service life-cycle and exhibit higher tip deterioration than alloyed electrodes. These electrodes can be used in welding of aluminum and magnesium alloys on AC.
Thoriated tungsten (2% ThO2) electrodes are widely used in industrial applications due to its excellent resistance to contamination, easy arc starting and stable electric arc. Concerns about safety, because thorium oxide is radioactive, led to the development of other electrodes containing small proportions (around 2%) of simple earth rare elements such as lanthanum, yttrium and cerium or even mixtures of several elements.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.29)
7-Shielding Gas Regulator for Automatic Welding: The regulator is a device that reduces source gas pressure to a constant working pressure, independently of source pressure variations. Pressure reduction can be made in one or two stages. Regulators in two stages give in general more stable output flow.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.31)
8-Electrode Feed Unit for GMAW: The electrode feed unit and the welding control mechanism are generally furnished in one integrated package. The electrode feed unit pulls the electrode from the reel and pushes it through a conduit to the welding torch (gun). This unit is composed of a direct-current motor, that varies the motor speed over a large range, a gear box and two pairs of rolls with a pressure adjusting screw and wire guides, that transmit mechanical energy , straighten and guide the electrode. Knurled rolls are used for hard materials, such as steel electrodes, and V and U type rolls are used for softer materials, such as aluminum electrodes. For soft electrodes or long conduits pushpull systems can be used too. Theses systems are composed of two feed units, one that is close to the wire reel that pushes the electrode, and the other unit in the torch that pulls the electrode. In automatic and robotic welding systems the electrode is fed from a spool (15-18 kg) or large drum (200-475 kg) to minimize wire supply changing. Normally, the electrode feeder for robotic welding is mounted separate from the power supply.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.39)
9-Arc Striking Techniques for GTAW: Arc initiation by touch striking was used formerly in manual GTAW, but this technique is very sensitive to tungsten contamination, adversely affecting the service life of the electrode. High-frequency-high-voltage (e.g. 3 kV at 5 MHz) supplies are currently used in arc striking and AC arc stabilization in manual GTAW systems. This arc starting technique usually produces interference in electronic equipment in the vicinity of the power source.Programmed touch striking is an alternative technique developed for automatic systems. In this technique current and voltage are limited when electrode touches in the work-piece, in order to prevent electrode contamination. A pilot arc starting can also be used to initiate the main electric arc, though a more complex torch is needed.
(Welding Robots Technology, System Issues and Applications, J. Norberto Pires, Altino Loureiro and Gunnar Bölmsjo,1st edition,P.30)
Ertan Toparlak
503091329
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