Methods that are used today for joining coil ends for various strip processes,

Methods that are used today for joining coil ends for various strip processes.

Through the years, the art and science of coil joining has greatly changed. As technology has advanced and the use of programmable logiccontrollers (PLCs) has increased, the degree of automation and the repetitiveness of weld parameters have brought about coil joiners that are truly automated and require no operators. Before discussing the truly automated units, this article will first review the various methods that are used today for joining coil ends for various strip processes, such as stamping lines, roll formers, tube and pipe mills, and continuous process lines.


     TIG Welding
Tungsten inert gas (TIG) welding is a process in which the two coil ends are sheared square and generally butted tightly together. A torch with a tungsten electrode is then traversed across the

material.

An arc is ignited between the electrode and the material. The material melts together and then solidifies, creating a “cast” weld This process is generally used for the following:

• Material ....…….Most weldable alloys,    copper, brass, aluminum, steel, stainless steel
• Thickness …...,.. .006 inch to .200 inch
• Welding speed .. .90 inches per minute (IPM) to 6 IPM

TIG welds are usually very close to the same strength as parent metal, and since no filler wire is used, the weld is approximately the same thickens as parent metal.


     TIG Applications
Typical applications for TIG welding coil ends include stamping presses, roll form lines, traverse winding lines, small tube mills, coil buildup lines, and rolling mills for the nonferrous industry. Since the weld is usually very close to parent metal thickness, it can generally pass through die and forming rolls without damage to these items. Also, quite often, the weld can be sent through are ducing mill without failure.


     MIG Welding
In the metal inert gas (MIG) welding process, the two coil ends are generally aligned with a slight gap between them. Instead of a tungsten electrode, the torch uses a wire which is fed from a spool. The wire is actually melted and fills into the gap. It also fuses with the parent metal of both coil ends.
MIG welding is generally used with the following application:

• Material …......……. Hot-rolled steel, stainless steel
• Thickness …...,……. .030 inch to .750 inch
• Welding speed .......  70 IPM to 15 IPM

 Depending on weld over-thickness and the material being joined, MIG welds can be 80 to 95 percent of parent metal strength. Compared to TIG, MIG is much faster, and strip fitup is generally not quite as critical.

Also, since a filler wire is added to the joint, there is usually a buildup in the weld area. This buildup can range anywhere from 5 to 90 percent of parent metal thickness. MIG welding applications are generally found in large tube and pipe mills; annealing, pickling, and coil buildup lines for the stainless steel industry; and certain continuous process lines, such as heavy-gauge galvanizing.

If a very simple, fast weld used for transport only is required, an overlap MIG weld can be made. The weld would have to be cut out at the exit end of the line.

     Plasma Welding
Plasma welding is similar to TIG in that wire is usually not inserted into the weld joint, and the two coil ends are tightly butted together. The arc is actually passed though a plasma, gas heated to a high temperature. This produces a small cylinder-type arc instead of the come-type arc created by TIG. This results in better penetration, faster weld speeds, and narrower heat-affected zones (HAZs).

The plasma process can be used on the following:

•  Material …........ Most weldable alloys
• Thickness …...... .015 inch to .280 inch
• Welding speed ... 30 IPM to 8 IPM

Most plasma welding systems are found in stainless steel strip processing lines and on some nonferrous applications. Because no wire is generally used and the strength of the weld can be quite high, this process can be used for coil buildup, even if re-rolling (reducing) will be required.

     Laser Welding
The process of laser welding can uses the same coil end locating

procedures as the TIG welding process, with more attention to precise fit of the butted coil ends. A laser welding head containing a focusing lens and a shielding gas nozzle is rapidly traversed across the coil ends. Infrared energy, the same wavelength, produced by the sun, is supplied from a welding head, where it is focused to a .006-inch to 0.12-inch spot.

The resulting narrow weld will be the closest to parent metal strength of any of the welding processes. The small HAZ and ideal weld bead geometry from the laser weld gives the best forming results of any of the joining processes. As with TIG welding, no filler wire is required.

Current coil joining equipment uses CO, lasers in the 1- to 6-kilowatt power range. It can be used on the following:

• Material ....…….....Most ferrous metals
• Thickness ……….006 inch to .300 inch
• Welding speed …240 IPM to 40 IPM