Page 43 - MetalForming May 2015

The benefits are especially true when compared to solid wire, which many consider to be the industry stan- dard. Conversions from solid wire to metal-cored wire can support the push toward greater productivity, in partic- ular, by way of faster travel speeds and higher deposition rates—as much as 20-30 percent more.
Metal-cored wire, a tubular filler metal containing metallic powders and alloys, carries higher current densities than solid wire of the same diameter (at equivalent amperage settings), due to its structure. This allows for more weld material to be placed in a joint in less time.
Productivity benefits provided by metal-cored wire, however, aren’t just found in the weld cell. This filler metal also provides advantages throughout the pre- and post-weld areas of many welding operations.
Repeatability In the Weld Cell
In any robotic welding cell, repeata- bility is key. The robot must produce the same weld over and over—and quickly—to provide the best quality in the shortest amount of time. Whether it’s in today’s automotive applications, driving toward lighter, thinner, stronger materials that can meet upcoming fuel requirements, or in a shop producing lower-volume parts, accuracy is non- negotiable.
When paired with metal-cored wire, robotic welding can offer key benefits directly in the weld cell, namely, a broad arc that can bridge gaps and provide a smooth weld-bead appear- ance; arc stability and minimal weld- pool turbulence, resulting in better deposition efficiency; and consistent arc starting and wire feeding for high weld quality.
While metal-cored wire excels with a standard spray-transfer process for materials thicker than 1⁄16 in., when welding thinner parts, such as auto- motive engine cradles or frames, pair- ing this filler metal with a modified short-circuit process is necessary. This
combination provides the best quality and travel speeds on flat and horizon- tal welding positions. It also minimizes subsurface porosity that may occur when welding materials such as galva- nized steel, and helps lower heat input to reduce the risk of burnthrough.
When welding with metal-cored wires in out-of-position applications, pulsed-welding programs are neces- sary to control the fluidity of the weld pool. Consult with a trusted filler-metal manufacturer or welding distributor for options, as certain American Weld- ing Society classifications of metal- cored wire perform better in these applications than others. Metal-cored wire paired with a pulsing program offers benefits when welding in-posi- tion, too, particularly with robots offer- ing seam-tracking capabilities. The pulsing action shortens the arc, making the weld puddle more manageable and lowering heat input into the part.
Consider packaging and wire diam- eter when implementing metal-cored wire into a robotic-welding applica- tion. Look for payout drums that feed the wire with the appropriate cast so that it feeds smoothly and makes a consistent connection with the con- tact tip to provide the best arc-starting. Depending on material thickness, wire diameter can be increased, which allows the robot to place a greater amount of weld metal into the joint in a shorter period of time.
Using a heavy-duty contact tip, such as a chrome-zirconium, helps ensure top performance from metal-cored wire. These tips better withstand the high vol- ume of wire passing through for longer periods of time than standard-duty con- tact tips. That means less downtime for changeovers, which helps support the greater productivity sought with metal- cored wire when paired with a robot.
Greater Efficiency in
Pre- and Post-Weld Areas
In robotic-welding operations— regardless of the industry—many activ- ities occur in the pre- and post-weld
areas. These range from pre-cleaning of the base material and applying anti- spatter before welding to removing spatter and powder-coating parts after. In many cases, metal-cored wire can eliminate some of these steps.
Activities such as tacking parts or loading fixtures, of course, are simply non-negotiable in the pre-weld area. To obtain the best quality, these must be addressed appropriately. Because metal-cored wire has added deoxidiz- ers, alloys and arc stabilizers, however, it generates very little to no spatter and can weld through some contaminants. These advantages reduce the time and cost for antispatter application, as well as the time needed to clean spatter from fixtures, flooring and the robot. It also minimizes the amount of post- weld grinding and sandblasting.
By removing such pre-weld activi- ties, companies operating robotic- welding systems can then reduce the associated time, labor and costs in this area of the welding operation and send parts straight to the weld cell.
In the post-weld area of a robotic- welding operation, metal-cored wire offers some of its best advantages— namely, it can reduce cleanup and rework. Because metal-cored wire offers good gap bridging and a smooth weld bead, and reduces instances of burnthrough, weld quality typically is quite high when coming out of the robotic-welding cell, with less need for rework.
By eliminating these activities, com- panies can increase the flow of com- pleted parts to other stages of produc- tion, such as painting or coating, to improve overall productivity. Also pos- sible: lower labor costs and faster return on investment by reallocating labor elsewhere in the welding operation to gain even higher productivity levels.
Because the goal of any robotic- welding operation is to have high arc- on time and high quality to drive pro- ductivity, it is important to look at all facets of the application—the weld wire included. MF
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