Welding Positioner

Remember the COG
Selecting the right positioning device for the job involves accounting not only for the weight and size of the weldment, but also for the center of gravity (COG) and how far it is from the positioning device. COG is the point at which the weldment balances on all axes equally. As the distance increases from the device, more torque is applied to the positioner. The COG changes as the welder adds material and parts to the positioner, so these changes must be taken into account.
The table rotates by a variable-speed electric motor and can be hand- or foot-controlled. The positioner motor and control should be selected based on the size and speed that are required to perform the desired welding operation.
The positioner manufacturer’s specifications will guide the motor and control choice. It’s important for welders to check the specifications for both horizontal and vertical loading to make sure capacity is adequate to handle the weldment. The positioner should be able to withstand the largest possible load.

Attach Weldment Correctly
How a weldment is attached to a positioning device is as important as the positioner itself, because this is the point where separation would naturally occur. Production fixtures are designed for a specific application performed repeatedly. This type of fixture is mounted permanently to the positioner, and its specific shape allows for easy part alignment.
Round parts often are attached by a three-jaw chuck. The part must not pull away from the jaws when the part extends from the table. Also, the part may expand or contract from the heating and cooling that occur during and after the welding process, which can change the grip that the chuck has on the workpiece.
Fixtures and chucks add weight and distance from the faceplate, which needs to be considered when sizing the positioning device. While the weight of a weldment applies torque to the device, the distance that weight is applied multiplies the torque by the increase in distance. For example, a 50-lb. weldment that is 3 inches away from the face of the positioning table creates 12.5 ft.-lbs. of torque in the vertical position. If the distance is increased to 6 in., the torque increases to 25 ft.-lbs. at the mounting surface. The increased torque may require a larger-capacity machine.
Many positioners have slots that allow the workpiece to be bolted to the face. Welding the part to the positioner is often a good way to prevent shear forces from sliding the part as it is maneuvered. Any of these methods, whether stand-alone or combined, will work if applied properly.

Use Turning Rolls for Cylinders
If a weldment is cylindrical, it is eligible to be rolled. Small turning rolls—powered or idler type—can rotate a pipe or vessel to enable downhand welds. The power rolls provide steady rotation, producing an even circumferential weld. Idler rolls are not powered but can be added in series to support longer pipes and vessels. Often these are used for adding flanges to pipe ends and connecting pipes and ends to vessels.
The combination of a roller-type pipe stand and a vertical-faced table positioner provides stability and safety when a round part is extended outward. When the rollers provide two points of contact, the weight is distributed evenly, and the COG can be supported.

Keep It Flat
Even with small positioning equipment it is important that the unit be mounted to a flat, even surface to prevent it from tipping. If mounting holes are provided, they should be used to secure the positioner to a stable surface to prevent tipping when or if it encounters an unexpected force. A positioner mounted to a workbench or stand must be secured as well.

Connect Ground Current to the Positioner
During welding, a ground current should be connected to the positioner itself. The ground current transfers from the table and into the chassis, which eliminates having to remove and replace a welding clamp continuously. Without proper grounding, electrical parts can be damaged and substandard weld deposits made.
The positioner should be compatible with the electric current produced by the welding process. Also, all ground cables must be secured tightly by removing any paint before bolting to the carriage.

Site Preparation

Choose a location for the welding positioner that provides sufficient space for safe operation and easy access. Ensure that the floor is level and can support the weight of the positioner.

Unpacking and Inspection

Carefully unpack the welding positioner and inspect it for any shipping damage. Check for all the components listed in the user manual.

Positioner Placement

Place the welding positioner in the desired location. If it is a large or heavy unit, use appropriate lifting equipment to move it into place.

Leveling

Use a level to ensure that the welding positioner is perfectly level. This is critical for accurate and stable positioning during welding.

Securing the Positioner

Once leveled, secure the welding positioner to the floor using appropriate anchors or fasteners. This step is essential for stability and safety during operation.

Power Connection

Connect the welding positioner to the power source according to the manufacturer’s specifications. Ensure that the power supply meets the equipment requirements.