Rotary geared tilting turntable welding positioners provide motion in two axes. The fixture work piece sits on a rotating turntable that rocks or tilts. The basic styles are a flat-135 degrees weld positioner that tilts the geared turntable from horizontal through vertical to 45[degrees] past vertical and a welding positioner that tilts from 90[degrees] forward through horizontal to 45 degrees backward. A flat-135degrees model is mounted on legs to provide enough clearance above the floor for the load to travel through vertical..
Welding turning rolls, which support fabrications weighing from a few hundred pounds to 1,000 tons, for rotating cylindrical objects such as tanks and pressure vessels for making circumferential welds. To make longitudinal welds, fabricators mount the welding head on a travel carriage. Some welding fabricators equip pipe turning rolls with special fixturing to hold non-cylindrical assemblies. Power turning rolls come in sets with a powered turning roll called a driver and one or more idler rolls. Their simplistic design promotes a low initial cost and keeps maintenance and repair costs low.
Headstock positioners have fixed vertical tables that rotate the assembly between the head and tail stock tables, head-tailstocks handle enormous weights. They rotate a vertical table about the horizontal axis, providing access to all sides of large weldments. The headstock is powered the tailstock is not. Some welding fabricators mount head- and tail-stocks on rails to allow an operator to adjust the distance between the two units. They may also mount small items, elbows or flanges in the headstock alone. Selecting the proper capacity of a head stock, consider the torque needed for the largest rotating weldment to be mounted, this dictates the required torque to accurately start and stop rotation without speed variation. This is a concern particularly when positioning weldments with components located far from the center of rotation, which creates excessive torque that can strain the positioner drive and gearing.
A drop center welding positioners, is a two-axis unit, comprises a beam running across and below the center points of a positioner setup. The part to be welded fits below the center of rotation of the positioner used to rotate the part. These are used positioners for handling odd-shaped bulky parts such as tank turrets and components of off-road vehicles.
The welder adjusts the welder positioner arm angles of balanced weld positioners, usually not powered, so that weldment center-of-gravity lines up with its axis of rotation. These rotating turntable positioners serve for fabrications that are too heavy to fixture welds conveniently but not big enough to require a powered tilt turntable positioner.
Welding positioners have charts giving weight load capacities at various centers of gravity for distances (usually at 4, 6 and 12" intervals), rotational speed ranges, and constant operating speeds. Many suppliers offers positioners with load capacities from 100 lbs. to 350 tons with tables from 12 to 60". diameter; square or round tables run from 12 to 96 in. along sides. Capacities of its tank turning rolls range from 2,000 lbs. to 350 tons. Head-and tailstock capacities run from 3 to 100 tons, and welding turntable capacities from 3 to 200 tons.
Fabricating shops use platen tables and modular fixtures the clamping, aligning, and fixturing parts to the welding table.
Platens are rigid cast-iron grids mounted on steel stands. Square holes, typically 1 3/4 in. square on 3 1/2-in. centers, position tooling and accessories. Tooling includes hold-down dogs for clamping and straightening; tapered pins for posts; and bending posts for bending rod and tube. Other platen tooling includes bolt-down arm clamp: for vises or C-clamps; nut-and-bolt assemblies for holding parts; U-clamps for gripping pipe and tube; riser blocks for holding parts at levels above the platen surface; magnetic clamps for alignment; and vertical- and horizontal-slide damps for quick-action clamping.
Modular fixtures come with a three-dimensional work table that provides a platform on which welders mount a variety of angles, blocks, and fixturing accessories. The tables, made of high-tensile-strength steel and ribbed to ensure stability and flatness typically to within 0.0004 in./ft, come in several sizes to use alone or joined.
Fixture elements match a holes-and-grid pattern on the table. Positioning and clamping bolts attach fixtures, work piece positioners, and other elements to the work tables, or to each other. Clamps include toggle clamps and threaded damps that feature a compensating mechanism that applies the clamping force perpendicular to the thread.
Fabricators select among two methods to automatically load sheet and plate onto fabricating equipment such as turret-punch presses and laser-cutting machines. These two methods can be termed work-envelope loading, where the sheet loads directly into the work envelope of the machine, and non-work-envelope loading, where material is loaded away from the work envelope of the machine.
An example of work-envelope loading is a sheet loader used on a turret-punch press---when removing and sorting parts coming off of the machine and loading a new work piece onto the press, the machine is idle, so this type of material-handling setup can limit production-run time. A non-work-envelope loader such as a pallet changer or dual-table shuttle system enables a laser-cutting machine to process one work piece while a second worktable is unloaded of cut parts and loaded with a new work piece.
Automated welding systems have the benefit of allowing less skilled workers to operate the automatic welding machines. Automatic welding requires precision part fit up. The cost for the tooling to do this is costly. The end benefit for customers ROI of weld fixture tooling can be short tern investment. The investment then allows fabricators to hire less skilled workers to preform welding tasks. The only machine downtime with this type of material-handling arrangement is during pallet change, as little as 30-60 seconds.