Frame welding station for switchgear and enclosure frames: a reconfigurable clamping bed for 500 to 1000 mm panel widths and two arc-welding robots

01

One clamping bed for 500, 650, 800 and 1000 mm panels

A single switchgear range already calls for four frame widths: ABB builds its UniGear ZS1 air-insulated switchgear, rated up to 24 kV, in panel widths of 500, 650, 800 and 1000 mm, as single-busbar, double-busbar or back-to-back and double-level versions. [1] A station that serves such a range is reset between widths rather than rebuilt.

A patent from the 28th Research Institute of China Electronics Technology Group describes one way to do this for the welded profile frames of equipment shelters, which it says are large, precise and made in small batches of multiple varieties. A porous grey cast-iron welding platform carries an array of holes that double as air connections. Clamping modules (a flat mounting seat, a 90° rotary clamping cylinder and a 7-shaped pressure head) and positioning modules (a mounting seat, a high-thrust double-shaft double-rod cylinder and an L-shaped reference seat) are pinned to the platform where each frame needs them, and quick-connect air lines link them to 24 V solenoid valves below. [2]

In the same patent a PLC with a touch screen stores the clamping scheme for each frame drawing; for a new drawing the operator divides the frame into separately controlled clamping zones on the screen and sets the order in which they close, and the stored scheme is recalled the next time that frame is made. The patent contrasts this with dedicated tooling, which it calls costly to build and hard to dismantle when changing over, and with manual clamping, which it links to measuring errors and poor frame flatness. [2]

List every frame size the station must take (width, depth, height), the profile section and thickness, how the frame is located (datum corner, holes in the profile), and the target changeover time between sizes.

02

Distortion and coating burn-off on hollow frame profiles

In a patent on frame pieces for switchgear cabinet racks, CES Control Enclosure Systems sets out why it avoids a weld seam to close its hollow profiles. The local heat input that melts the joint introduces thermal stresses that can distort the profile and change the material structure at the seam, so extra steps may be needed to realign it. The weld also burns off coating applied to the flat starting material, locally destroying it and possibly impairing the electrical conductivity and corrosion resistance of the frame. [3]

The same effects apply wherever a station welds frame joints in coated profile. Editorial note: ask the station supplier how the weld sequence and clamping hold squareness and diagonal size while the joints cool, how the frame is checked after release, and how the coating is repaired at the welds and earthing continuity is kept across welded joints.

A switchgear frame also has to hold the panel together in service: ABB states internal arc classification A-FLR for UniGear ZS1 and short-time withstand currents up to 63 kA for the single-busbar version. [1] Editorial note: such ratings belong to the type-tested panel design, so a welded frame should follow the joint details, profile and weld sizes of the design that was tested.

Give the supplier the profile material and coating, the allowed diagonal and flatness tolerance of the welded frame, and the joint details from the panel drawing.

03

Two arc-welding robots either side of the bed: reach and torch access

Yaskawa's AR1440 is one example of an arc-welding robot sized for such cells: six axes, 12 kg payload, 1440 mm horizontal reach and 2511 mm vertical reach on a YRC1000 controller. Yaskawa states that its slim, contoured arm allows dense robot placement and avoids fixture interference, its symmetric wrist gives equal torch access to both sides of a part, and a 50 mm through-hole in the arm carries the torch cable. [4]

Editorial calculation: for a 1000 mm-wide frame, the widest ABB ZS1 width, with one robot on each long side, each robot must weld to the frame's centreline 500 mm in. With 1440 mm horizontal reach, the robot base axis can then be at most 1440 − 500 = 940 mm from the near edge of the frame, before allowing for torch length, torch angle and the height of the joint. [1] [4] Joints on the upper rails of a full-height frame sit higher still, so check reach against the tallest frame, not only the widest.

The clamping modules on the bed are also obstacles for the torch: the CETC patent places pressure heads and reference seats at each clamping and positioning point, so the clamping scheme and the robot paths have to be planned together for each frame size. [2]

Ask for a reach study of the largest frame with the clamps in place, showing every joint reached at the required torch angle.

04

Frame sizes, profiles and joints for the welding station quotation

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Frames: [panel widths, depths, heights; number of variants]
Profiles: [section; thickness; material; coating]
Joints: [corner and rail joints; weld type and size from drawing]
Tolerances: [diagonal; flatness; squareness after release]
Clamping: [datum points; modules per size; changeover time]
Robots: [number; reach study; torch access]
Output: [frames per shift; loading and unloading]

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