CNC Gantry Spot Welding Machine for Large Stainless Steel Panels

A Stainless Panel A Few Dozen Welds Deep: The Head Goes To The Coordinates, The Operator Only Slides It In

Application story  ·  CNC gantry spot welding of large stainless panels - motorised head travel over a copper bed, pneumatic Z, one program per panel

On a panel this size the weld points sit where a hand gun cannot reach comfortably: the middle of a sheet two metres long, four hundred millimetres in from the edge, repeated down the length. So they get marked out with a rule and a scriber, and then they get welded wherever the operator's eye says the mark is - one panel to the next, a millimetre or two of variation, and nobody can tell until the assembly does not fit. A gantry works the other way round. The panel goes down once, the coordinates come out of a program, and the head travels to them.

CNC gantry spot welder: four-column steel frame, motorised carriage on the top beam, pneumatic welding head, copper bed, mobile control cabinet with touch screen

The Part: One Big Sheet And A Lot Of Small Joins

The panel is a long stainless sheet, and the parts welded to it are small: stiffener plates, hat-section brackets, a folded support near each end. Individually none of them is difficult. What makes the job awkward is where they sit - well inside the sheet, far from any edge the operator can lean over, and in a pattern that repeats along the length.

A hand gun on a cable reaches those points one at a time, and every one of them costs the same three things: a mark to aim at, a posture to get the gun square, and an electrode that has to be dressed after enough of them. A gantry takes those three costs out of the cycle instead of reducing them - the aim is the program, the square-ness is the guide rods, and the electrode is dressed on a schedule rather than when the welds start looking tired.

Panels on the bed: long stainless sheets with stiffener plates and hat-section brackets welded on the inside face, located by blocks on the fixture plate

The Copper Bed Is The Lower Electrode

There is no lower electrode arm on this machine. The bed is covered with a copper plate, and the panel lies directly on it, so the return current has the whole sheet to travel through and the whole plate to leave from. That single decision is what makes a gantry practical for large work: a conventional spot welder needs a lower electrode under every point, which on a two-metre panel means either moving the part or building a very long arm that flexes.

The copper plate is a consumable, and it is treated as one. Every weld leaves a small pit where the current leaves the sheet, so the plate is skimmed or replaced on a schedule, and the program is written to keep points from landing repeatedly on the same spot. What the plate gives back is a flat, fully supported surface for the whole panel - no part of it bounces, no part of it is unsupported when the electrode comes down.

The bed seen from the operator side: copper surface, fixture plate on its rails, welding head above and one of the two drag chains following the carriage

X By Rack, Z By Air

The carriage runs on the top beam on a linear guide, driven by a servo through a helical rack. Rack and pinion rather than a ballscrew is deliberate on a travel this long: a screw of that length whips and sags, while a rack is stiff for the whole stroke, and the position is held by the servo and the guide rather than by a screw's critical speed. The result is that the head arrives at the same coordinate at the near end of the beam and at the far end.

Vertical motion is pneumatic, not servo. The head slides on four chrome guide rods with a cylinder in the middle, which gives a short, stiff stroke and a press force set by regulator rather than by a motor's torque limit. On thin stainless that matters: the point has to be pressed flat before the current flows, and the force has to be the same at every point, or the visible face shows it. Current reaches the head through a short copper busbar dropped from the beam, and both the busbar and the electrode holder are water-cooled from an external chiller.

The head and its cable carrier: four guide rods around the cylinder, brass electrode below, copper busbar and cooling lines coming down from the beam

The Fixture Plate Runs In On Rails

Loading happens outside the gantry. The fixture plate travels on two linear guides set into the bed, so it pulls out to where a person can stand over it, the panel is laid on the locating blocks, and the plate is pushed back under the head. The blocks decide where the panel sits, which means the weld coordinates in the program are relative to the fixture and not to how the operator happened to place the sheet that morning.

The working height is set for standing work, and the control cabinet rolls on castors so it can sit at whichever end of the bed the operator prefers - it is a separate unit connected by cable, not bolted to the frame.

Fixture plate on its rails with the control cabinet in front: the panel is loaded outside the gantry and pushed in, so nobody reaches under the head

Teaching A New Panel Is Coordinates, Not A New Machine

A new panel means a new program, and nothing else on the machine changes. The points are either entered as coordinates or taught with the handheld pendant - jog the head over a point, store it, move to the next - and the sequence, the press time and the current for each point are stored with it. Panels of the same family differ by a few coordinates, which is a copy and an edit rather than a rebuild.

Two interfaces are provided for the same reason: the touch screen on the cabinet for running and monitoring, the pendant for setting up while standing at the bed and watching the electrode rather than a screen across the room.

Setting up with the handheld pendant: the operator stands at the bed, jogs to a point and stores it, with the cabinet screen running the machine behind him

What Comes Off The Bed

A panel comes off with its welds where the drawing put them, with the same set-down at every point, and with a visible face that has marks of consistent depth rather than a mixture of deep craters and cold touches. The next operation - folding, assembly, painting - receives a part that has not moved under it.

The machine in these photographs and in the video is the same unit, installed at the customer's plant and running their own panels. That is how these machines are proved: not on a test coupon in our workshop, but on the parts the customer sells.

On the customer's floor: the gantry over the bed, cabinet at the loading end, panels stacked beside the machine

Key Specifications

Where It Welds

•   Stainless door panels and wall panels with stiffeners welded on the inside face

•   Metal cabinet doors and enclosure panels with brackets, earth studs and mounting plates

•   Decorative sheet panels where the visible face must stay clean and evenly marked

•   Elevator and escalator cladding, machine covers and architectural metalwork

•   Any large flat part with a repeating pattern of spot welds that must land in the same place

Bed size, stroke and fixture are built from the customer's panel drawing and a sample. We run the program on the customer's own panels in our workshop and set current, press time and force before the machine ships.

How A Custom Machine Is Built

01   Panel drawing, weld-point layout and fixture concept review

02   Weld trial on sample panels - nugget, set-down and mark on the visible face

03   Process proposal - bed size, stroke, transformer and control selection

04   Gantry, carriage, head, bed and fixture design in 3D

05   Frame, rack and guide build, head and pneumatic/water circuit assembly

06   Control integration, programming of the weld points, dry run

07   Run-off on customer panels in our workshop before shipment

08   Delivery, installation and commissioning on site

09   Operator training in teaching new panels, then after-sales service and spares

Talk to Pudian Technology

Guangdong Pudian Automation Technology Co., Ltd builds resistance and laser welding equipment in-house - transformers, controllers, heads, fixtures and complete machines - one team, one solution. Send us the panel, the weld-point layout and the material, and we will weld sample parts and send them back with a parameter sheet.