Automatic Servo Spot Welding Machine for Automotive Motor Terminals

Welding The Terminals On An Automotive Motor: The Head Travels, The Motor Stays Clamped

Application story  ·  Servo-driven automatic spot welding of automotive motor terminals - custom electrode and press system, offset welding, guarded cell with manual load

An automotive motor with a control board on its end carries a ring of terminals - stamped pins and lugs that have to be joined to pads and busbars. They sit at different heights, on different sides, at angles that a straight vertical electrode cannot reach, and none of them can be trusted to be exactly where the drawing says. The operator clamps the motor once; from there the head goes to the terminals, not the motor to the head.

The cell: servo head and custom electrode assembly inside a glazed enclosure, water manifold and air preparation in the base, stack light on top, two-hand start at the front

The Part: A Motor, A Board And A Ring Of Terminals

The workpiece is a small automotive motor - the kind that drives a water pump, a throttle, an EGR valve or a tailgate - with a PCB and a moulded terminal carrier stacked on the stator housing. Around that carrier, terminal pins stand up out of the board and metal lugs sit between the plastic walls. Each of them is a separate weld, and each has to be made without cooking the components a few millimetres away.

That combination is what makes the job hard. The weld itself is nothing - two pieces of copper and a pulse. The problem is getting to twenty or thirty of them, one after another, with the electrode square to each terminal, without the board moving and without the heat spreading into the capacitors and the plastic.

The part: stator housing, control board and moulded terminal carrier; the pins and lugs around the board are the welds this cell is built for

The Head Travels, The Part Does Not

The welding head is carried on servo axes and moves from terminal to terminal under program control - the motor is clamped once at the start of the cycle and never touched again. Positioning the head instead of the part is the whole reason the cell can hold tolerance on a small motor: the fixture only has to locate the housing, and it does not have to index the board between welds.

Terminals are stamped and the carrier is moulded, so their real position wanders from part to part. The head takes that into account: the weld position for each terminal can be offset in the program, so a terminal that sits a little high, a little low or a little sideways is still welded on the flange rather than on the edge. This offset welding is what keeps the yield up when the parts come from a real stamping tool and not from a drawing.

Two copper electrodes coming down on the terminals, board and carrier below - the head arrives square to the weld face, whatever the terminal's position on this particular part

Two Electrodes, One Custom Press

The head carries a pair of copper electrodes that come down together, one either side of the joint, so the current passes through the terminal and the pad in a single short pulse. Pressing on both sides at once also keeps the force balanced: a single electrode pushing down on a terminal on a thin board lifts the opposite edge, and the next weld lands on a board that is no longer flat.

The electrode assembly and the press are built for this part, not bought as a standard spot gun. Terminal geometry, approach angle and clearance to the plastic walls all decide the shape of the electrode tip, the stroke of the press and where the force is applied. Both electrodes are water-cooled - the base of the cell carries a six-circuit manifold with individual flow meters, so a blocked circuit shows up as a reading rather than as a burned tip three days later.

Head and press over the fixture: servo-driven column, custom electrode holder, air lines to the press and the fume hood on the left

Inside The Cell: Fixture, Clamps, Water, Air

The motor sits in a locating seat on the machine table and is held by two quick-release clamps, one on each side, so the operator can load and unload with one hand each and no tools. The seat sets the height and the rotation of the housing; everything else - which terminal is welded, in what order, with what current - comes from the program.

Around the working area there is a glazed enclosure with hinged doors, so the head can be watched while it works and nobody can reach in during a cycle. The cycle is started with two buttons, one for each hand. Air preparation for the press and the six-circuit water manifold for the electrodes are built into the base of the machine, and the extraction hood at the head takes the smoke away from the operator's side of the glass.

Fixture with the motor removed: locating seat, clamp arms and the linear axis that carries the head past the weld positions

What The Operator Actually Does

01   Select the program for the motor variant on the HMI

02   Drop the motor into the locating seat, terminals facing up - no orientation jig needed beyond the seat

03   Close the two quick clamps, one each side

04   Start with both hands; the head goes to the first terminal and welds

05   The head moves to the next terminal and the next, in the stored order, until the ring is done

06   Head returns, clamps open, motor out, next one in

The operator's cycle is load, clamp, start, unload. Everything between the first and the last weld happens without touching the part, which is what makes the cell worth building: a hand-held welder on this part needs the operator to find every terminal by eye, and the thirtieth weld of the shift is never in the same place as the first.

The motor clamped under the head: housing held on the seat, terminal carrier up, hood at the left taking the fume away

Where The Yield And The Savings Come From

High yield on this kind of part is not one feature, it is three working together: the head goes to a programmed position instead of an eyeballed one, the offset per terminal absorbs the stamping tolerance, and the press applies the same force at every weld so the electrode does not dig into one terminal and skate off the next.

The energy saving comes from the same discipline. A pulse is delivered only where a weld is due, for as long as the schedule says, and the servo spends no time moving through positions where nothing is welded. On a part with dozens of small welds, that is most of the difference between a cell like this and a manual gun running off a fixed tap.

The cell from the service side: enclosure, glazed doors, water and air panels in the base, castors for positioning on the line

Key Specifications

Where It Welds

· Automotive motors with a control board - water pump, throttle, EGR and tailgate actuators

· Terminal pins and lugs welded to PCB pads and busbars inside a motor housing

· Stator lead-outs joined to terminal plates on small BLDC motors

· Actuator and sensor housings where terminals are welded after the board is fitted

· Any part with many small terminals that need a programmed sequence rather than a hand gun

The fixture and the electrode assembly are built from the customer's motor drawing and a sample. We weld the first parts in our workshop and set the terminal positions, the offsets and the weld schedule on the real part before the machine ships.

How A Custom Cell Is Built

01   Motor drawing, board layout and terminal list review

02   Weld trial on sample motors - nugget section and pull test on the terminal

03   Process proposal - head arrangement, electrode design, cycle estimate

04   Fixture, clamp and electrode assembly design in 3D

05   Frame, servo axes and pneumatic/water circuit build

06   Weld control and HMI integration, program for each motor variant

07   Assembly and run-off on customer motors before shipment

08   Delivery, installation and commissioning on site

09   Operator training, then after-sales service and spare electrodes

Talk to Pudian Technology

Guangdong Pudian Automation Technology Co., Ltd builds resistance and laser welding equipment in-house - transformers, controllers, fixtures and complete cells - one team, one solution. Send us the motor, the terminal list and the board, and we will weld sample parts and send them back with a parameter sheet.