Automatic Spot Welding Machine for Filter Capacitor Leads with Servo Positioning

Filter Capacitor Lead Spot Welding Cell: Servo Moves The Head, The Cell Checks Every Nugget

Application story  ·  Automatic resistance spot welding of filter and capacitor lead frames, stator lugs and busbar terminals

The operator loads a filter capacitor assembly into the fixture once. The servo head then runs the taught point sequence and welds every point on that part - the leads of both capacitors, the earth tab, the terminal lugs - without anyone moving the part by hand. When the cycle ends the cell says which points passed and which ones need a second look.

The cell: servo head inside the guarded work area, HMI at eye level, program and data on the front panel

The Servo Does The Pointing

Hand welding a filter capacitor is a positioning job, not a welding job. A capacitor body sits inside a moulded bracket, its leads are a few millimetres wide and close together, and the electrode has to land on the lead without touching the can or the plastic. That is exactly what an operator cannot repeat for a whole shift - and the reason a hand-welded filter tends to have one good lead and one that had to be touched up.

Here the point sequence is taught once and stored with the part number. The servo axes bring the head to point one, the cylinder fires, the current flows, the head lifts and travels to point two, and the cycle closes when the last point is welded. The fixture keeps the part in the same place every time, so the same program runs again on the next part without touching the machine.

Head and fixture from above: twin copper electrodes on the ram, the spring-loaded locating pins and the clamp that holds the bracket flat while the points are welded

A Floating Head That Follows The Part

Moulded brackets are never perfectly flat, and a lead that sits a little higher than the taught position should not change the weld. The head is mounted so that it can follow the part instead of fighting it: when the electrode meets a lead that is higher or lower than the program expects, the head gives and keeps its force on the lead. The weld position is then taken from the part, not from the program.

Warped brackets, spring-back in the lead frame and part-to-part moulding variation stop being a programming problem, and the electrode stops skating across the lead surface. The same head also absorbs the small height difference between a two-capacitor assembly and a single-capacitor one.

The Current Stays Where It Was Set

The power source is a high-precision medium-frequency inverter DC unit. On a capacitor lead the weld window is narrow: too little current and the lead only sits on the surface, too much and the plastic around it burns or the foil inside the can is damaged. A DC output with a fast current rise holds the set value from point to point and from part to part, so the schedule that welded the first part of the shift produces the same nugget on the last.

The head carries two copper electrodes side by side, so a lead pair can be reached inside one program instead of turning the part between welds, and the electrode tips are dressed on a schedule so the current path does not drift as the tips wear.

Floating head in close-up: electrode holders, the force and displacement sensing in the slide, and the air lines that fire the weld

The Nugget Is Measured, Not Assumed

Pressure and displacement sensors sit in the head. During each weld the cell records how the lead moved under the electrode - the lead collapses as the nugget forms, and how far and how fast it collapses is the signature of a good weld or a cold one. A point that falls outside the window is flagged at that point, while the part is still in the fixture, instead of being found at the end of the line.

Every welding element of every point - current, time, force, displacement - is monitored, stored and kept with the part serial. The records are traceable and the cell can be tied into the plant MES, so a filter that comes back from the field can be traced to the schedule and the point that made it.

Inside the guarded area: the head on its servo axes, the light curtain bars at the door and the monitor that shows the current program

What It Welds

The cell is built around the part, so the sample range follows the customer's product line rather than a catalogue. These parts were all welded on this machine:

· Filter capacitor lead - the lead frame that carries the capacitors and the terminal tabs

· Capacitor lead, single and twin capacitor assemblies

· Automotive capacitor lead, with the bracket and mounting ears in place

· Motor stator lead - the winding taps welded to the terminal posts

· Automotive component resistor lead

· Automotive motor busbar terminal and slip-ring terminal

Samples from the cell: capacitor leads, automotive capacitor leads, motor stator, filter capacitor leads and busbar terminals - all welded with the same head and the same control

A new part usually means a new fixture, a new electrode shape and a new program, not a new machine. The frame, the servo axes, the power source and the control stay; the fixture plate and the taught points are what change.

One Cell, One Operator

Loading and unloading happen at the front of the cell, on the same side as the HMI. The operator loads the bracket, presses start, and the cell welds every point and reports. There is no second station and no manual clamping step, so one person runs the cell and the cycle time is set by the welds, not by the handling.

The work area is closed by an aluminium frame with transparent doors and vertical light curtains at the opening: reaching in during the cycle stops the head. A stack light shows run, idle and fault from across the aisle, and the cabinet runs on castors, so the cell can be moved and levelled on its own feet when the line is re-laid.

Working area from above: the indexing table, the fixture plate and the energy chains that carry the axes - the part stays clamped while the head travels

Key Specifications

Where It Runs

Capacitor leads are welded in the same places wherever the product is made - the cell fits all of them:

· Filter capacitor assemblies for automotive and new-energy applications

· Film and electrolytic capacitor leads

· Motor stator leads and winding taps

· Busbar, slip-ring and terminal lugs

· Appliance, power supply and inverter filter modules

How A Custom Cell Is Built

01   Part drawing and sample review

02   Weld trial on our own cell

03   Process proposal and quotation

04   Fixture and electrode design in 3D

05   Manufacturing and in-house run-off

06   Installation and operator training

07   Pre-production run at the customer plant

08   Final acceptance and volume production

09   After-sales service and spare electrodes

Talk to Pudian Technology

Guangdong Pudian Automation Technology Co., Ltd builds custom welding cells in-house: fixtures, electrodes, feeding, welding and inspection - one team, one solution. Send us a part and the points that have to be welded, and we will run a weld trial and return the sections.