Thin-Sheet Circumferential Seam Welding Machine for Stainless Steel Sensor Housings

Seam Welding A Thin Diaphragm Round A 50 mm Sensor Body: One Turn, Ten Millimetres A Second

Application story  ·  Circumferential seam welding of stainless steel sensor housings with a thin corrugated diaphragm - 80 kVA, copper roller electrode, manual load

The part is a stainless steel sensor housing with a pressed diaphragm on top, corrugated in concentric rings, 50 mm across. The joint is one circle around the rim, and that circle is the seal as much as the weld: a millimetre missed anywhere on it is a sensor that leaks. Spot welding round that rim leaves a chain of marks with gaps between them, so the joint has to be rolled - continuously, at a speed the thin sheet can take.

The cell: rotary chuck under two roller welding heads, film-press unit between them, HMI on a swing arm, guard frame with light curtain and two-hand start

The Weld Is The Seal

A sensor housing is a thin-wall stainless part, and the diaphragm on top is thinner still - formed into rings so it can flex, which also means it distorts easily. The rim where the two meet is narrow, and it is the only place the two parts touch. Whatever the welding process does there decides two things at once: whether the housing is closed, and whether the diaphragm is still flat enough to measure pressure afterwards.

That is why the process is seam welding rather than spot welding. A spot schedule puts the whole current through one small area for a short time; on 0.2-0.3 mm sheet the first thing that happens is a hole, and the second is a warped diaphragm. Rolling the electrode spreads the same energy over a moving line, so the sheet is welded without being overheated at any single point.

The part: stainless sensor body with a corrugated thin diaphragm, welded all the way round the rim in one turn

80 kVA, And Why The Frequency Matters

The transformer is 80 kVA, which the process needs: welding a stainless rim is not a low-energy job, and the energy has to arrive in a controlled way rather than in one burst. The controller runs the output at 1 kHz with millisecond timing, so the current can be shaped inside the turn instead of being switched on and left to run.

In practice that control is what makes a thin sheet weldable at 10 mm/s. Each instant of the seam gets a short, repeatable pulse, the nuggets overlap into a continuous seam, and the heat stays local to the rim - the corrugation beside it never gets hot enough to move. No filler wire and no shielding gas: this is resistance seam welding, the joint is made from the material already there.

Two Wheels, A Spring Press, And A Press For The Film

Both roller heads sit above the chuck, left and right, each on its own Z-axis with a spring-loaded press. The spring is not a detail: on a rolled seam the electrode has to follow the sheet and keep a constant force while the part turns, and a rigid head on a thin rim either loses contact or dents it. Two heads also mean the wheel position can be set to the diameter and to which side of the rim is welded, without rebuilding the head.

Before the wheels come down, the diaphragm is held flat. A separate film-press unit - with its own button, so the operator can press the sheet without starting a cycle - brings three spring-loaded shoes down on the diaphragm around the chuck. Nothing on the sheet is free to lift while the wheel runs, which is where a rolled seam either comes out even or comes out with a wave in it.

Three spring-loaded shoes of the film press around the chuck, each on its own brass guide and spring - the diaphragm is held flat before the wheel is allowed down

Changing The Product Takes Three Minutes

The lower electrode is a set of three press blocks matched to the housing, and the manual three-jaw chuck holds the body square under the wheels. An X-axis slide moves the head group so the same cell covers a range of diameters instead of one - which is the point of a seam welder in a sensor line where the same family comes in several sizes.

Changing from one housing to the next is: swap the press blocks, recall the program, done - about three minutes. The controller keeps 15 fixed-point schedules and 31 robot-mode schedules, with the weld recipe for each product stored and called up in one keypress, so nothing has to be dialled in again by hand.

Copper roller wheels on the rim from both sides, film press in the centre, housing held in the three-jaw chuck below - the part turns, the wheels stay where they are set

What The Operator Actually Does

01   Fit the press blocks for the housing and recall the program - about 3 minutes for a product change

02   Drop the housing into the locating seat, lock it by hand in the chuck

03   Press the film-press button: the three shoes hold the diaphragm flat and the pneumatic clamp closes - about 10 s

04   Check the part is seated, then start with both hands - 1 s

05   The chuck turns, the lower head drives the upper wheel round, and the seam is welded at about 10 mm/s - about 20 s for a 50 mm diameter

06   The head lifts, the chuck opens, the part comes out - about 5 s, then the next one

At 50 mm diameter that is roughly 35 seconds per part: 20 seconds of welding and 15 seconds of handling. The operator's job is the part, not the process - the film press, the clamp and the weld schedule are all one button away from the start signal.

The Bench, The Guard And The Build

The machine stands 1,200 x 1,000 x 1,700 mm on a movable 1,200 x 1,000 mm table with castors, so it can be pushed into a line and levelled where it is needed. The working area is closed by a guard frame with a light curtain and a two-hand start: both hands are on the buttons, so neither is inside the wheels when the cycle begins. Air and water lines for the transformer and the electrodes run inside the frame.

Bench as built: two heads on their columns with rack-and-pinion height setting, rotary unit on the table, HMI and two-hand start at the front edge

Electrical integration is Mitsubishi with a Weinview HMI, water and air circuits are built in, and the welding transformer and controller are Pudian's own. The electrode is chromium-zirconium copper, kept as a spare part with about a 10 working day lead time. Lead time for the cell is 35 working days, and every machine is run off on sample housings before it ships.

Layout drawing: enclosure, two upper roller units, film-press unit, rotary chuck on the slide table, HMI on the swing arm - drawing for reference, the machine is built to the agreed final design

Key Specifications

Where It Welds

· Pressure sensor housings with a welded corrugated diaphragm

· Load cell and force sensor bodies with a thin closing sheet

· Stainless sensor and transducer housings in automotive and industrial instrumentation

· Bellows and membrane assemblies that need a closed seam rather than spot welds

· Thin-wall stainless parts in medical and food-grade instruments where the joint must be clean

The fixture is built from the customer's housing drawing and diaphragm sample. We weld the first parts on the machine and set the wheel position, the spring force and the schedule on the real part before it ships.

How A Custom Cell Is Built

01   Housing and diaphragm drawings, material and thickness review

02   Weld trial on sample parts in our workshop - seam tightness and diaphragm flatness checked

03   Process proposal - transformer size, wheel arrangement, cycle estimate

04   Fixture, press-block and film-press design in 3D

05   Frame, X-axis slide and pneumatic/water circuit build

06   Transformer, controller and electrical integration

07   Assembly and run-off on customer housings 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 cells - one team, one solution. Send us the housing, the diaphragm and the seam you need closed, and we will weld sample parts and send them back with a parameter sheet.