Fuse & Contactor Stamping: Contacts, Clips and Arc Parts

A fuse that fails to clear a fault is rarely the fault of the fuse body. More often the stamped silver contact welded shut under a motor-starting spike, the arc-extinguishing plate let the arc track into the housing instead of the chute, or the tin-plated copper clip ran hot until the spring finger lost its temper and the joint sagged into thermal runaway. In a 690 V motor feeder the difference between a clean break and a busbar fire is a few micrometers of contact-surface finish and a few degrees of temperature rise. The stamped parts inside a fuse or contactor carry all the consequences of those failures, and most buyers never see the drawings that decide them.

This guide treats the fuse and the contactor as one engineering problem, because they are: a stamped contact system that must carry current, break current, and do it thousands of times without welding, overheating, or drifting resistance. We walk the material selection, the force budget, the arc path, the standards that convert the design into a testable contract, the cost economics that decide whether the part is profitable, and the manufacturing and verification capabilities that make the numbers on the drawing real. Every figure cited comes from the drawing standards and production data this facility works to, and every section ends in a decision you can write on your own BOM today.

KEY_TAKEAWAYS

Contact material sets the floor: AgSnO2 runs 80-90 HV and wins on DC and high-current duty, while legacy AgCdO around 60 HV still dominates AC contactor channels but is squeezed by RoHS and REACH cadmium restrictions.
The copper backbone is C11000 ETP at 100% IACS, almost always tin plated, because every extra micro-ohm at the joint is watts of heat released inside the plastic housing.
The clip is a stamped spring: a finger rated at 5 N that relaxes to 3 N can more than double its contact resistance, so the force budget, not the shape, is the first thing a serious stamper checks.
Arc plates are stamped geometry, not just stamped metal: slot width and burr control decide how fast the arc reaches the splitter and how much let-through energy (I²t) the downstream device must survive.
IEC 60269 breaking capacity is a promise about stampings: gG fuses break 80-120 kA depending on format, semiconductor aR fuses often 200 kA, and the clip, contact, and end caps must survive the electrodynamic shock.
Production capability anchors the design: 21 presses including Aida high-speed lines rated to 300 SPM, positioning at ±0.005 mm, strip from 0.05 to 3.0 mm and up to 650 mm wide, under IATF 16949:2016 with XRF plating verification.

Silver Contact Materials - AgCdO Against AgSnO2

The contact face is where the current actually crosses from one stamped part to the next, so its material sets the floor for everything else. Two alloys dominate low-voltage switching: silver cadmium oxide (AgCdO) and silver tin oxide (AgSnO2).

AgCdO typically carries 10 to 15 weight percent cadmium oxide dispersed through a silver matrix. The CdO pinning phase raises the contact's resistance to welding and limits arc erosion under repetitive AC switching, which is why it held the contactor market for decades. A finished AgCdO(12) face runs around 60 HV and keeps a low, stable contact resistance even after thousands of make-break cycles. The catch is cadmium. RoHS and REACH have pushed cadmium onto exemption lists that keep shrinking, so new designs for the EU and automotive channels almost always spec the cadmium-free alternative.

AgSnO2 puts 10 to 12 weight percent tin oxide into the silver instead, frequently with a small indium oxide (In2O3) addition to improve wetting and lower the contact resistance that pure AgSnO2 tends to show. It is harder than AgCdO - roughly 80 to 90 HV - and it resists welding and arc erosion better on DC and high-current duty, which is why it took over in EV contactors and solar DC breakers. That hardness costs force: AgSnO2 needs a higher contact pressure to reach the same micro-ohm resistance as AgCdO, and it shows more material transfer from one face to the other over life. The stamping and riveting process has to feed that extra force budget or the joint drifts hot.

The decision rule follows the duty, not the habit. For an AC contactor running resistive or lightly inductive loads where the existing qualification is already done, AgCdO remains a defensible legacy choice while the exemptions still cover it. For anything new, anything DC, anything with high inrush (motor starts, capacitor banks, EV pre-charge), or anything that must ship into EU or automotive channels, AgSnO2 is the default - the extra contact force it needs is a design cost paid once in the spring layout, while a cadmium recall is a cost paid forever. When the contact assembly is built as a silver face bonded to a copper backing rather than a solid silver slug, the silver goes where the arc lands and the copper carries the current, which is exactly the split the stamping layout should preserve.

Property	AgCdO (12 wt%)	AgSnO2 (10 + In2O3)
Matrix hardness (HV)	~60	~80-90
Weld resistance	Good (AC)	Better (DC, high current)
Contact resistance trend	Low, stable	Higher, needs more force
Regulatory status	Cd restricted	Cd-free, RoHS-safe
Typical home	Legacy AC contactors, qualified lines	EV contactors, solar DC breakers, new designs

The Copper Backbone - C11000 and Tin Plating

Silver is too soft and too expensive to be the whole part, so the contact face gets welded or riveted onto a copper backing, and the clip, terminal and spring finger are stamped from copper outright. The workhorse is UNS C11000, electrolytic tough pitch copper: 99.90% minimum copper, annealed conductivity of 100% IACS, a resistivity of 1.724 µΩ·cm at 20 °C, and a density of 8.94 g/cm³. That conductivity is the reason the part stays cool - every micro-ohm of stray resistance is a watt turned into heat right where the plastic sits.

The copper is almost always tin plated. A 3 to 8 µm tin layer on the contact backing and a 5 to 12 µm layer on terminals and clips, done to ASTM B545, stops the copper from oxidizing in storage and on the rail, keeps the surface solderable, and limits fretting corrosion at the bolted joint. Tin's melting point is 232 °C, so the plating itself is a temperature warning: if the joint's temperature rise pushes the surface anywhere near that, the tin flows, the contact pressure collapses, and the resistance climbs. That is the mechanism behind most clip overheating, not a bad lot of silver.

Plating on a fuse or contactor part is a thickness map, not a single number. On this facility the selective reel-to-reel lines plate gold, silver, tin or nickel at 2 to 8 µm where the surface needs them, and structural parts that face corrosion get zinc at 5 to 12 µm qualified to ASTM B117 salt spray. The point of the map is that the contact zone, the solder tail, and the exposed spring body each want a different finish, and a barrel-plated part cannot deliver that split. Every plated lot is verified by X-ray fluorescence across the stamped surface, because a thin spot in the contact zone is a future hot spot, and it costs far less to catch on the reel than in the field.

Surface zone	Typical finish	Thickness band	Why it is there
Contact backing (under silver face)	Tin (ASTM B545)	3-8 µm	Oxidation barrier, solderable surface
Terminals and clips	Tin	5-12 µm	Storage life, fretting control, joint stability
Selective contact or solder zones	Gold, silver, tin, nickel	2-8 µm	Reel-to-reel selective plating where the duty demands
Corrosion-exposed structural parts	Zinc	5-12 µm	ASTM B117 salt-spray life on brackets and frames

Clips, Spring Fingers and the Force Budget

A clip is a stamped spring, and a spring finger is a row of them. The contact resistance across a stamped joint follows the force roughly inversely: a finger rated at 5 N that relaxes to 3 N can see its resistance more than double, and the heat that follows accelerates the relaxation. That is why the force budget is the first thing a serious stamper checks on a clip drawing - not the shape, the force.

Spring fingers for high-cycle duty get stamped from C17200 beryllium copper or phosphor bronze rather than C11000, because the copper alone loses temper at the temperatures a feeder sees. The trade is conductivity: BeCu runs around 22% IACS against copper's 100%, so the finger has to be short and the backing has to carry the bulk current. A good stamping layout keeps the high-force, high-cycle flexure in the alloy and the current path in the copper, riveted or welded at a bond that itself must pass a pull and a micro-ohm test.

The spring alloys are not interchangeable, and the drawing should say which one the flexure is made of. Beryllium copper buys the highest elastic limit, which means the thinnest finger at a given force, at a real cost premium. Phosphor bronze buys good fatigue life at moderate cost and is the usual default for clip bodies where the force requirement is not extreme. Plain copper, whatever its conductivity, is the wrong answer for anything that flexes in service, because it relaxes and the resistance climbs with the relaxation. When the force budget is tight, the die designer compensates with over-bend and stress relief rather than a thicker finger, because thickness changes the force curve and the mating geometry together. Springback compensation in the strip layout, typically a few degrees of over-bend on the forming stations, is where a 5 N finger actually lands at 5 N after a million strokes instead of 4.2 N after ten thousand.

Alloy	Conductivity class	Spring performance	Role in fuse/contactor
C11000 ETP copper	100% IACS	None - relaxes under heat	Current path, contact backing, terminals
C17200 beryllium copper	~22% IACS	Highest elastic limit	High-cycle spring fingers, louver contacts
Phosphor bronze	Mid	Good fatigue life at moderate cost	Clip bodies, general spring duty
Tin-plated steel (where used)	Low	Good spring in hardened tempers	Brackets, frames, latch springs

Arc-Extinguishing Stamped Parts

When a contactor opens or a fuse element melts, an arc forms, and the stamped arc plates decide where it goes. Splitter plates, arc runners and chute walls are stamped from mild steel or copper-nickel with slots and bends that force the arc to stretch, cool and quench against the filler or the chute. In a semiconductor fuse (the aR type) the current-limiting element itself is a stamped ribbon of silver or silver-copper, packed in quartz sand so the arc self-extinguishes within a half cycle.

The geometry of those stamped slots matters more than the alloy. A 0.3 mm change in slot width changes how fast the arc reaches the splitter, and that changes the let-through energy (I²t) the downstream device has to survive. Buyers who only specify material and thickness miss the dimension that actually clears the fault.

DC makes the job harder in a way the drawing must acknowledge. An AC arc sees a current zero every half cycle, which gives the arc a natural chance to go out; a DC arc has no zero crossing, so it has to be stretched and cooled mechanically. That is why DC contactor arc chutes are longer, why the splitter plates are packed tighter, and why the stamped slot geometry has less margin for error. On the stamping floor this shows up as a burr problem: a burr on a splitter edge concentrates the field and can re-strike the arc instead of letting it transfer to the next plate. Fine blanking holds burrs under 0.02 mm on these parts so the edge stays clean, and the tool room maintains the blanking clearance and sharpening intervals that keep it that way across the whole run.

Arc part	Typical material	Critical stamped feature	Failure if wrong
Splitter plates	Mild steel, copper-nickel	Slot width, edge burr	Arc does not transfer, housing tracks
Arc runners	Copper, copper-nickel	Profile, surface finish	Arc roots in one spot, local erosion
Chute walls	Steel, ceramic-coated steel	Bend accuracy, stack flatness	Arc leaks past the chute
aR fuse elements	Silver, silver-copper ribbon	Neck geometry, slot pattern	Wrong I²t, late clearing

IEC 60269 - Breaking Capacity and the Stamping Link

IEC 60269 is the standard that governs low-voltage fuses, and its breaking-capacity numbers are where stamping quality shows. A gG full-range fuse is rated to break 80 kA on the small 10×38 and 14×51 sizes, 100 kA on mid sizes, and up to 120 kA on NH and blade formats. Semiconductor aR fuses go higher still, often 200 kA, because the protected device cannot survive a long fault.

That rating is a promise about the stamped parts. At a prospective 120 kA the electromagnetic forces on the element and the clip are enormous; the clip must hold the element without distorting, the contact must not weld during the pre-arcing interval, and the end caps must stay bonded through the thermal shock. The standard also sets the time-current behavior - a gG fuse clears at 1.6× rated current within an hour and much faster as the current climbs - and a stamped contact that drifts hot will shift that curve, clearing late or nuisance-tripping early.

The fuse type letter is a contract about the protected circuit, and each class leans on a different stamped feature. gG and gL fuses protect general-purpose circuits end to end; aM fuses protect motor circuits and tolerate the starting inrush that would nuisance-blow a gG link; aR fuses protect semiconductors and must clear before the device's I²t rating is exceeded. When the element is a stamped ribbon, the neck geometry and the slot pattern ARE the time-current characteristic - they decide where the element melts, how fast the arc establishes, and how much energy passes downstream. A supplier that stamps the element and the clips on the same floor, with the same tool room and the same inspection discipline, closes the loop between the fuse type letter and the part that has to live up to it.

Temperature Rise and Contact Resistance - The Numbers

IEC 60269-1 holds screw terminals to a temperature rise of 60 K at rated current, referenced against an ambient that newer editions set at 40 °C. The clip-to-contact joint inside the body has to stay under that same ceiling, because the plastic around it does not forgive a hot spot. A stamped silver contact at rated force is usually specified at 0.5 mΩ or below, and production lots are often tested under 0.2 mΩ.

The watts are small but local. At 100 A through a 0.3 mΩ joint you dissipate 3 W in a part the size of a fingernail; at 0.5 mΩ it is 5 W. Spread that across a poorly plated, force-starved clip and the rise runs past the limit. The math is the same for a contactor pole: contact resistance times the square of the current is the heat you have to design the stamping to shed.

The measurement protocol matters as much as the target. Contact resistance is measured four-wire across the mated interface, and the production check should be run on a population, not a single golden sample, because a die that is drifting will show it in the spread before it shows it in the average. The same logic applies to the force check: a clip's normal force is measured at a defined deflection with a force gauge, and the distribution across the lot tells you whether the forming stations are centered or the temper is sliding. When the temperature-rise test on the finished fuse or contactor fails, these two distributions are the first place the investigation goes.

What the Press Park Has to Deliver

None of the numbers above are stamped by hand, and the press park is the first place a capability audit looks. The production envelope for fuse and contactor stampings spans thin, delicate terminal work and heavy current-carrying brackets, and no single press does both well. The park that covers the range runs 21 presses: Aida high-speed machines from 25 to 80 tons, 20 of them, rated up to 300 SPM for terminals, lead frames and connector work; Zhenli Micron 35 and 50 ton presses for EV terminal programs; and new-energy presses from 45 to 110 tons for the heavier busbar, bracket and cable-connector stampings. Maximum tonnage on the floor is 110 tons, positioning holds at ±0.005 mm, and the strip envelope runs 0.10 to 3.0 mm thick and up to 650 mm wide.

Why that envelope matters for a fuse or contactor part is the same reason it matters for a connector: the spring fingers are stamped at speed from thin strip, and the flatness and force of a finger are decided by the die, the speed, and the strip, not by anything downstream. A 300 SPM line with piloted progressive tooling holds pitch and hole position to ±0.005 mm, which is what keeps a multi-finger clip's contacts in one plane. The heavier new-energy presses carry the busbars and brackets whose flatness and surface finish decide joint resistance at high current. The tool room that supports both - wire EDM, CNC and grinding for die maintenance and repair - is what keeps a 20-station clip die cutting true at speed instead of drifting into burrs and springback surprises. Underpinning all of it is the quality lab with CMM, optical measurement and online vision, and a quality system certified to IATF 16949:2016, in a 10,000 m² plant in Dongguan Chang'an.

Press family	Tonnage	Count	Typical duty
Aida high-speed (Japan)	25-80 T	20	Terminals, lead frames, connectors, clips to 300 SPM
Zhenli Micron	35/50 T	2	EV terminal programs
New-energy presses	45-110 T	3	Busbars, brackets, cable connectors, heavy stamping

Cost Economics: Where the Contact Budget Goes

Silver is the biggest single material line on a fuse or contactor BOM, and the way it is bought decides whether the part is profitable. A solid silver slug on every contact wastes the metal that never sees the arc; a silver face bonded to a copper backing, or silver inlay or clad welding at 0.5 to 3 mm, puts the expensive metal exactly where the current crosses and lets copper carry the rest. The same logic runs through the plating: selective reel-to-reel plating at 2 to 8 µm on the zones that need gold, silver, tin or nickel costs a fraction of full coverage, and the saving compounds at volume because plating is charged per rack or per run, not per gram of part.

Strip utilization is the second lever. Progressive layouts on this class of part typically recover 60-80% of the coil, and on C11000 copper that recovery is real money, because scrap copper is a commodity line, not a rounding error. A strip layout that nests the clip body around the finger, or shares the carrier web with a second part number, raises the yield without touching the piece price. Buyers comparing quotes should ask for the utilization number on their actual geometry; a quote that assumes utilization below that band has material cost hidden somewhere, and a quote that hides the crossover between stamping and machining is hiding the math. Stamping pays for its die above roughly 50,000 pieces a year depending on complexity, and below that volume the die amortization dominates the piece price.

The third lever is tooling transparency. A quote should separate the die from the per-part price, because the two amortize differently: the die is a one-time decision that should be justified by the program volume, while the piece price is what you pay forever. When a program moves from prototype to production, the plating minimums and the setup cost per run often matter more than the marginal piece price, so the supplier should be able to show how the cost curve bends across three quantities. That is the conversation a DFM pass exists to start - and it is why the DFM response, not the brochure, is the cheapest capability test in the audit.

Failure Root Causes and How to Verify Them

The failures that send fuses and contactors back come from a short list of mechanisms, and each one has a verification that catches it before shipment. Contact welding under inrush traces to surface finish, plating porosity and force; the verification is X-ray fluorescence mapping of the plating plus a micro-ohm check on a population. Clip relaxation traces to temper, thickness and over-bend; the verification is a force-gauge distribution check at a defined deflection plus CMM measurement of the form. Arc tracking traces to slot geometry and burr on the splitter plates; the verification is optical measurement of the slots and a burr check on the blanked edges. Tin flow and hot joints trace to the temperature rise itself; the verification is the 60 K thermal test against IEC 60269-1. Thin plating traces to the plating line; the verification is XRF across the whole stamped surface, not a corner sample.

Failure mode	Root cause in the stamping	Verification
Contact welded shut	Surface finish, plating porosity, low force	XRF plating map, micro-ohm population test
Clip runs hot, joint sags	Temper loss, force relaxation, thin tin	Force gauge at deflection, thermal rise test
Arc tracks into housing	Slot geometry off, burr on splitter edge	Optical slot measurement, burr check
Late or early clearing	Element neck geometry drift	CMM element profile, time-current test
Corrosion at bolted joint	Thin or porous plating	XRF thickness map, salt-spray sample

The verification is only as good as the lab behind it. This plant runs the checks in-house - CMM and optical measurement for geometry, online vision on the press lines for feed and form drift, XRF for plating - so the loop from a failed sample back to the coil, the die and the lot is measured in hours, not in shipping cycles. That is the difference between a quality system and a certificate.

A Supplier Checklist for Fuse and Contactor Programs

When you send a fuse or contactor stamping out for quote, the drawing should carry the answers to the questions below, and the supplier's DFM response should confirm them within one business day. A quote that comes back with no questions is a quote priced by category, not by drawing.

Contact material family and grade (AgCdO or AgSnO2, wt% and temper).
Contact assembly route: solid rivet, bimetal, or silver inlay/clad welded strip at the specified bond width.
Plating zones with thickness in micrometers, not adjectives, and the verification method (XRF) and frequency.
Force target for clips and spring fingers, with the deflection at which it is measured.
Contact resistance target and the four-wire test protocol.
Arc plate slot dimensions with tolerance, and the burr limit on blanked edges.
Fuse type letter and breaking capacity class so the element and clip design can be checked against the rating.
Annual volume and program length, so the die amortization and the stamping-versus-machining crossover can be checked honestly.
Quality deliverables: IATF 16949:2016 status, control plan, first-article report, lot traceability to coil and heat.

The parts that hold a 120 kA rating and a 60 K rise are ordinary to look at - a clip, a ribbon, a set of plates - and they are anything but ordinary to make. Every one of the numbers in this guide is a decision that has to survive the press, the plating line and the test bench. See connector terminal stamping for the contact and plating decisions that carry over, spring stamping for the force-budget math behind clip fingers, terminal plating selection for the finish map, and power distribution stamping for the switchgear side of the same problem.

What the Stamping Process Actually Controls

The drawing sets the material, but the process sets whether the part meets the data. Fine blanking holds burrs under 0.02 mm on contact backings so an edge does not concentrate the electric field and initiate a weld. Silver-to-copper inlay or clad welding fixes the silver layer at 0.5 to 3 mm with a bond that survives pull and thermal cycling. Tin plating gets mapped by XRF across the whole stamped surface, because a thin spot is a future hot spot. Flatness and springback get controlled part by part, because a clip that relaxes 0.1 mm loses the force that keeps the resistance down.

The buyers who get reliable fuses and contactors are the ones who treat the stamped contact, clip and arc plate as the product, not the housing around them. The housing is commodity plastic and ceramic. The stamped silver, C11000 and arc steel are where the 120 kA gets broken and where the 60 K gets held.

FAQ

Why do contacts weld shut on motor-starting spikes?

Starting inrush can run several times the steady current, and the arc at make and break is what welds the faces. The stamped part's contribution is the force budget, the surface finish and the plating: a face that is clean, flat and held at rated force separates cleanly, while a porous or force-starved face welds. That is why the welding test is part of the contact qualification, not an afterthought.

AgCdO or AgSnO2 for a new contactor design?

For anything new, AgSnO2 is the default: cadmium-free, RoHS-safe, and better on DC and high-current duty. It needs a higher contact force to hold the same resistance, so budget the extra force in the spring layout. Keep AgCdO only for legacy AC programs where the exemption still applies and the qualification is already paid for.

Why does tin plating thickness matter so much?

Tin is both a finish and a fuse. Below a few micrometers it stops protecting against copper diffusion and oxidation; if the joint temperature rise pushes the surface toward tin's 232 °C melting point, the plating flows, the contact pressure collapses and resistance climbs. Thickness is specified in micrometers and verified by XRF for exactly this reason.

What is the difference between gG and aR fuses?

gG (gL) is a full-range general-purpose fuse that protects cables and circuits end to end, clearing slowly at mild overloads and fast at faults. aR is a semiconductor-protection fuse that must clear before the device's I²t limit is exceeded, which is why aR elements are stamped to tighter neck geometry and rated for higher breaking capacity.

Can a hot clip be fixed by re-plating alone?

Usually not. If the clip is running hot because the spring finger relaxed, the resistance problem is force, and no thickness of plating fixes a force shortfall. Re-plate only after the force distribution and the joint resistance have both been measured; the plating is the last link, not the first suspect.

Ray Chan here. If your BOM calls for fuse contacts, clips or arc plates and the numbers above look familiar, send the drawing over. We run a DFM pass on material, plating thickness and the contact-force budget before we quote a single part - thirty years of stamping these pieces means we have already seen the failure mode you are trying to avoid, and we would rather catch it on the drawing than on your production line. Send your drawing and put the checklist above to work.