Copper and brass pressed components

A brass terminal stamped from 1.0 mm C26000 can hold its hole position and still fail, because a 0.15 mm burr cuts through the tin plating and starts a corrosion cell inside the crimp. Copper and brass pressed components are decided by three behaviours that mild steel does not share: rapid work hardening, galling on the die face, and a burr that rolls over instead of breaking clean.

Mild steel gives you a warning before it fails. Copper does not. It forms easily on the first stroke, hardens, then tears at the punch nose on the third draw with the same tool and the same press setting. The drawing has to state the alloy and temper, and the tool has to be built for that temper rather than for the family of copper alloys.

Which grade suits copper and brass pressed components?

Grade and temper decide the whole route, including whether the part needs an anneal between operations. The values below are typical published figures for annealed strip; half-hard and spring tempers raise strength and cut formability.

Two rules come out of the table. First, conductivity and formability pull in opposite directions: C11000 carries 101% IACS and galls, while C51000 holds a spring and wears the die. Second, temper is a specification item, not a mill default. A part drawn in the annealed condition and one drawn in half-hard need different blank sizes and different die clearances, and the difference in springback is large enough to change the finished angle by several degrees.

State the temper on the drawing as a standard designation (H02, H04, or annealed O60) and ask for the mill certificate with the coil. A certificate that lists only "brass" is not enough to release a repeat order.

How much press tonnage does a brass blank need?

Blanking force is the cut perimeter multiplied by thickness and shear strength. For brass at about 300 MPa shear strength, a 40 mm outside diameter washer with a 20 mm hole in 1.5 mm strip works out as follows.

Outer perimeter is 125.7 mm, inner perimeter 62.8 mm, so the cut length is 188.5 mm. Force is 188.5 × 1.5 × 300 ÷ 1,000, which gives 84.8 kN, or 8.6 tonne-force. Add 25% for stripping and the job needs about 106 kN, or 10.8 tonne-force.

A 20 T press runs that at roughly half its rated capacity, which is the right place to be: the remaining headroom absorbs tool wear, a slightly thicker coil, and the spike when the punch breaks through. Press sizing is not only tonnage. Shut height, stroke length, bed area and the space a progressive die needs for its coil feed all constrain the choice, and a 20 T press with a small bed will not take a die that a 40 T press swallows easily.

For copper, use a shear strength nearer 210–250 MPa; the same washer comes out around 70 kN before stripping. Run your own numbers through the press tonnage calculator before fixing the press, and check the result against the die drawing rather than the part drawing.

How much strip does the layout waste?

Brass strip is the largest line in the piece price, so the layout decides whether the part is competitive. Take the same 40 mm washer in a 300 mm coil, nested six across with a 3 mm web and 3 mm edge trim. The used strip width is 261 mm and the feed pitch 43 mm, so each stroke consumes 11,223 mm² of strip. Six washers hold 5,655 mm² of metal, which is about 50% utilisation.

The rest leaves as skeleton scrap plus the 20 mm centre slugs. On a low-volume run that 50% is acceptable; on a million-piece programme it is worth paying for a two-row die or a narrower coil. Ask any quote to show parts per stroke and the strip width, because a 10% gain in yield beats most negotiation on piece price.

How does a repeat order stay consistent?

Copper and brass parts drift for reasons that have nothing to do with the press. A new coil lot with a different temper changes springback and burr. A reground die changes clearance. A plated batch that was degreased differently changes adhesion.

Three controls keep a repeat order inside tolerance. The die gets a maintenance schedule based on stroke count, not on rejection rate, with the punch and die radius measured at each service. Every incoming coil gets its certificate checked against the drawing, and the first part off a new lot is measured for the dimensions the temper affects. And the checking fixture stays with the approved sample, so a new operator compares against a known good part rather than against a memory of how the part used to look.

Why do copper parts gall and brass parts crack?

Galling is cold welding between the strip and the die face. Copper is soft, chemically clean and under high contact pressure at the die entry, so it picks up on the die radius and drags. Once a lump forms, every following part carries a score mark and the die needs polishing.

Brass rarely galls but cracks at the die radius when the clearance is wrong or the strip is too hard. Both failures are solved in the tool, not at the press.

Die clearance and burr

Clearance for copper and brass sits at 5–8% of thickness per side, slightly tighter than the 6–10% used on CRCA of the same gauge. Too little clearance produces secondary shear, a tall burr and rapid punch wear. Too much produces roll-over, a torn edge and a burr that leans.

The burr side matters more on these parts than on steel, because most copper and brass components are plated. A roll-over burr on the contact face of a terminal lifts the plating at the edge, and the crimp then cracks it. Specify the burr side and the maximum height. A common split is 0.05 mm on the functional edge and 0.10 mm elsewhere.

Die finish and lubrication

Die inserts in D2 or carbide, polished to a mirror on the draw radius, resist pick-up far better than a ground finish. Lubricant choice matters as much: copper needs a film that stays put under pressure, and a water-based lubricant that evaporates before the next stroke leaves the die dry. Brass stains if the lubricant is left on the strip, so parts are degreased after pressing and before plating or coating, never left overnight with lubricant on them.

How many draws does a copper cup need?

A single draw handles a blank-to-cup diameter ratio of about 1.8–2.0 in annealed copper and up to 2.1 in brass. Beyond that, the wall thins at the punch nose and tears regardless of blank-holder force.

Redraws reduce the diameter by a further 1.3–1.4 per stage. Between stages, the part is annealed to restore ductility: typically 400–650 °C for copper and 450–600 °C for brass, depending on alloy and the temper the mill supplied. The anneal is a process step with its own handling and its own oxide removal, which is why a two-draw part is rarely twice the price of a one-draw part.

Wall thinning is the number to control. Measure the wall at roughly 25%, 50% and 75% of cup height on the first article and compare with the blank thickness. Thinning above about 15% at the punch nose is a warning that the next tool adjustment will tear.

What inspection evidence should come with a pressed copper part?

Pressed parts are cheap to make and expensive to inspect badly, so agree the evidence before the first batch. For copper and brass work the report usually carries:

• Dimensions marked on the drawing revision, with hole position and flatness called out separately.
• Burr height measured on the functional edge and recorded, not judged by eye.
• Hardness in HV on the formed wall, which shows whether the anneal did its job.
• Conductivity in % IACS by eddy current where the part carries current, since a wrong temper changes it.
• Plating thickness by XRF on a sample, with the specification and the acceptance range.

Ganesh offers first article inspection and PPAP documentation on these programmes. The checking fixtures are built in-house alongside the press tools, so the fixture and the die share a datum and the report matches the drawing.

What Ganesh runs for copper and brass parts

Ganesh runs mechanical presses from 20 T to 300 T, with a 250 T punching press for louvres, perforations and high-hole-count panels. The in-house tool room designs and builds press tools, progressive dies, welding fixtures and checking fixtures, which means a copper terminal and its gauge are developed together rather than sourced separately. Tooling is quoted as a separate line from piece price, so the amortisation is visible instead of buried.

The custom part range covers 0.8–40 mm in mild steel, CRCA, stainless, aluminium, brass and copper, with ±0.5 mm typical sheet metal tolerance and tighter features by agreement. The plants hold ISO 9001:2015 and ISO 14001:2015, and the stamping and fabrication programmes supply customers including Mahindra, Minda, Godrej & Boyce and Indian Railways. The stamping capability page sets out the press range and the tool room scope, and the stamping and press tool hub holds the rest of the DFM material.

Do copper and brass parts need a different finish route?

Copper and brass tarnish without a barrier coat, and the tarnish is a functional problem on a contact face and a cosmetic one on a decorative trim. Three finishes cover most pressed parts.

Tin plating at 3–10 µm is standard on terminals and busbar ends. It solders well, keeps contact resistance stable and hides the base colour. Nickel at 2–5 µm suits parts that see repeated handling or want a harder surface, and it is a common undercoat before tin. A clear passivation or lacquer keeps a bare brass face bright but will not survive abrasion.

Two details decide whether the finish holds. The part must be degreased after pressing, because stamping lubricant trapped under a plated layer causes blistering in service. And the burr side must be controlled before plating, because a rolled burr produces a thin, cracked deposit at the edge.

What the press drawing has to settle

• Alloy designation and UNS number, plus temper.
• Thickness with the tolerance band, and grain direction if the bend or draw depends on it.
• Burr side and maximum burr height on functional and non-functional edges.
• Plating or coating specification with thickness range, and which areas stay bare.
• Critical dimensions for conductance, contact flatness and hole position.
• Annual quantity, release size and whether tooling is customer-owned.
• Whether a first article report or PPAP is required at each revision.

Send the drawing through the quotation route with the annual volume; the tooling decision depends on it more than on the part weight. If the part is a flat bracket rather than a formed or drawn component, compare the two routes first using stamping versus laser cutting by annual quantity.

When pressing is the wrong route

Copper is reflective and conductive, which makes laser cutting slower than on steel, but a flat copper busbar or a 6 mm brass plate with large openings is still a cutting job, not a press job. The constraints are set out in laser cutting copper and brass.

Stamping also loses below a few hundred pieces a year, where tooling cannot be recovered. If the part is a prototype or a low-volume spare, laser cut and bend it, then move to a die when the design stops moving. And if the drawing calls for a tolerance tighter than ±0.05 mm on hole position, plan a secondary operation or a dedicated checking gauge; a standard press tool will not hold it across a die life without one. The stamping defects guide covers the failure modes that appear when a tool is pushed past its clearance.