K-Factor for Copper: C110 Chart, Formula & Bend Allowance

For a first-pass 90-degree air-bend model, the practical K-factor for copper is approximately 0.35 for soft or annealed sheet, 0.40 for quarter-hard or half-hard C110, and 0.45 for hard copper. These are starting values, not material constants: alloy, temper, thickness, inside radius, grain direction and the actual press-brake setup must be validated together.

This is the copper-specific reference for K-factor, bend allowance and minimum bend radius. For the neutral-axis formula and bend-deduction workflow across steel, stainless and aluminum, use the broader sheet metal K-factor guide. Buyers ready to source formed electrical components can compare copper busbar fabrication and sheet-metal bending services against their released drawing, contact-surface requirements and production quantity.

Why copper sheet bends differently

Pure copper is highly ductile in an annealed condition, which makes it excellent for formed busbars, electrical contacts, heat-spreading parts and conductive enclosures. C11000 electrolytic tough pitch copper is at least 99.90% copper and, in the annealed condition, has high electrical conductivity and excellent cold-working capability according to the Copper Development Association alloy data.

That formability does not mean every copper sheet behaves the same. Cold rolling raises strength and hardness while reducing ductility. A soft C110 sheet may accept a tight bend with little springback; the same alloy in a hard temper may need a larger radius and a more aggressive overbend. Copper is also soft enough to record scratches, die lines and contamination from tooling that would leave steel visually acceptable.

The first instruction on a copper drawing therefore should not be simply “copper.” Specify the alloy, temper and thickness. Our copper material page covers C10100 and C11000 fabrication options, while the brass vs bronze vs copper guide explains when a copper-family alloy is a better fit.

Copper K-factor chart: starting values by temper

K-factor describes the position of the neutral axis through a bend. It is the distance from the inside surface to the neutral axis divided by material thickness. The value is used to calculate the amount of material consumed by the bend and therefore the correct flat pattern.

There is no single copper K-factor. The value changes with material condition and with the bend process. The following values are useful starting points for a 90-degree air bend, not guaranteed production values:

Copper condition	Initial K-factor	Use it as
Soft or annealed copper	0.35	A starting value for ductile C101/C110 sheet
Quarter-hard to half-hard copper	0.40-0.41	A practical starting range for general formed electrical parts
Hard copper or hard copper alloys	0.45	A conservative starting value before coupon validation

These values align with published sheet metal unfold references that derive approximately 0.35 for soft copper, 0.407 for half-hard copper and 0.452 for hard copper. Autodesk also emphasizes that K-factor depends on material, thickness, angle and the actual bending setup, and should be corrected from a measured sample rather than assumed from software defaults. See Autodesk’s K-factor calculation guidance and material unfold reference.

For the general theory and formulas, use our sheet metal K-factor guide. The important copper-specific lesson is that temper moves the neutral axis and changes the bend deduction enough to matter on short flanges, multiple bends and mating assemblies.

For copper RFQs, do not approve a flat pattern from this table alone. The initial K-factor should be tied to the exact alloy, temper, thickness, inside radius, grain direction and press brake tooling that will be used in production.

Copper K-factor starting values for CAD

If you need a first CAD value before supplier validation, use this conservative workflow:

1. Start with K = 0.35 for annealed or soft copper.
2. Start with K = 0.40 for quarter-hard or half-hard C110 copper.
3. Start with K = 0.45 for hard copper or harder copper alloys.
4. Keep the same alloy, temper, bend radius, tooling and grain direction when comparing the test coupon to the CAD flat.
5. Replace the starting value with the measured bend deduction from the actual production setup.

This is why copper parts with short flanges, multiple bends, connector holes or visible contact surfaces should be quoted as a fabrication process, not only as a downloaded flat pattern. For production RFQs, include the formed model, drawing and required contact-surface protection, then let the supplier confirm the final bend deduction.

Copper bend allowance calculation

The standard bend allowance equation is:

BA = (pi / 180) x A x (R + K x T)

Where:

• BA is bend allowance.
• A is bend angle in degrees.
• R is inside bend radius.
• K is K-factor.
• T is material thickness.

Consider a 2 mm half-hard C110 copper part with a 90-degree bend, a 2 mm inside radius and an initial K-factor of 0.40:

BA = (pi / 180) x 90 x (2 + 0.40 x 2) = 4.40 mm

For a 90-degree bend, the outside setback is (R + T), or 4.00 mm in this example. Bend deduction is therefore:

BD = 2 x OSSB - BA = 8.00 - 4.40 = 3.60 mm

That is a sound first flat-pattern calculation. It is not the final production number until a coupon made from the ordered copper lot is bent with the intended punch, V-die and grain direction.

Recover the copper K-factor from a measured bend coupon

A measured coupon lets the fabricator replace the initial CAD assumption with evidence from the actual forming setup. For a 90-degree C110 example, assume a 2.00 mm sheet, a measured 2.00 mm inside radius, two 50.00 mm outside flanges and a 96.40 mm flat blank:

1. Calculate the measured bend deduction: BD = 50.00 + 50.00 - 96.40 = 3.60 mm.
2. Calculate outside setback for a 90-degree bend: OSSB = (2.00 + 2.00) x tan(45 degrees) = 4.00 mm.
3. Recover bend allowance: BA = 2 x 4.00 - 3.60 = 4.40 mm.
4. Solve for the measured K-factor: K = [BA / (pi / 2) - R] / T = [4.40 / 1.5708 - 2.00] / 2.00 = 0.401.

This is an illustrative calculation, not a measured DRAmetal production result. Actual coupon dimensions, angle, inside radius and flange measurement convention must be recorded against the approved drawing. Autodesk’s sheet metal unfold-rule documentation documents the relationship between bend allowance, radius, thickness and K-factor.

What a supplier must record before approving a copper K-factor

A published chart provides a first-pass number; the controlled fabrication record explains whether that number remains valid for the actual part. Include these checkpoints in the drawing review and first-article package:

Approval input	Record before production	Why it changes the approved flat
Material identity	Copper alloy, temper, nominal thickness and supplied lot	A harder temper or different thickness shifts the measured bend behavior
Grain and feature orientation	Rolling direction, bend-line direction and nearby contact or mounting features	Grain orientation affects cracking risk and dimensional repeatability
Tool and method	Punch radius, V-die opening, forming method and intended press brake	A different tooling combination changes the formed radius and neutral-axis position
Representative measurement	Released angle, inside radius, formed flange dimensions and measured bend deduction	These observations replace the unverified chart value with setup-specific evidence
Change control	Drawing revision, approved flat, material substitution rule and revalidation trigger	A material or tooling change can invalidate an otherwise correct first article

Treat the chosen K-factor as a controlled process input, not a guaranteed copper constant. Use the sheet metal RFQ checklist to identify which measurements, records and customer approvals the supplier is expected to deliver.

Minimum bend radius for copper sheet

Minimum bend radius is normally expressed as R/T: inside radius divided by sheet thickness. The Copper Development Association defines minimum bend radius as the sharpest radius that can be formed without fracture or significant tensile-surface damage, and notes the direct trade-off between higher strength and lower formability in cold-rolled copper alloys.

Use these as conservative DFM starting points when mill-specific formability data is not yet available:

Material condition	Starting inside radius
Annealed copper	0.5T-1T
Quarter-hard copper	1T or greater
Half-hard copper	1T-2T
Hard copper	2T or greater

The tighter end of each range requires favorable grain direction, polished tooling and a confirmed material certificate. Appearance-critical or fatigue-loaded parts should use the larger radius even when a tighter bend can be made. The authoritative value is the mill’s bend-test data for the ordered alloy and temper, followed by a production-representative coupon.

Grain direction matters

Where possible, orient the bend line perpendicular to the rolling direction so the material bends across the grain. A bend line parallel to the grain is more likely to open surface cracks, especially in harder tempers. This is the same mechanism explained in our sheet metal grain direction guide, but it becomes particularly visible on polished copper surfaces.

Copper springback and angle control

Soft copper has low yield strength and normally exhibits limited springback. As temper and strength increase, springback becomes more significant. A drawing that permits multiple copper tempers without requalification is therefore asking the press brake process to absorb a material change it may not be able to absorb.

Control springback by:

1. Locking alloy and temper before approving the flat pattern.
2. Using a consistent V-die opening and punch radius.
3. Running a test bend from the production material lot.
4. Measuring the released angle, not the angle under load.
5. Applying controlled overbend in the CNC program.

Bottoming can reduce angular variation but uses greater force and may mark copper more heavily. Coining can force a very accurate angle, but it is rarely the first choice for appearance-critical conductive parts because of surface damage and work hardening. Our springback compensation guide explains these methods in more detail.

Tooling and surface protection

Copper transfers material to dirty tools and records small imperfections. A dimensionally correct part can still be rejected if a busbar contact area or visible panel is scratched.

For repeatable cosmetic results:

• Use clean, polished punches and dies reserved or thoroughly cleaned for non-ferrous work.
• Remove steel particles that can embed in copper and later create corrosion staining.
• Use protective film or urethane die protection where the surface specification allows it.
• Avoid dragging parts across the lower die or worktable.
• Define which faces are cosmetic and which electrical contact areas must remain coating-free.
• Deburr cut edges before bending so a burr does not imprint the opposite face.

Laser parameters also matter. Copper’s high reflectivity and thermal conductivity require a capable fiber laser and controlled edge quality. For formed parts, remove dross and sharp burrs before they reach the brake.

Features near copper bends

Holes and slots inside the deformation zone can stretch into an oval or pull the adjacent edge. As a starting rule, keep the edge of a hole at least R + 2T from the bend line. Increase that clearance for hard temper, large V-die openings or precision connector features.

If geometry forces a hole closer to the bend, use one of three controlled solutions:

• Cut the hole undersize and machine or ream it after bending.
• Add a relief feature that separates the hole from the bend zone.
• Form first and create the feature in a secondary operation.

Each option adds cost, but it is cheaper than accepting a distorted mounting or contact hole across a production batch.

What to put on the drawing and RFQ

A fabricator can quote copper much more accurately when the package includes:

• Alloy and temper, such as C11000 H02, not just “copper.”
• Nominal thickness and governing material specification.
• Grain-direction requirement on critical bends.
• Inside bend radius and angle tolerance.
• Critical flange dimensions measured in the formed condition.
• Cosmetic faces and maximum acceptable tool marking.
• Contact areas that must remain bare, flat and clean.
• Finish or plating requirements, including masking.
• Quantity tiers and whether first-article bend validation is required.

Do not dimension every feature tightly by default. Identify the electrical, thermal and assembly interfaces that actually control function, then allow normal fabrication tolerance elsewhere. That keeps both inspection and cost focused on what matters.

Copper K-factor questions engineers ask before an RFQ

Is 0.40 the correct K-factor for all C110 copper?

No. 0.40 is a practical initial value for some quarter-hard or half-hard C110 setups, not a material certification. Annealed and harder tempers can behave differently, and the measured radius, V-die, bend angle and rolling direction can shift the approved value.

Does a copper K-factor change when the material lot changes?

It can. Lot-to-lot thickness, temper and forming response may vary within the material specification. Define when a new lot, alternate mill, tooling change or revised grain direction requires a fresh coupon or first-article check.

Which page should I use to request formed copper components?

Use the custom copper busbar fabrication and drawing-review page when you need conductive formed parts made to a released drawing. Include the exact UNS grade, temper, contact surfaces, bend dimensions and inspection scope; use this article only for the engineering calculation.

Copper K-factor bottom line and RFQ next step

Use 0.35, 0.40 or 0.45 only to create an initial flat pattern for the stated copper condition. The released production value should come from a representative bend using the approved alloy, temper, thickness, radius, grain direction and tooling. Record the measured bend deduction and define which material or process changes trigger revalidation.

For a C101 or C110 part, send the controlled drawing for copper sheet-metal bending review with the alloy, temper, contact surfaces, bend dimensions and inspection scope. For conductive formed components, use the custom copper busbar fabrication page so the bend data and electrical interfaces are reviewed together.

For related reading: K-factor and bend deduction, minimum bend radius and bend relief, grain direction, and springback compensation.