---
type: process
name: "Electroforming"
category: "Forming"
subcategory: "Metal"
materials: ["Metal"]
tolerances: "The mandrel-contacting surface replicates the mandrel closely, so its accuracy is the mandrel's accuracy; wall thickness typically varies ±10–25% across a part unless shields and current thieves are used"
volumes: "1–10,000 parts; single pieces are entirely practical, and permanent mandrels amortize over hundreds"
lead_time: "4–10 weeks including mandrel manufacture and process development; plating alone runs days per part for thick walls"
url: https://manufacturingprocesses.org/processes/forming/electroforming
---

# Electroforming

Electroforming grows a metal shell by electrodeposition onto a mandrel that is afterwards removed, producing thin parts with sub-micron detail.

- **Category**: [Forming](https://manufacturingprocesses.org/processes/forming.md)
- **Family**: Metal
- **Materials**: Metal
- **Typical tolerances**: The mandrel-contacting surface replicates the mandrel closely, so its accuracy is the mandrel's accuracy; wall thickness typically varies ±10–25% across a part unless shields and current thieves are used
- **Surface finish**: The mandrel side reproduces the mandrel finish, including mirror and sub-micron textures; the solution side is rough and is machined where it matters
- **Typical volumes**: 1–10,000 parts; single pieces are entirely practical, and permanent mandrels amortize over hundreds
- **Lead time**: 4–10 weeks including mandrel manufacture and process development; plating alone runs days per part for thick walls

## Overview

Electroforming grows a metal part atom by atom, electrodepositing it onto a conductive mandrel until the wall reaches the required thickness, then separating the two. It is electroplating taken to the point where the deposit becomes the part rather than a coating.

Because the part's inner surface is a negative of the mandrel, replication fidelity is limited only by how well the mandrel was made — sub-micron features and mirror finishes transfer faithfully, which is why electroforming produces optical disc stampers, textured mold inserts, precision meshes and screens, waveguides, bellows, foil, and nozzles.

Nickel and copper are the workhorse metals, deposited from sulfamate or acid baths at roughly 0.001–0.002 in (25–50 µm) per hour. That rate is the process's defining constraint: a 0.020 in wall is a day or more of continuous plating. Typical wall thicknesses run 0.001–0.030 in (25 µm–0.75 mm), and volumes from one part to a few thousand.

## How it works

1. **Mandrel.** The mandrel carries the geometry, so it is made to the tolerance and finish the part requires — diamond turned, polished, photolithographically patterned, or machined. It must be electrically conductive; non-conductive mandrels (wax, plastic, glass) are metallized first with a sputtered or electroless conductive layer.
2. **Mandrel type.** A **permanent** mandrel is drafted, passivated stainless steel or chrome-plated steel, designed so the electroform can be pulled off and the mandrel reused hundreds of times. An **expendable** mandrel — aluminum dissolved in caustic, low-melting alloy, or wax — is destroyed to release the part and is what makes undercut and fully enclosed geometry possible.
3. **Passivation.** For permanent mandrels, a controlled thin passive film is deliberately created so the deposit adheres well enough to grow but releases cleanly at the end. Getting this wrong is the classic electroforming failure: the shell either falls off mid-build or refuses to come off at all.
4. **Deposition.** The mandrel is made the cathode in an electrolyte — nickel sulfamate is the standard for structural electroforms, typically operated around 120–140°F (50–60°C) in the pH 3.5–4.5 region — and current is applied. Metal deposits at a rate proportional to current density.
5. **Managing thickness distribution.** Current density is not uniform: it concentrates at edges, points, and protruding features, and starves in recesses. Left alone, a deposit is thick on the corners and thin in the grooves. Conforming anodes, current thieves, and non-conductive shields are used to even it out, and thickness variation of ±10–25% is normal without careful control.
6. **Separation.** The electroform is pulled from a permanent mandrel or the expendable mandrel is dissolved or melted away.
7. **Finishing.** The outer (solution-side) surface is rough and uncontrolled and is machined or ground where it matters; the mandrel side is finished already.

Internal stress in the deposit is a real design variable. Sulfamate nickel is chosen over other nickel baths largely because it deposits at low internal stress, and stress additives are used to tune it — a highly stressed thick electroform will distort or crack when it comes off the mandrel.

## Design guidelines

### The mandrel side is the good side

Every dimension, finish, and detail you care about must be on the mandrel-contacting surface. The solution side grows freely, follows the current distribution, and ends up rough and roughly parallel at best. Design the part so its functional surface is the one against the mandrel.

### Avoid deep, narrow recesses

Throwing power is poor. A deep narrow groove in the mandrel receives much less current density at its bottom than at its mouth, so the deposit there is thin — sometimes dramatically so. Keep aspect ratios of recessed features low, or accept a wall thickness that varies with depth. See the [surface finish chart](/charts/surface-finish-chart) for context on the finishes the mandrel needs to carry.

### Break every sharp external edge

A sharp external corner on the part corresponds to a sharp internal corner on the mandrel, where current crowds, deposits build fast, and nodules or treeing form. Radius the mandrel geometry wherever possible.

### Release geometry decides the mandrel type

If the part can be pulled straight off, use a permanent mandrel with a degree or two of draft and get hundreds of parts from one tool. If it has undercuts, re-entrant features, or is fully enclosed, an expendable mandrel is required — and it has to be remade for every single part, which changes the economics completely.

### Wall thickness and time

Design for the thinnest wall that carries the load. At roughly 0.001–0.002 in per hour, wall thickness translates directly into machine hours: 0.005 in is a shift, 0.030 in is most of a week. Typical production electroforms fall in the 0.001–0.030 in (25 µm–0.75 mm) band.

### Expect thickness variation

Without extensive shielding and thieving, plan on ±10–25% variation in wall thickness across a part, biased thick at edges and thin in recesses. If a uniform wall is critical, say so — it is achievable, but it costs anode tooling and development time.

| Feature | Recommended | Limit | Why |
| --- | --- | --- | --- |
| Functional surface | On the mandrel side | Solution side is uncontrolled | The deposit replicates the mandrel exactly |
| Wall thickness | 0.002–0.010 in (50–250 µm) | 0.030 in (0.75 mm) practical | Deposition runs 0.001–0.002 in per hour |
| Recess aspect ratio | Shallow and open | Deep grooves plate thin at the bottom | Current density falls inside recesses |
| External corners | Radiused | Sharp corners grow nodules | Current crowds at internal mandrel corners |
| Draft, permanent mandrel | 1–2° | 0° needs an expendable mandrel | The shell must pull off cleanly |
| Undercuts | Expendable mandrel only | New mandrel per part | Nothing can be pulled over an undercut |
| Wall uniformity | Accept ±10–25% | Tighter needs shields and thieves | Current distribution is inherently uneven |

## Cost drivers

Two things drive cost: mandrel work and plating hours. The mandrel is a precision part in its own right, made to the finish and tolerance the final component requires, and on a permanent-mandrel job it is the dominant fixed cost — amortized over hundreds of parts, it becomes small. On an expendable-mandrel job it is a per-part cost, and the process becomes expensive fast. Plating time is directly proportional to wall thickness at roughly 0.001–0.002 in per hour, and tank time is not compressible: doubling the current to speed it up degrades the deposit.

Volume breakpoints: single parts are entirely practical, which is unusual for a process capable of this precision. Permanent-mandrel work amortizes across hundreds to a few thousand parts. There is no high-volume regime — electroforming is never the cheap answer at scale, it is the only answer for certain geometries and surface requirements.

1. **Use a permanent mandrel wherever the geometry allows.** Adding a degree of draft to make a mandrel reusable is the single biggest cost lever in the process.
2. **Thin the wall.** Wall thickness is tank hours, one for one.
3. **Nest multiple parts per mandrel.** Plating several cavities on one mandrel in one tank cycle spreads the fixed time.

## FAQ

### How thick can an electroformed part be?

Typical production walls run 0.001–0.030 in (25 µm–0.75 mm). Thicker is possible but rarely economic, because deposition proceeds at only about 0.001–0.002 in (25–50 µm) per hour — a 0.030 in wall represents most of a week of continuous plating, and increasing the current to speed it up degrades the deposit.

### Which surface of an electroform is accurate?

The one that was against the mandrel. It is a faithful negative of the mandrel surface, reproducing sub-micron detail and mirror finishes. The solution side grows freely according to the current distribution and comes out rough and only roughly parallel, so it is machined afterward if it matters.

### What is the difference between a permanent and an expendable mandrel?

A permanent mandrel is passivated stainless or chrome-plated steel with a degree or two of draft, so the electroform pulls off and the mandrel is reused hundreds of times. An expendable mandrel — aluminum dissolved in caustic, low-melting alloy, or wax — is destroyed to release the part, which is the only way to make undercut or fully enclosed geometry.

### Why is electroformed wall thickness uneven?

Because current density is uneven. It concentrates at edges, points, and protrusions and starves in recesses, so the deposit builds fast on corners and slowly at the bottom of grooves. Expect ±10–25% variation without control measures; conforming anodes, current thieves, and non-conductive shields even it out at additional development cost.

### What metals can be electroformed?

Nickel and copper are the workhorses, along with nickel-cobalt for higher hardness and gold and silver for specialty work. Nickel sulfamate is the standard structural bath because it deposits at low internal stress, which matters because a highly stressed thick deposit distorts or cracks when it is separated from the mandrel.

### Electroforming or CNC machining?

Machining wins for anything thick, structural, or geometrically prismatic. Electroforming wins where the requirement is a thin shell with a precisely replicated surface — mold texture inserts, meshes, waveguide interiors, and optical stampers — because it copies a mandrel exactly rather than cutting a surface, and it can make walls far thinner than a cutter can reach.

## Alternative processes

- [Photochemical Machining](https://manufacturingprocesses.org/processes/cutting/photochemical-machining.md): Photochemical machining masks sheet metal photographically and etches away the unmasked areas, cutting burr-free flat parts with no hard tooling.
- [Metal Injection Molding](https://manufacturingprocesses.org/processes/forming/metal-injection-molding.md): Metal injection molding molds a powder-and-binder feedstock exactly like a plastic, then debinds and sinters it into a dense small metal part.
- [CNC Machining](https://manufacturingprocesses.org/processes/cutting/cnc-machining.md): CNC machining removes material from solid stock with a programmed cutting tool, producing accurate parts directly from a CAD model with no tooling.
- [Direct Metal Laser Sintering (DMLS)](https://manufacturingprocesses.org/processes/forming/direct-metal-laser-sintering-dmls.md): Direct metal laser sintering fuses metal powder layer by layer with a laser, building dense metal parts anchored to a supported build plate.

## Related processes

- [Electroplating](https://manufacturingprocesses.org/processes/finishing/electroplating.md): Electroplating deposits a metal coating from solution onto a conductive part by passing current through an electrolyte bath.
- [Photochemical Machining](https://manufacturingprocesses.org/processes/cutting/photochemical-machining.md): Photochemical machining masks sheet metal photographically and etches away the unmasked areas, cutting burr-free flat parts with no hard tooling.
- [Photo Etching](https://manufacturingprocesses.org/processes/finishing/photo-etching.md): Photo etching masks a surface photographically and etches shallow detail into it for decoration, marking or texture.
- [Vacuum Metalizing](https://manufacturingprocesses.org/processes/finishing/vacuum-metalizing.md): Vacuum metalizing evaporates aluminum inside a vacuum chamber so it condenses as a mirror-bright film on the part surface.

---

*Source: [Manufacturing Processes](https://manufacturingprocesses.org/processes/forming/electroforming)*

*Last updated: August 11, 2026*