Metal has the largest process library of anything you can build with. That is good news and bad news: almost any metal shape you can draw can be made somehow, but the same finished part can be produced by six different routes with a ten-to-one spread in cost, and picking wrong is invisible until the quotes come back.
This article surveys the major process families for metal products: how each physically works, what it is good at, and where it stops making sense.
Casting: pouring metal into a shape
Casting produces complex geometry no cutting process could reach economically. All casting shares the same limitations: molten metal shrinks as it solidifies, thick sections form voids, and every internal corner wants a fillet. What differs is tooling cost, tolerance, and surface finish.
Sand casting
A pattern is pressed into bonded sand to form a cavity, metal is poured in, and the mold is broken away. Pattern cost is low — often hundreds to a few thousand dollars — and there is essentially no size limit. Surfaces come out rough and dimensions loose, so every functional face needs machining afterward. Best for large parts, low quantities, and cast iron or steel where other methods are impractical.
Investment casting
Wax patterns are injected in a die, assembled onto a tree, dipped repeatedly in ceramic slurry, dewaxed, and fired. The resulting shell is filled with metal and broken away. It reaches fine detail, thin walls, and tolerances close enough that many surfaces need no machining, and it works in stainless, tool steel, and superalloys that die casting cannot touch. The head-to-head against machining is in investment casting vs CNC machining.
Die casting
Molten aluminum, zinc, or magnesium is injected under high pressure into a hardened steel die and solidifies in seconds. Cycle times are short, walls can be thin, and cast-in features like bosses and ribs come free. Steel dies are expensive and take weeks to build, so die casting only makes sense in the thousands of units and up. It is the standard route for volume aluminum housings, covered in aluminum die casting.
Bulk forming: deforming metal into shape
Forming does not remove material and does not melt it. It pushes solid metal into a new shape, which means grain structure follows the geometry rather than being cut through — the reason formed parts outperform machined ones in fatigue and impact.
Forging
Open-die forging hammers or presses hot billet between simple tools; closed-die forging squeezes it into a shaped cavity. Forged parts have the best strength-to-weight of any metal process and are the default for safety-critical load paths: lifting hooks, suspension links, tool heads, aerospace fittings. Forgings arrive near-net and get finish machined on the surfaces that matter.
Extrusion
Aluminum billet is heated and pushed through a shaped steel die to produce an unlimited length of constant profile. Die cost is unusually low — commonly a few thousand dollars — and a well-drawn profile integrates screw channels, snap features, fins, and slide tracks that would otherwise be separate operations. Any rail, frame member, or heat sink deserves an extrusion feasibility check.
Deep drawing
A punch pushes a flat blank into a die cavity, stretching it into a seamless cup or can. This is how battery cans, cookware, aerosol bodies, and sealed enclosures are made. Draw ratios are limited per stage, so deep parts go through several progressive draws with annealing between. Seamless is the key advantage: no weld, no leak path.
Roll forming and spinning
Roll forming passes strip through a series of contoured rollers to build up a profile continuously — the way steel studs, track, and trim are made. Metal spinning presses a rotating blank over a mandrel with a roller tool to produce axisymmetric hollow shapes such as cones, domes, and reflector housings, with tooling costs far below what a matching draw die would run. For low volumes of round hollow parts, spinning is frequently the cheapest answer nobody considers.
Stamping
Progressive die stamping feeds strip through a die that performs one operation per station, ejecting a finished part every stroke. Per-part costs drop to pennies at scale and rates reach hundreds per minute. Tooling is the barrier — tens of thousands of dollars and weeks to build, and design changes mean cutting steel again, which the economics in metal stamping and progressive dies lay out in detail.
Cutting: removing material
| Process | Typical thickness | Edge quality | Best for |
|---|---|---|---|
| Fiber laser | Up to about 1 in steel | Clean, small heat zone | Sheet parts, fast, high accuracy |
| Plasma | Up to several inches | Rougher, wider kerf | Thick plate, low cost per foot |
| Waterjet | Very thick, any material | Slightly tapered, no heat | Heat-sensitive alloys, thick stacks, composites |
| Wire EDM | Thick, conductive only | Excellent, near-mirror | Hardened steel, sharp internal corners |
| Photochemical etching | Thin foil to about 0.06 in | Burr-free, stress-free | Fine features, shims, screens, lead frames |
The choice among thermal cutters usually comes down to thickness and tolerance, which is the subject of plasma vs laser cutting. Waterjet earns its place whenever the heat-affected zone is unacceptable or the material is not something a laser handles well, as explained in what waterjet does that laser and plasma cannot. When a feature has to be produced in fully hardened steel, or when an internal corner needs a radius smaller than any end mill, the answer is EDM machining. For very thin, very fine, burr-free parts, photochemical etching beats every mechanical method because it applies no force to the material at all.
Conventional machining — turning, milling, drilling, grinding — remains the universal fallback and the finishing step for nearly every casting and forging. Its economics are per-part-forever, with no tooling amortization to help at volume.
Joining
Most metal products are assemblies, and how they are joined drives both cost and appearance.
- MIG and TIG welding. MIG is fast and suits thicker steel; TIG is slower, cleaner, and the standard for stainless and aluminum where the weld will be visible.
- Resistance spot welding. The volume method for sheet steel assemblies. Fast, cheap, no filler, leaves visible dimples.
- Laser welding. Narrow, deep, low distortion, minimal heat input. Increasingly the choice for precision and cosmetic assemblies.
- Brazing and soldering. Joins dissimilar metals below their melting points; standard for tubing, heat exchangers, and small assemblies.
- Mechanical joining. Rivets, self-clinching fasteners, clinching, and folded tabs. No heat, no distortion, and serviceable later.
Welding distorts. Any part with tight dimensional requirements after welding needs either a fixture, a post-weld machining operation, or a design that puts the tolerance somewhere the heat did not reach.
Finishing is part of manufacturing
Bare metal parts are rarely shippable. Finishing serves corrosion protection, appearance, and sometimes function.
Aluminum is usually anodized, which converts the surface into a hard oxide layer that can be dyed a range of colors. Steel is plated, painted, or powder coated; the durability and cost comparison is in powder coating vs wet paint. Stainless is passivated, electropolished, or bead blasted. Every finish adds material thickness, which means it must be accounted for in the tolerance of any mating feature — a common and expensive oversight.
Choosing between them
Reduce the decision to three questions. What is the dominant geometry — flat, round, hollow, or complex solid? How many will you make in three years? What does the material have to survive? Those answers usually eliminate every process but two, and choosing between those two is a quote comparison rather than an engineering debate. The material half is worked through in aluminum vs steel.
Projects House designs and sources metal products through a global manufacturing network, and routinely re-routes parts that arrived on the wrong process. Send drawings or a CAD file through our contact form for a process and cost review.