Manufacturing Methods Overview
Subtractive, additive, formative and joining — the four families and when each wins
All manufacturing is one of four families: subtractive (machining removes material), additive (printing adds material), formative (molding/stamping/forming shapes material under pressure) and joining/assembly (fastening, welding, adhesives). A part’s geometry, quantity and material decide the family; within a family, the specific process is an economic choice. Engineers who think in families select processes in seconds.
1. Subtractive: machining
CNC milling, turning, drilling and EDM remove stock from solid billets. Strengths: tightest tolerances (±0.025–0.127 mm), best surface control, any solid metal/plastic, no minimum quantity beyond setup. Weaknesses: material waste, cost scales with part complexity, and internal cavities need tool access.
Best for: precision components, low-to-mid volume, parts needing exact tolerances or specific metal tempers.
2. Additive: 3D printing
FDM, SLA, SLS/MJF and DMLS build parts layer by layer. Strengths: unlimited geometric freedom (channels, lattices, undercuts), no tooling, fast iteration, near-net metal via DMLS. Weaknesses: layered surfaces, anisotropic strength, tolerances ±0.2–0.5 mm, cost scales with volume not quantity.
Best for: complex geometry, prototypes, low volume, design iteration, internal channels.
3. Formative: molding, stamping, casting
Injection molding, sheet stamping, die casting, forging and extrusion shape material against a tool. Strengths: lowest unit cost at volume, fast cycle times, repeatability, excellent surfaces (molded). Weaknesses: tooling investment ($2k–100k+), design constraints (draft, wall, parting), long tooling lead.
Best for: production volumes above the tooling crossover (typically 500–5,000 for molding), identical parts in quantity, metals and plastics at scale.
4. Joining and assembly
Fasteners, welding, brazing, adhesives and interference fits combine subparts. Design for assembly (DFA) minimizes part count and fastener types; welding integrates strength but adds distortion; adhesives distribute load and seal. Assembly is where most product cost actually hides.
Best for: multi-material products, serviceable designs, large structures, and integrating printed/machined/molded parts into one product.
Quick reference
| Family | Example processes | Tolerance | Volume sweet spot | Unit cost |
|---|---|---|---|---|
| Subtractive | CNC mill/turn, EDM | ±0.025–0.127 mm | 1–5,000 | Medium |
| Additive | FDM, SLA, SLS, DMLS | ±0.2–0.5 mm | 1–100 | High (flat) |
| Formative | Molding, stamping, die-cast | ±0.3% / ±0.1 mm | 500–1M+ | Low |
| Joining | Weld, fastener, adhesive | assembly ± | varies | varies |
Sources & references
- ISO/ASTM 52900:2021 — Additive terms
- ASM Handbook — Vol 16 Machining
- Xometry Learning Center — Manufacturing Overview (public engineering reference)