Manufacturing has two heavyweights: subtractive manufacturing (cutting away material) and additive manufacturing (building layer by layer). Both turn raw materials into parts, but they work in opposite ways—each with unique strengths for different projects. Whether you’re making a metal bracket, a plastic prototype, or a complex medical tool, choosing the wrong one can waste time, money, or ruin your part’s performance. This guide breaks down their differences, uses real-world cases to show how they work, and gives you a step-by-step way to pick the right one.
First: What Are Subtractive and Additive Manufacturing?
Before comparing them, let’s get clear on what each process does. They’re opposites, and that’s why their uses vary so much.
Subtractive Manufacturing: “Cutting Down to Size”
Subtractive manufacturing starts with a solid block, plate, or rod of material (like aluminum, steel, or plastic) and removes excess material to shape it. Think of carving a statue from a stone block—you take away what you don’t need until you get the design you want.
The most common subtractive method is CNC machining, which uses computer-controlled tools (drills, mills, lathes) to cut with precision. Other subtractive processes include laser cutting (for 2D shapes), waterjet cutting (for tough materials like metal), and EDM (for tiny, detailed cuts).
Key Trait: Relies on “removing” material—so the final part’s strength comes from the original solid material (no weak layers).
Additive Manufacturing: “Building Layer by Layer”
Additive manufacturing (better known as 3D printing) builds parts from the bottom up, stacking thin layers of material (powder, filament, or liquid resin) until the design is complete. Imagine stacking sheets of paper to make a 3D cube—each layer sticks to the one below.
Popular additive methods include:
- FDM (Fused Deposition Modeling): Uses plastic filament (like PLA or ABS) melted through a nozzle.
- SLS (Selective Laser Sintering): Uses a laser to fuse nylon powder into parts.
- MJF (HP Nylon Multi-Jetting Fusion): Uses liquid agents and heat to bond nylon powder.
- SLM (Selective Laser Melting): Uses a laser to melt metal powder (for metal parts like titanium implants).
Key Trait: Relies on “adding” material—layers can create complex shapes, but they may leave weak spots between layers (called anisotropy).
Side-by-Side Comparison: Key Differences That Matter
To choose between them, you need to compare their performance on the factors that affect your project: cost, speed, material options, and more. The table below breaks down the critical differences (data from manufacturing industry studies and real-world quotes):
| Factor | Subtractive Manufacturing (e.g., CNC Machining) | Additive Manufacturing (e.g., 3D Printing) |
| Material Range | Wide—metals (aluminum, steel, titanium), plastics, wood, glass, stone, foam. | Limited—mostly plastics (nylon, PLA, ABS), some metals (titanium, steel via SLM). |
| Part Strength | High—solid material means parts are isotropic (strong in all directions). No layer weaknesses. | Medium—parts are anisotropic (weaker along layer lines). SLM metal parts are strong but costly. |
| Precision/Tolerance | Very high—tolerances as tight as ±0.025 mm (great for tight-fit parts like gears). | Lower—tolerances down to ±0.1 mm (SLM/DMLS is better, but still not as tight as CNC). |
| Complexity | Best for simple-to-moderate shapes (holes, threads, flat surfaces). Struggles with hollow/lattice designs. | Best for complex shapes (lattices, hollow interiors, organic curves). Can make designs CNC can’t. |
| Speed (Small Batches: 1–10 parts) | Slower—setup takes time (tool selection, machine programming). A metal bracket takes 2–4 hours. | Faster—no setup beyond uploading a CAD file. A plastic bracket takes 1–2 hours (FDM/MJF). |
| Speed (Large Batches: 100+ parts) | Faster—setup costs are spread over more parts. 100 metal brackets take 8–12 hours (CNC). | Slower—each part is built layer by layer. 100 plastic brackets take 20–30 hours (MJF). |
| Cost (Small Batches: 10 parts) | Higher—setup fees (\(50–\)200) plus material waste. 10 aluminum brackets cost ~$150 total. | Lower—no setup fees, less material waste. 10 plastic brackets (MJF) cost ~$80 total. |
| Cost (Large Batches: 100 parts) | Lower—setup fees spread out. 100 aluminum brackets cost ~$500 total. | Higher—layer-by-layer printing adds time/material costs. 100 plastic brackets (MJF) cost ~$600 total. |
| Material Waste | High—50–70% of raw material is cut away (chips/scraps). Some can be recycled, but most is waste. | Low—only uses material needed for the part. 3D printing (SLS/MJF) reuses 50%+ of unused powder. |
| Post-Processing | Minimal—parts often have smooth finishes. May need sanding or polishing for aesthetics. | Required—parts have layer lines or loose powder. Needs cleaning (for SLS/MJF) or sanding (for FDM). |
Real-World Cases: When to Use Each (And Why)
Numbers tell part of the story—but real projects show how these differences play out. Let’s look at three examples where the choice between subtractive and additive made or broke the project.
Case 1: Metal Automotive Brackets (Large Batch)
A car parts supplier needed 500 aluminum brackets for a new SUV model.
- Additive Option (SLM): Each bracket would cost \(12 (metal powder is expensive), plus \)200 for setup. Total: \(12×500 + \)200 = $6,200. Lead time: 2 weeks (layer-by-layer printing is slow for large batches).
- Subtractive Option (CNC Machining): Each bracket cost \(5 (aluminum block is cheap), plus \)300 for setup. Total: \(5×500 + \)300 = $2,800. Lead time: 3 days (CNC is fast for repeatable parts).
Result: The supplier chose CNC machining—saved $3,400 and got parts 11 days faster. The brackets needed to be strong and fit tightly (tolerance ±0.05 mm)—CNC’s precision was perfect.
Case 2: Custom Medical Surgical Guides (Small Batch)
A dental clinic needed 5 custom surgical guides (nylon PA12) for implant surgeries. Each guide had to fit a patient’s unique jaw shape (complex, organic design).
- Subtractive Option (CNC Machining): The complex shape would require custom tools (\(1,000 setup) and 10 hours of machining per guide. Total: \)1,000 + (\(50×5) = \)1,250. Lead time: 1 week.
- Additive Option (MJF): No setup fees—just upload the patient’s 3D scan. Each guide took 2 hours to print. Total: \(30×5 = \)150. Lead time: 2 days.
Result: The clinic chose MJF—saved $1,100 and got guides 5 days faster. The guides didn’t need ultra-tight tolerances (±0.1 mm was enough), and MJF’s ability to make complex shapes was critical.
Case 3: High-Temperature Engine Part (Metal, Small Batch)
An aerospace startup needed 3 titanium engine parts that could handle 600°C heat. The parts had a hollow interior to reduce weight (complex design).
- Subtractive Option (CNC Machining): Titanium is hard to cut—tools would wear out fast (\(800 setup) and take 8 hours per part. The hollow interior would need extra steps (drilling from both sides). Total: \)800 + (\(100×3) = \)1,100. Lead time: 5 days.
- Additive Option (SLM): SLM melts titanium powder into the complex shape—no extra steps. Each part took 4 hours to print. Total: \(200×3 = \)600. Lead time: 3 days.
Result: The startup chose SLM—saved $500 and got parts with the exact hollow design they needed. SLM’s metal parts are strong enough for high heat, and the small batch made additive cost-effective.
Step-by-Step: How to Choose Between Them for Your Project
Follow these 4 simple steps to pick the right process—no guesswork needed.
Step 1: Define Your Project’s Core Needs
Start by asking:
- What material do you need? (Metal? Plastic? Wood?)
- How many parts do you need? (1–10? 100+?)
- How complex is the design? (Simple holes? Complex lattices?)
- What tolerance do you need? (±0.025 mm? ±0.1 mm?)
Example: If you need 200 steel brackets (simple design, tolerance ±0.05 mm), your core needs are “metal, large batch, simple shape, tight tolerance.”
Step 2: Match Needs to Process Strengths
Use this cheat sheet to narrow down:
| Core Need | Best Process |
| Metal parts, large batch, simple shape | Subtractive (CNC Machining) |
| Plastic parts, small batch, complex shape | Additive (MJF/SLS/FDM) |
| Metal parts, small batch, complex shape | Additive (SLM) |
| Wood/glass/stone parts (any batch) | Subtractive (CNC/Waterjet) |
| Tight tolerance (±0.025 mm) (any material) | Subtractive (CNC) |
Step 3: Calculate Total Cost (Don’t Forget Hidden Fees)
Cost isn’t just per-part price—include setup fees, material waste, and post-processing:
- Subtractive: Add setup fees (\(50–\)500) and material waste (50–70% of raw material cost).
- Additive: Add post-processing costs (\(2–\)10 per part for cleaning/sanding) and, for metal, higher material costs.
Example: 50 plastic parts (nylon PA12):
- Subtractive: \(2 per part + \)100 setup + \(50 material waste = \)250 total.
- Additive (MJF): \(3 per part + \)30 post-processing = $180 total.
Additive is cheaper here.
Step 4: Test with a Prototype (If You’re Unsure)
If you’re on the fence, make a single prototype with both processes (if budget allows). Test the prototype for strength, fit, and finish—this will tell you which process works better for the final batch.
Tip: For plastic prototypes, use FDM (cheap, fast). For metal prototypes, use SLM (if complex) or CNC (if simple).
Yigu Technology’s Perspective on Subtractive vs. Additive Manufacturing
At Yigu Technology, we don’t force one process—we match it to your project’s goals. For clients needing large batches of metal parts (like automotive brackets) or wood/glass components, we recommend CNC machining for its speed and cost savings. For small batches of complex plastic parts (like medical guides) or intricate metal parts (like aerospace components), we use 3D printing (MJF/SLM). We also help with prototypes: FDM for quick plastic tests, CNC for precise metal fits. Our team calculates total costs (setup, waste, post-processing) upfront, so you never have surprises. For us, the best process is the one that makes your part well, on time, and within budget.
FAQ
1. Can I use additive manufacturing for metal parts instead of subtractive?
Yes—but only if you have a small batch or complex design. SLM (metal 3D printing) makes great complex metal parts, but it’s 2–3x more expensive than CNC for large batches. For simple metal parts (like bolts) or batches over 50, CNC is cheaper and faster.
2. Is additive manufacturing always better for complex shapes?
Almost always—additive can make hollow lattices, organic curves, and internal features that CNC can’t reach. The only exception is if the complex shape can be split into simpler parts that CNC can make, then assembled. For example, a complex plastic housing might be cheaper to CNC as two parts and glue together than to 3D print as one.
3. Which process produces less waste?
Additive manufacturing is far more efficient—SLS/MJF reuse 50%+ of unused powder, and FDM uses only the filament needed for the part. Subtractive manufacturing wastes 50–70% of raw material (chips/scraps), even with recycling. If sustainability is a priority, additive is the better choice.