Why Metal AM Requires Different Thinking
Metal 3D printing is not "FDM but with metal." The physics of laser melting at 10,000+ °C/s creates residual stresses, anisotropic microstructures, and post-processing requirements that don't exist in polymer AM. This guide gives you the engineering framework to design for DMLS - support strategy, alloy selection, the full post-processing chain - so your first metal build succeeds instead of cracking on the plate.
How DMLS / SLM Works
A high-power fiber laser fully melts metal powder in an inert atmosphere, producing >99.5% dense parts with properties approaching wrought material.
DMLS (Direct Metal Laser Sintering, EOS trademark) and SLM (Selective Laser Melting) are functionally identical processes - both use a high-power fiber laser (200–1000 W, 1064 nm wavelength) to fully melt metal powder layer by layer in an inert atmosphere (argon or nitrogen). The term "sintering" in DMLS is a misnomer - the powder is fully melted, creating near-fully-dense parts. The process operates inside a sealed chamber flooded with inert gas to prevent oxidation. A recoater blade or roller spreads a thin layer of metal powder (20–80 µm particle size), the laser melts the cross-section, and the build plate drops by one layer height (20–60 µm). This repeats for hundreds to thousands of layers. The resulting parts are >99.5% dense - comparable to wrought material - but the rapid heat/cool cycling creates significant residual stresses that must be managed through support structures, build orientation, and post-processing.
Laser power & spot size
Single-laser: 200–400 W, 80–100 µm spot. Multi-laser (EOS M400-4, SLM 500): 4× 400–700 W lasers for 4× throughput on the same build plate. Multi-laser machines are critical for production economics - they reduce build time by 60–75%.
Inert atmosphere
Oxygen content must stay below 0.1–0.5% (alloy-dependent) to prevent oxidation and porosity. Argon is standard for most alloys; nitrogen is used for austenitic stainless steels. Chamber purge adds 30–60 min to each build setup.
Support structures are mandatory
Supports serve three critical functions: (1) anchor parts to the build plate to resist thermal distortion, (2) conduct heat from the melt pool to the baseplate, (3) support overhangs. Supports are typically 50–70% of the engineering effort in DMLS build prep.
Residual stress
Rapid heating (10⁴–10⁶ °C/s melt rate) and cooling create enormous residual stresses - enough to crack parts or warp them off the build plate. Stress relief heat treatment is mandatory before removing parts from the plate.
Layer height: 20–60 µm
20 µm for fine features and better surface finish (very slow). 40 µm standard for most builds. 60 µm for faster builds with less critical surface requirements. Thinner layers = better accuracy but 2–3× longer build times.
Density: >99.5%
Properly processed DMLS parts achieve >99.5% density (some alloys >99.9% with HIP). This is comparable to wrought material and significantly denser than binder jetting (95–98%) or metal FFF (95–99%).
Pro Tip
DMLS build prep (orientation, support design, parameter optimization) is 50–70% of the engineering effort and directly impacts part quality. A poorly supported part will warp, crack, or fail stress relief. Budget engineering time accordingly - this is not "press print."
Metal Alloys Guide
DMLS supports a broad range of engineering alloys - from cost-effective AlSi10Mg to flight-critical Ti-6Al-4V and Inconel 718.
DMLS alloy selection is narrower than CNC machining but covers the alloys most commonly needed in aerospace, medical, and automotive applications. Important: DMLS microstructure differs from wrought equivalents - always verify material properties against your spec.
| Alloy | UTS (MPa) | Yield (MPa) | Elongation (%) | Key Properties | Common Applications |
|---|---|---|---|---|---|
| AlSi10Mg | 350–450 | 200–280 | 6–12 | Lightweight, good thermal conductivity | Heat exchangers, brackets, housings, motorsport |
| 316L Stainless | 520–600 | 200–300 | 30–50 | Corrosion resistant, biocompatible | Medical devices, fluid handling, marine |
| 17-4 PH Stainless | 900–1100 | 700–900 | 5–12 | High strength, age hardenable | Aerospace brackets, tooling, fixtures |
| Ti-6Al-4V (Grade 5) | 950–1100 | 850–1000 | 8–14 | Highest strength-to-weight, biocompatible | Aerospace structural, medical implants, motorsport |
| Inconel 625 | 800–950 | 450–600 | 25–40 | Extreme heat & corrosion resistance | Turbine components, exhaust systems, chemical processing |
| Inconel 718 | 1000–1200 | 700–950 | 10–20 | Highest strength superalloy, age hardenable | Turbine blades, rocket engines, high-temp structural |
| CoCr (Cobalt Chrome) | 1100–1300 | 700–900 | 8–15 | Biocompatible, extreme wear resistance | Dental copings, orthopedic implants, turbines |
| Maraging Steel (MS1) | 1100–1300 | 1000–1100 | 8–12 | Ultra-high strength, age hardenable | Tooling inserts, injection molds, dies |
| Copper (CuCr1Zr) | 250–350 | 200–280 | 15–25 | Highest thermal & electrical conductivity | Induction coils, rocket nozzles, EDM electrodes |
Pro Tip
For most applications: AlSi10Mg for lightweight brackets and housings, 316L for corrosion/medical, 17-4 PH for high-strength stainless, Ti-6Al-4V for strength-to-weight, Inconel 718 for extreme temperatures. If you're not sure, start with 316L - it's the most forgiving DMLS alloy to process.
Design Guidelines (DFM)
DMLS design rules center on support strategy, thermal management, and designing for the post-processing chain.
DMLS design freedom is enormous - conformal cooling channels, topology-optimized structures, consolidated assemblies - but it comes with constraints that don't exist in polymer AM. Every design decision affects supportability, residual stress, and post-processing.
| Feature | Recommended | Minimum | Notes |
|---|---|---|---|
| Wall thickness | 0.5 mm | 0.3–0.4 mm | Alloy-dependent; Ti-6Al-4V can go thinner than AlSi10Mg |
| Overhang angle | <35° from vertical | <45° | Below 45° requires supports; self-supporting at 35° for most alloys |
| Internal channels | ≥1.0 mm diameter | ≥0.5 mm | Below 1 mm, powder removal becomes unreliable |
| Conformal cooling | 3–6 mm dia., ≥2 mm wall from surface | - | The #1 DMLS value-add for tooling; 20–40% cycle time reduction |
| Support-free design | Diamond/teardrop cross-sections for channels | - | Replace round channels with self-supporting shapes (45° rule) |
| Min feature size | 0.4 mm | 0.2 mm | Limited by laser spot size and powder particle size |
| Hole accuracy | Add +0.05–0.10 mm to nominal | - | Small holes shrink due to melt-pool thermal expansion |
| Stress relief design | Add sacrificial ribs on large flat areas | - | Helps manage thermal distortion; ribs removed in post-processing |
| Build plate connection | ≥3 mm base for plate adhesion | - | Wire EDM cuts parts from plate; design a sacrificial base |
| Thin features (aspect >10:1) | Add ≥0.3 mm radius fillets | - | Stress concentrations at sharp corners cause micro-cracking |
Pro Tip
Design for self-supporting geometry wherever possible. Replace circular channels with teardrop shapes (flat at the top, rounded at the bottom) to eliminate internal supports. This single design change can reduce post-processing time by 50% on parts with internal cooling passages.
Post-Processing Chain
DMLS post-processing is the most extensive of any AM process - it often costs 30–60% of the total part price and adds 1–3 weeks to lead time.
Post-processing is where most DMLS programs go over budget. The chain below is typical for a production DMLS part. Not every step is required for every part, but skipping critical steps (especially stress relief) risks catastrophic part failure.
Step 1: Stress relief (mandatory)
Heat treatment at 600–1000 °C (alloy-dependent) for 1–4 hours while the part is still attached to the build plate. Skipping this step risks warpage, cracking, or dimensional shift when parts are cut off the plate. Cost: $50–200/build.
Step 2: Wire EDM or band saw (mandatory)
Cut parts from the build plate. Wire EDM is preferred for precision and clean cuts - band saw for large/rough parts. Cost: $20–100/part depending on cross-section area and number of parts per plate.
Step 3: Support removal
Supports are manually broken, ground, or machined off. This is the most labor-intensive step - complex internal supports can take hours. Poorly accessible supports (inside channels, deep pockets) may require EDM. Cost: $30–200/part.
Step 4: HIP - Hot Isostatic Pressing (optional)
Exposes parts to high temperature (900–1200 °C) and pressure (100–200 MPa of argon) to close internal micro-porosity, achieving >99.9% density. Required for flight-critical aerospace parts and fatigue-life-critical applications. Cost: $50–300/part.
Step 5: Heat treatment / age hardening
Many DMLS alloys (17-4 PH, Inconel 718, maraging steel) require age-hardening to reach full mechanical properties. Ti-6Al-4V may need solution treatment + aging. Cost: $30–150/build (furnace batch).
Step 6: CNC machining of interfaces
Critical mating surfaces, bores, and threads are CNC-machined to final tolerances. DMLS as-built: ±0.004″ / 150–400 Ra µin. Post-machined: ±0.0005″ / 16–63 Ra µin. Cost: $50–500/part depending on number of features.
Step 7: Surface finishing
Bead blasting (standard), tumble finishing, electropolishing (medical/food-contact), or shot peening (fatigue life improvement). Cost: $10–50/part for blasting, $50–200/part for electropolishing.
Step 8: Inspection
CMM dimensional inspection, CT scanning for internal defects (porosity, cracks), surface roughness measurement, material cert review. Required for aerospace (AS9100) and medical (ISO 13485). Cost: $50–500/part.
Pro Tip
Budget 30–60% of the total part cost for post-processing. On a $200 DMLS part, expect $60–$120 in post-processing. For complex parts with internal channels and CNC-machined interfaces, post-processing can exceed the raw print cost.
Cost Analysis
DMLS is the most expensive AM process per part. Understanding the cost structure prevents budget surprises.
DMLS cost is driven by three factors: machine time (dominant), material, and post-processing. Multi-laser machines are reducing the machine-time component, but DMLS remains 5–50× more expensive than CNC for simple geometries. The value proposition is geometric freedom, not cost.
| Cost Component | AlSi10Mg | 316L Stainless | Ti-6Al-4V | Inconel 718 |
|---|---|---|---|---|
| Machine rate (/hr) | $80–150 | $80–150 | $100–200 | $120–200 |
| Powder cost ($/kg) | $80–120 | $60–100 | $250–400 | $150–300 |
| Post-processing | +30–40% | +30–50% | +40–60% | +40–60% |
| Est. cost (small bracket, 1 pc) | $150–300 | $150–350 | $250–500 | $300–600 |
| Est. cost (small bracket, 10 pc) | $100–200/ea | $120–250/ea | $200–400/ea | $250–500/ea |
| Est. cost (small bracket, 50 pc) | $80–150/ea | $80–180/ea | $150–300/ea | $180–400/ea |
DMLS vs CNC: when is DMLS cheaper?
DMLS wins on cost when: (1) the CNC buy-to-fly ratio exceeds 10:1 (titanium/Inconel), (2) the part consolidates multiple CNC operations, (3) conformal cooling channels eliminate secondary drilling, or (4) the geometry requires 5-axis machining setups. For simple brackets, CNC is almost always cheaper.
Multi-laser machines change the math
4-laser machines (EOS M400-4, SLM 500) reduce build time by 60–75% vs. single-laser. For production runs of 20+ parts, multi-laser machines can bring DMLS cost within 2–3× of CNC for complex geometries.
Build height is the dominant time driver
A 100 mm tall build takes the same time whether it has 1 part or 20 parts at the same Z-height. Pack parts at the same height level and fill the plate to minimize per-part machine time. Tall, skinny parts are the most expensive per gram.
Pro Tip
For DMLS cost estimation, use this rule of thumb: $5–15 per cm³ of metal deposited (alloy-dependent) plus 30–60% for post-processing. A 50 cm³ AlSi10Mg bracket: ~$250–750 + $75–450 post = $325–1,200 total. Always include post-processing in your budget.
DMLS vs Metal FFF
Metal FFF (bound metal deposition) is the accessible alternative to DMLS - $100K vs $500K+, simpler workflow, but different capabilities.
Metal FFF (Fused Filament Fabrication for metal) - used by Desktop Metal Studio and Markforged Metal X - is the FDM equivalent for metal. A bound metal filament or rod is extruded layer by layer, then debound and sintered in a furnace to achieve 95–99% density. Here's the head-to-head comparison:
| Factor | DMLS / SLM | Metal FFF (BMD) |
|---|---|---|
| Density | >99.5% (as-printed) | 95–99% (after sinter) |
| Tolerance | ±0.004″ (±0.10 mm) | ±0.020″ (±0.50 mm) after sinter |
| Surface finish | 150–400 Ra µin (as-built) | 200–600 Ra µin (as-sintered) |
| Support structures | Metal supports (hard to remove) | Ceramic interface release (easier removal) |
| Machine cost | $500K–$2M+ | $100K–$200K |
| Materials | Al, SS, Ti, Inconel, CoCr, Cu (9+ alloys) | 17-4 PH, 316L, H13, Cu, Ti-6Al-4V (5–6 alloys) |
| Max part size | 400 × 400 × 400 mm (typical) | 150 × 200 × 150 mm (Desktop Metal) |
| Post-processing | Stress relief + EDM + support removal + machining | Debind (solvent/thermal) + sinter (24–48 hr) |
| Shrinkage | Minimal (0.1–0.3%) | Significant (15–20% linear, compensated in software) |
| Geometric complexity | Conformal cooling, lattice, internal channels | Limited by nozzle access (like FDM) |
| Per-part cost (small bracket) | $150–400 | $50–150 (in-house) |
| Best for | Complex, critical, high-performance metal parts | In-house prototypes, tooling, low-volume simple geometries |
Pro Tip
Think of Metal FFF as "CNC-light for the shop floor" - it puts metal AM capability in-house at a fraction of DMLS cost. But it doesn't replace DMLS for complex geometries, tight tolerances, or flight-critical parts. If your part needs conformal cooling, lattice structures, or >99% density, DMLS is the only option.
Applications & Use Cases
DMLS enables geometries that no other manufacturing process can produce - conformal cooling, topology optimization, and part consolidation.
Conformal cooling inserts for injection molds
DMLS-printed mold inserts with internal cooling channels that follow the part contour (impossible with gun-drilled straight channels). Reduces injection mold cycle time by 20–40% and improves part quality by eliminating hot spots. Maraging steel is the standard material.
Aerospace structural brackets
Topology-optimized Ti-6Al-4V brackets that reduce weight by 30–60% vs. CNC-machined equivalents. GE Aviation's LEAP fuel nozzle (consolidated from 20 parts to 1) is the poster child. Flight-qualified with HIP and CT scanning.
Medical implants
Patient-specific Ti-6Al-4V and CoCr implants: hip cups, spinal fusion cages, cranial plates. Lattice structures promote bone ingrowth. DMLS is FDA-cleared for Class III medical devices (510(k) pathway).
Rocket engines & propulsion
SpaceX SuperDraco chamber (Inconel), Relativity Space engine components, NASA injector assemblies. DMLS consolidates cooling channels, injector passages, and structural elements into single prints - reducing part count by 80–90%.
Heat exchangers
AlSi10Mg and copper heat exchangers with complex internal fin geometries and thin walls (0.3–0.5 mm) that maximize surface area. DMLS enables heat exchanger designs with 2–5× better thermal performance than conventional fabrication.
Rapid tooling and EDM electrodes
CuCr1Zr copper EDM electrodes with complex shapes, H13 tool steel inserts for die casting, and maraging steel injection mold cores - all with conformal cooling. Tooling is DMLS's fastest-growing application by revenue.
Pro Tip
DMLS's value proposition is geometric freedom - not cost. If you can make the part via CNC, CNC is almost always cheaper. DMLS wins when: (1) the geometry is impossible for CNC, (2) part consolidation saves assembly cost, or (3) conformal cooling channels improve downstream process economics.
Common Mistakes
DMLS mistakes are expensive - a failed build can cost $2,000–$10,000 in machine time alone.
Skipping DFM review before building
A DMLS build failure costs $2,000–$10,000 in machine time, powder, and inert gas. Invest 4–8 hours in build simulation (thermal distortion, support optimization) before committing to the build. Most service bureaus include DFM review - use it.
Under-budgeting post-processing
Raw DMLS cost is only 40–70% of the final part cost. Post-processing (stress relief, EDM, support removal, heat treatment, machining, inspection) adds 30–60%. Quote the complete workflow, not just the print.
Assuming DMLS properties equal wrought properties
DMLS microstructure (columnar grains, residual porosity, anisotropy) differs from wrought. DMLS Ti-6Al-4V fatigue life can be 20–40% lower than wrought without HIP. Always test with DMLS-specific coupons from the same build.
Designing round internal channels
Round channels require internal supports (the top of the circle is an overhang). Use teardrop or diamond cross-sections instead - they are self-supporting at 45° and eliminate the need for impossible-to-remove internal supports.
Not specifying HIP for fatigue-critical parts
DMLS parts contain micro-porosity (0.1–0.5%) that acts as fatigue crack initiation sites. HIP closes this porosity, improving fatigue life by 50–200%. For any part that sees cyclic loading - specify HIP in your requirements.
Choosing DMLS when CNC would be cheaper
A simple prismatic bracket costs $150–300 in DMLS vs. $30–80 in CNC aluminum. DMLS only wins on cost when geometry is CNC-impossible, buy-to-fly ratio is extreme, or part consolidation eliminates assembly labor. Don't use DMLS just because you can.
Pro Tip
Before committing to DMLS, always ask: "Can this part be CNC-machined?" If yes, get a CNC quote too. DMLS only makes economic sense when it delivers value that CNC cannot - geometric complexity, part consolidation, or conformal cooling.
Frequently Asked Questions
What metals can be 3D printed with DMLS?
How much does DMLS metal 3D printing cost?
DMLS vs CNC: when should I choose DMLS?
How accurate is DMLS?
Is DMLS the same as SLM?
DMLS vs Metal FFF (bound metal deposition): which is better?
Do DMLS parts need heat treatment?
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