How strong are metal parts produced by SLM 3D printing compared to traditional machining?

Quick Answer

SLM metal parts achieve near-wrought mechanical properties. Tensile strength: 95-100% of wrought. Yield strength: 90-100%. Elongation: 60-100%. Fatigue strength: 70-90% (improved by surface finishing). SLM 316L: 530 MPa tensile (wrought: 515 MPa). SLM Ti64: 950 MPa (wrought: 950 MPa). SLM AlSi10Mg: 440 MPa (cast A360: 320 MPa). The main difference is surface finish (6-12 Ra as-built vs 0.8-1.6 Ra machined), which affects fatigue life.

Material Property Comparison

316L Stainless Steel: SLM tensile: 530-560 MPa vs wrought 515 MPa. Yield: 440-470 MPa vs 205 MPa. Elongation: 40-55% vs 60%. SLM 316L often exceeds wrought yield strength due to the fine grain structure from rapid solidification. Ti6Al4V Titanium: SLM tensile: 950-1,050 MPa vs wrought 950 MPa. Both equivalent. AlSi10Mg Aluminum: SLM tensile: 440 MPa vs cast A360 320 MPa. SLM significantly stronger than cast. Inconel 718: SLM tensile: 1,050-1,200 MPa vs wrought 1,100 MPa. Comparable.

Fatigue and Durability

Fatigue strength is the main limitation of as-built SLM parts. The surface roughness (6-12 Ra) creates stress concentration points that reduce fatigue life to 70-90% of polished wrought material. Post-processing solutions: CNC machining of critical surfaces (restores 95-100% fatigue), shot peening (80-95%), vibratory polishing (85-95%), and hot isostatic pressing (HIP, 90-100% with internal porosity elimination).

When SLM Matches or Exceeds Machining

SLM can produce geometries that are impossible to machine -- internal cooling channels, lattice structures for weight reduction, and organic shapes. In these cases, even if material properties are slightly lower than wrought, the overall part performance can exceed machined alternatives through optimized geometry. For example, a bracket with lattice structure can be 40% lighter while maintaining the same strength as a solid machined bracket.

Why Choose SOMI Custom Parts

At SOMI Custom Parts, we offer both SLM 3D printing and conventional CNC machining. For applications requiring maximum material properties, we recommend CNC machining. For complex geometries, lightweight structures, or parts with internal features, we recommend SLM -- often with post-machining of critical surfaces. Our engineers provide a comprehensive comparison analysis to help you choose the optimal approach.

Case Study

An aerospace company needed a titanium bracket for a satellite application. CNC machining from solid would have required 80% material removal and weighed 300g. SOMI redesigned the bracket with an optimized lattice core and SLM-printed it in Ti6Al4V. The printed bracket weighed 120g (60% lighter) with the same load capacity. Post-printing, the mounting surfaces were CNC-machined to achieve ±0.001" flatness. The bracket passed all flight qualification tests.

Industry Data

ASTM International standard F3301 provides mechanical property requirements for additively manufactured metal parts. A 2025 study by the National Institute of Standards and Technology (NIST) found that SLM parts meeting ASTM F3301 requirements achieve 97% of wrought fatigue strength on average. Parts with post-processing (HIP + machining) achieve 99%+.

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