Designing for Function: 10 Core Principles of Additive Manufacturing for Engineers

Introduction

Additive manufacturing (AM) enables unprecedented design freedom—but it also introduces a new set of constraints. Designing for Additive Manufacturing (DfAM) isn’t just about getting a part to print; it’s about producing functional, manufacturable components optimized for specific processes and materials.

This white paper outlines ten essential principles engineers must apply to design robust, repeatable, and cost-effective polymer AM parts using technologies like FDM, SLS, MJF, and SLA.

1. Design for Layered Strength

AM parts are anisotropic—meaning strength varies by direction. Most processes build vertically (Z-axis), which is typically the weakest dimension due to inter-layer adhesion.

Engineering guidance:
Orient load-bearing features to align with the X-Y plane. Critical mechanical paths should never rely on Z-direction strength alone.

2. Respect Minimum Wall Thickness

Every AM process has a minimum wall thickness threshold below which features may deform or fail. Inadequate thickness compromises structural integrity and may result in failed prints.

Minimum guidelines:

• FDM: ≥0.8 mm supported; ≥1.2 mm unsupported
• SLA: ≥0.5 mm (supported)
• SLS/MJF: ≥0.75 mm (small features)

Use gradual transitions in thickness to avoid internal stress concentrations and improve reliability.

3. Simplify Overhangs and Minimize Supports

Supports increase material waste and require labor-intensive removal. Designing geometries that self-support is key to reducing complexity and cost.

Strategy:
Avoid overhangs >45° in FDM. For SLA, assume all downward-facing features require support. In SLS/MJF, supports are unnecessary, but consider powder removal paths.

Use fillets, chamfers, or “teardrop” hole geometries to maintain form without generating excessive supports.

4. Design for Surface Quality and Print Orientation

Orientation impacts both surface finish and dimensional accuracy. Vertical surfaces aligned with Z will show better resolution, while horizontal surfaces are more prone to layer stepping.

Recommendation:
Design with surface quality targets in mind. If cosmetic quality matters, orient cosmetic surfaces vertically or where they require the least support.

5. Adjust for Tolerance and Fit

Unlike machined parts, AM components have broader tolerances and variable shrinkage. Mating features should be designed with looser clearances unless post-machined.

Typical design allowances:

• Slip fit: +0.2–0.4 mm clearance
• Press fit: −0.1–0.2 mm interference
• Tight tolerances: Add machining stock or ream post-print

Always prototype functional fits early to validate alignment with the print process used.

6. Consolidate Where Possible

AM eliminates traditional manufacturing constraints like tooling or multi-step assembly. Take advantage of this by combining features or assemblies into one printed part.

Use cases:

• Combine brackets with fastener bosses
• Add cable routing into structural frames
• Incorporate snap fits, living hinges, or interlocks

Fewer parts means fewer joints, fasteners, and points of failure.

7. Optimize for Post-Processing

Many AM parts require cleanup—especially those printed with supports, complex geometries, or cosmetic targets. Designing with finishing in mind reduces labor and rework.

Design tips:

• Avoid fragile details in support-heavy zones
• Leave machining stock where precise features are required
• Use vent holes for cleaning internal voids in SLS/MJF
• Consider sanding, tumbling, or vapor smoothing as necessary

8. Match Material to the Application

Material performance is process-dependent. The same base polymer behaves differently when printed via FDM versus SLS. Know the environment your part will face—thermal, mechanical, or chemical.

Key materials:

• Nylon 12 (PA12): Strong, chemically resistant, good for SLS/MJF
• TPU: Flexible, abrasion-resistant, suitable for gaskets or shock isolation
• PETG/ABS: General-purpose, strong, moderately heat-resistant
• ULTEM™ 9085 (PEI): High-strength, flame-retardant, aerospace-ready

Data sheets are starting points; print orientation and post-processing also affect final part behavior.

9. Consider Failure Modes Early

AM parts fail for predictable reasons: weak Z-axis adhesion, unsupported bridges, excessive thermal stress, or bad tolerances.

Design defensively:

• Reinforce unsupported spans
• Use stress-diffusing fillets
• Add ribs or gussets to flat panels
• Avoid abrupt thickness changes

Failure in prototyping costs time. Failure in production costs trust.

10. Think in Volume: Orientation and Nesting Strategy

In production, build efficiency matters. Nest parts in ways that minimize build height, reduce thermal load, and enable repeatable yields.

Planning considerations:

• Flat orientation saves time but may compromise strength
• Part spacing affects airflow and cooling
• Access for cleaning and powder removal (SLS/MJF) is essential

Batch production success comes from design-stage optimization—not afterthought nesting.

Conclusion: Print with Purpose

DfAM isn’t about pushing geometry for its own sake. It’s about creating smarter, stronger, and more efficient components by designing with intent. When engineers account for material behavior, orientation, fit, and post-processing up front, they unlock the true value of additive manufacturing: flexibility without compromise.

Need support optimizing your next AM project?
RapidMade offers design-for-additive consultation, engineering-grade printing, and materials expertise to take your part from digital to functional with precision.

For the best 3D print services visit rapidmade.com or email info@rapidmade.com.