Additive manufacturing can produce forms that would be difficult or impossible to make using conventional processes. That freedom is valuable, but it does not mean that every CAD model will print successfully or perform as intended.
Design for Additive Manufacturing (DfAM) develops a component around the capabilities and constraints of the selected 3D printing process. It can improve performance, reduce weight, simplify assembly, control cost and make production more repeatable.
To optimise a design for additive manufacturing, define the part’s functional requirements first, then select the process and material before finalising its geometry. Control wall thickness, transitions, tolerances, orientation, trapped material and post-processing access. Validate critical features with prototypes or test coupons before committing to production.
Start with the part’s requirements, not its shape
Before altering the geometry, establish what the part must do and which requirements are critical:
- Loads, load directions and likely failure modes
- Operating temperature and environmental exposure
- Required stiffness, strength, impact resistance or flexibility
- Critical dimensions, fits and sealing faces
- Surface finish and appearance requirements
- Expected service life
- Production quantity and target cost
- Inspection and quality requirements
This prevents unnecessary features or tolerances from driving the method and price. It also distinguishes a visual model from a functional prototype or end-use component.
Select the process and material early
There is no single set of design rules for professional 3D printing. A feature that is straightforward in Selective Laser Sintering (SLS) may require supports in Stereolithography (SLA) or create thermal challenges in Selective Laser Melting (SLM).
| Process | Important design considerations |
| SLS | Powder supports the part during the build, enabling complex forms. Enclosed spaces need routes for powder removal. |
| MJF | Complex functional parts can be made without dedicated supports, but clearances, thermal behaviour and powder removal still matter. |
| SLA | Orientation and support placement affect finish. Hollow parts need drainage and access for cleaning and post-curing. |
| FDM | Layer direction, overhangs and support access can influence strength, accuracy and finish. |
| SLM | Metal powder-bed fusion requires management of supports, heat, residual stress, powder removal and subsequent machining. |
A thin feature in a ductile polymer will not behave like the same feature in a stiff, filled material. Process and material selection should therefore be part of design development, not a decision made after the CAD model is complete.
Use wall thickness deliberately
Very thin walls can distort, fail to resolve or break during handling. Excessively thick sections may add material and cost or increase thermal distortion in some processes. Aim for consistent walls, using ribs, gussets or efficient cross-sections where they provide stiffness more effectively than added thickness.
Avoid abrupt changes between thick and thin areas. Gradual transitions and fillets can reduce local stress concentrations.
Do not treat an online minimum wall thickness as universal. The appropriate value depends on the process, material, wall length, orientation, loading and surrounding geometry.
Design orientation and geometry together
Build orientation can influence mechanical behaviour, accuracy, visible layer effects, supports, distortion and post-processing. Identify important load paths, functional faces and critical features while the design is editable, so geometry and orientation can be developed together.
A cosmetic face may need to avoid support contact, while a long, flat component may need stiffening or a different orientation. Load-bearing features must account for the directional behaviour of the selected process and material.
Apply tolerances where they matter
It is rarely cost-effective to apply the tightest tolerance everywhere. Separate functional and assembly dimensions from cosmetic and non-critical ones, then identify what needs close control.
Pay particular attention to:
- Mating faces and locating features
- Shafts, pins, bearings and bushes
- Snap-fits and moving assemblies
- Threads and insert locations
- Sealing faces and fluid channels
- Features that will be machined after printing
Small holes may print undersize or lose definition because of their diameter, depth, orientation or surrounding section. Where precision is essential, print a pilot feature and finish it by drilling, reaming, tapping or machining. Test coupons with several clearances can establish reliable fits without repeatedly printing a complete assembly.
Make internal spaces accessible
Internal channels, hollow sections and lattices must be manufacturable and cleanable. Powder-based processes require escape routes for unfused material, while resin processes need drainage and access for washing and post-curing.
When adding a cavity or channel, ask:
- Can powder, resin or support material be removed?
- Are openings positioned for effective cleaning?
- Could material remain in a blind passage?
- Can the surface be inspected or finished if required?
If an internal feature cannot be cleaned, inspected or validated, its complexity may provide little benefit.
Consolidate parts with a clear purpose
Additive manufacturing can combine brackets, ducts, clips and fastener locations into one component, reducing assembly time, joints and tolerance accumulation.
Consolidation is less useful if a wear feature can no longer be replaced or inspection becomes difficult. Integrate only where doing so provides a clear functional or commercial benefit.
Design for post-processing and inspection
The printed component is not always the finished component. Plan support removal, machining, inserts and cosmetic treatments before release. Provide access for tools and fixtures, identify datum and clamping areas, and leave machining allowance where required.
If dyeing, sealing, painting or Vapor Smoothing is specified, confirm its effect on details and interfaces. Critical features must also be accessible to the chosen inspection method.
Submit clean, usable CAD data
A printable file should be watertight, correctly scaled and free from gaps, overlapping surfaces and unintended internal bodies.
Export the STL file with a good resolution (we recommend 0.01mm) to represent curves and small features without creating an unnecessarily large file. Retain the native CAD model so it remains easy to modify after design review.
Additive manufacturing design checklist
Before releasing a part for quotation or production, check that:
- The functional and environmental requirements are defined
- The process and material suit the application
- Walls and fine features suit their loading and orientation
- Thick-to-thin transitions are gradual and filleted where suitable
- Build orientation has been considered alongside function and finish
- Critical dimensions and fits are clearly identified
- Holes, threads and precision faces have a finishing strategy where needed
- Hollow areas, channels, supports and lattices can be cleaned
- Post-processing, fixturing and inspection access have been planned
- The exported file is watertight, correctly scaled and sufficiently detailed
- High-risk features have been tested before production
Optimisation works best as a collaborative process
Good DfAM connects design intent with manufacturing reality. Involve an additive manufacturing specialist before the geometry becomes fixed, while changes remain straightforward.
Graphite Additive Manufacturing works with engineers and product designers to assess applications, improve designs and select suitable technologies and materials. An early review can identify risks, control unnecessary cost and make better use of additive manufacturing.
Frequently Asked Questions
Often, yes, but it may not be optimised. Features created for tool access, mould release or assembly may be unnecessary, while walls, channels, orientation and finishing allowances may need to change.
There is no single tolerance for all 3D printing. Accuracy depends on the process, machine, material, part size, geometry, orientation and finishing. Identify critical dimensions rather than applying a general tolerance everywhere. View our accuracy guidelines.
No. SLS and MJF use surrounding powder to support parts during the build, while SLA, FDM and SLM commonly require supports for certain geometries. The limits and preferred design approach depend on the selected process.
Remove material that provides no value, avoid unnecessary size, consolidate useful features, limit tight tolerances and reduce avoidable finishing. Build volume, orientation and post-processing all influence price.
Involve them during concept development or early CAD design. It is then easier to compare processes and materials, plan finishing and change features before they create avoidable constraints. They should also be able to give you some ballpark figures on prices for different technologies and materials.
