Overview

There are several different problems that can arise when designing a 3D model. These are dependent on the technology, the application and the material selection. This is a collection of the most common best practices that can eliminate 80% of problems during the design process.

Designing Best Practices

Digital Becomes Physical

Models created in a digital environment are not limited by physical forces such as gravity or inner tensions. During 3D printing, your model becomes a physical object and is exposed to physical forces.

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• Avoid thin walls that can break easily.

• Avoid disconnected pieces within the geometry that will become separate objects during 3D printing.

• Keep your model watertight.

• Use one continuous flow to the outer surface.

Printing Technology & Material Guidelines

Each 3D printing technology has its own technical restrictions and material specifications. The restrictions are generally based on the method used to build the model.

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• For FDM and SLA printing, support structures are needed to support overhanging places. Generally speaking, powder technologies do not require support structures (exception being SLM).

• When printing bigger objects, hollow your model to save material (cost) and production time.

• For SLA and powder technologies (SLS, SLM, CJP), include escape holes to take away the inner material that was not sintered.

• When creating large parts, many elements – especially planar and thin elements – may warp or shrink. This is due to the cooling process and inner tensions resulting from the cooling process.

• 3D printing has its own resolution. In general, details smaller than 0.1 mm will not be visible after the production process.

• 3D printing has its own dimension tolerance, meaning that the dimensions of the physical object can be different from the digital one. In general, the tolerance is -/+ 2%

Wall Thickness

This is the most commonly overlooked aspect of physical objects. Unlike in the real world, in the digital world it is possible to create a surface without thickness. Thin elements, especially when clustered, will break, warp, or not have enough durability to support other parts of the model. Avoid creating models with elements that are less than 1mm thick.

File Resolution

3D printing is created from a mesh representation, which is an approximation when modeling using NURBS or solid geometry. When creating the triangulation, consider the number of triangles the file has when output. Using too many triangles will restrict the 3D printing because of technical limitations regarding resolution. Too few triangles will result in a rough (low resolution) model.

Detailed Modeling Tips

Before you start the modeling process, consider the technical limitations of the 3D print technology you choose. Based on this knowledge you can adjust your digital model accordingly.

Create solid bodies, not surfaces.

Model your object as a single watertight mesh – a mesh with one continuous flow. Every physical object requires a thickness of a minimum of 1-4 mm. Wall thickness depends on the size of the 3D printed object, material, and 3D print technology.

Shared edges do not translate to 3D Prints

Due to technical limitations, no two elements of your model can share an edge. If you want to print them as one object, they should be intersected into a single volume. If they should be separate prints, they should have complete walls and be placed directly abutting each other.

Unified normal

Each triangle face has a normal line that indicates the side of the model (inside/outside). All model normals must face in the same direction - outside of the object volume.

Ensure that all holes are filled

The mesh must not have missing triangles or walls or it will not process correctly. The mesh will be marked as inconsistent and will produce an error during the 3D print.

Build volume of the 3D printers

Each 3D printer has its own build space. The dimensions of the build space vary by machine and by technology. Keep your model bounding box within the total dimensions of the 3D printer build space.

1:1 scale

Because your model will have physical dimensions, it is best to model in a scale of 1:1 relative to the size of your final 3D print.

Scaling (costs and resolutions)

3D print cost and print time rise significantly based on the size of the printed object. Before developing the model, consider the target scale, details, and technical limitations of the 3D print.

Include gaps between moving or interlocking parts

If you want to create interlocking parts (for example, in SLS), there must be a clearance between each separate part. The amount of clearance depends on the technology. Note that interlocking parts cannot be produced in all 3D print technologies (for example, FDM).

Consider the strength of the components

Thin elements will break, warp, or not have durability to support other parts of the model. Avoid creating models with elements that have a thickness less than 1mm.

Overhangs

Depending on the materials and technology, overhangs may need to have additional thickness added to handle the weight or have extra printed support elements that are later removed.

Hollow the model and use escape holes

To make the 3D print less expensive, it is good practice to hollow out your model. For sintering processes, escape holes must remain, to allow for removal of unused material powder.

Warping

When printing large, flat parts, elements may warp. Those can be reinforced with additional material to avoid warping.

Surface details and engraves

Each 3D printing technology has a minimal detail size. Avoid small elements or thin engravings that do not account for those standards.