Advice of Design for Manufacturability (DFM)in Rapid Prototyping

When designing parts for Rapid Prototyping (also known as Additive Manufacturing or 3D Printing), the strategies to reduce lead time and cost are different from those for CNC machining.

Here are the key features and methods to achieve faster, cheaper prototypes:

1. Optimize Part Orientation and Minimize Support Structures

Support structures are the #1 driver of increased time, material, and post-processing labor.

• Problem: Designing a part with large overhangs (>45 degrees) or complex bridges. This requires extensive supports, which use extra material, increase print time, and are labor-intensive to remove, often leaving blemished surfaces.

• Solutions:

• Self-Supporting Angles: Design angles to be less than 45 degrees from vertical whenever possible, as they can often print without supports.

• Modify Geometry: Incorporate chamfers or fillets at the base of overhanging features to make them self-supporting.

• Hole Shape: Use teardrop-shaped or diamond-shaped holes instead of circular ones for horizontal holes, as they are self-supporting.

• Strategic Orientation: If possible, orient the part in the software so that complex features face upward, where they don't need supports, or to minimize the contact area of supports.

2. Hollow Out the Part (Create Shells)

Most rapid prototyping technologies allow for creating parts with a solid shell and a hollow, low-density infill.

• Problem: Designing a completely solid part. This consumes a massive amount of material and drastically increases print time.

• Solution: Use a thin outer shell and a sparse internal infill structure (e.g., a honeycomb or grid pattern). This can reduce material usage and print time by 50-80% without significantly sacrificing strength for prototyping purposes. Remember to add "escape holes" to allow unused liquid resin or powder to be removed.

3. Consolidate Assemblies into a Single Part

A key advantage of RP is its ability to create complex geometries that are impossible with traditional methods.

• Problem: Designing a multi-part assembly that requires each component to be printed separately and then assembled.

• Solution: Combine multiple components into a single, integrated part. This eliminates assembly time, fasteners, and the need for multiple print jobs. For example, design living hinges, integrated snap-fits, and interlocking parts as one piece.

4. Choose the Right Technology and Material for the Purpose

Not all prototypes need to be high-resolution or high-strength.

• Problem: Specifying an expensive, high-performance material (e.g., SLS Nylon or SLA Tough Resin) for a simple "look-and-feel" or "fit-check" model.

• Solution:

• For form and fit checks, use the fastest and cheapest technology available, like FDM (Fused Deposition Modeling) with standard PLA or ABS.

• For visual models, SLA (Stereolithography) or Material Jetting offer the best surface finish.

• For functional testing under stress, SLS (Selective Laser Sintering) or advanced FDM materials like ASA or Nylon are better choices. Matching the technology to the prototype's primary function avoids over-engineering and cost.

5. Design for the Specific Process's Strengths

Embrace the "complexity for free" aspect of additive manufacturing.

• Problem: Avoiding organic shapes and lightweight lattice structures because they are difficult for CNC machining.

• Solution: Incorporate organic, topology-optimized, or lattice structures. These are often stronger, lighter, and print just as quickly as a solid block of material. They use less material and can be designed to minimize stress concentrations.

6. Minimize Post-Processing Requirements

Labor for sanding, painting, and assembling is a major cost factor.

• Problem: Designing parts with high-gloss, smooth surface finishes as a default requirement.

• Solution:

• Specify "as-printed" finish where acceptable.

• Avoid designs that require complex support removal from hard-to-reach internal channels or delicate features.

• For SLA, orient the part to minimize "stair-stepping" on critical cosmetic surfaces, as this reduces the need for sanding.

Summary of Key Methods to Reduce Time and Cost:

• Minimize Supports: Use self-supporting angles (<45°) and smart orientation.

• Go Hollow: Use shells with sparse infill and include drainage holes.

• Consolidate: Combine assemblies into a single, integrated part.

• Match Tech to Function: Don't over-specify material and technology.

• Embrace Complexity: Use lattices and organic shapes that are native to 3D printing.

• Reduce Labor: Design to minimize sanding, painting, and support removal.

By designing with these additive manufacturing principles in mind from the start, clients can significantly accelerate their prototyping cycle and get functional parts in hand faster and at a lower cost.