Introduction to Design for Manufacturing (DFM)
Design for Manufacturing (DFM) is the practice of designing products specifically to suit the production technology being used. By considering the manufacturing method from the very beginning, engineers can save significant time, reduce production costs, and ensure the final product is more reliable.
In this guide, we explore how to reverse engineer and optimize plastic parts for FDM 3D printing, based on my recent engineering project.
1. Analyzing the Problem and Constraints
The project focuses on redesigning a drum for developing photographic paper. The original “competitor” design had several flaws:
- Over-complicated: The design was unnecessarily heavy and bulky.
- Poor Fit: It consisted of two parts that didn’t fit well together.
- Fixed Constraints: The outer diameter was fixed because it must fit inside a specific development tank.
The goal: Create a simpler, more reliable version that fits onto an existing mass-produced stem.
2. Key Design Decisions
The Compliance Pin
To ensure a “snug fit” on the stem, the design incorporates a compliance pin.
- This pin protrudes inward and acts like a spring.
- It pushes the rod against the wall of the cylinder, providing a reliable rotation without wobbling.
- Pro-tip: If the fit loosens over time, a heat gun can be used to bend the plastic pin back into position.
Geometry for FDM Printing
To avoid the need for supports and ensure high-quality surfaces, I followed these rules:
- Overhang Angles: While 45° is common, using angles up to 60° or 70° (relative to the vertical) helps prevent defects on faster printers.
- Entry Bevels: Large chamfers were added to the bottom so the stem can be easily inserted in total darkness.
- Rigidity: Iterations moved from “flimsy” loops to sturdier, thicker layers to ensure the part could be handled with one hand.
3. Parametric CAD Workflow
A professional DFM workflow uses parameters to link the design directly to the 3D printer’s hardware.
| Parameter | Logic |
|---|---|
| Nozzle Diameter | 0.4 mm (Standard) |
| Line Width | Set to 0.6 mm for strength |
| Wall Thickness | Calculated as 0.6mm * 3 lines = 1.8mm |
Why this matters: By designing walls that are exactly three line-widths thick, the printer creates a solid part with no internal infill, which is much faster and stronger.
4. Slicing and Production Settings
The final parts were sliced for a Bambu Lab A1 printer with the following optimized settings:
- Layer Height: 0.2 mm for optimal strength.
- Speed: Limited to 200 mm/s for reliability.
- Infill: 100% (made obsolete by our wall thickness design).
- Arachne Engine: Enabled to dynamically adjust line width.
Results: The entire set prints in approximately 1 hour 38 minutes and uses roughly 50 grams of PLA filament.
Conclusion
Effective DFM is about knowing your technology’s limits before you draw the first line in CAD. By aligning your geometry with your printer’s nozzle and layer capabilities, you create parts that are not only functional but also optimized for fast, repeatable production.