3D printing, technically known as Additive Manufacturing, is a technology that constructs three-dimensional objects by progressively adding material layer by layer. This stands in complete contrast to the “subtractive” concept of CNC, revolutionizing prototype manufacturing.
I. Why Choose 3D Printing for Plastic Prototypes?
Advantages:
- Unparalleled Design Freedom and Geometric Complexity:
- This is the core advantage of 3D printing. It can produce almost any shape, including highly complex internal structures, hollow designs, overhanging features, and fully assembled moving parts in a single print—features that are extremely difficult or impossible to achieve with CNC machining.
- Rapid Iteration Speed:
- The process from digital model to physical part is very straightforward, requiring no programming, toolpath planning, or custom fixtures. Designers can obtain a design validation model within hours, significantly shortening the product development cycle.
- Cost is Independent of Complexity:
- The cost of printing a part with an extremely complex structure and a simple solid block depends primarily on the amount of material used and printing time. This makes 3D printing uniquely cost-effective for creating prototypes with complex geometries.
- Almost Zero Material Waste:
- As an “additive manufacturing” process, it uses only the material necessary to build the object. Although support material (if used) is discarded, the overall waste is significantly lower than with CNC machining.
- Integrated Manufacturing and Assembly:
- It can directly print pre-assembled components, such as chains, gear sets, and hinged structures, eliminating subsequent assembly steps.
Limitations:
- Limitations in Material Properties:
- The mechanical, thermal, and chemical properties of printing materials often cannot fully match those of true engineering plastics. For example, the strength of FDM-printed ABS is typically lower than that of injection molded or CNC machined solid ABS.
- The materials exhibit anisotropy, meaning their strength perpendicular to the print layers is lower than their strength along the layers.
- Lower Surface Quality and Accuracy:
- Part surfaces usually have visible layer lines and require significant post-processing (like sanding, polishing) to achieve a smooth finish. The detail resolution and dimensional accuracy are generally lower than those of high-precision CNC.
- Poorer Strength and Durability:
- Due to the layered structure and inherent material limitations, 3D printed prototypes are often unsuitable for rigorous, high-load functional testing; they are better suited for “form and fit” checks rather than “strength testing.”
- Speed and Cost are Not Suitable for Small to Medium Batches:
- When dozens of identical parts are needed, 3D printing them one by one or in small batches means the total time and cost can quickly exceed that of CNC machining.