CNC Machining vs. 3D Printing for Rapid Prototyping

Prototype Trial Development

Basic Prototype Development Process

Rapid prototype development mainly includes non-metallic and metallic prototypes. These parts are used in place of production-tooling parts to verify structure, function, appearance, and other requirements.

Prototype production has no fixed point in the project-development schedule and is often adjusted to meet actual testing needs. As development cycles continue to shorten, prototype lead-time requirements are also being compressed. This has driven the adoption of technologies such as 3D printing and rapid tooling to meet rapid-prototyping needs. Current processes for non-metallic prototypes mainly include high-speed CNC milling and engraving and 3D printing. Common processes for rapid metal prototypes include CNC machining, laser powder-bed fusion, and soft-tool stamping. The selected process and material vary with the part structure, intended use, and service environment.

CNC Process Route for Rapid Prototyping

CNC machining is currently one of the most commonly used processes for prototype production. Its typical route includes reviewing the part, process analysis, process planning, NC programming, program transfer, and CNC milling and engraving.

High-Speed CNC Milling and Engraving for Non-Metallic Prototypes

High-speed CNC milling and engraving for non-metallic prototypes is mainly used for large plastic prototype parts and transparent acrylic materials. Automotive front and rear bumpers, instrument panels, and door interior trim panels, for example, can be machined in sections and then bonded and surface-finished. These parts can be used for appearance reviews, assembly validation, and other testing during new-vehicle development.

Process Selection for Rapid Metal Prototypes

Metal CNC machining is similar to high-speed CNC milling and engraving for non-metallic prototypes, but metal prototypes generally need to be machined as one piece and do not require the CAD model to be split into sections. They do, however, require the design of fixtures for repositioning and reclamping. Because metals and non-metallic materials have different hardness levels, their programming parameters also differ significantly. Without splitting the model in the early stage, later bonding and finishing are usually unnecessary; only operations such as tapping threaded holes are needed. Machining parts such as steering knuckles, suspension brackets, and metal stamping dies can meet assembly-validation requirements during new-vehicle development.

The Complementary Value of 3D Printing and Other Rapid Processes

CNC machining is a subtractive manufacturing process, while 3D printing is an additive manufacturing process. CNC milling and engraving removes a large amount of excess material, whereas 3D printing can be programmed directly from a digital model and produce a physical part. It therefore offers high material utilization. Depending on the underlying principle, 3D-printing processes include stereolithography (SLA), fused deposition modeling (FDM), digital light processing (DLP), and metal laser powder-bed fusion. Their typical process includes data preparation, part production, and post-processing. Compared with CNC machining, the process chain is shorter and usually requires less preparation and post-processing time.

Soft-Tool Stamping for Prototypes

Soft-tool stamping is often used to build prototype vehicles. These parts generally do not require high tensile strength but have demanding lead-time and cost requirements. Tooling design therefore focuses mainly on forming rather than tensile strength, and a blank holder is generally not included. After forming, laser-cutting equipment can be used directly to pierce holes and trim the part.