Machines and processes used for rapid prototyping in China

The core principle of rapid prototyping is to create a physical part from a digital model as quickly as possible, often for form, fit, or function testing. The choice of technology depends on the prototype's purpose, material requirements, and geometry.

1. For Visual and Form-Fit Prototypes (Concept Models)

These prototypes are used to check the look, feel, size, and assembly of a design. Speed and cost are often the highest priority.

Primary Machine: 3D Printer (Additive Manufacturing)

• Fused Deposition Modeling (FDM)

• Best For: Low-cost, large-sized concept models, basic housings, and functional parts with simple geometries.

• Process: A thermoplastic filament is heated and extruded through a nozzle, building the part layer-by-layer.

• Material Characteristics: PLA, ABS, PETG. Parts have visible layer lines and moderate strength.

• Stereolithography (SLA) & Digital Light Processing (DLP)

• Best For: High-detail concept models, parts with intricate features, smooth surfaces (e.g., for painting), and molds for casting.

• Process: A laser (SLA) or projector (DLP) selectively cures a vat of liquid photopolymer resin, solidifying it layer by layer.

• Material Characteristics: Various resins (standard, tough, flexible, castable). Parts are smooth and detailed but can be brittle and UV-sensitive.

• Material Jetting (PolyJet)

• Best For: Ultra-high-detail models with multiple materials or colors, simulating overmolding or complex textures.

• Process: Works like a 2D inkjet printer but with photopolymer resin. It jets tiny droplets of material which are instantly cured by UV light.

• Material Characteristics: Can combine rigid, flexible, transparent, and colored materials in a single print. Excellent surface finish.

2. For Functional and Durability-Testing Prototypes

These prototypes need to mimic the mechanical, thermal, or chemical properties of the final production material (often a metal or engineering plastic).

Primary Machine: CNC Machining (Subtractive Manufacturing)

• CNC Milling & Turning

• Material Properties: Parts are fully dense and have the identical mechanical properties of the raw material.

• High Precision: Excellent for testing parts that must mate with existing components.

• Wide Material Selection: Virtually any machinable metal or plastic can be used.

• Best For: Prototypes that must be made from specific, high-strength materials (e.g., aluminum, stainless steel, PEEK, Nylon).

• Process: A solid block of the desired material is carved away using cutting tools to form the final part.

• Why it's chosen for functional prototypes:

Primary Machine: Industrial 3D Printers

• Selective Laser Sintering (SLS)

• Best For: Complex, functional plastic parts that require good strength and heat resistance, such as ducts, housings, and snap-fit assemblies.

• Process: A laser fuses (sinters) tiny particles of nylon powder layer by layer. The unsintered powder supports the part during build, allowing for highly complex geometries.

• Material Characteristics: Nylon (PA12, PA11). Parts are strong, slightly porous, and have a rough surface finish.

• Multi Jet Fusion (MJF)

• Best For: Functional nylon prototypes and small-batch end-use parts. Similar to SLS but often faster and with more consistent mechanical properties.

• Process: An inkjet array deposits a fusing agent onto a bed of nylon powder, and then an infrared energy source passes over to fuse the areas where the agent was deposited.

• Material Characteristics: Nylon (PA12). Excellent strength and detail, with a slightly better surface finish than SLS.

• Direct Metal Laser Sintering (DMLS) / Selective Laser Melting (SLM)

• Best For: Fully functional metal prototypes (e.g., aerospace brackets, medical implants, heat exchangers) with complex internal channels or lightweight structures.

• Process: A high-power laser precisely melts fine metal powder, fusing it into a solid part layer by layer.

• Material Characteristics: Stainless steel, aluminum, titanium, Inconel. Parts are very strong but often require post-processing (heat treatment, support removal).

3. For Prototypes Requiring Specific Textures or Finishes

These are often consumer products where the final part will be injection-molded.

Primary Process: CNC Machining + Finishing

• Process: The prototype is CNC machined from a block of plastic (like ABS or PC). Then, it undergoes a series of manual and automated post-processing steps:

1. Sanding & Polishing: To remove tool marks.

2. Painting: To achieve the desired color and texture.

3. Texture Coating: Applying a surface texture (e.g., leather grain, grit) to mimic the final molded part.

• Why it's chosen: It can produce a prototype that is visually and tactilely almost identical to a mass-produced injection-molded part.

Alternative Process: 3D Printing (SLA/MJF) + Urethane Casting

• Process:

1. A high-resolution 3D printed master pattern is created (using SLA or MJF).

2. A silicone mold is built around this pattern.

3. Once the mold is cured, the pattern is removed, and polyurethane resin is poured into the mold to create copies.

• Why it's chosen: Ideal for creating 10-50 prototype units in various colors and material properties (rigid, flexible, transparent) without the high cost of an injection mold.

Summary Table: Matching Prototype Needs to Machines

In conclusion, the "best" process for a rapid prototype is a trade-off between speed, cost, material properties, and accuracy. A simple visual model will use a different machine than a prototype destined for a rigorous functional test in a jet engine.