Introduction to CNC Rapid Prototyping Materials and Finishes in China

China's CNC machining industry is a global hub for rapid prototyping, offering a vast selection of materials and surface finishing techniques. This allows suppliers to produce functional prototypes, master models, and pre-production parts that closely mimic the final product in both form and function.

I. Commonly Used Materials

Chinese CNC prototyping suppliers typically stock a wide range of materials to meet various mechanical, thermal, and aesthetic requirements. They are broadly categorized into plastics and metals.

A. Plastics (Polymers)

1. ABS (Acrylonitrile Butadiene Styrene):

• Characteristics: Tough, impact-resistant, good mechanical strength, easy to machine and post-process.

• Common Applications: Consumer electronics housings, automotive interior parts, functional prototypes, ductwork.

2. Polycarbonate (PC):

• Characteristics: Excellent impact strength and transparency, good heat resistance and dimensional stability.

• Common Applications: Transprotective shields, lenses, high-strength components, medical device prototypes.

3. Nylon (PA 6 & PA66):

• Characteristics: High strength, stiffness, good wear and abrasion resistance, and good chemical resistance.

• Common Applications: Gears, bearings, hinges, and other high-wear mechanical parts.

4. POM (Polyoxymethylene / Acetal):

• Characteristics: High stiffness, low friction, excellent dimensional stability, and great machinability. Known for its "slippery" feel.

• Common Applications: Precision gears, conveyor parts, insulators, fasteners.

5. PMMA (Acrylic):

• Characteristics: Crystal-clear transparency, good weather resistance, and stiff but brittle.

• Common Applications: Light covers, displays, lenses, transparent enclosures.

6. PP (Polypropylene) & PE (Polyethylene):

• Characteristics: Excellent chemical resistance, lightweight, and flexible. Can be challenging to bond and paint.

• Common Applications: Fluid containers, living hinges, chemical-resistant parts.

B. Metals (Aluminum, Steel, Brass, etc.)

1. Aluminum 6061:

• Characteristics: The most common prototyping aluminum. Excellent strength-to-weight ratio, good machinability, corrosion resistance, and responds well to various surface finishes.

• Common Applications: Aerospace brackets, automotive parts, electronic enclosures, robotic components.

2. Aluminum 7075:

• Characteristics: Very high strength, comparable to many steels. Excellent for high-stress applications but less corrosion resistant than 6061.

• Common Applications: Aerospace frames, high-performance automotive and bicycle parts.

3. Stainless Steel 304 & 316:

• Characteristics: High strength, excellent corrosion resistance, and durability. 316 offers superior chemical resistance ("marine grade").

• Common Applications: Medical instruments, food processing parts, marine hardware, surgical components.

4. Mild Steel (e.g., Q235):

• Characteristics: Very strong and cheap, but prone to corrosion unless treated.

• Common Applications: Heavy-duty structural prototypes, jigs, and fixtures.

5. Brass:

• Characteristics: Excellent machinability, good corrosion resistance, and aesthetic appeal with a gold-like appearance.

• Common Applications: Decorative fittings, electrical components, plumbing prototypes.

II. Common Surface Finishing Methods

After CNC machining, parts often have visible tool marks. Surface finishing is applied to improve appearance, enhance performance, or add protective properties.

A. For Aesthetic Enhancement

1. Polishing & Buffing: Creates a smooth, reflective, mirror-like surface. Commonly used on metals like aluminum and stainless steel, and plastics like ABS and acrylic.

2. Bead Blasting (Sand Blasting): Propels fine media (like glass beads) at the part to create a uniform, matte, satin-like surface texture. Excellent for hiding tool marks and providing a premium feel on both metals and plastics.

3. Painting & Powder Coating: Applies a layer of paint or electrostatically charged powder (cured in an oven) to add color and texture. Powder coating is very durable and common for metals.

B. For Functional & Protective Enhancement

1. Anodizing (Type II & Type III Hardcoat): An electrochemical process primarily for aluminum that increases corrosion and wear resistance.

• Type II: Can be dyed in various colors (e.g., black, red, blue) for aesthetics and mild protection.

• Type III (Hard Anodizing): Creates a much thicker, extremely hard, and wear-resistant surface layer, usually in darker shades like gray or black.

2. Passivation: A chemical treatment for stainless steel that removes free iron from the surface and enhances the formation of a protective oxide layer, maximizing its natural corrosion resistance.

3. Chromate Conversion Coating (Alodine / Chemfilm): A chemical coating for aluminum that provides good corrosion resistance and serves as an excellent primer for paint. Often has a distinctive iridescent greenish-gold color.

4. Electroplating: Deposits a thin layer of another metal (e.g., nickel, chrome, zinc, gold) onto a part substrate for hardness, wear resistance, corrosion protection, or appearance.

5. Silk Screening & Laser Engraving: Used to add permanent logos, labels, instructions, or serial numbers onto the finished part.

Chinese rapid prototyping suppliers excel at combining these materials and finishes to deliver high-quality, cost-effective prototypes that meet international standards, making them a preferred choice for global companies.