The “secondary processing techniques for plastic products” represent a core industrial field. It refers to all subsequent processes that rework already formed (e.g., via injection molding, extrusion) plastic semi-finished or finished products to enhance their appearance, function, or added value.
I. Surface Treatment and Decoration
This category aims to improve appearance, increase wear resistance, add texture, or achieve special visual effects.
Painting/Spraying
Purpose: Coloring, providing a protective layer (scratch-resistant, chemical-resistant), achieving special textures ( rubberized paint, metallic paint).
Process: Uses a spray gun to atomize and apply coating onto the workpiece surface. Key steps include surface cleaning, primer application, and baking.
Applications: Automotive interiors, electronic product housings, home appliances.
Printing
Screen Printing: Suitable for flat or simple curved surfaces, used for printing logos, text.
Pad Printing: Specifically for irregular, concave-convex surfaces, like buttons, golf balls.
Heat Transfer Printing: Transfers patterns from a carrier film to the workpiece using heat and pressure, enabling complex multi-color patterns, wood grains, and metallic textures.
Hydrographic Printing (Water Transfer Printing): Allows for full-coverage patterns on complex 3D objects, such as camouflage or carbon fiber patterns.
Metalization
Electroplating: Uses electrolysis to deposit metal (e.g., chromium, nickel) onto the plastic surface, providing a metallic look, enhanced aesthetics, and wear resistance. Commonly used for automotive grilles, faucets.
Vacuum Plating: Metal (e.g., aluminum) is evaporated and condenses onto the plastic surface in a vacuum chamber. It is environmentally friendly and can achieve various colors, widely used in consumer electronics.
Others
Texture Etching (Mold Texturing): Uses chemical solutions to etch textures onto the mold surface, thereby replicating patterns like leather grain, wood grain, or geometric designs on the plastic part, improving grip and aesthetics.
Laser Engraving/Marking: Uses a laser to etch permanent markings, serial numbers, or patterns onto the surface. It offers high precision and is permanent.
II. Joining and Assembly
These techniques are used to combine multiple plastic parts or components of other materials.
Bonding/Adhesive Joining
Purpose: Uses specific adhesives (e.g., UV cure glue, instant adhesive, epoxy) to firmly bond components.
Advantages: Uniform stress distribution, suitable for joining different materials.
Applications: Fixing lenses to housings, structural component assembly.
Welding
Ultrasonic Welding: Uses high-frequency vibration to generate friction heat at the contact surfaces, causing them to melt and fuse. It is fast, creates high-strength bonds, and suits high-volume production.
Hot Plate Welding: Uses a heated metal plate to simultaneously melt the two facing surfaces, which are then joined under pressure and cooled.
Vibration Welding: Similar in principle to ultrasonic welding, but suitable for larger or irregularly shaped parts, like automotive intake manifolds.
Laser Welding: A non-contact method offering high precision and no residue, often used for precision medical devices and electronics.
Mechanical Fastening
Screw Assembly: The most common detachable fastening method.
Snap-fit Assembly: Uses elastic deformation for a quick “click-in-place” assembly, requiring no additional parts and offering low cost.
III. Mechanical Machining and Modification
These processes involve “subtractive” or “additive” machining of formed plastic parts to achieve specific dimensions or functions.
Mechanical Machining
Purpose: Precision finishing of molded parts or directly creating parts during the prototyping stage.
Process: CNC Milling/Turning. Suitable for small batches, high-precision parts, or for creating features difficult to mold directly (e.g., deep holes, fine threads).
Applications: Precision machining of plastic gears, prototype manufacturing, medical implant machining.
Insert Molding/Embedding Inserts
Purpose: To embed metal parts into a plastic component to provide strength, conductivity, or threaded features.
Process: The most common is Ultrasonic Insertion, where metal nuts or studs are vibrated into pre-formed holes in the plastic. Inserts can also be placed In-Mold during the injection molding process