01 Definition of Electroplating
The broad definition of electroplating: includes electrodeposition of metals or alloys, electrophoretic deposition, electroless plating, immersion plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), and conversion coating (anodizing, phosphating, passivation, etc.).
The narrow definition of electroplating: it is a process in which metal ions in the plating solution are reduced to metal atoms on the cathode surface under the action of a DC electric field to form a metal layer.
Functional electroplating / anti-corrosion electroplating / decorative electroplating; single-metal electroplating / alloy electroplating / composite plating.
Simple salt electroplating / complex salt electroplating.
Strongly acidic electroplating / weakly acidic electroplating / alkaline electroplating.
Metal electroplating / non-metal electroplating.
02 Common Electroplating Production Lines
(1) Linear gantry type: flexible parameter control, convenient parameter storage, high precision, and each arm can be controlled independently. It is suitable for parts with multiple varieties, multiple plating types, and high requirements.
(2) Ring-type line: low cost, high efficiency, but process parameter adjustment is limited and control precision is low. It cannot achieve single-arm control and is suitable for simple, mass production of a single variety with low requirements.
(3) Barrel plating line: the drum panels are formed by sheet bending or by welding special grid plates. Each station is independently driven with driven rollers, chain transmission, 45° helical gear directional transmission, and independent motor and reducer drive. Speed variation can be achieved with a frequency converter or DC motor.
(4) Dedicated strip plating line: the strip is continuously passed through the electroplating tank to complete surface treatment, ensuring both the stability and uniformity of the coating and the continuity and integrity of the strip, which facilitates packaging and subsequent processing.
03 Plastic Electroplating Racks
After parts are unloaded each cycle, the plating rack requires stripping treatment. During racking, there must be no incompletely stripped areas, plating nodules, or damaged insulating layers on the rack surface. The rack materials are as follows:
(1) Brass / copper: mainly used for cathode bars and rack frames. Brass has a certain strength; copper provides better conductivity but at higher cost.
(2) Phosphor bronze: used for spring clips inside rack hooks. It has good elasticity and conductivity, but high cost.
(3) Stainless steel: generally 316 stainless steel, used for part hooks and the outer layer of rack hangers. It has good corrosion resistance and is easy to strip, but has poor conductivity.
(4) Titanium: used for anode baskets and auxiliary anodes. It has poor conductivity but good corrosion resistance.
(5) Copper-clad titanium: used for positions requiring high electrical conductivity and high corrosion resistance.
(6) Green coating on rack surface: polyvinyl chloride (PVC) coating. It can also be used for stop-off plating on part welding posts.
04 POP (Plating on Plastics) Chrome Plating in Automotive Interior and Exterior Trim
POP chrome plating technology has obvious advantages in automotive interior and exterior trim: first, the metallic texture and luster; second, light weight and low density; third, injection molding + electroplating process offers low cost.
At present, two types of materials are mainly used for plastic electroplating in vehicles: ABS or ABS/PC accounts for more than 95%, and nylon (PA) accounts for less than 5%.
PA electroplating is mainly applied to parts with high requirements for strength and mechanical properties, such as interior and exterior door handles. Its applications in the whole vehicle include radiator grilles, decorative strips, and mirror housings.
The following are common faults and their troubleshooting.
(1) Copper burning.
Causes: low plating solution temperature; solution composition outside the process range; additive imbalance; poor agitation; excessive current; parts with flash or overly sharp corners.
Treatment: raise temperature to 23–30°C; analyze and adjust additives; perform Hull cell test and adjustment; strengthen agitation; reduce current; remove flash and avoid such features in design.
(2) Skip plating.
Causes: incomplete cleaning of chromic anhydride; oxidizing substances in the air; excessive conditioning; insufficient active palladium on the part surface.
Treatment: strengthen cleaning and reduction; purify air and enhance ventilation; adjust conditioning time, concentration and temperature; ensure the palladium concentration is maintained and the part surface is not damaged after palladium adsorption.
(3) Poor coverage (yellowing).
Causes: improper ratio of chromic anhydride to sulfuric acid; too much or too little trivalent chromium; additive imbalance.
Treatment: analysis and adjustment; Hull cell test and adjustment.
05 Conclusion
Although plastic electroplating technology is now widely used in the design of automotive interior and exterior trim, the selection of plastic materials for electroplating must comprehensively consider multiple material factors.
From the plastic raw material to a finished electroplated decorative part, the process goes through two major stages: injection molding and electroplating. Any process error may cause the entire product to be scrapped.
Defects in plastic electroplated parts have the characteristics of being transferred and accumulated. Whether in design, manufacturing or assembly, once a defect exists, it will accompany the entire production process and cannot be overcome by subsequent process adjustments. On the contrary, the defect will gradually amplify and become more obvious.