Post-processing of plastic parts
Post-processing of plastic parts is an essential step in the injection molding process. Its purpose is to eliminate defects created during the molding process, improve product performance and appearance, and ensure that the parts meet the requirements of practical applications. For some plastic parts with complex structures or high surface quality requirements, it is often difficult to achieve the final use standard through injection molding alone, and a series of post-processing optimization processes are necessary. For example, in the production of automotive interior parts, the surface of plastic parts may have defects such as weld marks and sink marks. Post-processing such as polishing and spraying can not only conceal these defects but also enhance the surface’s wear and corrosion resistance. In the production of electronic device casings, post-processing such as electroplating or vacuum coating can give plastic parts good conductivity and decorative properties, improving the overall quality of the product.
There are many different post-processing processes for plastic parts, including mechanical treatment, chemical treatment, surface coating, and pre-assembly treatment. Mechanical treatment primarily corrects physical defects on the surface of plastic parts, such as sanding to remove burrs and flash, and using a polishing machine to fine-polish the surface to improve gloss. For parts requiring high dimensional accuracy, mechanical cutting may also be required to adjust the dimensions. Chemical treatment involves using chemical solutions to react with the surface of the plastic part to achieve surface modification. For example, chemical etching increases the surface roughness of the plastic part to improve the adhesion of subsequent coatings; oxidation treatment forms an oxide film on the surface of the plastic part to enhance its corrosion resistance.
Surface coating is an important post-processing method to enhance the appearance and performance of plastic parts. Depending on the coating material and process, it can be divided into various types, such as spraying, electroplating, and vacuum coating. The spraying process atomizes the paint and evenly applies it to the surface of the plastic part. After curing, a protective film is formed. This not only beautifies the appearance, but also protects against UV rays and aging. It is widely used in products such as home appliance housings and car bumpers. Electroplating uses the principle of electrolysis to deposit a thin metal film on the surface of the plastic part, such as chrome plating or nickel plating. This gives the plastic part a metallic luster and texture, while improving its hardness and wear resistance. It is often used in the processing of decorative plastic parts. Vacuum coating technology evaporates metal or compounds and deposits them on the surface of the plastic part in a high vacuum environment, forming a uniform film. It has the advantages of being environmentally friendly and having strong adhesion. It is suitable for precision plastic parts with extremely high surface quality requirements.
For some plastic parts with internal stress, post-annealing is a critical process for eliminating stress and preventing deformation or cracking. During the injection molding process, as the melt cools and solidifies in the mold cavity, internal stress can easily form within the part due to uneven temperature distribution and inconsistent shrinkage. If not promptly eliminated, the part may deform or even crack during use due to changes in ambient temperature or stress. Annealing heats the plastic part to a certain temperature (usually below the plastic’s glass transition temperature) and maintains this temperature for a period of time, allowing the molecular chains within the part to relax and release internal stress. For example, polycarbonate (PC) parts often require annealing after molding to avoid cracking caused by excessive internal stress and ensure the product’s dimensional stability and safety.
The choice of post-processing process for plastic parts must be determined comprehensively based on the material properties, usage requirements, and specific issues encountered during the molding process. Production efficiency and cost control must also be considered. In actual production, a comprehensive quality inspection system should be established to conduct comprehensive inspections of plastic parts before and after post-processing, such as through appearance inspection, dimensional measurement, and mechanical property testing, to ensure that the treatment effect meets the expected standards. With the increasing awareness of environmental protection, future post-processing technologies for plastic parts will place greater emphasis on green environmental protection, such as developing solvent-free coatings and adopting energy-saving and emission-reducing coating processes, thereby minimizing environmental impact while ensuring treatment results. Furthermore, the application of intelligent technologies will also promote the upgrading of post-processing processes, such as improving processing accuracy and efficiency through automated polishing equipment and achieving coating uniformity and consistency through the use of robots for spraying operations, creating broader development space for post-processing of plastic parts.
