Basic Knowledge of Plastic Kits

Time:

2022-12-20 13:33

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Web scraping

The plastic component design should be as successful as possible. For areas where reliability is difficult to ensure—such as those prone to feeding difficulties in the mold or easy ejection issues during mold correction—consider pre‑providing a slight clearance for the molded part.

　　 Plastic kit The design should be as successful as possible. For areas where reliability is difficult to ensure—such as cases where mold feeding is challenging or part ejection becomes problematic during mold modification—consider pre‑providing a slight clearance in the molded part.

　　Common plastics include ABS, AS, PC, PMMA, PS, HIPS, PP, and POM. Among these, the most frequently used transparent plastics are PC, PMMA, PS, and AS. The housings of high-end electronic products typically employ an ABS–PC blend; display panels are made of PC, and if PMMA is used, it requires a surface‑hardening treatment. HIPS and ABS are primarily utilized for the housings of everyday consumer electronics. Due to its excellent resistance to aging, HIPS is increasingly replacing ABS.

　　Surface treatments include electroplating, spray coating, screen printing, and pad printing. ABS, HIPS, and PC materials exhibit excellent surface‑treatment results; however, PP materials have relatively poor surface‑treatment performance and typically require pre‑treatment. Other techniques include in‑mold decoration (IMD), in‑mold labeling (IML), and, in recent years, the development of semi‑transmissive, semi‑reflective mirror‑manufacturing technologies.

　　Differences and Advantages of IMD and IML:

　　1. The substrate of IMD films is typically a highly peelable PET, whereas IML films are usually made of PC.

　　2. During IMD injection molding, only the ink on the diaphragm bonds with the resin, whereas IML uses resin to coat the entire diaphragm.

　　3. IMD is automatically fed and positioned by the film‑feeding machine, while IML is manually hung by an operator.

　　1.1 Exterior Design

　　For plastic components, if the exterior design is flawed, the mold may be rendered unusable, so utmost care is essential. The design should ensure an aesthetically pleasing, streamlined appearance with smooth, natural transitions between curved surfaces, while also adhering to ergonomic principles. In most consumer electronics used in everyday life, the housing typically consists of an upper shell and a lower shell. In theory, the shapes of these two halves can match; however, in practice, factors such as mold‑making tolerances and injection‑molding parameters often lead to dimensional discrepancies—resulting in either “face scraping” (where the top shell is larger than the bottom) or “bottom scraping” (where the bottom shell is larger than the top). Such surface misalignments are generally considered acceptable.

　　Generally, the top cover, with more button openings, exhibits greater molding shrinkage; therefore, a higher shrinkage rate—typically 0.5%—is selected. In contrast, the bottom cover experiences less molding shrinkage, so a lower shrinkage rate—usually 0.4%—is chosen. Consequently, the shrinkage rate of the front cover is typically 0.1% higher than that of the bottom cover.

　　1.2 Plastic Component Assembly Design

　　Refers to the design of assembly dimensions between components that have an assembly relationship. The primary focus is on controlling clearance fits and tolerances.

　　1.3 Stop Groove

　　This refers to the interfit between the upper and lower shells. The nominal dimensions of the design should allow for a clearance of 0.05–0.1 mm, and the mating surfaces should be chamfered at an angle of 1.5°–2°. Chamfers or rounded corners should be provided at the ends to facilitate assembly. The upper and lower shells should be mated with a fillet‑to‑fillet fit; the internal corner radii of the mating surfaces should be relatively large to increase the gap between the fillets and prevent interference at the fillet junctions.

　　1.4 Plastic Kit Snap-Button Location

　　This primarily refers to the mating of the upper and lower shell’s snap‑fit features. When determining the number and placement of these snaps, the overall external dimensions of the product should be taken into account, with an even distribution and balanced positioning. Snaps located at corners should be positioned as close to the corner as possible to ensure tighter engagement and help prevent common corner‑related gaps. The snap‑fit design should also allow for a controlled clearance.

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