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Rotational molding (rotomolding) and injection molding are two distinct plastic manufacturing processes with unique advantages and applications. Understanding their differences is critical for selecting the right method for specific product requirements.
1. Process Overview
Rotational Molding: A hollow mold filled with powdered plastic rotates biaxially in an oven. The material melts, coats the mold's interior, and cools to form a seamless, stress-free part. Ideal for large, hollow, or complex geometries (e.g., tanks, containers).
Injection Molding: Molten plastic is injected under high pressure into a rigid mold. It solidifies quickly, enabling high-speed production of precise, intricate parts (e.g., gears, electronic housings).
2. Mold Design & Cost
Rotomolds use simpler, low-cost molds (often aluminum or mild steel) without high-pressure resistance requirements.
Injection molds require hardened steel molds to withstand extreme pressure, increasing upfront costs.
3. Material & Wall Thickness
Rotomolding supports polyethylene (PE) and polypropylene (PP) in powder form, producing uniform wall thickness and stress-resistant parts.
Injection molding works with a wider range of thermoplastics (pellets), but thick walls may lead to sink marks or uneven cooling.
4. Production Efficiency
Rotomolding has longer cycle times (heating/cooling phases) but lower tooling costs, suited for low-to-medium volumes.
Injection molding achieves rapid cycles (seconds to minutes), ideal for mass production despite higher initial investments.
5. Product Characteristics
Rotomolded parts are lightweight, durable, and seamless, perfect for large hollow structures.
Injection-molded parts offer superior dimensional accuracy and surface finish for complex, high-tolerance components.
Rotational molding excels in cost-effective, low-volume hollow products, while injection molding dominates high-precision, high-volume manufacturing. The choice depends on design complexity, material, budget, and production scale.
