How to properly set the draft angle of the rice cooker shell mold parts?
Release Time : 2025-11-25
The draft angle setting of rice cooker shell mold components is a crucial aspect of mold design, directly impacting the smoothness of product demolding, surface quality, and mold lifespan. The core logic lies in balancing material shrinkage, frictional resistance, and product functional requirements through a well-designed draft angle, preventing surface scratches, deformation, or mold wear caused by demolding difficulties.
Rice cooker shells commonly use plastic materials such as PP, which have a high shrinkage rate upon cooling and tend to cling to the core. If the draft angle is insufficient, the friction between the material and the mold will significantly increase during ejection, leading to a sharp increase in demolding force. This can result in surface scratches or even product deformation and cracking. For example, a certain brand of rice cooker shell experienced large-area whitening during ejection due to an insufficient draft angle design. The surface defect was ultimately resolved by adjusting the draft angle from 1° to 2° and optimizing the ejection speed. Therefore, the primary function of the draft angle is to counteract the "clamping force" generated by material shrinkage, ensuring smooth product ejection from the mold.
The complexity of the product shape directly influences the selection of the draft angle. Rice cooker shells typically include sidewalls, reinforcing ribs, and snap-fit mechanisms, among which the slope of the sidewalls is of paramount importance. If the shell is tall or thick, the clamping force generated by shrinkage is stronger, requiring a larger slope; conversely, a lower slope can be used for shorter, thinner-walled structures. For local features such as reinforcing ribs, their slopes must be coordinated with the overall design to avoid uneven force distribution during ejection due to slope differences. For example, the slope of reinforcing ribs is usually 0.5° to 1° smaller than that of the sidewalls, ensuring smooth demolding while maintaining structural strength. Furthermore, the slope of moving parts such as snap-fit mechanisms needs precise control; if the direction or magnitude of the slope conflicts with the movement trajectory, it may lead to jamming or functional failure.
The mold structure constrains the setting of the demolding slope. Multi-cavity molds require uniform slopes across all cavities to avoid asynchronous demolding due to slope differences; side-pulling or angled ejector structures require strict verification of the interference between the slope and the movement trajectory, typically with the angled ejector not exceeding 12° to prevent self-locking. For example, a rice cooker mold experienced jamming during ejection due to an excessively large draft angle. This was resolved by reducing the draft angle and optimizing the ejection system. Furthermore, the polishing precision of the mold also affects the draft angle selection. High-gloss molds require a slightly larger draft angle to counteract the microscopic vacuum adsorption effect and prevent whitening during ejection.
The ejection system design must match the draft angle. The number, position, and ejection speed of ejector pins must be adjusted according to the draft angle. A larger draft angle results in lower ejection resistance, allowing for a reduction in the number of ejector pins. A smaller draft angle necessitates adding ejector pins or optimizing the layout to avoid localized stress concentration. For instance, a rice cooker shell, due to insufficient draft angle, relied solely on a single ejector pin during ejection, causing product tilting and deformation. Stable demolding was achieved by adding ejector pins and adjusting the draft angle to a reasonable range.
Special scenarios require targeted adjustments to the draft angle. For textured shells, the draft angle needs to be increased proportionally with each increase in texture depth to offset the increased friction. Transparent or high-gloss parts require extremely high surface quality; insufficient draft angle can easily lead to scratches during ejection, necessitating an appropriately increased draft angle. Furthermore, the draft angle of precision components or functional surfaces must be strictly controlled to avoid affecting assembly accuracy or motion performance.
Practical experience is a crucial basis for optimizing draft angle design. Through trial molding and adjustments, the optimal draft angle parameters can be gradually found. For example, a rice cooker mold initially designed with a 1.5° draft angle, but after trial molding, it was found that demolding resistance was still relatively high. By adjusting the draft angle to 2° and optimizing mold polishing, successful demolding was finally achieved. In addition, accumulating draft angle design cases for different materials and structures can form a standardized parameter library, improving design efficiency.
The draft angle setting for rice cooker shell mold components needs to comprehensively consider material properties, product shape, mold structure, ejection system, and practical experience. By designing the angle appropriately, the smoothness of demolding, surface quality, and mold life can be significantly improved, laying the foundation for stable production and quality assurance of rice cookers.
