The wall thickness design of non-standard customized plastic shells is a critical step in product development, directly impacting the shell's mechanical properties, molding quality, and reliability. Unlike standard parts, non-standard customized shells require personalized design based on specific application scenarios, load conditions, and material characteristics. Therefore, a comprehensive consideration of multiple mechanical factors is necessary to ensure the product meets functional requirements and possesses long-term stability.
Wall thickness design must first consider the material's mechanical properties. Different plastic materials (such as ABS, PC, PA, or modified engineering plastics) exhibit significant differences in tensile strength, flexural modulus, and impact toughness, directly determining the shell's load-bearing capacity. For example, high-rigidity materials can have their wall thickness reduced to decrease weight, while tough materials require increased wall thickness to improve impact resistance. A mismatch between material selection and wall thickness design can lead to brittle fracture or excessive deformation under stress. For instance, a shell for an industrial device developed cracks during transport vibrations due to the use of low-toughness materials and insufficient wall thickness; the problem was resolved by switching to toughened materials and optimizing the wall thickness distribution.
Structural stress analysis is the core basis for wall thickness design. Non-standard customized housings typically need to withstand static loads (such as the equipment's own weight), dynamic loads (such as vibration and impact), or environmental stresses (such as thermal stress caused by temperature changes). During the design phase, finite element analysis (FEA) is required to simulate the stress distribution of the housing under actual operating conditions, identify high-stress areas, and thicken them accordingly. For example, stress concentrations are prone to occur at support structure connections, around mounting holes, and at edge corners; these areas require local thickening or rounded transitions to reduce the risk of cracking. One medical device housing cracked due to insufficient consideration of the preload force of mounting screws, resulting in excessively thin walls around the holes. This was subsequently improved by increasing the wall thickness around the holes and optimizing the screw layout.
Wall thickness uniformity significantly affects molding quality and mechanical properties. Excessive wall thickness variation leads to uneven melt flow, causing defects such as shrinkage cavities, bubbles, or warpage, while also reducing the overall structural rigidity. The design should follow the principle of "gradual transition," avoiding abrupt changes in wall thickness; for example, transitions from thick-walled to thin-walled areas should be achieved through slopes or curved surfaces. A consumer electronics casing experienced localized shrinkage due to a sudden change in wall thickness, affecting its appearance and assembly precision. This issue was resolved by adjusting the wall thickness gradient. Furthermore, uniform wall thickness reduces mold cooling time and improves production efficiency.
Balancing stiffness and strength is a key objective in wall thickness design. Increasing wall thickness improves structural stiffness, but excessive thickness leads to material waste, increased costs, and longer molding cycles; conversely, excessively thin walls may fail to meet strength requirements. Design should achieve "thin-wall" design through structural optimization (such as the use of reinforcing ribs, bosses, or rib plates), reducing material usage while maintaining overall strength. For example, a car interior casing reduced its wall thickness from 3mm to 2.5mm by adding longitudinal reinforcing ribs, while simultaneously increasing stiffness by 15%, achieving a balance between lightweighting and performance.
Environmental adaptability is also a crucial factor in wall thickness design. At high temperatures, plastic materials may experience creep or thermal deformation, requiring increased wall thickness or the use of heat-resistant materials to improve stability; at low temperatures, material brittleness increases, necessitating the avoidance of cracking due to thin-walled structures. Furthermore, chemically corrosive environments (such as acids, alkalis, and solvents) require increased wall thickness or surface coating to extend the shell's lifespan. For example, the shell of a certain outdoor device failed to account for UV aging, leading to accelerated embrittlement in thin-walled areas. This was resolved by using weather-resistant materials and increasing the wall thickness in critical areas.
Assembly and functional requirements impose special demands on wall thickness design. If the shell needs to fit tightly with other components (such as snap-fit or threaded connections), the wall thickness must meet assembly tolerances to avoid loose fits due to insufficient thickness or assembly difficulties due to excessive thickness. For instance, the snap-fit structure of a communication device shell broke after repeated disassembly and assembly due to an unreasonable wall thickness design. Durability was improved by optimizing the wall thickness at the snap-fit root and adding rounded corners.
The wall thickness design of non-standard customized plastic shells requires a comprehensive consideration of material properties, stress analysis, molding processes, environmental adaptability, and assembly requirements. A balance between performance and cost must be achieved through scientific calculations and simulation verification. The design process should avoid empiricism and instead establish a mechanical model based on specific working conditions. This model should be continuously optimized through mold prototyping and performance testing to ultimately ensure that the shell has reliable mechanical properties and long-term stability under complex usage scenarios.
