Chinese Auto Plastics: Molding Control & Full Weather Resistance Tests
Based on domestic automotive industry standards and actual vehicle application environments, this paper systematically sorts out standardized injection molding control rules for automotive plastic components, as well as complete classification schemes, test conditions and acceptance thresholds of weather resistance tests. Combined with mainstream modified materials including ABS+PC, modified PP and ASA widely used on Chinese vehicle models, the content integrates full-process molding parameter adjustment, residual stress improvement and domestic standardized aging test systems, forming unified production and inspection guidance suitable for interior and exterior injection plastic parts manufactured by China’s automotive enterprises.
Raw Material Pretreatment Management for Automotive Injection Plastics
Most automotive plastic materials are modified engineering plastics with obvious moisture absorption characteristics, and all raw materials need to meet the national standards for automotive non-metallic materials issued in China. ABS+PC, ASA and other exterior decorative plastics require hot air drying at 80℃ to 90℃ for 4 to 6 hours, with the moisture content strictly controlled below 0.04%. Sufficient drying can effectively eliminate surface silver streaks and internal bubbles caused by water vapor gasification during melting, and prevent irreversible molecular degradation of PC components under high temperature. Flame retardant modified automotive plastics shall adopt lower drying temperature to avoid decomposition of flame retardant additives, which may lead to surface black spots and mold deposits during mass production. Dried raw materials should be stored in heat-preserved feeding hoppers at 70℃ to prevent secondary moisture absorption in high-humidity workshop environments.
Standard Molding Parameter Matching for Vehicle ABS+PC Parts
Different parameter ranges shall be configured according to the installation position and structural characteristics of plastic parts. For conventional ABS+PC automotive components, the barrel temperature is maintained between 200℃ and 245℃, and the maximum melt temperature must not exceed 265℃ to stop material yellowing and toughness loss caused by excessive thermal decomposition. Exterior high-gloss appearance parts adopt mold temperature from 70℃ to 110℃ to reduce residual internal stress formed in the molding stage, while interior ordinary structural parts use constant mold temperature of 50℃ to 80℃ to balance production cycle and dimensional stability. The whole injection process follows medium pressure and low shear molding logic, which reduces surface defects such as obvious weld lines and sink marks, and lays a good foundation for the long-term weather resistance of finished products. After demolding, all plastic parts need 24 hours of natural standing in constant temperature workshops to release partial internal stress; key stressed parts like buckles and decorative fasteners shall receive low-temperature annealing treatment to further enhance anti-cracking performance after long-term aging.
Domestic Full Weather Resistance Test System for Automotive Plastics
All test items are carried out in accordance with Chinese national standards GB/T 32088, GB/T 16422 series and QC/T automotive industry specifications, and test plans are divided into three categories targeting exterior parts, interior parts and engine compartment components respectively. Artificial accelerated xenon lamp aging serves as the core routine inspection project. Exterior injection parts use full-spectrum xenon lamp exposure with irradiance set as 0.55W/m² at 340nm, equipped with standard illumination and water spray circulation, and the test cycle lasts 2000h to 4000h depending on appearance grade. Interior plastic parts adopt window glass filtered xenon lamp mode with irradiance of 0.35W/m² at 340nm, without periodic water spray, and the test duration ranges from 1000h to 2000h. Plastic parts installed in engine cabins need additional thermal oxygen aging test under constant high temperature of 120℃ to 150℃ to simulate long-term high-temperature oxidation environment. A complete set of auxiliary supporting tests includes high temperature and humidity aging, high-low temperature alternating cycle, neutral salt spray corrosion and chemical medium resistance test, which comprehensively reproduce complex outdoor service environments in China.
Natural Atmospheric Exposure Verification Test Requirements
To verify the accuracy of artificial accelerated aging data, manufacturers shall arrange natural exposure tests at China’s official exposure test bases. Exterior plastic samples are placed in hot and humid Hainan test field and dry and hot Xinjiang test field for 12 months of uninterrupted outdoor exposure, while interior samples are tested under glass filtered sunlight conditions. The color difference, gloss retention and mechanical property change data obtained from natural exposure shall be used as the benchmark to judge whether the parameter setting of artificial aging test is reasonable, ensuring the test results can truly reflect the actual aging performance of plastic parts after years of vehicle operation.
Unified Acceptance Criteria After Weather Resistance Aging Test
Visual and optical indicators are the primary judgment standards for finished automotive plastic parts after aging. For A-class exterior appearance components, the color difference ΔE shall not exceed 2.0; the gloss retention rate of high-gloss parts is required to be above 80%, and matte parts shall keep more than 70% of original gloss. Any surface defects including chalking, microcracks, blistering, whitening and sticky surface are defined as unqualified items. In terms of mechanical performance, the tensile strength retention rate of aged samples shall be no less than 85% of the original value, and the impact strength shall remain above 70% to avoid brittle fracture during assembly and use. The dimensional deformation of all parts shall be controlled within drawing tolerance, without assembly jamming or abnormal gap change after aging. Transparent decorative plastic parts require light transmittance reduction less than 10% and no obvious fogging phenomenon.
Synergy Between Molding Process Control and Weather Resistance Performance
The weather resistance of automotive injection plastic parts is not only determined by raw material formulation, but also deeply affected by molding process quality. Insufficient drying, excessive shear temperature and low mold temperature will leave high residual stress inside products, which greatly increases the risk of cracking and discoloration under long-term aging environment. Strictly implementing standardized injection parameter control can reduce internal defects of plastic parts from the production source, and cooperate with complete domestic weather resistance test standards to screen out unqualified materials and process schemes in advance, so as to produce automotive plastic parts that meet long-service-life requirements under China’s diverse climatic conditions.
