New energy vehicle injection molded parts serve in harsh working conditions such as high temperature in cabin, outdoor low temperature, alternating temperature difference and damp heat aging for a long time. Plastic parts used in motor cabin, battery periphery, internal and external structural parts and wire harness often suffer from low-temperature brittle fracture, high-temperature softening and deformation, dimensional drift after temperature cycle, assembly loosening and surface cracking. Different from civil injection parts, vehicle plastic parts have extremely high requirements on -40℃ low-temperature impact resistance, 85℃ high-temperature heat resistance, high and low temperature cycle stability, aging resistance and constant dimensional accuracy. Only full-link optimization from material selection, formula modification, product structure, mold technology, injection molding and post-treatment can stably meet the vehicle high and low temperature acceptance standards.
1. Main Failure Modes of Vehicle Parts Under Temperature VariationThe operating temperature range of new energy vehicles is extremely wide, with extreme low temperature as low as -40℃ in winter and normal closed cabin high temperature reaching 80～85℃, even close to 90℃ after sun exposure. Frequent alternating temperature difference easily causes various quality defects. At low temperature, the toughness of plastic parts decreases significantly, leading to brittle fracture, corner collapse and cracks under slight vibration and extrusion. Under high temperature working conditions, material modulus and rigidity decrease, resulting in creep, warpage and collapse, enlarged assembly gap and abnormal noise after loosening. After long-term high and low temperature cycles, molecular structure aging and internal stress release cause dimensional deviation and warpage, accompanied by surface whitening, stress cracking and weathering attenuation, directly affecting vehicle safety and service life.
2. Optimization of Material Grade and Modified Formula
Material is the core foundation to determine high and low temperature resistance. Prefer special heat-resistant modified base materials for new energy vehicles. Cabin high-temperature parts adopt modified PA66, PA46, glass fiber reinforced PBT and PC/ABS heat-resistant alloy, with long-term service temperature stably above 85℃ and short-term resistance to 90℃ high temperature without softening. Low-temperature exposed parts adopt toughened modified PP, low-temperature resistant PC and elastomer toughened PA, which can stably withstand -40℃ extreme cold without brittle fracture. Low-temperature toughening agents, high-temperature antioxidants and thermal stabilizers are added to improve molecular chain flexibility and thermal stability, reducing rigidity mutation and embrittlement tendency under high and low temperature. For glass fiber reinforced parts, the glass fiber content should be controlled within a reasonable range. Excessively high glass fiber content improves high-temperature rigidity but greatly reduces low-temperature toughness, easily causing low-temperature cracking, realizing the balance of heat resistance, cold resistance and rigidity.
3. Product Structure Adapted to High and Low Temperature Working ConditionsReasonable structural design can greatly reduce the risk of deformation and cracking under temperature variation. The overall wall thickness of plastic parts is kept uniform to avoid local thick material accumulation. Large arc transition is adopted for thickness variation to eliminate stress concentration at right angles and sharp corners and prevent stress cracking under low temperature force. Avoid slender thin-wall and long-span cantilever structures, which are prone to creep and warpage at high temperature and brittle fracture at low temperature. Key stress parts such as assembly buckles, reinforcing ribs and fixing columns are properly thickened and reinforced with arc transition to reduce fatigue stress caused by alternating high and low temperature. The same assembly should adopt materials with similar shrinkage rate to avoid tensile deformation and assembly failure caused by excessive difference in thermal expansion coefficient during temperature change.
4. Mold Design Adapted to High and Low Temperature MoldingMold temperature control system affects the internal stress and later temperature stability of molded parts. Symmetrical and balanced layout of water channels is adopted with mold temperature fluctuation controlled within ±2℃ to ensure uniform cooling and low internal stress of parts. Prefer side gate and fan gate with smooth feeding, enlarge the section of gate and runner to reduce melt shear orientation stress. Lower internal stress means less prone to cracking and deformation after high and low temperature cycles. Appropriately increase demolding draft angle for precision vehicle parts with evenly distributed ejection points to avoid mechanical stress caused by forced demolding, and residual stress will be released rapidly under high and low temperature to induce cracks. The mold shrinkage rate is reserved and compensated according to high and low temperature environment to offset dimensional deviation caused by thermal expansion and cold contraction.
5. Optimization of Injection Molding Process Parameters
The molding process takes low internal stress and uniform molecular arrangement as the debugging direction. Appropriately increase mold temperature to slow down the cooling speed of part surface, leave sufficient relaxation time for molecular chains and reduce frozen orientation stress. Adopt medium and low injection speed to weaken melt shear strength and avoid hidden residual stress caused by excessive molecular stretching. Multi-stage gradual decreasing holding pressure is adopted to avoid excessive high pressure stress accumulation. Extend cooling time reasonably to realize synchronous shaping and shrinkage inside and outside parts, reducing secondary deformation induced by later temperature change. Raw materials are strictly dried according to standards to avoid internal micro-defects formed by water vapor and volatile substances. Micro-pores will become crack initiation points under high and low temperature, greatly reducing weather resistance and temperature resistance life.
6. Post-molding Treatment and Stability EnhancementKey injection parts of new energy vehicles must increase annealing setting treatment to release residual molding internal stress, preventing cracking and deformation caused by stress release during subsequent high and low temperature cycles. Finished products are stored at constant temperature to avoid sudden cooling and heating before delivery and prevent premature material aging and stress defects. Mass production must pass high and low temperature cycle verification according to vehicle standards with alternating cycle from -40℃ to 85℃, sampling inspection of appearance, size and strength changes before mass production to screen hidden dangers of insufficient temperature stability in advance.
7. SummaryThe optimization of high and low temperature resistance for new energy vehicle injection parts cannot rely solely on material replacement or fine-tuning process. It must form a complete system of material modification, structural design, mold temperature control, injection process and post-treatment verification. Select special materials adapted to temperature range, avoid stress concentration through uniform arc structure, reduce residual internal stress through balanced mold temperature control and low-stress injection process, and cooperate with annealing setting and high and low temperature sampling verification. All-round improvement of parts resistance to brittle fracture, deformation and aging under extreme cold, high temperature and alternating temperature difference meets the strict vehicle service standards and long-term service reliability of new energy vehicles.
