Product surface whitening (stress whitening)

In the '2079851475616104458 (vacuum forming) production process, the product exhibits the quality defect of "Product surface whitening (stress whitening)". The specific manifestation is that stress whitening appears locally on the product. This defect is relatively common when processing materials such as PP, PS, PET, PVC, ABS sheets, and its occurrence conditions are usually related to the unreasonable settings of sheet heating temperature, forming pressure/vacuum level, mold temperature, and cooling time. When the "Product surface whitening (stress whitening)" situation is severe, it will cause a series of chain quality defects in the product in terms of appearance, dimensional accuracy, mechanical properties, etc., which not only reduces the functionality and safety of the product in use, but also directly increases the scrap rate and production cost. Therefore, this problem requires systematic diagnosis and optimization from multiple dimensions such as material selection, the status of the '2079851475616104458 machine, heating oven, mold, and vacuum/air pressure system, and sheet heating temperature, forming pressure/vacuum level, mold temperature, and cooling time.

1. Over-stretching. This factor causing the problem reflects that certain process conditions or material characteristics in '2079851475616104458 (vacuum forming) processing have not met the optimal molding requirements. Such problems are often cumulative and hidden, and should be investigated and verified as key focus items during process debugging and finalization to ensure that hidden dangers are eliminated at the source. 2. Sheet temperature too low causing cold stretching. Temperature is the core factor affecting melt fluidity and viscosity. A temperature set too high will cause the melt viscosity to decrease, insufficient melt strength, and even thermal degradation; a temperature that is too low results in poor melt fluidity and insufficient plasticization, making it impossible to fill or form smoothly. A reasonable temperature window should be optimized and determined within the recommended range according to the melting characteristics and thermal stability of the material. In addition, the insufficient overall coordination of sheet heating uniformity and stretch ratio control is also a factor that cannot be ignored; there are complex interactions and coupling relationships among the process parameters, and the deviation of any one parameter may aggravate the degree of "Product surface whitening (stress whitening)" through chain effects. In terms of equipment maintenance, the regular overhaul and precision confirmation of the '2079851475616104458 machine, heating oven, mold, and vacuum/air pressure system are not in place, causing the actual operating parameters of the equipment to deviate from the process requirements, which will also become a potential inducement of the "Product surface whitening (stress whitening)" problem.

1. Increase the sheet temperature. When implementing adjustments, it is recommended to adopt the single-factor variable method, adjusting only one parameter at a time and fully evaluating the effect, to avoid simultaneous changes of multiple parameters making the cause of the problem untraceable. The adjustment amplitude should be small rather than large; each adjustment is recommended to be controlled within 5%~10% of the original value, and after adjustment, run stably for at least 3~5 mold cycles to observe the effect. 2. Reduce the stretch ratio. Adjustments should follow the principle of gradual progress; the amplitude of each adjustment should not be too large, and it is recommended to decrease by 5%~15% of the current value. After each adjustment, observe the product quality changes stably for at least 5~10 mold cycles, and continue adjusting only after confirming that the improvement direction is correct; avoid one-step excessive adjustment. 3. Optimize the forming speed. Optimization work must be based on an accurate diagnosis of the root cause of the problem, and blind attempts must be avoided. It is recommended to first determine the key influencing factors and their interactions through the process DOE test method or historical production data analysis, and then carry out parameter optimization and structural improvement in a targeted manner to achieve twice the result with half the effort. In terms of material management, incoming inspection of raw materials upon arrival and in-process inspection of work-in-progress should be strengthened, and the key performance indicators of PP, PS, PET, PVC, ABS sheets should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the "Product surface whitening (stress whitening)" problem can be attributed to the combined action of multiple factors such as Over-stretching, Sheet temperature too low causing cold stretching. Solving this problem requires starting from aspects such as Increase the sheet temperature, Reduce the stretch ratio and adopting systematic governance measures. In actual production, it is recommended to establish a prevention and rapid response mechanism for this problem, and achieve stable production and continuous improvement through sheet heating uniformity and stretch ratio control.