Failure Analysis of Yellowness Issue in Automotive Headlamp and its Remedies

Automotive headlamps, constructed using different components are likely affected by haziness, dirtiness, fogginess, cloudiness, or white patches caused by oxidation, chemical attack, water vapors, flying debris, and dirt. In the present work, we have identified the root causes of outer lens yellowness issue in a headlamp and provided possible remedies. For this attempt, two headlamps were analyzed for the yellowness root cause analysis and their failure prevention. Several parts of the headlamp assembly, such as outer lens, dust caps and housing assembly, were characterized for the thermal, structural, and morphological analysis. Yellowness is mostly caused by the liberation of lower temperature volatile organic compounds due to thermal decomposition and oxidation of lower molecular weight additives present in the polymers. Thermal properties of clear transparent headlamp parts (OK) and yellow colored headlamp parts (NOT-OK) were analyzed using differential scanning calorimetry, thermogravimetric analysis. The chemical structure similarity of the NOT-OK and OK headlamps parts was characterized by the fourier transform infrared spectroscopy analysis. The liberation of lower temperature volatile organic components and their deposition onto the inside layer of the outer lens resulted in the yellowness issue in the headlamp. The headlamp component that contributed to the liberation of lower temperature volatile organic components was identified and remedies have been implemented for the failure prevention in future headlamp parts.