Development of Mold-in-Colored LFI Composite Hood with Non-Destructive Defect Prediction Using A-Scan Ultrasonic Testing

Mold-in-colored composite parts manufactured by LFI (Long Fiber Injection) process are increasingly applied to industrial components due to advantages such as elimination of painting processes and reduced mold investment costs. Recognizing these advantages, our company successfully developed and commercialized a mold-in-colored hood using LFI technology.
During initial production, the hood exhibited surface quality issues such as wrinkling and roughness following thermal cycling tests. Investigation revealed that these defects resulted from meso-sized void formation and non-uniform porosity distribution. Through systematic process parameter control—including humidity, pressure, and mold temperature adjustment—we successfully reduced void sizes to micro-scale with uniform distribution, thereby resolving the surface quality problems.
Beyond porosity control, intermittent glass fiber agglomeration remained a critical quality issue potentially affecting structural performance. To address this challenge, we developed a non-destructive defect detection methodology utilizing A-Scan ultrasonic testing, which is widely recognized for composite defect evaluation. The method enables real-time prediction of fiber concentration through acoustic impedance ratio analysis and has been validated against CT imaging for detecting fiber bunching with high accuracy.
Future research will focus on advanced polyurethane resin material development to simultaneously reduce cycle time and further enhance surface quality. This integrated approach—combining process optimization, non-destructive quality assurance, and material innovation—demonstrates the practical pathway for high-performance composite manufacturing in automotive applications.