plastic sheet material used for forming box blanks are provided with soft , bendable score lines by applying frictional heat through rapid vibration . the sheet material is clamped under high pressure between a resilient make - ready and a scoring tool , and is subjected to the vibratory action which generates frictional heat sufficient to melt the plastic material at the engaged interface , thereby forming a score line along which the sheet material may be bent to form an assembled box . a completed box blank may be formed in a single operational step , by cutting the box , impressing the score lines , and impressing embossments , if required , simultaneously in a single operational cycle of seconds duration .