Abstract: The design and manufacturing of auto-body welding lines are important to production
quality and efficiency of automobiles. Carlines are grid lines parallel to the axes of an auto-body
coordinate system and used to position key components in the coordinate system. The carlines are
used as datum references for the manufacturing and inspection of auto-bodies, so that they are of
importance in guaranteeing manufacturing precision of auto-bodies. An algorithm is proposed for
carline generation based on coordinate system transformation. At first, local coordinate systems are
created. And then the revolution of jigs and their constituting parts is calculated and stored through
the transformation between the local coordinate systems and the auto-body coordinate system. Finally,
carlines are generated by projective transformation and marked automatically. In comparison to the
traditional method, it can greatly improve the efficiency of carline generation as well as ensure the
correctness of carlines. An automatic carline generation software module has been implemented and
applied in the design of auto-body welding lines.

Key words: auto-body welding line, computer aided design, carline, coordinate transformation