The quality and time of the machining process are highly affected by process planning, which determines process parameters such as the operation sequence and machining method. However, process planning remains largely dependent on the skills of operators. Thus, currently, skill transfer is an urgent challenge because the number of skilled operators capable of process planning is decreasing rapidly. In our previous study, skills were identified from interviews by obtaining gaze data of skilled operators when examining mechanical drawings of two different shapes. However, the influence of factors such as workpiece material on process planning was not investigated and remains unresolved. Therefore, in this study, eye-tracking technology was adopted to detect the movement of the operator’s eyes and gather gaze data when understanding mechanical drawings with different workpiece materials. The gaze data were analyzed using a heat map to identify the areas where skilled operators focus on compared with unskilled operators. From the results of interviews with skilled operators based on the gaze data analysis, skills related to workpiece material could be appeared in detail and acquired regarding the operation sequence. The skills were generalized according to the mechanical properties of the workpiece material. The generalized skills were incorporated into a computer-aided process planning system developed in the previous study. Based on the identified skills incorporated, the operation sequence was allocated by referring to the workpiece material. Furthermore, machining experiments confirmed that the allocated operation sequence effectively improves the quality of the machining process.

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