Step 4 Make a program by starting with zero time (origin O) and moving through the various stages of completion (points) till the point marked 'finish is reached. Choose path consisting only of horizontal, vertical and 45 lines. A horizontal line represents work on job I while job 2 remains idle, a vertical line represents work on job 2 while job 1 remains idle and a 45 line to the base represents simultaneous work on both the jobs. Step 5 Find the optimal path (program). An optimal path is one that minimizes idle time on job I as well as job 2. Obviously, the optimal path is one which coincides with 45 line to the maximum extent. Further, both jobs cannot be processed simultaneously on one machine. Graphically. this means that diagonal movement through the blocked out areas is not allowed. A good path, accordingly, is chosen by eye and drawn on the graph (path OUVWXYZ). Step 6 Find the elapsed time. It is obtained by adding the idle time for either job to the processing time for that job. The idle time for the chosen path is found to be 4 + 6 = 10 hours for job 1 and 4 hours for job 2 . Total elapsed time = 34 + 10 = 44 hrs. (considering job 1) = 40 + 4 = 44 hrs. (considering job 2). Step 7 The optimal schedule corresponding to the chosen path is shown in Fig. 5.5. B E Job D 6 10 18 22 28 40 f52 B A D E Job 2 10 18 24 28 40 44 5 10 20 30 35 40 44 1 15 25 Time (hrs.) Fig. 5.5 The optimal schedule on various machines for jobs 1 and 2 as evident from Fig. 5.5 is Machine A : job 1 precedes job 2, machne B job 2 precedes job 1. machine C job 2 precedes job 1 machine D job 2 precedes job 1, and machine E job 2 precedes job 1. EXAMPLE 5.6-3 Two major parts P, and P2 for a product require processing through six machine centres. The technological sequence of the parts on six machines and manufacturing times on each machine are Machine sequence: FDB Part P, Time (hrs.): 2 4 5 6 1 Machine sequence: B A E F C D Part P, Time (hrs.): 2 5 3 2 3