Line balancing and plant capacity

Sequencing Jobs through two work centers:

• Johnson’s rule : is a technique that mangers can use to minimize the make span for a group of jobs to be processed on two machines or at two successive work centers.

• It also minimizes the total idle time at the work centers.

• For the technique to work several conditions must be satisfied:

• 1.Job time must be known and constant for each job at each work center.

• Jobtime must be independent of the job sequence.

• All jobs must follow the same two step work sequence.

• Job priorities cannot be used.

• All unit in a job must be completed at the first work center before the job moves on to the second work center.

• Determination of optimum sequence involves the following steps

• List the jobs and their times at each work center.

• Select the job with the shortest time.if the shortest time is at the first work center schedule that job first, if the time is at the second work center schedule the job last.

• Eliminate the job and its time from further consideration.

• Repeat steps 2 and 3 working toward the center of the sequence and all the jobs have been scheduled.

• When significant idle time at the work center occurs job splitting at the first work center just prior to the occurrence of idle time may alleviate some of it and shorten throughput time.

Plant Capacity:

• Capacity can be defined as products or productive resources per a particular unit of measure.

• Capacity can be defined as a measure of the ability to produce or serve that is having enough worker or equipment time to do the job.

• Capacity utilization is a measure that should indicate to what degree he potential capacity is used.

• Utilisation =Number of direct productive hours per

• day

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• Total number of scheduled hours per day