Using the Johnson’s rule, identify the optimal sequencing of these jobs. The jobs must go through the machines in the same order starting with the sanding machine.

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Using the Johnson’s rule, identify the optimal sequencing of these jobs. The jobs must go through the machines in the same order starting with the sanding machine.

Johnson’s rule: identify the optimal sequencing of these jobs

CASE 4: SHORT-TERM SCHEDULING
Stan’s Furniture Refinishers has 7 items of furniture to sand first and then varnish using the sending and varnishing machines, respectively. The items and their times on these two machines are shown in the table:

Item                       Sanding time, hrs.              Varnishing time, hrs.
A                                             8                                              7
B                                             6                                              4
C                                             5                                              8
D                                             8                                              12
E                                             10                                           14
F                                             12                                           8
G                                             4                                              6

Questions.
Using the Johnson’s rule, identify the optimal sequencing of these jobs. The jobs must go through the machines in the same order starting with the sanding machine.

 

Identify the cumulative flow time for the initial sequencing and for the sequencing based on the Johnson’s rule. Provide the existing sequence chart and Johnson’s rule charts.

 

Compare and explain your results.

 

More details;

 1.    What is Johnson’s Rule
Johnson’s Rule is a technique that can be used to minimise the completion time for                   a   group of jobs that are to be processed on two machines or at two successive work                   centres.

 

2.    Objectives of Rule
         The Objectives of the Johnson’s Rule are:

To minimise the processing time for sequencing a group of jobs through two work centres.
Minimise the total idle times on the machines.
To minimise the flow time from the beginning of the first job until the finish of the last job.

 

3.    Conditions for the Rule
In order for the technique to be used, several conditions must be satisfied:

Job time(including setup and processing) must be known and constant for each job at each work centre.
Job times must be independent of the job sequence.
All jobs must follow the same two-setup work sequence.
Job priorities cannot be used.