Question

Kristin has decided to start a new business of baking and selling cookies to order and cater to the university students on campus when they study in the evenings and stay up till after midnight. She has named her business Cookie Cult. The following is the list of tasks she came up with for completing one cycle of cookie production. After a car arrives; inspector checks paper work and sets up machine Inspector collects payment for the service Inspector checks emission data and prepares report Machines collects exhaust emission data Task Preceding Tasks Time (seconds) A - Receive order - 30 B - Clean equipment from previous run A 40 C - Program mixer A 15 D - Mixer produces the cookie mix B, C 60 E - Prepare baking tray for oven D 20 F - Program oven D 15 G - Oven bakes cookie E, F 50 H - Cool and box cookies G 30 I - Accept payment and deliver cookies H 20 On a typical evening (5 PM to 2AM), Cookie Cult expects to receive and fulfil 400 such orders. Kristin wants to set up an assembly-like system to meet this demand. Your job is to help her set up and balance the assembly line in order to facilitate a fast-paced production. Kristen’s employees may still perform manual work at various stages of the process but assume there are enough skilled employees on hand. a) Draw a precedence diagram of the tasks. (7 points) b) What is the workstation cycle time? (7 points) c) What is theoretical minimum number of workstations? (7 point) d) Balance the assembly line using the “shortest task time” as the primary rule.

Answer 1

Given:

Daily demand = 400 units per day = 400 units per 9 hour day = 400 units in (9*60*60) secs

a) Precedence Diagram:

b) Workstation Cycle Rate = (9*60*60) / 400 = 32400 / 400 = 81 secs

c) Minimum number of workstations= sum of total task times / cycle time

                             = (30+40+15+60+20+15+50+30+20) / 81 = 280/81 = 3.45 workstations = 4 workstations

Task Table

Task	Task time	Precedence
A	30	NA
B	40	A
C	15	A
D	60	B,C
E	20	D
F	15	D
G	50	E,F
H	30	G
I	20	H

                                                                                                                                       

The total station time is nothing but the cycle time. So, total station time of each station is 81 sec

In order of Shortest task time as well as task precedence, task order: A>C>B>D>F>E>G>H>I

Workstation 1:

                             First task = A

                             Time left= 81 – 30 = 51 sec

                             Second task = C

                             Time left= 51 - 15 = 36 sec          

                 

So, workstation 1: A->C

Workstation 2:

                             First task = B

                             Time left= 81 - 40 = 41 sec

So, workstation 2: B

Workstation 3:

                             First task = D

                             Time left= 81 - 60 = 21 sec

                             Second task = F

                             Time left= 21 - 15 = 6 sec            

So, workstation 3: D->F

Workstation 4:

                             First task = E

                             Time left= 81 - 20 = 61 sec

                             Second task = G

                             Time left= 61 - 50 = 11 sec          

So, workstation 4: E->G

Workstation 5:

                             First task = H

                             Time left= 81 - 30 = 51 sec

                             Second task = I

                             Time left= 51 - 20 = 31 sec          

So, workstation 5: H->I

Work Station	Tasks	Workstation Time	Idle Time
1	A->C	45 sec	36 sec
2	B	40 sec	41 sec
3	D->F	75 sec	6 sec
4	E->G	70 sec	11 sec
5	H->I	50 sec	31 sec

Were you able to assign all the tasks to the theoretical minimum of workstations: No

Efficiency =(sum of total task time/(cycle time * no of workstations)) * 100

               = (280/(81*5))*100 = 69.135%

**Do rate the solution. Thank You.