Category Archives: Facility Decisions: Layouts

Predetermined Motion-Time Data

Predetermined Motion-Time Data

As with elemental standard-time data. predetermined motion-time data tables create a time standard for a job or task. There are. however, significant differences between the two approaches. Whereas the elemental standard-time data tables provide times for job-specific work elements. the predetermined motion-time data tables provide times for basic motions such as a “reach of a given length” or “the grasp of an object of a given weight.” These motions, in their most basic elements, can be defined in terms of therbligs, which were described earlier in this chapter. Because they are generic in nature. predetermined motiontime data can be applied to a wide range of manual tasks, By comparison, the elemental standard-time data tables are typically specific to a given company or industry,

Problems 3

Problems 

I. An assembly line makes two models of trucks a Buster and a Duster Busters take 12 minutes each and Dusters take 8 minutes each. The daily output requirement is 24 of each per day. Develop a balanced mixed-model sequence to satisfy demand .

2. The tasks and the order in which they must be performed according to their assembly requirements are shown in the following table. These are to be combined into workstations to create an assembly line. The assembly line operates 7 hours per day. The output requirement is 1,000 units per day

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a. What is the takt time?
b. Balance the line based on the I,000 unit forecast, stating which tasks would be done in each workstation.
c. For b above, what is the efficiency of your assembly line?
d. After production was started, Marketing realized that they underestimated demand and will need to increase output to 1,100 units. What action would you take? Be specific in quantitative terms, if appropriate?

3. An assembly line operates seven hours per day and produces 420 units per day. The following tasks are required with their respective performance times and preceding tasks?

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Compute the takt time and the theoretical minimum number of workstations. and prepare an initial line configuration. Determine the efficiency of your assembly line.

4. An initial solution has been given to the following process layout problem. Given the flows described and a transportation cost of 52.00 per unit per foot. compute the total cost for the layout. Each location is 100 feet long and 50 feet wide as shown on the figure below. Use the centers of departments for distances and compute using rectilinear distances.

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5. An assembly line will operate eight hours per day and produce 480 units per day. The task times and precedence relationships are summarized below. Prepare an initial assembly-line configuration using the longest-operating-time rule, and determine the efficiency of your layout.

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6. An assembly line is to be designed that will operate 7'1::. hours per day and supply a steady demand of 300 units per day. Following are the tasks and their task performance times.

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a. Draw the precedence diagram.
b. What is the takt time?
c. What is the theoretical minimum number of work station?
d?. Assign tasks to workstations. stating what your logic rule is ?
e. What is the efficiency of your line balance?
f Suppose demand increase by 10 percent. How would you react to this?

7. Given the following data on the task precedence relationships for an assembled product and assuming that the tasks cannot be split what is the theoretical minimum takt time?

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a. Determine the minimum number of stations needed to meet a takt time of 10 minutes according to the "largest number of following tasks" rule.
b. Compute the efficiency of the balances achieved.

8. Simon's Mattress Factory is planning to introduce a new line of "pillow-top" mattresses Current plans are to produce the mattresses on an assembly line. Mattresses will be built on individual platforms pulled by a chain in a track in the floor. This will allow workers to completely walk around the mattress. Tools will be suspended from the ceiling so that there will not be a problem with tangling cords or wrapping them around the platform. The assembly-line process starts with the basic spring foundation and builds the mattress as it progresses down the line. There are 12 operations required. and their times and process sequence are as follows:

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Tentative plans are to operate the line 7'1l hours per day. Demand for the mattre ses is expected to be 70 per day.
a. Draw the schematic diagram.
b. What is the takt time?
c. What is the theoretical minimum number of workstations?
d. Create a reasonably balanced assembly line.
e. Supposing the plan was to produce these in ajob shop layout, Discuss and crnpare the
characteristics, pros, cons. and so forth of a job shop versus assembly line for this matters production.

9. XYZ Manufacturing Company received a contract for 20.000 units of a product to be
delivered in equal weekly quantities over a six-month period. XYZ w orb _50 day per
year on a single-shift. 40-hour work week.

The table below states the tasks required and their precedence sequence and task
times in second .

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a. Develop an assembly line that meets the requirements.
b. State the takt time.
c. What is the efficiency of the line?
d. Supposing the vendor a liked you to increase output by 10 percent. State specifically how you would respond to this.

10. The following ta ks are to be performed on an assembly line:

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The workday is 7 hours long and the demand for completed product is 750 unit per day.
a. Find the takt time.
b. What is the theoretical number of workstations?
c. Draw the precedence diagram.
d. Balance the line using the longest-operating-time rule.
e. What is the efficiency of the line balanced as in d''
f Suppose that demand rose from 750 per day to 800 unit per day What would you do?
g. Suppose that demand rose from 750 per day to 1.000 units per day. What would you do?

Problem 2

Problem 2

The following tasks mu t be performed on an assembly line in the sequence and time specified .

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a. Draw the schematic diagram.
b. What is the theoretical minimum number of stations required to meet a fore cased , demand of 400 units per eight-hour day?
c. Use the longest-operating-time rule and balance the line in the minimum number of stations to produce 400 units per day.
d. Compute the efficiency of the line.
e. Does your solution generate any managerial concerns?

Solution:

a. Draw the schematic diagram.

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b. Theoretical minimum number of stations to meet D = 400 is

N, = _S = 245 seconds = -245 = 3.4 -> 4 tations
T (60 seconds x 480 minuteS) 72
400 units

c. Use the longest-operating-time rule and balance the line in the minimum number of stations to
produce 400 units per day.

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Solved Problems

Problem 1

(Room A), schedule advising (Room B), grade complaints (Room C), and student counseling (Room D). The office is 80 feet long and 20 feet wide. Each room is 20 feet by 20 feet. The present location of rooms is A, B, C, D; that is, a straight line. The contact summary shows the number of contacts that each advisory in a room has with other advisers in the other rooms. Assume that all advisers are equal in this value.

Contact summary: AB = 10, AC = 20,pD = 30,
BC = 15, BD = 10, CD = 20.

a: Evaluate this layout according to one of the methods presented in this chapter.

b. Improve the layout by exchanging functions within rooms. Show your amount of improvement using the same method as in a.

'Solution
a. Evaluate this layout according to one of the methods in the chapter.

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Using the material handling cost method shown in the toy company example (pages 327-330). we obtain the following costs, assuming $1 per contact between adjacent rooms and an additional $1 per contact for each room in between

AB = 10 x I = 10
AC = 20 x 2 = 40
AD = 30 x 3 = 90
BC = 15 x I = IS
BD = 10 x 2 = 20
CD = 20 x I = 20
Current cost = 195

b_ Improve the layout by exchanging functions within rooms. Show your amount of improvement using the same method as in a. A better layout would be either BCDA or ADCB.

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Internet Exercise

Internet Exercise

Using PLANT and LAYOUT as suggested key words search the Web to identify and describe in detail the plant layout for an individual company. As an alternative, go to the McGraw-Hill Operations Management homepage at http.z/www.mhhe.com/pom and take a plant tour of a company and describe the physical layout or the operation.