Assembly Lines. Worked out Problems:

Transcription

1 Assembly Lines Worked out Problems: Problem1. A product whose work content time = 50 min is to be assembled on a manual production line. The required production rate is 30unit/hr. From previous experience with similar products, it is estimated that the manning level will be Assume that the proportion uptime E = 1.0 and that the repositioning time = 0.Determine: (a) cycle time and (b) ideal minimum number of workers required on the line. Problem2. A manual assembly line has 15 workstations with one operator per station. Work content time to assemble the product =22min. The production rate of the line =35 units/hr. Assume that the production uptime E = 1.0 and the repositioning time =6sec. Determine the balance delay. Problem3.A small electrical appliance is to be produced on a single model assembly line. The work content of assembling the product has been reduced to the work elements listed in table 1. The table also lists the standard time that have been established for each element as well as the precedence order in which they must be performed. The line is to be balanced for an annual demand of 100,000 units / yr. The line will operate 50 wk /yr, 5shifts /wk, and 7.5 hr /shift. Manning level will be one worker per station. Previous experience suggests that the uptime efficiency for the line will be 96%, and repositioning time lost per cycle will be 0.08 min. Determine: (a) total work content time, (b) required hourly production rate R P to achieve the annual demand, (c) cycle time, (d) theoretical minimum number of workers required on the line, and (e) service time to which the line must be balanced.

2 Problem4. Solve problem 3 using largest candidate method. Problem5. Solve the problem 3 using kilbridge and Wester method. 6. A manual assembly line must be designed for a product with annual demand = 100,000 units. The line will operate 5owk/yr, 5shift/wk and 7.5 hr/shift. Work units will be attached to a continuously moving conveyor. Work content time = 42.0 min. Assume line efficiency E= 0.97, balancing efficiency = 0.96 and repositioning time = 6 sec. Determine: (a) hourly production rate to meet demand and (b) number of workers required. 7. A single model assembly line is being planned to produce a consumer appliances at the rate of 200,000units/yr. The will be operated 8hr/shift, 2 shift/days, 50 wk/yr. Work constant time =35.0 min. For planning purposes, it is anticipated that the proportion uptime on the line will be 95% Determine (a) average hourly production rate,(b) cycle time and (c) theoretical minimum number of workers required on the line.(d) if balance efficiency is 0.93 and the repositioning time = 6 sec, how many workers will be required? 8. An overhead continuous conveyor is used to carry dishwater base parts along a manual assembly line.the spacing between appliance=2.2 m, and the speed of the conveyor=1m/min. The length of each workstation is 3.5 m. there are a total of 25 stations and 30 workers on the line. Determine (a) elapsed time a dishwater base part spends on the line (b) feed rate, and (c) tolerance time. 9. The table below defines the precedence relationships and element time for a new mode toy. (a) Construct the precedence diagram for this job. (b) If the ideal cycle time = 1.1 min, repositioning time =0.1 min, and uptime proportion is assumed to be 1.0, what is the theoretical minimum number of workstations required to minimize the balance delay under the assumption that there will be

3 one worker per station? (c) Use the largest candidate rule to assign work element to stations. (d) Compute the balance delay for your solution. 10. Solve Problem 4 using the Kilbridge and Westor method inpart Suggested Brief Answers: Ans 1 Given data Work content time = 50 min, Production rate = 30 units /hr Manning level H = 1.25, Proportion uptime E = 1.0 Repositioning time =0 (a) Cycle time = = (60 1)/30 = 2 min (b) Ideal minimum number of workers required. Ans 2 W * = Minimum integer = = 25 Given data Number of workstations n =15, work content time = 22 min Production uptime E =1.0, repositioning time =6sec Production rate = 35 units/hr The cycle time is given by = = (60 1)/35 = 1.7 min

4 And = - = = 1.6 min Balance delay is given by d = = ( )/ (15 1.6) =.083 Ans 3 (a) The total work content time is the sum of the work element time in Table 1 = 4.0 min (b) Given the annual demand, the hourly production rate is = 100,000 / ( ) = units/hr (c) The corresponding cycle time T C with an uptime efficiency of 96% is = 60(0.96)/ = 1.08 min (d) The theoretical minimum number of workers W * = Minimum Integer = = 4 workers (e) The available service time against which the line must be balance is T S = =1.00 min

5 Ans 4The work elements are arranged in descending order according to their values given in table. Work elements are arranged in descending order in table 2, and the algorithm is carried out as presented in table 3. Five workers and stations are required in the solution. Balance efficiency is compound as:

6 Fig2 Solution for given problems which indicate (a) assignment of elements according to the largest candidate rule and (b) physical sequence of station with assigned work elements. = 4/ (5 1.0) = 0.80 Balance delay d= The line balancing problem presented in fig 2. Ans 5

7 In the Kilbridge and Wester method, work elements in the precedence diagram are arranged in to column as shown in fig 3. The element can then be organized in to a list according their column, with the element in the first column listed first. We have developed such a list of elements for our problem in table 4. If a given element can be located in more than one column, then list all of columns for that element, as we have done in the case of element 5.In our list, we have added the feature that elements in a given column are presented in the order of value; that is we have applied the largest candidate rule within each column. This is helpful when assigning elements to stations, because it ensure that larger elements are selected first, thus increasing our chance of making the sum of in each station closer to the allowable limit. Once the list is established, the same three step procedure is used as before.

8 The work elements are arranged in order of column in Table 4. The Kilbridge and Wester solutions are presented in Table 5. Five workers are again required, and the balance efficiency is once more = Note that although the balance efficiency is the same as in the largest candidate rule, the allocation of work elements to stations is different. Ans 6 a= 53unit/hr, b= 46 Ans 7 a= 250units/hr, b=0.228min, c=153, d=294 Ans 8 a= 87.5min, b=.45/min, c=3.5min Ans 9 (b) = 4, (d)= The above mentioned problems are referred from the below text books. I am thankful for the authors. REFERENCES 1. Automation, Production System, and Computer Integrated Manufacturing, by Mikell P. Groover. 2. Systems Approach to Computer-Integrated Design and Manufacturing, by Nanua Singh.