|
||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
| UNIT F. PROCESS ORGANIZATION AND PRODUCTION PLANNING |
| COMPETENCY: 013.00 : Evaluate and improve a manufacturing system. |
| OBJECTIVE: 013.01 : Develop a production schedule. |
|
by Dr. Bill DeLuca |
|
In the previous step, time and motion studies were used to determine the time and labor required to perform each operation. Now this information will be used to determine the number of work cells that will be needed, the number of employees required to produce the product, and the cycle time or time required to produce each product. Time and labor variables are the basis of production line balance. These variables are interrelated and the way they are optimized will determine the overall cost of producing the product. If one person is fabricating a part, each process must be done in sequence.
Example 1: Cycle time for One Employee in One Cell
In Example 1, one worker doing three operations in sequence can produce a product in 66 seconds. The cycle time is the sum of the time it takes to perform each operation. Typically, cycle time is reduced by increasing employees so operations can be done simultaneously.
Example 2: Cycle Time for Three Employees in Three Cells
By adding 2 employees, the cycle time was reduced by 30 seconds. All of the operations are done simultaneously so the cycle time is the time it takes to perform the longest operation. However, the system is not efficient. There is a great deal of slack time or time when a worker has nothing to do. In the example above, employees performing operation P1 and P2 have 15 and 25 seconds of slack time, respectively. To balance the line, one employee can be used to perform both P1 and P2.
Example 3: Cycle Time for Two Employees in Two Cells
The cycle time remains the same but only two employees are needed to produce the product. Since slack time is reduced, parts will flow better through the line. Example 2 and 3 have a cycle time equal to the longest operation. Cycle time can be reduced further by dividing workstations so more than one cell is used to perform an operation. Dividing P3 into two cells reduces the duration by one half. Cycle time is now 20 seconds, the time to perform the longest operation P1.
Cycle Time = 20 Seconds, Number of Employees = 4 Work CellsAs these examples show, balancing a production line involves setting-up work cells to minimize cycle time and slack time. A work cell is an area where employee(s) perform one operation or several operations in sequence. When balancing a line, operations are done in sequence if the same workstation or employee is assigned to the task. If both are different, operations are scheduled simultaneously.Review the examples above. The cell is numbered in the column following the workstation. Examples 1, 2, 3 and 4 contain 1, 3, 2 and 4 cells, respectively. Example 1 contains one work cell because all of the operations are done in sequence by one employee. Examples 2 and 4 have a cell for each process. All of the operations are done simultaneously. One employee is used to do two operations in Example 3 so this design contains 2 cells. Work Cell Utilization
The choice depends on how it affects labor cost and capacity. Keep in mind, labor cost is not always associated with the number of employees. If you remove an employee from the system, increased cycle time may cause an increase in labor cost. To determine the best away to go, use math to model different scenarios. Look at labor cost and plant capacity, make comparisons, then decide. Labor CostWith the number of employees and cycle time known, labor cost can be calculated. Labor cost is equal to:Labor Cost = Wage x Cycle Time x Number of Employees To calculate Labor Cost, Wage and Cycle Time must be in the same time unit. Wage, which is usually in hour units, can be converted to wage per minute by dividing the hourly wage by 60. To convert to seconds, divide hourly wage by 3600. In the examples above, cycle time is in seconds. If employees are paid $15.00 per hour, they make 25 cents per minute or .416 cents per second. Labor Cost per Minute = $15.00 / 60 = $0.25 Labor Cost per Second = $15.00 / 3600 = $0.00414 The calculated labor costs for the examples above are:
Give it a try! Enter data in the program below. Click the "=" button to calculate labor cost. Try different scenarios to see how labor cost can be reduced. Just a Matter of Time...Or, is it?Give these calculations, what's so great about mass production? It cost less for one person to produce the product. The key to profit is to match market demand with plant capacity. Plant capacity is the number of products that can be produced in a give time period. If there are seven working hours in a day, one employee with a cycle time of 66 seconds could produce 382 products. Two employees with a cycle time of 36 seconds could produce 700 products. Four employees with a cycle time of 20 seconds could produce 1260 products per day. The potential profit from a day's work is much greater with four employees.Mass production requires a mass market. Market demand is the number of products you expect to sell in a specified time period. If market demand is not great enough to sell 700 or 1260 products per day then there is no advantage to increasing capacity. The extra profit would be sitting in a warehouse collecting dust. That is why the system must be designed to match capacity with market demand. Not all products are produced using a mass production system. Other production system commonly used are:
Line balance requires analysis and evaluation of related system variables. The process involves:
Using math to transform variable relations into values that provide useful information for decision making. Calculating labor cost based on cycle time and number of employees, comparing different scenarios, and choosing the method that will maximize profit is a process that relies on mathematics to aid decision making. 
When line balance is complete, you know: Copyright © 1996, 1999, 2000 by V. William DeLuca |
||||||||||||||||||||||||||||||||||||
|
|
