The Decision Sciences Journal of Innovative Education

Teaching Assembly Line Balancing: A Mini-demonstration with Duplos or “The Running of the Dogs”

Lynn A. Fish, Ph.D.

Canisius College

2001 Main Street

Buffalo, NY 14208

(716) 888 – 2642

Fax: (716) 888 – 3215

email: fishl@canisius.edu

Introduction and Innovation

Literature has shown that student responses to teaching concepts through experienced-based learning are very positive [Heineke et al., 1995; Brown et al., 1998]. The assembly line balancing mini-demonstration with “Duplos” presented here is a hands-on exercise that develops students’ understanding of operations management concepts and skills through assembly of six Duplo “dogs”. (Duplos are a larger version of Lego’s building blocks that can easily be seen from a distance.) Specific learning objectives of the exercise are to develop a student’s understanding of assembly line balancing quantitatively and qualitatively. Assembly line issues, such as bottleneck and unbalanced workstations, quality, task times, product assembly, and space allocation, are presented through this activity. Over 900 undergraduate and graduate students at an AACSB accredited college in the under-graduate and graduate programs, positively favor this demonstration as a learning mechanism.

Initial Instructor Preparation

Prior to using this demonstration for the first time, an instructor needs to acquire Duplo blocks by Lego (Lego PreSchool Building Set #1685) including 6 curved pieces ("heads"), 6 shorter curved pieces ("tails"), 30 square blocks (2x2 contact points), and 18 rectangular blocks (4x2 contact points). The 2004 costs for this set are $19.99. Note, an instructor may choose to utilize a different set of Duplos (and hence, a different set of products to be built); however, the exhibits that follow will address building this specific assembly product – Duplo “dogs”.

Classroom Instruction:

Prior to the mini-demonstration, classroom instruction should review facility layout terminology and quantitative analysis associated with an assembly line balancing. Specific terminology the instructor should discuss includes, but is not limited to, the following: what an assembly line is, its purpose, advantages and disadvantages to assembly lines, line balancing quantitative measures, the purpose of line balancing, task times, cycle time, idle time, efficiency, and balance delay. A basic review of these concepts can be found in Principles of Operations Management by Heizer and Render (2004) or another operations management textbook.

The Demonstration: Assembly Line Balancing - Assembling “Duplo” Dogs

To begin, a table is setup at the front of the classroom. The blocks are separated into three stations: Workstation #1: 18 rectangular duplos, Workstation #2: 30 square duplos, and workstation #3: 6 “heads” and 6 “tails”. One assembly worker is selected for each of the three workstations. The instructor demonstrates the assembly tasks at each assembly station to each worker as outlined in the “Dog Assembly” exhibit. Workers are instructed to perform their tasks as quickly as possible and are not allowed to correct another workers’ work or go back and modify their own. Three student timers, capable of timing in seconds, are selected from the class. Each timer is assigned a specific worker to time and instructed to time only the time the worker is “working”. The instructor states that the previously developed cycle time, based upon demand and operating time, has been set at 15 seconds. (Note the 15 seconds is based upon prior experience with the demonstration and is required to be more than expected. A pre-stated cycle time is used to solidify the fact that cycle time is a function of forecasted demand and operating time, and is independent of the actual task times. Originally, this was not pre-stated. One student was misled to believe that cycle time was a function of the actual task times, not the quantity that management wished to obtain from the line. Also, since individual workers have different assembly times, the time was set above any actual assembly time to avoid attempting to explain “negative idle time”. ) The class is instructed to watch the workers, where the inventory builds up, which worker is ahead of the others, and which worker appears to be behind. A signal is given to start the assembly and workers proceed to build the six units as described above. The class should observe that worker #1 is typically ahead of worker #2 and work builds up between the workers. Worker #2 struggles to keep up with the work, while worker #3 waits impatiently for the part. It should be noted that the specific worker positions that wait or are struggling will be dependent upon the individual skills, and may not correspond to this exact situation. That is, the bottleneck may actually be different dependent upon the individuals involved.

Following completion of the assemblies, the timers give the actual working time for each worker. The class then proceeds to calculate the idle time for each workstation (based upon 15 seconds at each workstation), line idle time, efficiency and balance delay. The Student Worksheet can assist the students with these calculations. Classroom discussion on the calculations and post-activity discussion as outlined below, ensues.

Post-Activity Discussion:

Following a discussion on the calculations, discussion topics and suggested questions that assist in concept development include the following. General concepts of

1) Quantitative Discussion: What are considered to be "good" efficiencies? How was the actual cycle time calculated? How does this relate to what we actually found? Where is the idle time? What if we had more assemblies – what would be the effect on idle time?

2) Bottleneck: Where is the bottleneck? Why aren’t the workstations the same? What impact would the assembly precedence have on this line? Is there a different task assignment that would balance this line better? What impact would this change have?

3) Product Assembly: Where do the task times when we are developing an assembly line come from? That is, how do we develop task times before the product is even developed? How does this relate to the cycle time? What can management do when they don’t equal?

4) Quality: What about quality? What happens if workers produce “junk” in this system? What if workers were allowed to inspect and rework their defects?

5) Task Times and Learning Curves: If we had different workers, what would the effects be on task times and idle time? What affects would there be if the workers performed 1000 or more assemblies on the task times?

6) Conveyor Impact: What if we had a conveyor moving materials between workers, instead of the “push” system? What would be visually the same and different?

7) Raw materials and space requirements: If this was a “real” line, where would components be stored? How close would workers be then? Traditional assembly lines have had large raw materials storage on the line. What impact does this have on the worker’s ability to communicate, on value-added space, and inventory?

Summarizing the Demonstration

The instructor should complete the demonstration by summarizing the quantitative and qualitative aspects of the demonstration. Specifically, the instructor should stating that the individual task times are based upon the product sequence (developed by engineering) and are independent of the cycle time, which is based upon the forecasted demand. The efficiency follows from the task assignment and cycle times, and due to precedence, may not be able to be improved. Also, the location of the bottleneck is a function of the tasks versus the cycle time as well as the individual’s dexterity. Task times are based upon the “average, normal worker” and may not be exactly what every line worker can accomplish. Workers will improve their individual task times over time and we call this the “learning curve”. A conveyor can mechanize the movement of materials between workers, is usually capital intensive to install, and can assist in regulating the workflow between workers. However, a conveyor does not allow workers to correct quality errors as we’ve shown here. By using a “red-line” stop system, improved quality can be gained on an assembly line. Also, it is difficult to motivate individual workers to improve their piece rate or quality on an assembly line. Typical assembly lines have huge stores of raw materials between them, taking up valuable space and inhibiting communication between workers.

Student Feedback

This robust demonstration has been utilized for 907 students (487 undergraduates and 420 graduates). As shown in Table 1, student feedback indicates that 95.6 % (867) favor continued use of this demonstration to assist in learning, 1.10 % (10) did not find it assisted their learning, and 3.31 % (30) are undecided.

Table 1. Do you favor continued use of the assembly line balancing demonstration to assist in learning?

	Yes		No		Undecided		Absent
	# students	%	# students	%	# students	%	# students
Undergraduates	468	96.1	5	1.03	14	2.87	2
Graduates	399	95.0	5	1.19	16	3.81	10
Total	867	95.6	10	1.10	30	3.31	12

REFERENCES

Brown, K. Hyer, N. L., Smith-Daniels, D., & Sprague, L. (1998) More cinematic ticklers for the OM classroom. Decision Line, 29(3), 15-17

Heineke, J. and Meile, L. (1995) Games and Exercises for Operations Management. Prentice Hall, NJ.

Heizer, J. and Render, B. (2004) Principles of Operations Management. 5^th ed. Pearson -Prentice Hall, Upper Saddle River, NJ.

Student Worksheet

Workstation #	Total Assembly Time (Seconds) (Column A)	# Assemblies	Workstation Time (per Assembly) (Column B)	Idle Time (Column C)
1		6
2		6
3		6
			Time to Complete One Assembly (Sum Column)	Idle Time

Method:

1) Obtain Total Assembly Time (seconds) from respective Workstation Timers. Insert in Column A.

2) Complete the calculations for the table:

Column B: Workstation Time (per Assembly) = Total Assembly Time / # Assemblies

Note: This demonstration discusses development of 6 “dogs”; hence, # assemblies equals 6.

Column C: Idle Time = Cycle Time (15 seconds) - Time per Assembly

Also,

Time to Complete One Assembly (Sum Column) = Sum of Workstation Times (per assembly)

Idle Time = Summation of Idle Time Column

= (# workstations * Cycle Time) / Total Time to Assemble One “Dog”

Note: Idle Time can be calculated by two different methods. Both are equivalent and a point of discussion.

3) Assembly Line Performance Measures: calculate the following

Efficiency = Sum of Workstation Times / (# Workstations * Cycle Time)

Balance Delay = 100% - Efficiency %

Exhibit: Dog Assembly

Terminology:

Rectangle (duplos) are “rectangles”, that is, they have 8 insertion points and viewed from above they look like:

Square (duplos) are “square”, that is, they have 4 insertion points and viewed from above they look like:

“Head” – one square duplo, with 4 insertion points, but with long sloping top edge and two insertion points at top.

“Tail” – one square duplo, with 4 insertion points, a short sloping top edge and no insertion points at the top.

Workstation #1:

Step 1. Takes one rectangle and insert over the width of one of the other rectangle, as shown in Figure 1a.

Figure 1 a: Assembly Station #1

Step 2: Insert the top rectangle over a second rectangle, by width, as shown in Figure 1.

Figure 1b: Assembly Station #1

Step 3: Pass the assembly on to Workstation #2.

Workstation #2:

Step 1: Inserts one square block at one of the ends of the "bridged" rectangle, as shown in Figure 2a.

Figure 2 a: Assembly Station #2

Step 2: Inserts one square block at the opposite end of the "bridged" rectangle, as shown in Figure 2b.

Figure 2b: Assembly Workstation #2

Step 3: Insert another square block over one half of one of the original squares, as shown in Figure 2c.

Figure 2c: Assembly Workstation #2

Step 4: Inserts another square block over one half of the other original square, as shown in Figure 2d. (Note: the blocks should form another "bridge" and be touching on the same level.)