MGT 240 Module 2 Labor Content and Line Balancing Example

Forty-Five Seconds per Chair: Takt Time, Labor Content and Balancing an Office Chair Assembly Line

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Business Administration Program, Aspen University

MGT 240: Operations Management

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Month Day, Year

Forty-Five Seconds per Chair: Takt Time, Labor Content and Balancing an Office Chair Assembly Line

Ridgeline Seating, a composite manufacturer near Grand Rapids, Michigan, assembles task chairs for offices from purchased parts: bases, casters, gas cylinders, seat mechanisms, cushions, backs and arms. Its assembly line runs one eight-hour shift with 7.5 productive hours, or 27,000 seconds, and four workers. Orders from a large office furniture dealer will raise demand from 180 to 200 chairs a shift next quarter. The line currently produces about 186 chairs a shift. This paper calculates takt time, labor content and line balance and recommends how to meet the new demand.

Takt Time and Labor Content

Takt time is the pace demand requires: 27,000 seconds divided by 200 chairs equals 135 seconds per chair. Labor content is the total work to make one chair. Timed observations of each task over two weeks produced the averages in the table, totaling 440 seconds. The minimum number of workers is labor content divided by takt time, 440 divided by 135, or 3.26, so at least four workers are needed.

Task Times and the Current Line

Station 1 takes 145 seconds, station 2 takes 140, station 3 takes 105 and station 4 takes 50. The cycle time, set by the slowest station, is 145 seconds, so the line produces 27,000 divided by 145, about 186 chairs. Labor efficiency is labor content divided by workers times cycle time: 440 divided by 580, about 76%. Station 4 is idle most of each cycle.

How Work Should Be Specified

Spear and Bowen (1999) studied the Toyota Production System and found that its success rested on rules most observers missed. The first is that all work is highly specified as to content, sequence, timing and outcome, so that problems show immediately. Another is that improvements are made by the people doing the work, using a scientific method, under a teacher's guidance. At Ridgeline, tasks are learned by watching and vary between workers; the 80-second back attachment ranged from 65 to 95 seconds depending on who did it.

Workers Designing Standard Work

Adler (1993) described how the NUMMI plant, a joint venture of General Motors and Toyota, used detailed time-and-motion standards that workers themselves designed and improved. Rather than feeling controlled, many workers valued standards they had written, because the standards made the work fair and the improvements were theirs. Ridgeline's workers suggested three changes when asked: ordering bases with casters attached, using a jig to hold the back during attachment and switching to quick-connect arm fasteners. Together these cut labor content by 45 seconds, to 395.

Specialization and Variety

Staats and Gino (2012) studied workers in a Japanese bank's mortgage processing operation and found that specializing in the same task on a given day made workers faster, while variety across days improved productivity over time. For Ridgeline, workers will hold a station for a full day but rotate stations across the week, which also allows cover when someone is absent.

Two Options Compared

Option one adds a fifth worker and splits tasks into five stations: casters and cylinder, 75 seconds; mechanism and cushion, 130; back, 80; arms and inspection, 105; and boxing, 50. The cycle time is 130 seconds, producing about 207 chairs, but efficiency falls to 440 divided by 650, about 68%, and the added worker costs about $52,000 a year. Option two applies the method changes and rebalances four stations: casters, cylinder and mechanism, 130 seconds; cushion and back, 130; arms, inspection and boxing, 135. The cycle time is 135 seconds, exactly meeting takt and producing 200 chairs. Efficiency is 395 divided by 540, about 73%. The jig and fasteners cost about $9,000 once, and pre-attached casters add about $0.40 per chair, or roughly $20,000 a year.

Testing the Balance Against Variation

Task times are averages, and individual cycles vary. Observations showed that the cushion and back station ranged from about 120 to 145 seconds per chair. With all three stations designed at 130 to 135 seconds and no space between them, a slow cycle at one station holds up the others, and the line would fall below 200 chairs on many days. Variation at a station running near takt costs output, because a slow cycle cannot be made up when every station is fully loaded. Ridgeline will place room for one chair between stations, so a slow cycle can be absorbed by a fast one, and will track station times weekly. If the cushion and back station regularly exceeds takt, the supervisor will move inspection tagging to the third station's worker on busy days.

Quality and Physical Strain

Faster lines can raise errors and injuries. The back attachment, the longest task, requires holding the back in place while driving four bolts, which strains wrists; the jig removes the holding and should reduce both time and strain. The quick-connect arm fasteners eliminate cross-threaded bolts, the most common defect found at inspection. Inspection remains a separate task, and the inspector can stop the line if defects repeat, following Spear and Bowen's observation that Toyota's workers address problems as they appear.

Recommendation

Ridgeline should adopt option two. It meets demand with four workers, costs less than half of a fifth worker in the first year and raises efficiency. Because the line would run exactly at takt, the supervisor should cover short absences, and the company should plan a short overtime period when orders spike.

Conclusion

Ridgeline's line falls short because its slowest station takes 145 seconds against a takt time of 135. Adding a worker would solve the problem at high cost and low efficiency. Cutting labor content through changes the workers themselves proposed, as Spear and Bowen's and Adler's research suggests, balances four stations at takt and leaves the line easier to improve further.

References

Adler, P. S. (1993). Time-and-motion regained. Harvard Business Review, 71(1), 97-108.

Spear, S., & Bowen, H. K. (1999). Decoding the DNA of the Toyota Production System. Harvard Business Review, 77(5), 96-106.

Staats, B. R., & Gino, F. (2012). Specialization and variety in repetitive tasks: Evidence from a Japanese bank. Management Science, 58(6), 1141-1159. https://doi.org/10.1287/mnsc.1110.1482