Question

A single model assembly line is being planned to produce a consumer appliance at the rate of 150,000 units/yr. The line will be operated 8 hr/shift, 2 shifts per day, 5 days/wk, 52 wk/yr. Work content time = 35.8 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 the balance efficiency is 0.93 and the repositioning time = 6 sec, how many workers will actually be required?
(e) Considering point (d), what is the assembly line labor efficiency?

Answer 1

(a) To determine the average hourly production rate, we need to calculate the total number of units produced per hour.

Total units produced per year: 150,000 units/yr

Total hours per year: 8 hr/shift × 2 shifts/day × 5 days/wk × 52 wk/yr = 8320 hr/yr

Average hourly production rate:
`\displaystyle\sf \frac{150,000 \, \text{units/yr}}{8320 \, \text{hr/yr}} \approx 18.03 \, \text{units/hr}`

Therefore, the average hourly production rate is approximately 18.03 units/hr.

(b) To calculate the cycle time, we need to convert the work content time to hours and divide it by the proportion uptime.

Work content time: 35.8 min =
`\displaystyle\sf \frac{35.8 \, \text{min}}{60 \, \text{min/hr}} \approx 0.597 \, \text{hr}`

Cycle time:
`\displaystyle\sf \frac{0.597 \, \text{hr}}{0.95} \approx 0.628 \, \text{hr}`

Therefore, the cycle time is approximately 0.628 hr.

(c) The theoretical minimum number of workers required on the line can be calculated by dividing the work content time by the cycle time.

Theoretical minimum number of workers:
`\displaystyle\sf \frac{0.597 \, \text{hr}}{0.628 \, \text{hr}} \approx 0.951 \, \text{workers}`

Since we can't have fractional workers, the theoretical minimum number of workers required on the line would be 1 worker.

(d) To calculate the actual number of workers required, we need to consider the balance efficiency and the repositioning time. We'll divide the work content time by the cycle time multiplied by the balance efficiency.

Actual number of workers required:
`\displaystyle\sf \left( \frac{0.597 \, \text{hr}}{0.628 \, \text{hr}} \right) * 0.93 \approx 0.883 \, \text{workers}`

Again, we can't have fractional workers, so the actual number of workers required would be 1 worker.

(e) The assembly line labor efficiency can be calculated by dividing the actual hourly production rate (taking into account the balance efficiency and repositioning time) by the average hourly production rate.

Actual hourly production rate:
`\displaystyle\sf 18.03 \, \text{units/hr} * 0.93 \approx 16.76 \, \text{units/hr}`

Assembly line labor efficiency:
`\displaystyle\sf \left( \frac{16.76 \, \text{units/hr}}{18.03 \, \text{units/hr}} \right) * 100\% \approx 92.89\%`

Therefore, the assembly line labor efficiency is approximately 92.89%.