Optimizing Mail Sorting Efficiency: A Pull System Approach to Reduce Stress in the U.S. Postal Service

Introduction

In today’s fast-paced world, efficient mail sorting processes are crucial for the U.S. Postal Service to meet its customer demands and reduce stress among its employees. This essay explores the implementation of a pull system to address the stress caused by the stamp canceling machine outpacing the sorting clerks. By understanding the key parameters and calculations involved, we can determine the optimal number of tubs to circulate between the sorting clerks and the canceling machine.

The Problem

Currently, the sorting department processes stamped letters by machine-canceling them and loading them into tubs containing 425 letters each. Postal clerks then read and key in zip codes from these tubs into an automated sorting machine, with an average processing time per tub of “p” days. The rate at which tubs are processed is one tub every 450 seconds. The goal is to sort 95,000 letters during a 12-hour shift while considering a safety stock policy variable, “x,” of 0.20, and an average waiting time plus material handling time of 15 minutes per tub.

Solution Approach

To optimize the sorting process and reduce stress, a pull system is proposed. This system allows the sorting clerks to pull tubs from the canceling machine area when they are ready to process another batch of mail. The number of tubs that should circulate between the sorting clerks and the canceling machine is a critical factor in ensuring efficient sorting without overburdening the clerks.

Calculations: a) Average Processing Time per Tub (p): To calculate “p,” we need to find the processing rate per tub, which is the reciprocal of the time it takes to process one tub: Processing rate per tub = 1 / (450 seconds) Now, convert this rate to days: Processing rate per tub = 1 / (450 seconds * 1 day / 86,400 seconds) ≈ 0.00027778 days per tub (rounded to five decimal places).

b) Average Waiting Time per Tub (w): The average waiting time per tub, “w,” can be calculated using Little’s Law, which relates the number of tubs in the system (N), the processing rate (λ), and the average waiting time (w): N = λ * w Given that N should be equal to 0.20 times the processing rate, we can express N as 0.20 * λ: 0.20 * λ = λ * w Now, solve for “w”: w = 0.20 Therefore, the average waiting time per tub is 0.20 days.

c) Number of Tubs in Circulation: Now, using Little’s Law and the values we’ve calculated, we can determine the number of tubs that should circulate between the sorting clerks and the canceling machine: N = λ * w N = (1 / 450 seconds) * 0.20 N = 0.00222222 tubs Rounded to five decimal places, the number of tubs that should circulate between the sorting clerks and the canceling machine is approximately 0.00222 tubs.

Conclusion

Implementing a pull system with the calculated parameters can significantly reduce stress in the sorting department of the U.S. Postal Service. By maintaining an average waiting time of 0.20 days per tub and optimizing the number of tubs in circulation, the sorting process can efficiently handle 95,000 letters during a 12-hour shift. This approach not only enhances operational efficiency but also improves the well-being of postal clerks, ensuring a smoother and more stress-free working environment.