Flow Rate and Flow Time
Flow rate, flow unit, flow time, and inventory are crucial measures that can be taken to determine the efficiency of a production line. According to Little’s Law, changing the flow time can determine the flow rate if the inventory is held constant. In my previous work experience, I worked in the production department at a book publishing company. I could apply flow rate, time, and unit when managing the production line.
Flow Unit
A flow unit is a single product under inventory management. In my company’s case, a flow unit was an individual paperback book, awaiting final publication. The books produced were bound after feeding the manuscript into the digital printers. After that, the paperback books were packed in boxes and made ready for the distribution process. Therefore, a flow unit was a single paperback book that had undergone the process of printing, binding, and packaging.
Flow Rate
The flow rate refers to the rate at which each flow unit, paperback books, went through the production line. Flow rate is often expressed as units per time, considering the total units produced and the time taken. For example, my company would produce 8,000 paperback books daily. Given that the printing machines were running for a continuous duration of 8 hours per day, the flow rate could be calculated as:
- Total paperback books: 8000
- Machine Running Time: 8 hours
- Flow Rate: 8,000 ÷ 8 = 100 paperback books per hour
Flow Time
Flow time involves the total time for a flow unit, a paperback book, to move through the entire production line. The time measures the duration from the initial manuscript editing, typesetting, and printing to the packaging stage. Flow time is expressed as hours, days, months, and years depending on the reported metrics. For example, in my company, the flow time per minute can be calculated as follows:
- Flow Rate: 100 paperback books per hour
- Flow Time (In minutes); (1 ÷ 100) x 24 = 0.24 minutes
Inventory
Inventory refers to the stock of flow units and paperback books during a particular stage of the production process. The publication process at my company involved various stages, with the first one being manuscript editing and the last one being packaging. In a single day, we could publish an average of 8,000 paperback books, our inventory.