Lead time reduction is something all manufacturers wish to achieve. By identifying work-in-process (WIP), value stream mapping helps to pin-point which processes in a production sequence drive overall lead time. Finding ways to reduce work-in-process (WIP) helps to reduce lead time.

When creating a value stream map the first thing to do is to list the step-by-step process of how things can be achieved in the least possible time while reaching good outcomes. Being successful early on leads to gaining momentum. Continuous refining of processes is required to achieve these results.

Lead time can be determined in a few ways. The first way to determine lead time is by reviewing the historical information captured by routers attached to materials. In the absence of routers, you can also reference your ERP’s (enterprise resource planning system’s) historical material data.

Another way to calculate lead time is by utilizing Little’s Law. While collecting data for your value stream map, be sure to count inventory at each location. Once done, simply divide all work-in-process by the daily demand. The result is lead time days. For example, let’s say you have 500 units of WIP between two sequential processes and your daily demand is 100 units. In this case, lead time would be 5 days (5 Days = 500 Units WIP / 100 Daily Demand).

It’s important to not mix these methods. Use either one or the other. It doesn’t really matter how lead times are determined since the kaizen events that follow will be aimed at reducing lead time.

Your kaizen team should consider all WIP as the waste it actually is. That said, WIP should not be indiscriminately eliminated across the board. The goal is to only have a minimum amount of WIP needed as determined by process cycle times. Thus, in some scenarios, some WIP may always be necessary. To calculate the correct amount of WIP, divide an operations total cycle time by customer takt time. This is Standard Work-in-Process (SWIP). For example. If the total cycle time of a process is 75 minutes and customer takt time is 100 minutes. Then SWIP would be 1 unit (0.75 rounded up).

Some things have to be taken into consideration when reducing work-in-process. The time to change over equipment can take longer than a SMED (single-minute exchange of die). Maybe oversized equipment inhibits optimal layout or there’s a significant worker shortage driving up process time. Regardless, visual controls will need to be implemented to ensure that WIP never exceeds defined SWIP and is quickly and effortlessly identified when it does. Reoccurring violations are candidates for future kaizen events.

Value stream mapping is a lean tool that intends to document every step in the process. This is also the key to reducing lead time as each step of the procedure is refined and revisited to ensure that it leads to process improvement and efficiency. Continuous kaizen will help alleviate the wastes in the process and help balance supply and demand.

Falcon helps manufactures overcome their inventory challenges. Contact us to discover how.