I got hesitatin’ stockings,
I got hesitatin’ shoes,
Oh Lord, I got those Hesitation blues!
Tell me, How long, do I have to wait?
Can I get you now?
Or, must I hesitate?
Hesitation Blues, by the Reverend Gary Davis, tells a story of the frustration associated with unrequited love or perhaps it’s from misaligned goals. The fellow in the song suffers an endless wait because the target of his affection has other priorities. He must wait
Waiting is one of the key types of waste. Waiting occurs when Work in Process (WIP) is not moving through the production process. Workstations and personnel are idle, waiting for work. You’re on station, your parts inventory is ready, your tools are primed for action, there’s just nothing to do. Therefore, you wait. If this is a five minute, once a month event, it’s not so bad. If it happens continually, it is extremely wasteful.
The minutes spent waiting add up to hours, the hours compound themselves into weeks, and soon the weeks are extending over multiple months of time spent in complete inactivity.
In the world of manufacturing waiting occurs within the assembly process because of an imbalance in the flow of materials through that process. Each station has a throughput capability. One manufacturing process my require 30 minutes to process a single unit while another requires ten minutes and yet another requires a full hour.
This disparity in processing time causes Work in Process (WIP) to stop moving forward, which in turn causes down line processes to wait on work. This is made worse in linear processes where each successive process depends on completion of the previous process.
The goal is to synchronize the production process to match customer demand. This, in turn, facilitates a steady, even production of product with no bottlenecks along the way. No one waits on product and no one is overwhelmed trying to keep up with demand for product.
The first step in this process is to establish the Takt time. This is taken from a German word, taktzeit. Taktzeit translates roughly to clock cycle or time cycle. In manufacturing the desire is to establish a steady, minimally fluctuating production pace. This is almost like the heartbeat or pulse rate of the production process.
Takt time is calculated by dividing available production time by demand. If your plant operates on eight-hour shifts and your demand per shift is 8 units, the resulting takt time is 1 hour. If your demand is rated at 16 units, your takt time is 30 minutes.
The takt time is used to tailor your production process, making resources available and capacity adjusted to match, as closely as possible, the established takt time.
An examination of your production processes will reveal the assorted throughput capabilities of each sub-process or workstation. Some of these will exceed the takt time requirement and other will fail to produce sufficient volume to keep up with demand.
If station A is through putting 100 units per hour and Station B is only able to handle 50 units per hour, there are two options. You can reduce resources available at Station A thus cutting the production to match Station B. Similarly, you can add resources to Station B bringing the throughput there up to that of Station A. Takt time tells you which of these two options is the most desirable.
By organizing your production processes into work cells you can make you overall production process more responsive to changes in customer demand. Work cells combine multiple assembly or processing steps into a single unit. Each unit is balanced in terms of takt time and through put. As demand fluctuates, cells are added or taken away to meet changing demand needs.
This facilitates a steady amount of work distributed evenly over the entire production process that minimizes backlogs, bottlenecks and downstream waiting.
If we pay a short visit to our hamburger stand, we can see ample evidence of this as well. The number of people flipping burgers, dropping fries and taking orders is widely variable between noon and 3:00 pm. The number of customers is also variable. At noon, you will see 20 customers waiting in five lines. There will be five cashier/order takers, three burger cooks and two fry cooks making sure the orders are processed quickly. Each customer is waiting no more than three minutes from the time they step into line to picking up their bag of goodies and heading for a table.
By 3:00pm, the scene has changed. Four customers wait in a single line, one cashier is taking orders and one person is in the back cooking burgers and making fries. But even though over all demand is reduced to 20% of the peak demand experienced at noon, the customer is provided with the same level of service as are the lunch patrons . . . fresh burgers and hot fries in about three minutes.
In conclusion, no one likes to wait on love, hamburgers or work in process.