Four Significant Lean Metrics

Lean is a quality improvement model that improve processes by removing waste or non-value added activities. Lean achieves this by optimizing flow and thereby the resources . Flow represents the manner in which the work progresses through the system.

When there is a  good flow , the work progress through the system consistently and continuously.  Customers receives the delivery at the right time and at right quantity.

When the flow is bad, customer waiting time increases, stops due to bottlenecks absence of feedback loop between departments which means that upstream processes do not produce based on the demand of downstream processes, inventories are high.

It is important to visualize the flow , measure the right flow parameters in order to identify the weaknesses and optimize it.

Cycle Time ( CT )

Cycle time can be defined as the time taken complete a specific task in the value stream.

Start your stop watch when the task / process starts and stop the stopwatch when it ends. This time is called as cycle time. For example in a manufacturing process time taken to complete one unit in a particular workstation or in a service industry , time taken by a customer service executive to complete one call can be called as cycle time

When there is only one workstation for the complete assembly then cycle time is time taken to assemble one unit

In some cases the cycle time can be calculated by including the time that supports the process viz., loading and unloading time. Sometimes the cycle time is calculated by only accounting the touch time -i.e., time to work on the unit and leaving everything else.

Cycle time may include small stops , slow runs but does not include downtime , change over time or time taken due to any abnormal conditions

Cycle time can be calculated for one piece or in a batch production it can be calculated for one batch .

Cycle time per unit = process duration / total units produced in that duration.

For example in a workstation , 100 units were produced in 80 minutes , then Cycle time is 80/100 = 0.8 minutes  or 48 seconds per unit

Cycle time loss can be calculated by comparing the bench mark  cycle time (ideal cycle time ) with actual cycle time.

Cycle time loss = Process run time – ( Total units * Ideal Cycle time )

In continuation to the above example , If the ideal cycle time of the process is 0.5 minutes then cycle time loss = 80 – ( 100 * 0.5) = 30 minutes cycle time loss

Cycle time can be reduced by preventive maintenance measures , removing obstacles, training.

Change over time ( CO )

 The time taken for transition time between production runs . for example in manufacturing the change over time is the time between the last product rolls off the line in a given production run to when the start of the next run begins

Changeover time = the time elapsed from the last good part of the previous run, to the first good part of the following run

It includes clean up time , set up time and start up time.

For example in a hospital changeover time is the time between two surgeries. The changeover time includes cleaning up the operation theatre, resetting the equipment,

By reducing changeover time

Throughput time

While Cycle time is the time taken for a unit / piece to go through one process or operation , throughput time is the time taken for the unit to go through entire value stream. It can also be defined as the time taken between an order placed and order delivered . This is often called as call to cash time . In a manufacturing process the time taken from the first to last process. In a hospital it is the time taken between the patient entry to exit .

Throughput time includes the following

• Cycle time – the time the unit actually spent in  each process
• Inspection time – the time taken for assessing the quality of the product or service component
• Movement time – the time taken for the unit to move between processes
• Waiting or queue time – the time the unit waiting to be processed

Throughput time can be reduced by reducing process cycle time, by reducing movement time by improving layouts , by enabling single piece flow to reduce waiting time .

Takt Time

Takt is a Sanskrit word means rhythm  ( also Takt is a short form of German Word Taktzeit which means Baton). Takt time is calculated to know the demand rate of the customer upon which the production rate has to be synchronized . The rate at which we need to produce a product in order to satisfy customer demand .

Takt time can be calculated by calculating available work time over customer demand rate.

Worker’s break , scheduled maintenance and changeover are excluded when computing the available production time.

Takt time = Available work time / Customer Demand Rate

Assume the available working time is 10 hours per shift and a lunch break of 1 hour and tea break of 20 minutes. There is a mandatory briefing in the morning for 10 minutes . The scheduled work days are 6 per week.

The customer demand is 60000 units per week

Calculating Available Work time per day = 10 hrs – 1 hr – 20 minutes- 10 minutes = 510 minutes=30,600 seconds per day  

Calculating customer demand rate per day = 60000/ 6 = 10,000 units per day

Takt time = Available time ( 30,600 seconds per day) / 10,000 units per day = 3.06 seconds per unit.

If the cycle time and throughput time does not match with the Takt time , it leads to over production or under production. Over production leads to inventory and bottle necks which is a waste  and under production leads to late delivery.

In conclusion reduced cycle time will optimize the bottleneck process  and improve delivery per process, lower the difference between sum of cycle time of the processes and throughput time to eliminate non value added time and thereby improve responsiveness to customer or reduce the time to market, match the throughput time with Takt time to keep the inventory levels low.

https://www.dozuki.com/blog/how-to-reduce-changeover-time-standard-work-instructions

https://manufacturing-software-blog.mrpeasy.com/cycle-time