In a lean manufacturing environment, standardized work is a key element to success. By repeating a set method, the process is more organized and improvement opportunities become more apparent. The process should be centered around human motion; ensure the repeatable process is ergonomically correct. The four main elements of standardized work are takt time, line balancing, work sequence and standard in-process stock.
The first step is determining the takt time. Takt time is the time in which one part needs to be produced based on available time and customer requirements.
The formula would look something like this, time available per shift (in seconds) divided by the customer requirement per shift. If there are 25,000 production seconds available per shift (8 hours less lunch and breaks) and the customer requires 1000 parts each shift, the takt time would be 25 seconds. This means that a part needs to be produced every 25 seconds in order to keep up with customer demand without working any overtime (the ideal situation). Once takt time is determined, the work sequence and line balancing can be calculated.
Line balancing is the next step in standardized work. This will involve time studies of all the different jobs within the process. The concept is that all jobs within an area or line will require the same amount of time to complete (cycle time). The more detail in the time study, the easier it will be to balance work load between operators.
As an example, there are 5 workers on a production line. The cycle times for each operation are as follows; operator 1 – 20 seconds, operator 2 – 30 seconds, operator 3 – 25 seconds, operator 4 – 23 seconds and operator 5 – 27 seconds. Using the takt time of 25 seconds from our example above, the goal would be to have no job more than 25 seconds and have enough operators in this area so each one would have 25 seconds of work.
In this example, moving 5 seconds of work from operator 2 to 1, and 2 seconds of work from operator 5 to 4 would balance out the work load on this line. Of course, rarely do the times work out like this in real life, however the two basic concepts are to ensure no operator has a cycle time greater than the takt time and have every operation as close in cycle time as possible.
Now that the line balancing is complete, the work for each operator must follow a standard process. This process is known as the work sequence.
In order to achieve the best quality results every time, the process must be set up in such a way that each operator that performs the job does so in the same manner. The work sequence should contain as much detail as possible. Instruction as to which hand an operation should be performed with may be necessary based on the layout of the components that make up the finished product. By setting up the work sequence, it is easy to observe when something is being done out of order. Be very cautious of sharing a responsibility between operators. Ensure each part of an operation is assigned to only one operator. If one operator performs a process one time and then a different operator perfroms that same process the next time, you leave yourself wide open for a process to be missed.
Another consideration when setting up work sequence is ergonomics. The process should be set up so that the operator performs the function in the most ergonomically manner possible.
The last major step in standardized work is in-process stock. Keeping to the concept of just in time, the parts between operations should be minimal.
For a continuous process where parts move from one operation to the next, the target in-process stock should be one piece. Based on the cycle time, this may not be possible, but should be the target you are striving for. The actual number of parts between processes will depend upon the actual operations. The better the line balancing, the less parts that will be required between operations. The key here is to ensure that the bottleneck process (slowest process) always has a supply of parts to process. Any lost time here will be unrecoverable without overtime.
Standardized workshould improve safety through safe motions, help quality through repeatable proceses, increase efficiency through elimination of unnecssary steps and form a foundation for kaizen.