Some times the hardiest thing is to find your process constraint. Remember, a constraint is any resource with less throughput than the demand placed on it. They regulate the output of your whole process. First, you need to understand “demand”. Demand is not what the supervisor wants, although many times it feels like it if the supervisor does not understand constraint management. Demand is the rate at which you need to run the process to meet customer needs or demands. If you are not making it for a customer then it is not a demand you really need to meet.

Where do we look for possible candidates as possible constraints? We go walk the process and look for:

• Areas where a lot of WIP (Work in Process) or material is waiting for processing. This is one of the Seven Types of Wastes.
• Areas that work a lot of overtime. This is not just paid overtime but also unpaid. If your company is good, employees many times will work extra hours just to make things happen sooner, this counts as overtime also.

At those operations that you see the above happening review the following:

• Spaghetti Charts (Physical Process Flow Chart) of these operations. Is there a lot of movement?
• Line balance at these operations. Is the product balance uneven?
• Constraint Capacity. Is capacity below the demand?
• The demand on the operation. Are the demands real?

If the answer to any of these four questions is yes this step is a possible constraint.

To validate these steps as a constraint we need to use TAKT time to understand the constraint need. TAKT time is the time which should be taken to produce a product based on customer demand. With that said if every step or operation of a process is working at or above that rate then the whole process is meeting the customer demand. It only takes one step of the process to be below that TAKT time to make the whole process fail to meet the demand placed upon it. Once we have the TAKT time, we can compare it to the actual throughput and validate the step as a constraint or not. TAKT time is the total net operating time per shift or day, divided by the total customer(s) requirements needed per shift or day. Net operating time is the total time minus breaks and lunch (if things are not running during that time). For example lets say your customer demands are 1000 (parts, transactions, assemblies) per shift and a shift is 8 hours or 480 minutes. Now lets say that we have two 20 minute breaks during the shift and no lunch breaks (employees do take lunch but the operation is still running). That means our net operating time is 440 minutes (480- 20- 20= 440). So TAKT time is 440/1000 = .44 minutes or (.44min * 60 seconds) 26.4 seconds per item. That means that in this process every step has to complete their tasks in 26.4 seconds.

Once you have the TAKT time for each of the process step that you had identified above then you can list all those steps by TAKT time and actual time. Those that exceed the TAKT time are constraints; those that do not exceed the TAKT time are not constraints.

Well there you have how to identify a constraint in your processes. Next week I will address exploiting the constraint the second of five steps in constraint management. As always if, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.

Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

Tags: Constraint Idenitfication, Constraint Management, Method, Six Sigma Process

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