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Apr 13, 2015

Value Stream Mapping - Common Mistakes

During many first time Value Stream Mapping exercises, we have noticed some common mistakes. Many times when the mistake is made, it is not recognized and the Value Stream Mapping tool is called into question. It's like trying to use excel as a word processor, it kind of works but you just don't quite get the results you were expecting. So here are some of our observations. 1. You start to follow the people doing the work. We all start out understanding that we are doing Value Stream Mapping on a product or service however at some point, the person doing the job leaves the product and does something else. Rather than staying with the product we start to follow the person. It may even seem like we should follow the person as the task they are doing is related to the product we are following. For example in a dentist's office, the product we will follow is the patient. The patient comes in, they register, they sit down and they wait. They get called into the office and the dentist performs the work, they leave. The nurse takes their folder and does some work to it, she then works on the computer to update the file and finally, she puts the file away. In this case we have stopped following the patient and we have started to observe the work being performed by the nurse. 2. Trying to do a final Value Stream Map without the product or service actually being performed. We all know that it is sometimes difficult when you are training people to do Value Stream Mapping to always 'see' the product move through the entire process. It is sometimes necessary to leave the client with homework to actually observe the process and fill in all the boxes. There are cases however where companies think that there is not enough time to get a complete Value Stream Map, the process is too long or won't be running for another month and they need to present to management a savings plan by the end of the week. They frequently think that they can go to their engineered standards and fill in the information boxes and then predict their savings. In this case the person has forgotten some of the basis of Lean. First without observing the inventory, they don't have a Value Stream Map, they have a Process Map. Second without observing how the time standards were arrived at, how will you determine waste opportunities. Third the person doing the work may have many distractions - for example it may take me an hour to change the brakes on a car but every time I start, I have to do 3 oil changes. We need to observe the work and more importantly what's happening to our product when the work isn't being done. Office Value Stream Mapping A close relative of point number 2 is doing Value Stream Mapping in the office. With so much information on the computer today, many companies have all the information on their processes and value streams on their computers. If you want to know how many people are in an area we can get it, how much inventory between processing steps and what the processing times are are all kept in real time. Layouts of the plant floor are kept and actual distances traveled can be calculated right from the drawing. For many companies it really is possible to put an entire Value Stream Map together in an office and for it to be technically correct. Although the Value Stream Map may be technically correct we are missing the opportunity to observe what is happening. For example a company knew from their standard that a pallet of material could be wrapped in 2 minutes and 30 seconds. They had to be forced out to the floor to actually observe the operation and to prove they were right that they went out there. What they observed was the pallet took closer to 25 minutes to complete because the operator had to answer 4 phone calls. They didn't realize that this was part of the job of the operator. If you don't observe, you will never figure out why your lead-time is so long. Much of what takes place in day-to-day operations is never recorded in any standard. Things like phone calls, interruptions, or reprioritization of work. 4. Double counting of time. It takes a while to understand what to put into an information box and what is a processing step. For example Changeovers. We know that they go into the information box because all the books say so. Sometimes however people still ask why that time doesn't get recorded on the lead time line. How about travel time? I have to travel for 15 minutes between processing steps so I should have a box on my Value Stream Map representing travel time. Should it be counted as processing time? What do we include in processing boxes? The key here is to separate the things that cause inventory to build up, from the actual work to complete the part or service. Long changeover times cause inventory to build up, long distances to travel cause inventory to build up. Therefore these items are causes to be eliminated. They are responsible for the inventory we see in the company. We will account for them in our lead time calculation when we count the inventory. Understand the causes of inventory build up versus the actual steps to completing a product or service for the customer. Shared Resources 5. Ignoring shared resources. In most companies there are resources that are shared. These resources are required to support more than one product family. They may be people, assembly lines, equipment, instruments etc. An example would be a laboratory receiving area. They receive the samples for many labs and distribute them. If we forget this during our Value Stream Mapping process we would get the wrong results. Let's choose a simple example. A receiving area receives samples for 2 labs. Each lab receives 80 samples a day. Therefore they receive 160 samples and over an 8 hour period must supply each lab, 10 samples each. Therefore, they need 20 samples an hour and this requires 2 people. During the Value Stream Mapping, we mistakenly only account for the one product families' work. We believe that they need to supply only 10 samples per hour and we only require one person for 8 hours. This is a simple example and we would probably catch it. However, lets say you have hundreds of products and many product families you may miss this error. Remember to identify the shared resources. If you don't you will incorrectly calculate important numbers like the Takt time and cycle times. 6. Mixing product families. Sometime when Value Stream Maps start to get really complex with many branching streams going in and out of the main Value Stream, it is because the people doing the Value Stream Mapping didn't do a good job of defining the product families before starting the Value Stream Mapping. This problem is generally aggravated by one or both problems identified earlier - either not identifying a shared resource or following a person and not the product. By not doing a good job with the product families we can get distracted and follow the wrong processing path. Let's say we are following a product family that only goes through a lathe machine and is then shipped. The lathe may also be used in a product family that goes to a welding and, then to an assembly area and onto a de-burring area etc. If we haven't properly identified the family we may start to follow the Value Stream Map through assembly and de-burring when we should have gone from the lathe straight to the shipping area. Make sure you know your product families before you start Value Stream Mapping. These are not the only mistakes you can make during your initial Value Stream Mapping sessions; however they are common to many companies when they start to learn about Value Stream Mapping. Avoiding these mistakes will help you to use the Enterprise Value Stream Mapping ® tool better. Like anything else the more you practice the better you will get. Chuck trained in statistical process control at the University of Tennessee and in the design of experiments at MIT. He is certified by the American Society for Quality as a Quality Manager. His diversified technical background leading Lean and other major improvement initiatives across a wide range of industries has provided him with the professional expertise necessary to direct others on how to implement Lean the 'right' way.