Learn how to analyze a value stream and its processes to identify waste, bottlenecks, and other causes of process issues.
- At this point, you've already created a value stream map to help you visualize the end to end process. Now we put that map to work by analyzing the value stream. Remember, a value stream is the end to end process consisting of activities and resources, including information, used to transform inputs into outputs that are saleable to customers. A value stream map is a diagram that shows all the steps involved in getting a product or service from supplier to customer.
It shows the material and information flows from order to delivery. Your value stream map and DDL process maps were created earlier during the measure phase. So how do you analyze them? When analyzing a value stream map, here are some key points to consider. Is throughput keeping pace with Takt rate, or customer demand rate? Are there glaring wait times and high WIP between major process steps? Is workload balanced? Does every process or major process step in the value stream add value? Look at each major process box and evaluate its process metrics, such as long process times, low yields, or high defect rate and rework rates.
Examine the summary timeline and totals for the value stream. Is there a huge difference between total lead time and total processing time? What is the rolled throughput yield, or RTY of the value stream? Let me explain rolled throughput yield. We'll use the example of golf. Folks who play golf like to hit par or better. As you may know, par is the number of shots a very good player will take to complete the hole.
There are 18 holes in a golf course. What is the likelihood of hitting par for each hole? Let's just say you have a 95% probability of hitting par for each hole. So your yield is 95%, or 0.95. That's very good. But, is it good enough? And is it good enough for the whole game? What do you think is the probability of hitting par for all 18 holes? It is 0.95 times 0.95 times 0.95 and so on.
Do that 18 times, and you get 0.3972, or about 40%. So the rolled throughput yield is only 0.40, or 40%. Most processes have multiple steps or activities. In the golf example, there are 18 steps, 18 holes, and while the yield for each step is impressive at 95%, the overall end to end process yield is what really matters for winning the game.
It's your rolled throughput yield, or RTY, to which you must pay attention. For the golf example, it's only 40%. That will really make you rethink your golf game. In general, rolled throughput yield offers a more accurate picture of the end to end of process performance. Your RTY number is the likelihood of getting everything right, the first time, from start to finish. You'll determine the RTY for the value stream or end to end process in your analysis.
If the rolled throughput yield is not satisfactory, ask, which of these processes or major process steps have low yields? This will enable your team to identify which processes need to be decomposed into detailed process maps for a more granular view so that you can perform a more detailed analysis of that particular process. In summary, analyze the value stream map first. Based on that analysis, then do a selective deep dive analysis into just the poorly performing processes by examining their detailed process maps.
- How Lean Six Sigma integrates lean into DMAIC
- Understanding the purpose and steps of the Analyze, Control, and Improve phases
- Using analysis tools
- Hypothesis testing
- Data collection planning
- Improving processes with FMEA, Just in Time, and Kaizen methodologies
- Planning and implementing process controls