The Other Approach to Lean

Product Quantity Analysis, the Process Matrix and the Spaghetti Chart

Product Quantity Analysis, the Process Matrix
and the Spaghetti Chart

Total Productive Maintenance, Six Sigma, Set-up Reduction or 5S methods may be used either separately or together to help a facility’s team define the best path to a lean goal. But let’s take a step back. What is the other approach to lean?

It starts with data analysis and ends with strategic planning. In this approach, we ask, “What are the dominant products that are produced in the company? How similar are the processes used to create them?  How well do they currently flow together within the facility?”

To best answer these questions, we use three lean tools from the Toyota Production System: The Product Quantity (PQ) Analysis, the Process Matrix and the Spaghetti Chart.

3 lean tools from the Toyota Production System: The Product Quantity (PQ) Analysis, the Process Matrix and the Spaghetti Chart.

We create a Spaghetti Chart by taking an existing plant layout and drawing the path that a product takes as it moves through the facility. If each product is drawn with a different color, the spaghetti chart will not only reveal criss-crosses, repeat trips and reversals in flow, but it will also reveal how well the processes of different products are aligned.

A well-executed Product Quantity Analysis will help us quickly see the highest to lowest demand for all products produced within a facility. To do a PQA, we graph the total quantity of products over a timeframe (six months to a year) on the y1 axis of a chart, with the cumulative percentage of the total products on the y2 axis of the same chart.

This exercise typically reveals the 80/20 rule, where approximately 80% of production volume exists in 20% of the products.

To optimize floor space, equipment and manpower we need to find out if the top 80% of products can flow down the same production line. To do this we use a Process Matrix, which categorizes our product families.

To create the Process Matrix, we use an Excel spreadsheet. Each unique product is identified in the first column. Beginning with the product that has the highest volume (as identified within the Product Quantity Analysis) each process step is identified in each of the subsequent columns. Under each process step, a number is placed in the box indicating which step it occurs in the process. These numerical steps should match what is on the process routers (as well as on the spaghetti chart). Together, the Excel sheet and spaghetti chart serve as a complete data set that tell a full story of what is happening.

We add each product to the spreadsheet in subsequent rows from left to right. It is important not to go backwards in the rows with numbering to a process that was utilized by another product in an earlier step (such as typically seen on the spaghetti chart). Instead, a new column is inserted and that same process step identifier is written at the top. The goal is to ensure that every product flows from left to right in numerical order without any reversals.

Once this is complete for every unique product in the cell, it should be printed out large and reviewed with the team.

The cross-functional team will then review the process matrix and spreadsheet to pinpoint where the process is not aligned, i.e., where process steps are occurring at different times for each product requiring duplicate processes.  The goal is to see if the process can be re-engineered to align work at the same time for each product. Where this is not possible, a duplicate workstation may be required.

Work should progress through the line with no reversals. Once the matrix is fully re-engineered and complete, the team reviews all products and notices the ones that share common steps.

By definition, a product family should follow the 80/30 rule: 80% of the processes are common across all products in a product family and the work content total for each product does not vary more than 30% between the products in the product family. Every product that meets these requirements can be considered part of the same product family and should be produced in the same production line.

With this full set of data completed, the team will have a full understanding of where to focus their improvement efforts. A strategic plan can then be set by the team working closely with the leadership team. Typical plans will implement flow lines where feasible (line improvement), followed by kaizen events to address bottlenecks identified by inventory accumulation, long lead times or subsequent data analysis (point improvement).

As seen in:

Plant Engineering

About the Author

Nicole N. Snurkowski, Lead Consultant, Lean Sensei
Nicole Snurkowski is a lead consultant and associate with more than 25 years-experience in lean system management in the areas of aerospace development, manufacturing, operations and supply chain. Trained by the Shingijitsu Consulting firm in the Toyota Production System and in Porsche’s Line Back Logistics, she has led many transformations at UTC in three of their divisions; Pratt and Whitney, Sikorsky and United Technologies Aerospace Systems. She has achieved ACE practitioner certification and has taken clients to ACE Gold and Silver certification levels. Read More >

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