How to perform data analysis using PQ Analysis, Process Matrix and Spaghetti Charts
Some lean initiatives begin with going after implementing a lean objective throughout a facility, such as Total Productive Maintenance, Six Sigma, Set-up Reduction or 5S.
Another approach that is more strategic in nature, starts with data analysis where the following questions are asked, “What are the dominant products that are produced in the company and how similar are the processes used to create them? How well do they currently flow together within the facility?”
In order to best answer these questions, three lean tools from the Toyota Production System are used. The Product Quantity (PQ) Analysis, the Process Matrix and the Spaghetti Chart.
Map the current state of flow with the spaghetti chart
The Spaghetti Chart is created 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.
Understand which flows are dominating with the PQ Analysis
The objective of the Product Quantity Analysis is to be able to quickly see the highest to lowest demand for all products produced within a facility. This is accomplished by graphing 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 the volume exists in 20% of the products.
It is desirable to see if the top 80% of products can flow down the same production line in order to optimize the use of floor space, equipment, manpower, etc. In order to determine which products can flow down the same production line, the Process Matrix is used to determine product families.
Reveal the part families and how they flow with the Process Matrix
To create the Process Matrix, a simple excel spreadsheet is used. Each unique product is identified in the first column. Starting with the product that has the highest volume, as identified within the Product Quantity Analysis, each process step is then 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). This is done so that the charts serve as a complete data set that tell a full story of what is happening.
Each additional product is then added to the spreadsheet in the subsequent rows of the spreadsheet, again numbering from left to right. It is important not to go backwards in the rows with the numbering in order to go to a process that was utilized previously by another product in an earlier step (like is typically seen on the spaghetti chart). Instead, a new column is inserted and that same process step identifier is written at the top. The object 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.
Re-engineer processes for improved flow
The cross-functional team will then seek to identify in the process matrix where the process is not aligned, i.e., where process steps are occurring at different times for each product requiring duplicate processes. They should see if the process can be re-engineered to align the work to happen at the same time for each product. Where this is not possible, a duplicate workstation may be required. A product should never return back to the beginning of the production line in order to be worked when designing the line. It is very important for future cell design, that the work progress through the line with no reversals.
Once the matrix is fully re-engineered and complete, the team should review all of the products and notice the ones who have the most common steps. By definition, a product family should follow the 80/30 rule. The 80/30 rule applies when 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.
Use the collective data analysis to set the company’s lean strategy
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 their leadership team. Typical plans will be to 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).
Please go to the “Shop” page on this website and download the, “How to Perform Standard Work Analysis and Cell Design” training in order to see examples of this along with next steps to be taken to complete the analysis and begin cell design.
Published on: Jun 13, 2017 @ 18:13