Lean Line Design Knowledge Gap - How to Spot It and How to Solve It

In my firm's Lean Manufacturing practice we see this issue over and over: poorly designed production lines that employ an entire department with continuous improvement projects under the banner of "Kaizen".

Do not get me wrong, Kaizen (Japanese for continuous improvement) is a great thing, especially when embraced as an integral part of the company's culture. We teach and encourage our clients to adopt Kaizen and to practice it, but no amount of Kaizen will overcome a bad production line design. It is better to design the line properly up-front. In other words, it is better to "Pre-Kaizen" the line.

We see lots of half-baked attempts at line design methodologies. The great majority fall flat on their face because they lack a scientific approach, while reserving the line design activity to the internal specialists, the selected few. That is nonsense. The design of a Lean Manufacturing line, like any other endeavor of an aspiring Lean Enterprise, must be carried out as a team activity. You do need the right training and a methodology to provide you with a roadmap.

The goal of this article is not to make you a line design professional. My goal is to show you the elements of a solid line design methodology, so you can decide if the line you work tirelessly to improve should be re-designed from scratch to get better results.

Let's review what is needed for a proper line design and give you a sense of what the methodology looks like. To design any manufacturing line you must answer the most basic of questions:

• What are you going to make? These are the products.
• How many do you want to be able to make? This is the designed volume.

Notice that the second question refers to a decision about capacity. Yes, we all talk about Customer Demand but you do not know what demand will actually be until the order comes in. You may, and should, do market research, review order history, and forecast until your heart is content, but in the end Design Volume is a strategy decision.

The answers to those two questions are documented in a spreadsheet with the following columns: Part Number, Part Description, and Designed Volume.

The next step in our Line Design roadmap will be to figure out how to make those products. For that, you need to go to the manufacturing floor and look for all the processes needed. A process is defined as a series of sequential tasks of like-work performed at constant volume. A simpler definition, however, is this: a process is work performed by a person, a machine or both. The goal of a process is to advance a product towards completion. Now you have a list of products and a list of processes. You must now document the relationship between the two.

A product is the result of applying work, the processes, to raw materials. Those processes follow a time sequence. To display the relationship of processes to make a product you will create what is called a "Process Flow Diagram" or PFD. You will need to document a PFD for each product in your product list. The good news is that many products will have the same or very similar PFDs. A PFD has a "fishbone" look to it, as it must display all the processes including side processes known as "feeders". Each PFD represents a linear equation that will become part of a mathematical model for the calculation of the necessary resources to support the designed capacity.

The PFDs alone offer an unwieldy view of the manufacturing floor. They must be organized to make more sense. For that, you need to create a "Process Flow Matrix". This is a table where the products are the rows of the matrix and the processes are the columns. You enter one product at a time in the matrix and enter an "X" in the cell that indicates that product requires that process. Once you finish with all the products you will have a tool to help you identify groupings of products that share the same, or very similar, process paths. This is what we call a "Product Family" in Lean line design. A product family will give you the first indication of what products can flow together in the same line with the least risk of major imbalances.

Once you finish the Process Flow Matrix and identify the Product Families, you will create a PFD that encompasses all the individual PFDs you created thus far. This is the "Multi-Product PFD" or "Mixed Model PFD" and will be a critical tool when you start working on your Layout.

The other critical element of data that the Process Flow Matrix offers is the "X". Each "X" indicates work that needs to be documented. That work, marked by a single "X", has an amount of time associated with it and gathering that time information is one of the major tasks you will undertake for your line design. My recommendation is to use a form called the "Standard Work Definition" (SWD). This form will allow you to document the work elements, the materials, the standard times by category, and the quality requirements of each detailed work step. From each SWD you will extract the standard manufacturing time per product per process (the "X"), and with this information you will create another version of the Process Flow Matrix called the "Standard Time Matrix". The Standard Time Matrix has each "X" replaced with a standard time. When processes have machine and labor times, you will have to divide the process column in two in order to enter both, machine and labor times. Thank you Excel!

In the Process Flow Matrix you now need to add a column to document the Designed Volume per product. With the volume per product in place, you will be able to calculate the volume per process, as indicated by the "X" in each cell. When you add the volumes vertically, you now have volumes per process and you are getting very close to being able to calculate Takt time per process.

One small detour is to determine which processes have Scrap, Rework, and Options. Whenever a process has any of these, volumes will be affected and you must include the adjustments in your calculations. You will have to develop three more versions of the Process Flow Matrix where you will replace each "X" with the Scrap, Rework, or Option Percentage. With those volume modifiers in place, you can sum vertically and calculate the true volume per process. For that, you need to add a row at the bottom of your spreadsheet to display them. Thanks again, Excel.

You are missing just one piece of data to calculate Takt: the number of work minutes per day. You can either have the total number for the day, or the work minutes per shift and the number of shifts. These numbers need to be realistic, and not simply a statement of company work policy. Determine the number of work minutes per shift that your plant has available to do actual work. You will start with the number of minutes in a shift, deduct lunch and breaks, deduct continuous improvement time, and any other deductions that are unique to your plant.

You can now perform the Takt time calculation. Takt time is a relationship of time and volume. It is calculated as the work minutes per process divided by the volume per process. Takt is a design feature and it defines the theoretical maximum production rate of the manufacturing line.

I must emphasize one more time that my goal in this article is not to make you a professional line designer, but to give you an understanding of the element you need to plan for in your line design. I am skimping on some of the details to make this article a reasonably easy read.

With Takt time under your belt, you must now focus on calculating the number of resources per process. The number of resources in a process are calculated by dividing the Standard Time in the process by the process Takt time. Since every process has as many Standard Times as products going through it, but the formula only allows for one Standard time, you will calculate a weighted average Standard Time for every process. The weighting factor is the product's volume. By dividing the Weighted Average Standard Time by Takt, you have the number of resources necessary to support the designed volume for the process. It is important to highlight that not all resources are created equal and the result of the formula must be interpreted properly. The result can run the gamut from number of people, to workstations, to number of machines, to inventory, to number of units of product inside a machine, and more.

Once you calculated the number of resources per process, get the Multi-Product PFD back on the table and annotate it with Takt time per process, Highest and Lowest Standard Times, Weighted Average Standard Time, and Number of Resources per process. With this tool, you are ready to start developing the Conceptual Layout. This is a block layout for which you should assume to have no constraints, or the "ideal layout".

With the Conceptual Layout finished, you can start working on a CAD layout for the actual building. I like working this phase interactively with the team and the CAD operator to get a clean layout in one shot.

As you can see, designing a line is not just a question of throwing Post-It Notes around on a piece of butcher paper, or moving machines in the hope that things will come out better. There is a proven methodology that can be applied. All it takes is your determination to design a solid line, using Lean line design methods, which will minimize but not eliminate the need for future Kaizen work.

One final note: quite a few important elements of the methodology like workstation design, balancing tools, operator training, and deployment plan are not discussed here. However this article was not intended to be a book on the Fundamentals of Flow Manufacturing, but a short treatise on the noticeable gap in line design knowledge among Lean practitioners.

Gerard Leone, MSIE, MBA, is the Lean Hospital practice leader with the Leonardo Group Americas. The Leonardo Group is based in Munich, Germany and Denver, CO in the USA.
Gerard is has been a consultant to manufacturing companies for almost 20 years and to hospitals for 8 years. You can reach him at gleone@leonardo-group.com or visit the Lean Hospital Group website at http://www.leanhospitalgroup.com or visit the Lean Factory website at http://www.leanfactorygroup.com