Welcome to Part 3 of a 5-part series on Lean Design. In Part 1 I made the case that the achievement of “flow” is a major goal in the design of a Perfect Value Stream, and in Part 2 I discussed different ways to measure flow and why this is important. In this lesson I’ll cover the step-by-step method for designing a value stream that can flow. Think of this lesson as “Lean Industrial Engineering”.
As I said in Lesson 1, if you are building a house, you don’t start cutting boards and nailing them together, and hope that through a “Kaizen” process you’ll get to your dream home. You need a set of drawings. Similarly you need to design your Value Streams, first on paper, and then implement and manage them in the physical world. The optimum design will be the outcome of a proven methodology, and not simply the result of being smart or applying random lean thinking.
Taiichi Ohno said “Without standardization there is no Kaizen”, so having a Value Stream design based on data and a repeatable methodology gives you a solid foundation for continuous improvement. The need for large Kaizen projects for your new design, however, will be small if the design was done correctly up-front. Too much large-scale Kaizen is an indicator of initial poor design.
The methodology described below (briefly) will not apply to every Value Stream. It is intended for Value Streams where the work is repeating, that includes a grouping of similar products or services, and where the variability in processes and work times from product to product is relatively low. The more you get outside of these boundaries, the more difficult it will be to flow the work (although not impossible). Here is the method:
STEP 1: DEFINE YOUR PRODUCTS
Create a list of the products (or services) to be included in this design. You will be defining a “family” of products/services that share the same processes (80%+) and share similar processing times (30%+). Going outside of these ranges is not impossible, but it will make it more difficult to balance the work flow from product to product. You may need to create “representative part numbers” for customized products or services: parts numbers that represent a final product for design purposes. Don’t forget about including service parts, if these are to be built in the same Value Stream.
STEP 2: SET THE VOLUMES
For each of the products on your list, establish a daily volume or demand. Fractions are OK. You will need to discuss this with Sales and Marketing, since the number you are looking for is not necessarily today’s volume. You want to plan for the future. The sum of the volumes will give you a measure of the total Value Stream designed daily capacity in units.
STEP 3: DOCUMENT THE PROCESSES
For each product, create a Process Flow Diagram (PFD), a simplified flow-chart that shows the required processes and how they are connected. Process names and connecting arrows are sufficient, so these diagrams are considerably simpler than a Value Stream Map. Products can share the same PFD if the processes and process relationships are exactly the same.
STEP 4: CREATE A PROCESS FLOW MATRIX
Summarize your Process Flow Diagrams into a single matrix, with products listed in the first column, volumes listed in the second column, and the required processes listed in the following columns, in order of the flow. If a product requires a process, put an “X” in that cell in your matrix. This document will give you a visual cue to the level of process commonality: 100% commonality would result in an “X” in every cell. Eliminate from the product family products that are not a good fit. Use a spreadsheet to do this work.
STEP 5: ADD PROCESS TIMES
Spoiler alert: this will be a time-consuming step if you don’t already have process-related times documented. For every product and process relationship, i.e. wherever you have an “X” in your Process Flow Matrix, replace the “X” with a process time, usually expressed in minutes. If you need to document process times, through published time standard or by doing time studies, this will take some time. Sorry, but this is required data.
STEP 6: ADD EFFECTIVE WORK MINUTES
Add a row at the bottom of your Process Flow Matrix to document the Effective Work Minutes for each process, the number of minutes per day that the process will actually be available. Deduct from the total time in the day the times when the Value Stream is not available, like lunch, cleanup, breaks, etc. The remaining time is the time when the process is available to do work.
STEP 7: PERFORM CALCULATIONS
Congratulations, you are now ready to perform some calculations! You need to calculate two things: the Takt Time for each process in your matrix, and the resources required to build the mix of products, again for each process.
Calculate Takt Time by dividing the Effective Work Minutes by the total volume for that process. Alert: if a product does not use a process, that product’s volume will not be included for that process. Takt Time is the “beat” of the process and is expressed as minutes per unit. It is the maximum speed of the line.
Next, calculate required resources per process by dividing the work time by the Takt Time. Calculate a weighted average work time if your times vary, using the volume of each product as the weighting factor. Remember that if you have different resource types in a single process, you’ll need to do the resource calculation separately for each, since the work content times could be different. For example, if you have both machines and people working in a process, you would need to have two resources calculations, one for each resource type.
STEP 8: CREATE A CONCEPTUAL LAYOUT
Now you are getting into the design of the flow. Now the real fun begins! There are a lot of decisions that will need to be made at this step, and here is a partial list of considerations:
- Should the work in a process be done sequentially, like an assembly line, or does it need to be done in parallel?
- If work is done at the same time, as with a main line and a feeder line, how should these processes be connected?
- Could Value Stream performance be improved with the addition of some buffers (In Process Kanbans)? If so, how many and where?
- How will demand be communicated to the line or Value Stream? Is there one place when an order can be dropped, or are there multiple points that need order information?
- Can workers move up and down the line easily? Have you avoided created barriers to movement?
- How will material be delivered to each location, without disturbing the work flow?
These are questions that can be discussed prior to the creation of a final CAD-based design (which you will need eventually). The conceptual layout is a block diagram that allows you to experiment easily with different layout options, and to resolve some of these basic flow questions. The CAD layout step will go much more smoothly if you do this first.
STEP 9: LINE BALANCING
If the work in a process is done sequentially, like an assembly line, and there is more than one workstation needed, then you will need to divide up the work content among the workstations that you calculated. This will need to be done product by product, since the work steps and work times can vary. The goal is to distribute the work content as evenly as possible across the available workstations, understanding that it will be difficult or impossible to balance the work perfectly. This is not a minor detail, and you need to spend time to get as close as possible to a “level load” from one workstation to another for each product.
There are many other details that you will need to address, just at the design stage. Simulation modeling, for example, is a very useful software tool that allows you to test your proposed design with changes in mix and volume, and take into consideration various types of variability. At a minimum a simulation model is an insurance policy to avoid surprises later on, and chances are excellent that you will end up with an improved design by testing it with simulation.
One of the final deliverables at the design stage will be a detailed, dimensionally correct, CAD-based layout. This is the drawing that your engineers and facilities people will use to create the physical design. Even office Value Streams may have a physical component, if your goal is to have groups of people working more closely together to achieve flow.
In Part 4 of this series I will be discussing the steps needed to bring your new design live, and some recommendations related to standard work for line leaders.