Mixed Model Production(Heijunka)

Filed under: LeanSep 15th, 2009 | no responses

Mixed Model Flows (Mixed Model Production) are a somewhat common occurrence in Lean. They are parts of your Value Stream that produce multiple products…..not one product….within a given time period.  This is called “Heijunka” or Load Leveling in the Toyota Production System.

Lean implementation can be more straightforward in dedicated parts of your value stream – those places where only one product is made and where one-piece flow cells (1à) are appropriate.

But what if your value stream produces more than one product? What if it produces many products in any given month, or week? MMF is the solution you may have been looking for.

What is MMF? Simply stated: Mixed Model Flow is making value flow by taking out the waste in your value stream so that multiple products can be made in the same value stream each time period.

This is accomplished by making the MMF part perform AS IF it were a dedicated asset. Each product “flows” at the rate of customer demand, even though multiple products are made there.

HOW DO YOU DO THIS?

There are a series of steps.

First, you must understand what kind of business you’re in. The basic question here is are you in a MTS (Make To Stock) or a MTO (Make to Order) business? Make To Stock means you will have some sort of Finished Goods Inventory (FGI) at the end of your MMF. Make To Order means your product will dovetail directly into a “customer process” at the end of your MMF line.

Second, you need to spend time understanding (really understanding) your product families. A product family is a combination of products that share similar processes. In your MMF value stream there are most likely a number of products. For example, some Circuit Card Assembly operations have as many as 250-1500 different products. But this doesn’t mean they will have that many product families. Generally speaking, when you look closely at your products and the common processes they travel through, you’ll end up with a small set of product families….somewhere in the range of 7-12 is common.

Third, you start getting a bit more technical. You have to figure out what the Takt Time is for the product family. That’s right, the product family! What is the average rate of customer demand for the family of products? This TT becomes important in setting up and in staffing the MMF line.

Fourth, you will need to begin defining Value for each product family from the Customers’ perspective. What are their expectations? Where is the value being created in your current flow? Where is the non-value added cost being incurred (the waste)? Also included here is the work of creating a Current State Value Stream Map of your MMF. What does it look like? How does it work? What are the outcomes in terms of VAT (Value Added Time) and Lead Time?

Fifth, where in your MMF can you achieve 1-piece flow for each product family? This is where you can create CELLS in your MMF.

Sixth, where you can’t flow, where will you install pull systems? Basically this means where will you put supermarkets and FIFO lanes? These are essentially inventory buffers between the shared resource part and the 1à flow parts of your MMF value stream. There’s quite a bit of hard work required here, since Supermarkets will have to be sized appropriately, located in the right spots, Kanban cards (Withdrawal & Production) created, procedures changed, etc. in order to make this happen. The same for FIFO Lanes.

At this point you’re ready to tie this thinking together on your Future State Value Stream Map. You can “flow where you can” and “pull where you can’t flow” on a Future State map. Of course, this doesn’t mean you’ve physically accomplished “flow & pull” yet, but at least you have the concept on paper of where and how it’ll be achieved in the future.

Seventh, you need to determine how often you want to make each product family. That’s right, each product family! This will be your production interval. This is important because it determines your product family mix, your lot sizes and the frequency of changeovers in your MMF Value Stream.

Eighth, you will want to be working on SMED/Quick Changeover in your MMF. This is where you build the capability to rapidly and efficiently switch between one running product and the next running product to achieve true Mixed Model Flow.

Ninth, you need to balance the operator work in the MMF. When completed, this becomes the Standard Work based on actual customer demand for the products in each Family. You also need to check machine capacity compared to this customer demand to be sure you have adequate capability to meet the demand in the interval you’ve chosen.

Tenth, you will have to figure out where to schedule the MMF. The key is one point and only one point in the whole Value Stream is to be scheduled. Once that point is selected, you “pull” up to that point and “fast flow” from that point to the customer. Typically this schedule point is found immediately after the shared resource asset in your MMF Value Stream.

Eleventh, you are now ready to “go live” with your MMF Value Stream and basically test & debug it’s operation. There will be a number of fine tuning elements to make it work, but this is normal.

Twelfth, once up and running in your MMF, you now have the opportunity (continuous opportunities) to improve it’s operation.

The only advice we can give you is to be bold and get started with your MMF. Following the process described above will insure you are successful. Virtually all of the Lean Tools are available for use in MMFs. And the results beat the old “batch & que, push scheduling system” that’s in place today for your shared resources.

Good luck!

PS: JCM Work Designs’ 5-day Mixed Model Flow Workshop Agenda is listed here for your information. This is how we teach, and you learn & apply the MMF methodology to your own business enterprise.

I. Review Lean Value Streams

II. MMF Through Shared Resources

III. ID Product Families in MMFs

IV. Map the Current State MMF VS

V. Dedicated Assets & Shared Assets in MMFs

VI. Mapping the Future State MMF VS

VII. Takt Times for EACH Product Family

VIII. AWCTs & Machine Capacities

IX. Determining the Interval

X. SMED/QCO for the Shared Assets

XI. Balancing the Work in the MMF

XII. Use of FIFO Lanes

XIII. Installing Supermarkets

XIV. Balancing the Product Mix

XV. Standardizing the Work

XVI. ID’ing and Scheduling the Pacemaker

XVII. Determining Pitch, the Interval, and using a Heijunka Box

XVIII. The MMF Finished Goods Supermarket

XIX. Using the Lean Toolbox

XX. Implementation Planning

XXI. Continuously Improving the MMF

JCM Work Designs/The Lean Sigma Team can design and conduct a this workshop to meet your specific needs.  Please contact us for a formal proposal.

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.