Heijunka, also known as level-loading, production-leveling or production-smoothing, is a foundational element of the Toyota Production System. It facilitates system stability by addressing workload unevenness (mura) through the leveling of both volume and mix over time, see Figure 1. Heijunka also serves as a pacing mechanism for operations, often reflected in the use of heijunka, leveling, or schedule boxes, which are typically designed using pitch intervals, see separate pitch post. Successful heijunka reduces lead time, inventory, and worker physical and psychological stress that can accompany fluctuating workloads. Some prerequisites include quick changeovers, capable processes, standardized work (or at least defined work content), good visual management, and a solid understanding of customer demand – volume, mix, and variation, see separate demand segmentation graph post.
Figure 1. Example of volume and mix leveling
The heijunka cycle (Ch) represents a regular, repeatable production sequence to facilitate the leveling of mix. The lean practitioner can readily calculate it using a simple spreadsheet and one or more illustration iterations of the proposed cycle, followed by some real PDCA at the gemba. See Figures 2 and 3, as well as the related formulas. As with the concept of takt time, consider Ch more as a design parameter, than a precise and rigid blueprint for developing the heijunka system.
- Figure 2.Example heijunka cycle calculation
.
See the Resources>Templates menu options for a downloadable example Excel heijunka cycle calculation spreadsheet.
Figure 3. Heijunka cycle illustrated
It bears repeating, don’t sweat the math if the ratios aren’t perfect whole numbers (that only happens in the examples provided by teachers and consultants). Pragmatically round when appropriate and remember that mix is often a dynamic thing. Good, simple and visual heijunka standard work will cover for real-life variation.
There are 65 Comments
Excellent work Mark. Hats Off.
Nital Zaveri
CEO-Concept Business Excellence Pvt. Ltd.
www.sixsigmaconcept.com
Hi Mark, good piece of work.... to make sure I really understand it, i tried to recreate the excel sheet based upon your formulaes, calcs and pictures, but i have troubles with the bits around Ch adjustments and the n/a ... i can't get to the right numbers. Would you be willing to mail me your spreadsheet producing the Ch calculation example so I can see where i am going wrong?
Can you Sen d me the spread sheet mark it was a really tricky and cool method evaluate heijunka constant
Hello Mark,
Excellent explanation.
Please can I have the spreadsheet too?
Devendra
Mark, In Fig 2 step D, I am unable to calculate the same numbers for product B as it relates to columns "2 cards every x cycle" and "3 cards every x cycle".
For product B & "2 cards every x cycle", calculation is (1/(3.11-3))*2 = 18.
For product C & "2 cards every x cycle", calculation is (1/(2.00-2))*2 = n/a
Please help/ advise where i am making mistake.
H Ashok,
We can certainly calculate the number of multi card adjustments for B (for example, a 2 card adjustment every 18 cycles would be the number). However, I was looking for the lowest whole number (or as close to a whole number as possible) - thus every 9 cycles was a good "solution." Accordingly, I used n/a for 2 cards and 3 cards. There is no adjustment for "C" because it is the lowest period demand and is used as the basis for the production ratio. In other words, it is a 1:1 relationship, by definition.
I hope that makes sense.
Best regards,
Mark
It remains incorrectly labeled as "Monthly>
Please feel free to delete my message and your response (and not publish this one), since it no longer adds value now that the error has been corrected. Keep the comments lean, reduce non-value added activity!
Mark, Very detailed explanation! Thanks a lot.
Please help me understand in step C will actual cycle time be a factor to define which calculated production ratio multiple be more practical? I am also assuming the sequence of build is for a mixed model cell, not dedicated product assembly cells. Please confirm.
Also i used 65 working days in a quarter to calculate daily demand. My numbers did not match your table in Fig 2. Please share your calculations for me to check where I made mistake.
Mark,
Best detail explanation I have seen! Thanks so much for sharing. This is very much based on demand and takt time, how do set up time and cycle time get looked at in the schedule? In a cell we are creating, we have cycle times that are above takt time prior to improving it. I would like to pick the optimum batch size for the current cycle and set up time and have it adjusted as we improve setups and cycle times. Please share the spreadsheet with me as well!
Thanks,
Albert
Hi Albert,
I just sent you the spreadsheet. Sorry for the slow response.
If you have significant set-up times, then heijunka cycles, as such, probably do not make sense for you. I would consider using a signal kanban for scheduling batch processes. The post, "Pull System Design: Brief Thoughts on Sequence and Math," may be a good start for you.
Let me know if you have any questions.
Best regards,
Mark
Hi Mark... Interesting, Obliged if you kindly share the spreadsheet?