I remember a very humbling experience of thinking that I knew how to solve problems and being shown just the opposite by an hourly associate. That was during my internship while I was in graduate school; I was haughty, boasting that I came from a top university and demonstrating in my thoughts and body language other prideful nonsense. I’ve learned that you can learn something from anybody. I’d like to think that I’ve become wiser since then and have changed my behavior to reflect that experience.
That particular experience involved a scheduling activity of auto parts being received, followed by a “stowe” process, where these auto parts would then be placed in storage bins. I sat back and observed from some time and even participated in the actual stowing of the material in the warehouse. My aim was to improve that particular process and regulate the stowing activity with the drumbeat of the receive activity.
Since I was a prideful graduate student, I decided to pull out my discrete event simulation and operations research toolbag — you know, stuff that is clinically interesting, but sometimes not useful — only to be taught by a few hourly associates a simple and elegant way to level the work of receive-to-stow: Takt Time.
Takt Time (Grab Takt Time Calculator Here) is the maximum allowable time in order to meet demand; Takt Time is the pace by which product is produced and must fall within the Takt Time or set equal to the Takt time; if not, then there will be customer demand that might go unfulfilled.
Takt Time is defined as the following:
Takt Time = (Net Available Production Time / Required Output Rate)
I do not have a picture for you, so please bear with the verbal explanation. For this process, we are dealing with a supply parts distribution center that stores material for cars. There are several receive-runs from tier-2+ suppliers to this warehouse where the parts are consolidated and stored.
This warehouse is divided into zones. The parts arrive in a bin on the receive dock, and the bins are then placed on a manual conveyor belt to a staging area. We have labor (people) that take these bins, place them on carts, and walk to the respective zone to offload the bin. Then the associate team member returns to pick up another bin.
Here is the question: how frequently should we tell the tier-2 suppliers to make a part drop-off? And, how much material should they plan on delivering for each run? Other questions: If you are a tier-2 supplier, at what point does it make economic sense to ship a less-than-truckload (LTL)? What about quantity-discount discussion?
All good questions, but I won’t consider most of them for this post. I want to localize our discussion on “How frequent should the tier-2 suppliers make a run to this center?”
Assume that the end-to-end system is a clean Pull from the customer all the way down the supply chain using a series of simple but elegant Kanban cards. Also further assume that the information flow downstream and material flow upstream has no defects or rework. We are only dealing with the question of regulating the pace between Stowe-and-Receive.
Takt Time can answer this question: Assume we have 1 person that works 6 productive hours. Let’s also assume that in order to meet upstream demand (parts-to-manufacturing plant) is known and stable and is 150 bins per 6 hour day. Given this, we have arrived at a Takt Time — how much maximum time can be alloted per Stowe.
Takt Time = [(6 hours * 60 minutes) / (150 Bins)]
Takt Time Per Run = 2.4 Minutes
This means that for each operator, she has at most 2.4 minutes to receive-walk-stowe and then return for the next run. Each run would represent a Cycle — hence, the term Cycle Time.
Improving Takt Time
We don’t really improve Takt Time, per se. We can reduce the Cycle Time and the content of the work involved in that Cycle, such as reducing or eliminating waste and non-value added steps, thereby influencing the Takt Time, or overall beat of the line. Specifically, we can do the following:
- Reduce Variation
- Reduce Idle Time
- Reduce set-up time
- Reduce or eliminate waste
- Better manage constraints
To have a shorter Takt Time, improvements must be made on Cycle Time — that is, each cycle has to become shorter, which in turn would result in an improved Takt Time. It’s important to note that, in proper nomenclature, you cannot improve Takt Time — Takt Time is-what-it-is; a fact. It is Cycle Time that can be improved, which is a component of Takt Time.
Back to the Beginning
Back to the question of how to regulate Receive-to-Stowe: the aggregate Takt Time of all [(stowers * productive hours * 60 minutes) / Customer Demand]. The Customer in this case is the nearby manufacturing plant that meets the upstream demand of the customer, manifested in orders from auto dealers.
So, we see Pull all the way from the customer downstream to the atomic component parts.
Dumber-by-the-Minute = Wisdom
The hourly associate that showed this to me and explained, in a very down-to-earth and human way, helped me to “see” the world in a different way. She helped me to better understand my local concern and how that is truly an important part of the overall story for this business; that experience helped me to gain some wisdom, withhold judgment, helped me to understand that my education from a fancy school really doesn’t mean much, and that experience was the catalyst of my Lean Journey, which I’ve been on now for 8 years. I’m still quite young in both age and in experience, but am so thankful for humbling and growing experiences.