Standardized Work, SWIP and One piece flow -The Core Mathematics of Lean
Much like how Waiting Time had its own connotations, SWIP or Standardized Work in Process or Progress will elicit different responses depending on who you speak with. Some people say it is Standard set of work done, and some people delve into their company operations to see their Work in process.
A company owner maybe new to these concepts and he has absolutely no inkling which way to go. Read on for more information.
SWIP or Standardized Work in Progress is the minimum necessary process inventory to maintain one-piece flow.
Standard Work has three components --- TAKT Time, Work Sequence and SWIP.
Standard Work in Process (SWIP) = (Manual time + Auto time)/TAKT Time
Okay now, let us take an example to understand this. The customer demand is 100 units and the available time with a company is 400 minutes of production, factoring in the breaks.
TAKT Time = 400/100 = 4 minutes per piece
Assume that the manual labor time per piece is about 2.5 minutes and automatic time is 1.5 minutes,
The Total Time = 2.5 Minutes + 1.5 minutes = 4 minutes
Thus, SWIP = 1.
This is the minimum necessary process inventory needed to maintain one-piece flow.
The SWIP formula we have used here is actually an important one to remember, because it correlates to Crew Size, which would be referred to in one of the later articles.
For now, the SWIP of 1 means you need 1 piece of SWIP per person. What does that mean – Simple, 1 piece of minimum inventory is necessary per person.
Single piece automatic Cycle machines
Let us assume you have a process where the machine handles the piece. It is here that the manual labor intervention is minimized to a great extent. The company’s work would now load the piece on the machine, walk away, come back and unload and load again.
SWIP (Single piece auto) = Automatic Cycle Time/TAKT Time
Single piece automatic Non-Machines Cycle
Ok now, this is interesting. A piece is unloaded from the machine that has handled it right now. You would find that you need to give it some time to cure, i.e. time for the hot piece to cool, time for it to dry up etc. You don’t actually sit and do anything to the product. The drying or the cooling happens automatically.
SWIP (Single piece non-machine auto) = Automatic Cycle Time/TAKT Time
Do you have any batch processing cycle?
If you have any part of your process where parts would be loaded and unloaded not as a piece but as a batch due to equipment constraints, you need to work on SWIP (Batch time)
SWIP (Batch time) = [(Automatic Time)/(TAKT Time)]*2
Okay good, now let us move on and calculate the SWIP quantity. Remember this is the minimum necessary process inventory.
SWIP (Total) = SWIP (Manual) + SWIP (Single piece auto cycle) + SWIP (Single piece non-machine cycle) + SWIP (Batch cycle).
Oh yes, there are plenty of calculations involved and the company owner probably realized he failed his Mathematics sessions. Shouldn’t be a bother anyways because all that the owner needs to do is hire a good mathematician, or probably a qualified Lean practitioner and this should be taken care of.
Quick note --- If your Standard Work is producing faster than the TAKT Time, you are exceeding capacity. Means you are overproducing. (Who said working fast is always beneficial).
If your Standard Work is producing less than TAKT Time, your customers are probably waiting for your products. Waiting kicks in. (Tortoises don’t help either, do they?)
In terms of a Standard Work specification, one would like to see a one-piece WIP for each process step (Manual) and a one-piece WIP for machines. This would allow you to do your job in parallel with the machines.
Alright then, with the knowledge on SWIP, let us move on and learn about One-piece flow. There is just one bit about Standard Work and SWIP, which I will reserve as a grand summary.
One piece flow
Also known as Single Piece Flow, this reserves as our discussion topic for the company owner, who seems to have taken a liking to Standard Work and SWIP! So much so that he has already taken out his calculator and started calculating the TAKT Time.
What is One-Piece Flow?
It is considered as the Ideal State of operations, where parts are manufactured one at a time and the parts move through the production cycle, one at a time and finally gets transferred to the customer. One-piece flow is one of the pillars of TPS, JIT, Lean, TOC and other concurrent philosophies.
How does One piece flow work?
- First, the batch sizes are recorded taking historical data, providing a baseline for the process
- Optimum batch sizes are calculated with inputs from various factors like critical work centers, largest inventory costs, highest risk sizes, Unpredictable processes etc. A separate article talks about this batch size, so we will keep our eyes open for that one.
- Action is taken to improve metrics with the use of SMED, KANBAN, JIT and others (Some you know already and some we’d talk about).
Normally to do and accomplish one-piece flow, you’d make use of Process Map, Value Stream Map, Process Operating Characteristics.
Thus, in this chapter we have spoken about how a company would benefit in a big way by looking at Standard Work and SWIP. One quick note then --- SWIP is closely related to One-Piece Flow, if you didn’t guess it out as much, by now.
We have tried to understand how SWIP is calculated and what are the various considerations fuelling the calculation.
Not many drawbacks I could think of to tell the company owner, assuming he would get fine with the complexities (In essence, One piece flow is actually a simple concept to understand), but I could just say that implementing One-piece flow may result at times to spike up the Idle time in your workers.
Again --- That is in our control and not in the control of our customers, so the company owner should be pleased about it anyways.
A quick recap --- SWIP is the minimum number of units to be present in the process to make the process flow. In doing so, it would support Standard Work.
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