Available (Availability), Uptime and EPE in VSM (Value Stream Mapping)

Peters

Quite Involved in Discussions
#1
I have problem - how to understand 3 terms in VSM boxes:

1. available or availability -
What's this?
Is it in pieces? In percents?
Per shift/day/week/month?

2.Uptime
What is the definition?
How to estimate it?

3.EPE
What's this?
How to estimate it? How to use this?

Can anybody help me?
I couldn't find this in the past topics...
 

Peters

Quite Involved in Discussions
#2
OK.
Let’s talk about boxes in Strategos VSM (see attachment).
Box “machine”.

1. C/T=44 sec. (Cycle Time) - time (in seconds) that elapses between one part
coming off the process to the next part coming off

I don’t know why below the box is 45 sec but it’s small problem

2. C/O=60min. (Changeover Time) - time to switch from producing one product on the process to another

Do we use this indicator in this graph or this indicator is minor importance?
How often do we do exchange of tool? After every lot?

3. Lot/batch=1000pc.

OK. Do we use this?

4. Avail=27600. Available Capacity??? in seconds? in pieces? in …?

5. Uptime=87%. (Uptime)- percentage time that the machine is available for processing

And this 13% - what’s that? Exchange of tool? Breaks? Waiting?

6. EPE they don't use in this graph. But it can be found in symbols/definitions (EPE (a measure of production rate/s) - Acronym stands for "Every Part Every___").

And I don't understand this. Do we need this indicator?

7. The only effect of calculation in VSM graph is TIME? (Lead Time versus Total Cycle Time?). Of course time is money :cool: But why don't we estimate money directly...

I know :cool: Too many questions :cool: Maybe I'm too scrupulous :notme:
 

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Marc

Retired Old Goat
Staff member
Admin
#3
I was browsing some older posts and I came across this one which was never answered. Does anyone have any thing to share or help with? This could be a good informational thread.

Also see these existing Value Stream Mapping and VSM discussion threads.
 

ngkjrs

Learner Always
#4
Availability is measured in time

Uptime is the opposite of downtime. If downtime is 1% uptime is 99%. It can be measured in time or in percentage.

EPEI stands for Every part Every Interval

Here's more on EPEI. Let's say that we have 4 items being produced in the process each with unique demand, cycle times and changeover times.

EPEI is the length of time needed to make the required demand of each of the 4 items including the changeovers between items.

1 - Calculate the total run time needed daily for production by multiplying the daily demand X cycle time for each item and adding up the times.
2 - Subtract the total production time from the available work time for a day which gives you the total amount of time available for changeovers.
3 - Add up the total amount of changeover time required for all items.
4 - Divide the total changeover by the time available for changeovers (step 2) to get the number of days to cycle through all of your items.

This is a very simple case. A more elaborate situation might involve factoring in downtimes, yield loss, rework, perhaps different kinds of changeovers, etc. But the above is the key concept.

EPEI directly sets required WIP levels. If I run a process to a 5 day EPEI, then I need to have 5 days of inventory (plus safety time etc) since I only produce a particular item every 5 days. If I can reduce EPEI to 3 days, then I only need 3 days of inventory buffer. One big benefit of focusing on reducing changeovers is to drive the EPEI lower which in turn reduces the need for inventory.

I've found that EPEI is a conceptually tough concept for people to really understand. The best way I've found to explain it is this: Let's use all of our available time to run as many changeovers as possible so that we can reduce our production lot sizes to as small as possible. By doing this we can reduce our WIP inventory to as low a level as possible without impacting our service levels.

I've found that EPEI is the key metric for high mix, low volume value stream improvements with the goal being to drive to lower and lower EPEI.
 

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