Calculating OEE – A Simple Example, Part 2

In our previous post (Calculating OEE – A Simple Example, Part 1) we saw how to calculate OEE using only the Good Parts count and the Planned Operating Time. Now we are going to calculate OEE for the same example using the Availability, Performance and Quality Losses. This is a more complex way of calculating OEE but it provides us with the data to identify the main reasons for loss.

Remember our example:

Over a 12hour shift, our Filling machine fills 11,000 bottles. The manufacturer has specified that the Standard Time for this Filler to fill one bottle is .05mins/bottle. Over the course of the shift there are some Planned Downtimes: 2 x 15minute tea breaks and 1 x 30minute lunch break.

Planned Operating Time

 Planned Downtimes:

    15mins | Morning Tea Break
    30mins | Lunch Break
    15mins | Afternoon Tea Break

 Planned Downtime:  60mins

Total Time:   720mins

Therefore:
 Planned Operating Time = 720mins – (15mins + 30mins + 15mins)
     = 660mins

Availability

Now let's look at Availability. In our previous post we defined Availability as ((Planned Operating Time) – (All Availability Losses)) / (Planned Operating Time)

We know our Planned Operating Time is 11hrs. So if we know our Availability Losses we can calculate Availability. Availability Loss are all downtimes related to Breakdowns and ChangeOvers.

Over the course of our Shift we logged downtimes as follows:

 Availability Losses:

    25mins | ChangeOver
    10mins | No Caps in Hopper
    15mins | No Air

 Availability Loss: 50mins

Planned Operating Time: 660mins

Therefore:
 Actual Operating Time = 660mins – (25mins + 10mins + 15mins)
     = 610mins

and:
 Availability  = (Actual Operating Time) / (Planned Operating Time)
     = 92.4%

 

 Performance

The Performance Loss is a combination of Short Stops and Speed Loss. Short Stops are momentary downtimes which aren't Breakdowns or ChangeOvers which stop the machine and interrupt production but do not generally require technical support. In general for Manual Systems Short Stops are ignored as it can be onerous to record each stop. This results in the loss associated with Short Stops being built in to the Cycle Time Speed Loss. In Automatic Data Capture Systems it is more realistic to log Short Stops.

Rather than take a Cycle Time measurement and assume that this Cycle Time was constant over the whole shift it is often more realistic to calculate the Net Operating Time by working back from the more easily measured Throughput (ie sum of Good Parts and Defect Parts).

We know that the number of Bottles filled was 11,000

Defects:

250 | Underfilled

100 | No Cap

Defect Parts: 350

Good Parts: 11,000

Thus we can calculate our Good Time (ie Standard Time to produce Good Parts) and our Defect Time (ie. Standard Time to produce Defect Parts).

Good Time = 11,000 x 0.05

= 550mins

 

Defect Time = 350 x 0.05

= 17.5mins

 

Where 0.05mins/bottle is our Standard Time to produce one bottle.

 

Therefore:

Net Operating Time = (Good Time) + (Defect Time)

= 567.5mins

 

and working back we see that:

 

Perfomance Loss = (Actual Operating Time) – (Net Operating Time)

= 42.5mins

 

We now know the Net Operating Time therefore we can calculate the Performance.

 

Performance = (Net Operating Time) / (Actual Operating Time)

= 93.0%

 

Just for the sake of completeness let’s say that the machine stopped 10 times due to Falling Caps. Each stop was 6 seconds in duration and didn't require any technical intervention. We can say that the machine suffered 1min of downtime due to Short Stops.

Subtracting the Short Stops from the Performance Loss gives us the Speed Loss (Slow Running). ie the Loss due to the fact that the machine was running at a slower rate than the optimum rate specified by the manufacturer.

 

Speed Loss = (Performance Loss) – (Short Stops)

= 41.5mins

As a matter of interest our average Cycle Time over the Shift was ((Net Operating Time) + (Speed Loss)) / ((Good Parts) + (Defect Parts)) = (609) / (11,350) = 0.0537mins/bottle. Thus the Filler took on average 0.0037mins more then the Standard Time to fill each Bottle.


Quality

Finally we consider Quality Losses, ie the time taken to produce Defect Parts. In the above section we have already calculated the Good Time and the Defect Time. Defect Time is another name for Quality Loss and Good Time or OEE Time is the same as Fully Productive Time.

Thus we have every thing to calculate Quality.

 Quality  = (Fully Productive Time) / (Net Operating Time)
    = 96.9%

Note: Quality is only equal to (Good Parts count) / ((Good Parts count) +(Defect Parts count)) when the Standard Time is the same for all parts run on the machine over the shift.

Now the final calculation;

 OEE   = Availability x Performance x Quality
    = 92.4% x 93.0% x 96.9%
    = 83.3%

By taking the long way round we have generated 3 additional KPIs and we have a lot more data which we can use to focus in on the causes of loss.

Let's briefly take a look at the Level 1 Losses in a table ordered by size of loss

Availability Loss 50.0mins
Performance Loss 42.5mins
Quality Loss 17.5mins

This tells us that in this example downtimes are the most significant type of loss.

And now look at the individual losses in a similar table

Speed Loss (Slow Running) 41.5
ChangeOver     25.0
No Caps in Hopper 15.0
No Air 10.0
No Cap (Defect Time) 12.5
Underfilled(Defect Time) 5.0
Short Stops 1.0

Here we see that Speed Loss is in fact the biggest individual loss. In the absence of a downtime monitoring system Speed Losses are often missed as it can appear that the machine is running perfectly well when in fact it is producing much less then it should.

When generated on a shift by shift basis these tables are helpful in the day to day operational management of the machine. However when calculated over longer periods of time you can build up a very insightful picture as to the real causes of loss – as opposed to your presumptions – which may or may not in fact be correct.

In our next post we will show how Provideam can help to organise the data you have collected manually into a database which can be analysed in many different ways. The beauty of a database over a spreadsheet, like Excel, is that the data can easily be grouped and filtered by all sorts of interesting criteria in a rapid and flexible manner.
 

OEE Loss (by Object) Shift Report with Pie Chart

 

OEE Loss (by Object) Shift Report with Pie Chart

A standard Provideam Loss Report might appear like the example in figure 1 below.


Fig. 1 OEE Loss by Object Report

 

In this report we see a breakdown of the losses for AssemblyMC1 for the Day Shift on the 2nd of October. The losses are displayed both in graphical

and tabular format. The upper table shows a list of the losses sorted in descending order of magnitude of the Time function. The lower table shows a

selected list of functions calculated over the shift. These ‘overall’ functions help to put the loss figures in context.

 

To help us get a perspective on the actually losses we have included the OEE Time in this report (the green pie segment). This is the total time

that the machine was running at its optimum rate. It is a feature of Provideam that you can specify whether to include or exclude categories of loss

on your reports.

 

To create a report like that shown in figure 1 above, follow these steps;

Step 1: Click on the ‘New Report’ icon
Step 2: Select the OEE Loss (Group by Object) option

 


Fig. 2 OEE Loss by Object Report – New OEE Loss Report

Step 3: Click Next to move on to the Area/Machine (Object 1) selection.
Step 4: Select AssemblyMC1 from the list of available Machine items.

 


Fig. 3 OEE Loss by Object Report – Select Object

Step 5: Click Next to move on to name the Object.

By default the Report Wizard enters the Object Description shown below. You may edit this if you wish.

 


Fig. 4 OEE Loss by Object Report – Edit Object Description

Step 6: Click Next to move on to on to the Loss selection.
Step 7: Choose Level 1 Loss and select All from the list of available Level 1 Loss items. This option results in all time, from OEE Time to Planned

Downtime, being included in the Loss Report.
Step 8: Check Show for Level 3 Desc. This results in a breakdown by Level 3 Description on the final report.

 


Fig. 5 OEE Loss by Object Report – Select Loss

Step 9: Click Next to move on to Functions selection.
Step 10: Select Time from the list of available Loss Function items.
Step 11: Select PlannedOpT, UpTime, Downtime, Good Parts and Defect Parts from the list of available Production Function items.
Step 12: Use the Up and Down buttons to order the Functions. They will appear in the final report in the order  you set here.
Step 13: Check the Show Grand Totals checkbox.

 


Fig. 6 OEE Loss by Object Report – Select Functions

Step 14: Click Next to move on to Period selection.
Step 15: Select the Shift period option.

 


Fig. 7 OEE Loss by Object Report – Select Period

Step 16: Click Next to move on to the final screen in the Report Wizard.
Step 17: Select the Pie Chart Graph option.
Step 18: Check the Show Graph option.
Step 19: Click Run Report to run this Report.

You may save the report definition as a Report Template at this stage. Report Templates can be shared with other users and also scheduled for

automatic delivery by email.

 


Fig. 8 OEE Loss by Object Report – Select Graph Style

Step 20: Select a Date and Shift.

 


Fig. 9 OEE Loss by Object Report – Select Report Period Parameters

Step 21: Click Run Report to generate a report preview.

 


Fig. 10 OEE Loss by Object Report – Preview Shift Report