Yield monitoring - Kg in and Kg out

piningg

Involved In Discussions
#1
Hello

We want to monitor and set control limits of our product yield using kg in ( raw materials put in the machine ) vs kg out ( finish product ).. so basically it's the waste we're monitoring here.
Our dilemna is we're not continously making constant no. of kilos every run, sometimes we're running 1000kilos and sometimes 500kilos so..
Questions are;
yield by using kg in and kg out method is an attribute or variable data?
what chart to use, X bar chart or P chart??
 
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#2
Hello

We want to monitor and set control limits of our product yield using kg in ( raw materials put in the machine ) vs kg out ( finish product ).. so basically it's the waste we're monitoring here.
Our dilemna is we're not continously making constant no. of kilos every run, sometimes we're running 1000kilos and sometimes 500kilos so..
Questions are;
yield by using kg in and kg out method is an attribute or variable data?
what chart to use, X bar chart or P chart??
Both metrics are variable (yield and kgs lost)

You might need a little more thinking. Is the loss depending on the size of the batch?

Take a look at the historic data and plot yield (out/in) and kgs lost on a run chart, calculate control limits.

Create a chatter plot (lot weight vs kgs lost and lot weight and yield) to see if they are dependent.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#3
in addition to the scatter diagram to look for independence, I have been successful using a p chart with variable sample size for %yield (yield is categorical - counting - data and not continuous data. The I, MR chart can be useful if the base size is fairly constant, but this is rare for my applications.
 
A

adrianpask - 2011

#4
If i may add an additional component to the mix - every time you have a yield loss not only is this a loss in raw materials, it's also a loss to productivity or OEE.

For example, if a customer places and order for a 1000 units and you produce 100 units of waste your customer is highly unlikely to accept a short order - you have to make 1100 units. Therefore not only have you lost yield on the lost product, you've also lost production time because you've had to over produce.

If you want to know the real cost of your waste you may want to consider:

1. Work out how long it takes you to produce each unit

2. Multiple this by the number of units you waste to get a time loss per day

3. Multiply this by your fixed cost per hour to get a rough estimate of your productivity loss (there's lots of ways to do this - including multiplying by the cost per unit, or contribution to business, or....or....or....this is perhaps a decent start point).

4. Compare this to your raw material loss

The reason i raise this is that i know many manufacturers who track raw material loss in £ but don't track how much time they've wasted producing this out of spec material.

In my experience and opinion a focused OEE improvement activity not only improves raw machine output, it has a huge knock-on effect to quality, safety, and housekeeping KPI's.

If you want some ideas on how to track this automatically check out the website link in my profile as i have a system that can do this in real time for you out on the machine.

Regards,

Adrian.
 

piningg

Involved In Discussions
#5
in addition to the scatter diagram to look for independence, I have been successful using a p chart with variable sample size for %yield (yield is categorical - counting - data and not continuous data. The I, MR chart can be useful if the base size is fairly constant, but this is rare for my applications.

as far as I know base size is not constant..
 

piningg

Involved In Discussions
#6
Both metrics are variable (yield and kgs lost)

You might need a little more thinking. Is the loss depending on the size of the batch?

Take a look at the historic data and plot yield (out/in) and kgs lost on a run chart, calculate control limits.

Create a chatter plot (lot weight vs kgs lost and lot weight and yield) to see if they are dependent.
we know that's the bigger the kgin is the better yield we have and the smaller the kgin the lower yield
 
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