D
Dave.
Hi, I am new to the forum and looking for some help please. I am currently working at a UK food manufacturing company looking at their packing process and I am wanting to perform a capability analysis. I am relatively new to Six Sigma (but not Lean), and I am a bit stumped.
In the UK, when products are packaged to a nominal weight, manufacturers can use the average packing system, where they must conform to 3 packers rules by law.
1. The average weight of goods must not be less than the nominal weight (Qt).
2. 2.5% of goods can weigh between T1 and T2.
3. No goods can weigh less than T2.
where
T1 = Qt-TNE
T2 = Qt-2*TNE
and
TNE = 1.5% of Qt for products 1000g to 10,000g
I have taken 50 measurements (see end of post) of product weights as they roll off the process and plotted an I-MR chart which shows some special causes. The problem is now that I am struggling to do a Capability analysis of this data. I know that yo need to have a process in control before producing a Capability Analysis, but I thought whilst I was doing the I-MR chart, I would get 100% familiar with CA as it will be useful in other food companies I am working at.
The problem is that whilst the measurements taken follow a normal distribution, I don't want them to and the reason is this.
Say the target weight =2500g, T1=2462.5g and T2=2425
Therefore I am taking my LSL to be 2425g as this is the minimum legal requirement. As this is a food product there is no USL from the customer as this is Giveaway. The manufacturer however wants to limit Giveaway to 0.8%. This gives me a USL of 2520g.
Technically speaking, for this process to be in control, it needs to be Skewed to the right, with the peak just above the target, within the USL and LSL, with 2.5% of the left tail between T1 and T2, and nothing below T2. Cp, Cpk, Pp, Ppk and Cpm will not be a fair representation of this process if a Normal Distribution is applied.
I presume there is a way of doing this as this is a common theme in many food factories that pack to the average weight system, but after 3 days of searching on line I haven't really come up with anything.
Please can some one point me in the right direction and explain. I did post on another forum and all I got was "try looking at Cpm".....Not much online about that specifically....either that or I am just looking in the wrong places.
Thanks in advance for your time and guidance.
Dave.
Measurements:
2504.2 2512.6 2465.1 2462.9 2450.9 2501.6 2473.7 2470.1 2463.2 2474.9 2471.2 2483.8 2489.4 2463.5 2500.4 2499.5 2530.1 2495.8 2492 2500.6 2533 2526.1 2510 2495 2506.9 2507.9 2492.4 2488.3 2494.7 2512.3 2496 2527.8 2537.8 2493.3 2490.2 2459.1 2485.1 2483.7 2442.7 2494.9
In the UK, when products are packaged to a nominal weight, manufacturers can use the average packing system, where they must conform to 3 packers rules by law.
1. The average weight of goods must not be less than the nominal weight (Qt).
2. 2.5% of goods can weigh between T1 and T2.
3. No goods can weigh less than T2.
where
T1 = Qt-TNE
T2 = Qt-2*TNE
and
TNE = 1.5% of Qt for products 1000g to 10,000g
I have taken 50 measurements (see end of post) of product weights as they roll off the process and plotted an I-MR chart which shows some special causes. The problem is now that I am struggling to do a Capability analysis of this data. I know that yo need to have a process in control before producing a Capability Analysis, but I thought whilst I was doing the I-MR chart, I would get 100% familiar with CA as it will be useful in other food companies I am working at.
The problem is that whilst the measurements taken follow a normal distribution, I don't want them to and the reason is this.
Say the target weight =2500g, T1=2462.5g and T2=2425
Therefore I am taking my LSL to be 2425g as this is the minimum legal requirement. As this is a food product there is no USL from the customer as this is Giveaway. The manufacturer however wants to limit Giveaway to 0.8%. This gives me a USL of 2520g.
Technically speaking, for this process to be in control, it needs to be Skewed to the right, with the peak just above the target, within the USL and LSL, with 2.5% of the left tail between T1 and T2, and nothing below T2. Cp, Cpk, Pp, Ppk and Cpm will not be a fair representation of this process if a Normal Distribution is applied.
I presume there is a way of doing this as this is a common theme in many food factories that pack to the average weight system, but after 3 days of searching on line I haven't really come up with anything.
Please can some one point me in the right direction and explain. I did post on another forum and all I got was "try looking at Cpm".....Not much online about that specifically....either that or I am just looking in the wrong places.
Thanks in advance for your time and guidance.
Dave.
Measurements:
2504.2 2512.6 2465.1 2462.9 2450.9 2501.6 2473.7 2470.1 2463.2 2474.9 2471.2 2483.8 2489.4 2463.5 2500.4 2499.5 2530.1 2495.8 2492 2500.6 2533 2526.1 2510 2495 2506.9 2507.9 2492.4 2488.3 2494.7 2512.3 2496 2527.8 2537.8 2493.3 2490.2 2459.1 2485.1 2483.7 2442.7 2494.9