tqm loss fun

8/13/2019 TQM Loss Fun

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Taguchi Quality Loss Function


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The Goalpost (Traditional)

View of Quality Traditionally, companies measure quality by the

number of defects or the defect rate. In this system,defects are identified through inspections of the

materials and products. Upper and lower qualitylimits are established. Everything that does not fallwithin the limits is considered a defect.

This view is referred too as the goalpost viewbecause it can be conformed to the use of goalpostsin football. If the extra point goes between the goalposts it is considered a success. It does not matterwhether or not it is in the center or close to thesides. However, if the ball goes wide, left or right, itis unsuccessful. Exhibit 1 shows this view.


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The Quality Loss Function

(QLF)

The quality loss function is based on thework of electrical engineer, Genichi

Taguchi. This view disagrees with the traditional

(goalpost) view.

The quality loss function recognizes thatproducts falling between specific limitsare not all equal.


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Taguchi defines quality as the lossimparted to society from the time aproduct is shipped.

Societal losses include

failure to meet customer requirements

failure to meet ideal performance

harmful side effects


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1. Nominal is better

approach

In this approach, the closer to thetarget value, the better.

It does not matter whether thedeviation is above or below the targetvalue.

Under this approach the deviation isquadratic.


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L = loss in rupees/ dollars

y = output value

m = target value of output

k = constant

Example:

Thickness of windshield in a car

Refrigerator / air conditioner temperature control

2mykL


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2. Smaller is better

approach The smaller is better approach is when a

company desires smaller values.

As the value gets larger, the loss incurredgrows.


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2ykL

L = loss in rupees/ dollarsy = output valuem = target value of outputk = constant

Example:Minimization of heat loss in a heat exchangerRadiation leakage from a microwave appliancePollution from an automobile


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3. Larger is better

approach Larger is better occurs when a company

desires higher values of a characteristic.

Under this approach, the larger thecharacteristic, the smaller the quality lossfunction.


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2

0

y

kL

L = loss in rupees/ dollarsy0 = minimum consumer tolerated output valuek = constant

Example:Maximizing the product yield from a processStrength of adhesivesWelding strength


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Example If the specifications are 10 + 3 for a particular quantity

characteristic and the average repair cost is Rs 1000,

determine the loss function. Determine the loss functionat y = 12.

k = A/2 = 1000/32 = 25.6

L = 111.11(y-10)2

At y = 12

L = 111.11(12-10)2 = 444.44


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Uses of QLF 1. Reduce Costs

There are three ways that managers can use QLF toreduce costs.1. Move the average of the actual distribution closer to the

target value.

2. Reduce variability.

3. Do a combination of both.

2. Setting Specific Limits

The data from the quality loss function can be usedto determine where limits should be set to helpminimize losses.

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