Design for manufacturing Flashcards
What may process variations be due to
- Machine misalignments
- tool wear
- material property variations
What does a symmetrical distribution around a mean target look like?
SKETCH
What is the most preferable distribution of variations in manufacturing
symmetrical about the mean
What is the ideal value of z where z = t/sigma
z should be between 4 and 7.5
4 sigma corresponds to _____ parts per million failure for two tails
63
7.5 sigma corresponds to ____ parts per million failure for two tails
0
< 4 sigma is considered ____
too many failures
> 7.5 sigma is considered to be ____
too much precision (too costly)
What is the 6 sigma philosophy
6 sigma is considered the ideal balance between precision and the number of failures
What does a asymmetrical distribution around the mean target look like
SKETCH
When can an asymmetrical distribution occur and give an example
when there is tool wear
tool wear on a lather can cause the shaft diameter to increase and therefore the distribution shifts to the right
Which value of z is used in analysis of an asymmetrical distribution
the largest value of z (z2) as it gives the worse case scenario
How can z2 be calculated
z2 = (xm - L2)/sigma
How can unsymmetrical distribution in machine variance be avoided
by regular checking of the tool for wear and regularly checking the machine settings
What is Cp and how is it calculated
In industry, Cp is used which is a capability measure of a symmetric distribution
Cp = t/(3 x sigma)
What value must Cp have if the process is capable
Cp < 1.33
What is Cpk and how is it calculated
Cpk is the capability measure used in industry for a asymmetric distribution
Cpk = (xm-Ln)/(3xsigma)
What does xm stand for
the actual mean
What does Ln stand for
the worst case tolerance limit
How do you calculate the drift from mean
Drift from mean = target mean - actual mean
When should Cpk be used over Cp
If Cp - Cpk > 0.5 then Cpk must be used
What is the equation to calculate the standard deviation
EQUATION
Describe the house of quality design method
it helps to convert customer requirements into engineering requirements.
It help to determine the most important engineering requirements
It is subjective but nevertheless can help teams to improve product quality
What is the disadvantage of the quality of house design method
It is subjective but nevertheless can help teams to improve product quality
Describe the table produced to complete the quality of house design method
column of customer requirements, then each have a customer priority rating (1-5), these are then compared to engineering requirements that form the other columns, which get given a score of 1, 3 or 9 depending on their relationship to the customer requirements
The points rating is then found through multiplying the priority rating and the score and adding these together for each engineering requirement
What are the series of questions to ask when introducing a new product and trying to work out the right manufacturing strategy for it
- what is the best product footprint?
- What is the best product family?
- Should the product be a service?
- Should a company be ‘first to market’ or a ‘fast follower’
- When should a product be retired from the market
- Which parts of the product should be bought from suppliers and which parts made by the firm
- should there be mass customisation
- what should the product architecture be