quality control Flashcards
What are prevention costs in quality control
A type of quality cost, an investment into the brand by protecting consumers from nonconforming goods and services. Includes const of palnning, process control, information system and training
What are appraisal costs in quality control
costs of scertaining quality level including tests and inspections their instrument maintanence
What are internal failure costs in quality control
The cost of unsatisfactory quality f.ex network costs, cost of corrective action, downgrade costs or the cost of repairing failed processes
What are external failure costs in quality control
Consts incurred after poor quality goods reach the customer f.ex costs of complaints and returns, recall costs, warrenty costs and product liability costs
What is the 1:10:100 Rule in quality control
If an error is identified in the design stage the cost is 1$, if detecred dirrring the production process it can be fixed fore 10$ but if it is not discovered before it reaches the customer it could cost 100$ to fix it
What is supplier certification and management in quality control
It ensures the integrity of incoming materials
What are in process controls in quality control
It pervents defects and ensures that defective output does not repeat the process
What are finished goods controls in quality control
To verify that the manufactured product meets standards before it reaches the customer
What are some reasons fore sampling in quality control
Testing may destroy the product it is faster, cheaper and saves on testing costs
What assumptions are often made when sampling fore quality control
That the smaple is normally distributed which is likely due to the central limit theorem if the size is larger than 30
What is the sample mean and standard error
The sample mean is calculated normally but the standard error is calculated by dividing the population standard deviation by the square root of the sample size
How do you construct a confidence interval for the population mean if you have the sample mean, the popuaton standard deviation and the sample size
y = x+- Z*o/(n)^2
y = population mean
x = sample mean
Z = z fore confidence interval f.ex 1.96 for 95%
o = population satandard deviation
n = sample size
How do you calculate standard error if you have a sample size and the proportion of faulty items
s = ((p*(1-p)/n)^.5
When is a process normally functioning in statistical process controle
When it stays within the Upper and lower controle limits UCL and LCL
What are p charts in quality controle
Charts illustrating the number of faulty units over time, often with an upper and lower controle limit
Which is the primary concern UCL or LCL
UCL, it means to many products are faulty, if they thend towards the LCL measurement might be insuficient
What are some indications of a process under control
No points are outside the controle limit and they seam to fall randomly around the central ine although most are close to the middle indicating a normal distribution
How do you check if a process is not random
Through test runs. If (r-(n/2)+1)/((n-1)/4)^.5 where n is the number of observations and r is the number of test runs is greater than the normal distribution Z we can conclude that the data series is not random
What is reliability
The probability that something is working as it shall in a given time period
What is the different between series and pararell system reliabilities
Series systems fail if one subprocess fails while pararell systems work as long as at leas one component works
How do you calculate series system reliability
If R is the probability a process will work in the given time you multiply the R of each sub component to calculate the reliability of the entire system.
How do you calculate pararell system reilability
If R is the reliability of one component the system reliability is
1 - (1-R)*…(1-Rn) as the system reliability increases with each component
How does pararell and series system reiliability change when you add more components
Pararell become more reliable while series become less
