1.8 UNANSWERED PROBLEMS
1. Write the values displayed on the vernier scales below.
2. Draw the appropriate diagram for the data below. The data indicates sources of photocopy problems.
3. a) The data below has been plotted from QC samples, add the lines required to complete the X chart.
b) We are designing a new product and want to produce it on the process described in #3 a). What tolerance is required to obtain 6 sigma quality?(6%)
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5. Given the attached “Frequency Distribution Analysis Sheet”
a) What is the average?
b) What value is at +2 sigma?
c) What is the mode?
d) What is the median?
6. Are the ISO9000 quality standards part of SPC? Justify your answer.(5%)
7. a) Given the results from a Designed Experiment, as listed below, what are the main effects of A and B?
b) Draw a graph from the data in a), and explain the significance of the effects.(5%)
8. At Joe’s Barbatorium a once a day inspection is done of one customer at random. The QC inspector checks 1000 hairs for length, any over 1” are considered defective. For the last week the counts have been 10, 2, 25, 0, 7.
a) Select the correct type of attribute chart to track quality.(4%)
b) Draw the chart selected in a).(11%)
9. Develop a double sampling plan OC curve given that, (20%)
N = 1000
n1 = 50
c1 = 2
r1 = 4
n2 = 100
c2 = 3
10. Generally, why should production try to meet specifications, not exceed them?
11.
a) Draw a fishbone diagram for the production of cookie dough. The quality to be measured is the ratio of chocolate chips to dough per cubic meter. Note: the components are weighed separately, and then mixed together in a large tub.
b) Select the most reasonable causes from a), make up a tally sheet, fill it with some data, and draw a Pareto chart. You must consider that there are three different operators that may do the weighing and measuring.
12.
a) We have found a box of gum for practical jokes. Most of the gum is normal, but some pieces will result in purple tongues when chewed. Would inductive, or deductive statistics be used to determine how many of the sticks are for jokes without chewing them all?
b) Assume we are counting the number of fish in a pet store aquarium. Give an example of a grouped, and ungrouped count.
13. Four samples have been taken at the start of a new process run. But, one of the values, X1, was accidentally erased after the calculations were done. Using the data below, find the missing value.
14. Is the data below normal? Justify your answer.
15. The data below was measured over a two week period for a 1.000” shaft with a tolerance of +/- 0.010” .
a) Draw accurate X, R and s control charts.
b) Determine if all the data values are normal (56 in total) using the normal distribution graph paper.
c) Determine Cp and Cpk.
d) What would the tolerance have to be if we required 6 sigma quality?
16. A manufacturer ships 10,000 balloons a day to McDonalds. A daily sample of 50 are removed and tested. The table below lists the number that burst when inflated.
a) Select the correct type of control chart, and draw it accurately.
b) If McDonalds sets a maximum of 3 rejects in 50 samples, draw the OC curve.
c) For the OC curve drawn in b), identify the consumers risk when 3% of the balloons are non-conforming.
17. List some material and process variables that can affect quality.
ans. Quality can be affected by speeds, feeds, hardness, surface contamination, purity, temperature, etc.
18. Why is standard devistion important for process control?
ans. Standard deviation is a measure of distribution in a process that varies randomly with a gaussian distribution.
19. Describe SPC (Statistical Process Control).
ans. Statistical process control uses statistical methods to track process performance, and then probability to estimate when it is undergoing some non-random or systematic change. When this occurs the process is no longer under control.
20. What is the purpose of control limits in process monitoring?
ans. Control limits are hard boundaries that the process should not work outside. If a value is outside these limits the process should be stopped.
21. What is process capability and how is it used?
ans. Process capability is used to measure the precision of a machine.
22. What would happen if the SPC control limits were placed less than +/-3 standard devistions.
ans. There will be more of the distribution outside the limits, and hence more rejects.
23. What factors can make a process out of control.
ans. Factors can put a process out of control. A sudden jump will be caused by a change in tools/operators/components/materials. A slow change in the mean will result from slipping gages/tools, or tool wear. A single anomaly can lead to a single control point outside the range (e.g. somebody drops their gum in the machine).
24. What is acceptance sampling and when should it be used?
ans. Acceptance sampling is used for parts that are being made by another manufacturer who does not provide process quality information. This technique uses random inspection of parts as they arrive to ensure conformance to quality limits.
