solution

Case Study

Teleplast company (hypothetical name) is one of the leading manufacturing companies of “plastic injection moulding parts” for the telecommunication market. With the increase in competition in telecommunication product supplier market, the company is planning to reduce cost and simultaneously provide better quality products in order to achieve higher profits. As a result, the company is planning to design and implement a quality improvement program. Quality improvement for the company also aims at improving the productivity and reducing the rejection rate. The quality improvement should be focused on both the internal and external customers. In order to appropriately design the quality improvement program, the company’s Sr. Manager Ravi decided to personally have look on the number of defective parts. In the previous 30 weeks, Ravi took a random sample of 200 plastic injection moulded parts in each week for determining the rejection rates. The table given below indicates the number of defective parts obtained each week through the sample:

Sample Week	Defective Lenses	Sample Week	Defective Lenses	Sample Week	Defective Lenses
1	5	11	10	21	2
2	10	12	4	22	5
3	1	13	3	23	3
4	0	14	5	24	6
5	7	15	2	25	11
6	6	16	7	26	7
7	12	17	1	27	9
8	11	18	1	28	3
9	3	19	12	29	0
10	2	20	13	30	1

Questions

1. Using 95% confidence level, plot the overall percentage of defective parts (p) and upper and lower control limits on a control chart.

2. Plot the percentage of defective lenses in each sample. Do all the samples fall within the control limits of Teleplast. What should be done when one falls outside the control limits.

3. What should be reported by Ravi about the quality of production?