# Statistical Process Control

### Statistical Process Control

Standard Operating Procedure for inline Q. A, using Statistical Process Control charts OBJECTIVE To remove or minimize, cost of poor quality. SCOPE This procedure is applicable for all kind of critical points for which variable charts are being made to know about the process stability. RESPONSIBILITY 1) Q. A. Manager Q. A. Manager is responsible for allotting the critical points in a particular product to in line Q. A. ’s. 2) A. Q. M. A. Q. M. is responsible for carrying out the SPC effectively in their given lines.

He is also responsible to assist the in line QA’s in case of any difficulty. 3) In Line Q. A. ’s In line Q. A. ’s are responsible to fill the variable chart correctly and take appropriate actions required after depicting the charts. PROCEDURE ? One Variable chart is to be prepared against each critical point. ? Take 5 samples at random produced in a particular hour and start measuring critical points on each sample. ? Write down the measurement difference as per the size-measurement specification given on variable chart in the period of that hour. After the five pieces are inspected, find out the median and range of these five readings by the following method. o Arrange the data in ascending order and write down the third no. in the median array for that particular hour. o To calculate range note down the difference between the maximum reading and minimum reading of that particular hour. Write it down in the range array. ? Calculate Upper Control Limit and Lower Control Limit by using the following formula: o Calculate X Bar for previous days 8 hours reading by following formula

X1+X2+X3+X4+X5+X6+X7+X8 X = 8 Where X1 ….. X8 are the median readings for previous day 8 hour. o Calculate R for previous days 8 hours reading by following formula R1+R2+R3+R4+R5+R6+R7+R8 R= 8 Where R1 ….. R8 are the range readings for previous day 8 hour. o UCL and LCL for median chart will be calculated by the given formula: __ UCL = X+0. 691* R LCL = X-0. 691 * R o UCL and LCL for Range chart will be calculated by the given formula: UCL = 2. 14 * R LCL = 0 * R ? Now once limits of median chart as well as range chart are calculated start marking the points of median and range on the median and range graph respectively that to corresponding to that particular hour. ? If any point is found to lie outside the control limits, immediate action should be taken to bring the process in control. ? One point should be kept in mind that process should lie somewhere near central line. It means your process is stable and predictable.