control limits

process out of control but with a very widen spec limits thats why though ur process is meeting customer expectations but not under control… check if there is any process change? check if the baselines needs to be revisted…probably u could also be clubbing two different processes in same control chart.

data from two process can be represneted by bimodla distribution having 2 or more peaks in histogram .
 
FYI
 
Regards
Amit

dimi,
 
Overly narrow control limits, with a large # of OOC data points, is a potential indication of poor subgroup selection and/or autocorrelation in the data.  Another potential contributing factor could be the number of data points being used to create the points that are ultimately plotted this would magnify the impact of poorly selected rational subgroups.
 
Are you using Xbar-R or Xbar-S?  Have you assessed the process data to understand where the independent variance component lies?  Tools that can help provide this insight include:  Multi-vari studies, COV/REML, and GLM analysis.
 
Regards,Erik

dimi,
I suspect you are using binomial data with very large sample sizes.
I suggest you follow the advice of Dhananjay at post your data here so we might help.
Happy Holidays,
Dr. Scott

Without specific data, I say you are suffering from one or two classical situations, overcontrol and / or measuring nearly identical parts.
Overcontrol:  one reading, one adjustment (lots of points are out of control, 50% above the control limit and 50% below).  Operators are trying too hard to control the process based on one reading.  Try this, never make a process adjustment based on inidividual readings.  Only, adjust if the subgroup average is out of control.  If you are in an overcontrol situation, statistically, you do not know what your process looks like.  You need to instruct your folks to not make any adjustments for 2 days.  Let the process define itself. 
Measuring nearly identical parts.  Once set up, in the short run, the process will produce nearly identical parts, R is nearly zero, hence the control limits will be very narrow.  If this happens, you will throw your process into an overcontrol condition.  If your process is producing nearly identical parts, then you do not need to monitor your process.  You need to monitor your set up, nominal is best.