Precontrol Chart could improve "first shot" quality control

Nowadays, many companies practice short run production. In this sense it is a good policy to have a tool to ensure that the first produced part is in design specification for every critical parameter ...

Two charts are particularly designed to do the job: Specification Chart and Precontrol Chart. Both should have place into every Quality Software. I have started with Precontrol Chart  and release (b1.02) was first to incorporate it.

Bellow is the first stage of a typical work-flow. Starting point is to set up the parameters in Pick Report pop-up form. If "Tgt Cp:" value is set to 0.00 the application would launch Precontrol Chart. Otherwise, will execute Specification Chart.

If the drop-down list points "All" parameter then generated chart will use collected data for all cavities and will plot the values using one form. In this example, the values are filtered by period (Start and End Date) and by Variable RefN (WT - weight).

Clicking on Precontrol button will open the precontrol chart for all cavities  ...

Here, red lines represent Upper and Lower Specification Limits. Green lines are Precontrol Limits that divide Print Tolerance Zone into four equal zones. The blue line shows Nominal value. Using this type of chart the Quality Operator could get very good impression if the process is capable to produce part in limits from the start. If not, the process should be stopped and adjusted by the processor.

Because, the main goal is to set up the process in such a way, that every measured feature to fall into green zone, it is valid that for Cp=1 about 86% of produced parts iare expecting to fall between green lines and around 7% between green and red ones (named as yellow zone).

The model is based on book "Quality Control" sixth edition written by Dale H. Besterfield (pg. 230)

The application allows to launch the chart using only one cavity data. Thus, the plotted points are not so over-crowded. and can be easily analyzed.

The above plotted results are far from the target zone. Here is a chart which points appears to be placed perfectly ;)