Statistical process control, commonly known as SPC (Statistical Process Control)
is a set of techniques aimed at detecting variations in a production process and taking appropriate corrective actions in order to achieve an improvement in the quality of the product obtained.
The use of SPC boomed in the early 1980s, especially in the automotive sector.
As a consequence of the results obtained by the Japanese companies, the large
automobile manufacturers decided to adopt these techniques and demand the use of them from their suppliers.
As a consequence of this, it can be stated that for some years SPC became a fad that led to its abusive use, so the results obtained were not always good.
characteristics
It uses powerful statistical tools, which instantly process the collected information and alert to any sign of abnormality in the process, reducing the occurrence of waste and manufacturing downtime.
All SPC parameters are configurable, thus allowing its adaptation to the characteristics of any type of product and manufacturing process used in the company, even for forms of series or continuous production. It incorporates organization, classification and search tools, which provide simple and immediate access to data in the form of spreadsheets and graphs, making it possible to critically evaluate the degree of adequacy of the processes in relation to the specified objective.
What is it for?
Currently the SPC is applied more moderately, attending to a few basic considerations:
- The SPC should be implemented in those places where it is really possible to carry out actions as a consequence of the information obtained. A significant set of parameters to be controlled by SPC should be selected, as small as possible, so that the monitoring of this control is feasible with the human resources that are available.
In summary, the SPC should not be a bureaucratic tool that makes the process more expensive in exchange for providing us with useless information or that we do not have the capacity to analyze, but rather an effective aid that provides the right information to speed up decision making.
The SPC contributes to the cost reduction of organizations because it focuses on minimizing variation. The topics that, among others, are explained in the seminar are: the concepts of variation, control, adjustment and capacity; special and common causes; prevention against detection; R & R studies; measures of central tendency; graphs of XR, Xs variables; attribute charts p, np, u, c; precontrol charts; rules for determining statistical control and its interpretation and SPC for short runs.
SPC elements
- SPC studies are divided into different sections, which are detailed below. The modules common to studies by variables and by attributes are definition, data and a module that allows to visualize all types of graphs simultaneously. The graphs for studies by variables are XR or XS graph, histogram and Henry's line. By attributes are graph p, np, c or u, cumulative absolute pareto, cumulative absolute pareto, cumulative relative pareto, and cumulative relative pareto. All study data can be copied and pasted into the same or a different study. All graphics can be copied and then pasted into another application. There is the possibility to import and export data to ASCII files. XR / X-SS chart On the XR or XS chart,Control limits and optionally tolerance values are displayed. Subgroups with warnings are also indicated by a small red triangle in place of the green dot for subgroups without warnings.
Main Advantages
1. It allows “preparing the ground” for the subsequent introduction of data, so that the people who will take the data daily only have to worry about carrying out the measurement and checking the results to see if everything is going well or if there is any warning.
2. Clearly differentiate responsibilities, between the operator or flying inspector who performs the sampling and the person who sets the parameters (limits, tolerances,…) that mark the validity or otherwise of the data taken. In order to better define this difference in functions, the program enables the activation of a password system that guarantees that the process parameters will only be modified by authorized persons.
