STABILITY ANALYSIS OF THE TECHNOLOGICAL PROCESS OF MECHANICAL WOOD PROCESSING USING CONTROL CHARTS

Abstract

This paper presents a quality control tool, that is, a quality control method, which in this case concerns
the mechanical processing of wood, but in general, it can be implemented in any form of production (mechanical
engineering, traffic, food technology...). The goal of the research is to show the way of applying the control chart
method, that is, to determine the stability of the technological process of mechanical wood processing in order to be
able to define appropriate corrective measures in order to improve that part of the production process. The control
chart that was created in this paper is a graph consisting of a horizontal (abscissa) and a vertical axis (ordinate). The
order of observations is plotted on the abscissa, and the corresponding values on the ordinate. Apart from the
precise creation of control charts, their correct interpretation is also of great importance. It is easiest to interpret
control charts where the process is "outside statistical control", that is, the process where the values of individual
measurements are outside the control limits. This means that some special cause of variation is present in the process
and an adjustment needs to be made. However, placing all points within the control limits, that is, obtaining a
control map on which the process is "within statistical control", does not necessarily mean that such a process is
acceptable by statisticians. On the basis of the results, that is, on the basis of the graph that has the shape of a broken
line, we observe whether the control limits have been exceeded, and we draw certain conclusions about the stability
of the process. If the graph is between the control limits, we can conclude that our process is stable and under
control, that is, that our quality variation is within normal limits. If there are any jumps, ie. if some value in some
observation is out of bounds (above the upper control limit or below the lower control limit), then we conclude that
our process is not stable, not under control and that our quality variation is not within normal limits. In that case,
certain corrective measures were proposed, which should improve the technological process of mechanical wood
processing and bring it under control.
Control charts, as an engineering-mathematical tool, are a very suitable tool for achieving the goals of statistical
control. Optimal application of control charts ensures constant monitoring of the process, direction towards the
desired flow and undertaking of possible corrective measures. Also, their application ensures the fulfillment of the
designed or required quality characteristics, that is, the fulfillment of the requirements of a certain standard. With
their simplicity of application and reliability, they provide users with convenience in work and relevant process
indicators, and provide process controllers with valid data about the process flow. As such, they represent a tool that
keeps the entire process within the given limits.