Process variations are undesired changes in production processes that can affect final product quality characteristics. These effects can be seen as fluctuations in: edge size, edge shape, geometry (sagging), wing radius, optics, and residual stresses. Uncontrolled process variation has an effect on manufacturing processes, reducing repeatability, and causing fluctuation in quality and productivity. Additionally, uncontrolled process variation greatly increases the waste (scrap) rate. The influence of individual process variation varies from minor to significant. However, all existent variations contribute to the magnitude of effect and can create a negative synergy that potentially leads to greatly fluctuating end results and waste pieces. There are several sources of process variations within the gravity bending process, and sources must be defined, measured, analysed, improved and controlled - ideally to the point of elimination. These actions have an essential role in improving gravity bending process repeatability and reduction of waste. This article reviews the common sources of process variations within gravity bending systems and discusses the required actions to both control and eliminate these variations.
