Probabilities in safety of machinery – risk reduction through fixed and moveable guards by standardized impact tests, part 2: possible improvements with FE impact simulations

Beginning with the development of the European machinery directive, international standards concerning the safety of machine tools have been constantly updated, improving the ballistic protection of safety guards. Nowadays, the main characteristics of the guard taken into account for a safe design are material and thickness. Type C safety standards for machine tools and type B safety standards for safety guards prescribe tests with given penetrators and impact energies that have to be retained by a flat safety guard. Specific customer requirements, a style-oriented machine tool design or further evolved safety requirements lead to a large variety of machine tool safety guards in the market. They often possess considerable differences in size, fixing and shape when compared to the test patterns defined by the relevant standards. For each of these differing parameters, significant influences on penetration resistance have been determined. While the simplification of test conditions was inevitable to make a harmonized standardization and an effective experimental dimensioning process possible, nowadays FE simulations offer the possibility to analyze far more cases with reasonable costs. For this, FE models reproducing standardized tests for woodworking (INAIL) and metalworking (IWF) machine tools will be presented and compared to experimental results. Then a model which focus is on clamping of the test pattern is presented. This allows the authors a detailed analysis of how appropriate the clamping is and of possible integration of FE simulations in the dimensioning process of machine tool guards. The posed FE impact simulations are used to give a first answer to “real world” problems which are difficult to test such as the dispersion of standardized test results due to projectile inclination. Also, quantitative values of the influence of the overlap on the impact test results with non-square windows will be analyzed. Indications for required design parameters of safety guards are given.