NOTE 1 Direct testing aims to investigate individual machine tool properties, such as geometric or positioning accuracy. Short-term capability evaluation is meant to prove that a machine tool has the capability to fulfil a specific process task. It is, therefore, important to recognize that the short-term capability test is focused only on the manufactured product. This means that direct testing methods are more suited for the determination of error sources on the machine tool and for deriving constructive improvements of a machine tool that is used in a wide production spectrum; a short-term capability test is less suited for detection of error sources of the machine tool. Therefore, it is expected that short-term capability evaluation for the acceptance of metal-cutting machine tools in machining processes be primarily carried out on workpiece-dependent special-purpose machines, e.g. working stations of transfer lines, with a process-determined cycle time of less than 10 min, so that at least 50 workpieces are manufactured in one shift as the statistical uncertainty increases strongly for a smaller number. In principle, short-term capability evaluation can also be performed on universal machine tools, such as machining centres used for large batch production if they meet the above-mentioned statistical requirements.
NOTE 2 The term “short-term capability”, which is a widely used term in machine tool industry, corresponds to the term “process performance index” specified in ISO 3534‑2:2006 for normal distribution.
