As the need for precision increases, so does the need for more precise measurement tools. While every machinist has his micrometer and gages, more and more shops are investing in the high-end advanced measuring devices — coordinate measuring machines (CMMs) and lasers.
In the 2006 AMERICAN MACHINIST Benchmarking Survey, 42.2 percent of all respondents said their shops use advanced measuring devices. As a machining-specific technique, the use of advanced measuring devices is substantially more common than multitasking (38.4 percent), prefixturing (38.4 percent), multiple pallet changers (28.9 percent), proprietary software (25.2 percent), multiple spindle machines(21.5 percent) and five-axis machining (19 percent).
Advanced measuring devices are almost as common as maximizing machine cutting (47.1 percent), tooling presets (46.3 percent), chip-removal systems (45.0 percent) and maximizing machine uptime (45 percent).
What is most interesting is that 54.9 percent of the top shops used advanced measuring devices while only 38.7 percent of all other shops did.
CMMs and lasers are used for dimensional measurement, profile measurement, angularity or orientation measurement, depth mapping, digitizing or imaging and shaft measurement. The machines are available with features such as crash protection, the ability to program offline, the ability to use for reverse engineering, temperature compensation and CAD-model importing capability. They come in a wide range of sizes and styles with a broad range of probe options, and can be operated manually or by computer software. Typical configurations are benchtop, free-standing and hand-held or portable.
CMMs have four main components: the machine itself, a measuring probe, a control system and measuring software. Measuring probes can be either mechanical, optical or laser. When optical and laser probes are used on a CMM, they change the CMM to measuring microscopes or multi sensor measuring machines.
In 1994, the international standard ISO 10360 "Acceptance and reverification tests for coordinate measuring machines" was established. This standard describes detailed test procedures for the various applications of a CMM such as length measurement, form inspection, the use with and without a rotary table, continuous scanning and multiple-stylus probing. The standard also contains a useful vocabulary. The old German standard VDI/VDE 2617 and U.S. standard B89 are used by some CMM manufactures, but potential customers should request machine specifications in the ISO 10360 standard so that performance of different CMMs can be accurately compared.
While the AMERICAN MACHINIST Benchmarking Survey indicates the percent of shops using advanced measuring devices, it did not address how those devices were used or how they specifically impact shop performance and profitability. Data on the performance of shops using and not using advanced measuring devices was cross tabulated with shop performance measurements such as amount of scrap and rework, finished product first-pass quality yield, customer order lead time, on-time completion rate and net profit margin. The cross tabulations indicate that shops using the advanced measuring devices have seen performance improvements over the last three years equal to or better than the performance improvements of shops that do not use such devices. However, because there are so many factors that influence those performance measurements, the results of the cross tabulations are not conclusive.
The survey does indicate that the use of advanced measuring devices has become an important adjunct to machining techniques, especially in the top performing shops. While the survey does not specifically say how they impact shop performance, as with any other tool, the ways that CMMs can be used to improve productivity depends on the individual shops, the creativity of its managers and the special needs and circumstances in which they are used.
