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Inspection/Measurement 18 MoldMaking Technology —— FEBRUARY 2018 Machine and process monitoring technology can monitor both machines and machine processes by detecting broken tools and mitigating crashes while providing vital data on the condition of machine components to support predictive and preventive maintenance. By Jorge L. Peña-Mena Low-Cost Machine and Process Protection E very shop deals with two universal truths: People are part of the process and make mistakes, and sooner or later, all mechanical devices will either wear out or break. The consequences of both truths can range from merely expensive to catastrophic. A modest investment in machine and process monitoring technology can, and nearly always does, pay large dividends over the long run in sparing moldmakers from the consequences of human error and the breakdown of machines. Sensors 101 Modern sensor technology comes in one of two forms: micro electro-mechanical systems (MEMS) and piezoelectric devic- es. Each has a distinct set of capabilities and advantages for machine monitoring applications. MEMS sensors are miniature machines with integrated electronics that are produced by technologies similar to those used in the manufacturing of semiconductor devices. Because MEMS sensors are highly reliable and are relatively inexpensive, they are widely used in all sorts of electronic devices where their small size, low consumption of power, ease of integration, high level of functionality and superb performance encourage and enable innovation. The major advantage of a MEMS sensor in a machine- monitoring application is its ability to detect vibration at extremely low amplitudes. For example, a MEMS sensor can detect vibration in a spindle rotating at speeds as low as 2 rpm. Because the signal processing electronics are integrated into a MEMS sensor, MEMS sensors also tend to be less expensive than comparable piezoelectric units. Piezoelectric sensors use the current that is generated by deforming a crystal to measure the amplitude of a vibration. Piezoelectric sensors are not able to detect low amplitude vibrations nearly as well as MEMS devices. They deliver a non- linear response in that region. However, piezoelectric sensors are extremely rugged and are able to survive crashes generat- ing up to -70 Gs, while most MEMS sensors experience damage at about -18 Gs. A further advantage of piezoelectric sensors is their ability to respond to vibration and acceleration in three axes instead of one or two for MEMS devices. The combination of rugged- ness, 3D sensing, and the ability to serve as both a vibration and crash detection device make piezoelectric sensors the technology of choice for most large machine tools. Vibration Analysis While acceleration sensing is the key to crash protection, vibration detection provides the critical inputs for machine- condition monitoring. Every component of a machine tool generates a characteristic vibration profile, which changes predictably over time as it experiences normal wear. By peri- odically measuring the vibration profile and comparing the A modest investment in machine and process monitoring technology can help alleviate the expensive or catastrophic consequences of human and equipment limitations. Image courtesy of Marposs.