Page 55 - MetalForming April 2016

Shops schedule PdM tasks based on gauging deteriorating operating con- ditions or rate-of-decay. With this strat- egy, periodic or continuous monitoring detects the onset of wear or degrada- tion. Technicians use this information to predict potential problems and schedule the required maintenance.
An example: installing force trans- ducers behind punches to monitor punching forces. As punch points wear, the force required to produce the required hole increases. A critical force, established for each punch, can be used to signal the press technician to sharpen or replace a punch or series of punches.
PdM and PM represent very differ- ent strategies, even though the two terms often are used interchangeably. PM plans prescribe time-based activi- ties (number of cycles, number of hours, etc.), while a PdM plan com- prises event-based activities deter- mined through the acquisition of data (force, temperature, vibration fre-
quency, signature analysis, etc.). Reliability-centered maintenance (RCM), or proactive maintenance, is an extension of PdM that seeks to improve process performance in addi- tion to maintaining the equipment. RCM practices focus on determining the root causes of maintenance fail- ures and dealing with those issues before problems occur. Shops might even perform maintenance on healthy equipment, to improve performance and save or make more money. Rigor- ous use of proactive maintenance can actually make maintenance profitable.
Here’s an example:
The press shop’s PM schedule requires
changing or sharpening punches every 50,000 hits. It undertakes process improvements to improve punch life and reduce tool-maintenance costs. It finds that by investing in higher-qual- ity powdered-metal tool steel and by applying an engineered surface coat- ing, punch life increases to 100,000 hits between maintenance.
Pretty good, but by practicing RCM the shop can do better. For example, design of experiments and root-cause analysis might reveal that most of the punch wear occurs due to excessive tipping moments, caused by large clearances in the press connections and slide-guiding system. Mainte- nance on the press restores the machine clearances to factory specifi- cations, reducing slide tipping to with- in acceptable limits and, in turn, reducing punch wear. As a further cost savings, the toolroom replaces the expensive powdered-metal tool-steel punches with the original high-speed- steel punches, and eliminates the added surface coating. At the same time it maintains 200,000 hits between maintenance.
To learn more about tooling and press maintenance, attend PMA’s Die Maintenance and Press Maintenance seminars in Nashville, TN, May 3-5, 2016. To register, visit: www.pma.org/ meetings. MF
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