Page 14 - MetalForming February 2019

Tooling by Design
By Peter Ulintz
Die Maintenance, at What Cost?
What are the actual costs for die maintenance in your organization? How do you measure them? And, do you think that die-maintenance costs should increase or decrease over time?
Actual die-maintenance costs remain unknown at many organizations because the work performed, die repair, not maintenance, often is intermixed or combined when it comes to cost tracking. As a result, management often sets internal goals to reduce die-maintenance costs.
However, I propose that management should want, and even expect, die-maintenance costs to increase over time. To understand why, let’s look at the four distinct types of maintenance programs:
• Reactive Maintenance
• Preventive Maintenance
• Predictive Maintenance
• Proactive Maintenance.
Reactive maintenance responds to a failed tool or defect
in the stamping. For example: An excessive burr caused by a chipped punch results in die restoration by sharpening or replacing the chipped punch and returning the die to pro- duction. This is nothing more than a repair activity, although many organizations have come to know it as “firefighting.”
Preventive maintenance consists of formal procedures and tasks that help prevent unplanned breakdowns and ensure that the tooling operates properly. The tasks and time intervals may be determined using owners manuals, industry best practices, technical handbooks, experience with similar processes or even a best guess.
Be aware that preventive-maintenance programs can have adverse consequences, such as over-maintenance. An example: a preventive-maintenance schedule that requires punches in a die to be changed or sharpened every 100,000 hits, even though the quality of the punch point has not degraded because, possibly, the stamped material resided at the low end of thickness and tensile-strength specifications. The second condition, under-maintenance, involves failure
Peter Ulintz has worked in the metal stamping and tool and die industry since 1978. His background includes tool and die making, tool engineering, process design, engineering management and advanced product development. As an educator and technical presenter, Peter speaks at PMA national seminars, regional roundtables, international confer- ences, and college and university programs. He also provides onsite training and consultations to the met- alforming industry.
Peter Ulintz
Technical Director, PMA pulintz@pma.org
Cost Savings via PPM
High
Cost of Downtime Overtime and Expedited Parts Shipment(s)
Cost of Repairs
Cost of PPM
Low
Amount of Predictive/Preventive High Maintenance (PPM) Performed
conditions not identified or corrected in a timely manner, resulting in broken die components. Stamping material at the high end of both thickness and tensile-strength limits may produce more off-center loading in the press, requiring punches to be sharpened more frequently than prescribed in the schedule.
Predictive maintenance uses actual equipment-perfor- mance data to determine when maintenance should occur, thus improving upon preventive maintenance. Predictive- maintenance tasks include those that can indicate deterio- rating conditions or rate-of-decay. With this strategy, in-die load sensors or strain gauges provide periodic or continuous monitoring to detect the onset of wear or degradation at a critical die station, providing information that helps predict potential problems and the best time for maintenance.
Note the difference between preventive and predictive maintenance. Though frequently used interchangeably, each term denotes a fundamentally different strategy.
1. Preventive maintenance: time-based (e.g., number of cycles, number of hours, number of days, etc.)
2. Predictive maintenance: event-based, determined through the acquisition of data (e.g., force, temperature, vibration frequency, etc.).
Proactive maintenance or reliability-centered mainte- nance, seeks to improve process performance in addition to maintaining the equipment. It focuses on determining the root causes of maintenance failures and dealing with those issues before problems occur, thereby serving as an extension of predictive maintenance. Rigorous use of proactive main- tenance can make maintenance activities profitable.
12 MetalForming/February 2019
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Total Cost: Repair and Maintenance