Maintainability/Preventive Maintenance Analysis
DEFINITION
Maintainability Analysis is the method of determining how to best design a product for ease of maintenance. A Maintainability Prediction is the method of determining how long a product will take to be repaired once it fails. A Preventive Maintenance Analysis is the method of determining how often a product will need to be maintained periodically in order to keep it in good working order.
SITUATION
Whenever a product can be repaired after it fails, and whenever preventive maintenance is required on a product, we need to put some thought into how to design the product for maintenance.
OBJECTIVES
To use these analytical tools to help design a product for ease of maintenance.
VALUE TO YOUR ORGANIZATION
Opportunities for failure can occur during maintenance as well as during operation. By making the product easier to maintain, we are effectively improving its reliability.
RELIABILITY INTEGRATION
An example of Reliability Integration during Preventive Maintenance is as follows:
Performing HASS on spares in conjunction with Preventive Maintenance
Performing Preventive Maintenance/parts replacement on subsystems that have no wear-out mode, or too soon before the subsystem goes into wear-out mode can actually reduce the reliability because we will be taking out a part in its steady state failure period (bottom of bathtub curve) and replacing it with one at the infant mortality period (left-most part of bathtub curve). One way around this is to perform HASS on the subsystem prior to shipping as a spare.
METHODOLOGY
Maintainability Analysis
The Maintainability Analysis primarily focuses on how easy a product is to repair once it fails. This is closely related to the Human Factors Analysis because a large part of the repair process involves the user. During this analysis, we will analyze your product for ease of maintenance and calculate the Mean Time to Repair (MTTR) for your product, a measure of the average repair time. This is calculated by averaging the repair times for each individual replaceable assembly, weighted by failure rate.
The main components that go into this calculation are
- time to detect and isolate a failed assembly;
- time for user to replace the assembly; and
- time to validate the repair was successful.
Preventive Maintenance
be replaced on a continual basis. This analysis will calculate how often these products should be replaced and tie it back into the maintainability analysis to determine the overall cost of maintaining the product in the field.
These services can be closely tied to the Failure Modes, Effects and Criticality Analysis (FMECA) service or they can be performed independent of the FMECA.
CASE STUDIES/OPTIONS
The following case studies and options provide example approaches. We shall tailor our approach to meet your specific situation.
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Calculating Maintenance Times to Determine Spares Requirements
For a Semiconductor Manufacturing Equipment company, we calculated their maintenance times, both unscheduled as well as scheduled, to determine how many spares to keep on site.
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Calculating Availability and Mean Time to Repair (MTTR)
A Networking company had a high availability target to hit and, therefore, the Mean Time to Repair (MTTR) was critical and had to be calculated accurately. For this, we calculated each of the elements that go into the MTTR – Isolation time, diagnostic time, repair and replace time, and checkout time.
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Using What-If Analyses to Improve Availability and Mean Time to Repair (MTTR)
A Military subcontractor had a high availability target and found that they were not meeting their target. We determined the highest MTTR elements and then developed some “what-if” scenarios to improve the time.
