Understanding Different Maintenance Strategies: PM, CM, PDM, TPM, RCM, and SMED

Posted on Aug 22, 2024 in Other subjects

Preventive Maintenance (PM)

Preventive Maintenance (PM) encompasses activities performed on plant equipment, machinery, and systems before failure occurs. This proactive approach aims to protect assets and prevent or eliminate performance degradation.

Definition: Maintenance carried out at predetermined intervals or according to prescribed criteria, intended to reduce the probability of failure or degradation and limit the impact of any issues.

Importance of MTBF (Mean Time Between Failures)

A key metric in PM is MTBF. Selecting the right PM activities is crucial:

  • Routine Maintenance: Repetitive and periodic activities like lubrication, cleaning, and minor adjustments.
  • Running Maintenance: Activities performed while the machine or equipment is operating, often as precursors to actual preventive maintenance.
  • Opportunity Maintenance: Leveraging unplanned opportunities during scheduled maintenance on other equipment.
  • Window Maintenance: Activities performed during a planned downtime window when the machine or equipment is not needed.
  • Shutdown Preventive Maintenance: Activities performed during a complete production line stoppage.

Advantages of PM:

  • Satisfies most maintenance objectives.
  • Ideal for machines and facilities where failure would cause significant production losses.
  • Includes replacements, adjustments, major overhauls, inspections, and lubrication.

Factors Affecting PM Efficiency

  • Adequate staffing in the maintenance department.
  • Choosing the right equipment for the working environment and workload.
  • Proper staff qualifications and training.
  • Executive management support and commitment.
  • Effective planning and scheduling.
  • Proper implementation of the PM program.

Age-Related Failures Curves

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Random Failures Curves

Random failures often outweigh age-related failures.

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Key PM Activities:

  1. Operational, visual, or automated checks
  2. Lubrication, filtration, or servicing
  3. Inspection, functional checks
  4. Restoration
  5. Discard

Corrective Maintenance (CM)

Corrective Maintenance (CM) involves actions like repair, replacement, or restoration after a failure occurs. The goal is to eliminate the failure’s root cause or reduce its recurrence.

Types of Corrective Maintenance:

  • Remedial Maintenance: Eliminating the failure source without interrupting production. This often involves taking the faulty item offline and replacing it with a reconditioned one or transferring its workload to a redundant system.
  • Deferred Maintenance: Delaying corrective actions until a time that minimizes disruption to the production process.
  • Shutdown Corrective Maintenance: Performing corrective actions during a complete production line stoppage.

Objectives of Corrective Maintenance:

  • Maximize the effectiveness of critical plant systems.
  • Eliminate breakdowns.
  • Eliminate unnecessary repairs.
  • Reduce deviations from optimal operating conditions.

Key Differences:

  • CM vs. PM: Corrective maintenance reacts to failures, while preventive maintenance aims to prevent them.
  • CM vs. Run-to-Failure Maintenance: Corrective maintenance is planned and scheduled, while run-to-failure maintenance waits for a failure to occur before taking action.

Steps in Corrective Maintenance:

  1. Fault detection
  2. Fault isolation
  3. Fault elimination (adjusting, aligning, calibrating, reworking, removing, replacing, or renovating)
  4. Verification of fault elimination

Disadvantages of CM:

  1. Requires accurate identification of incipient problems.
  2. Effective planning relies on skilled planners, a comprehensive maintenance database, and readily available resources.
  3. Needs proper repair procedures, adequate repair time, and verification processes.

Predictive Maintenance (PDM)

Predictive Maintenance (PDM) focuses on detecting changes in equipment condition (signs of failure) to perform maintenance proactively and maximize service life without increasing failure risk.

Types of Predictive Maintenance:

  • Condition-Based Predictive Maintenance: Relies on continuous or periodic condition monitoring equipment to detect signs of failure.
  • Statistical-Based Predictive Maintenance: Uses statistical data from meticulous stoppage records to develop failure prediction models.

Key Difference: PDM vs. PM

PDM uses real-time condition monitoring to determine the actual mean time to failure, while PM relies on industry average life statistics.

Common PDM Techniques:

  • Visual inspections
  • Vibration monitoring
  • Thermography (temperature monitoring)
  • Ultrasonic testing
  • Lubricant analysis
  • Electrical condition monitoring
  • Nondestructive testing

Total Productive Maintenance (TPM)

Total Productive Maintenance (TPM) elevates maintenance to a core business function, emphasizing proactive and planned maintenance to minimize unscheduled downtime and maximize equipment effectiveness.

Key Goals of TPM:

  • Zero failures
  • Zero defects
  • Zero breakdowns
  • Zero accidents

Overall Equipment Effectiveness (OEE)

TPM often involves calculating OEE, which considers availability, performance, and quality. Improving OEE is a key indicator of successful TPM implementation.

Advantages of TPM:

  • Maintains product quality
  • Increases production uptime
  • Reduces operating costs
  • Reduces machinery requirements
  • Ensures equipment capability
  • Enables rapid problem solving
  • Facilitates 5S implementation

Disadvantages of TPM (Before Implementation):

  • Excess inventory
  • Slow lead times
  • Suboptimal quality
  • Higher costs compared to competitors
  • Lower capacity
  • Difficulty capturing new business
  • Requires significant time and commitment for successful implementation (at least two years)
  • Needs deep involvement from personnel, organized templates, and comprehensive training

TPM Implementation:

The goal is to minimize maintenance time while maximizing effectiveness. TPM often involves distinct pillars or phases, including autonomous maintenance, planned maintenance, quality maintenance, focused improvement, early equipment management, training and education, and safety, health, and environment.

TPM Tools and Techniques:

  • Cleaning maps
  • F-tags
  • F-tag log sheets
  • Initial training
  • Failure maps
  • Failure classification (Pareto analysis)
  • 5 Whys
  • Fishbone diagrams
  • Fault tree diagrams
  • OCAP list

Reliability Centered Maintenance (RCM)

Reliability Centered Maintenance (RCM) is a systematic approach that combines reactive, preventive, and predictive maintenance strategies. It prioritizes reliability and considers the consequences of failure. Developed in the aviation industry, RCM is known for its cost-effectiveness.

Key Principles of RCM:

  1. Systematic process
  2. Focus on reliability and failure consequences
  3. Use of decision diagrams
  4. Determination of maintenance requirements based on the operating context

Characteristics of RCM:

  • Systematic and analytical
  • Prioritizes reliability and minimizes failure consequences
  • Employs decision diagrams for analysis
  • Considers the operating context of assets
  • Focuses on reliability and consequences of failure
  • Adapts to changes in equipment life cycle
  • Requires engineering expertise for planning and implementation
  • Often incorporates 5S principles

RCM Implementation:

RCM involves a thorough analysis of equipment and potential failures, considering the consequences of each failure and determining the most effective maintenance strategy. It often utilizes databases and standards like SAE JA1011.

Objectives of RCM:

The primary objective is to optimize maintenance and achieve the highest level of reliability at the lowest possible cost. While the planning phase can be time-consuming, implementation is typically rapid.

Single-Minute Exchange of Die (SMED)

Single-Minute Exchange of Die (SMED) is a lean manufacturing technique aimed at drastically reducing the time required to changeover production equipment from one product to another. The goal is to achieve changeovers in a single-digit number of minutes (less than 10 minutes).

SMED Process:

  1. Create a SMED Team: Assemble a dedicated team to focus on the SMED process.
  2. Select the Target Tool/Machine: Choose a tool or machine with a long changeover time, a bottleneck in the process, or one that requires frequent changeovers.
  3. Document the Current Process: Thoroughly document the existing changeover process, including task allocation, photographs, and videos.
  4. Create a Gantt Chart (Bar Graph): Calculate element times in seconds and plot the data on a Gantt chart to visualize the changeover process.
  5. Define a Target Time: Set a realistic target time for the changeover process and establish a timeline for the project.
  6. Analyze the Elements: Categorize each element as internal (requiring the machine to be stopped) or external (can be done while the machine is running). Convert internal elements to external whenever possible and reduce the time for all remaining elements.
  7. Repeat the Exercise: Continuously improve the changeover process through repeated analysis and optimization.

Benefits of SMED:

  • Reduced downtime
  • Increased production flexibility
  • Lower inventory levels
  • Improved responsiveness to customer demand
  • Increased overall equipment effectiveness (OEE)