Scenario
At the end of each month, equipment engineers fill out a downtime report listing over 30 breakdown records, which they submit to their supervisor for archiving. The next month, the same problems recur and are recorded again.
Downtime records exist, but no one ever analyzes them. This report merely documents history without preventing future occurrences.
Correct Classification of Downtime
Classification is the basis of analysis; incorrect classification renders analysis meaningless.
| Downtime Type | Definition | Included in OEE Loss? |
|---|---|---|
| Unplanned Breakdown | Sudden equipment failure | Yes (Availability Loss) |
| Planned Maintenance PM | Scheduled preventive maintenance | No (Planned Downtime) |
| Line Changeover / Mold Changeover | Product type switching | Yes (Performance Loss) |
| No Order Standby | No production demand | No (Demand Loss) |
| Waiting for Materials | Materials not arrived | Yes (Availability Loss) |
| Waiting for Operator | Insufficient manpower | Yes (Availability Loss) |
Only after clear classification can one identify which type of loss is largest and who should be responsible for improvement.
Using Pareto to Find the Most Costly Problems
Step 1: Compile the total downtime hours for each failure cause (monthly or quarterly)
Step 2: Sort in descending order and plot a Pareto chart
Step 3: Identify the top few causes responsible for 80% of the total downtime hours
Typically, the top 3 causes account for 70-80% of downtime. By resolving just these top 3, overall OEE can be significantly improved.
Calculating Downtime Cost
To secure resources, downtime problems must be quantified in monetary terms:
Downtime Cost = Downtime Hours × Hourly Production Loss
Hourly Production Loss = Standard Output × Unit Gross Profit
Example: Machine standard output 100 units/hour × Gross profit $50/unit = $5,000/hour
Monthly downtime 40 hours = Monthly loss $200,000
Using this figure to apply for improvement budgets is far more convincing than simply stating "the machine often breaks down."
From Downtime Analysis to FMEA Prevention
After identifying high-frequency, high-cost failure modes, conduct FMEA analysis:
- Identify Failure Mode: e.g., "Bearing Overheating"
- Find Potential Causes: insufficient lubrication, cooling failure, overload
- Evaluate Effects: downtime hours, impact on downstream production lines
- Calculate RPN = Severity × Occurrence × Detection
- Prioritize high RPN items for developing preventive measures (PM, sensors, operating SOPs)
Golden Quote
"Downtime records are not historical archives; they are signals from your equipment telling you where problems exist. Organize these signals into a Pareto, and you will know exactly where to allocate this year's equipment budget."