In an engineering company, one of the machine centres is scheduled for two shift operations at the rate of 8 hours per shift. The time allowed for changing tools, shift breaks, direct plant maintenance activities, etc. is 1 hour per shift. Thus, the planned up time is 14 hours a day and 336 hours per month. The maintenance manager has analysed the downtime data for the last three months and found out that the machine centre has stopped for 262 hours due to various breakdowns distributed on 89 occasions. The production manager reported a production of 4,576 pieces during the above-mentioned period. The theoretical cycle time for producing each piece is 6 minutes and actual cycle time is 8 minutes. The quality control department rejected 456 pieces as they did not confirm to the prescribed standards.
It was also found that the failures causing the downtime were distributed as follows:
Group 1: 25 per cent were due to incorrect operation.
Group 2: 55 per cent were due to incorrect lubrication and bad adjustment.
Group 3: 20 per cent were due to sudden failures such as broken shafts and fuses.
The downtime was found to have the following time components:
Time to find the failure: 10 per cent Time to find spare parts, tools and drawings: 20 per cent Time lost for want of spare parts: 25 per cent Waiting for personnel: 5 per cent Repair time: 40 per cent Five per cent of all maintenance jobs were planned and 95 per cent of the jobs were unplanned urgent repairs.
1. Calculate the overall equipment effectiveness (OEE) of the machine centre.
2. What is the availability?
3. What is MTTF?