This article explains how SMT manufacturers analyze time and productivity for manufacturing machines and assembly lines using Machine Utilization (MU), Line Utilization (LU), and other key metrics including Availability, Performance, and Quality. This article provides a top-down explanation. For a bottom-up explanation, see How Global KPIs Solution Calculates SMT Manufacturing KPIs for Line Utilization (Bottom-Up Explanation).
Vendor Theoretical Targets
Machine vendors define theoretical target throughput rates for their machines. For example, the vendor "BusyBot" might say that their ChipBot 1000 model Pick and Place machine with a 200X head has a Theoretical Target of 200,000 Chips Per Hour (CPH).
Manufacturer Derated Targets
Machines rarely perform at vendor theoretical throughput rates. In practice, manufacturers define their own "derated" (reduced) target rates based on factors like the results of their own internal performance testing, whether the machine is being used on a New Product Introduction (NPI) or Production line, and/or what kind of product the machine is manufacturing. For example, the manufacturer might assign a BusyBot ChipBot 1000 with a 200X head a (derated) Target of 150,000 CPH when used on a Mass Production (MP) line.
Machine Utilization (MU)
Machine Utilization calculates what percentage of its derated Target output the machine produced during a period of time.
Target production during a period of time is the derated Target rate times the period of time. We assume that the machine running continuously at full speed 24x7 with no breaks, slowdowns, or downtime, so this is different than Overall Equipment Effectiveness (OEE) that compares output against the scheduled production time. In our example, Target production of the ChipBot 1000 would be:
Daily Target production = 150,000 CPH * 24 hours = 3,600,000 placements
Weekly Target production = 150,000 CPH * 24 hours/day * 7 days/week = 25,200,000 placements
So if the BusyBot in reality made 1,200,000 placements during a day:
Machine Utilization % = 1,200,000 placements / 3,600,000 placements * 100 = 33%
Line Utilization (LU)
Line Utilization is exactly like Machine Utilization, but it is applied to an entire line instead of a single machine. It measures what percentage of the (derated) Target output the Line produced during the period of time.
In our example, if there were two other BusyBot ChipBot 1000s with 200X heads on the line and one did 800,000 placements and the other did 1,000,000 placements:
Line Utilization % = (3 million placements) / ((150,000 CPH + 150,000 CPH + 150,000 CPH) * 24 hours) * 100 = 27.7 %
"All Time" is the 24 hour day. Availability is measured against Planned Production Time (PPT). So a manufacturer first defines the scheduled working shifts for the day and any planned breaks like lunch our or scheduled maintenance.
For example, let's say Manucom International has two shifts of 8 hours on their SMT assembly line and each shift gets a one hour lunch break. On Monday, there's also one hour of scheduled maintenance. So on Monday:
Planned Production Time = 16 hours - 3 hours = 13 hours
After work begins, one hour is lost for unscheduled maintenance because a part breaks. So:
Actual Production Time = 13 hours - 1 hour = 12 hours
Therefore the Availability percentage is:
Availability = Actual Production Time / Planned Production Time * 100 = 92%
Target Throughput for the Line of three ChipBot 1000s would be:
13 hours * (150,000 CPH + 150,000 CPH + 150,000 CPH) = 5,850,000 placements
However, in reality, the line didn't run continuously at top speed for all 13 hours. There were various short breaks. The Line actually made 4,800,000 placements. So:
Performance = 4,800,000 placements / 5,850,000 placements * 100 = 83%
99% of finished products passed inspection at the Automatic Optical Inspection machine, so Quality was 99%.
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