Dasarathi G V
Director in Leanworx
Dasarathi has extensive experience in CNC programming, tooling, and managing shop floors. His expertise extends to the architecture, testing, and support of CAD/CAM, DNC, and Industry 4.0 systems.
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- Machine downtime in a typical CNC shop floor can be anywhere between 20 to 50 %.
- The lower number in mass production and the higher one in small batch production with frequent setups.
- Working 3 shifts, this translates to between 5 to 12 hours a day. That’s HUGE.
- Good news: CNC machine monitoring software can cut machine downtime dramatically, at an extremely low cost.
CNC monitoring software – benefits in machine downtime and production
1. CNC machine downtime due to work ethics issues: This includes starting production late at the beginning of the shift, stopping production early at the end of the shift, extended meal breaks, sleeping in the night shift, etc. If this totals 1 hour in each shift of 8 hours, that is 12.5 % of the total available time.
2. CNC machine downtime due to systems issues: Power shut downs, no raw material, machine breakdown, high setup times, accidents, etc.
The problem is that you cannot do anything about this because you do not know how much the downtimes are, and what their causes are. A machine monitoring system tells you this, and enables you to take corrective action. It helps you completely eliminate work ethics issues, and substantially reduce systems issues. In our experience with installations of our Leanworx machine monitoring system, we see a 25 % reduction in downtime in the first month itself. That’s 1.25 hours in mass production to 3 hours in batch production. Downtime details, downtime analysis and Pareto charts in the CNC machine monitoring software enable you to identify the top causes of downtime, focus on them and reduce downtimes.
3. Misuse of Feed rate override (FRO) on CNC: This is typically done to over-produce in the day shifts to compensate for under-production in night shifts. E.g., the FRO is set to 120% in shifts 1 and 2, or in the first half of the night shift. This reduces the surface finish, which may not be an issue in roughing operations but affects quality in finishing operations. It reduces the tool life. It can also affect chip breaking, because insert chip breakers are designed to operate between specific feed rate ranges. Another reason for FRO values other than 100% is that the operator reduces the feedrate for the trial part, and forgets to set it to 100 % for the regular production. The cnc production monitoring system can generate alerts when the cycle time deviates from the standard cycle time by a specified amount. The cycle time details report shows you cycle times of every cycle, so you can identify periods when FRO is not set to 100 %. The CNC machine monitoring software will give you shift-wise reports of downtime at the start and end of shifts, and big downtimes within shifts with no reason. You can use this to identify operators responsible for these, and correct their work ethics issues
4. Downtime due to excess part unload and load time
This is caused by the actual time to unload and load the part being more than the standard time that has been assigned. E.g., the standard part unload-load time is 30 seconds, but it is actually taking between 1 and 2 minutes on the machine. This adds up to a large amount of downtime over a shift. The cause could be a poorly trained operator, or operator fatigue as the shift progresses because the part is heavy. The problem can be fixed by operator training or providing mechanical aids (like a crane). The CNC machine monitoring software will give you details of every cycle, with the cycle time and part unload-load time. Reports will be shift-wise, with the operator assigned to the shift. You can use these reports to reduce the downtime caused due to this reason.
5. Downtime due to high setup times
This happens when the actual setup time during a part change is more than the standard time allotted. The cause may be a poorly trained operator, poorly designed fixtures, etc. The fixes could be operator training, better fixtures that can be located and clamped on the machine faster, modular tooling, quick-change tooling, probing system for faster work offsets determination. The CNC machine monitoring software will show you the actual and planned setup time for each setup, to enable you to focus on the high setup times and eliminate their cause.
6. Rejection loss
Part rejections result in loss of raw material, and loss of CNC machining time. The cost of the machine time also includes the cost of all operations that have preceded the operation in which the rejection happened. Rejections may be because of a poorly trained operator, a machine that does not have the process capability to produce the part, bad tooling, etc. Reports from the monitoring software tell you when the rejections happened, who the operator was, etc. This will help you narrow down to the cause of the rejections, eliminate them, and reduce rejection losses.
These benefits of monitoring your CNC machine translate to one or more of these, all of which increase the OEE and profits :
1. Increase your profits Your production has gone up, buy investment is the same, resulting in a direct increase in profits.
2. Produce more with the same number of machines Avoid buying new machines to add capacity. Instead of buying more machines to increase capacity, you have improved the utilization of the existing machines at a fraction of the cost of new machines.
3. Reduce the number of machines for the same production If your orders are inflexible and there is no necessity to produce more, you can reduce the number of machines. This translates to less floor space, less power consumption, fewer personnel.
4. Avoid running in the night shift In a number of shop floors, it is common to see machines idling for up to half the night shift. This means you are actually running only 2.5 shifts. If you can downtime by 25 %, you can increase production in the first and second shifts and eliminate the night shift. Leading to less power consumption for the machines and for the lighting, and fewer personnel.
CNC machine monitoring solutions - cost-benefit
You can get good CNC machine monitoring solutions for Rs. 80 per day per machine. Here is a list of machine types, and how much downtime you need to reduce per day to break even with the system. MHR is the machine hour rate.
CNC lathe (MHR Rs. 200): 22 minutes.
CNC VMC (MHR Rs. 600): 8 minutes
CNC HMC (MHR Rs. 1000): 5 minutes.
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