Keep Machine Tools Running Smoothly with a Comprehensive PM Program |
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Spending hundreds of thousands of dollars on precision machine tools and then failing to properly take care of them doesn't make sense, yet many companies do just that by neglecting to implement and adhere to a thorough preventive maintenance program. PM takes time and money, but its advantage is noteworthy when you consider that the practice helps you protect your machine tool investment, avoid troublesome breakdowns and reduce down time. But it's not enough to implement just any preventive maintenance program. To give your system the best chance of success it should focus on preserving machine tool accuracy, which is best achieved by maintaining mechanical and lubrication systems, as well as electrical controls. Accuracy is at the heart of every machine tool's function. So preserving it is critical and there are several factors to be considered in doing so. First, remember that each machine tool has certain design limitations and staying within these can significantly extend its life and aid in maintaining parts accuracy. Too often, machine tools are pushed beyond the limit on every cut. Not only does this reduce accuracy, but these machines usually fail frequently and catastrophically. Shops that routinely overload their machine tools risk excessive down time and major remedial repairs. Avoid overloading and stay within the manufacturer's guidelines for work piece weight. Also, keep spindle loads at or below 80 percent. The pay-off for these practices will be a boost in machine up-time. Cleaning machine tool guide-way systems is another simple task to help maintain machine tool accuracy. On most machine tools, the ways are protected by wipers and/or way covers. These components must be checked frequently and repaired or replaced as necessary. Removing chips from the ways should be a priority. Inspect way covers monthly and check the wipers at least once every six months. Ban the use of high-pressure air hoses to clean off machine tool ways. As an alternative, wipe and vacuum them. Another enemy of machine tool ways is coolant, which can wash off the oil film that's necessary for lubrication. Old coolant can develop rust and |
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corrosive agents, and it can seep into every crack and crevice of the machine tool. Unfiltered coolant carries metal fines onto and into machine slides. Keep coolant off ways as much as possible, and make sure that you maintain your coolant and replace it when necessary. There are two more crucial aspects of a comprehensive machine tool PM plan, maintaining lubrication systems and electrical controls. Proper lubrication is fundamental for any machine tool. A well-maintained lubrication system slows wear, helps preserve alignment, aids in achieving part accuracy, prevents major breakdowns and prolongs machine tool life. In caring for lube systems, remember to maintain proper pressure, ensure that lubrication flow isn't hindered or interrupted and keep the lubrication medium clean. Achieving these goals requires regular monitoring of the system, eliminating contamination sources and periodically changing fluids and replacing filters. All these tasks are easy to perform, yet they are frequently neglected, often resulting in costly repairs and disrupted production schedules. Machine tools use several types of lube systems. One is an oil bath set-up. Imagine the rear axle of a car and the "pumpkin ball" inside of which the axle gears mesh together and you get an idea of how this system works. One negative aspect of this type of system is that it's prone to failure due to oil contamination because there is no filter. To avoid this problem, change the oil frequently. Another type is a recirculating oil system, which uses a pump-and-delivery arrangement much like a car's engine to keep a machine tool's gearbox and drive train components running smoothly. Maintaining a recirculating system requires changing the oil and filter periodically. Over time, the lubricant breaks down, robbing it of its viscosity and anti-friction capability. Some machine tools are equipped with a terminal lube system, which "consumes" oil. This set-up is common on machine tool guide-ways. To ensure long life and proper operation, keep the oil or grease reservoir cleaned and filled to the proper level. A sure sign of trouble with a terminal lube system is a failure to consume oil. You can tell if that's happening by frequently checking the reservoir. If it's always full, the system isn't consuming oil and there's a malfunction somewhere. A useful way to make certain that a machine tool's lube systems are getting proper care is to check the OEM's recommendations. How often does the manufacturer suggest changing filters? What is the OEM's guidance on fluid specifications and levels? Some businesses that use machine tools have the critical properties of their oil tested to confirm it's spent, instead of simply changing it at some predetermined time interval. This could produce a sizeable savings where large oil reservoirs are involved. Just proceed cautiously and make sure the oil meets the manufacturer's specifications at all times. Performing preventive maintenance on a machine tool's electrical controls mustn't be overlooked, either. These controls typically include relays, motor starters, drives, programmable logic controls and other sensitive electrical components that are housed inside the control cabinet. To enable electrical controls to operate properly, keep them clean and cool, which can be challenging, considering the typical environment in which machine tools operate. Air contaminated with oil, coolant mist and metal particulate can invade electrical control boxes. These contaminants can be ideal conductors and may cause havoc inside a control box full of electrical components. Accumulation of these contaminants on electrical/electronic components diminishes their ability to maintain a normal temperature and may lead to heat-related failures. The harder the machine is run, the more heat is generated in the control enclosure and the more frequent the failures become. How do you achieve both cleanliness and coolness? First of all, don't leave doors on control cabinets open. This happens a lot. Heat inside the enclosure builds and workers "solve" the problem by opening the cabinet door. Worse yet, sometimes a fan is placed in front of the open enclosure, which directs a steady blast of air at the controls inside. Don't do this! It may fix the heat problem, but it also blows airborne contaminants into the delicate contents of the control cabinet. If the control box on a machine tool is heating up, there are three suitable ways of dealing with it. First, you can install filter-equipped vents at the top and bottom of the cabinet. The top-and-bottom configuration permits convective air flow inside the box, thereby maximizing the cooling effect. The filters block contaminants. Another solution is to enhance the filter-equipped vents with a fan, which intensifies the passage of cooling air through the box. The third remedy is to attach an electrical-component air conditioner to the enclosure. Once one of these methods is used to cool the inside of the cabinet, keeping the interior tidy is simply a matter of periodically cleaning or replacing the control-box vent filters. If the machine is CNC controlled, there is an additional maintenance issue to be mindful of, preserving the crucial data these systems contain. Accomplishing this means keeping fresh batteries installed in the backup device. Follow the manufacturer's recommendations and instructions when installing new batteries. If not done properly, important data could be erased. Some manufacturers sell a data backup kit. If one is available for your CNC, consider getting it. Finally, remember that even if a PM plan addresses machine tool accuracy by rigorously maintaining mechanical and lubrication systems and electrical controls. It's worthless if someone isn't made responsible for implementing it and seeing that it's strictly followed through detailed recordkeeping. Once you've accomplished that, your plan will soon become routine and so will the savings and production benefits that it produces. Authored by Jim Leigh, Co-owner, Pyramid Rebuild & Machine For more information contact: Pyramid Rebuild & Machine, LLC 123 S. Thomas Road Tallmadge, OH 44278 330-633-4452 Fax: 330-633-4408
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