This subject is a hot issue in many shops and factories around the country and the world. Production managers insist on parts and throughput, maintenance managers demand machine time to work on the machine, and accountants want the bottom line to be in the black! How do we balance all these issues and keep our machines performing at peak efficiency? PM is the acronym for several words, Periodic Maintenance, Predictive Maintenance, and Preventative Maintenance; or, one of the most technical, TPM, Total Productive Maintenance.
As you can see, a lot of people a lot smarter than me have put a lot more thought into PMs than I have. Like most things in life, you can analyze and over-analyze ‘til you’re blue in the face, but the bottom line in machining is: How can we make good parts, on schedule, for the least amount of money?
As I have mentioned in earlier blogs, I spent the first 12 of my 30 plus years in the technical field in the aircraft industry. As much as some companies dislike to do PMs, in the aircraft industry you hope to ONLY do preventive maintenance! You might find it interesting, so let me share with you how the aircraft industry approaches doing maintenance and keeps the skies safe for all of us. Let me start off by defining the different types of PMs. All types are utilized in aircraft and for specific reasons.
Periodic Maintenance is just as it sounds. It’s based on a periodic time and/or cycle. A cycle in airplanes equals a takeoff and a landing. Many commercial airplanes have a life time of 20,000 cycles or more. With carbon airplanes, they are hoping to double this, as carbon doesn’t fatigue like aluminum does.
Predictive Maintenance is based on the history of a part’s or component’s life time. For example, a manufacturer might know their hyd pump will run 3,000 hours before it starts to show a decrease in performance. It might be a good idea to change it when that time approaches. Another example might be a clamp on a hydraulic line. Every time a mechanic touches an airplane, it’s documented and reported to the manufacturer. After a couple years, the manufacturer reviews the maintenance on a particular type of airplane and sees that this certain clamp has been changed more frequently than expected. They may modify the inspection frequency, mandate a clamp change at a certain period, or make an airworthiness directive and change the design. A clamp may seem like a small thing, but what if punctures a hole in the hyd line preventing the landing gear from extending? Everything counts!
The final PM is Preventative Maintenance. This is usually based on visual inspections and tests. An example would be brakes. It is impossible to factor in all the things that brakes will be subject to, to do one of the other types of PMs. Some of the variables would be aircraft weight, pilot’s usage versus reverse thrusters, wet versus dry landings, and so on. Through visual inspections, we “try” to prevent failures. As far as brakes go, there are pins that are easily visually inspected before each flight. This is by far the most common type of PM in the machine tool industry.
I hope you found that mildly informative, but how does all this pertain to my machine tool you ask? Fortunately, machine tools aren’t as complex as airplanes, or as costly in human lives, but it sure puts a kink in our day if they break.
This is how I, and CMS, recommend that a preventative maintenance schedule be set up.
The first line of defense is the person who operates the machine on a daily basis. They get to know the machine intimately. Their primary role is to produce parts, but there are many things they can check and monitor without losing production time. Things such as air pressure, oil and grease levels, air and fluid leaks, broken or loose components, strange sounds, smoothness of tool changes, power consumption of the spindle, light bulbs, safety equipment. Depending on their level of competence, they could also do machine health checks and alignments. This equates to a pre-flight inspection of an airplane before every flight.
This generally would involve a more skilled person or a high level operator to visually inspect the machine. It would generally include cleaning the machine, topping off all fluids, and repairing any small issues that are not big enough to stop production for. This is also a good time to open the bellows to clean up excess lubrication and look over the servo drive hardware and gearboxes. If alignment isn’t done on a daily basis this would be a good time to run some checks. This procedure could take as little as 15 minutes, or up to an hour, depending on what is found. Any problems should be corrected at this time. In aircraft, this would equate to an overnight stop and an example of what could be corrected would be a seat that didn’t recline. Not a big enough deal to ground a plane, but it’s still broken and needs to be fixed.
Similar to weekly, but one step more involved. Open up some panels and clean and inspect components. Check wire tracks, bearings for correct lubrication, power draw on axis drives, backlash on axis movements, electrical cabinet for cleanliness, filters on chillers, quality and quantity of fluids. All of these checks need to be evaluated and reevaluated continuously. What might not be an issue at a plastics shop might cause a huge problem at a composite or graphite machining facility! This is an “A check” or “B check” for airplanes. It would generally be pulled into a hangar for this.
We strongly recommend customers have CMS come in on an annual basis to do a full inspection and correct any problems the customer isn’t comfortable performing—changing a spindle or rotary seal for example. We have the advantage in that we only work on CMS machines. We know where to look and what wears out. We also have the advantage of knowing what a machine should sound like. Sound can be a wonderful diagnostic tool. The operator who hears the machine daily might not notice a sound that slowly degrades, but one of our guys will hear it across the plant.
These inspections take from 1 to 3 days. All covers and bellows will be removed, things are cleaned and visually inspected. Electrical components are tested, light bulbs changed, safety devices checked, doors realigned, and tools checked. We usually like to work with someone from the customer’s staff to help refine their procedures and show them what to look for, as well as showing them some tricks we have learned along the way.
After the machine has been inspected and repaired and assured it is operating correctly, we do a full calibration and realignment of the machine. This also varies depending on the customer’s requirements. It could be as simple as cutting a square and measuring, to the use of multiple lasers and electronic levels and ballbars. CMS has invested in the best equipment in the world and has dedicated countless hours in training and evaluations to be able to offer the best the world has to offer in alignment and calibration.
To keep with the analogies we have been using, with aircraft this level would be called a “C check”. What this entails in airplanes is quite extensive. This was one of my favorite things to do as an aircraft mechanic. I generally worked on Boeing 747s. A “C check” happened once every 5 years of so, and would take 5-6 weeks to finish. That’s 5-6 weeks of 24 hours a day with an army of licensed aircraft mechanics. Here’s what happens:
The plane is towed in the hangar and completely enveloped in scaffolding. It’s hung from the ceiling and extends from the ground. You couldn’t even see the plane it is so extensive. From here, we would swarm the plane removing every panel possible. The engines would come off, the landing gear would be removed, and the flaps, slats, flight controls, gear doors, and the entire interior would be removed. Then another army of cleaners would come in with high pressure washers, scrubbers, and solvents and make to plane look nearly new. Our turn again, the inspections would start, repair schedules would be made, and it would start to go back together. As it once again became an airplane, the operational checks would start. After 5 or so weeks the scaffolding would come off and the final calibrations would be done, new engines would be run up and tested, ground ops would be checked, then a test flight. After that we had a nearly new, perfectly operating airplane to start on the next cycle of inspections while continuing to be productive and safe piece of equipment.
As you can see a machine is a machine is a machine! Mechanical devices need love, too. With a little care and planning, PMs on machine tools will not cost a company money, but rather will save them money. A well-developed plan will not reduce production but enhance it. Down time and bad parts are more costly than any PM program, and in more ways than just lost time. Take the time to review your program and please contact CMS North America if you need assistance. It’s our goal to keep you productive.