Add Life to Live Tool Heads
Tool system suppliers often come in contact with shops that either view live tool heads as perishable items or view them as everlasting and thereby do not properly inspect performance or condition. Unfortunately, both of these viewpoints lead to a costly mistake and one that can be avoided with the implementation of a simple preventive maintenance plan.
Shops that regularly inspect and maintain their live tool heads can achieve up to five times more service life and lower overall toolholder costs than those that do not. A live tool system preventive maintenance program ensures part accuracy, increased cutting tool life, reduced scrap, improved reliability and overall confidence in lights-out operations. Furthermore, such a program dovetails with OEE and Six Sigma practices that focus on the effectiveness and efficiency of a manufacturing facility.
From a financial perspective, if a shop fails to maintain a live tool head and continues to process parts, the head’s spindle and gears will eventually wear, creating an expensive repair, not to mention scrapped parts. Outsourced spindle and gear repair can cost upwards of $2,200. But with a routine maintenance program in place, a shop, for the same amount of money, can have a live tool head serviced four times and keep it in operation at least three times longer.
Keep in mind, however, it is difficult to quantify the exact maintenance intervals and service life for a live tool head because every shop has its own unique manufacturing methods. Plus, several application variables must be taken into consideration. These can include everything from workpiece material type to cycle times to coolant condition. Consider that two hours machining titanium, for example, is much harder on a live tool head than even ten hours of cutting graphite.
Proper Coolant Care
Despite these variables, it is a fact that coolant contamination is the number one cause of live tool head failure, particularly when heat buildup is involved. If live tool heads get too hot, the heat can deform the contact surface of the seals that hug the spindles, making it easy for the coolant and fine metal chips to enter the heads and begin the corrosion process.
Additionally, with compromised seals, coolant can wash out the lubricants that live tool bearings depend on to function properly. Chips can also create pits in the rolling elements and raceways of the bearings when they contaminate a head. In either case, a shop must replace or repack the bearings, or they will rust and fail.
When a shop does not properly maintain the concentration and water quality of its coolant, not only does the heat removal process suffer so do all the components inside of the machine tool. Once the coolant supply becomes overly contaminated, it becomes a miasmic cesspool that is difficult to get back to an acceptable zero point condition without having to halt machine production time for cleaning.
To maintain coolant concentration, it is best to measure it using a refractor as opposed to visually with the naked eye. With a refractor, shops can determine if the coolant is rich or lean. If the concentration is rich and the shop adds more concentrate, there becomes a reduction in coolant capacity. On the other hand, if the coolant is lean and a shop does not add enough concentrate, there becomes the risk of shorter tool life, poor surface finish and machine corrosion.
Water quality is an equally important factor in coolant system maintenance, and involves test strips to check the water’s PH balance and hardness. A PH level between eight and 10 is acceptable, while anything below seven indicates a weak coolant concentration, creating a higher chance for corrosion and bacterial contamination.
A water hardness reading between 150-400 parts per million is acceptable for most coolants. Readings above this range increase the chance of corrosion and bacterial contamination. Plus, as the water hardness becomes more excessive, the water and coolant concentrate begin to separate. High hardness levels often occur over time when shops “top off” the coolant supply with tap water that contains hard minerals. Therefore, it becomes important to use deionized water for topping off and tap water for new coolant batches only.
Five-Point Preventive Maintenance Inspection
Proper coolant care is probably the only controllable variable, amongst all manufacturing facilities, in increasing live tool head service life. However, there is a general five-point preventive maintenance inspection that EXSYS/Eppinger suggests shops perform at least every three months. And while EXSYS/Eppinger recommends such inspections, machine operators will have to make the judgment call for exactly how often the inspections are needed based on the variables of the particular mill/turn operations at hand.
The first inspection point measures spindle runout. Operators can determine runout by simply resting a dial test indicator tip on the inner surface of the collet pocket and rotating the live tool head. The maximum runout for live tools is typically around five microns in the collet pocket. Excessive runout in the spindle puts an additional load on the bearings, ultimately decreasing overall service life.
While the dial test indicator is in the collet pocket, it is also possible to simultaneously check for radial play, the second inspection point. If movement shows up on the indicator when you toggle the spindle, then there is some sort of problem that can be anything from a bent spindle to a bad bearing.
Ease of rotation marks the third inspection point. Live tool heads should rotate smoothly, be free of any binding, and should have no real audible noise coming from the bearings while you spin the tool.
The fourth inspection point involves a visual inspection of the live tool head, with a particular focus on the collet pocket and the system’s drive connection, to check for any damage, wear or rust.
For inspection point number five, if the live tool holder has an easily accessible cover plate, the operator should remove it and inspect for coolant contamination. But remember, if a live tool head is still under warranty, it should not be disassembled completely.
A down machine is an unproductive machine, and it takes little time to perform the five-point inspection that could prevent such a scenario. In fact, once an operator gets acclimated to the process, it should only take a few minutes.
To get the most out of the five-point inspection, it is best for operators to create and make entries in a maintenance log — EXSYS/Eppinger offers a template to its customers for this purpose so they can track a live tool head’s performance throughout the years. Over time, operators will be able to tell when they should remove a live tool head for routine service as well as establish an accurate maintenance budget.
Operators should also maintain a similar log for coolant maintenance to give them an idea of when the system requires cleaning or a new coolant batch be poured. The log should include variables such as concentration ratio, filtration system, water hardness and bacteria levels.
Live heads with minor problems, such as those requiring seal and bearing replacements, should be sent out for service as many times as possible before being discarded. Keep in mind that if a live head suffers a catastrophic crash, it is most likely past the point of inspection.
When it is time to service a live tool head, it is best to outsource the work to a service department that specializes in repairing heads to OEM specifications. Properly trained technicians can save shops time and increase the longevity of the live tool head.
A good practice is to always have spare live tool heads on hand to avoid unnecessary machine downtime when a head goes out for service. While spares are an additional investment, they bring forth substantial savings in the long run. After all, standard repairs on live tool heads can take between one and two weeks, while comprehensive repairs can take up to four.
While live tool heads only represent a small portion of the overall machining process, they are a big contributor to improving machine tool efficiency. Therefore, shops should never view them as perishable items. And when properly cared for, live tool heads can deliver high value and production accuracy over a long service life – making a preventive maintenance program for them that much more important.