Maximize Productivity with Accessories
When you plan a purchase, remember to include accessory items that can improve shop productivity in the package
By Brian J. Hogan
Machine tools represent significant capital investments. It's logical that shops, managers, and engineers spend a great deal of time evaluating such new equipment.
But there are many smaller items, often capable of boosting productivity at relatively low cost, that are not given much attention when the purchasing decision is made. Consequently, those lower-cost items are bought ad-hoc, often in a rush, at higher cost than would be necessary if they were included in the original buying decision.
Every new machine purchased by a manufacturing operation, whether a small contract manufacturer or a Tier 1 supplier to the automotive OEMs, is bought with a view to improving productivity. With a little forethought, and the addition of some simple accessories, the productivity of new equipment can be optimized from the first day it's powered up.
Once a machine leaves the controlled facility where it's manufactured, the shop environment it enters will influence its performance. Machine tool accessories can help ensure its longevity, maximize its performance, and keep it operating at peak efficiency.
"Accessories are a great way to keep a new machine working at its best," explains Chris Kaiser, president and COO at BIG Kaiser Precision Tooling (Elk Grove Village, IL). As an example of the correct use of accessories, Kaiser points to spindle maintenance. "Because tolerance requirements today are getting tighter and tighter, companies should take special care to make sure spindles stay uncontaminated. Even the smallest piece of dust or a particle on the surface of a spindle can throw everything out of whack during machining," he says. "Spindle cleaners should be used multiple times per day."
Spindle accuracy has a direct effect on the accuracy and rigidity of the machine tool as a whole. Any particles or contamination that gather between the two mating surfaces of the spindle and toolholder will cause those surfaces to wear, weakening the fit and impacting machine accuracy. Spindle cleaners are a simple way to help maintain spindle precision and prolong the life of the machine tools, cutting tools, and toolholders. "Accessories like spindle cleaners should be a key part of every company's maintenance routine from the very beginning, because it's easier to maintain than restore original operating conditions," says Kaiser.
Unlike spindles, which operate within the controlled environment of a machine, toolholders can be exposed to many pollutants inside a shop. During storage and between uses, toolholders run a high risk of picking up oils, dust, and other particles that can contaminate their surfaces. Toolholder taper and bore cleaners come in many styles and sizes to match all types of tooling. The most common taper cleaners are for HSK and V-flange shanks, and multiple bore cleaner designs are offered for uses on shrink-fit tooling bores, milling-chuck bores, and the internal tapers of collet chucks. It's important to keep the clamping geometries of tooling systems clean.
"Another accessory item that can help maintain spindle accuracy, as well as extend the life of a new machine and keep it in original condition, is a spindle gage bar," explains Kaiser. "A gage bar measures spindle runout, which directly affects output, tool life, and spindle life. It should be an important component of a shop's regular maintenance program."
A precision gage bar is a perfectly concentric steel cylinder that measures spindle rotation against its centerline, representing the only absolute part of the equation. It's designed to test runout and spindle accuracy. Lower runout yields increased output, longer tool life, and—most importantly—extended spindle life.
Measuring spindle accuracy is critical to achieving superior part quality during machining. Achieving top spindle performance requires controlling runout. Machine tool runout is caused by wear of the spindle bearings, or by the ground spindle geometry becoming deformed. Regular inspection with a precision gage bar helps identify potential problems, and can reduce downtime and costly repairs of the machine tool spindle.
"T-slot covers and chip fans should always be purchased with a new machine to optimize productivity," Kaiser asserts. He describes these accessories as "very lowcost items that can provide significant time savings relating to cleanup and setup. Chip fans can even be programmed into the machining cycle, minimizing spindle downtime and maximizing operator efficiency."
Chip fans can perform in-process cleaning without stopping production. They mount securely in either a collet chuck or end mill holder, and become part of the machining cycle. Programming a chip fan into the machining cycle decreases the accumulation of nonproductive machine time in a cell as multiple machine cycles end simultaneously.
Chip fans come with a pre-drilled hole that allows coolant-through spindles to direct coolant through the center of the fan to rinse tables, fixtures, and workpieces. Next, the fan rotates and blows air over the work area to remove chips and coolant, thus providing two cleaning operations in one. Chip fans offer a safe and economical means of cleaning surfaces, without operator interaction, while the machine is closed. Doing so keeps all chips and coolant inside the enclosure where it can be reprocessed by the machine.
T-slot covers are protection plates that prevent chips and coolant from collecting inside T-slots on machining center tables. When certain slots aren't being used, these covers can be pushed in place to keep the slots clear of debris. Quite simple to remove, these aluminum inserts give the operator a clean machining surface to work from when changing setups.
"All of these accessories are relatively inexpensive when compared with their return on investment. But they can help machine shops operate much more efficiently by minimizing manual operations, maximizing efficiency, and delivering top part quality," says Kaiser. "By incorporating accessory items with the initial machine purchase, companies can improve productivity and extend the life of their new machine."
Workholding products and accessories are another area where clear thinking and planning can benefit manufacturing operations of all sizes, according to Sidney N. Roth, president of SMW Autoblok Corp. (Wheeling, IL). "More and more," says Roth, "large companies are moving away from custom-designed products toward standard products, even when those standard products may not offer some features that the custom-designed and built workholding can offer. This is partly a matter of cost."
Custom workholding, Roth points out, can cost anywhere from 1½ to twice as much as a standard product. Also, availability can quickly become an issue. It's easier to replace a standard product than a custom product, which certainly won't be in stock. Even if the workholding supplier is rebuilding a previous special order, says Roth, delivery time can easily be 12 weeks. "This is a long time to leave a mission-critical spindle idle," he points out.
Not enough shops purchase spares. "What is the cost of carrying a spare chuck in stock, when a mission-critical spindle is idled because of a crash that damages a chuck," asks Roth. This issue has to be faced whether the chuck is a standard or a custom item. If the process is critical, the manufacturing operation should consider purchasing a spare chuck, or asking the supplier to carry one or more in stock. "A supplier will be more willing to accommodate the customer if the chuck is a standard item rather than a custom design," says Roth, "and the same goes for special jaws, locators, mandrels, and collets."
When you buy workholding, think about what actually happens in your shop and conform your purchasing to the reality of shop-floor operations. "We have one customer who refuses to carry inventory on special collets used to locate parts in their manufacturing," Roth observes. "These collets have a life in use of about two weeks, because the machine operators damage them. Production time for these special collets is 4–6 weeks. During that time the spindle stops running and the customer is upset. I don't want to stock these collets because the customer will not give me a blanket purchase order for them. The lesson is that it's necessary to carry adequate spares for both chucks and jaws to produce critical parts." Roth says most of SMW Autoblok's high-volume production customers keep a minimum of three sets of spare jaws in the toolroom, in case they damage the set that's used on the chuck.
Some high-volume customers buy a supply of spare jaws at the time of their initial purchase order rather than waiting until production begins. Typically, if Autoblok doesn't receive the order for spares with the original order, the customer will wait until the runoff jaws have been damaged or worn out before ordering spares, according to Roth. Naturally, this process pretty much guarantees a production stoppage.
Manufacturing operations also make mistakes when they treat workholding as an afterthought. Quick jaw change (QJC) technology has been around for nearly 30 years, and is available on pulldown chucks, shaft chucks, diaphragm chucks for gear turning, indexing chucks, and static workholding for machining centers. Because few manufacturers have the big production runs that were common a few years ago, QJC has become a mainstream technology. More customers are demanding JIT delivery of small lots (100 or fewer parts), and that's difficult to deliver with workholding that doesn't employ QJC.
Sealed chucks offer advantages to high-contamination operations (e.g. cutting cast iron without coolant) or high-volume production. Users don't need to stop this type of chuck to lubricate it, Roth points out, and a spindle that's turning produces more parts. He says many sealed chucks can run for six months (or more) without lubrication. Also, a sealed chuck maintains consistent gripping. Coolant, centrifugal force, chips, and so forth can cause an unsealed chuck to begin losing its lubricant. As it loses lubrication, the chuck's gripping force decreases (it can fall 50% during a 10-hr shift). With a sealed chuck, gripping force stays constant, which helps reduce scrap rate.
"Toolholders play a critical role in connecting all other elements to maximize machining performance, but these accessories are often the last piece in the manufacturing process that is discussed. Because the toolholder is the critical connection between the machine spindle and the cutting tool, selecting the right toolholder for the application is critical. "If you want a good finish or need to hold a tight tolerance," says Preben Hansen, vice president of Lyndex Nikken (Mundelein, IL), "investing a lot of money in good quality machines with expensive spindles and cutting tools, and then purchasing a low-quality toolholder will not produce your desired results."
To maximize machining performance, several characteristics of your machine's toolholder are very important. You need toolholders that offer rigidity, accuracy, gripping torque, and balance. Using a toolholder with these characteristics greatly reduces or eliminates vibration, extends cutting tool life, extends spindle life, and results in better part surface finish and dimensional accuracy. To protect the investment you make in a high-quality machine, a first-class spindle, and premium cutting tools, it's essential to use a quality, balanced toolholder.
Some manufacturers now have a dedicated manufacturing engineer whose sole responsibility is to cut costs on current manufacturing processes. More and more, Hansen says, these engineers understand that cheaper, lower-quality toolholders do not cut costs. "In a real shop, when toolholders of poor quality are employed, the machining process takes longer and the spindles and cutting tools wear out faster," he states.
Manufacturers need to think about developing smarter manufacturing processes from front to back. It's clear that tool life and spindle life are both affected by the toolholder. Operations can experience lower productivity and spindle degradation due to poor-quality toolholders. However, manufacturers don't always look at this situation until there are problems. The initial purchase price of so-called accessory items drives too many purchasing decisions. "It's beneficial to do true long-term cost analysis on the overall process," Hansen observes, "not just look for the lowest cost on each specific element. The bottom line is that a high-performance machine coupled with all high-performance accessories allows the machine to perform to its maximum potential and produce the highest-quality parts."
This article was first published in the December 2007 edition of Manufacturing Engineering magazine.
Published Date : 12/1/2007