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Multiple spindles are key to high speed holemaking.

What does high speed hole making mean to you?

Most manufacturers are familiar with "fast cutting" in terms of high speed machine tool spindles and related cutting tool technology. High speed holemaking can also be reached through multiple spindle systems that can create anywhere from just a few to several thousand holes at a time. The latter solution is focused on high production as well as high speed holemaking.

Imagine that you're working with one spindle on a flexible machining center. In response to a demand for increased output, you've applied the latest in high performance tooling technology. You've updated all your programs. Everything is tuned in; you're meeting your new goals. Then you're hit with a demand to increase production even further. Your machines are already working as fast as they can, so it may seem that the only solution is to purchase more machining centers. But before you decide how many more machines you need, consider how much production would increase if you could move the high production requirements from your flexible machines to a dedicated production holemaking environment.

Zagar Inc, a Cleveland, OH, machine tool builder, specializes in high production holemaking solutions. Manufacturers seek dedicated production solutions for two main reasons says John Zagar the company's president. First, because they have high production requirements on a newly designed part; or second, because they currently use flexible machining centers to produce a part or a family of parts in large quantities, and they have reached a production plateau. Whatever the reason, the goal is the same: to produce a large number of parts in a short period of time. In most cases, this involves creating multiple holes in a single pass.

"Suppose you need to machine nine holes into a part, and each hole requires drilling, chamfering, and tapping," says Tom Pellegrin, Zagar product manager. "You could use an 18-position (two nine-hole patterns) multi-spindle head to perform all 27 operations in one pass.

"One of the nine-spindle clusters would be equipped with step drills for drilling and chamfering. The second cluster of spindles would be equipped with the appropriate taps. Through an automated part fixture, the part would be drilled and chamfered at the first cluster, then moved to the second for tapping. This entire process would take approximately five seconds. With a single spindle machine, this process would take approximately 3 min. In the same amount of time it would take the spindle machine to produce one part, the dedicated machine could complete 36 "."

On a milling mission

There's often more to high speed holemaking than straight drilling and tapping. Milling shapes presents production challenges as well. For instance, when The Boeing Co needed to increase the already aggressive production schedule of its Delta IV rocket program, Zagar used multi-spindle milling technology to design a gearbox that reduced milling time by 40%. The Zagar package, which consists of a five-spindle, gear-driven head with a quick-change machine mounting system and a pulse-mist lubrication system, is used to mill triangular pockets into the aluminum skin that forms the rockets' booster cores.

In Zagar's five-spindle setup, the main center spindle, which drives the other four, is connected to the machine tool's spindle with a CAT #50 taper milling machine mount. The four corner, or orbital, spindles each have #63 HSK sockets for quick-change, high velocity toolholding that handles a cutting load up to 25 hp. Rotating at 7200 rpm, the center spindle (#100 HSK sockets) cranks the four orbital spindles up to 10,000 rpm. Such high-speed spindle rotation requires special hybrid bearing packs, which Zagar developed in collaboration with Cincinnati Machine.

High speed production machining is most effective when coupled with high speed part handling. Indexing systems, made possible through CNC technology, facilitate simultaneous load and unload as a part of the machining cycle. One application that uses this technology is an automated production tapping system Zagar designed for Engineered Sintered Components, an automotive component manufacturer in Troutman, NC.

Automation for automotive

Engineered Sintered Components wanted to automate its process and subsequently increase the production of a powdered metal automotive part in which they needed to tap three holes. The solution incorporated a Zagar CNC Ball Screw-driven Feed Unit and a Multi-Spindle Head. These components created the nucleus of an automated production tapping system in which all components work in tandem.

The CNC-controlled feed unit provides accurate spindle rotation through the Multi-Spindle Head and a controlled feedrate that matches the thread being tapped. This machine produces a finished part every 5.5 sec.

"An on-board robotic parts handling system/automatic gauging system loads the part onto an automatic indexing fixture," explains Randy Roberts, Zagar vice president. "The automation sequence moves the part to the first station, where part presence is confirmed. The part then moves to the second station, where it is tapped, and then on to the third station, where it is gaged to confirm the success of the tapping. If the tapping is unsuccessful, the machine stops. The operator rejects the part and confirms the cause of failure before the production cycle continues. Good parts move on to the next production phase."

According to Bob Jewell, Zagar's chief engineer, higher speed holemaking would be impossible without advances in bearing technology--namely, ceramic hybrids. Ceramic hybrids, bearings with silicon nitride balls and steel inner and outer races, outperform conventional steel ball bearings so dramatically that they are no longer a luxury, but a necessity in many high speed holemaking applications.

The ceramic hybrids, which were used in the above Boeing application, increase productivity through faster acceleration and deceleration, which boosts metal cutting time and reduces downtime. They are more durable than their metal predecessors, and they run cooler.

High speed chip removal

Along with special bearings that can "take the heat," faster moving spindles often require special cutting fluid treatments.

"It's very important to get the cutting fluid to the tip of the cutting tool, especially when the holes to be drilled are more than four diameters deep," Mr Jewell says. "The best way to accomplish this is to force the fluid through the cutting tool at high pressure. In order to filter and recycle the coolant well enough to push it back through the cutting tool, a pump with tight clearances and an inducer must be used."

According to Mr Jewell, there are several benefits to using this high pressure method, rather than the flood coolant method. The forced coolant lubricates and cools the cutting tool at its hottest point. And, at high pressure, the coolant will push the chips out of the hole. High speed, multi-spindle holemaking opens a whole new arena of chip making and removal. Selecting the right cutting fluid is imperative, but it's largely a trial-and-error process. Prior experience, in-house testing, and advice from cutting tool manufacturers are all helpful factors in this area.

"It's important to study and evaluate customer applications, not just from the standpoint of metal removal requirements, but also with consideration of all the operations that will be performed on the part prior to and following the holemaking process," says Mr Zagar.

Across the board, customers' high speed holemaking issues and concerns include production rate and cost per hole. The best way to deal with these issues is to produce the holes in multiples whenever possible. Although multiple-spindle machining may sometimes be limited in terms of its rotational speed, what makes it so valuable is the fact that it can produce multiple holes--from just a few to several thousand--in far less time that it would take to machine each hole individually
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Comment:Multiple spindles are key to high speed holemaking.
Publication:Tooling & Production
Geographic Code:1USA
Date:Jul 1, 2000
Words:1261
Previous Article:The masters' rounds of metalworking.
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