July 2011 / Volume 63 / Issue 7|
By Susan Woods, Contributing Editor
Courtesy of Schunk Improving productivity when changing out cutting tools.
In today’s demanding manufacturing environments, fast changeover and setup are key methods for improving productivity. Machine shops can minimize downtime by changing cutting tools faster from their holders.
At the low end of toolholder technology are side-lock holders, which are typically for endmills. These holders have one or two setscrews that press against the flat on the tool shank to secure it. Side-lock holders are the least accurate of all types of holders and create a lot of runout.
“The side-lock holder is a pretty old technology in terms of precision,” said Jeff Keith, product manager, tooling components for Schunk Inc., Morrisville, N.C. “Accuracy and repeatability are not that good. Tool life is not that good because the cutting loads are not evenly distributed.”
Still, side-lock holders are common. “It is application-related,” Keith continued. “It might be a roughing application and the operator isn’t that concerned about accuracy. And it is an established technology, so the typical shop has a cabinet full of these things to use up.”
As for quick tool change, side-lock holders require only loosening and tightening the screw(s) to change the cutting tool, and that takes less than a minute. Another quick-change benefit is the holder can stay in the machine spindle while the tool is being changed.
In the middle of the technology spectrum are collet toolholders, or collet chucks. These consist of a collet holder body, a collet (usually made of spring steel) that is inserted into the body and a nut that screws over the collet. The collet forms around the tool shank and exerts a strong clamping force when the nut is tightened.
“With collet chucks, you have to loosen the nut, take out the collet, clean it, put the collet back in the nut, put in the new tool, then put that assembly back in the holder and tighten it,” said Brendt Holden, president of Haimer USA LLC, Villa Park, Ill. “So it takes slightly longer to change a cutting tool with the collet chuck than the side-lock holder, but it is more accurate. But you must put it together properly. If you just slap it together quickly, you will have inconsistency.”
The collet chuck also can remain in the spindle during tool change. Also, one holder accepts a range of tool shank sizes by changing the collet. The side-lock technology, on the other hand, requires a dedicated holder for every tool shank size.
While it is important that all toolholder shanks and bores be cleaned regularly, it usually just takes a quick wipe with a towel or shot of shop air. With collet holders, which should be cleaned thoroughly after every tool change, cleaning takes longer. “Because there are more parts, small chips get inside the slots in the collet and between the collet and the nut,” Holden said. “So you need to take it apart and clean it carefully in between tool changes.”
Courtesy of Schunk
Courtesy of Rego-Fix
Collets should also be inspected daily for wear, according to Justin London, sales engineer for Briney Tooling Systems, Bad Axe, Mich. “Damaged collets should be replaced immediately because damage reduces the collet’s accuracy and compromises its gripping ability. Remember, collets are typically made of a softer material than the holder, so they wear faster.”
At the high end of the technology spectrum are hydraulic clamp toolholders. Inside these holders is an internal chamber filled with oil. The holder is tightened and released with a screw. As the screw is tightened, it pushes a piston and seal assembly that forces the oil up inside the chamber to accurately clamp the tool.
“Again, you are simply loosening or tightening a screw to actuate it, but this holder is very accurate,” Keith said. “It has vibration dampening characteristics, giving you a better surface finish and tool life. It is more expensive than the side-lock or collet holder but works much better in all applications.”
Hydraulic holders can also be left in the spindle while the tool is changed. Also, reduction sleeves are available to accommodate smaller tool shanks.Wait a Second
Other highly accurate toolholders are available, but they require more change time because a secondary activation device is needed, and they must be removed from the spindle. They are also more expensive.
With shrink-fit toolholders, a dedicated heating unit expands the holder so the cutting tool can be removed and a new one inserted. As the holder cools, uniform contraction grips the tool shank. This technology improves tool assembly rigidity and runout. However, shrink-fit technology requires a dedicated holder for every tool shank size.
“These types of holders tend to be more accurate because you are not using a screw or collet,” said Marc Wijtenburg, managing director, T-Tool USA LLC, Weston, Fla. “There is no variable such as whether the screw or nut was tightened properly. Any time there are multiple pieces in a system, you are adding error, so to speak.”
Shrink-fit holders do take more time to change than side-lock or collet holders. “You have to take the holder out of the spindle, take it over to a heat-shrink unit, wait for it to heat up and cool down and then take it back to the spindle,” Keith said.
A high-end heat-shrink unit typically heats up in less than 1 minute and cools down in less than 3, so it is a 4- or 5-minute process.
Holden said Haimer’s heat-shrink units can heat up a tool in 5 seconds and cool down in 30 seconds. “But we have a three-station carousel where you can work on one holder and as it starts to cool, rotate the carousel to the next holder, etc. By the time you are done with the third, the first is ready.”
Schunk’s Tribos polygonal clamping system is another toolholder that requires a secondary device. The holder bore in its natural state is a polygon shape. The holder is placed in a hydraulic press and the polygon shape is squeezed round so the tool can be changed. When the press is released, the bore springs back to its original polygon shape and clamps the tool. Tool change occurs within 20 seconds—“as quickly as you can pump the press, change the tool and pull it out of the press,” Keith said. As with hydraulic holders, reduction sleeves can be used with Tribos holders to accommodate various tool shank sizes.
Rego-Fix’s powRgrip system is another toolholder system that requires a secondary device. This collet system consists of a holder body, specialty collet and hydraulic press to insert the collet into the holder. “The collet holder has a very shallow taper,” said David McHenry, product engineer for Rego-Fix Tool Corp., Indianapolis. “It is a self-locking taper because it is so shallow, but because it does have a taper in it, you can get it out. It takes about 10 seconds for total tool change.” With powRgrip, operators can place different size tool shanks in the same holder.
Jim Smith, sales engineer for Briney Tooling Systems, noted that if the majority of holders in a shop require a secondary device, then this work should be done by personnel not running the machines. “This will free up the operator to focus on the job at hand and keep machine downtime to a minimum.”
Theoretically, tool change is faster for side-lock, collet and hydraulic holders, because the holder can be left on the spindle while the tool is changed, but few shops actually do it.
“With today’s machining centers, you normally use the automatic toolchanger carousel located on the side of the machine,” McHenry said. “You just open the door, pull the used tools out and replace with the new tools, all while the machine is running.” But, he added, smaller shops with older machines are still changing tools manually.
Courtesy of Haimer
But the aforementioned styles can still be changed faster offline as well because no secondary device is required. Most shops have setups ready to go as needed, no matter what the holder style.
“Even with the ATC, the operator still has to put the tool assemblies together,” T-Tool’s Wijtenburg said. “Typically, you would have additional setups already prepared in case you crash. If it is a shop where productivity is very high, a broken tool can cause a hiccup in production. So a lot of shops will have tools already set up.”Balancing and Presetting
Part of the setup process is balancing and presetting the tool assembly. While balancing adds time to the process, it is well worth the effort, especially for high-speed applications. Unbalance can cause vibrations that create chatter and ultimately will produce poor surface finishes and shorten tool life. When unbalance is extreme, spindle damage can result.
Courtesy of T-Tool
Precision toolholders come prebalanced to a G2.5 balance grade at 20,000 rpm. Most manufacturers also state their side-lock and collet holders come prebalanced. However, they are given a lower balance grade, such as G6.3, at a lower spindle speed, such as 8,000 rpm.
Even with a prebalanced holder, the tool assembly should be balanced on a balancing machine after each tool change. However, depending on application, the degree to which balancing is required varies. A balancing machine can cost from $20,000 to $40,000, so it is not an investment to be taken lightly.
“Balance is always important, but it goes back to the application,” said Schunk’s Keith. “The faster the spindle speed, the more important balance becomes. Depending on the application, it can be an issue for shops running machines in the 6,000- to 8,000-rpm range. If you are running slower than that, balancing is typically not an issue. If you are running faster than that, it becomes a big issue. It is critical if you are running faster than 20,000 rpm.”
He noted that a mold and die shop running at 40,000 rpm generally needs to check balance after every tool change. “But if an operator is doing a roughing operation and is just using a side-lock holder, he has, by default, said, ‘balance is not that important to me.’ ”
Haimer’s Holden believes balancing even lower-end assemblies can be beneficial for slower speeds. “Some shops with machines that can run 8,000 rpm still might only finish pass at 2,000 rpm. They don’t want to go faster because it creates vibration and they cut oversize. So that is where balancing a side-lock holder assembly is useful. They can go faster, say, 4,000 rpm, and increase the feed rate.”
Presetting the tool assembly also adds to setup time but can save time in the long run. “You can save a lot of time in setup from operation to operation if you preset off-line,” said Rego-Fix’s McHenry. “A lot of customers have one or two presetters and they bring all the tools over for a job and measure all the tool lengths going into that machine. They can input those tool lengths very quickly, which saves them from having to touch off every tool.”Lathe Holders
VDI toolholders, first developed in Germany, provide quick-change tooling for lathes. The holder, together with the cutting tool, attaches to the turret plates using a single screw. Tool changes typically can be performed within seconds, rather than within minutes as with traditional toolholding systems.
“The connection of the toolholder to the turret is made by a single screw mechanism attached to a serrated clamp. This clamp holds the holder accurately and rigidly in place,” said Leigh Bickham, product manager, ITI Tooling Co. Inc., Ramsey, N.J. “This is in contrast to a bolt-on holder, where it is bolted directly onto the turret plate with multiple bolts. Instead of removing the bolts to take the holder off, with a VDI holder you have one screw to loosen and the holder is free to be removed.”
Courtesy of ITI Tooling
The advantage of the bolt-on tooling, known as base-mount tooling, over VDI is added rigidity. So while it takes longer to change the BMT toolholder, if there is a lot of material to be removed with large, heavy cuts or when long boring bars are needed, BMT tooling should be considered.
An even quicker way to change lathe tooling is ITI Tooling’s quick-change Varia toolholding system. With this system, a small, interchangeable toolholding module with the cutting tool is exchanged instead of removing the entire VDI holder. “You still have the VDI holder on the lathe, but instead of removing the entire unit from the turret, you take out the module by pivoting one quick-release cam,” Bickham said. “You pick up a fresh tool already preset into another module and put that assembly into the VDI holder that is in the turret.” That VDI holder is already aligned with the spindle, so tool realignment isn’t necessary.
Whatever the toolholding system, the fastest way to accomplish tool change is to preset the holders away from the lathe. “The objective is to have additional toolholder elements preset with the tools ready for the next operation,” said Bickham. “They can all be preset while the machine is running so when the time comes to change, it is just a quick effort.”Swiss Choices
Swiss-style machine tools feature tool blocks or turrets, and tools are close together and must be set up by hand—a time-consuming process. They typically are held on straight-shank holders.
Courtesy of ITI Tooling
T-Tool’s Zeta clamping system is a collet nut system that allows quick clamping using a ratchet tool without any danger to the operator’s hands. “Zeta definitely helps speed up manual tool change, especially on this type of machine where you have multiple tools sticking out,” Wijtenburg said. “Zeta keeps your hands away from the other tools so you can easily change bits, and the tools used to change out the Zeta collet nuts are held on by a special profile that prevents you from dropping the bit into the machine.”
Rego-Fix offers SwissQuick adapter holders. This system offers a way to preset tool assemblies offline for tool length, then change them on a Swiss-style machine in seconds, eliminating the process of touching off newly installed tools. “Normally, when a tool wears you have to take the entire straight shank holder off and put on another one and touch off that tool to know where it is at,” McHenry said. “The SwissQuick allows them to leave the cylindrical holder in place and just change the nose, which threads on. They can preset tools outside the machine and not have to touch off every time.”
Toolholders are easy to overlook because they are less costly than other machining components. But with a little knowledge and effort, the time it takes to change cutting tools can be decreased, increasing productivity and minimizing downtime. CTEAbout the Author: Susan Woods is a contributing editor for CTE. Contact here by e-mail at firstname.lastname@example.org.
Courtesy of Click Change
Hold that insert—but change it fast
can also include insert replacement, and Click Change Inc. offers lathe-type insert holders, or tool bodies, for changing carbide inserts fast. The holders replace a standard stick tool that goes in a lathe.
The holders allow an operator to change inserts in just seconds instead of minutes. “We replace the screw typically used to hold the insert in place with a clamp mechanism that you operate with your finger,” said Charles Van Horssen, president of Phoenix-based Click Change. “The clamp mechanism has a pin that engages into the hole in the insert and pushes down and pulls back on that center hole. This seats the insert into the pocket.”
The holders also reduce the skill level required to change inserts, reducing operator-induced variability. Some operators consistently overtighten holding screws, which can break them and, sometimes, even break the insert, Van Horssen noted.
He also noted that some screw-type holders have a pin in the center. “If you turn that pin the wrong way, it will skew that insert a little to the left or right rather than pulling it back into the pocket,” he said. “It is difficult to see that because it doesn’t move very much and then the operator can be cutting undersize by 0.003 " or 0.004 ". That is just one of the problems for an operator working in hard-to-reach, dark, wet places.”
Click Change holders are available for the four most common basic insert shapes—CNMG, DNMG, VNMG and SNMG. They are available in shank sizes from 0.625 " to 1.500 " (16mm to 32mm). The holders typically last a couple of years before needing to be repaired or replaced, according to Van Horssen. The holders can be repaired with a replaceable seat.
“On every insert change, you are going to save a dollar or two in labor and machine time with our holders because your machine is going to be running that much quicker,” Van Horssen said.
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