Toolholder Turnaround

Courtesy of Schunk

Schunk’s Tribos polygonal clamping mechanism.

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

Schunk’s Celsio shrink-fit toolholder.

Courtesy of Rego-Fix

Rego-Fix’s powRgrip toolholder and collet before assembly.

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

Haimer’s Power Clamp New Generation shrink-fit unit has a three-station carousel.

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