Toolholding for high performance machining
- Published: June 28, 2012
A toolholding system for high performance machining developed by German tooling manufacturer Haimer is gaining in popularity in North America.
Licenses for the Safe-Lock system have been acquired by Widia, Walter, Sandvik Coromant, Kennametal, Helical, HAM, Emuge Franken and Data Flute.
The Safe-Lock principle works like this: spiral-shaped grooves are ground into the cutting tool shank. In combination with corresponding carbide drive pins in the tool holder (shrink fit, collet or hydraulic chucks), they prevent the tool from twisting or even being pulled out of the chuck during extreme machining, which can lead to enormous costs when expensive workpieces are involved. The interplay of pull-out protection and the best runout accuracy leads to low-vibration and efficient machining. This enables a doubling of metal removal rates by considerably increasing cutting depths and feed rates. Tool wear is proportionally reduced, too, claims Haimer.
Many workpieces are milled from the solid, with up to 90 per cent of the material often being machined. To optimize the process and achieve high material removal rates, high torques and low rpm are usually selected. However, such high performance cutting (HPC) generates high tensile forces. Coupled with high cutting and feeding forces, they lead to twisting movements of the cutting tool in the chuck, posing the danger of the cutting tool being pulled right out of the chuck. This especially applies to tool holders offering precise clamping with good runout accuracy, such as shrink-fit, hydraulic or milling chucks.
A customer will often get a false sense of security when higher holding torques in Nm are cited. Franz Ziegltrum, engineer and quality manager at Haimer, warns, “unfortunately, the problem is more complicated than that. A slipping of the cutter cannot be prevented through clamping force alone. This is a slow and creeping process. If the clamping force of a chuck were exceeded, the cutter would turn inside the chuck and break immediately. You can’t master dynamic processes in heavy machining simply with frictional clamping forces.”
Up to now, with a lack of alternatives, many users have had to resort to conventional Weldon holders, whose clamp screw causes positive locking. This allows the generation of infinitely high torques, until the cutter ultimately breaks. However, these Weldon toolholders also bring the following known disadvantages with them: unprecise radial runout, which hinders productivity due to occurring vibrations; poor clamping, because the shaft requires a bit of space in the chuck; poor balance properties due to the one-sided clamping surface, and a short tool life for HPC tools, which are generally very expensive.
Haimer claims only its Safe-Lock system offers relief and can replace Weldon as the standard with unique advantages.
The Safe-Lock system has proven its practicality on several occasions. For instance, a comprehensive endurance test with impressive results was conducted at Boeing in Portland, OR. The Safe-Lock system has been employed as a standard system there since 2009.
A Safe-Lock shrink-fit chuck with a 32-mm clamping bore and a length of 120 mm was used on a vertical portal milling machine with an HSK-A 100 interface. For roughing as well as fine machining, one and the same coated solid carbide tool was used, having an effective cutting length of 83 mm. A critical airplane component made of Ti6AL4V, a titanium alloy conventional in aircraft construction, was used as a test workpiece.
At no time was there a danger of the tool being pulled out of the chuck. Thanks to Safe-Lock, it did not move in the chuck during the entire machining process. What is more, tool life more than doubled. In addition, differences were noted on the surface of the workpiece. During roughing and finishing operations, no vibrations, and consequently no chatter marks, were generated, unlike the Weldon chuck. Based on this, the company achieved significant productivity increases in material removal rates.
In 2009, Boeing Portland became the first of Haimer’s end customers to be licensed to grind Safe-Lock™ grooves into their own special tools that they had developed or produced themselves. Since that time, their roughing processes using Safe-Lock™ have been running reliably and productively: a true competitive advantage in the field of demanding machining.
Sandvik Coromant was one of the first global tool manufacturers to select the new toolholding system. Since March of 2012, Sandvik Coromant has incorporated it into its current program, under the product name iLock, to primarily supply solid carbide end mills with the grooves.
Kennametal had also been searching for fail-safe and high-precision toolholding systems when they discovered Haimer’s Safe-Lock system. Keith Wiggins, leader of global tooling systems product management, is familiar with the problems encountered in heavy duty machining.
“For years now we have been investigating a holding solution that has best possible accuracy with a fail-safe security clamping system that would gain the full potential from our cutting edge performance. With the Safe-Lock from Haimer we now have a high precision guaranteed non-slip holding solution to complement our tool holder offering.”
Walter AG also has a corresponding licensing agreement with Haimer. Jochen Vogel of product marketing milling says “the axial forces generated during the milling of ISO S materials with solid carbide cutting tools require toolholders to exhibit the highest degree of clamping force. With the new Safe-Lock system, we are not only able to guarantee protection from pull-out, but we can also utilize precision tool holders with the best runout properties.”