Heavy duty machining – The Safe-Lock system

30th August 2016
Posted By : Anna Flockett
Heavy duty machining – The Safe-Lock system

When it comes to roughing and heavy duty machining, the importance of the tool holder is still understated. Crucial for the productivity of the machining operation is the metal removal rates in these types of processes. By using special shrink fit chucks with drive pins and spiral grooves in the tool shank it is now possible to perform high-feed full slotting of up to 2xD (50mm) or more in difficult to machine materials. 

Application studies conducted by the machine tool manufacturer Heller have proven the effect of the HAIMER Safe-Lock system.

Especially within the aerospace, energy and mechanical engineering sector, production managers have to bridge the gap between economic efficiency and high process reliability when working with materials that are difficult to machine.

Located in Nuertingen, Germany, the company is known for its high quality 4 and 5-axis CNC machining centres, CNC mill/turning centres CNC machines for crankshaft and camshaft machining as well as flexible manufacturing systems.

The availability of their products and their competency in managing special processing demands stem from Heller´s in-house manufacturing, which relies on closer collaboration with customers, suppliers and research institutes to remain on the forefront of innovation.

Roughing is a highly promising process

Werner Kirsten (pictured), who is working in the Technology Development Department at Heller and is responsible for the area of ‘difficult to machine materials’, explained: "Our service includes optimising the machining processes together with our customers and suppliers. To support such services with practical trials, our Technology Centre is equipped with a variety of machines".

In most cases the aim is to increase the productivity without compromising the process reliability. Technologist Kirsten added: "We often achieve this aim with an optimised roughing operation which ultimately results in a reduced finishing process. By maintaining the same technological values, but shortening the finishing depth of cut by 50%, the overall machining time is reduced to half. However, this requires process reliable and controllable systems during roughing."

All machining components in the process chain have to be considered in order to improve productivity. The machine tool is the most evident component of the machining process; however the tool, the tool holding system, the coolant supply and other elements are also essential for a successful operation.

"In the end the weakest link of the process chain limits the success," Kirsten emphasised. In his opinion most machine shops don't pay attention to the tool holder even though it is especially significant for high performance cutting. "Many of the trials which we carried out during the last few years have proven this point.”

We realised that the tool holder has an incredible influence on the machining process, he continued. “In the case of reinforced shrink fit chucks, for example, the vibration node is closer to the bearing point (due to the larger mass). The result is a smoother machining process with less vibration and a better surface finish quality while using the same tool, machine, process parameters and fixturing technology."

Tool holding - an important factor for productivity

By selecting the right tool holder you can even achieve good productivity and surface quality results using basic standard cutting tools. Werner Kirsten refers to comparative tests with basic four-edge cutting tools without an inner coolant supply.

As an alternative to a standard shrink fit chuck he selected a HAIMER Power Shrink Chuck with Cool Flash which ensures that the coolant is transported directly to the cutting edges. "Compared to using a normal shrink fit chuck and external coolant, we were able to achieve significantly better results."

When a group of representatives from the aerospace industry, the Technical University of Dortmund and Technical University of Hamburg-Harburg visited Heller, an especially extensive milling application study was conducted in Titanium Ti-6AI-4V.

Gaining new insights from difficult cases

The available machining centre was a four axis Heller H 5000 with a gear unit and HSK-A100 spindle, which yields torques up to 2.290Nm. In order to demonstrate the machining potential, different 25mm diameter end mills were used to mill full slots into a titanium plate. To simulate holder conditions used in the aerospace industry, the tools were clamped into reinforced shrink fit chucks. At an axial cutting depth of 0.5-1.0xD the machining process was found to be very reliable.

Since the spindle was not running at full capacity, the trial participants agreed to increase full slotting depth to 2xD. Kirsten explained: "Under these conditions the tool pulled out of the shrink fit chuck during the machining operation, creating a slot closer to 2.5xD as it progressed through the part. Towards the end of the slot the tool finally broke as a result of increased cutting forces.

The milling specialists all agreed that the clamping force of the chuck was the limiting factor in this process. As soon as the axial pressure and process related vibrations are too high the tool moves out of the chuck and further into the work piece. At the same time the cutting pressure increases such that in the end the tool breaks and the work piece is irreversibly damaged.

Reasons and possible countermeasures were discussed intensively. In the end, Werner Kirsten developed the idea that the tools are forced to navigate towards the spindle when the holding forces are exceeded. This is how he ultimately noticed the patented HAIMER Safe-Lock system which in addition to frictional clamping forces, has the same helix pattern as the tool.

Theoretically, he realised that even if the tool got loose while using Safe Lock, it would be pulled into the holder through the helical drive keys and not into the part. A movement that can be easily prevented through the use of length pre-setting screws.

Prevent tool pull-out

Werner Kirsten got in contact with HAIMER, the European market leader for tool holding technology, in order to test the Safe-Lock system: "We wanted to know if our ideas could be put into practice using the HAIMER system in an even less forgiving environment."

The Heller technology developer repeated the described trial, with a few major changes. HAIMER Safe-Lock grooves were subsequently added on similar solid carbide tools, but the application would be run again with a reduced spindle taper interface (HSK 63 instead of HSK 100), with a less rigid 5-axis gear driven spindle and a less stable diagonally fixtured work piece.

The result: Despite these additional limiting factors, the tool was able to process a full slot of 2xD=50mm with complete process reliability. Werner Kirsten said: "This way we were able to indirectly prove that Safe-Lock works and that the shrinking technology has even more potential with HSK-A100, especially on 5-axis machining centres with gear spindles." Afterwards this sample machining on Ti-6AI-4V was carried out various times, including during the Airshow in Farnborough, whereby it was proven that the previous limit of 1xD=25mm full slotting in titanium could be doubled with the use of Safe-Lock.

Kirsten summarised the results as followed: "For roughing operations this is a reliable process. Therefore I consider the HAIMER Safe-Lock system a practical, easy to handle and process reliable addition to the shrinking technology which we already utilise, especially in connection with standardised tools of other manufactures."

A number of tool manufacturers are offering Safe-Lock products

From the onset of its creation, HAIMER recognised the incredible potential of the Safe-Lock system, which is why the company created a licensing programme to give innovative tool manufacturers the ability to integrate the patented pull-out protection system into their tools.

The result of their vision to create a more open system has been a tremendous success, with leading cutting tool manufacturers having now signed licensing agreements, including Walter, Widia, SandvikCoromant, Seco Tools, Sumitomo, Kennametal, Helical, Emuge Franken, Data Flute, Niagara, OSG,SGS Tools and recently Mapal.

Through the steady increase of Safe-Lock tooling in the market via Haimer and its licensed partners, the system has become the new standard for heavy machining and roughing. In fact, the popularity and simplicity of Safe-Lock is such that it is also replacing the old Weldon clamping system, particularly when new milling strategies such as trochoidal (dynamic) milling are involved.

President of HAIMER Group Andreas Haimer explained: "With our Safe-Lock system we found a solution that combines a high run out accuracy with 100% pull out protection. The system has established itself successfully as a standard in the aerospace industry and generally speaking for roughing and heavy duty machining. And now more and more companies that make use of the trochoidal (dynamic) milling strategy are also making the switch to Safe-Lock, and for a good reason."

During trochoidal milling operations, where the cutting speed and axial depth of cut can be increased through software support, productivity is significantly improved. However, the increased cutter engagement and cutting forces that result from the higher cutting performance create a situation where tool-pull out can occur very easily.

Prior to Safe-Lock, this problem was prevented with Weldon shanks and chucks. However customer had to sacrifice speed and accuracy due to the nature of this clamping system. A shrink fit chuck with Safe-Lock offers the same safety as the Weldon system, but provides the additional advantage of accuracy and balance. The ideal balancing and run out characteristics of the shrinking technology in combination with the clamping safety of the Safe-Lock system permit greater productivity achieve through faster permissible speeds and increased tool life all with complete tool security assurance.


You must be logged in to comment

Write a comment

No comments




Sign up to view our publications

Sign up

Sign up to view our downloads

Sign up

GISEC Global
23rd April 2024
United Arab Emirates Halls 2-8 - Dubai World Trade Centre
The Magnetics Show US
22nd May 2024
United States of America The Pasadena Convention Center
2024 World Battery & Energy Storage Industry Expo (WBE)
8th August 2024
China 1st and 2nd Floor, Area A, China Import and Export Fair Complex