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Horn Blog

Special tools for DIFFICULT recesses

April 2021
22
Author: paulhorn
Company: Hartmetall-Werkzeugfabrik Paul Horn GmbH
Special tools for  DIFFICULT recesses

“We have been relying on tools from Paul Horn GmbH for more than  30 years. The solution to our latest problem has once again reminded us of why”, explains Roland Burghart, who is in charge of turning at the Donaueschingen plant of SICK Stegmann GmbH. The problem related to the creation of axial recesses in intricate sensor components made from titanium. HORN solved the task through a combination of measures, which included various special versions of its Mini system. Working in conjunction with HORN technical consultant Karl Schonhardt, the HORN designers devised a cut distribution for the difficult machining task. The quality requirements for the components are extremely demanding.

The workpieces are installed inside highly sensitive gas flow measurement sensors. At the heart of these measuring units lie the oscillating transducers. The sensors are used, for example, in gas pipelines, for measuring flare gas, for vapour flow measurement, as well as in biogas plants. Sensor technology from SICK is intended to protect people from accidents, avoid damage to the environment and supply accurate data. For this reason, the company demands a high standard of quality from its products. This starts with the individual parts and components. Tight tolerances, high surface quality and difficult to machine materials are all part of everyday life for the SICK employees working in the area of CNC manufacturing.

To ensure high corrosion resistance, the engineers from SICK selected the titanium alloy Ti 6Al-4V (Grade 5) for the transducers. This alloy accounts for approximately 50 percent of worldwide demand for titanium. And that is because it offers a good balance between high strength and low density. The mechanical properties of this titanium alloy are superior to those of pure titanium. One of the problems it poses during machining is that it has a tendency to work harden. When the friction becomes excessive due to the feed rate of the cutting edge being too low, work hardening of the material is induced. This shortens the life of the tools dramatically. When turning and milling titanium, it is vital to have sharp cutting edges, the right cutting parameters and the appropriate tool coating in order for the machining of this material to be productive.

Large part quantities require well-conceived tool solutions

“The machining of titanium alloys no longer poses any major challenges for experienced machinists – when the machining operations are straightforward”, says Schonhardt. However, in this case, the axial recesses and thread on the transducers called for an appropriate tool design and an intelligent machining strategy. Burghart’s team produces various versions of the transducer in diameters ranging from 4 mm (0.157") to 12 mm (0.472"). “To accommodate different applications, we have several variants of the parts, all of which we produce here at the Donaueschingen plant. The members of the transducer part family are manufactured around the clock on a three-shift system. That is another reason why having a productive tool system was so important to us”, explains Burghart.

Special version of the Mini system

“Based on our experience and many years of cooperation with Mr. Schonhardt, HORN was always going to be the first port of call for this machining task”, affirms production manager Markus Mucha. To create the axial recesses, the HORN designers opted for the Mini 114 system. As well as being suitable for numerous standard versions of the system, the blanks are also a good choice for grinding customised cutting edge profiles. Three different tools are used to create the profile for an axial recess. “Due to the recess contour, the very tight shape and geometric tolerances of the small workpiece, and the high surface quality to be achieved on the face, a cut distribution proved necessary”, explains Schonhardt. From the time of the initial enquiry, it took around six months for the grooving process to be implemented for all variants of the part family. “The collaboration ran very smoothly. We initially started with three tools. These proved practical right away and produced very good sample products. After that, we introduced the other variants”, comments Burghart.

The grooving process works as follows: The first tool cuts the first internal contour along the collar, leaving a finishing allowance on the face. The second tool copies the conical shape and inner diameter in two axes. The third cut is made – as a finishing operation – on the bottom face by tool number three. For this, the insert moves into the workpiece along two axes so that it can then machine the face by performing an axial motion. The face subsequently acts as a functional surface of the component and tight tolerances apply in respect of the surface quality to be achieved. Further machining is carried out on the internal contour by producing an undercut for an internal thread on the outer diameter. HORN realised all machining operations with the Mini 114 grooving system. In terms of machines, SICK relies on the TRAUB TNL20 from INDEX.

The machine concept of the TRAUB TNL20 sliding/fixed headstock automatic lathe has been consistently aligned with the everyday requirements of users. For instance, the kinematics of the sliding headstock lathe allow productive machining to be carried out with two, three or four tools simultaneously. The generously proportioned and vertically arranged work area ensures the necessary degrees of freedom and a high level of process reliability. The crucial gains in productivity with the sliding headstock automatic lathe are down to its excellent dynamics. The newly developed machine bed made of grey cast iron provides the basis for the machine’s superb vibration-damping properties. In addition, the rigidity and thermal stability ensure a high standard of workpiece quality during both sliding and fixed headstock turning.

Additional HORN systems

It is not just the Mini system that is being used for the part family, but also the HORN Supermini tool system. Schonhardt suggested using this system to produce the internal thread. The tolerance class for all threads is 4H. The experts in Donaueschingen also use the Supermini system to create the axial recess on the back of the part. For parting off, Burghart relies on the modular 842 grooving system from HORN in conjunction with inserts from the S100 system. “The cartridge design has given us a great deal of flexibility during use and, on top of that, has significantly increased the stability of the overall system”, says Burghart. Depending on which variant of the part is being produced, up to twelve HORN tools are used per workpiece.

“Given the set-up time of around eight hours per variant, we particularly had our sights set on long tool life, a high level of process reliability and accurate insert exchange”, clarifies Burghart. Alongside the cutting edge geometry that has been specifically designed for titanium and the sharp micro-geometry of the cutting edge, the tool coating also plays a  major role in ensuring process reliability when cutting titanium alloys. “We developed our IG35 coating for use with titanium and other super alloys”, reports Schonhardt.

Smooth properties and high heat resistance

Due to the low coefficient of friction, the aluminium titanium nitride coating prevents the formation of built-up edges. Thanks to HiPIMS coating technology, the coating exhibits very smooth properties and a high heat resistance. Furthermore, the tool coating is free from coating defects such as droplets or other coating faults at the cutting edge. HORN adapts the coating system, the chipbreaker geometries and the micro-geometries to typical applications, such as internal and external grooving, Swiss-type (sliding headstock) turning and circular and solid carbide milling. The user can achieve higher cutting values, enabling a shorter cycle time, which in turn has a positive impact on unit costs. The use of the new coating also results in higher surface quality.

“After 30 years of close collaboration, our trust in HORN as a tool partner has once again been reaffirmed. We were also more than satisfied with the expertise and wealth of specialist knowledge demonstrated by Mr Schonhardt in relation to the application and use of the tools”, says Burghart.

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