Category: Mastering Processes

HORN Mastering Processes: Hard Machining

 

Mastering Processes: Hard Machining

Shorter machining times, high surface quality and the saving of grinding operations. These are just three of the advantages that hard machining with a geometrically defined cutting edge can bring to the user. With a high level of know-how in tool technology, Paul Horn GmbH offers numerous tool solutions to economically machine steels harder than 56 HRC. The cutting material CBN has proven itself suitable for grooving operations.

CBN (cubic boron nitride) is the second hardest known material on earth after diamond. Tools made of CBN wear much more slowly than other cutting materials when used appropriately. On  one hand, this makes it possible to achieve higher shape and dimensional accuracy, and on the other hand, hard materials (steel up to 70 HRC) can be machined reliably. There are no different grades of CBN. Differentiation is made by the CBN volume fraction, the fillers, the grain size and the ceramic/metallic binder phase (cobalt/nickel). This results in different CBN substrates. Numerous tool systems from Horn can be equipped with the cutting material CBN. In most cases, these are tools specially adapted to the respective application. However, Horn also offers standard tools equipped with this  very hard cutting material.

Hard machining with CBN cutting materials is usually done dry. This is possible because the cutting material has  high heat resistance and the high temperature within the chip formation zone has a positive effect. An insufficient supply of coolant or interruptions in cutting lead to high, thermally induced stresses in the structure of the insert. This can lead to cracks in the structure and thus possibly destroy the insert. During hard machining, the steel in the shear zone undergoes intense heating and is thus softened. Most of the heat generated in the shear zone is dissipated via the chip and not  transmitted into the workpiece. This means that there is no thermal influence on the insert edge  in the process. While carbide  suffers a massive loss of hardness at around 800 degrees Celsius, the hardness of CBN remains almost unchanged even at up to 1,200 degrees Celsius. Another important aspect is the chemical resistance, especially at the prevailing temperatures.

Numerous Advantages

Hard machining with a geometrically defined cutting edge in combination with CBN  has numerous advantages over grinding . High metal removal rates are possible with this process, which results in shorter machining times. Conventional machines  may be used. This offers the possibility of complete machining of the component. Even complex contours can be easily produced on a lathe. With grinding, on the other hand, the  wheels have to be elaborately profiled. The high surface quality that can be achieved with hard turning also saves on further grinding operations.

HORN Mastering Processes: Swiss Turning and Micromachining

 

Mastering Processes: Solutions for Micromachining and Swiss-type Turning

Outer diameters of 0.1 mm (0.004″), recesses of 0.5 mm (0.020″) and feed rates of 5 µm (0.0002″) – welcome to the world of micromachining! Screws for hearing aids, balance weights for automatic wristwatches or micro-turned parts for medical assemblies: Manufacturing such parts requires know-how, precise machines and special tools. With cutting depths of down to 0.01 mm (0.0004″), users place very high demands on the tools used. They include shiny surfaces and high dimensional accuracy of the components through the use of low cutting force. HORN has developed suitable solutions with the μ-Finish system for micromachining as well as with other tool systems and manufacturing processes for Swiss-type lathes.

The demands on the tools for micromachining with Swiss-type lathes are high. Due to the sometimes very small cutting depths, the tool edges must be very sharp in order to keep the cutting force as low as possible. However, the ground cutting edges are susceptible to microchipping. Even limited chipping in the range of a few µm at the cutting edge has a negative effect on the surface of the machined workpiece. Furthermore, the surface quality of the rake face plays an important role. To counteract built-up edges, the rake face must have good sliding properties. For this reason, it is finely ground or polished.

Changeover Accuracy of 2.5 µm

Clamping of the inserts is another important point in tool design. When machining turned parts of small diameter, the centre height of the tool must be precisely measured. Even slight deviations in centre height have a negative effect on the quality of the workpiece when machining the smallest diameters. In the best case, the machine operator should be able to turn the insert without having to readjust the centre height. With the μ-Finish system, HORN offers a changeover accuracy of +/- 0.0025 mm (0.0001″) when indexing a double-edged insert. This is made possible by the precise peripheral grinding of the insert in conjunction with the stable insert seat. In addition, the contact surfaces of the square shank toolholder are also ground, which has an effect on the holistic precision of the HORN system.

The grinding of a sharp, flawless tool cutting edge requires a lot of know-how. Grinding wheels with the finest grits, special new grinding techniques and a microscope with 400x magnification are necessary to ensure that the tool performs as required. In the process, every batch of the μ-Finish system produced is subject to 100 per cent inspection. Important quality assurance criteria are the tightly toleranced high surface quality of the rake and flank surfaces, the centre height and, in particular, the sharpness of the cutting edge. There must be no visually recognisable irregularities on the cutting edge with the µ-Finish system.

HORN presents itself as a holistic supplier of tools for all Swiss-type machining operations. The extensive insert portfolio can be easily adapted to the requirements of different processes in sliding-headstock turning. Close partnerships have been established with the companies Graf Werkzeugsysteme, Boehlerit and W&F Werkzeugtechnik to provide solutions for the interfaces between the cutting insert and the machine, including for ISO tools.

Broad Knowledge

Horn’s know-how does not only apply to cutting tools. The tool manufacturer also supports its customers and partners with knowledge of the correct application data and the development of new tool systems and manufacturing processes for sliding-headstock operations. This includes, for example, competence in driven tools, tool holders for backworking and entire tool solutions.

HORN Mastering Processes: High Feed Milling

 

 

Tool Systems manufactured by Paul Horn GmbH offer users the ability to design machining processes for high productivity and cost efficiency. Especially in tool and mould making, high feed milling can be used economically and productively. High performance milling is not only defined by high infeeds, but in high feed milling also by small infeeds coupled with high traverse speed of the cutter.

 Machining applications have changed and challenges have become more complex and demanding. Shorter product life cycles and reduced development times dictate that several different components must be produced on one machine in shorter cycle times. For the tool manufacturer, this requires designing tool systems for the different applications. It means, for example, that a tool may not only be used for corner milling, but should also have the optional ability to plunge cut. Another aspect is modern machine dynamics. The acceleration and deceleration of the axes as well as their synchronisation have been significantly optimised. For relatively new technologies such as trochoidal and high feed milling, tool systems must be able to withstand the high dynamic loads.

Low Infeed – High Metal Removal Rate

A few years ago, Horn introduced a system for high feed milling – DAH cutters for face milling. Due to the load being in the axial direction, the tool and spindle mainly experience compressive force and the shear forces are relatively low. Due to their low tendency to vibrate, the tools are able to withstand the high loads typically generated by a feed per tooth of fz  = 1 mm at cutting depths ap up to 1.2 mm. The large radius on the main cutting edge of the three-edged inserts creates a soft cut, ensuring an even distribution of the cutting forces and long tool life. On the inside, a small cutting edge radius ensures trouble-free and fast plunging. A primary and secondary clearance angle leads to a stable wedge angle and very good cutting edge stability. Due to significantly higher feed rates compared with conventional milling, metal removal rate in high feed milling is significantly increased, despite the lower infeed depths.