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.