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.

 

 

HORN: New Coating RC2 / RC4

New Horn coating RC2 / RC4

With the new RC2 and RC4 coatings, Paul Horn GmbH is exhibiting new developments in the field of high-performance tool coatings. The high toughness and hardness allow the machining of steels at high cutting speeds and lead to a significant increase in tool life. The high temperature resistance enables productive use in dry machining as well as with minimum quantity lubrication. Numerous tool systems are available from stock with the new HiPIMS coating. In-house coating enables fast delivery times even for special tools.

Horn is constantly investing in new and modern technologies. In 2015, the company CemeCon delivered the world’s first of three HiPIMS systems to Horn. The High Power Impulse Magnetron Sputtering technology brings specific advantages and new possibilities in the coating of precision tools. It enables the build-up of dense, compact coatings that are very hard and tough. The coatings have a homogeneous structure and uniform coating thickness even if the tool geometry is complex. Research and development of new and existing coatings and technologies is a central component of success. Horn employs a team of engineers who work exclusively on this subject. Since in-house coating started, research and development projects have been carried out in cooperation with equipment manufacturers.

HORN Mastering Processes: Grooving

When Paul Horn introduced the type 312 indexable insert to the public in 1972, it was a small revolution in the grooving process. Horn was the first manufacturer ever to develop a tool system with a vertically mounted, three edged carbide insert for grooving. Today, the grooving process with indexable inserts is indispensable in modern manufacturing. Radial grooving, parting-off, face grooving and internal grooving to µ-precision are now part of everyday life in the machining industry. Paul Horn’s incentive at the outset was for the technical perfection of his products and the Horn company continues to set similar standards in tool technology for this machining process.

 

The 312 insert is still popular with users today. Horn has not stopped developing and optimizing successful product families. At the same time, Horn has completely integrated the value creation for its entire product range into its own production. The possible applications of the tool have grown considerably after the insert was originally used almost exclusively in the automotive industry. The “312” is intended for external machining and is used, among other things, for producing workpieces in the medical industry, in the manufacture of hydraulic components and for making everyday objects such as jewellery or ballpoint pens. However, it is not only the type 312 insert that has made the precision tool manufacturer known as a specialist for machining between the flanks. Numerous other tool systems followed the idea from 1972, which are now successfully used for grooving worldwide.

Basically, the grooving process involves a narrow cutting edge that penetrates the workpiece in a radial or axial direction. The art of grooving is, among other things, controlling the chip flow. Chip sticking, jamming or long, stringy swarf must be avoided in practice, as they have a negative influence on process reliability and can lead to tool breakage and damaged flanks. Depending on the material to be machined and the type of machining, Horn has developed different chipbreaker geometries that ensure reliable chip formation, control and breakage. Another important point for economical grooving is a sufficient supply of coolant. Where in the past cooling was external with the classic flood coolant, today modern tool carriers are used, mostly with an internal coolant supply. This ensures effective cooling of the shear zone between the tool cutting edge and the workpiece. For parting-off, Horn also offers a type S100 insert, which supplies the contact zone with coolant at high pressure directly through the insert. Tools are exposed to high loads during parting-off. The quality of the carbides used, the quality of the cutting edge and the insert coating also play an important role in reliable and economical parting-off.

Grooving in Practice

A user produces a wide and deep groove in an aerospace component using the trochoidal grooving method. It is very well suited to the production of of deep, wide grooves where high metal removal rate must be generated.The machinists produce the component from 1.4548 (X5CrNiCuNb17-4-4), a steel with high corrosion resistance, strength and toughness. Roughing is carried out using a full radius Grooving insert S229 with a radius of 2 mm. The grooving process is designed as follows: The 30 mm wide and 15 mm deep (incremental) recess is trochoidally roughed using the full radius indexable insert with a cutting speed of vc = 140 m/min at a cutting depth of ap = 1 mm The programmed feed rate is fn = 0.25 mm -1. The finishing allowance is 0.2 mm. Finishing also involves using a cutting insert from the S229 system. The finishing operation is carried out from two sides with a 3 mm wide grooving insert. The corner radius is 0.2 mm. The total production time to complete the groove is less than two minutes.

 

Face Grooving in the Medical Sector

For the production of a thin-walled valve cover made of titanium for a cerebrospinal fluid shunt system, the SuperMini system type 105 is used. On one hand, the customer uses a tool for the face grooves and, on the other, a special tool for finishing the lid fit. For the narrow fit on the lid with a length of 0.5 mm, Horn had to design the SuperMini tool with a corner radius of 0.05 mm. The difficulty in machining titanium always arises from the dissipation of heat as well as the control of chips. For use as an implant, the user has strict criteria regarding the surface quality and the absence of burrs on the component. By optimizing the cutting paths with a CAM system, the experienced colleagues in the machining department were able to double the tool life from 1,000 to 2,000 components.

Although Horn’s tool portfolio has expanded considerably, not only in the area of grooving but for all applications in the field of demanding machining tasks, grooving and thus machining between two flanks is still considered the supreme discipline.

Looking ahead to the AMB 2022 trade fair in Stuttgart and IMTS 2022 in Chicago, Horn is presenting innovations and expansions in the area of grooving.

 

 

HORN Mastering Processes:  All-Rounders for Milling

Horn Circular Milling System with large range of Diameters, Cutting Teeth (Edges) and Cutting Widths.

 Groove Milling, Parting Off and Gear Cutting: these are just three processes that the Horn circular interpolation milling system accomplishes productively. As a true all-rounder, the extensive tool portfolio of this tool system tackles several other milling tasks as well. It can be used from an inside diameter of 8 mm for precise boring, for slot milling of narrow grooves from a width of 0.2 mm or for milling splines. The system has proven to be a problem solver in its numerous standard variants, as well as in special custom shapes for other milling processes.  

The circular milling system from Horn offers the user a number of advantages: it is fast, reliable and achieves good surface finish. The tool, which is interpolated on a helical path, plunges into the material either at an angle or almost horizontally. This makes it possible, for example, to produce threads reproducibly to high quality. Compared to machining with indexable inserts for larger diameters or solid carbide cutters for smaller diameters, circular milling is generally more economical. Circular milling cutters have a wide range of applications. They machine steel, special steels, titanium, aluminium and special alloys. The precision tools are particularly suitable for groove milling, circular interpolation of holes, thread milling, T-slot milling, profile milling and gear cutting. However, they are also effective in special applications such as milling sealing grooves or machining connecting rods.

 

The Horn milling system provides vibration-free cutting even with a long overhang.

Milling of Splines

The production of splines on a drive shaft had the potential for improvement. The shaft, which is 200 mm in diameter, almost 5,000 mm long and weighs around 600 kg, is used in the construction of large engines. The user previously had the teeth machined externally. Horn suggested that the spline teeth be machined using its 635 circular milling system in the same set-up as the turning operation. The special profile of the tool’s six teeth matches the nominal profile of the tooth flanks on the workpiece. The overhang of the tool is long due to the cutting conditions but the vibration-damping solid carbide shank means there are no problems with tool vibration. All Horn tools for circular milling have an internal coolant supply. The precise interface between shank and insert allows micron-accuracy concentricity and run-out of the insert during changeover. Roughing and finishing are done with the same tool. In addition to the significantly faster production time and the elimination of subcontracting out production, the quality of the splines has also increased.

 

Slot milling a with the Horn 606 Circular Milling System

Slot Milling in Micromachining

Another application example is the machining of a valve component. The workpiece has a diameter of 1.6 mm and a length of around 3 mm. To enable the valve to be adjusted, a 0.3 mm wide by 0.5 mm deep slot has to be milled on the face of the component. The user previously machined the slot with a fine HSS saw blade. However, the variable stability of the process offered the potential for improvement. Horn solved this problem with its 606 milling system. The six-edged insert with a cutting width of 0.3 mm provided the user a secure milling process.

Horn has expanded the circular milling system to include tools for producing narrow grooves. The enlargement of the tool system offers the user the possibility to produce narrow grooves less expensively. Horn supplies the tools in cutting widths from 0.25 mm to 1 mm as standard, depending on the diameter. The maximum milling depth tmax is between 1.3 mm and 14 mm, also depending on the tool diameter. Subject to the material to be machined, the cutting inserts are available with different coatings. The solid carbide tool shank, due to its mass, ensures vibration damping during milling. All variants of the tool are equipped with an internal coolant supply.

These are just two application examples of the many possibilities offered by the Horn circular milling system. The flexibility in the design of the cutting edges, the precise interface between the cutting insert and the shank, the numerous diameter variants as well as the different numbers of teeth that may be milled per insert characterize this tool system.