Heckert NC quills

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Heckert NC quills: For higher cutting values and improved process reliability

Metalworking can be demanding in many ways. Mould elements situated inside the workpiece pose a particular challenge. To machine these precisely and economically, a horizontal machining centre with NC quill is recommended – from the Heckert compact or large machine series, for example.

How can large gearbox housings for construction and agricultural vehicles, planetary gear carriers for wind turbines or even large flow bodies for the chemical industry be machined in an economically and technically optimal way? Especially when high-precision bores, bearing seats and similar elements have to be created deep inside?

Such workpieces are clamped on a correspondingly large machining centre and then on a boring mill for the internal mould elements – accompanied by the expense of machine changes, loss of time and loss of accuracy due to reclamping errors.

Or you can use the machining centre for complete processing. This avoids the negative aspects of changing machines. For this, however, the machine must be equipped with long tools in order to reach the elements situated in the workpiece. This is also a costly affair, often accompanied by uncertain machining results in limited quantities.

Or – the user decides on a machining centre that is equipped with a work spindle designed as an NC quill. This can machine deep surfaces and bores with short standard tools, thus saving tool costs. Extremely smooth running also increases tool life and surface quality. Compared to the use of long tools, the quill solution offers machining with higher cutting values and improved process reliability.

Many years of experience in quill construction

Starrag’s Heckert plant in Chemnitz offers machining centres with such a quill support. Klaus Frost, head of the test workshop, reports: “We developed our first quill with a 125 mm diameter and 500 mm extension travel in the mid-90s. It was intended for gearbox housing construction in the tractor sector and immediately proved its worth to the world’s leading manufacturers. Because of this, they were able to produce bearing bores in a much higher quality than previously possible with conventional tools – and in largescale production.”

Classic application: Machining the bearing surfaces of an angular gearbox housing.

The Heckert developers already recognised the potential of such fully enclosed milling centres. Initially, they developed the 125 mm quill for the Heckert CWK 1000 to 1600 series – large machining centres that were transferred to the Heckert Large Athletic HEC 1000 to 1800 series in the early 2000s. With the development of the Heckert Athletic HEC 500 to 800 compact machines, customers also wanted a quill support in these smaller centres. No sooner said than done – from 2008, the 125 mm quill was also available as an option for this.

With the growing demand for wind turbines featuring gearbox housings with even larger dimensions, manufacturers expressed the desire for a more powerful quill with even greater extension travel. This was fulfilled in 2004 with a 150 mm quill that can extend the tool 750 mm beyond the edge of the pallet into the workpiece. This proved to be a successful model that was continuously improved in the following years – for example, with thicker walls and a water-cooled motor that enabled spindle power to be increased to 82 kW (S6). Due to internal and external cooling, the speed could be increased to a maximum of 5,000 rpm. The 125 mm quill also received a watercooled motor, boasting 53 kW of power and a speed of up to 4,000 rpm.

Successful application in heavy machining

Eckardt Vogel, application technologist and quotation project manager, explains that large gear manufacturing has remained an important area of application to this day: “Our quill machining centres are still purchased for classic gearboxes for tractors, agricultural tractors and other agricultural vehicles as well as for stepped gearboxes in construction machinery, for planetary gear carriers and conventional gearboxes in wind turbines. However, we also supply manufacturers of gearboxes for mixing plants in the process industry and for flow bodies in the chemical industry. A niche application has also developed in electrical engineering. This involves boring out stator housings for heavy electric motors, as required in the power-generating industry.” In almost all cases, this involves heavy machining of various types of cast iron as well as high-alloy steels.

The success of quill technology is based on the fact that there is virtually no competitive alternative, either economically or technically. Eckardt Vogel explains the tooling problem for machining centres without a quill in detail: “To reach the inner areas of a gearbox housing, tools with a long projection length are needed that tend to vibrate considerably. They must be vibration-damped, finely balanced and equipped with all kinds of refinements in order to achieve acceptable concentricity.” In addition, there are usually problems with the tool magazine and tool changer. This is because an exemplary cutter head tool with a 400 mm long shaft is extremely heavy and has a very large tilting moment. This means that a pick-up solution must be installed in the workroom. “That’s not desirable either,” the application technologist just knows: “Besides, you end up needing more than one tool – one for each depth and each attachment. This has a very unfavourable impact on manufacturing and, ultimately, unit costs.”

In contrast, a quill gives the user a high level of flexibility. To a large extent, they can fall back on relatively inexpensive standard tools. A second effect of the two Heckert quills is that due to their low-backlash sliding guide, they have a strong vibration-damping effect, which makes higher cutting values possible, increases process reliability and produces better surfaces.

Sophisticated design and monitoring

The features of the Heckert quills are largely identical to those of the otherwise normal spindles. Both offer the HSK-A100 or SK50/BT50 tooling interfaces, which are also available with a face contact. The quill is designed for internal coolant supply at up to 80 bar. “This is an important factor,” emphasises test workshop manager Klaus Frost. “Because with internal machining, the coolant is not supplied to the cutting edge of the tool externally.”

“I know customers who report a payback on their quill within a year.”

Carsten Bergmann, Product Manager Heckert

Beate Göbel, the designer responsible for the 125 mm quill, explains further design details: “We introduce motor speed and power into the quill spindle via a drive free of lateral forces. We also put a great deal of technical effort into the bearing. The 125 mm quill, for example, is equipped with a 170 mm diameter angular contact ball bearing lubricated for life. The 150 version contains an oil/ air-lubricated angular contact ball bearing with a diameter of 200 mm. And we offer work spindle diagnostics for the quills, as is common with our other spindles, but expanded to include additional quill-specific bearings.” In addition to the bearings, the following conditions are monitored: Spindle imbalance, vibration during machining and impact. The data is stored in the evaluation device and can be read out and visualised via evaluation software.

That still leaves the question of cost. According to Carsten Bergmann, Product Manager Heckert, the quill support will set you back 120,000 euros more – taking a Heckert HEC 630 as an example. However, he emphasises that the investment is definitely worth it when you consider the possibilities that it opens up, such as complete machining, the savings in tooling costs and the benefits in terms of productivity and unit costs. Carsten Bergmann provides assurance, saying “I know customers who report a payback on their quill within a year.”

For all interested parties, the Product Manager points out that the new H series is currently being upgraded at the Starrag plant in Chemnitz to include the Heckert H95 and H105 models: “The Heckert H95 will replace the previous compact machine Heckert HEC 800. We will present this machine at EMO 2023 equipped with a 125 mm quill.”