Precise heart transplant

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industrial

Precise heart transplant - Starrag supplied high-precision Heckert HEC 800 to KAPP NILES

In 2024, KAPP NILES, a specialist for gear grinding machines, replaced a jig boring machine for precision finishing in its Coburg production facility. The new machine: a high-precision Heckert HEC 800 machining center. For Sascha Forkel, Head of Cubic Machining, the exchange was akin to a heart transplant: “It is a key machine in our production operations, without which we would no longer be able to supply.” It is now clear that the operation was a success!

A glance into the production halls of the Coburg-based KAPP NILES factory clearly suggests that special machines are developed here. “Order and cleanliness as well as a high-quality machine fleet are the prerequisites to build our gear grinding machines”, says Sascha Forkel. Under his management cubic parts up to one cubic meter in size are machined here: “These are key components for our machines, which are used for the high-precision manufacture of toothing and profiles.” Each one of these components must adhere to extreme shape, positional, and dimensional tolerances of up to 3 μm so that KAPP NILES machines can satisfy the high customer requirements. In the end the toothing should mesh into the gears exactly and quietly – whether in the automotive industry, mechanical engineering, or in other applications. The components – made from up to 80 per cent cast iron, the rest is made from steel – are pre-machined by Forkel's team on various machining centers. An allowance of 0.3 mm remains on all areas with quality requirements. Bore holes maintain an extra 1 mm in diameter.

Then it gets complicated, as the cutting expert explains: “During the finishing process we operate in tolerance ranges of a few micrometers, not only in shape and position, but also in the positions relative to each other. The surfaces must also be of the highest quality.”

The heart of production

Up until recently this task was undertaken by a 16-year-old jig boring machine, for which, however, the supply of spare parts was no longer guaranteed. The failure risk and associated extended production downtime were too high for the persons responsible. They preferred to arrange an exchange as a precautionary measure.

Top priority: Like its predecessor, the new machine must guarantee reliable precision cutting in the micrometer range. Following a market analysis KAPP NILES shortlisted three suppliers. The machine operators were also included in the selection process. They selected the most challenging component for trial machining runs: a complex motor housing. The three shortlisted machines were tested under identical conditions: same component, same pre-machining, same clamping devices, same NC programs and tools. The machine operators from KAPP NILES clamped the pre-machined parts for the machine manufacturers in order to achieve comparable results across the board. “Experienced machine operators and NC programmers who work on the machine are required”, highlights Sascha Forkel. “The machine will be the new heart of our production, but it is not solely responsible for success. Only when the machine, operator, and NC programmer work together in perfect harmony can the components be manufactured with high precision.” For the final assessment, all three sample components produced were measured on the same measuring machine at KAPP NILES. “Following the measurement results and taking into account other technical details. We decided on the supplier Starrag and the Heckert HEC 800 machining center, equipped with the high-precision kit and other add-ons promoting accuracy”, reports Sascha Forkel.

Mechanical accuracy versus software compensation

Apart from the measurement results, the mechanical accuracy of the machine was a decisive selection criterion. Rainer Krause, the Area Sales Manager at Starrag who is responsible for KAPP NILES, explains: “Heckert machining centers already have high mechanical accuracy. It is in a tolerance range that is only half the size of what is typical for machining centers.”

Sascha Forkel confirms this. He points out that various manufacturers have similar accuracies for their machines; however, this is based on compensation in the control software. In his experience this can cause problems: “One example: We generally produce bore holes on this machine with single-edged tools. The compensation in several axes can cause warpage, meaning the bore hole is not cylindrical. This is a no-go for us.” In addition to the already high basic accuracy, the high-precision kit, which Starrag offers for its Heckert machining centers, was another decisive factor. Water cooling for stands, axis drives, and ball screws ensures the thermal resistance of the machine. The water is cooled or heated so that it maintains the default temperature in the range of ± 1 K. All heat sources such as motors and hydraulics are also protected from the accuracy-relevant components of machine stand and bed. Another component of the kit is hand-trimmed guides which ensure optimized positioning accuracy.

Development in detail

Starrag Area Sales Manager Rainer Krause describes the procedure once the order has been placed: “We developed the offer from a technological perspective so that KAPP NILES can represent its entire range of parts with our Heckert HEC 800.”

All measures were secondary to the topic of accuracy. For instance, the Chemnitzbased designers further restricted the tolerance of the circular axes and in particular reduced the wobble of the B-axis. Because the KAPP NILES cutters must add bearing bore holes from two sides, which requires the highest possible indexing accuracy.

For the spindle, KAPP NILES chose a direct drive solution developed by Starrag. “The smallest inaccuracies of a gear spindle would have been too much for us”, argues Sascha Forkel. “We even limited the maximum speed from 12,000 rpm to 10,000 rpm in order to achieve higher process reliability.”

Sascha Forkel, Head of Cubic Machining KAPP NILES

“We developed the offer from a technological perspective so that KAPP NILES can represent its entire range of parts with our Heckert HEC 800.”

The rapid traverse rate and acceleration ramps were also reduced to avoid machine vibrations where possible. Rainer Krause highlighted the close cooperation with Sascha Forkel and his team: “We discussed a great deal in this phase and specified the plans down to the last detail – through to the gentle positioning of the pallet on the set-up point. Because if this is done too roughly, vibrations occur which continue into the machine.” Another relevant point was the accessibility of the machine. The machine operators wanted practical and safe access to the machining area for set-up and measuring tasks. As a result, steps, handrails, and a platform in front of the machine were designed. The entire operating peripherals were lifted accordingly. An automatic drilling system was also implemented.

Automation for uncritical parts

The addition of an automation system was planned right from the start. “Our goal was to be able to machine uncritical parts without human interaction”, explains Sascha Forkel. “As we had no experience with pallet automation, we were totally reliant on Starrag's expertise here.” As Starrag works with various automation partners, the local conditions were decisive for the recommendation. Rainer Krause explains: “Taking into account the spatial conditions at KAPP NILES, an Erowa LoadMaster system was chosen. With a pallet station for nine workpiece carriers, it promised the largest capacity-related advantage.”

Pallets are one of the core competencies of the Chemnitz-based machine manufacturer, as Rainer Krause emphasizes: “We manufacture them ourselves. Their impact on the accuracy produced on the workpiece is too high. For KAPP NILES, we supplied a total of nine pallets, six of which are in a standard design, i.e. precision milled and sanded, and three hand-milled for particularly challenging components.” The Heckert HEC 800 with Erowa LoadMaster now occupies the same size footprint as the predecessor machine – with increased efficiency. “As planned, uncritical components are machined in a fully automated operation. These are parts with tolerances of 10 μm and higher, i.e. with H6, H7 fits.” KAPP NILES jargon: rough machining.

Trust – an important business principle

Sascha Forkel is convinced that he has found the right partner with Starrag and the Chemnitz-based Heckert specialist. “It is an advantage when medium-sized mechanical engineers work together. Both sides know what they are talking about and what matters. A special relationship of trust was established on this project.” Visits to the Chemnitz factory and Heckert reference clients were also a contributing factor. The extent of that trust was reflected in particular in the retrofitting. Instead of the originally planned gradual operation from jig boring machine to the Heckert machining center, the persons responsible decided on a hard cut, which Sascha Forkel describes as follows: “We dismantled our old machine in July 2024. We then had two weeks for preliminary work in the hall because the Heckert HEC 800 arrived on time in the middle of August.” The site acceptance test took place in November, and after an introduction phase it went into production from January 2025. “Granted, the cut was a bold move”, says Sascha Forkel. “But through the close contact with the Chemnitz-based Starrag experts, we assessed the risk as relatively low that anything would go wrong during the exchange and the new Heckert would not deliver from the beginning. Our conclusion: The heart transplant was a complete success.”