Increased capacity without increased space

GEA Refrigeration Germany GmbH in Berlin has replaced three somewhat ageing milling machines with new Heckert HEC 630 Athletic and Heckert HEC 800 Athletic machining centres for the machining of screw compressor housings. In doing so, they have been able to reduce processing times by around 40 % while generating additional manufacturing capacity in the same amount of space.

What do a wind tunnel in Vienna, an indoor ski resort in Dubai and the Stutt- gart trade fairs have in common? They all contain cooling equipment from GEA. The international technology group also supplies refrigeration and air-conditioning solutions suitable for many other industrial applications, such as for engine test benches and spray booths, warehouses and cold chains for food products like yoghurt or ice cream.

At the heart of these units is the GEA Grasso screw compressor, manufactured at the company’s Berlin site. In 2016, a total of around 1,500 compressors left the factory, in 28 different models with flow volumes ranging from 280 m3 to 1,100 m3. Their special features: high efficiency and long service life.

Important advantages of the Heckert HEC 630 and HEC 800 machining centres: large working area and quills for creating deep bore holes with high process reliability.

Screw compressor manufacturing in the GEA refrigeration plant, Berlin:Three new Heckert HEC centres reduce processing time for housing units by around 40%.

Such a screw compressor essentially consists of rotors and housings. Each manufacturer keeps the rotor profile a particularly closely-guarded secret, as it lays the foundation stone for efficiency. But suction, pressure and rotor housings also have a marked effect on quality. Strict shape and position tolerances have to be adhered to, from the flange faces up to the mating holes for the rotor bearings. Production Manager Hanno Heim explains: “Axis parallelism is particularly important to guarantee years of trouble-free service from the rotors. We are therefore moving in areas of higher than 20 μm accuracy for position, and higher than 10 μm in terms of concentricity and angularity.”

Pressure to modernise machining

Processing housing units places high demands on the machines. As well as the aforementioned precision, high levels of reliability and large travel paths are required. Not least for the extra-large screw compressors, whose housings have a volume of around a cubic metre and a weight of roughly 1.5 tonnes.

A Heckert machine

Ronny Kolbe (left) and Burghardt Krüger jointly create and optimise the CNC programs for the new machining centres. They were essential to the successful introduction of the machines.

“Investment in the new machining centres increases the production capacity to such an extent that previously utsourced housing machining can now be brought back into their own factory.”

In order to ensure economic housing machining for the entire product range, GEA took the decision to make their facility in Berlin state of the art. Since numbers have grown so much recently that part of the production had to be moved out, returning to entirely in-house production required additional capacity.

The plan was to replace two ageing horizontal machining centres. This came with the need to dramatically reduce machining times (especially downtimes), to increase machining accuracy and to devote particular attention to high-pre- cision depth machining of bore holes. A high level of machine availability was also in the list of requirements along with the latest Siemens 840 D sl controller and a switch to HSK-100 tool holders. “We considered every detail in terms of opti- mising the machining process”, stresses Production Manager Hanno Heim. “Then we thoroughly compared the relevant machines from various manufacturers. This included time studies for a reference component, involving all the necessary machining processes.”

Ronny Kolbe and Burghardt Krüger

Machine operator Sascha Sagert enjoys work- ing with the new HEC centres.The new control panel and the latest Siemens CNC 840 D sl provide a clear overview of the work.

HEC 630 Athletic collects the most plus points.

After evaluation using a sophisticated points system, GEA managers decided to make their purchase from Starrag, a global technological leader in the manufacturing of precision machine tools. A Heckert HEC 630 Athletic horizontal machining centre was ordered first, followed a few months later by a Heckert HEC 800 Athletic for the machining of large parts.

Several factors swayed this decision. For one, the HEC 630 promised a calcu- lated time saving of 36% over their previous machining process. In comparison, the closest competitors only offered between 30 and 32 %. The Heckert machining centre came out on top in the technical machine evaluation, and what’s more, previous good experiences made a new partnership with the Chemnitz-based machine manufacturer very appealing.

From a technical point of view, the Heckert HEC 630 triumphed with its overall design. Its axle configuration makes it extremely stable: X and Y-axes in the tool, with the Z-axis in the machining table. This is supported by the rigid and thermo-symmetrically designed main components. Together with the digital AC feed drives, complex profile rail guides and ball screw spindles in all linear axes, these provide a solid basis for a reliable machining process.

Production Manager Hanno Heim is pleased about the additional production capacity brought by the modernisation measures. Now all the housings can be machined in GEA's own factory again.

Burghardt Krüger, a process engineer involved in machining housing for many years at GEA, was involved in the decision. He emphasises a strength which other manufacturers aren’t able to provide: “Starrag offers a quill even on its mid-sized 630 and 800 Heckert HEC machining centres. For our deep bore holes, this is an enormous advantage because it enables us to use short, compact tools which bring high precision and process reliability.” The alternative to a quill (125 mm in diameter and 500 mm extension length) is to use long, heavy tools. These are more expensive and also tend to vibrate and bend, increasing the likelihood of machining inaccuracies.

Large working area and convenient chip collection

Burghardt Krüger also mentioned the working area, another important detail: “With the Heckert HEC machining centres, we have been able to considerably increase the interference range and traversing paths compared to previous models. This means we can go one machine smaller than in the past, which really helps when installation space is limited.”

The working area is also designed in such a way that the chips fall freely into the centrally-positioned swarf conveyor. This prevents chips from piling up in the working area and endangering process reliability. Krüger also rates the use of fixed plates instead of telescopic covers positively, as they provide the functional elements with optimal protection from chips and coolant. This enables higher acceleration and rapid traverses, as the plates do not need to be carried along with the linear axes.

With an extended Z-axis and a machine table capable of supporting up to 2.5 tonnes, the Heckert HEC 800 Athletic is ideal even for the largest GEA Grasso housing.

40% reduction of machining times

After the successful benchmark set by the Heckert HEC 630, GEA decided on a second machine in the same range: a Heckert HEC 800 Athletic, which is equipped specifically for processing large housings with its extended Z-axis and machining table capable of supporting up to 2.5 tonnes.

Ronny Kolbe works particularly intensively with the new Heckert HEC machining centres. The specialist in production planning and control works together with Burghardt Krüger to create and optimise the CNC programs that are run on it. He also mentions another plus point which has already been proven in practice–the tool magazine with 255 pockets that can automatically accommodate tools of up to 340 mm in diameter and up to 800 mm in length: “This capacity makes us very flexible and means we don’t have to constantly re-tool, even for the smallest series runs. We were also able to reduce clamping operations per housing from three to two.” Despite its large tool wealth, the tower magazine requires only a small footprint in comparison to other solutions, which is a key argument in cases where space is confined.

Heckert machine

Successful teamwork:The GEA employees (from left) Ronny Kolbe, Sascha Sagert, Burghardt Krüger and Hanno Heim thank Ulrich Seidel, representing all involved Starrag and Heckert employees, for a professional, reliable and co-operative partnership.

Over 40% savings.

The results of the modernisation measures are pleasing: In practice, processing times for housings in the GEA Grasso M series have been reduced by around 45 % on the Heckert HEC 630. The savings for the XL screw compressors in the GEA Grasso LT range, machined on the Heckert HEC 800, are of a similar magnitude. It was proven practical successes such as these which convinced management to replace another machine sooner than planned. In December 2016, the Heckert CWK 1000 made way for an additional Heckert HEC 800 in the Berlin GEA factory. The shorter processing times not only reduce manufacturing costs. They increase production capacity to such an extent that previously outsourced housing machining can now be brought back into their own factory.

The new investment also means that the Berlin GEA plant is well equipped for the future and “Industrie 4.0”. This is why Head of Maintenance, Manuel Marks, is delighted to be looking after the three new machines: “These machines can be monitored remotely with Starrag Conect. This means I can find out about the current operating parameters of individual machines, such as parts program, axle position, spindle speed, NC block, tool etc., at any time from anywhere with a tablet and an internet connection. Preventive maintenance is therefore replaced by situation-specific maintenance, because I can monitor the condition of the machine constantly by means of temperature and vibration sensors. The software detects increasing wear or failing lubrication so that I can respond at exactly the right time.” The software also reports faults and error messages, and offers direct access to the complete machine documentation when required. If GEA later decides to enhance its manufacturing with further machines from the Starrag, these can be integrated easily into the Starrag Connect system.