Industry 4.0 in the production of prestressed concrete turnout sleepers

Prestressed concrete turnout sleepers are characterized by a great variety of versions. After ordering, clients purchasing these products expect ever shorter lead times, with ever more increasing the requirements on the quality simultaneously. In order to enable this, Rail.One has now put a facility into operation, based on the Industry 4.0 approach for the first time. This facility was opened in the Bavarian town of Schwandorf, in November 2019 (see Fig. 1). The plant was primarily implemented by Weckenmann Anlagentechnik GmbH & Co. KG.

1. Basic information on Industry 4.0

Several stages of evolution have been passed since the beginning of industrial manufacturing. The first stage started with the transition from an agricultural economy to an industrial economy and is usually referred to as the industrial revolution. The second stage originated in the introduction of electricity at the beginning of the 20th century and is characterized by the assembly-line work developed in those days. With the further development of electronics and in particular of information technology (IT), the third stage then began in the 1970s. Since then, it has been possible to control machines selectively, to coordinate individual processes and to optimize them more and more with the aid of control technology. This also allowed companies to comply with the request for differentiation and individualization of products in mass production.

For the first time, it was referred to the fourth, and so far last, stage on the Hannover Messe trade fair in 2011. Terms such as „smart manufacturing“, „smart factory“ or also CIM „computer integrated manufacturing“ are used in an international context to refer to this stage. A basic principle is the fact that the entire value chain is digitized from the order to the delivery. The production components that had yet been passive in the previous stage become independent now and control or configurate themselves according to the respective order situation. The information needed here is received from a master computer and all the information necessary for the production process is provided by data bases. It is also characteristic that the digital components are decentralized and are interconnected by networks that can be connected according to the situation.

2. The concept of the facility

A wide variety of different turnouts exists in rail transport. They are used both in straight lines and in curves. According to the speed of the traffic the turnouts have to take, they can also have different lengths. A concrete sleeper installed on the track must ensure that the acting static and dynamic loads due to the rail traffic are directly transferred into the subgrade. At the same time, the track has to be kept in position permanently. For a concrete sleeper installed below a turnout, it must moreover be ensured that all mechanical components for the operation of a turnout can be attached to the sleeper and that the correspondingly occurring loads can be transferred. For turnout sleepers, these boundary conditions lead to the fact that each sleeper has individual fastening points which are already implemented in the production process by means of anchors or dowels. It is particularly challenging here to position these fastening points accurately. In respect of their geometrical position, these fastening points have to be manufactured with a tolerance of only +/- 0.1 mm. Sleepers having identical dimensions can only be used at the start and the end of a turnout, whereas all sleepers differ from each other within a turnout. At present, the data base of turnout sleepers comprises about 10,000 individual customized sleepers for the use in Germany alone. Every year more types are added because a lot of railroad tracks require special solutions.

Nowadays, prestressed concrete turnout sleepers are primarily manufactured on long prestressing beds. In this process, the necessary customized fastening points and the length of each individual turnout sleeper are realized with the aid of a so-called „base plate“. The accurate position of the fastening points is implemented by means of drill holes placed and measured accordingly. Stock is kept of these plates, and then they are inserted in the long prestressing bed respectively.

Long prestressing beds provide many advantages, but they are limited in terms of automation or productivity, and they require above all a considerable volume of enclosed space. These disadvantages can normally be compensated by carousel systems – that is to say, plants where molds are carried in a circuit. Such systems do already exist for the production of turnout sleepers made of concrete, and plants have already been operating in Poland and Italy for several years now. However, using these systems, base plates are still exchanged in the molds which means an enormous effort in terms of logistics and labor. Therefore, this process should be developed even further in Schwandorf. The central idea in this respect was not to exchange base plates any more in the future. Hence, a completely new production process was the result at the end of the planning phase. Many processes which are done manually in traditional carousel systems were replaced by state-of-the-art articulated robots and automated gantry and transport systems (see Fig. 2). In addition to this, the entire manufacturing process should be incorporated in a digital environment according to the concept of Industry 4.0.

3. Practical implementation

The facility in Schwandorf, inaugurated in October 2019, was especially designed for the requirements and dimensions of a carousel system. The mixing plant is provided with a housing and is connected to a stationary cooling/heating system, allowing the production of concrete in a consistent quality throughout the year and at a fresh concrete temperature independent of the ambient conditions. The system is fitted into a building with a floor space of about 2,200 m² in a space-saving way. Modern articulated robots are integrated at several places. A robot is used to spray the molds featuring different lengths with release agent, another robot is exactly placing the various mounting parts needed into the molds complying with the specified tolerance of +/- 0.1 mm (see Fig. 3). The prestressing steel strands together with the anchoring elements are prepared by a fully automated upsetting machine and are placed into the molds automatically by means of a gantry system. Prestressing takes place in a fully automated process and the casting process is semi-automated. Vibrators (MagVib system of Weckenmann GmbH & Co. KG), being magnetically attached to the molds from below, are used to compact the concrete in the molds of varying in lengths. Owing to the frictional and complete connection of the vibrators, the compaction energy is introduced into the mold without any loss and the noise emission is low during compaction. Therefore, an otherwise normal soundproof cabin was not necessary.

The machines and molds used in the production process are controlled by a conventional PLC. The PLC communicates permanently with a master computer, providing all information required in the production process. The master computer, in turn, is constantly connected with the internal ERP system (SAP) of the company. As soon as an order has been placed for a turnout, it is recorded by the ERP system. All technical details are recorded in the associated data base. An order required for the purchased parts related to the turnouts is placed automatically whilst taking into account the production deadline. The implementation in production is also assumed by the master computer, optimizing the utilization of the molds according to the specific algorithms. In addition, the master computer provides the various equipment components with important information, such as quantity, type and location of mounting parts, prestressing force, length of the prestressing steel strands or the information for the production of the labeling. During final assembly, the master computer provides the workers with important information displayed on a large screen about the assembly of each individual turnout sleeper. Each individual mold is equipped with RFID chips so that the circulation system can record the position and the condition of the respective mold at any time. Finally, all turnout sleepers are marked with a QR code via the master computer. A wireless QR code reading system was installed additionally that communicates with the ERP system via the master computer. Hence, the company is in the position to identify each sleeper in the storage area unambiguously. This also ensures a corresponding allocation to the production orders and the complete traceability.

This kind of approach, of course, requires an ERP system allowing for flexible and individual programming. Because only in this way, it is possible to shape lean and efficient processes. In addition, the requirements on hardware, data security and the availability of production data were incorporated in the concept of the entire facility, right from the beginning. It was thus ensured that problems in data communication will not immediately lead to production downtimes.

The result is tremendous: Productivity is almost double that of conventional manufacturing processes and the efficiency of support processes (such as gathering of data for quality assurance or managing of machine maintenance) could be increased considerably thanks to the high level of digitalization. Moreover, the digitalization of the entire processes allows for a rapid response to special customer requests. If, for example, some sleepers were damaged on a construction site and replacement will be urgently needed, it is possible to integrate them in the ongoing production within a few hours, providing them for delivery on the next day and within 24 hours.


Text: Dr. Ludwig Friedl, CTO PCM Rail.One AG

PCM Rail.One AG
Dammstr. 5
92318 Neumarkt/Germany
+49 9181 8952-250
Weckenmann Anlagentechnik
GmbH & Co. KG
Birkenstraße 1
72358 Dormettingen/Germany
+49 7427 94930

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