Supplying forgings to the railway equipment market is problematic: production lots for high-precision finished parts may vary widely, from high volumes to replacement level, and yet the products represent a very high value. The producers of these forgings must be highly qualified and reliable to the customers that build railway carriages of various types and functions.
Danieli Breda has been designing and building forging plants for more than 50 years, and recently it developed an innovative, compact, and cost-oriented axle forging plant in response to producers’ need for operations that address the increasing necessity of operational flexibility and high-quality product standards.
In 2012, DB was awarded a contract by Mogilev Metallurgical Works (MMZ), a scrap-based steelmaker in Mogilev, Belarus, for an integrated plant to produce railway axles.
The plant is designed to process ingots, continuous-cast blooms, or rolled billets with various cross-sections, such as polygonal, round, square or rectangular shape, thus offering significant flexibility in the choice of the feeding stock.
Danieli Group supplied all the production process technology for the plant, including equipment for log cutting and heating; reheating and heat treatment; straightening; end cutting; ultrasonic testing; shot blasting; and a complete product-testing laboratory for analysis and certification.
The Group also developed and supplied the advanced automation system necessary to manage the production process. Dimensional control of each axle is ensured by a real-time, non-contact laser measurement system: monitored values for axle sizes are tracked constantly during forging, making it possible for the operator to take corrective actions, as required.
Traditionally, axle forging operations target the product type and quality requirements of local markets, in high-quantity batches. Often, this limits a plant’s flexibility to address the wider demand — which is important, as the current market for railway components is effectively global. The integrated axle forging plant designed by DB for MMZ overcomes these limits thanks to its flexibility for managing small production batches with different production standards, and the ability to produce over 100 different axle types (locomotives, high-speed carriages, metro and commuter train cars, trams, freight wagons) in the same plant.
Wider range, smaller lots, high quality
The demands of such an integrated concept required optimized production equipment, covering every design detail from the plant footprint to the finished material surface, to achieve the best results in terms of product quality and production cost.
The complex is designed to process bottom-poured ingots, continuous-cast blooms, or rolled billets of various cross-sections (polygonal, round, square or rectangular), thus providing the operators exceptional flexibility in the choice of source material, and reducing the transformation costs considerably.
In traditional radial forging plants, the deformation process involves only the surface of the workpiece, with limited center consolidation of the material: by selecting a vertical forging press for the integrated plant, the material is forged up to its core, which achieves very sound center consolidation. The results for the forged axles, in terms of resistance to fatigue and mechanical stress, are considerably improved.
Thanks to properly shaped dies and in-line shot blasting, the forgings present a round and smooth surface, so the necessity of finish-machining the forged axles is reduced.
Equipment and process design
Traditional forging plants have a footprint of approximately 7,000 m2; by optimizing the layout and selecting a compact forging press and smart handling system, the footprint of the integrated plant is approximately 2,000 m2. The provides a considerably lower capital expense as well as lower space requirements.
The fully automated operation also operates with reduced manpower requirements, fewer than 10 persons per shift. Transit time for the material, starting from the input batch up to the finished product, is equal to 8-10 hours, saving almost 40% versus the standard transit time. This, plus the possibility of producing batches of less than 20 parts, promotes quick identification for any quality issue that may occur, and a timely corrective action.
The core of the process is the open-die forging section, based on the DB-designed, highly dynamic PFC 11 open-die forging press, fully integrated with two RMF 2/4 rail-bound manipulators, each with a loading capacity of two metric tons.
The press has a nominal force of 1,100 mt at an operating pressure of 350 bar. During the planishing phase, the press can reach a maximum speed of 90 strokes per minute, thus ensuring high-quality finished surfaces. Thanks to the positional accuracy of ±1 mm, the different axle diameters being produced require only minimal finish machining.
The dies are shaped in such a way as to contain material spread as much as possible, and to ensure the maximum roundness on the finished axles. The dies are installed on slides so as to be shifted during the axle forging process. The process of shifting and locking the dies is completely automatic.
The hydraulics system room is modular and built to optimize space and pipe length, to ensure highly dynamic response with regard to pressure and speed in all working conditions.
This automated axle forging concept also involves two railbound manipulators, each one with 3 mt of lifting capacity and 6 mt*m charging moment, both capable of handling the input material during the complete forging process, and totally integrated in the forging automation system. Further, each manipulator has a travelling speed of 40 m/min, a positional accuracy of 2 mm, and a rotational accuracy of ±1°.
The entire plant is managed by an advanced automation system, capable of handling the forging sequence and all other production processes. The DanForge® automation system optimizes open-die forging by reference to production “recipes.” Each individual axle family to be produced corresponds to a dedicated recipe, which optimize the respective steps in the forging process. Then, according to the production schedule, every detail of the process is prearranged, starting from the cut-to-measure of the feedstock up to the optimal reheating curve, the forging steps, and the finishing of the product.
Level 2 automation provides reliable and safe tracking of each piece during its production sequence, always keeping control over the production status and material throughput of the plant.
To ensure the correct dimensional profile of each axle, a real-time non-contact laser measurement system is installed. This system provides the operator with a constant reference to the sizes of forged axles in production, so as to implement the proper corrections as required.
Listing the advantages
The integrated complex developed by DB consists of the following elements, each one incorporating production equipment developed and supplied by the Group:
• Entry section, where the ingots, blooms, or billets are cut-to-length;
• Robotic manipulator for furnace charging/discharging;
• Rotary hearth furnace for reheating;
• Forging section, with vertical forging press and manipulators;
• Handling section, with cooling bench and marking;
• Heat treatment section (normalization and/or quenching/tempering);
• Straightening machine and measurement;
• Exit section, where the forged axles are cut-to-length.
In addition, the complex includes a complete product-testing laboratory (NDT and ultrasonic testing) for material analysis and product certification according to international standards. Also, automatic shot blasting is installed in-line to ensure high-quality surfaces on the forged products. Automated stacking is in place to palletize the finished axles.
Thanks to the compact and automated design, the DB compact integrated complex effectively addresses the current requirements of railway products forgers:
• There are no restrictions on the types or sources of feedstock;
• The forgings are monitored for dimensional accuracy in
real-time during production;
• The forgings’ metallurgical properties are improved, with better sound-centering, uniform grain flow, and microstructure throughout the length and section of the axle, and improved fatigue and tensile strength are observed, too;
• The compact design results in lower capital investments and reduced operating costs, and lower power and media consumption.
The forging complex supplied and installed at MMZ ensures highly profitable production of up to 50,000 railway axles per year, and offers a competitive alternative to radial forging operations, with the flexibility needed to supply shifting market demand, even in cases of small orders.
Roberto Bonora, Mauro Baldassi, and Claudio DiStefano are executives with Danieli Breda, the forging plant builder and developer. This report is adapted from their recent presentation to IFM 2017. For information, contact Mr. DiStefano at [email protected]
