Key Engineering Materials Vols. 651-653

Abstract: In this study the bonding properties of three layer-plated aluminum sheets are investigated. The alloys applied in specific layers were as follows: AlMn1Si0.8 (core alloy) and AlSi10 (liner). The bonding was performed on a Von Roll experimental roll mill using hot rolling. The experimental temperatures were 460, 480 and 500 °C, respectively. To qualify bond development, T-peel test was used. The test was performed using an Instron universal material testing machine. T-peel test can be well used for the qualification of bond strength as the peel-off force and bond value developed on contacting surfaces are proportional. In addition to T-peel test, optical micrographs and SEM micrographs were also captured, in which typical bond faults were sought. The study aims at modelling the technology used in industry and exploring some typical bond faults as well as suggesting the causes generating these and their remedy. The impact of surface roughening before heating was studied as well. Also, the study aimed at confirming the suitability of T-peel test to qualify bond strength.

Abstract: Ring Rolling is a complex hot forming process where different rolls are involved in the production of seamless rings characterized by extreme dimensions (i.e. external diameter higher more than 1m). Because each roll can be independently controlled from the other ones different speed laws must be set; usually, in the industrial environment, a milling curve is introduced to monitor the shape of the workpiece during the deformation in order to ensure a correct ring production. In former works the authors focused their attention on the influence of different milling curves for an industrial case and the results underlined that a ring produced with a good quality and lower loads and energy could be obtained imposing a linearly descending trend to the Idle roll speed law. However different approaches could be used in order to evaluate the mentioned speed law.In this work the authors enhanced the knowledge about the optimization of the Idle roll speed law: different Idle roll speed laws were designed and simulated and the results were compared in order to identify the best speed law that guarantees a good quality ring with lower loads and energy required for manufacturing.

Abstract: The forging process plays an important role in the automotive industry thanks to the good mechanical properties of the forged parts. Nowadays, due to the European policy of increasing efficiency in raw material and energy usage, the metal forming sector is demanding new innovative technologies. In this context, rotary extrusion technology is a very promising metal forming alternative to the drilling techniques after forging processes.The presented work is focused on hollow shafts that are usually manufactured using a combination of forming and metal cutting techniques. Deep drilling is the most common technique to obtain internal holes in the automotive hollow parts, but it is an expensive process in terms of material usage. In this framework, rotary extrusion appears as an alternative technology that leads to the reduction of material usage and process time. The tubular shape is formed with the combination of two forming processes: flow forming and backward extrusion.This paper presents the development of a simulation methodology, the process design for a hollow part, the specifications of the experimental unit, and the manufactured prototypes in order to validate the simulation model. Also the incremental process is improved thanks to a sensitivity study of the rollers geometry. Rotary extrusion experiments are done using a modified flow forming machine and 20% material saving is achieved when obtaining the deep hole in comparison to the current deep drilling technology. The process design and numerical model tasks carried out try to provide the industry manufacturers an alternative technology to drilled parts considering the advantages of rotary extrusion parts.

Abstract: Lean alloyed pipeline steel X80 with experimental chemical composition was taken for the present research. Rolling schedules for researched steel were developed for continuous mill 2000 by means of numerical simulation using HSMM, AusEvol+ and AusEvol Pro software. Developed schedules were analyzed in order to choose several of them, which guarantee the required final mechanical properties. The chosen schedules were realized on Gleeble-3800 system by tension-compression tests for experimental chemical composition. Mechanical testing of received samples was made. After that physical simulation of strip flattening, forming, expanding and coating using Gleeble-3800 system was produced and mechanical testing of received samples was made to compare results with samples after rolling simulation and with requirements submitted to pipeline steel X80.

Abstract: To reduce the failure of dies by abrasive wear, mechanical fatigue and thermal fatigue in closed-die forging usually measures like nitriding, deposition of ceramic layers by Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD) or deposition welding are used. However, after some time wear appears and the dies have to be replaced. A new concept implements sheet metal die covers, which are placed on the die engraving during forging and will absorb abrasive wear, thermal and mechanical load. The inexpensive cover will be replaced quickly by a new one after it is worn-out. This concept is regarded in a first numerical and experimental study by comparing a covered die (C) and an uncovered die (U) for the production of the same part. A one-time use of the die cover showed a reduction of the peak temperature by 140 K and of the temperature amplitude by 37 %. The temperature reduction and the increase of inner radii of the engraving to fit the 1mm thick die cover doubled the expected die life time. The experiment showed that the soft deep drawing steel DC04 is not suitable in the current case for a die cover and a higher strength sheet metal should be applied.

Abstract: In the past, different methods have been investigated regarding the production of curved workpieces by open-die forging as a significant demand for open-die forged parts with excellent mechanical properties exists. Current ways to produce curved workpieces by open-die forging have the disadvantages of complex preforms and inflexibility. One alternative approach to realize the production of curved workpieces by open-die forging is to actively control the material flow in open-die forging by superimposed manipulator movements during a forging stroke. Since the currently formed material between the forging dies is in a plastic state during the deformation, the required bending forces can be reduced significantly. This concept is investigated in a first study for the cold-forging of an aluminum alloy by numerical simulation and experiments on laboratory scale. For the process, the bite ratio, height reduction and the intended bending angle were identified as most important process parameters. Both numerical and experimental investigation proved the feasibility of the process principle since the bending forces, moments and the bending work can be reduced significantly.

Abstract: Radial-axial ring rolling is a hot forming technology to produce seamless rings, which are used in several industrial sectors, such as gear manufacturing, aviation and aerospace as well as transportation and energy. The use of allowances in the industrial production of these rings via radial-axial ring rolling is still very common to ensure that the rings’ final dimensions are reliably inside the given tolerances. Rolling a ring with allowances causes a lot of additional costs, for example purchasing and processing of the extra material.To enable ring manufacturers to reduce allowances for periodical ring errands, a rating of rings directly after the rolling process is benefical. In this paper the approach using image processing and thermography to detect the outer diameter and the surface temperature of the rolled ring to allow for a rating will be presented.

Abstract: It is a common understanding that hot forging will improve the properties of a steel part in relation to when the same part is made by casting solely. A study has been performed where two crank pin disks of a particular steel alloy, one hot forged and the other cast, both in quenched and annealed condition, have been tested using a new innovative “eye”-specimen bending test. The used test procedure is described, and it is shown that the forged and the cast material will collapse and beak down in very different way in this test.

Abstract: To reduce production costs and to improve performances of hot rolled products, it is necessary to optimize the production line. The rolling mill is one of the major factors which affect the internal quality. In fact the process tends to reduce the size of defects during the strain. The production line consisting of 24 stands has been modeled with a commercial FE-code FORGE®. First, a model has been developed and adjusted according to industrial data. Then a parametric study was carried out in order to estimate the influence of the process parameters on the internal quality of the rolled material.

Abstract: In the current paper there was made an attempt to develop an experimental method of physical (lubricant’s flash point T_fp) and subjective (forgings’ quality) parameters coupling for hot isothermal-like forging operation. The quality forgings could be manufactured both by high and low lubricant’s flash point. The increase of T_fp value in exothermal reaction follows to the increase of the released heat amount by the lubricant, because it needs more initial activation energy transmitted from the external source to initialize transformation of the material from one aggregate state into another (from liquid or solid into gaseous or sol-like). This can prevent the temperature decrease on the punch due to strong convective heat transfer with the environment through the building of the isolation temperature shield on the punch contact surface at the beginning of the punch stroke. On the other hand it can cause the defect building on the forgings like penetrations, which could not be eliminated during cleaning operation before mechanical treatment due to chemical interactions of the dissolved active agents, or unfilled sections.