Community Research and Development Information Service - CORDIS


REFORCH Report Summary

Project ID: 315106
Funded under: FP7-SME
Country: Germany

Final Report Summary - REFORCH (Resource efficient forging process chain for complicated high duty parts)

Executive Summary:
In times of increasing international business competition forging companies try to increase their competitiveness by optimization of different factors such as efficient use of resources in the forging process, optimization of processes or managing costs. In common forging processes for geometrically complicated parts such as crankshafts, an excess on material (flash) is technically needed to produce a good part, which results often in a material utilization between 60 % and 80 %. But the material costs in forging represent up to 50 % of the total production costs. A fairly new development is the flashless precision forging technology. Precision forging is a special technology of flashless forging in closed dies. The main advantages of this technology are very good work piece tolerances, along with more than 99 % material utilization and less or none post-machining operations. Precision forging has not spread into industrial production, especially not for long parts or complicated geometries. This can be explained by the disadvantages of the process and the long lasting and difficult development time. For the tool design high reproducibility and high precision are enquired. Goal of the project “REForCh - Resource Efficient Forging Process Chain for Complicated High Duty Parts” was the combination of the advantages of both forging technologies and minimizing the disadvantages. Thus, the development of a flash-reduced forging sequence for a two-cylinder crankshaft was the main goal, to save material and energy.

At first, the investigation of a conventional forging process chain for a two-cylinder crankshaft which is currently in production has been done. Based on the current process chain, a new, flash-reduced forging sequence has been developed, by help of modern Finite-Element-Analyses. Too reach the goal, a significant flash reduction for a geometrically complicated part such as a crankshaft, the development of a new technology was necessary. At first, closed die flash preforming operations are necessary. Afterwards a multidirectional forging in closed dies allows a final forging with a significant flash reduction. In total the new process chain consist of five forging stages, an upsetting, two flashless preforming operations, a flashless multidirectional forging and a flash-reduced final forging. For two model products, two different crankshafts, this process design has been done and for one of them tested in an industrial environment. The process was designed in such a way, that existing equipment, e.g. the forming presses and the induction heater, could be used without any changes. The evaluation of this technology took place based on the preformed tests.

After the two preforming operations of the parts, an intermediate heating was necessary, to get a homogenous temperature distribution before the multidirectional forging process. A homogenous temperature distribution within the part is necessary to allow for an even material flow in the forging process. Therefore, a special induction reheater was developed for the reheating of a preformed crankshaft. A main goal for heating in forging is to reach a certain constant temperature throughout the workpiece within a minimum time and a maximum of efficiency. The heating line can be adapted to different two-cylinder crankshafts and can be used in-line. The whole heating process is controlled by special designed software and digital controllers.

Additionally, the material properties of the used material (38MnVS6) have been investigated for the conventional forging process. After the trials of the new forging process chain, the same investigations have been performed. A significant increase in material properties could be determined due to different forming operations, which is another advantage besides the savings in material and energy.

Project Context and Objectives:
In work package 1 an overview about the equipment of the forging company has been worked out. Additionally two model products and requirements and proceedings of the material analyses have been fixed. Two model crankshafts have been chosen by the consortium for the subsequent work packages (see Deliverable 1.1). The suggested material, 38MnVS6 which is a common forging steel, has been approved by all partners.

Within work package 2 the conventional forging processes were simulated and analyzed first. Afterwards the flash reduced forging sequences for both two-cylinder crankshafts were developed using FEA. This included the shapes of the flashless preforming dies. Moreover identifying the optimal process parameters (e.g. workpiece and tool temperature) was an important part of the WP2. The sequence for the crankshaft to be forged in WP6 consists of two preforming operations in closed dies, a multidirectional forming operation, and a conventional finish forging operation.
The simulations were evaluated and compared with the existing conventional forging sequence by the following parameters:
• mould filling
• folds
• die wear
• temperature
• required press forces
To achieve these goals, the process chain was improved by multiple iterations which included e.g. different designs of the shapes of the dies, different dimensions of the raw billet or different temperatures. The results of this development are presented in D2.1. The development of the process chain to be tested was only slightly delayed. But the second process chain took longer time to develop. This was done in parallel to other work packages.

Work package 3 is divided into two different tasks. It was planned that an induction heater will be developed first. But it was decided by the steering commitee that in the first task no new generator will be developed, but the existing induction heating process at OMTAS will be improved by the variation of voltage, frequency, etc.. This has been performed by 2D analyses of the induction heating process. Please see D3.1 for details.
The second part of work package 3 contained the development of a controlled intermediate induction heating to provide a defined inhomogeneous temperature distribution in the workpieces for the following final forging operation. At first a simulation model has been developed. The model allows performing the simulation of the electromagnetic field distribution which leads to the induced power (Joule losses) inside the workpiece and the consequential transient thermal calculation and analysis during the whole reheating process. As results, the model provides the knowledge on 3D transient temperature distribution within the workpiece as well as all information on electrical parameter of the process. These simulations are the base for the induction reheating which is developed in WP5. Details are provided in D3.2.
Delays in WP3 are results of different problems at the FEA design of the models. Due to additional numerical simulations, which were necessary to get a complete filling of the cavity in WP2, the preforming operations changed and so did the 2nd preforming geometry. Consequential there was a delay in FEA simulation.

In workpackage 4 the forging tools were designed and manufactured. In the FEA simulations done in WP2, the loads on the tools, such as normal stress, could be investigated directly and considered in the designing process. Afterwards, the boundary conditions of the tools were fixed due to the requirements and possibilities of the forging presses. The designs of the molds could be directly taken from the FEA simulations in WP2. Additionally base plates, clamping mechanism and connections were constructed in the CAD-software “CreoParametric”. Afterwards the tools were manufactured and tested.
There were a couple of smaller issues, which resulted in a delay of WP4. In the workplan only four forging stages were estimated. Due to the complex material flow in the forging stages and constraints of the forging presses, one additional forging operation, an upsetting operation, had to be added. It has been decided to test the preforming tools at OMTAS not in IPH, due to missing ejectors at OMTAS. So the tools were designed in a way that the parts can be ejected manually. The preforming tools were manufactured and tested at OMTAS. Due to the fact that the deviation of the material flow between reality and FEA results was more than usual, adjustments on the tools in line with additional FEA simulations had to be performed. Necessary changes on the dies were discussed and fixed. Afterwards, the upsetting and 1st preforming operation was changed slightly in some areas. But bigger changes were necessary on the 2nd preforming die, which had to be completely manufactured again. The design and the manufacturing of the multidirectional forging tool took longer than expected. The design of different details such as little available space in the final forming press at OMTAS, the needed press stroke for the multidirectional forging or the space for the springs in the tools, took a long time. After the manufacturing of the multidirectional tool at AURRENAK the tool was tested in a hydraulic press, first. The tests showed issues with the outer guiding and the backwards movement, which is done by springs. Therefore different adjustments on the guiding system were done. The tools are presented in D4.1 and D4.2.
WP5 is based on the developments of WP3, as in WP5 the heating systems for the primary (initial) and reheating are optimized respectively built. The primary heating was tested and the cylindrical billets were successfully heated at OMTAS.
To design the reheating system, pretrials were performed at EMA-TEC, first. This was necessary to order and built up most of the components for the induction reheater. In parallel additional FEA simulation could be made to fix the contour fitting shape of the induction coils. The reheating system is able to compensate temperature losses within a short cycle time, supplying a homogeneous heated part for the following multidirectional forging. Core ability of this system is the possibility to reheat areas within a part group with a varying mass distribution along the longitudinal axis. For the induction reheater the shape of the induction coils had to be designed in a way, that an easy and quick loading and unloading at the induction reheating system can be realized. After the manufacturing of the reheater without the form-fitting shapes of the coils, pretrials of the induction reheater at EMA-TEC with power supply, cooling systems and a simple non contour fitting cylindrical coil system were done, to verify frequency and power consumption. Based on further numerical simulation and the pretests at EMA-TEC the layout for the two coils and the different zones of the crankshaft were fixed. Afterwards the coils were implemented in the reheater. Verification of the numerical results was done at the ETP under laboratory conditions. Deviations in heating time and power consumption can be explained by variation in frequency, which is related to the kind of heating and by deviation of the final preformed crankshaft at the final trials at OMTAS. Detailed results are explained in D5.1 and D5.2.

In WP6 the demonstration of the developed process chain took place at the Forge OMTAS. First, the induction reheater and the multidirectional forging tool had to be shipped to OMTAS. Afterwards, the induction reheater has been set up and implemented in the forging line. The preforming tools were mounted on a RAVNE 630 tons mechanical press. The multidirectional forging tool and the conventional final forging die have been mounted on a 4000 tons EUMUCO eccentric press.
Tests have been made with the changed preforming tools. After several adjustments, the process was stable. Then the multidirectional forging tool has been tested, first without parts, as such a tool has never been tested at a fast moving eccentric press. Afterwards, the whole forging line has been tested and parts have been forged. The results of this workpackage are described in the deliverables D6.1 and 6.2.

Workpackage 7 consisted of two tasks. Task one was the analysis and characterization of the material. The analysis included metallurgical tests, such as analysis of grain flow or HRTEM microscopy. The mechanical tests included tensile strength, impact resistance and low cycle fatigue tests. These tests were done for the conventional forged parts from OMTAS with the high amount of flash. Additionally, the tests were done for the flash-reduced forged parts, produced by the new process chain in WP6. An improvement in all mechanical properties could be determined. The detailed results of this workpackage are presented in D7.1.
In the second task of this workpackage, the evaluation of the new technology which includes the economic and ecologic evaluation has been done. The savings in material, energy and CO2 have been calculated for OMTAS and for the scenario, that this technology is used in the whole European Union. Based on a large database, the life cycle costs and the total savings in CO2 have been calculated. The results are shown in D7.2.

Project Results:
Three main goals have been achieved during the process. First, the design and successful testing of a flash reduced forging process chain for an industrial two-cylinder crankshaft. The forging sequence consists of five forging stages, four flashless and the final operation flash reduced. Second achieved goal was the successful development of an induction reheater. This reheater is able to reheat a preformed crankshaft to a homogenous temperature distribution without overheating of areas. Additionally the induction heater is able to heat up a preformed crankshaft from room temperature to forging temperature (1250 °C). In the complete heating process nor overheating, neither heavy scale formation or an inhomogeneous temperature distribution occurred. Third achieved goal was the successful design of a multidirectional forging tool. This tool can be used in an industrial environment not only in trials but in a batch production. Due to the new forging sequence, the material analyses showed improved material properties of the used steel 38MnVS6 (1.1303/1.5231).

Design of new flash reduced forging sequence
The process design was done by help of modern FEA simulation software Forge3 which is the most popular software to design hot forging processes. The usual method to design a new forging forging sequence is the top-down method: starting from the geometry of the final (machined) part, a forged part is derived. Next the preforms are derived preliminary. In multiple iterative processes theses preforms are simulated and optimized. Due to the complexity of the forging sequence in REForCh and the boundary condition that the final forging dies won’t be changed, a second preform has been constructed in CAD. Afterwards the multidirectional forging operation has been designed and optimized. After this process was fixed, the remaining stages were developed, to achieve a preform as necessary. Therefore, this process design was interlaced, which was required due to the requirements of the process.
Initially it was planned to use four forging stages: two flashless preforming operations, a multidirectional forging operation and a flash-reduced final forging operation. Due to the fact that a defined preform after the second forging operation had to be achieved, a third preforming operation, an advanced upsetting had to be done. Otherwise the press forces would have been higher than the maximum press forces of the trial presses and the forging operation could not have been performed. Additionally unacceptable flash would have been occurred.
For the design of the forging sequence, a material model for the forging steel had to be built up accordingly. Although the material is common in forging processes, a similar material model for 38MnVSi5 is widely used. But to be able to design the process as real as possible a more exact model for the material 38MnVS6 was build up. The material model is based on the “Hensel-Spittel” equation. The equation allows an accurate modelling of the design of flow curves. The main parameters used in this equation are the strain, temperature and forming speed. Different exponents are used in this equation to allow for a proper design. However, the equation is not able to represent material properties such as anisotropic behavior of material. These are properties that are inherent to the material, based and changing in the production process.
In the design of the forging process the most complex task was the design of the multidirectional forging tool. Every parameter of the multidirectional tool, e. g. the length of the outer dies, the angels at the inner dies, the thickness of the inner dies, the radii on the edges or the shape of the crank webs have been changed. In addition, different kinematics have been simulated. There are different interdependency behaviors, which alter the material flow in the multidirectional forging die based on the kinematics and the geometry of the different dies of the multidirectional forging tool. The number of performed simulations for the multidirectional forging itself was over 200, to achieve a part which is suitable for final forging.

Improvement of initial induction heating and design of induction reheater
In the new process chain, two induction heating processes are necessary. First, there is the initial induction heating. Second, there is the induction reheating between the 2nd preforming operation and the multidirectional forging operation. The initial heating was also necessary in the conventional process chain, but due to changed dimensions of the raw billet the process had to be improved. The induction reheating had to be designed completely. This was the most complex task, because typical induction heating processes are only applied on round or square parts, not on geometrically difficult parts.
The heating process represents a coupled problem, characterized by the interaction of electromagnetic and temperature field. To solve this problem, finite element simulations can be used. The FE-models allow performing the simulation of the electromagnetic field that induces Joule losses in the work piece and the consequent transient thermal analysis during the whole heating process. As results the model provides the knowledge on temperature distribution within the work piece as well as the information on electrical parameters of the process. Electromagnetic and thermal material properties used in the model are temperature dependent and ensure the correct behavior of the model in the whole investigated temperature range. The material properties are adapted for each time step of the transient thermal analysis at each position in the work piece. The simulation of the initial heating process of cylindrical billets was done in a 2D axially symmetric model the reheating process was modelled in 3D, because of the complicated work piece geometry.
The existing heating equipment at OMTAS had to be used for the initial heating. Main feature of this induction heater are two coil section which can be adjusted individually. Therefore the first part of optimization by FE-simulation of the heating sequence was to concentrate on the following given parameter: voltage inductor coil section 1, section 2 and time per heating step. Additionally different frequencies for both sections were also taken into account. After a trial-plan with suitable parameters was developed, the simulations were performed. By the results gained in the simulations, the required energy for the initial induction heating could be reduced from 440 kWh/t to about 390 kWh/t.
The major part was the design of a model to simulate the induction process for a complicated geometry like a preformed crankshaft. The 3D model itself is reduced by its half due to mirror symmetry. Even there are no direct hardware limitations today, the reduction of the numerical models are of biggest interests to reduce calculation time. Especially for optimization and 3D calculations procedures. With the help of symmetry and mesh adaption it is possible, even for a relative complex model like a two-cylinder crankshaft to achieve simulations times which are can be handled by normal computer systems. For the design of the induction reheating process, a lot of different parameters, e. g. voltage, frequency, power, distance between preformed crankshaft and coils or shape of coils were considered. After iterative optimization loops, the gained data was used to build up the induction reheater. The components were successfully assembled and tested at EMA-TEC.

Design of forging tools
During the process design only the molds (gravure) of the forging tools are fixed. All other parameters, e. g. the thickness of die walls to withstand the forces and temperature in a forging process or clamping resp. mounting systems had be had to be fixed. In forging, there are typical boundary conditions to consider when designing forging tools. First, the available space in the press has to be considered. All the tools have to fit in the press but necessary dimensions of the tools (e. g. thickness) have to be kept to allow the tools to withstand the forces they are exposed in the process. This is sometimes a conflict, because not enough space is available. Additionally, external systems such as clamping systems or fixed ejector positions have to be considered in the design. The systems have to fit but the tools must not be weakened.
In flashless forging there are additional boundary conditions which have to be considered. First, an accurate guiding has to be ensured. Due to close tolerances between the forging tools, especially the punch and the dies, an accurate guiding is important, to avoid flash (especially thin flash between closed dies) and abrasive tool wear, due to high friction between different parts of the dies. Furthermore, the tools have to be kept close by disc springs. It is very important to use a sufficient number of springs. The compression has to be high enough to allow the dies to close before the actual forming takes place. Additionally the forces have to be high enough to keep the dies closed. Both factors increase the height of the column of disc springs. This is a critical factor, because most forging presses require a minimum and a maximum height of the tool, which are mandatory for the functionality of the forging press.
The design of the preforming tools has been done without major difficulties, due to an available space in the press which was huge. But the design of the multidirectional forging was complicated and long-lasting, because all abovementioned boundary conditions had to be considered very carefully. The bolster plate of the multidirectional tool had to be designed to fit in into the clamping system of the MP4000 final forging press at OMTAS. The final height of the tool had to match the height of the final forging die of 230 mm. Due to a relatively movement of the pressure plate with the dies, the height of 230 mm is the end height after forming. The total height of the multidirectional tool in opened position is the final height plus the movement of the pressure plate of 45 mm. To keep the upper and lower die closed to each other disc springs are used between the pressure plate and the bolster plate. The disc springs had to provide a closing force of 60 tons. As disc springs with a closing force of 60 tons are not available with a stroke of 45 mm and an installation height of 130 mm two kind of disc springs were designed. The main disc springs are providing a basic closing force along the complete stroke with a maximum force of 25 tons. The maximum closing force is required only at the end of the stroke, so additional disc springs are mounted below the pressure plate and are only providing an additional closing force of 50 tons along the last 15 mm of the stroke.
In the multidirectional tool friction between the moving parts of the dies had to be considered. Typical forging tools don’t have different parts which are moving onto each other, thus friction between die parts is not an issue. But in the multidirectional forging tool are a lot of different tool parts. And all surfaces with a relatively movement towards each other have a high die wear due to the friction and this had to be considered. The solution to avoid unacceptable die wear was to use special friction plates. The inner dies are moving on a friction plate while the press force is pushing a normal force in stroke direction on the pressure plate. A very high die wear was expected in this area, so the pressure plate was designed with a bronze friction inlay while the dies were designed with high resistant steel. With this strong/weak friction pair no die wear occurs at the inner dies. All other remaining friction pairs are designed with a hard steel/hard steel combination, because the resulting normal force for the die wear concerning friction is lowered by the wedge angles used for the transformation of the die movements and forces.

Forging at OMTAS
At OMTAS the flash reduced forging process chain with the preforming tools, the multidirectional forming tool and the conventional final forging tool, as well as the reheating was installed. In a first step, the preforming operations were tested.
As preforming press, a RAVNE630 mechanical press was used. This press has a maximum press force of 6,300 kN. The press had no measuring system force the actual press force. But the preforming processes were designed to need a maximum forming force of 4,500 kN. No overload of the machine occurred, thus the press forces were sufficient. After several trials the forged parts and the dies were analyzed. It could be determined, that the material flow differed from the design on the FEA simulations. An anisotropic behavior of the steel occurred. The material did not get elongated as much as predicted by FEA simulations, but widened more. This leaded to several problems, e. g. sticking of tools or an inacceptable amount of flash in the second preforming operation. Especially the flash would have led to folds in the multidirectional forging operation. After several adjustments the preformed parts were tested again and the results were significantly better.
The adjusted preforming tools were run-in with different dimensions of the raw billet and a batch of preforms was produced. Afterwards the induction reheater was tested with hot parts directly taken from the preforming process as well as with cold preformed parts which were cooled down to room temperature and heated up again from 20 °C to 1250 °C.
As these processes worked, the multidirectional forging tool was tested. These tests were made on a MAXIPRESS MP4000, an eccentric press with a maximum press force of 40,000kN. First, no preformed parts were inserted, to check the mechanical function of the tool in the fast moving press. After several smaller adjustments on the tool, the tests were successful. Afterwards preformed parts were inserted in the multidirectional tool and forging tests were done, which were successful, too. After the functionality of the multidirectional forging tool was proved, parts were forged in the conventional final forging die. Hence, the whole process chain worked.
The focus in these test were on the preforming tools, so preformed parts could be produced without flash. Additionally, the ideal height of the multidirectional forging tool to achieve a mass distribution as intended had to be determined and parameters of the reheating process had to be adjusted.
In the RAVNE630 press, the preforming tools were mounted. The tool’s geometries were derived from the FEA-simulations at IPH. The tests were carried at the maximum forging temperature of 1250 °C, which ensured the best material flow.
The ideal forging stroke had to be determined, to achieve a height of the upsetted part of 50 mm (ends of crankshaft), of the first preformed part of 33 mm (area next to crank webs) and of the second preformed part of a height of 52 mm (whole part).
First, tests were made without billets, to ensure that the guiding system worked and the tools did not collide. Then raw billets were inserted into the upsetting operation. This process worked directly as intended and the final height of the upsetted part could be achieved. Next, the upsetted part was inserted into the first preform. In the first preform deviations of the geometry occurred. The final height of the part could not be achieved in the first trials. Adjustments on the height of the tools by help of sheet metals (distance pieces) were done. After different trials, the final height could be achieved, but the part did not elongate as predicted by FEA simulations. As a nest step, the second preform was tested. It could be expected that there will be additional issues, due to the deviations in the first preforming. Further issues occurred, such as sticking of tools due to flash between the punch and the upper die. OMTAS decided that bigger changes on the tools are necessary to resolve the issues and to ensure a working process without the risk of damage on the tools and the dies. Other temperatures were not tested, due to the issues in the preforming, which already occurred, even the best i. e. easiest material flow was guaranteed by the forging temperature of 1250 °C.
After the redesign, raw billets with different dimensions were tested. Raw billets with a diameter up to 62 mm (65 mm were envisaged) can be used in the process. The length of the billet is 280 mm. A compensation of the smaller diameter is generally possible be use of longer parts. With these parts and the redesigned forging tools, parts could be forged successful without flash.
Afterwards the multidirectional tool could be tested and the forging stroke, which corresponds to the way of the movement of the elements which do the forming, adjusted. As the eccentric press can be adjusted in steps of 0.1 mm by its control system, this task could be done successful. The optimal distance between the base plate and the pressure plate of the tool, which were used as reference, was determined to 75 mm. If this distance is kept, the multidirectional forging operation produces good preforms. The final forging operation was done as in the conventional forging process.
The induction reheating system consists of the power supply EMA-TEC FUP with 50 kW output power, the heating station and the water cooling compartment. The process parameter (heating time, output power) are set by the operator according to the current work piece temperature after preforming. The temperature monitoring is being done online before and after the reheating process by means of infrared camera and pyrometer and the measured data are evaluated and stored by the control system. The electrical parameters are measured directly by the reheating system itself (output power).
The work piece is manually transported from the preforming press RAVNE 630 and put into the feeding unit of the reheating station. The temperature distribution is measured and the output power used for reheating is set by the operator. The work piece is moved in into the defined position within the inductor and the reheating starts. After a defined heating time (about 35s) the generator is switched off and the work piece is taken out from the inductor. The temperature is measured and the work piece can be transported into the MAXIPRESS MP4000.
Due to the contact between the billet and the cooler preforming dies, the billet is cooling down in the different forging stages. Additionally, heat radiates form the preforms when they are taken form one die to another. By decreasing temperatures of the billet, the flow stress increases. Thus, a higher force is needed to form the part and more important the material does not flow as if it at the maximum temperature of 1250 °C. A surface temperature of the parts after the second preforming between 950 °C (crank webs, ends of crankshaft) and 1100 °C (center area between crank webs) was measured.
• It is recommend to keep the initial temperature of the raw billet at the maximum temperature of 1250 °C
• The lowest possible temperature is around 1100 °C due to the maximum press force of the forging presses

General remarks on thermal behavior:
• Average temperature decrease due to forging observed: about 200 °C
• temperature losses due to the forging vary with cycle time,
• temperature profile partially instable, especially on crank webs

Induction reheating:
• reheating by induction within the required time is possible
• approximate generator power needed for compensation of temperature
losses about 27 kW,
• good agreement with data provided by numerical simulation.

The preforms were geometrically measured in order to identify the variation in the geometry. These measurements showed, that the mass in the middle of the work piece is all times similar (deviations are less than 1 mm, maximum 0.8 mm, and minimum 0.03 mm) but bigger deviations occur on the crank webs and at the total length of the part. The total length of the preforms varies about 5 mm. The length of the crank webs vary also about 5 mm. This can be explained by the manual handling of the parts. It can be expected, that this is no issue and in future adjustments, e. g. centering mechanisms can be used to improve the tolerances.
The material consumption is an important factor in the forging industry due to rising costs of steel. To evaluate the mass utilization 5 parts were measured. The average weight of the raw billet is 7,4 kg. The final part has a weight of about 7 kg. Therefore the mass utilization is about 94 %. The scale is about 80 g per part.

Material investigation
The forged parts were analyzed concerning mechanical characteristics, low cycle fatigue and grain flow. These parameters provide useful information about the mechanical loads the parts and the steel can withstand. The used steel, 38MnVS6 (very similar to 38MnV5) is a precipitation hardening steel, which means he has a good workability in hot condition and get strengthened during the cooling process. The forming process and the strain (forming degree) have an impact on the mechanical properties. The same investigations were performed for crankshafts forged by the conventional process with the flash ratio of 54 % and with the new flash reduced forging sequence with the flash ratio of about 6 %. Additionally, the material has been investigated in its original stadium, i. e. raw and not forged. But these tests lead to much smaller values of the mechanical properties which could be expected, because precipitation hardening steels have to be heated and forged to get become strengthened.
Parameters for the testing were as followed:
Mechanical testing consisted in tensile strength, impact bending (KCU 2) and low cycle fatigue. The test bars were cut longitudinally from the forged parts. The testing of tensile strength was done at 20°C, 400°C and 470°C, using longitudinal specimens with 10 mm diameter, according to ASTM E8, ASTM E 21, ISO 6892. The testing equipment was Universal testing machine type EU40 tf. Impact bending test was done on 10 x 55 mm square section testing bars, according to and ASTM E23, ISO 148 and Impact testing machine type WPM30. Low cycle fatigue was performed on electro-hydraulic servo-controlled testing machine INSTRON 8801 – 100KN, ; ±1% precision of load measurement, high temperature system (±20C), dynamic extensometer INSTRON HTD, Lo=12,5 mm, class B1 acc. ASTM E 83. Five test bars (acc fig. 1) were cut and tested. The testing parameters for low cycle fatigue have been selected considering:
• Maxim load up to 5 values, starting with 0.6x σmax and decreasing up to 0.4x σmax;
• R = 0.1(asymmetry coefficient) at 5Hz frequency;
Macro and micro structural examination of the samples cut from the forged crankshaft have been performed. Grain flow was analysed on a longitudinal section of the crankshaft along the parting line, according to Romanian specification STAS 11961/1. The sample was etched in a 50% HCL solution. The microstructure was analysed using a FEY Quanta Inspect F scanning electron microscope and a high resolution by a TECNAI F30 G2 STWIM transmission electron microscope (HRTEM). Samples have been cut from low fatigue test bars, both for microstructure analysis and fracture surface. Samples for microstructure analysis have been polished and etched with Nital 2% reagent.
Main aspect of the material investigations is to determine the difference between parts forged with the conventional technology and the new technology. At room temperature the tensile strength is equal as expected. The yield strength increased from 686 MPa to 745 MPa. The percentaged elongation is reduced from 12.3 % to 10.1% and the reduction of area from 26% to 24%. The impact resistance is decreased to about 21.6 Joule in the new technology. At elevated temperature level of 400°C, the tensile strength is about 130 MPa higher and the yield strength of the samples forged with the new technology is about 150 MPa higher. At a temperature level of 470° C the differences are smaller, but there is still a difference of 15 MPa in tensile and 35 MPa in yield strength.
The samples microstructure is ferritic-pearlitic with sulfide inclusions. A coarse structure observed in the forged raw material has been eliminated during the forging process due to the higher degree of deformation achieved in the final stages of forging. Low cycle fatigue tests at 500 MPa showed, that the material can withstand a high amount of cycles. The parts forged with the conventional forging sequence could withstand more than 24000 cycles. The samples of the new technology showed a significant increase in the number of cycles due to the new forging sequence. At an increased load of 550MPa the tests cycles increased to 48200 cycles. At a load of 600MPa the tests cycles increased from 29 to 41873. At the highest load of 710MPa which is near the yield strength, even 713 cycles could be performed. It is important to mention that the highest level of load was chosen to simulate a very severe complex condition, using values near the yield stress which is not the case during the application of the part. Broken tests samples in the low cycle fatigue tests of the conventional forged crankshafts were examined. The 38MnVS6 fracture surface examination has showed a ductile aspect, but the possible reason for the fracture was a defect in the machining.

Energy, economical and environmental evaluation
The electrical efficiency is generally determined by the relationship between the work piece (billet) diameter and the heating coil diameter. These diameters should be approximately matched to achieve high electrical efficiency. For ideal energy efficiency there would be a dedicated inductor for each and every billet diameter in the production schedule. A more practical approach is to examine the production schedule and designate a family of induction coils, where each coil is suitable for a range of billet diameters. The number and size of the coil represent a compromise between the competing objectives of optimal inductor/work piece matching and operational flexibility. Thermal efficiency is primarily influenced by the heating cycle time and the induction heating train length. Recall that the rate of heat loss by radiation is proportional to the fourth power of the surface temperature (Bolzmann law). Thermal efficiency is therefore improved by minimizing the heating interval that work piece is held at elevated temperatures. The goal is therefore to heat the billet quickly and briefly, subject to process requirements for reliable, accurate and uniform billet heating. Radiation heat losses can also be reduced by insulating and/or lining the heater coils. In any case, optimal thermal efficiency requires optimization of induction heater train.
Inductor efficiency strongly influences the total system efficiency. Heating steel to the enthalpy temperature of 1250 °C requires a specific energy input of about 240 kWh/ton. In the most industrial applications, depending on the adjustment between the inductor and work piece, the required system input power from the grid is between 380 and 550 kWh/ton. For the following comparison an average value of 450 kWh/ton will be used, corresponding to the inductor efficiency greater 75 %. The resonance circuit efficiency should be at least 97 %, and is determined by the design and sizing of the capacitor battery and associated bus work. Since transformers with off the shell efficiencies of 99 % are already available, there is little opportunity to improve the operational productivity through additional transformer.
In the new forging process investigated in the frame of the project REForCh, primary heating up to 1250 °C takes place before the preforming operation. In the conventional forging chain the required energy to heat a part is about 440kWh/ton. Due to the improved initial heating process and the reheating process this amount increases up to 470kWh/ton. At values of frequency f = 3.8 kHz, heating time t = 80s and a total power P = 22.0 kW the total specific energy consumption of the Setup of the reheater at OMTAS was between 70 and 75.5 kWh/t.
During the forging operations some material is lost due to scale occurrence. The hot material on the surface is in contact to air and reacts with oxygen. Increasing the temperature increases scale, especially at hot temperatures. The scale is a common accepted problem of the hot forging method which cannot be removed. This hard oxidation layer has negative effects on to the die life, die filling and the environmental cleanliness. The cost of the storage and the elimination of the accumulated scale are high. Due to the efficient reheating process, the scale formation is not much higher than in a conventional forging sequence.
In order to compare the die life between the conventional forging sequence and the new flash-reduced forging sequence, it is necessary to make a serial production of the crankshaft in forging conditions. It is expected, that a batch size of 2000 parts is sufficient to gain information about the die life of the new forging sequence. The expectation is that a higher die life will be achieved in the final forging die. FEA results are supporting this expectation.
The economic advantage for OMTAS is high. For an initial planned production of 10,000 crankshaft/ year, realized by the new forging technology, 34 tons steel / year saving and 18,972 €/ year financial benefit result, considering that the carbon steel price is 558 €/ tonne. If the new forging technology extends to the entire production of 200,000 crankshaft / year, the following savings will result: 680 tons steel / year and 379,440 € / year financial benefit, considering the same steel price. Due to the reduced material consumption the absolute energy consumption is also lower, although the relative power consumption is higher due to the reheating process. 3.4 kg steel per crankshaft saving results by the new forging technology, which haven’t to be heated means 1.581 kWh / crankshaft energy saving. As a consequence, for an initial planned production of 10,000 crankshafts/ year, this results results in 1,264.8 € / year benefit, considering that the average energy cost is 0.08€ / kWh. If this technology is used for the production of 200,000 crankshafts per year. This results in an economic benefit of more than 25,000€ per year.

The new forging technology reduce the material and energy consumption and it has a significant economic and environmental impact. This flash reduced forging is an economical alternative to the conventional forging process, which offers several financial advantages. Following the evaluation of carbon footprint based on Life cycle inventory of a steel for automotive, results in an reduction of greenhouse gases of about 275 tons per year for the company OMTAS.

Potential Impact:
In the following the planned dissemination activities are described. All partners approved it at the final meeting of the steering committee, held at METAV in Bucharest, Romania on 30th September 2014. Thereafter all partners had the chance to make comments on or to make their objections against the planned way of disseminating the results. The planned actions below are agreed by all partners will be performed within 2015. In the following the planned dissemination activities and IPR are described for each SME and RTD partner.

Distributing the flash reduced forging technology in industry
In the recent past industry was interested in the completely flashless forging technology of crankshafts which has been developed by IPH over the last decade. But due to the high costs and high boundary conditions the industry hesitated to use this technology. The flash reduced forging technology is cheaper and therefore IPH expects to find customers which will be highly interested to use this technology for their products.

Presenting results on a conference
IPH supported OMTAS in the presentation of first results on the IFC - International Forging Congress, 29.06.-01.07.2014, Berlin. Moreover IPH presented results at the conference Modelling for Electromagnetic Processing, 16.09.-19.09.2014, Hannover.
Additionally IPH will present further results at the 3rd International Conference on Recent Trends in Materials and Mechanical Engineering, January 15-16, 2015, Auckland, New Zealand.

Publication in scientific and industrial journals
IPH wrote five publications which will all be submitted during the next months or are already in a review process. The next publications to be published will have the title "Investigation of simulation parameters for flash reduced forging of two-cylinder crankshafts" in the scientific journal "journal of materials".

Website will stay online
The project website will stay online for at least one year after the project. IPH will update the website with new publications made by the partners to show the results of the project REForCh.
Furthermore, the download area of will stay the safe platform for important internal data of the project like: General project issues deliverables and data of project meetings.

Publication in scientific journals together with EMA-TEC
ETP wrote a publication for the scientific journal “heat processing”. The title of the pulication is "Simulation of primary heating stage in resource efficient forging chain" and he envisage publication is January 2015. Another paper is planned to be published by ETP in 2015 concerning the reheating of a part with a geometrically difficult shape.

Presenting results on a conference
ETP presented the results of their development on the conference Modelling for Electromagnetic Processing, 16.09.-19.09.2014, Hannover.

ETP has already implemented an overview of the project REForCh on their website ( They will update the website after the project as well.

Open workshop for industry together with EMA-TEC
ETP holds an annual meeting named “Elektrothermische Prozesstechnik“. This workshop will be done in cooperation with the Forschungsgemeinschaft Industrieofenbau e.V. (FOGI). The target audience for this workshop is industry. EMA-TEC will present the reheater they will build in the course of REForCh.

Integration of project contents in a student lecture for Master degree named “Electrothermal processing” at Leibniz Universität Hannover
This lecture deals with different kinds of electrothermal processing. The general results of REForCh will be integrated into this and probably other student lectures, too.

Integration into Laboratory experiments for students
It is envisaged that some of the results will be integrated into practical experiments to the main topic “Induction heating” which are necessary for 5th semester B.Sc. students of electrical engineering. Furthermore, ETP will check if the integration in a basic existing laboratory for younger students can be done.

Workshop for industry and academia
METAV has planned to organize a workshop about the topic ”Advantages of using MA steels in automotive industry”. This open workshop will be accessible for represents of the industry and academia. It will be held in collaboration with University Politechnica of Bucharest. The foreseen date is February 2015.

Lecture in collaboration with Materials Science and Engineering Faculty, Univ. Politechnica Bucharest.
In March 2015 a lecture will be hold in collaboration with the University Politechnica in Bucharest. The lecture will comprise strengthening mechanism in forged MA steels.

Publication in scientific journals
In the near future METAV write two publications for scientific journals. One publication will deal with nanostructural aspects of a multidirectional foged microallyoed steel and the other one will deal with A carbon footprint for steel in automotive industry.

Presentation of project results at a congress
OMTAS held a presentation of the results of REForCh at the 21. International Forging Congress which took place in Berlin at the end of June 2014. The paper and the presentation were prepared together with IPH and it presented the flash reduced process chain. This congress is organised by EUROFORGE, an association of forging industry across whole Europe and 11 associated countries outside of Europe. About 750 participants from more 30 countries attended the conference. Therefore, the idea and the results of the project were spread to a lot of different forging companies as well as suppliers and customers.

Training of OMTAS engineers
A training of OMTAS engineers was performed form 18.11.2014 to 20.11.2014 in IPH. Engineers from IPH trained engineers from OMTAS in the expert use of FEA software FORGE3 and the development of forging sequences.


Acquire customers from the forging sector
Due to their new gained knowledge, AURRENAK will present their new competence to existing and new partners. They will try to start collaboration with existing forges, which does not have the possibility to analyse their processes using FEA.

Publications in scientific journals together with ETP
Please read paragraph “Publications in scientific journals together with EMA-TEC” from ETP.

Open Workshop for academia and industry together with ETP
Please read paragraph “Open Workshop industry together with EMA-TEC” from ETP.

Commercial use of re-heating technology
EMA-TEC will try to acquire new customers by selling them re-heating inductors that are able to heat up parts that vary highly in their geometry. EMA-TEC will start to make discussions at their existing customer basis to further development of the idea of the variable re-heater.

List of Websites:

Research Institutes:
IPH – Institut für Integrierte
Produktion Hannover gGmbH
Hollerithallee 6
30419 Hannover

ETP – Institute of


Industrial Partners:
Omtaş Otomotiv Transmisyon Aksamı San. ve Tic AŞ


Aurrenak S. Coop.

Related information


Bernd-Arno Behrens, (Shareholder)
Tel.: +49511279760
Record Number: 182675 / Last updated on: 2016-05-11
Information source: SESAM