Simufact Forming Research Articles

Multivariable regression and gradient boosting algorithms for energy prediction in the radial-axial ring rolling (rarr) process

Energy prediction and starvation have become an essential part of process planning for the XXI century manufacturing industry due to cost-saving policies and environmental regulations. To this aim, the research presented in this paper details how machine learning-based algorithms can be an effective way to predict and minimize the energy consumptions in the widely spread radial-axial ring rolling (RARR) process. To analyze this bulk metal forming process, 380 numerical simulations have been developed using the commercial SW Simufact Forming 15 and considering three largely utilized materials, the 42CrMo4 steel, the IN 718 superalloy, and the AA6082 aluminum alloy. To create the database for both multi-variable regression and machine learning models, ring outer diameters ranging from 650 mm to 2000 mm and various process conditions including different sets of tool speeds and initial temperatures have been considered. For the case of the multi-variable regression model, to account for all the cross-influences between all the parameters, a second-order function including 26 parameters has been developed, resulting in a reasonable average accuracy (94 %) but also in an impractical huge equation. On the other hand, the machine learning model based on the Gradient Boosting (GB) approach allows obtaining a similar accuracy (96 %) but its compact form allows a more practical utilization and its training can be expanded almost indefinitely, by adding more results from both numerical simulations and experiments. The proposed approach allows to quickly and precisely predict the energy consumption in the RARR process and can be extended to other manufacturing processes.

Numerical Simulation and Experimental Investigation of Friction Stir Rivet Welding Process for AA6061-T6

This article proposed a novel friction stir rivet welding process to join aluminum alloy 6061-T6 sheets in lap configuration with threaded rivet employed. The material flow behavior and temperature distribution of FSRW process are analysed using Simufact Forming 15.0 software, and joints have been obtained on the modified CNC machine with 1200rpm rotational speed and 10s dwell time. Rotational speed and dwell time are important factors which affecting mechanical properties of FSRWed joints. The welding heat input is determined by the rotation speed, while the heat time of plasticized materials is controlled by dwell time during FSRW process. In order to obtain FSRWed joints with excellent mechanical properties, welding heat input is taken as measurement standard, and the reasonable range of rotational speed and dwell time have been investigated by numerical simulation and statistics. The macroscopic morphology of 3 mm and 4 mm thick aluminum alloy 6061-T6 FSRWed joint we obtained shares uniform characteristic with the numerical simulation forming appearance whose upper surface tests smooth but exists “flash”, and stir zone, heat affected zone, thermo-mechanically affected zone and base metal four distinct zones can be observed in transverse section. The results of numerical simulation and experimental study show that the potential process we proposed takes advantages of solid-state welding and riveting technology. Not only metallurgical bonding can be obtained between upper and lower sheets, but also mechanical properties will be strengthened by riveting.

The Chosen Aspects of Skew Rolling of Hollow Stepped Shafts.

The paper presents chosen aspects of the skew rolling process of hollow stepped products with the use of a skew rolling mill designed and manufactured at the Lublin University of Technology. This machine is characterized by the numerical control of spacing between the working rolls and the sequence of the gripper axial movement, which allows for the individual programming of the obtained shapes of parts such as stepped axles and shafts. The length of these zones and the values of possibly realizable cross-section reduction and obtained outlines are the subject of this research paper. The chosen results regarding the influence of the technological parameters used on the course of the process are shown in the present study. Numerical modelling using the finite element method in Simufact Forming, as well as the results of experimental tests performed in a skew rolling mill, were applied in the conducted research. The work takes into account the influence of cross-section reduction of the hollow parts and the feed rate per rotation on the metal flow mechanisms in the skew rolling process. The presented results concern the obtained dimensional deviations and changes in the wall thickness determining the proper choice of technological parameters for hollow parts formed by the skew rolling method. Knowledge about the cause of the occurrence of these limitations is very important for the development of this technology and the choice of the process parameters.

Experimental and Numerical Assessment of the Hot Sheet Formability of Martensitic Stainless Steels

Hot formed sheet components made of Martensitic Stainless Steels (MSS) can achieve ultra-high strengths in combination with very high corrosion resistance. This enables to manufacture complex lightweight sheet components with longer lifespan. Nevertheless, the hot formability of MSS sheets has not been accurately evaluated considering high temperatures and complex stress and strain states. In this work, the hot sheet formability of three MSS alloys under thermomechanical process conditions was investigated. Initially, mechanical properties of this sheet material were determined by uniaxial tensile test. Finite Element Method (FEM) simulation of a hot deep drawing process was performed under consideration of thermo physical calculated material models using the software JMatPro® and Simufact Forming® 15.0. The resulting strains and cooling rates developed locally in the work piece during the forming process were estimated. The numerical results were validated experimentally. Round cups were manufactured by hot deep drawing process. The resulting maximum drawing depth and hardness were measured. In general, all three alloys developed very good formability at forming temperatures between 700 and 900 °C and increased hardness values. However, they are highly susceptible to chemical composition, austenitization temperature, dwell time, and flange gap. A statistic approach is given to explain the correlation between hardness and its influencing factors.

A Rotary Compression Process for Producing Hollow Gear Shafts.

This paper presents selected numerical and experimental results of a study investigating the process of forming hollow stepped gear shafts from tubes by rotary compression. The objective of the study was to determine whether the rotary compression process is an effective method of producing hollow stepped gear shafts and to identify limitations of this manufacturing method. A theoretical analysis involved the numerical modeling of the proposed process by the finite element method (FEM). 3D simulations were performed using the commercial simulation software package Simufact Forming. The analysis involved examining the material flow pattern along with thermal and force parameters of the process. The FEM results were verified with experimental tests conducted under laboratory conditions. The experiments were performed on a machine specially designed for the rotary compression of hollow parts. Results demonstrate that it is difficult to form a stepped gear shaft in one operation. For this reason, such parts should be formed in two operations. The first operation involves the forming of a hollow stepped shaft by rotary compression, while in the second operation, a gear is formed on one of the steps of the shaft.

Thermomechanical Treatment of Martensitic Stainless Steels Sheets and Its Effects on Their Deep Drawability and Resulting Hardness in Press Hardening

The deep drawability of three Martensitic Stainless Steels (MSS) alloys under conventional press hardening thermomechanical process conditions was investigated. The three alloys differ in the content of the main elements C and Cr. Firstly, the metallurgical properties of the alloys were determined, i.e., the phase mass fraction diagrams and the concentration of alloying elements in solid solution at the austenitic temperatures with help of the JMatPro® software version 7.0. Derived from this analysis, specific thermomechanical process parameters were defined to evaluate experimentally and numerically the hot sheet formability of the alloys during the deep drawing process. The hot deep drawability of the MSS alloys was experimentally assessed. The hot deep drawability was evaluated with the resulting maximum drawing depth values. In general, all three alloys developed very good formability at forming temperatures between 700 and 900 °C. However, they are susceptible to chemical composition, austenization temperature, dwell time, and flange gap. The hot formability behavior of the alloys as well as the resulting hardness showed very good concordance with the calculated metallurgical values. Finally, a numerical analysis was conducted using Simufact Forming® 15.0 software. The interval time during hot blank transfer to the tool determines the initial and final forming temperature. The effect of the time interval on the forming temperature was analyzed numerically and validated experimentally. It was also possible to determine the maximum level of plastic strain in the deep drawn cup.

A fully coupled thermo-mechanical numerical modelling of the refill friction stir spot welding process in Alclad 7075-T6 aluminium alloy sheets

Refill friction stir spot welding (RFSSW) is a solid state joining technology that has the potential to replace processes such as the open-air fusion bonding technique and rivet technology in aerospace applications. Selection of proper RFSSW parameters is a crucial task which is important to ensure the mechanical strength of the joint. The aim of this paper is to undertake numerical modelling of the RFSSW process to understand the physics of the welding process, which involves large deformations, complex contact conditions and steep temperature gradients. Three-dimensional fully coupled thermo-mechanical models of RFSSW joints between Alclad 7075-T6 aluminium alloy sheets have been built in the finite-element-based program Simufact Forming. The simulation results included the temperature distribution and the stress and strain distributions in the overlap joint. The results of numerical computations have been compared with experimental ones. The numerical model was able to predict the mechanics of material flow during the joining of sheets of Alclad aluminium alloys using RFSSW. The predictions of the temperature gradient in the weld zone were in good agreement with the temperature measured experimentally. The numerical models that have been built are capable of simulating RFSSW to reduce the number of experiments required to set optimal welding parameters.

Influence of Process Parameters on Forming Load of Variable-Section Thin-Walled Conical Parts in Spinning

Thin-walled conical parts with variable-section are usually made of superalloy material, with poor plasticity and complex forces, which are difficult to form and control. In this research, a thin-walled conical casing of superalloy GH1140 with variable-section is studied; the real stress–strain curve of the material is fitted and the load-displacement curves of superalloy GH1140 are obtained through a universal testing machine. To clarify the equivalent stress distribution on the upper surface of the thin-walled casing during the forming process and after unloading the rotary wheel, the finite element model of the thin-walled conical casing during the spinning forming process is established with the Simufact Forming finite element analysis software. The effects of processing parameters, such as the mandrel rotational speed ω, the roller feed ratio f and the gap deviation rate δ between the roller and mandrel, on the spinning forming load were obtained. The distribution and numerical trend of the tangential residual stress after forming were detected by X-ray diffraction, and the causes of defects such as flange instability were analyzed. The results of the forming test and the test of residual stress conform well with the simulation, which verifies the stability of the model. The research provides a theoretical basis for improving the forming quality of thin-walled parts with variable-section.

Modeling the Failure Behavior of Self-Piercing Riveting Joints of 6xxx Aluminum Alloy

Self-piercing riveting (SPR) is a mechanical joining process which is applied for joining similar and dissimilar lightweight materials in modern car body manufacturing. For qualifying SPR joints, cross sections must be investigated with respect to predefined quality features. Thus, numerous tests must be carried out in order to determine the maximum load capacity of SPR joints for different load angles. The growing number of materials used for the body-in-white requires a reliable and time efficient routine for predicting the joining behavior and the load capacity of SPR joints. In this study, the load capacity of three SPR joints was investigated numerically and experimentally using so-called KS2 samples. The results of axisymmetric two-dimensional finite element simulations (Hönsch et al in J Phys Conf Ser 1063:1-6, 2018) are the basis for three-dimensional simulations of the destructive testing procedure. The experimental setup of destructive testing was modeled using the FE software Simufact Forming 15. The numerically determined load capacity was validated with experimental data. Comparing the failure modes and the force–displacement curves revealed good agreement of simulations and experiments. Therefore, the presented simulation is a powerful tool for predicting the behavior of SPR joints under different load cases.

Numerical simulation of hybrid joining processes: self-piercing riveting combined with adhesive bonding

Reliable simulation of hybrid joining processes using conventional finite element (FE) tools is challenging, because the liquid adhesive must be somehow included in the model. Thus, in this work the viscoelastic properties of the adhesive are substituted with “equivalent” mechanical properties. The complex viscosity of an epoxy-based single-component adhesive was determined at five temperatures between 20‒55 °C and at seven shear rates between 1‒150 s-1 using a rheometer. Flow stresses and strain rates were calculated from the complex viscosities and from the shear rates. For each temperature investigated the relationship between flow stress and strain rate was fitted with a power-law, which enables modeling the actually liquid adhesive as solid with strain rate-dependent flow stress. In order to validate the material model, a defined volume of adhesive was uniaxially compressed. This testing setup was also modelled using the FE software Simufact Forming 15. In the model the Young’s modulus of the adhesive was iteratively adapted until good agreement between the numerical and the experimental force-displacement curves was achieved. The obtained mechanical properties were finally used for modeling the adhesive layer between two 2.0 mm-thick 6xxx aluminum alloy blanks in the hybrid riveting-bonding process. An axisymmetric model including deformable (rivet, upper blank, lower blank, adhesive layer) and rigid (punch, die, blankholder) components was built in Simufact Forming. The cross-section of the hybrid joint obtained from simulation showed very good geometrical agreement with cross-sections obtained from the joining experiments, and just small differences between the calculated and the measured force-displacement curves was observed.

Limits of the Process of Rotational Compression of Hollow Stepped Shafts.

This article presents the results of theoretical–experimental testing of the process of rotational compression of hollow stepped shafts. The advantages of the technology and the potential area of its application were discussed. Further on, the limits of the rotational compression technology, preventing the manufacturing of high-quality products, were presented. The research was conducted on the basis of numerical modelling using the finite element method in Simufact Forming, as well as the results of experimental tests performed in a forging machine for rotational compression. On the basis of the results obtained, it can be stated that the process of rotational compression of hollow stepped shafts can be hindered by the following phenomena: uncontrolled slip, deformation of the semi-finished product wall, twisting of the formed steps, material cracking, and deformation of the cross-section of the formed steps. The possibility of those hindrances occurring depends heavily on the assumed technological parameters of the process. For this reason, knowledge of the cause of occurrence of those limitations is vital for the development of the technology and the choice of the process parameters.

Effect of the Forming Zone Length on Helical Rolling Processes for Manufacturing Steel Balls.

This paper begins with a brief overview of the methods for producing balls. It then discusses the rolling processes for producing balls in helical passes. Next, a method for designing tools for helical rolling (HR) is described. Six different cases of rolling using tools with helical passes of different lengths are modeled by the finite element method (FEM). The simulations are performed with the use of Simufact Forming version 13.3. Based on the 3D simulations, the distributions of effective strain, damage criterion, and temperature, as well as the variations in loads and torques, are determined. This study also predicts the rate and manner of wear of the helical tools, depending on the tool design. As a result, it has been found that an increased length of the helical forming passes is advantageous in terms of tool service life. It has also been found that excessive elongation of the forming zone is not cost-effective.

Determination of the critical socket depths of 10.9 and 8.8 grade M8 bolts with hexagonal socket form

In this work, the effect of various socket depths of fasteners was investigated for the sake of weight reduction. M8x1.25 × 50 Full Thread (FT) bolts with 10.9 and 8.8 grade were examined in detail. The finite element simulations were performed by using SIMUFACT Forming Software. Empirical studies including fatigue and torque-tension experiments were conducted with the bolts having various socket depths. In addition, the effect of washer as used in most assembly conditions was investigated. One of the analytical methods used in the literature was also employed to compare the results obtained by the numerical and experimental methods. Based on the results obtained in this study, critical socket depths leading to the shift of failures from the thread region to head region were obtained for the investigated M8x1.25 × 50 FT bolts with 10.9 and 8.8 grades. The experimental results were compared with the analytical model and found that the analytical model underestimated the critical socket depths for both 10.9 and 8.8 grade bolts.

Research on the power spinning method of large high-strength cylindrical parts

Counter-roller spinning is an effective method to form large metal cylindrical parts due to its small forming force, low mold cost, and flexible processing. A finite element (FE) simulation model of counter-roller spinning was established by Simufact Forming software to process a tubular blank with an internal diameter of 1970 mm and wall thickness of 26 mm. The simulation results show that the radial spinning force of the inner and outer rollers is minimum, and the difference of the radial spinning force between the outer roller and inner roller is smallest when the process parameters are as follows: thinning ratio of the tubular blank Ψt = 20%, forming angle of the roller αρ = 25°, feed rate of the roller f = 1 mm/r, and pairs of rollers m = 4. Comparatively, the average radial spinning force of mandrel spinning is about 1.70 times that of counter-roller spinning. In the stable spinning stage, the equivalent strain difference decreased gradually with the increase of the thinning ratio and increased steadily with the increase of the forming angle of roller. As the feed rate of the rollers increased, the ovality of the workpiece tended to decrease gradually, the deviation value of outside diameter also decreased progressively, and the straightness accuracy increased. The results of the counter-roller spinning experiment show that a mouth-expanding defect exists in the workpiece, which is consistent with the simulation results. In addition, the internal surface quality of the workpiece was better than the external surface quality under the same feed rate. If the feed rate is not reduced, the surface quality will continue to deteriorate as the pass number of spinning increases. After the cumulative thinning ratio of 30CrMnSiA alloy, structural steel reached 69%; the workpiece surface exhibited a peeling defect and required annealing before spinning could be continued. In addition, the deviations between experimental and FE results of the average radial spinning force and the ovality and straightness were less than 12% and less than 15%, respectively.

Additive Manufacturing Assisting the Design of Closed - Die Forgings

Rebielskij-type design of a rolled con rod preform and appropriate upper and lower dies are presented. The proposed process was tested by Simufact Forming program and modifications made to satisfy the criteria of shape, stress and strain state and temperature distribution during processing. Based on the CAD documentation, a STL file was prepared for 3D polymer printing the die, the con rod preform and the forging. The results will enable 3D printing of prototypes in the appropriate metallic materials, leading to tool manufacture and processing in industrial conditions.

Study of the Influence of the Main Parameters of “Rolling-ECAP” Process on the Stress-Strain State and the Microstructure Evolution Using Computer Simulation

The paper presents the results of computer simulation of the combined process, which combines longitudinal rolling and equal-channel angular pressing (ECAP). The simulation was carried out in the program Deform-3Dto assess the impact of the main parameters of the process on the stress-strain state. Analysis of the influence of various factors on the stress and strain state of the process showed that such factors as the junction angle of the matrix channels and the workpiece heating temperature have a significant impact on the distribution of stresses and accumulated deformation throughout the volume of the workpiece in the implementation of the combined process "rolling-ECAP". At the same time, the variation of the values of the friction coefficients and the lengths of the matrix channels within the permissible values does not play a significant role in changing the SSS parameters in this combined process. As a result of studying the microstructure evolution after modeling in the Simufact Forming program, it was found that the combined method "rolling-ECAP" allows to significantly grind the initial grain size. It is established that the influence of the workpiece heating temperature plays a significant role in the degree of grain grinding. In order to reduce the spread of values and alignment of grain size across the section, it is necessary to subject the workpiece to several deformation cycles. After the third pass, the average grain size difference between the central and surface zones is only 3 μm, which is much smaller than that after the first pass (7 μm). This allows us to talk about a fairly uniform study of the structure of the cross section of the workpiece.

Forming and Oxidation Behavior During Forging with Consideration of Carbon Content of Steel

Developments in technology rely increasingly on the numerical simulation of single process steps up to whole process chains using commercially available or user-written software systems, mostly based on the finite element method (FEM). However, detailed simulations require realistic models. These models consider the relevant material-specific parameters and coefficients for the basic material, surface phenomena, and dies, as well as machine kinematics. This knowledge exists to some extent for certain materials, but not in general for groups of steel that depend on alloying elements. Nevertheless, the basic material and its behavior before, during, and after hot deformation must be understood when designing and describing die-forging processes by experimental and numerical simulations. This is why a new mathematical approach has been formulated for forming behavior and recrystallization kinetics, taking into account the carbon content of the base material, the initial microstructure, and the reheating mode. Furthermore, there have been no studies investigating the influence of varying a single chemical element, such as the carbon content, with regard to the oxidation behavior, including the internal structure (e.g., pores) at high temperatures. In this context the majority of studies were performed with steel grade C45 (material no. 1.0503), which was chosen as base material for the experiments conducted. To identify the effects of the alloying element carbon on the material and oxidation behavior, steel grades C15 (material no. 1.0401) and C60 (material no. 1.0601) were also investigated. The investigations revealed a dependence of the material behavior (microstructure and surface) on the alloying system. Based on the experimental results, the mathematical models formulated were parameterized and implemented in the FE-software Simufact Forming (Simufact Engineering GmbH, Hamburg, Germany) by means of user subroutines. Furthermore, a correlation between the thickness of the oxide scale layer and friction was determined in ring compression tests and accounted for in the software code. Finally, real forging tests were carried out under laboratory conditions, with all three investigated steels for calibration of the materials as well as the FE models.

Evaluation of different levels of prestressing for cold forging tools by numerical simulation analysis

Cold extrusion is known as a metal forming process and used due to its dimensional precision. However, the process definition is obtained by empirical methods where experiments are performed previously and based on a “trial and error” method. To reduce costs, companies have been looking for the support of numerical simulation softwares with metal forming application. This study describes the investigation of the effect of different levels for prestressing of cold extrusion gear tool by using the software Simufact Forming. The dimensional deviations of the gear tooth were obtained from two numerical simulations and compared. The application of shrink rings for the prestressing of tooling was evaluated using two different methods to compare their efficiency. The first one is using conventional shrink rings with tool steel, while the second is the stripwinding concept developed by the company STRECON. To produce spur gears, the low carbon steel SAE 10B22 was used.

Finite Element Simulation of Hot Forging Process for KVBM Gear

In this study, the forging operations of gear has been modeled. This gear is a part which is manufactured with the help of hot forging industry for reduce the cost. The authors propose to reduce the initial billet volume of AISI 4340 steel for the forged through process optimization using the Finite Element (FE)method. The object of this research was to predict the effect of several parameters, such as effective stress, effective plastic strain, temperature and die contact, on the forming of the gear, utilizing computer simulation and experimental results. For this purpose, Solidworks CAD and Simufact Forming FE software were used for the modeling and analysis of the forging process. The billet volume and the preform design were predefined in order to reduce scrap by using preform type C. The experimental results showed that the initial billet volume was reduced at 32 %, which compared favorably with the simulation result of a 40 % reduction. The maximum preforming force of simulation result was diferent with the experiment result at 18 along with the maximum finishing force of simulation result was different with the experiment result at 11 %. It was also found that the effective stress decreased with increasing the temperature, and the press force decreased when the initial billet volume was decreased, which resulted in a decrease of effective plastic strain as well.

Effect of socket depth on failure type of fasteners

In this study, the effect of socket depth on failure types of fasteners were investigated in detail. Socket depth plays a vital role in structural integrity of fasteners particularly in weight reduction studies. Therefore, experimental studies were carried out by cold forged bolts having various socket depths. Fatigue and torque-tension tests were conducted to examine the critical socket depths under different loading types. Finite element analysis were also performed using SIMUFACT FORMING software. According to experimental and numerical investigations, it was shown that the socket depth has significant influence on failure mechanism of fasteners. Depending on the depth of sockets, the locations of the failures were shifted from the threads to the head of fasteners. The main reason for this type of shift was associated with the higher stress levels due to decrease in cross-sectional area of fastener heads. Consequently, it was shown that the critical socket depth is very important parameter in terms of structural integrity of fasteners and it has to be taken into account in the design stage of the every fasteners.