Key Engineering Materials Vol. 639

Abstract: Nowadays, lightweight design is a relevant issue in the automotive industry and in the field of electric mobility. The utilization of Press Hardened Components (PHC) made of manganese-boric steels enable weight saving through the reduction of the sheet metal thickness with sufficient component reliability. Because of the hard martensitic structure, by default, laser cutting is applied for piercing and trimming the contour after the Press Hardening Process (PHP). Due to the high energy consumption, in combination with long cycle times, this process is cost intensive.Instead of laser technology, shear cutting would be an interesting alternative for Press Hardened Steels (PHS) but this process poses substantial challenges for the industrial application. In order to cope with the difficulties of shear cutting operations of PHS, this work presents an alternative for processing PHS. This new method is called notch shear cutting.

Abstract: Solid Bonding based welding processes allow to obtain defect free joints with low residual stress and low distortion. However, the engineering and optimization of solid bonding processes is difficult and requires a large number of time and cost consuming test trials. In this way, proper numerical models are essential tools permitting effective process design. The aim of this research was the comparison of the material process conditions during two different manufacturing processes taking advantage of the same metallurgical phenomenon, namely solid bonding. Linear Friction Welding, used to weld non-axisymmetric components and Accumulative Roll Bonding, used to increase the mechanical properties of sheet metals, were considered. Numerical models were set up, validated and used to design the process by studying the complex material behavior during the solid bonding of different aluminum alloys. An implicit approach was used for the Linear Friction Welding and Accumulative Roll Bonding processes, leading to the understanding of the main process variables influence on the field variables distribution and the occurrence of actual bonding.

Abstract: Various solid state or ‘meltless’ recycling techniques have recently been developed for light metal scrap in form of chips. Main objective of all approaches is to bypass the need for remelting in order to reduce the overall required energy, and to avoid the material losses that occur during this step. Within this paper, the use of Spark Plasma Sintering (SPS) is proposed as a novel solid state recycling/welding technique for sheet metal scrap. Aluminium 5182 alloy scrap, derived from sheet metal, was successfully consolidated into a fully dense billet via SPS. The use of pulsed electric current heating, in temperatures well below the alloy melting point, combined with mechanical pressure, enchased the densification process resulting into a void-less material. The recycled SPS sample was fully densified and microstructural investigation has been performed in order to confirm effective oxide film breakage. The results illustrate the effectiveness of SPS in aluminium scrap consolidation, also in form of sheet scrap, providing additional means in solid state recycling. The involved mechanisms that contribute to oxide film fracture and scrap consolidation in SPS are being discussed.Keywords: Aluminium, recycling, spark plasma sintering (SPS)

Abstract: Compound dies are widely used for production of pierced blanks with high accuracy. Stripper is one of the major components of a compound die. In this paper, research work involved in the selection, modeling and prediction of life of stripper of compound die is presented. Knowledge based system (KBS) approach is used for selection of size of stripper. The knowledge base is constructed through coding of production rules of IF-THEN variety in AutoLISP language. Further, a CAD system is developed for automatic modeling of stripper of compound die. This CAD system works in conjunction with the KBS developed for selection of stripper. An artificial neural network (ANN) model is developed for prediction of life of stripper. Various factors affecting life of stripper are investigated through FEM analysis and the critical simulation values are determined. The proposed ANN model is trained by using FEM simulation results. The proposed work is tested successfully on different sheet metal parts taken from stamping industries. A sample run is also demonstrated in this paper.

Abstract: Due to the increasingly shorter development times in the automotive industry the aspect of a continuous virtual product validation is getting more important. For example, in the field of the body in white construction the metal forming-specific process steps in the press shop and the hemming processes in the body shop are designed with the aid of finite element simulations. Even though the computing speeds of the latest finite element solvers are increasing constantly, there is still a huge effort in time to do the pre-and post-processing of a hemming simulation. In order to improve the response time of the hang-on-parts’ manufacturing process verification, a metamodel-based part analysis is aspired. Based on a categorization of the part outline, which has to be analysed, a validation of the hemming process is carried out by using mathematical metamodels in terms of predicting failure probability and production feasibility. By splitting up the part outline into individual segments a fast analysis can be achieved. Here, an automated process is evaluating each segment individually with a special diagnostic technique. The system delivers output results, such as plastic strain values, the tendency of wrinkling, flange length, roll in, etc. Especially in an early development phase, this procedure is advantageous to compare and evaluate different hemming concept alternatives on an efficient way. The high variety of hang-on-parts, which have to be validated, requires that the simulation outlay has to be as small as possible. With this new diagnostic technique an automated hemming validation of hang-on-parts can be executed without doing a finite-element-simulation. So, there is no simulation model which has to be set up, calculated and evaluated. This helps to reduce the time effort and the amount of simulation loops for validating a hemming process. Furthermore, the degree of the part maturity is increased in an early development phase very efficiently.

Abstract: This paper deals with non-trivial problem aspects of laser cutting tool path generation that, to the best of our knowledge, received relatively little attention in the scientific literature. It is shown that some aspects such as plate edge nesting, skeleton and remnant cutting, and clamp positioning can be modeled and solved with little additional effort using existing tool path algorithms. However, concepts such as collision avoidance, pre-cut optimization, and bridge utilization prove to be more challenging and will require more profound algorithmic adjustments if these have to be taken into account fully. An even harder problem aspect is generating tool paths that are thermally feasible. Since laser cutting introduces net heat into the metal sheet, the metal sheet tends to heat up as the cutting progresses. Quality deterioration can occur if the laser spends too much time cutting in the same region. It is shown how to model the easy problem extensions in order to handle them using existing problem approaches and solution approaches are suggested to tackle the harder concepts. In addition, a proof of concept is presented that shows that thermal feasible tool paths can be generated through a multi-start heuristic utilizing a thermal penalty function. A finite difference method iteratively (or concurrently dependent on the used heuristic) evaluates the thermal feasibility and updates the penalty function.

Abstract: Nowadays achieving overall sustainability in industrial activities is the natural consequence of diminishing non-renewable resources and stricter regulations related to environment and occupational safety/health.In industrial sector, CO₂ emissions derive both from direct and indirect emissions. The second type is due to the use of electricity and currently represents more than thirty percent of global amount. For this reason energy consumption reduction is critical aspect in several industrial environments. Power consumption reduction is possible by modifying manufacturing conditions, utilizing alternative technologies and increasing resource utilization rate.The current market demand is characterized by request of small lots with different characteristics, which requires a complex management of the manufacturing production flow.Production planning and scheduling models, arising in flexible manufacturing environments, allows to combine several aspects such as: technological questions (e.g.: minimize manufacturing times and costs) economic criteria (e.g.: maximize production rate) and environmental prospective (e.g.: emissions reduction). A good manufacturing scheduling allows to saturate the system, avoiding bottlenecks, by means of the adaptation of the plant productivity to the request one.In this paper, authors describe an optimization framework focused on the minimization of energy and production costs by means of an intelligent production scheduling. In order to assess the performances, different real case production scenarios, in which the manufacturing activity is mainly based on machining operations, have been analyzed. In this work, several technologies, with various capabilities, have been taken into account in order to perform production activities. In addition, the scheduling has the possibility of using production technologies with low environmental impact and lower productivity, where the increase of the activity duration does not deteriorate the system performance. In this way several production schedules are feasible and the main scheduling aim focuses in obtaining the required productivity to fulfill demand and minimize energy consumption.

Abstract: Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. Comparing to conventional sheet forming processes, ISF is of a clear advantage in manufacturing small batch or customized products such as cranial implant. Although effort on cranial reconstruction by using incremental sheet forming approach has been made in recent years, research has been mostly based on the single point incremental forming (SPIF) strategy and there are still considerable technical challenges for achieving better geometric accuracy, thickness distribution and complex cranial shape. In addition, the use of a backing plate or supporting die reduces the process flexibility and increases the cost. To overcome these limitations, double side incremental sheet forming (DSIF) process is employed for forming Grade 1 pure titanium sheet by using different toolpath strategies. The geometric accuracy and thickness distribution of the final part are evaluated so the optimized tool path strategies are developed. This leads to an assessment of the DSIF based approach for the application in cranial reconstruction.

Abstract: Sheet metal stamping is an important manufacturing process because of its high production rate and low cost, so the fracture prediction of stamping parts has become important issues. Recent experimental studies have shown that the quality of stamping parts can be increased by using ductile fracture criteria. This paper proposed a modified ductile fracture criterion based on the macroscopic and microscopic continuum damage mechanics (CDM). Three-dimensional (3D) explicit finite element analysis (FEA) are performed to predict the fracture behaviors of sheet metal stamping process. An approach to determine the material constants of modified ductile fracture criterion is presented with the help of uniaxial tensile tests and compressive tests. The results show that the modified ductile fracture criterion enables precise cup depth and fracture location of sheet metal stamping under nonlinear paths. Compared with typical ductile fracture criteria, the results predicted with modified ductile fracture criterion correlate the best with the experimental data.

Abstract: With the requirement of aviation and aerospace fields for high-strength Ti-3Al-2.5V titanium alloy bent tubes with high-performance, it is great significance to research the plastic deformation of Ti-3Al-2.5V tubes under compression to obtain desired flow stress curves. A finite element (FE) model of axial compression of Ti-3Al-2.5V tubes was established in this study. Using this model, deformation behaviors of Φ12 mm × t0.9 mm Ti-3Al-2.5V tubes with different ratios of thickness to height (t/h) compressed under different frictions were analyzed. It is shown that the non-uniform deformation degree of the tubes increases with the decrease of t/h and the increase of friction coefficient. This means that a large t/h value and small friction can help to attain a uniaxial compression condition to obtain desired flow stress curves. Such compression conditions for the Φ12 mm × t0.9 mm Ti-3Al-2.5V tube is that, t/h is not less than 0.6 and the friction coefficient is not greater than 0.05