Forming Limits of a Sheet Metal After Continuous-Bending-Under-Tension Loading,”

Forming limit diagrams (FLD) have been widely used as a powerful tool for predicting sheet metal forming failure in the industry. The common assumption for forming limits is that the deformation is limited to in-plane loading and through-thickness bending effects are negligible. In practical sheet metal applications, however, a sheet metal blank normally undergoes a combination of stretching, bending, and unbending, so the deformation is invariably three-dimensional. To understand the localized necking phenomenon under this condition, a new extended Marciniak-Kuczynski (M-K) model is proposed in this paper, which combines the FLD theoretical model with finite element analysis to predict the forming limits after a sheet metal undergoes under continuous-bending-undertension (CBT) loading. In this hybrid approach, a finite element model is constructed to simulate the CBT process. The deformation variables after the sheet metal reaches steady state are then extracted from the simulation. They are carried over as the initial condition of the extended M-K analysis for forming limit predictions Several cases are studied, and the results under the CBT loading condition show that the forming limits of post-die-entry material largely depends on the strain, stress, and hardening distributions through the thickness direction. Reduced forming limits are observed for small die radius case. Furthermore, the proposed M-K analysis provides a new understanding of the FLD after this complex bending-unbending-stretching loading condition, which also can be used to evaluate the real process design of sheet metal stamping, especially when the ratio of die entry radii to the metal thickness becomes small

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

M-K Analysis of Forming Limit Diagram Under Stretch-Bending

Since the forming limit diagram (FLD) was introduced by Keeler, etc., five decades ago, it has been intensively studied by researchers and engineers. Most work has focused on the in-plane deformation which is considered as the dominant mode of the majority forming processes. However the effect of out-of-plane deformation becomes important in the accurate prediction of formability when thick sheet metals and/or smaller forming radii are encountered. Recent research on the stretch-bending induced FLD (BFLD) has been inconclusive. Some studies indicated that the bending effect will enhance a sheet metal's formability while others suggested otherwise. In this paper, we present an in-depth study of the through-thickness bending effect on the forming limits. The Marciniak-Kuczynski (M-K) analysis is extended to include bending, and models based on both flow theory and deformation theory of plasticity are proposed. The study is limited to the right-handside of FLD where the bending is along the major stretch direction. The radial return method is adopted as the framework to integrate constitutive equations. The results show that the bending process decreases the sheet metal formability with the flow-theory based model, while the opposite is true if the deformation theory based analysis is adopted. A detailed examination of the deformation histories from those two models reveals that the loading-unloading-reverse loading process during stretch-bending holds the key to the understanding of the conflicting results. The insight gained from the proposed FLD prediction model in this paper provides a new understanding of how the bending process affects the FLD, which can be used to predict and explain the localized necking phenomenon under the stretch-bending condition

A Hybrid Forming System: Electrical-Assisted Double Side Incremental Forming (EADSIF) Process for Enhanced Formability and Geometrical Flexibility

The objectives of this project are to establish the scientific bases, engineering technologies and energy/emission impact of a novel dieless forming process, Double side Incremental Forming (DSIF), and to explore the effectiveness of its hybrid variation, Electrical-Assisted Double Side Incremental Forming (EADSIF), on increasing the formability of metallic sheets. The scope of this project includes: (1) the analysis of environmental performance of the proposed new process as compared to conventional sheet metal forming processes; (2) the experimental investigation of the process capabilities of DSIF and EADSIF via the self-designed and newly established lab-scale EADSIF equipment; (3) the development of the essential software in executing the new proposed process, i.e., the toolpath generation algorithms; and finally (4) the exploration of the electricity effect on material deformation. The major accomplishments, findings and conclusions obtained through this one and a half years exploratory project are: (1) The first industrial medium-size-scale DSIF machine using two hexapods, capable of handling a sheet area up to 675 mm x 675 mm, was successfully completed at Ford. (2) The lab-scale of the DSIF machine was designed, fabricated and assembled to form a workpiece up to 250 mm x 250 mm. (3) Parts with arbitrary freeform double-curvatures using the genetic, not geometric-specific tooling were successfully formed using both machines. (4) The methodology of the life cycle analysis of DSIF was developed and energy consumption was measured and compared to conventional forming processes. It was found that the DSIF process can achieve 40% to 90% saving when the number of parts produced is less than 50. Sensitivity analysis was performed and showed that even at very large number of produced parts (greater than 2000), incremental forming saves at least 5% of the energy used in conventional forming. (5) It was proposed to use the offset between the two universal tools in DSIF to actively create a squeezing effect on sheet metal and therefore, increase the geometric accuracy. The idea was confirmed through both experimental and numerical validations. (6) A novel toolpath strategy, i.e., the so-called In-to-out toolpath or accumulative toolpath, was proposed to further increase formability and geometric accuracy compared to the SPIF configuration. A dimensional form accuracy of 1 mm can be achieved using the new strategy. (7) The effect of electricity on magnesium alloy was experimentally investigated. It was found that the formability has a ridge with respect to the applied current density and pulse duration. This finding implies that there are multiple choices of process parameters that are workable depending on the desired microstructure. The above results demonstrated that DSIF/EADSIF is a promising forming technology that can create impacts in revolutionizing how the prototyping and small volume production of sheet metals will be fabricated, i.e., it can (1) eliminate the need of casting and machining of drawing dies; (2) tailor material utilization to function requirement therefore achieving a light weight product; (3) reduce the amount of sheet metal scraps; and (4) shorten the engineering and manufacturing time for sheet metal parts from the current 8 {approx} 25 weeks to less than 1 week after the technology is fully developed. DSIF/EADSIF can be implemented in aerospace, automotive and appliance industries, or be used for producing personalized and point-of-use products in medical industry. Our analysis has shown that once developed, verified and demonstrated, the implementation and growth of DSIF will increase U.S. manufacturing competitiveness, advance machine tool and software industries, and create opportunities for emerging clean energy and low-carbon economy with estimated energy savings of 11 TBtu and CO2 reduction of 1 million tons per year. The work has been disseminated into three (3) journal articles and two (2) provisional patent submissions. A new company has been spun off from this research group aiming to commercialize the technology. A team, consisted of Northwestern Kellogg Business school students and Northwestern McCormick Engineering school graduate students, has independently examined business facts and business models, and has assisted in developing go-to-market strategy. One of the key recommendations for utilizing the full potential of this work is to demonstrate the DSIF/EADSIF concept in a true large-scale industrial setup, i.e., being able to form sheet size of 1.5 m x 1.5 m, where technical challenges, such as machine design, shape compensation, dynamic effect on geometrical accuracy, need to be further explored

A Hybrid Forming System: Electrical-Assisted Double Side Incremental Forming (EADSIF) Process for Enhanced Formability and Geometrical Flexibility

The objectives of this project are to establish the scientific bases, engineering technologies and energy/emission impact of a novel dieless forming process, Double side Incremental Forming (DSIF), and to explore the effectiveness of its hybrid variation, Electrical-Assisted Double Side Incremental Forming (EADSIF), on increasing the formability of metallic sheets. The scope of this project includes: (1) the analysis of environmental performance of the proposed new process as compared to conventional sheet metal forming processes; (2) the experimental investigation of the process capabilities of DSIF and EADSIF via the self-designed and newly established lab-scale EADSIF equipment; (3) the development of the essential software in executing the new proposed process, i.e., the toolpath generation algorithms; and finally (4) the exploration of the electricity effect on material deformation. The major accomplishments, findings and conclusions obtained through this one and a half years exploratory project are: (1) The first industrial medium-size-scale DSIF machine using two hexapods, capable of handling a sheet area up to 675 mm x 675 mm, was successfully completed at Ford. (2) The lab-scale of the DSIF machine was designed, fabricated and assembled to form a workpiece up to 250 mm x 250 mm. (3) Parts with arbitrary freeform double-curvatures using the genetic, not geometric-specific tooling were successfully formed using both machines. (4) The methodology of the life cycle analysis of DSIF was developed and energy consumption was measured and compared to conventional forming processes. It was found that the DSIF process can achieve 40% to 90% saving when the number of parts produced is less than 50. Sensitivity analysis was performed and showed that even at very large number of produced parts (greater than 2000), incremental forming saves at least 5% of the energy used in conventional forming. (5) It was proposed to use the offset between the two universal tools in DSIF to actively create a squeezing effect on sheet metal and therefore, increase the geometric accuracy. The idea was confirmed through both experimental and numerical validations. (6) A novel toolpath strategy, i.e., the so-called In-to-out toolpath or accumulative toolpath, was proposed to further increase formability and geometric accuracy compared to the SPIF configuration. A dimensional form accuracy of 1 mm can be achieved using the new strategy. (7) The effect of electricity on magnesium alloy was experimentally investigated. It was found that the formability has a ridge with respect to the applied current density and pulse duration. This finding implies that there are multiple choices of process parameters that are workable depending on the desired microstructure. The above results demonstrated that DSIF/EADSIF is a promising forming technology that can create impacts in revolutionizing how the prototyping and small volume production of sheet metals will be fabricated, i.e., it can (1) eliminate the need of casting and machining of drawing dies; (2) tailor material utilization to function requirement therefore achieving a light weight product; (3) reduce the amount of sheet metal scraps; and (4) shorten the engineering and manufacturing time for sheet metal parts from the current 8 {approx} 25 weeks to less than 1 week after the technology is fully developed. DSIF/EADSIF can be implemented in aerospace, automotive and appliance industries, or be used for producing personalized and point-of-use products in medical industry. Our analysis has shown that once developed, verified and demonstrated, the implementation and growth of DSIF will increase U.S. manufacturing competitiveness, advance machine tool and software industries, and create opportunities for emerging clean energy and low-carbon economy with estimated energy savings of 11 TBtu and CO2 reduction of 1 million tons per year. The work has been disseminated into three (3) journal articles and two (2) provisional patent submissions. A new company has been spun off from this research group aiming to commercialize the technology. A team, consisted of Northwestern Kellogg Business school students and Northwestern McCormick Engineering school graduate students, has independently examined business facts and business models, and has assisted in developing go-to-market strategy. One of the key recommendations for utilizing the full potential of this work is to demonstrate the DSIF/EADSIF concept in a true large-scale industrial setup, i.e., being able to form sheet size of 1.5 m x 1.5 m, where technical challenges, such as machine design, shape compensation, dynamic effect on geometrical accuracy, need to be further explored

Approaches for model validation: Methodology and illustration on a sheet metal flanging process

Model validation has become an increasingly important issue in the decisio