Sheet Metal Parts Research Articles

Numerical investigation of the clinched joint loadings considering the initial pre-strain in the joining area

The components of a body in white consist of many individual thin-walled sheet metal parts, which usually are manufactured in deep-drawing processes. In general, the conditions in a deep-drawing process change due to changing tribology conditions, varying degrees of spring back, or scattering material properties in the sheet blanks, which affects the resulting pre-strain. Mechanical joining processes, especially clinching, are influenced by these process-related pre-strains. The final geometric shape of a clinched joint is affected to a significant level by the prior material deformation when joining with constant process parameters. That leads to a change in the stiffness and force transmission in the clinched joint due to the different geometric dimensions, such as interlock, neck thickness and bottom thickness, which directly affect the load bearing capacity. Here, the influence of the pre-straining in the deep drawing process on the force distribution in clinch points in an automotive assembly is investigated by finite-element models numerically. In further studies, the results are implemented in an optimization tool for designing clinched components. The methodology starts with a pre-straining of metal sheets. This step is followed by 2D rotationally symmetric forming simulations of the joining process. The resulting mesh of each forming simulation is rotated and 3D models are obtained. The clinched joint solid model with pre-strains is used further to determine the joint stiffnesses. With the simulation of the same test set-up with an equivalent point-connector model, the equivalent stiffness for each pre-strain combination is determined. Simulations are performed on a clinched component to assess the influence of pre-strain and sheet thinning on the clinched joint loadings by using the equivalent stiffnesses. The investigations clearly show that for the selected component, the loadings at the clinch points are dependent on the sheet thinning and the stiffnesses due to pre-strain. The magnitude of the influence varies depending on the quantity considered. For example, the shear force is more sensitive to the joint stiffness than to the sheet thinning.

Sheared edge defect segmentation using a convolutional U-Net for quantified quality assessment of fine blanked workpieces

Fine blanking allows for the economic mass production of sheet metal parts of high dimensional accuracy. The smooth cut section at the sheared edge is an important quality characteristic that is, however, reduced by the formation of tearings and fractures in the cut-off zone. At present, the smooth cut section cannot be assessed immediately as no capable methods for a 100% inline quality control of sheared edges for fine blanking exist, causing high scrap rates. To address this deficit this work proposes U-Nets to segment tearings and measure the cut-off height at sheared edges. A systematic model search together with a transfer learning strategy is conducted based on a dataset of 80 images of sheared edges of fine blanked reference workpieces. After a hyperparameter optimization, trained models are able to measure the cut-off height on the test dataset with a mean relative error of 1.1% and a mean absolute error of <1 px corresponding to an average measurement error of 7.5 μm. Besides the natural ability to incorporate additional disturbances in a real-world application, investigations of the reproducibility and the impact of the dataset size indicate that the proposed U-Net model is easy to set up and achieves a comparable average performance of 1.14 ± 0.31 px (17.1 ± 3.7 μm) even for non-optimal model initialization and small training datasets. For this reason, the shown approach is a promising solution for an inline machine vision system.

Rule and optimization-based selection of car body parts for the application of tailor rolled blank technology

The majority of parts in modern car bodies is manufactured from sheet metal. Rarely these parts are fully stressed due to design space restrictions and complex requirements. The usage of tailor rolled blanks (TRB) enables the reduction of sheet thickness in areas less loaded and thus reduces part weight. Technically most sheet metal parts are potentially suited for the application of TRB. Economic circumstances like the additional flexible rolling process and technology-specific nesting constraints limit the application to a subset of parts. The search for the best candidate parts taking mass and cost into account is currently challenging. This article presents an optimization strategy for the selection of the parts in a vehicle structure that are best suited for the application of TRB. As a first step, a priori preferencing is performed to select parts based on engineering rules. Using a reduced number of candidate parts, high quality metamodels are trained to perform multiobjective optimizations of all possible combinations of remaining parts, revealing the most efficient part selection under consideration of mass and cost.

A low-cost open-source automated shot peen forming system

The aerospace industry relies on shot peen forming to form sheet metal parts and correct distortion in machined parts. The shot peen forming community is developing simulation and planning methods to meet the industrial need for automation. Researchers need to invest in expensive industrial robots contained in large blasting cabinets to perform the experimental validations of their proposed methods. To bypass this need for expensive industrial-grade equipment, this work presents a low-cost shot peen forming system that enables researchers to validate their methods experimentally on small samples. Conventional installations can cost a few 100,000 USD while the proposed prototype only costs 400 USD to produce. Such a prototype can operate on a tabletop with conventional electrical installations. The use of small samples for validation further reduces the cost of experiments and allows for faster development.

Path planing for robotic polishing of sheet metal parts

Path planing for robotic polishing of sheet metal parts

Determination of Limit Drawing Ratio of SS 304 Steel using Sheet Hydroforming Process with Female Die

Sheet hydroforming with female die process (SHF-D) is easily applicable without pressure and blank holder force control compared to the sheet hydroforming with punch process. Shallow parts can be produced easily with using SHF-D process which is used a lower cost production method in a wide variety of sectors. Limiting drawing ratio (LDR) is indication of formability of sheet metals is determined by using cylindrical punch die. In this study, for the first time, the LDRs of the SS 304 material with different thicknesses was determined experimentally by using the SHF-D instead of sheet hydroforming with punch unlike in the literature. Finite element analysis of SHF-D process has been realized. The results showed that relatively shallow sheet metal parts can be easily produced without the control of pressure and blank holder by means of SHF-D using obtained LDR. It is important to know the forming limit in the SHF-D, since it can be a more economical production method, especially in the manufacture of shallow and large parts used in the automotive and aerospace industries and obtain more quality products than that from classical deep drawing process. By knowing these ratios, die design and parts manufacturing can be realized less costly. The LDR was experimentally obtained as 1.82 with using the sheet hydroforming with female die for the SS 304. The FEA results are in good agreement with experimental results. So, it is useful to analyze the finite element method before designing the dies that will be used with the SHF-D.

Application of laser barcode technology to sheet metal parts identification

Purpose: In the development of ideas for Industry 4.0, information about the element production cycle has become more and more important. Knowledge of the subsequent forming processes, determination of the machine on which the process has been carried out and of the type and wear of the tool, leads to smart production management, which plays an increasingly important role in the metal forming industry. To meet the current expectations for these challenges, an advanced technology needs to be introduced for monitoring the manufacturing processes by deploying flexible solutions. This technology must include, but not be limited to, identifying and tracking the product using laser marking. Design/methodology/approach: Laser marking allows a permanent mark in the form of a barcode to be applied to the sheet metal surface. Commonly used marking methods and the condition of the sheet metal surface can affect the marking contrast. This paper presents a concept for recording individual stages of sheet metal forming and determination of the impact of the laser marking technology on the contrast of the applied barcode. To ensure accurate control of the deformation stages, the bulging process of the spherical dome has been used as an example. Findings: Analysis of the influence of laser marking method on the barcode recognition accuracy can contribute to the development of smart management of the production process according to the idea of Industry 4.0. Research limitations/implications: A large plastic deformation has been applied to the sheet metal surface and no limitation in a barcode reading process (using vision scanning technology) was indicated. Also, the geometry deformation (different angle view of the CCD camera) of the barcode image has introduced no additional problems with a barcode reading. Originality/value: The optimal parameters of a laser marking technique for barcode marking, which are critical for the material that is subjected to metal forming operations that deform it, have been studied. The results shows that traceability is an attractive solution for tracking technological data in the production chain for a single-shaped product. Keywords: manufacturing control, laser marking, vision analysis, sheet metal forming, barcode quality. Category of the paper: Technical paper.

Multi-objective optimization of fixture locating layout for sheet metal part using Kriging and MOBA

Owing to the multi-objective attribute and excessive computational burden of finite element analysis (FEA) during the optimization of fixture locating layout, a new multi-objective optimization method for the sheet metal fixture design based on the Kriging surrogate model and multi-objective bat algorithm (MOBA) is proposed in this paper. The fixture locating layout is treated as the design variable while the overall deformation and maximum deformation of sheet metal under its dead weight are treated as the objective functions. The training and testing sample sets are generated by Latin hypercube sampling (LHS) and FEA. Kriging surrogate model is built by learning from the training sample set and the multi-objective optimization model for fixture locating layout is constructed based on the established Kriging surrogate model. MOBA is employed to find Pareto optimal solution set for the sheet metal fixture locating layout. Finally, a bi-objective optimization case of fixture locating layout for the sheet metal part based on the “4-2-1” locating principle is conducted to verify the proposed method.

STUDY OF METHOD ALLOWING TO AVOID STEPPED RELIEF IN SHEET METAL STAMPING USING TOOLS PRODUCED BY CUT-STACK-BOND SHEET METAL LAMINATION TECHNIQUE

The aim of the article is to investigate novel sheet metal forming approach using tools produced by cut-stack-bond (CSB) sheet metal lamination (SML) in order to prevent the negative impact of stepped relief of dies and punches on the surface quality of formed parts. The stamping process was realized through the following experimental scheme. A flat blank of sheet metal is placed between the die and the punch together with two flat gaskets of sheet metal and then the blank and the gaskets are jointly subjected to the shape change. Experimental results show that novel approach allows obtaining shaped parts without any stepped relief that is typical for the die and the punch produced by CSB-SML. This approach opens wide practical application areas for CSB-SML production of metal forming tools (dies and punches) due to ensuring lower manufacturing time and cost. In the present paper, the features of both bending and drawing processes that use CSB-SML tools were comparatively studied. The proposed method allowing to avoid stepped relief can be effectively applied for production of different high-quality sheet metal parts with intricate shape.

3D-swivel-bending (SB³)

The trends in the evolution of the production structure of the automotive industry and the development of alternative drive concepts are accompanied by the fact that comparatively smaller batch sizes are produced for a large variety of models. These trends require production techniques to meet the demand of flexibility. The requirements for manufacturing processes, especially for forming processes, are low-tool production, fast set-up, and quick product changes. 3D-swivel-bending is a developed manufacturing technique to produce cross-section and load-adapted sheet metal parts and profile components. Such components are used in lightweight structures, often found in developments in automotive and aerospace industries.

Characterization of sheet metal components by using an upsetting test with miniaturized cylindrical specimen

Especially for safety-relevant components local characterization of the mechanical properties is necessary for product testing. For sheet metal parts with a complicated geometry conventional specimens for standardized tests cannot be extracted due to size limitations. Thus, a novel extraction procedure of miniaturized upsetting specimens is investigated. Taking a miniaturized upsetting specimen out of the sheet component allows for the first time the characterization of sheet metals in a standardized upsetting test under uniaxial compression stresses. Furthermore, this enables the analysis of strain hardening behavior of components and a direct validation of finite element simulations based on the true stress.

Finite Element Study on Forming Metal Sheets with an English Wheel

Because of the application trends of Industry 4.0, small-volume large-variety production becomes the daily life in the manufacturing industry. Techniques to flexibly shape sheet metal parts are therefore more and more inquired. This paper is thus aimed to have a preliminary glimpse at the shaping process made by the English wheel, which is broadly used by craftsmen, via Finite Element Analysis. As a result, the parts shaped by an English wheel with a zigzag path show a curved surface having a homogeneous curvature. The more the impression from the bottom roll onto the sheet metal, the smaller the radius of the bottom roll, and the thinner as well as the more compliant the sheet metal, the larger the curvature of the shaped metal part.

Formability analysis on titanium grade2 sheets in multi point incremental forming process

Single point incremental forming (SPIF) is found to be a good alternative to the conventional sheet metal forming techniques and is suitable for the production of small batch and custom made parts. The major disadvantage of the SPIF process is the time required to complete the job. In this work, a multipoint incremental forming (MPIF) tool which gives better contact on the workpiece and completes the job in less time compared to SPIF is used. The present work investigates the formability and failure mechanism of titanium grade 2 sheets in MPIF process. The major operating parameters selected for the study are step depth, feed rate and speed. Formability of titanium grade 2 sheets increases with decrease in speed and step depth while keeping the feed rate constant. Based on the results it was found that the MPIF process can be effectively utilized for forming sheet metal parts.

Effect of steel forming on vehicle side impact behavior

Abstract Despite the seemingly daily development of high-strength new generation steel sheets, steel sheets still remain the most important engineering material used in a vehicle body. These steel parts in a vehicle body, meant to absorb energy during impact, are generally produced by steel forming methods. These steel forming operations may contain processes such as deep drawing, bending, cutting, spring back, spinning. According to the production conditions and type of processes used during the production of sheet metal parts, thinning, thickening, plastic deformation, folding, tearing and wrinkling may occur. In order to achieve more reliable impact simulations, these effects in the forming process should be conferred on impact analysis. Within the scope of this study, an analysis of the critical parts in steel forming that absorb the most energy during the side impact was conducted – first for vehicles. In a subsequent impact analysis, the effects of changes (thickness distribution, residual stress, plastic deformation, etc.) during steel forming were examined.

AUTOMATION OF SHEET METAL COMBINATION DIE DESIGN PROCESS

This paper proposed a novel methodology for designing and manufacturing of sheet metal dies based on features of sheet parts. Also, combination is designed according to die cupping and punching features of sheet metal parts. The proposed approach is an attempt to make seamless integration of computer aided design with computer aided manufacturing. The features used in this study are taken from MusumiTM Catalogue as well as from various small and medium scale sheet metal industries. Work is divided into two phases. In the first phase, the relevant geometrical and topological data is extracted by reading STEP AP 203. In the second phase, a combine adjacency matrix and rule-based system is developed to recognize sheet metal features for die manufacturing. The system showed excellent performance for all types of features contained in the MusumiTM catalog and for different sheet metal industries. The proposed system for automated design of combination dies for sheet metal parts has been tested successfully for various types of industrial deep drawn parts. It reduces the die compoment design time from hours to minutes. selection of die components and drawings generated by the system were found to be reasonable and very similar to those actually used in the sheet metal industries for production of these typical components on combination dies.

NUMERICAL SIMULATION OF SINGLE POINT INCREMENTAL FORMING FOR ASYMMETRIC PARTS

Single point incremental forming (SPIF) that will produce non-symmetric sheet metal parts has been rarely dealt with so far. SPIF of a Francis hydro-turbine vane made of aluminum alloy is studied as a typical example in this work. At first, a concave geometry, encompassing the desired vane shape is designed, from which the formed part will be ultimately cut out. The necessary SPIF toolpaths are created by using the CAM software normally used for milling processes. Based on these toolpaths, a finite element simulation is setup using shell elements with a particular emphasis on substantial time scaling and due care on tool-sheet contact parameters. For validation purposes the part was manufactured and digitized by a white light scanner. It exhibited tolerable deviation from the targeted nominal geometry. Simulation predicted a significant part of this deviation, proving its indispensability in checking out toolpaths and process parameters for non-symmetric parts, yet at non-negligible computational time.

The Experimental Investigation of Punching of the AM60 and AZ61 Magnesium Alloy Sheets by Using Varied Punch Shapes

The using of magnesium alloys for industrial sheet metal part production has become increasingly common in recent years. This research aims to characterize the effects of the cutting-edge shapes of the punches on the blanking forces and the sheared edge qualities in the blanking/piercing operations of magnesium alloy sheets. Magnesium sheets (AM60 and AZ61) were produced by casting and rolling processes. AM60 and AZ61 Mg alloys produced by casting were rolled by using two different speeds, 2.5 m/min and 7.5 m/min. Material thickness was adjusted to three mm in the rolling process. Blanking tests were carried out on a die-set and hydraulic press by varying shaped punches. In the experimental studies, flat-ended, concave shaped, and 16° angled punches were used. A loadcell was fixed to the experimental setup to determine the blanking forces. The results showed that the AM60 alloy was more resistant to shearing than the AZ61. The lowest blanking force was obtained by use of the 16° angled punch. It was determined that the using of flat-ended punches for blanking operations was more convenient according to the usage purpose of the parts while all three punches can be used for piercing operations.

Strength enhancement of AlMg sheet metal parts by rapid heating and subsequent cold die stamping of severely cold-rolled blanks

A trade-off between high strength and formability is forcing the automotive industry today to use several different aluminum alloys in structural assemblies. This leads to a reduced recyclability, which ultimately affects the sustainability of the entire product. In this work, it is demonstrated that a severely cold-worked AA5182 sheet metal blank can be formed to a sound part through a heat treatment of 10 s at 300 °C and a subsequent cold die forming. The high dislocation density in the as-received feedstock is induced by means of cold-rolling and promotes a yield strength of 326 MPa. The rapid heating with a heating rate of 24 K/s allows to increase the local ductility of the investigated material in a warm condition by more than 200% while preserving the initial grain structure of the material. Combined with additional work-hardening during forming, the final yield strength of the formed part is 319 MPa. The recovery kinetics of the as-received AA5182-H19 sheet are examined between 150 °C and 300 °C with dwell times between 1 s and 30 s. It is found that above 250 °C the fraction of residual strain hardening is a function of temperature and time. The resulting dislocation structures are investigated by a series of SEM, EBSD, and TEM measurements. Furthermore, the ductility enhancement is studied by a series of tensile tests with in-situ contact plate heating and fractographic analyses. Because the process under discussion allows to combine high strength and formability within one alloy, it is a promising approach to substitute 6000-series aluminum alloys in mixed-material assemblies and therefore make them easy to recycle.

Impact of the electromagnetic field pressure on the bending of high convex-side

A large number of aircraft parts made of sheet materials are used as flanges, common to such parts is the presence of walls, sides, and various elements that increase rigidity and reduce mass. These sheet parts are complex, mostly closed forms, which by plastic deformation methods require a rather complex stamping tools. Technological methods of manufacturing have certain disadvantages associated with the need to refine the shaping. In addition, the frequent updating of product designs and their constant improvement with a significant amount of experimental and small-scale production required the creation of technological methods that provide a significant reduction in terms of preparation. When punching sheet metal parts, in particular, by the pressure of magnetic-pulse field, the accuracy of shaping is mainly influenced by the shape of the flange in the process of deformation. At the final stage of shaping, an impact contact occurs between the flange of the part with the die or form-block. On impact, elastic unloading of the flange occurs due to the removal of inertial tensile stresses along the generatrix. After the impact contact, dynamic springing or rebound of the flange occurs.

A novel method for approximating local changes in the surface absorption for laser marking using 3D laser scanning

Laser marking is a non-contact technique, which achieves colouring by using a laser beam to increase surface oxidation. Controlling the amount of heat induced into the part is essential in ensuring the desired degree of oxidisation. However, the induced heat is not only dependent on the process parameters, but also on the surface absorption, which in turn is dependent on the material, laser wavelength, and surface quality, i.e., current degree of oxidation and contaminants as well as surface roughness. This paper proposes a method for correlating backscatter from a 3D laser scanner with the surface absorption of sheet metal parts. The purpose is to determine local changes in the surface absorption caused by surface oxidation and contamination. The method utilises a 3D laser scanner, which projects a laser line at the surface and measures the resulting backscatter at an angle. The proposed solution applies a bi-directional reflectance model to reduce the influence of varying scanning angles. The method’s sensitivity to variations in surface treatments is investigated and validated against backscatter spectroscopy measurements. The results show that the proposed method can identify changes in the absorption. However, these were, in some cases, more than 70% higher compared to spectroscopy measurements.