Sheet Forming Process Research Articles

Study of lubrication and wear in single point incremental sheet forming (SPIF) process using vegetable oil nanolubricants

The aim of the present study focuses on investigating the performance that sunflower and corn oils, added with 0.0125, 0.025, 0.05 and 0.1wt% of SiO2 nanoparticles, have when these are used as lubricants during Single Point Incremental Sheet Forming (SPIF) process of 6061 aluminum sheet alloys. In an attempt to explain the differences between friction conditions, the Stribeck curve was used to address the influence that the reinforced lubricants have on the friction and roughness values attained during SPIF process of the aluminum alloy samples. To study the wear effects that the nanoparticles have on the surface samples, the Scanning Electronic Microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) techniques were used to observe the surface morphology and chemical composition. Fourier Transform Infrared Spectroscopy (FTIR) technique was used to study the interaction of the SiO2 nanoparticles with vegetable oils. Experimental results showed a significant surface wear reduction when 0.025wt% of SiO2 nanoparticles are added into the vegetable oils.

The performance of tool shape on efficiency and quality of forming in incremental sheet-forming process

Incremental sheet-forming process is an economical alternative of conventional sheet metal forming process to manufacture parts in small or medium batch size as well as to produce sheet metal prototypes. In the present investigation, to study the effect of tool shape on efficiency and quality of the formed component, two different kinds of tools of same diameter with hemispherical end and spherical end are employed. Forming time is considered as a measure of process efficiency and profile accuracy as a quality of forming. The Taguchi experimental design is applied for experimentation. ANOVA is performed to know the level of significance of the process parameters. It is found that incremental depth step is the most significant process parameter affecting forming efficiency followed by forming speed (feed). Forming speed, wall angle and incremental depth step are the most significant parameters that affect the forming quality.

The performance of tool shape on efficiency and quality of forming in incremental sheet-forming process

The performance of tool shape on efficiency and quality of forming in incremental sheet-forming process

Effect of Incremental Forming Process Parameters on Aluminum Alloy Using Experimental Studies

Incremental Sheet Forming (ISF) process is Innovative and cost effective technology trend for forming products in manufacturing industries. The current research is to study and investigate the influence of incremental sheet forming process parameters on response surfaces of aluminium alloy sheet components. In this experiment, Aluminium alloy AA1050 sheet was selected to process forming by using CNC machining centre without expensive dies. Individual and interactive effect of different factors such as, thickness of sheet, tool diameter, vertical step, feed rate, and tool rotational speed at different levels were assessed to improve the processing time. For the design of experiment (DOE), Taguchi’s L27 orthogonal array was used to investigate and optimize the influencing ISF process parameters. From ANOVA results, it was found that for thickness reduction, the influencing factors were as following; feed rate (21.40 %); for roughness, tool rotation speed (20.43 %) and for hardness, thicknesses of sheet (39.49 %). Response Surface Methodology (RSM) showed that optimal values obtained were 0.46 mm, 10 mm, 0.6818 mm, 2232.32 mm/min., and 2626 rpm for thickness of sheet, tool diameter, vertical step, feed rate and tool rotational speed respectively. For percentage thickness reduction of 59.6%, minimum roughness 2.09μm, and maximum hardness 41.7 BHN, the confirmatory test showed values of 64.78 % thickness reduction, roughness of 2.14μm and hardness of 44.82 BHN that were in agreement with the predicted value.

Development of Tool Path Correction Algorithm in Incremental Sheet Forming

The problem of obtaining sound parts by Incremental Sheet Forming is still a relevant issue, despite the numerous efforts spent in improving the toolpath planning of the deforming punch in order to compensate for the dimensional and geometrical part errors related to springback and punch movement. Usually, the toolpath generation strategy takes into account the variation of the toolpath itself for obtaining the desired final part with reduced geometrical errors. In the present paper, a correction algorithm is used to iteratively correct the part geometry on the basis of the measured parts and on the calculation of the error defined as the difference between the actual and the nominal part geometries. In practice, the part geometry is used to generate a first trial toolpath, and the form error distribution of the resulting part is used for modifying the nominal part geometry and, then, generating a new, improved toolpath. This procedure gets iterated until the error distribution becomes less than a specified value, corresponding to the desired part tolerance. The correction algorithm was implemented in software and used with the results of FEM simulations. In particular, with few iterations it was possible to reduce the geometrical error to less than 0.4 mm in the Incremental Sheet Forming process of an Al asymmetric part, with a resulting accuracy good enough for both prototyping and production processes.

A New Incremental Sheet Forming Process Based on Layer Manufacture

Sheet dieless digital forming is a new sheet metal dieless forming technology. This paper introduced the fundamentals of the Sheet dieless digital forming process. Based on the principle of “layered manufacture” in rapid prototype technology, this process resolves the intricate three-dimensional geometry information of the workpiece into a series of two-dimensional data, which can be used by an NC system to control a forming tool to make a curvilinear movement over the raw sheet metal layer by layer until the component wanted is formed. This paper introduced the Sheet dieless digital forming system and metal digital forming technology.

Surface and Microstructure Considerations in High Speed Single Point Incremental Forming of Ti6Al4V Sheets

Flexible sheet metal forming processes represent a big challenge, which involved a number of researchers all over the world in the last decades. Among these, Incremental Sheet Forming (ISF) process is one of the most investigated and promising due to its simplicity, cheapness and applicability. Furthermore, the possibility to increase the process velocity makes the ISF more suitable than in the past; as a consequence, its application potential is surely increased. It was already highlighted that high speed significantly raises the process temperature, improving the workability of Titanium alloys. In this process configuration, no further heating source is strictly required because the temperature increase is generated due to the plastic deformation and the friction conditions at the interface between the punch and the sheet. While the process feasibility has been already investigated, a lack of knowledge in the literature is present focusing on the analysis of the process impact on the material properties. Accordingly, an experimental campaign on Ti6Al4V sheets has been performed, considering a punch speed two orders of magnitude higher than the conventionally used one. The obtained surfaces have been compared to sheets worked by traditional velocity in order to accurately analyze the impact of high speed. Furthermore, microstructural analyses have been carried out confirming the high speed suitability. All the details are reported in the manuscript

Study on Step Depth for Part Accuracy Improvement in Incremental Sheet Forming Process

Incremental Sheet Forming (ISF) is a new-emerging sheet forming process well suited for small batch production or prototyping because it does not need any dedicated dies or punches. In this forming process, sheet metal parts are formed by a smooth-end tool in a stepwise way, during which plastic deformation is highly localized around the tool end. The part geometric accuracy obtained in the current ISF process, however, has not met the industry specification for precise part fabrication. This paper deals with a study on step depth, a critical parameter in ISF, for improving the geometric accuracy, surface quality and formability. Two sets of experiments were conducted to investigate the influence of step depth on part quality. Dimensional accuracy, surface morphology and material fracture of deformed parts were compared and analysed. An optimum value of step depth was suggested for forming a truncated cone. The present work provided significant fundamental information for the development of an advanced ISF control system on tool path control and optimization.

Simulation and Experimental Observations of Effect of Different Contact Interfaces on the Incremental Sheet Forming Process

Incremental sheet forming (ISF) is a promising forming process perfectly suitable for manufacturing customized products with large plastic deformation by using a simple moving tool. Up to now, however, the effects of contact conditions at the sheet interface are not well understood. The aim of this work is to study the effect of tool type and size on the formability and surface integrity during the forming process. Experimental tests were carried out on aluminum sheets of 7075-O to create a straight groove with four different tools (ϕ 30,ϕ25.4,ϕ20 andϕ10mm). One tool tip was fitted with a roller ball (ϕ 25.4mm) while the other three were sliding tips. The contact force, friction and failure depth were evaluated. A finite element (FE) model of the process was set up in an explicit code LS-DYNA and the strain behavior and thickness distribution with different tools were evaluated and compared with the experimental results. This study provides important insights into the relatively high formability observed in the ISF process. Microscopic observations of the surface topography revealed that a rolling tool tip produced better surface integrity as compared with a sliding tool tip, wherein, distinct scratch patterns in the tool traverse direction were evident.

Comparative Study between Programming Systems for Incremental Sheet Forming Process

Incremental Sheet Forming (ISF) is a method developed to form a desired surface feature on sheet metals in batch production series. Due to a lack of dedicated programming system to execute, control and monitor the whole ISF, researchers tried to utilize programming systems designed for chip making process to suits for ISF. In this work, experiments were conducted to find suitability and quality of ISF parts produced by using manual CNC part programming. Therefore, ISF was carried out on stainless steel sheets using Computer Numerical Control (CNC) milling machines. Prior to running the experiments, a ball-point shaped tool made of bronze alloy was fabricated due to its superior ability to reduce the amount of friction and improve the surface quality of the stainless steel sheet metal. The experiments also employed the method of forming in negative direction with a blank mould and the tool which helped to shape the desired part quickly. The programming was generated using the MasterCAM software for the CNC milling machine and edited before transferring to the machine. However, the programming for the machine was written manually to show the differences of output date between software programming and manual programming. From the results, best method of programming was found and minimum amount of contact area between tool and sheet metal achieved.

Microstructure Evolution of Ti-6Al-4V during Superplastic-like Forming

Superplastic-like forming is a recent developed sheet-forming process that combines hot drawing (mechanical pre-forming) with gas forming. It is an efficient way to form sheet metals into complex parts for automotive and aerospace industries. In comparison with conventional superplastic forming process, the forming time for superplastic-like forming can be significantly shortened as the hot-drawing step would have produced a pre-formed component before gas forming. The other advantage of the superplastic-like forming is its capacity for lower temperature forming, for which superplasticity is not possible. Non-superplastic grade Ti-6Al-4V sheets were successfully formed by superplastic-like forming at 800°C in 16min. The maximum percentage thinning of 54% occurred at the outward corners. In this paper, electron backscatter diffraction (EBSD) was used to examine the microstructure evolution of Ti-6Al-4V at different forming stages during superplastic-like forming process. Some small equiaxed grains, regarded as newly recrystallized grains, were observed near the deformed area after hot drawing. Grains became more randomly distributed as the recrystallization continued during gas forming stage. The as-received structures were finally replaced by the equiaxed grains with an almost random misorientation distribution after the forming process. Dynamic recrystallization was considered as the main deformation mechanism for the non-superplastic grade Ti-6Al-4V alloy.

A Plasticity Induced Anisotropic Damage Model for Sheet Forming Processes

The global fuel crisis and increasing public safety concerns are driving the automotive industry to design high strength and low weight vehicles. The development of Dual Phase (DP) steels has been a big step forward in achieving this goal. DP steels are used in many automotive body-in-white structural components such as A and B pillar reinforcements, longitudinal members and crash structure parts. DP steels are also used in other industrial sectors such as precision tubes, train seats and Liquid Petroleum Gas (LPG) cylinders. Although the ductility of DP steel is higher than classical high strength steels, it is lower than that of classical deep drawing steels it has to replace. The low ductility of DP steels is attributed to damage development. Damage not only weakens the material but also reduces the ductility by formation of meso-cracks due to interacting micro defects. Damage in a material usually refers to presence of micro defects in the material. It is a known fact that plastic deformation induces damage in DP steels. Therefore damage development in these steels have to be included in the simulation of the forming process. In ductile metals, damage leads to crack initiation. A crack is anisotropic which makes damage anisotropic in nature. However, most researchers assume damage to be an isotropic phenomenon. For correct and accurate simulation results, damage shall be considered as anisotropic, especially if the results are used to determine the crack propagation direction. This paper presents an efficient plasticity induced anisotropic damage model to simulate complex failure mechanisms and accurately predict failure in macro-scale sheet forming processes. Anisotropy in damage can be categorized based on the cause which induces the anisotropy, i.e. the loading state and the material microstructure. According to the Load Induced Anisotropic Damage (LIAD) model, if the material is deformed in one direction then damage will be higher in this direction compared to the other two orthogonal directions, irrespective of the microstructure of the material. According to Material Induced Anisotropic Damage (MIAD) model, if there is an anisotropy in shape or distribution of the particles responsible for damage (hard second phase particles, inclusions or impurities) then the material will have different damage characteristics for different orientations in the sheet material. The LIAD part of the damage model is a modification of Lemaitre’s (ML) anisotropic damage model. Modifications are made for damage development under compression state and influence of strain rate on damage, and are presented in this paper. Viscoplastic regularization is used to avoid pathological mesh dependency. The MIAD part of the model is an extension of the LIAD model. Experimental evidence is given of the MIAD phenomenon in DP600 steel. The experimental analysis is carried out using tensile tests, optical strain measurement system (ARAMIS) and scanning electron microscopy. The extension to incorporate MIAD in the ML anisotropic damage model is presented in this paper as well. The paper concludes with a validation of the anisotropic damage model for different applications. The MIAD part of the model is validated by experimental cylindrical cup drawing wheras the LIAD part of the model is validated by the cross die drawing process.

Brass 70/30 and Incremental Sheet Forming Process

This work addresses through bibliographies and experiments the behavior of sheet brass 70/30 for Incremental Sheet Forming process - ISF, based on the parameters: wall angle (), step vertical (ΔZ) strategy and the way the tool. Experiments based on the method called Single Point Incremental Forming - SPIF. For execution of practical tests, we used the resources: software CAD / CAM, CNC machining center with three axles, matrix incremental, incremental forming tool and a device press sheets. Furthermore, measurement was made of the true deformation () and thickness (s1). Practical tests have shown that the spiral machining strategy yielded a greater wall angle, compared to the conventional strategy outline.

Superplastic-like forming of Ti-6Al-4V alloy

Superplastic forming of titanium alloys is used for producing structural components, since it is an effective way to manufacture complex-shaped parts in a one-step operation. An optimized sheet-forming process has been designed incorporating a non-isothermal heating system to establish a fast forming process. This work sought to expand the advantages of the technology to the forming of Ti-6Al-4V alloy at 800 °C and shorter cycle time. The minimum thicknesses area was found at the outward corners, showing a maximum percent thinning of 54 %. In addition to stress variations, the cracks resulting from hot drawing and the oxidation on the sheet surface are the other reasons leading to thickness reduction. From the oxidization behavior of Ti-6Al-4V alloy, it was revealed that the decrease in forming temperature from 900 to 800 °C significantly reduced the formation rate of oxide film on the sheet surface. The study also showed that the main microstructure evolution of Ti-6Al-4V alloy under these conditions was recrystallization.

Evaluation of Geometric Accuracy and Thickness Variation in Incremental Sheet Forming Process

Abstract The aim of this study is to evaluate dimensional conformity and thickness variation of a pyramid geometry obtained by negative single point incremental sheet forming. DC04 mild steel, which has been widely used in automotive and numerous applications due to high formability, was used for experimental investigations. Dimensional accuracy of whole geometry and surface roughness are investigated under the influence of toolpath parameters such as tool diameter, feed rate and vertical step down. In this paper, geometric accuracy and thickness are evaluated by production tolerances of conventional methods and results show that thickness reduction of formed sheet and geometrical deviation of side faces are out of tolerance for all cases.

Improving Formability in SPIF Processes through High Speed Rotating Tool: Experimental and Numerical Analysis

Single-point incremental forming (SPIF) is a quite new sheet-forming process which offers the possibility to deform complex parts without dedicated dies using a single-point tool and a standard three-axis CNC machine. Although the process mechanics enables higher strains with respect to traditional sheet-forming processes, research has been focused on further increasing the maximum forming angle. In the paper, a new approach is used to enhance the material formability through a localized sheet heating as a consequence of the friction work caused by high speed rotating tool. Numerical simulation was utilized to relate the effect of temperature with the main field variables distribution in the sheet.

Coupled finite element simulation and optimization of single- and multi-stage sheet-forming processes

This article presents the development and application of a coupled finite element simulation and optimization framework that can be used for design and analysis of sheet-forming processes of varying complexity. The entire forming process from blank gripping and deep drawing to tool release and springback is modelled. The dies, holders, punch and workpiece are modelled with friction, temperature, holder force and punch speed controlled in the process simulation. Both single- and multi-stage sheet-forming processes are investigated. Process simulation is coupled with a nonlinear gradient-based optimization approach for optimizing single or multiple design objectives with imposed sheet-forming response constraints. A MATLAB program is developed and used for data-flow management between process simulation and optimization codes. Thinning, springback, damage and forming limit diagram are used to define failure in the forming process design optimization. Design sensitivity analysis and optimization results of the example problems are presented and discussed.

Analysis of the Influence of Geometrical Parameters on the Mechanical Properties of Incremental Sheet Forming Parts

Incremental Sheet Forming (ISF) process may be classified within the field of sheet metal forming processes, more specifically in the asymmetric incremental deformation process. Some studies have been carried out on the influence of different parameters in the process. However, there are few publications that evaluate the influence of these parameters using design of experiments by finite element modelling. This study provides a better understanding of the process, which will enable an optimization of the ISF process and its comparison with other metal forming processes. Furthermore, this study will be the basis for determining the development of the equipment necessary to carry it out.

Robust Design of Incremental Sheet forming by Taguchi's Method

Although the competitiveness of Incremental Sheet Forming process can be recognized by the literature review, some intrinsic aspects penalize its industrial application. In particular, even if the idea to take advantage from the bigger formability appears of great interest, on the other hand the not homogeneous thickness distribution reduces the industrial suitability. However, a significant improvement in the thickness distribution can be obtained by using an “artificially modified” tool trajectory. In fact, previous experimental investigations carried out by the authors showed that it is possible to influence the thinning phenomenon by applying a proper tool trajectory. The present study was executed with the aim to design a robust procedure able to highlight how to modify the tool trajectory in order to improve the thickness distribution along the profile. More in particular, the study is based on the coupled use of the numerical analysis and the Taguchi's method. All the results are widely discussed in the paper.

Recent development trends in sheet metal forming

Sheet metal forming is one of the most important key technologies in manufacturing industry. It may be reasoned by several facts, among them the economy of the sheet-forming processes concerning the material and energy consumption, as well as the overall cost efficiency. To keep this key role of sheet metal forming in manufacturing industry, a continuous development is necessary concerning the materials, the development of new innovative forming processes, the tooling and manufacturing equipment. The ever-increasing requirements stated by the automotive industry may be regarded as one of the main driving forces behind sheet-metal-forming innovations. In this paper, some recent developments in sheet metal forming will be overviewed concerning the materials and process developments, as well as the application of various methods of Computer Aided Engineering (CAE).