Single Point Incremental Sheet Forming Research Articles

A Hybrid Optimization Approach of Single Point Incremental Sheet Forming of AISI 316L Stainless Steel Using Grey Relation Analysis Coupled with Principal Component Analysiss

A Hybrid Optimization Approach of Single Point Incremental Sheet Forming of AISI 316L Stainless Steel Using Grey Relation Analysis Coupled with Principal Component Analysiss

A Research on the Enhancing of the Formability of Stainless-Steel Sheet Sus304 by Multistage Single Point Incremental Sheet Forming (MSPIF) Technology

Although the Incremental Sheet Forming (ISF) technology has been studied and applied from the last decade of the previous century with more than 30 years of experiences and ameliorations of the researchers of this field, but the ability of deformation of the formed material sheet still has remained in a restrictive modest value. This sheet forming technology could be divided into 2 mains branches: Single Point Incremental Forming (SPIF) and Two Point Incremental Forming (TPIF) wherein the first one is usually applying in research and the second branch is used in production. The ISF is suitable for forming sheet for a single product or for small batch production with a great advantage of a no-need pestle and mold manufacture in advance, but the formability of formed sheet material cannot bigger than a limited formed angle of about 80o that depends on the material and the forming parameters. There are some ameliorations for increasing the formability of the formed sheet such as heating the formed sheet in Hot SPIF or Multistage SPIF (MSPIF)… All the effort and amelioration measures are confronted with different difficulties. In this paper, we concentrate to study on the MSPIF technology on stainless steel SUS304 by simulation method with the proof of experimental method. The results were also compared to the simple SPIF to show its own pros and cons on the related field such as the technology, the productivity and the lubrication.

Learning-based model predictive control for two-point incremental sheet forming

Two-point incremental sheet forming (TPIF) is known to provide higher geometric accuracy compared to single point incremental sheet forming (SPIF). However, it may not always ensure that the maximum allowable absolute geometric error for complex industrial parts is below 0.75 mm. To overcome this challenge, we propose an on-line learning-based model predictive control (MPC) approach to enhance accuracy in TPIF. In this proposed design, the controller parameters can be updated adaptively and effectively on-line, based on historical data, current state, and system inputs, even with unknown system dynamics in future steps. The developed controller is experimentally validated using three benchmark shapes, namely a dog-bone shape, a hemispherical shape, and a water-drop shape, each with different geometric features, in TPIF. The experimental findings demonstrated that the percentage of errors below 0.75 mm can be significantly increased from less than 42 % without control to over 92 % with control for all the tested shapes, while maintaining the safety of the manufacturing process. This highlights the effectiveness and robustness of the developed MPC controller in achieving higher precision for complex parts. This will unlock TPIF capability to form custom high-accuracy parts, thereby enabling ISF as a commercially viable process with increased robustness and accuracy in the future.

Fabrication and Analysis of Denture Plate Using Single Point Incremental Sheet Forming

Incremental sheet forming (ISF) is a metal forming technology in which small incremental deformations determine the final shape. The sheet is deformed by a hemispherical tool that follows the required shape contour to deform the sheet into the desired geometry. In this study, single point incremental sheet forming (SPIF) has been implemented in dentistry to manufacture a denture plate using two types of stainless steel, 304 and 316L, with an initial thickness of 0.5mm and 0.8mm, respectively. Stainless steel was selected due to its biocompatibility and reasonable cost. A three-dimensional (3D) analysis procedure was conducted to evaluate the manufactured part's geometrical accuracy and thickness distribution. The obtained results confirm the capability of SPIF to produce thin-walled biomedical components with satisfactory dimensional accuracy, as geometrical deviations between the developed and the actual models are predominantly in the range of ±0.25mm.

Effect of Step Size on the Formability of Al/Cu Bimetallic Sheets in Single Point Incremental Sheet Forming

Single Point Incremental Forming (SPIF) is an unconventional forming process that is suitable for prototype production and small lot production due to the economical tooling cost, short lead time, and the ability to create symmetrical and asymmetrical complex geometries without the use of expensive dies. This article presents the effect of the step size Δz of a forming tool made of 145Cr6 tool steel on the formability and maximum forming angle, mechanical properties, hardness, surface roughness, microstructure and texture of bimetallic Al/Cu sheets. Experiments were conducted at a constant rotational speed and feed rate, with the use of rapeseed oil as a lubricant. The tests were carried out with the use of a forming tool on both sides of the bimetallic sheet. The shape and dimensions of the formed elements are determined by non-contact optical 3D scanning. It has been proved that an increase in the step size Δz affects the deterioration of the surface quality of the specimens (an increase in the Ra parameter from 0.2 μm to approximately 3 μm for the step size of 1.2 mm), while a small step size down Δz favours the geometric stability of the samples. With increasing step size (at Δx = Δy = const.), the drawpiece wall continually thinned until the material fractured. Based on the results, it was shown that increasing the step size Δz over 1.1 mm causes cracking of the drawpieces. Furthermore, greater thinning of the Al/Cu sheet was observed in the range of step size Δz between 0.7 and 1.0 mm for aluminum side and step size Δz ≤ 0.6 mm and Δz ≥ 1.1 mm for copper side. It was also found that the mechanical properties of the bimetal sheet decreased as a result of incremental forming. The greatest decrease in strength and ductility was recorded for a pitch of 1.2 mm. Strength decreased from 230 MPa (for sheet in initial state) to approximately 80 MPa, elongation from 12% to approximately 8.5%, and hardness from 120 HV10 for Cu and 60 HV10 for Al to approximately 30 HV10 for both layers.

Application of machine learning on tool path optimisation and cooling lubricant in induction heating-assisted single point incremental sheet forming of Ti-6Al-4V sheets

Induction heating-assisted single point incremental sheet forming was established for Ti-6Al-4V thin sheets at closed and above beta-transus temperature (980 °C). In order to eliminate geometric inaccuracy and adherence of lubricant on the surface caused by elevated temperature, a cooling lubricant system was designed for the forming tool to decrease the thermal expansion and friction. A radial basis function (RBF)-based tool path optimisation was developed to study the measured geometric accuracy, temperature, and forming force. By adjusting cooling lubricant control and integrating the RBF framework, the first optimised tool path was used to collect the results and to validate with the finite element (FE) model and theoretical geometric profiles. The output data were further studied by RBF and generate a second optimised tool path. The measured geometric coordinates revealed that the error percentage has been reduced to less than 5%. Further, the microstructure evolution analysed by scanning electron microscopy (SEM) indicated noticeable oxidation and alpha-layer for temperature around 1040 °C and the phenomenon was removed at temperature closed to 950 °C. The surface roughness and energy-dispersive X-ray analysis (EDX) revealed the optimised tool path distributed significant improvement in surface quality. The cooling lubricant system indicated optimal performance with RBF optimised tool path to support constant temperature and reduce friction and lubricant adherence on the surface.

Analysis of the Possibility of Forming Stiffening Ribs in Litecor Metal-Plastic Composite Using the Single Point Incremental Forming Method

Efforts to reduce COx are extremely important, which forces the use of materials and technologies that reduce the weight of means of transport in order to reduce energy consumption. Currently, aluminum alloys and FRP composites are still too expensive for mass industry applications. Presented in this study, Litecor is a three-layer composite that combines the high strength of steel with the low density of plastic. Thanks to the use of external steel covers 0.3 mm thick and a light core 0.7 mm thick, high stiffness was achieved while maintaining a relatively low weight. The weight reduction in comparison with steel blanks with the same stiffness is up to 40%. Litecor is mainly developed by ThyssenKrupp, it is a promising construction material, but it requires development the technology of forming and joining. In this study, the possibility of forming the Litecor layered composite was investigated using the single-point incremental sheet forming (SPIF) method. As part of the research, the stiffening ribs were shaped, the maximum depth of the embossing was determined. The degree of thinning in selected cross-sections of the embossing was determined. The influence of the rotational speed of the tool and the feed rate on the properties of the shaped surface was also analyzed. Incorrectly selected shaping parameters have been shown to damage the zinc coating on the inner surface of the embossing.

Experimental and simulation studies on hybrid incremental sheet forming

In the present research work, parts are formed using two-step hybrid incremental sheet forming (HISF) process. The effect of process parameters such as preform tool size, tool diameter, and preforming depth on thinning in the formed part is studied. A simulation model is developed and simulation results are compared with the experimental results. Also, results of HISF process are compared with the results of single point incremental sheet forming. The simulation results are in good agreement with the experimental results. It is observed that HISF process results in lower thinning as compared to SPIF process. Further, it is found that preform tool size has considerable influence on the minimum thickness of formed part. Large preform tools result in relatively lower thinning.

A novel tool to enhance the lubricant efficiency on induction heat-assisted incremental sheet forming of Ti-6Al-4 V sheets

For heat-assisted single point incremental sheet forming (SPIF) works of Ti-6Al-4 V sheets, the use of lubricant has shown significant effects on surface quality and geometric accuracy at higher temperatures. Molybdenum disulphide (MoS2) is a common lubricant widely used in SPIF works, however, it usually indicates ineffective performance at high temperatures. This article has studied different lubricants of MoS2 lubricants and proposed a novel mixture of MoS2 to provide better surface quality and improve geometric accuracy. A forming tool with a ball-roller and water channel was designed to enable the MoS2 mixture to pass through the tool tip, allowing easy application of the lubricant on the localised area and reduce the thermal expansion on the ball-roller. Surface roughness analysis has revealed that the water-cooling MoS2 mixture performed well in reducing friction effects and achieved better geometric accuracy. Forming forces measurements, scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX) and micro-hardness tests also indicated that a higher strain hardening behaviour was detected for the water-cooling MoS2 mixture.

Automatic generation of 3d spiral tool path for incremental sheet metal forming of mechanical parts with complex geometry

Incremental sheet metal forming is a flexible manufacturing technology that allows to form of various components on the same milling machine, without expensive tools. A hemispherical tool moves along a CNC-controlled tool path and deforms the sheet into the desired shape. The tool path has a significant role in the geometric accuracy of the final part. There has been very little research on the problem of the forming of sophisticated parts with asymmetric wall angles. This paper presents a new approach to generating optimized tool paths for single-point incremental sheet forming (SPIF). At first, a strategy is proposed for the automatic generation of a 3D tool path during forming in a single-step operation. Then, a systematic technique of creating intermediate shapes is investigated by defining tool paths interpolated from the final part shape. The proposed methodology is applied to form a hip cup prosthesis. This part has a complex asymmetric geometry with important angles, a multi-step approach is used. The proposed methodology to define the different tool paths was implemented in Matlab. A numerical simulation of the incremental forming process is performed to predict the final geometry of the aluminum sheet. A comparison of desired and predicted geometries shows the reliability of the proposed method.

Experimental studies on single point incremental sheet forming of stainless steel 409L alloy

Single Point Incremental Forming (SPIF) is a sheet metal forming process in which a sheet metal blank is plastically deformed through a progressive action of single point tool and more reliable for batch production of complex shape of sheet metals with simple numeric control vertical milling machine. In this study, the formability behaviour of stainless steel 409L on both conventional and incremental forming technique were analysed experimentally. The effect of process parameter of SPIF like tool size, spindle speed, feed rate and vertical step down on the formability of stainless steel 409L was investigated experimentally. The forming limit diagram (FLD) and fracture limit curve (FLC) of SS 409L for both the forming processes were plotted and compared. Formability of SS 409L during SPIF increased comparing with conventional forming technique.

Accuracy and Sheet Thinning Improvement of Deep Titanium Alloy Part with Warm Incremental Sheet-Forming Process

Incremental forming is a recent forming process that allows a sheet to be locally deformed with a hemispherical tool in order to gradually shape it. Despite good lubrication between the sheet and the tip of the smooth hemisphere tool, ductility often occurs, limiting the formability of titanium alloys due to the geometrical inaccuracy of the parts and the inability to form parts with a large depth and wall angle. Several technical solutions are proposed in the literature to increase the working temperature, allowing improvement in the titanium alloys’ formability and reducing the sheet thinning, plastic instability, and failure localization. An experimental procedure and numerical simulation were performed in this study to improve the warm single-point incremental sheet forming of a deep truncated cone in Ti-6Al-4V titanium alloy based on the use of heating cartridges. The effect of the depth part (two experiments with a truncated cone having a depth of 40 and 60 mm) at hot temperature (440 °C) on the thickness distribution and sheet shape accuracy are performed. Results show that the formability is significantly improved with the heating to produce a deep part. Small errors are observed between experimental and theoretical profiles. Moreover, errors between experimental and numerical displacements are less than 6%, which shows that the Finite Element (FE) model gives accurate predictions for titanium alloy deep truncated cones.

Emerging Trends in Single Point Incremental Sheet Forming of Lightweight Metals

Lightweight materials, such as titanium alloys, magnesium alloys, and aluminium alloys, are characterised by unusual combinations of high strength, corrosion resistance, and low weight. However, some of the grades of these alloys exhibit poor formability at room temperature, which limits their application in sheet metal-forming processes. Lightweight materials are used extensively in the automobile and aerospace industries, leading to increasing demands for advanced forming technologies. This article presents a brief overview of state-of-the-art methods of incremental sheet forming (ISF) for lightweight materials with a special emphasis on the research published in 2015–2021. First, a review of the incremental forming method is provided. Next, the effect of the process conditions (i.e., forming tool, forming path, forming parameters) on the surface finish of drawpieces, geometric accuracy, and process formability of the sheet metals in conventional ISF and thermally-assisted ISF variants are considered. Special attention is given to a review of the effects of contact conditions between the tool and sheet metal on material deformation. The previous publications related to emerging incremental forming technologies, i.e., laser-assisted ISF, water jet ISF, electrically-assisted ISF and ultrasonic-assisted ISF, are also reviewed. The paper seeks to guide and inspire researchers by identifying the current development trends of the valuable contributions made in the field of SPIF of lightweight metallic materials.

Study of Friction and Wear Effects in Aluminum Parts Manufactured via Single Point Incremental Forming Process Using Petroleum and Vegetable Oil-Based Lubricants.

This paper focuses on studying how mineral oil, sunflower, soybean, and corn lubricants influence friction and wear effects during the manufacturing of aluminum parts via the single point incremental forming (SPIF) process. To identify how friction, surface roughness, and wear change during the SPIF of aluminum parts, Stribeck curves were plotted as a function of the SPIF process parameters such as vertical step size, wall angle, and tool tip semi-spherical diameter. Furthermore, lubricant effects on the surface of the formed parts are examined by energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM) images, the Alicona optical 3D measurement system, and Fourier-transform infrared spectroscopy (FTIR). Results show that during the SPIF process of the metallic specimens, soybean and corn oils attained the highest friction, along forces, roughness, and wear values. Based on the surface roughness measurements, it can be observed that soybean oil produces the worst surface roughness finish in the direction perpendicular to the tool passes (Ra =1.45 μm) considering a vertical step size of 0.25 mm with a 5 mm tool tip diameter. These findings are confirmed through plotting SPIFed Stribeck curves for the soybean and corn oils that show small hydrodynamic span regime changes for an increasing sample step-size forming process. This article elucidates the effects caused by mineral and vegetable oils on the surface of aluminum parts produced as a function of Single Point Incremental Sheet Forming process parameters.

Parameter identification of GTN damage model using response surface methodology for single point incremental sheet forming of IF steel

ABSTRACT The single point incremental sheet forming (SPIF) is an advanced sheet metal forming technique, also known as dieless sheet forming. Formability in incremental sheet forming is defined by the maximum formable wall angle or the depth of forming. In this work, the formability in SPIF is predicted by the Gurson-Tvergaard-Needleman (GTN) model. The parameters of the GTN model was optimised by the response surface methodology (RSM). These parameters were determined by the tensile test experiment and simulation correlation. The optimised parameters were used in the numerical analysis of SPIF process to predict the failure. The results are in good agreement with experimental results and model predicts depth of forming with acceptable accuracy. Further, as the wall angle of the component increases the formability decreases in SPIF, which is well predicted by the numerical model with optimised parameters. In addition to this, the thickness reduction and damage evolution for varying wall angle has been reported with help of numerical analysis.

Reprint of: Residual stress inclusion in the incrementally formed geometry using Fractal Geometry Based Incremental Toolpath (FGBIT)

Single Point Incremental Sheet Forming (SPISF) is a well-known flexible alternative to conventional generative manufacturing processes. In SPISF, the geometry to be formed is fragmented into series of 2D slices and the plastic deformation is achieved through layer by layer movement of a Numerically Controlled (NC), hemispherical or ball end forming tool. The whole plastic deformation is the sum of all localized strains developed during each increment. Spiral, constant z incremental toolpaths, and their variants are common conventional toolpaths for SPISF. Several researchers have investigated these toolpaths extensively. Fractal Geometry Based Incremental Toolpath (FGBIT) is a recently developed toolpath for SPISF that improves the process formability and stress distribution. Unlike conventional toolpaths, FGBIT deforms the base region of the formed geometry which induces work hardening and residual stresses into the work piece. This may lead to the forming of high strength components. The residual stress distribution over the base region of the formed component (square cup) has been investigated in this study. Further, a comparison based on residual stress distribution between FGBIT and conventional incremental toolpaths is presented. Residual stresses have been measured by using nanoindentation technique. Pile up generation near the periphery of the indent is investigated for conventional and FGBIT based toolpaths. It has been observed from the experimental results that, the strength of the formed component increases due to induced compressive surface residual stresses while using FGBIT hence, metal components with high fatigue life and better strength-to-weight ratio can be formed.

Optimization of wall thickness and geometric accuracy in stretch forming combined with incremental sheet forming using grey relational analysis (GRA)

Abstract In this paper, experimental investigation of hybrid forming process which combines stretching and single point incremental sheet forming (SPIF) process is done. The process combination has many advantages such as higher formability, short forming time, uniform material distribution etc. as compared to SPIF process alone. The process comprises of partial forming of part shape using stretching in first step, followed by forming of complete part shape using SPIF process in second step. Effect of three parameters namely stretching amount, pitch and tool diameter is investigated on response characteristics namely wall thickness and geometric accuracy of formed parts. Taguchi’s L25 orthogonal arrays (OA) is used to design the experimental plan. It is observed from the experimental results that, stretching amount and pitch has considerable influence on wall thickness. Also, pitch and tool size significantly affect part accuracy. Grey relational analysis (GRA) is used for multi-performance optimization of most affecting parameters to optimize the wall thickness and geometric accuracy. Validation of optimization process is done by carrying out experiments using optimized values of process parameters. It is observed that the optimum set of process parameters results in optimum wall thickness and geometric accuracy of formed parts.

Characterization of residual stresses in an asymmetrical shape produced through incremental forming

The nature and magnitude of residual stresses affect the performance and service life of the formed components. The state of residual stresses in the axisymmetric shapes have been characterized in Single Point Incremental Sheet Forming (SPIF). However, any study detailing thorough distribution of residual stresses on an asymmetrical shape has not been reported. In the present work, a detailed analysis pertaining to the distribution of residual stresses on an asymmetrical pyramid and stress-parameters relationship (s) are reported. The maximum stresses were induced in the smaller face (or side) of the pyramid followed by the region(s) bordering the edges/corners of the larger face, while the minimum stresses were induced at the bottom of the pyramid. The maximum compressive stresses ranged from −11 MPa to−292 MPa, and the maximum tensile stresses ranged from +6 MPa to +341 MPa. The cause-effect analysis reveals that the diameter and wall angle were the most influential process parameters. Further, as measured on the face center, the stresses varied from +1050 MPa (max tensile) to −650 MPa (max compressive). The results will prove helpful for the process and product design.

A new way to identify thin sheet behaviour: Micro-InDef

Incremental forming is a rapid prototyping process which uses a forming tool toform a sheet metal according to a predetermined trajectory. In this work, a micro incremental deformation test (Micro InDef test) derived from the principle of single point incremental sheet forming is developed and proposed. A complex mechanical loading is applied and has a strong potential for the identication of inelastic behavior using inverse method. In the rst part, this work addresses the parameters identication and validation procedures of ductile damage behavior of ultra-thin sheet metal under very large strain during this instrumented Micro InDef test. An inverse nite element method based on the comparison between numerical and experimental axial forming forces of the micro incremental deformation test is employed to extract a coupled ductile damaged plastic model. In the second part, the objective is to prove the reliability of ductile damage parameters identication using forming force. The richness of data contained in forming force is quantied and compared to the one from tensile test. Firstly, the verication of the estimated parameter's reliability is done via a simple analysis based on the forming force sensitivity to material parameters and secondly by calculating elastoplastic and elastoplastic with ductile damage.

Thin Sheet Behaviour Identification by µ-InDef and Identifiability Analysis

Incremental forming is a rapid prototyping process which uses a forming tool to form a sheet metal according to a predetermined trajectory. In this work, a micro incremental deformation test (Micro InDef test) derived from the principle of single point incremental sheet forming is developed and proposed. A complex mechanical loading is applied and has a strong potential for the identification of inelastic behavior using inverse method.In the first part, this work addresses the parameters identification and validation procedures of ductile damage behavior of ultra-thin sheet metal under very large strain during this instrumented Micro InDef test. An inverse finite element method based on the comparison between numerical and experimental axial forming forces of the micro incremental deformation test is employed to extract a coupled ductile damaged plastic model.In the second part, the objective is to prove the reliability of ductile damage parameters identification using forming force. The richness of data contained in forming force is quantified and compared to the one from tensile test. Firstly, the verification of the estimated parameter’s reliability is done via a simple analysis based on the forming force sensitivity to material parameters and secondly by calculating elastoplastic and elastoplastic with ductile damage