Incremental Forming Process Research Articles

Influence of Single-Point Incremental Force Process Parameters on Forming Characteristics and Microstructure Evolution of AA-6061 Alloy Sheet

Single-point incremental forming (SPIF) process comprises a set of process variables, such as forming tool diameter, vertical pitch, spindle rotation speed, and tool velocity, which may affect the forming behavior of the sheet to be deformed. The objective of this work is to study the effect of SPIF process parameters on forming characteristics and microstructure development for the AA-6061 (T6) aluminum alloy sheet. The SPIF experiments and finite element (FE) simulations were performed at different process parameters to achieve conical shapes from the AA-6061 blanks. The effect of process parameters on forming forces, thickness uniformity in wall region of the cone and surface roughness of the blank was analyzed. A detailed microstructure study was performed to analyze the effect of process variables on microstructure and texture evolution during the SPIF process. This study reveals that the process parameters are likely to influence the texture development especially at high tool diameter and vertical pitch values. Therefore, suitability and consequences of using different combinations of tool diameter and vertical pitch values are discussed for AA-6061 alloy.

Review on multi-stage incremental forming process to form vertical walled cup

Using incremental forming, forming of a vertical walled cup was impossible in a single-stage due to the reason that failure is followed by thinning at transition region (in between the wall & base of the cup). However in the recent years, forming of a cup with vertical wall or maximum wall angle compared to Single-stage Single Point Incremental Forming (SPIF) are being done successfully by many researchers using Multi-stage Single Point Incremental Forming (MSPIF) process. The reason behind the implementation of MSPIF process is that the thinning will be postponed even when the maximum wall angle is achieved, with number of intermediate stages during Incremental Forming. In the case of Single-stage Incremental Forming, wall angle beyond a certain limit can’t be obtained due to the reason that thinning will occur suddenly at transition region. In this paper, a review is presented on MSPIF process to form cup with vertical wall or maximum wall angle compared to Single-stage Incremental Forming. In addition, tool path design, different forming strategies, effect of forming direction & strategy, Rigid Body Translation (RBT) during intermediate stages, geometrical accuracy of formed part such as dimensional deviation & step formation at base, Formability using Forming Limit Stress Diagram (FLSD) and Thickness distribution and comparisons of MSPIF process are discussed. Further, works proposed for future to improve the process is also presented in this paper.

Study on formability and dislocation density in forming of hemispherical cup

The aim of this work is to study formability and dislocation density in the plastically deformed cup by both punch and die forming process and single point incremental forming (SPIF) process. The stainless steel grade 202 (SS 202) sheet metal was used for this study. The formability from forming limit diagram (FLD) and dislocation density by X-ray diffraction line profile analysis (XRDLPA) were determined for the cup formed by both forming processes and compared with each other. The amount of strain induced transformation (SIT) was also found from microstructure for the cup formed by both forming processes and compared. The cup with hemispherical shape was formed by SPIF process and its amount of deformation and dislocation density was also found.

Numerical investigation on forming behavior of friction stir tailor welded blanks (FSTWBs) during single-point incremental forming (SPIF) process

Tailor welded blank (TWB) is a product which is developed by joining two or more than two materials having same/different thickness and/or properties before any forming process. The method to join the materials can be any of the conventional or advanced methods. TWB offers advantages like overall weight and cost reduction in a product. Despite of such advantages, the application of TWBs is partially resisted by the disadvantages associated with it like formability reduction and weld line movement during the forming operations. A lot of effort has been done in order to overcome the mentioned limitations of the TWBs. However, for homogeneous blank, single-point incremental forming (SPIF) results in better formability so in present work, the attempt has been made to study the forming behavior of TWB during the SPIF process. In this work, the effect of TWB material parameters like yield strength ratio, thickness ratio, strength coefficient ratio and strain index ratio of the parent materials has been investigated on the weld line movement and % thinning of the blank through finite element analysis. In order to perform the numerical analysis, ABAQUS/Explicit was used. Using SPIF, round cup geometry is formed from a flat TWB and effect of different initial positions of tool is investigated. It has been found that when the forming process is started from the weld and tool is travelled toward strong material of the blank, it leads to the minimum thinning, weld line shift and plastic equivalent strain (PEEQ).

Comparison of Predicted Forming Limit Curves with Measured Experimental Data on Hot-Dip Zinc-Coated Cold-Rolled Steel by Incremental Forming Process

Single Point Incremental Forming (SPIF) is a die-less forming process with advantages of high-flexibility, low-cost and short lead time. The high local strains that are applied to the metal sheet, often exceeding the conventional formability limit. This paper is focused on comparison of predicted forming limit curves with measured experimental data on Hot-Dip Zinc-Coated Cold-Rolled sheet, with 0.20 mm thick is studied in single point incremental forming. Truncated square pyramid and cone are formed to study the formability of blank sheets at room temperature. It was found that both Formulation of plastic instability criteria and Keeler’s formula gives the lowest FLC. FLDs have predicted failures in forming process consistently with the real experiments. The experimentally obtained cracking limit differ from analytical one and empirical one by about 3.398 and 2.135 true strain respectively at FLD0, the corresponding plane strain values.

Tool Path and Sheet Thickness Distribution of Axisymmetric Cup in Single Point Incremental Forming

This study involved planning different tool paths for an axisymmetric cup to explore the forming characteristics of the single point incremental forming (SPIF) process. In addition, this study developed a gradient theory to compute the inclined angle between the tangential and horizontal directions of the cup formed using single point incremental forming. The sheet thickness distribution of the cup was also calculated. To verify the theory, circle arc cups were formed by CNC machining using different tool paths. It was found that the cup formed using the spiral evolutional snail-line tool path produced a better surface than that formed using the equal height evolutional tool path. The sheet thicknesses of circle arc cups obtained by the experiment and using the cosine law were compared. A larger deviation was noted in the initial portion of the cup, whereas a smaller deviation was found in the other portion. This study also adopted a dual-conical cup to investigate the relationship between thickness and the initial inclined angle at the initial portion. It was found that a larger initial inclined angle led to good coincidence between the experimental and theoretical sheet thicknesses.

STUDY ON FORMING FORCES OF PARTS PROCESSED BY SINGLE POINT INCREMENTAL FORMING WITH DUMMY SHEET

The present paper describes the experimental investigation on influence of process parameters on maximum forming force in Single Point Incremental Forming (SPIF) process using dummy sheet. Process parameters namely dummy sheet thickness, tool size, step size, wall angle and feed rate are selected. Taguchi L18 orthogonal array is used to design the experiments. From the analysis of variance (ANOVA) dummy sheet thickness, tool size, step size and wall angle are significant process parameters while feed rate is insignificant. It is found that as dummy sheet thickness, tool size, step size and wall angle increase magnitude of peak forming force increases while there is marginal decrease in forming force as feed rate increases. Predictive model is also developed for forming force. Validation tests are performed in order to check the accuracy of developed model. Optimum set of process parameters is also determined to minimize forming force. Experimental results are in good agreement with results predicted by the developed mathematical model.

Formability Analyses on Single Point Incremental Sheet Forming Process on Aluminum 1050

In recent years, there is a lot of demand on metal forming processes in which sheet metal forming process has lots of applications in the automotive and aerospace industries. In sheet metal forming operations, incremental forming is an emerging technology in which, single point incremental forming (SPIF) process is die-less in incremental forming process and providing a competitive alternative to economical and effective in fabricating low volume products. The objective of this work is to analyze the forming analysis on truncated pyramid product by avoiding cracking and maintaining the optimum forming conditions. The formability is analyzed by using ABAQUS software and simulation, different process parameters were varied such as sheet thickness, tool diameter, step depth, spindle rotational speed on aluminum AA1050 alloy. From the simulation results, stress stain and stain distribution were evaluated on the deformed sheet. The product produced is truncated pyramid dimension having square base of side and fillet at corner.

Geometrical Study of Channel Profile under Incremental Forming Process: Numerical Simulation

Incremental forming is one of the innovative manufacturing technologies in plate sheet forming techniques. With the incremental forming process, plate formation can be as desired and also easily applied to the manufacturing with a limited number of products. This paper is conducted to find out the smallest geometry of deviation between the design with the results of the process and the best step-down selection using a single point incremental forming (SPIF). The variable variations used in this research was 2-6 (mm) of step-down where this process uses a punch tool in the form of a hemispherical / half ball and with 2 clamps. Numerical simulation method with explicit finite element model was used as a virtual experiment with the helical shaped tool movement. The tool moves to form a blank with a size of 12x160x200 mm into a channel profile with a speed of 8 mm/s. The result showed that the deviation between the product and the design has increased from step down 2-6 mm. The smallest deviations were 3.63 mm for x axis and 12,549 mm of total depth or 4.57% for y axis with 2 mm step down parameter. Whereas for step down 4 mm had the deviation of 3.9 mm and 13.853 of total depth. But for step down 6 mm had failed / damaged.

Optimization of Single Point Incremental Forming Process Using Ball Nose Tool

In the present work, an attempt is made to study effect of tool geometry on incremental forming performance of annealed aluminum 5052. Here, type of the tool, feed rate and step down are considered as process input parameters and their effects on forming height and surface roughness are studied. Total numbers of 18 experiments have been carried out according to full factorial experimental design. In order to find optimal parameter setting, adaptive network based fuzzy inference system has been associated with simulated annealing algorithm. Here, the optimal results were selected to maximize the forming height and minimize the surface roughness. The obtained results revealed that using the ball nose tool significantly enhances the formability and surface quality due to conversion of sliding friction to rolling type. In addition, it is found that selection of ball nose tool as well as feed rate of 200 mm/min and step down of 0.4 mm causes achievement of desired quality characteristics.

Homogenization of elasto-plastic functionally graded material based on representative volume element: Application to incremental forming process

In the present paper, as a first endeavor, homogenization of elasto-plastic functionally graded material (FGM) is investigated based on representative volume element (RVE) and used for the first time in the single point incremental forming (SPIF) process. The effective properties of elasto-plastic spheres-reinforced FGM composite are determined using the numerical RVE method and Mori-Tanaka model. In order to implement the homogenization equations and numerical algorithm into Abaqus Software, user-defined material, (VUMAT) and (VUSFLD) subroutines are employed. The accuracy of the proposed homogenization methodology is highlighted through comparisons of the present results with those taken from the literature and an excellent agreement is found. During SPIF process, the effect of the power-law index on the formability, plastic deformation, forming force along Z_direction and Von Mises distribution is analyzed. Parametric studies are conducted to show the influence of cone wall angle and sheet thickness on the formability and the thinning along the SPIF process.

Modeling and Analysis of Single Point Incremental Forming Force with Static Pressure Support and Ultrasonic Vibration.

In order to solve the problem of low accuracy caused by instability and springback during the single point incremental forming (SPIF) process, static pressure support (SPS) and ultrasonic vibration (UV) are introduced into the technology for auxiliary forming. In order to qualitatively and quantitatively study the mechanism of static pressure support–ultrasonic vibration-single point incremental forming (SPS-UV-SPIF) force, a typical truncated cone is used as the research object. The working principle and motion rules of the technology are analyzed. The sheet micro-element of the sidewall area is taken as an analysis object. The spatial stress balance equation of the sheet is constructed. The various stresses are integrated and calculated. The forces in each area of the sheet are analyzed and modeled. Finally, an analytical model for SPS-UV-SPIF force is established. The influence law of the static pressure parameter and the vibration parameter on the forming force is obtained. The corresponding SPS system and UV system are designed. The Kistler forming force test system is built. The experimental results are consistent with the theoretical analysis results, which verifies the correctness of the analytical model.

Comparison between Deep-Drawing and Incremental Forming Processes from an Environmental Point of View

Deep-drawing is an industrial forming process which allows the user to process large batches of sheet metals parts. One of the major drawbacks of this process is the complexity and the high cost of dies. In comparison incremental forming is a flexible process, allowing the user to obtain sheet metal parts without the need of using a die. The present paper aims to present a comparative study of the two forming processes by presenting the main advantages and drawbacks of each one. The comparative study, aimed on the industrial implementation of the incremental forming process requires a comparison of the two processes regarding the environmental impact. Thus, the results of the study will justify the selection of the incremental forming process in the case of small batches sheet metal parts in conditions of minimal impact on the environment.

Effects of three parameters on forming force of the single point incremental forming process

This research has examined the effects of three parameter groups on the forming force of single point incremental forming (SPIF) process. The parameters under study include the material types (sheet aluminum, brass and copper), the forming angles (30°, 40° and 50°), and the tool revolution speeds (200, 400 and 600 rpm). The metal forming was carried out using a spherical edge tool which was pressed onto the metal surface to form work pieces of truncated pyramid shape. In the experiment, the forming forces were measured and analyzed to determine an optimal parameter combination, with regard to the material type, forming angle and revolution speed, for the SPIF process. The experimental results showed that all three parameter groups exerted varying influences over the forming force of the SPIF process. The findings indicated that the sheet brass exhibited the highest force value and that the smaller forming angle contributed to the greater forming force. In addition, the higher tool revolution speed resulted in the lower forming force.

A Comparative Study of Simulation Models on Incremental Forming Process by Using the Enhancement Tools

Incremental Forming IF is a suitable sheet metal forming technique for producing complex forms by local deformation. The forming tool movement follows the designed tool path controlled by the CNC machine programme. The main categories of the process are single point, SP and two points, TP "with enhancement tools". Additionally, the product design determines the enhancement tool type used and its obstacles. The enhancement tools are used for improvement of the product profile quality, while maintaining the simplicity of the process. The material formability is affected by mechanical properties and characteristics of the product profile. The limits are concerning the forming tools used and the blank thickness. On the other hand, due to the difficult environment of these process models, numerical methodologies controlled by Finite Element Method, FEM are currently in extensive use. The research offers the main data and results of a comparing study on the influence of using the enhancement tools in IF through FEM. The study purposes to identify the scientific differences of the IF processes, "with and without enhancement tools" by evaluating the thickness and strains distribution of the deformed blank section. In addition, the analysis and the evaluation of the final product profile have been studied.

Experimental and analytical evaluation of Incremental Sheet Hydro-Forming strategies to produce high forming angle sheets

Incremental Sheet Hydro-Forming (ISHF) is a hybrid process of Incremental Sheet Forming (ISF) and Sheet Hydro-Forming (SHF). In the ISHF process, a single ball tool moves over one side of the surface of the sheet and hydraulic support is provided in another by using the pressurized hydraulic fluid. In the current research, an attempt has been made to achieve high forming angles using ISHF. The forming strategy, multi-stage & multi-step (MSMS), has been proposed to improve the formability in ISHF. The MSMS has resulted in the improvement in the formability and forming angle achieved is 78.75o. The primary issue, identified in MSMS forming strategy, is the failure of the product due to thinning of the sheet. To address the failure of the sheet due to thinning, a modified version of MSMS was proposed. This modified version of MSMS has shown tremendous improvement in the formability of the ISHF. The forming angle upto 90o has been successfully achieved using the modified version of MSMS. Analytical models have been developed for MSMS forming strategy and for the modified version of MSMS forming strategy. The experimental results are closely the same as predicted by analytical models.

Considerations Regarding the Industrial Implementation of Incremental Forming Process

Incremental forming is a promising manufacturing process which allow the user to obtain sheet metal parts, in a flexible manner, without the use of a die. However, the industry is still reluctant to apply the process on an industrial scale. Several drawbacks of the process which hinder its industrial implementation are reviewed in the paper. Among them, the low accuracy of the parts and the low productivity of the process are considered. The lack of dedicated technological equipment and specific CAM software tools are also seen as major drawbacks. Moreover, the lack of any analytical tools to predict the plastic behaviour of the processed part and to predict the moment when it loses its integrity influences the adoption of incremental forming on a large scale. Aside of summarizing these drawbacks, the paper tries to develop a decision-making system, based upon fuzzy logic, for assessing the degree of industrial implementation of the incremental forming process, if certain conditions are met.

Effect of Preheated Microstructure Vis-à-vis Process Parameters and Characterization of Orange Peel in Incremental Forming of AA1050 Sheets

The present investigation systematically analyzes and compares the influence of microstructure and crystallographic texture of AA1050 sheet to that of the most critical process parameters, namely tool dimension, and incremental step depth, in single-point incremental forming (SPIF) process. The sheet samples were preheated at different temperatures to reform the original, i.e., distorted and misoriented grain distribution. The results from experimental and statistical analyses report higher sensitivity of global spring back, surface topography and forming limits strains to variations in microstructure and texture than tool diameter and incremental step depth. The preheating of the sheets resulted in the formation of preferential texture by grain reformation, which leads to the increase in the fraction of homogeneous orientated grains. Such grains increase the maximum forming limit strains and reduce the global spring back in SPIF. Fractography analysis of the failed components revealed that improvement in formability due to grain homogenization (developed texture) may be attributed to larger average void diameter. Empirical models were also developed, and optimized levels of parameters were identified to maximize the efficiency of the SPIF process. Further, qualitative and quantitative characterization of orange peel roughness was carried out by segregating the external formed surface into surfaces subjected to orange peel roughness and tool-induced texture.

Influences of Vibration Parameters on Formability of 1060 Aluminum Sheet Processed by Ultrasonic Vibration-Assisted Single Point Incremental Forming

With increasing design complexities of thin-walled parts, the requirement of enhanced formability has impeded the development of the single point incremental forming (SPIF) process. In the present research, the ultrasonic vibration-assisted single point incremental forming (UV-SPIF) method was introduced to increase the formability of sheet metals. AL1060 aluminum alloy was adopted as the experimental material, and a truncated cone part was considered as the research object. The simulation model of UV-SPIF was established to analyze the distribution of plastic strains in the formed part. A forming angle was selected as the measuring index of formability of the aluminum sheet, and the influences of different vibration parameters on formability were evaluated. An experimental platform was devised to verify the accuracy of the obtained simulation results. It was found that ultrasonic vibration effectively improved the forming limit of the sheet. When the amplitude was 6 µm and the frequency was 25 kHz, the sheet yielded the best formability with the largest forming angle of 67 degrees.

Analytical modeling and experimental validation of the forming force in several typical incremental sheet forming processes

Abstract Incremental sheet forming (ISF) is recognized as an advanced forming process which is highly flexible in cost-effectively producing small batched sheet metal parts. The forming force is dramatically reduced due to the local deformation and successive forming characteristics compared with traditional stamping process, and has vital impact on forming quality. It may however, be noted, that the forming force prediction models widely used are empirical ones, which needs further improvement for wider applicability. Besides, the force fluctuation in ISF has impact on the geometric accuracy, which has been less studied so far. In the present work, the analytical models for predicting the forming force for single-pass single point incremental forming (SPIF), multi-pass incremental forming (MPIF) and incremental hole flanging (IHF) processes are developed based on the new analytical models used to calculate the contact area and the through-thickness stress. A series of experiments of typical sheet metal parts in different geometries for different materials with varied process parameters including wall angle, step depth, tool radius and sheet metal thickness are used to validate the proposed analytical models. The new prediction models are proved to calculate the forming force and force components along the axial, tangential and radial directions with high accuracy for SPIF, MPISF and IHF processes. Moreover, the mechanism of force fluctuation is also investigated, and it's proved that the force fluctuation is caused by varied elastic deflection of the deforming sheet metal.