Two-point Incremental Forming Research Articles

Comparison of Vibration Assisted Single Point and Two-Point Incremental Forming of Sheet Metal

Vibration-assisted single-point incremental forming (VASPIF) and two-point incremental forming(TPIF) are two innovative techniques employed in sheet metal forming processes, each offering distinct advantages and limitations. VASPIF utilizes high-frequency oscillations applied to the forming tool to reduce friction and improve material flow, resulting in enhanced formability and surface finish. Conversely, TPIF employs two independently controlled forming tools to deform the sheet metal incrementally, allowing for greater geometric complexity and improved accuracy compared to VASPIF. However, TPIF typically requires more complex tooling and setup, potentially increasing manufacturing costs and setup time. Both techniques have shown promise in improving the formability of sheet metal components while offering unique capabilities suited to specific manufacturing requirements. Vibration-assisted single-point incremental forming (VASPIF) and two-point incremental forming (TPIF) are two advanced methods used in sheet metal forming, each with its unique characteristics, advantages, and limitations. In this comprehensive comparison, we will delve into the fundamental principles, process parameters, applications, advantages, and challenges associated with both techniques. Starting with VASPIF, this innovative approach involves applying high-frequency oscillations to the forming tool during the incremental forming process. These vibrations serve to reduce friction between the tool and the work piece, facilitating material flow and enhancing formability. By effectively decreasing the frictional forces, VASPIF enables the deformation of difficult-to-form materials and improves the surface finish of the formed parts.

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.

A rapid kinematic method for the prediction of sheet performance in two-point incremental sheet forming

A rapid kinematic method for the prediction of sheet performance in two-point incremental sheet forming

Experimental Studies on Die based Two Point Incremental Forming

Incremental sheet forming (ISF) is an interesting new field of study in rapid sheet metal forming. ISF employs a basic mould to make parts with curved surfaces that do not require special equipment. To fulfil the needs of small scale and diversified markets around the world and address the difficulties of long production cycles and high prices, this technique has a wide variety of uses from aerospace to medical research. This work attempts to develop a Two Point Incremental Forming (TPIF) setup for the forming of stainless steel (AISI 316 L) sheets of uniform thickness. In this work, the forming process has been carried out by varying process parameters such as tool diameter, step depth, spindle speed and feed rate. Forming is carried out in a Vertical Milling Centre (VMC) with a hemispherical tungsten carbide tool. The output responses such as wall angle of the formed component, forming time, surface roughness, depth of the formed component was measured and was compared with the selected input parameters.

Experimental and numerical studies on two-point incremental forming of woven fabric composite sheet

Stamping of fiber reinforced plastic (FRP) composite sheet, especially the woven fabrics and their prepregs, has been extensively researched. However, for small-batch production, high cost and long cycle due to design of complicated molds are still critical issues in composite manufacturing. In this paper, a novel hybrid process is proposed to reduce manufacturing costs and cycles of composite parts in small-batch production with the combination of incremental sheet forming and autoclave process. To verify the process feasibility, two-point incremental sheet forming of a typical pyramid part using plain fabric prepreg was preliminarily studied through experimental and numerical methods. A metal-fiber-metal (MFM) sandwich panel configuration consisting of two dummy sheets and core fabric prepreg layer was used to prevent the woven fabric from directly contacting the forming tool and support die, which can avoid viscous friction and guarantee the practicability of the ISF process. Based on the mechanical properties of the plain weave obtained from uniaxial tension and bias extension tests, a continuous approach-based finite element model (FEM) was established in PAM-FORM. Next, cross section profiles, peripheral outlines and shear angle distributions were extracted from experimental and simulation results. The corresponding comparison results were used to evaluate prediction accuracy of the established FE model. Finally, the influence of fabric layer on dummy sheets, fabric deformation history and the influence of friction coefficient on simulation results were analyzed.

Experimental and numerical investigation for sheet thickness thinning in two-point incremental forming (TPIF)

Experimental and numerical investigation for sheet thickness thinning in two-point incremental forming (TPIF)

Effect of process parameters on formability in two-point incremental forming-machining of planar and twisted AA5083 blades

The deformation machining process (DMP) involves machining and incremental forming of thin structures. It can be applied for manufacturing products such as curved-surface blades without using 5-axis computerised numerical control machines. This work presents the effect of tool diameter and forming temperature on spring-back and dimensional accuracy of a simple fabricated part. The results of the first phase of the study are utilised to design the fabrication process of a curved surface blade. A feature-based algorithm is used to design the tool path for the forming process. The dimensional accuracy of the final product is improved through warm forming, two-point incremental forming, and extension of the bending zone to the outside of the product edges. The results show that DMP can be used to fabricate complex curved-surface workpieces with acceptable dimensional accuracy.

Targeted residual stress generation in single and two point incremental sheet forming (ISF)

The mechanical properties and the operating life of a formed component are highly dependent on the residual stress state. There is always a high magnitude of residual stresses in the components formed by incremental sheet forming (ISF) due to the localized deformation mechanism. Hence, a thorough understanding of the generation of the residual stresses by ISF is necessary. This study investigates the residual stress generation mechanism for two process variants of ISF, i.e., Single Point Incremental Forming (SPIF) and Two Point Incremental Forming (TPIF). This understanding is used to control and targetedly generate the residual stresses to improve the part performance. In this regard, the residual stress state in a truncated cone geometry manufactured using SPIF and disc springs manufactured using TPIF was experimentally analyzed. Validated numerical models for both process variants were developed to study the residual stresses in detail. The residual stress state in SPIF is such that the tool contact side develops tensile residual stresses and the non-contact side undergoes compressive residual stresses. The tool step-down variation was used to control residual stresses and improve the fatigue strength of truncated cones manufactured using SPIF. For TPIF, two different forming strategies were used to analyze the residual stress generation mechanism and the role of major process parameters. The residual stresses for TPIF are pre-dominantly compressive in both directions of forming tool motion. For both process variants of the ISF process, it is shown that the residual stresses can be beneficially utilized to improve mechanical properties of the components.

A comparative investigation of damage models for fracture prediction in two-point incremental forming

Two-point incremental forming (TPIF) shows higher forming limits than single-point incremental forming (SPIF) especially for producing complex industrial functional components. However, unexpected failure still occurs occasionally under certain forming conditions in TPIF. In this paper, the applicability of six damage models for failure prediction in TPIF is evaluated. The procedure of damage parameter calibration and finite element modelling are presented. The predicted failure depth and location with these damage models are evaluated under different loading conditions. Furthermore, the stress and strain and damage evolution in TPIF are provided and discussed in detail. It is concluded that the failure location and depth can be predicted more accurately by the Ayada model than others in this work. It is noted that once double-sided contact occurs in TPIF, it reduces the variation of triaxiality through the thickness, altering the accumulation of damage.

Manufacture of an aerospace component with hybrid incremental forming methodology

Single point incremental forming is a promising sheet metal forming technique for small batch production. However, the technique is unable to manufacture vertical walls without significant thickness variation and geometrical errors. Two-point incremental forming has the capability of manufacturing vertical walls but requires actuators and intricate rig designs. This paper presents a design facilitating vertical wall manufacturing using a die similar to that used for two-point incremental forming but without actuators. The geometry is created in six passes with a toolpath that can be generated on any leading computer-aided manufacturing software. Manufacturing with this technique reduces geometrical errors in critical areas and improves thickness distribution. This research will be of interest to anyone looking to manufacture prototypes with flat-based geometries in a cost-effective manner.

Prediction of Tool Force in Two Point Incremental Forming by Slab Analysis

Two-Point Incremental Forming (TPIF) method is a novel technique for producing free form shell parts. The main purpose of this study is to analyze the TPIF process, and, by approximate calculation, to find the force applied to the tool. One of the limitations of an incremental forming process is that during this process force applied to the tool is born by the machine. In this research, an equation for approximate prediction of the force applied to the tool is presented using the values of the yield stress of the sheet, friction coefficient, tool radius and thickness of the sheet; hence, the applied force can be calculated. By increasing the forming angle, the amount of the created local strain increases and the change in thickness and the force applied to the tool is enhanced. However, by increasing the angle of punch wall, less compressive stress is applied to the metal sheet due to the reduction in contact between the surface of the tool and punch wall. Analytical equations presented are validated by the results from experimental tests.

Effects of Process Parameters on the Thickness Uniformity in Two-Point Incremental Forming (TPIF) with a Positive Die for an Irregular Stepped Part.

Incremental sheet forming (ISF) is a novel flexible forming technology with advantages, such as a low forming force, low-energy-consuming equipment, and good forming performance. The lack of available information about the formability of the two-point incremental forming (TPIF) process makes it limited for practical applications. Taking an irregular stepped part as the target part, the effects of process parameters on the thickness uniformity when using TPIF with a positive die for AA1060 aluminum alloy sheets were investigated. First, the set of optimal parameters regarding the diameter of the tool head, feed rate, and the step size were obtained through orthogonal experiments. Furthermore, the optimal parameter set of the number of forming passes, the direction of movement of the forming tool, and the forming angle was determined and the optimal forming result was numerically and experimentally verified. This demonstrated that the parameters affecting the thickness uniformity of the irregular stepped parts were, in descending order, the diameter of the forming tool, the feed rate, and the step size, with corresponding optimal values of 12 mm, 15,000 mm/min, and 0.4 mm, respectively. With an increase of the number of passes and a decrease of the forming angle between adjacent passes, and adopting an alternating clockwise and counterclockwise toolpath, the thickness uniformity of the formed parts was effectively improved.

Deformation Feature of Sheet Metals During Inclined Hole-Flanging by Two-Point Incremental Forming

Incremental hole-flanging is an applicable extension of incremental sheet forming (ISF), but the knowledge on the deformation of metallic sheets during the course is lack, especially when the axes of the flanged necks are not perpendicular to the sheet plane. The current study used Al 6061 and SUS 304 stainless steel sheets with the thickness of 1 mm and 0.3 mm to examine the inclined hole-flanging processes on the flat plates by two-point ISF processes. It was found that, although as a whole the thickness variation is thinning, the decreasing degrees within upper and lower domain are not equal, and the difference increases with the inclination angle. Crack, buckling and local deformity are typical defects found in the experiments. The maximum springback increases with tool diameter, inclination angle and feeding pitch. Due to the material properties and a thinner thickness, local deformity is easier to take place on SUS 304 sheets during forming. Utilizing the tool feeding path along the oblique plane can obtain even force and consequently, more uniform deformation. Moreover, the equations for preliminarily determining the dimension of precut holes were derived according to the radial developed length of the flanged neck.

On the manufacturing of highly-customized near net-shape medical implants using magnesium alloy sheet

The purpose of this work is defining a global methodology framework for the manufacturing of medical implants using Mg alloys by Incremental Forming process from the results attained by the authors in this field.The methodology proposed considers two main steps, an indispensable related to material characterization that includes from the classical and mechanical to spifability testing and it includes numerical simulations. And another one related mainly to implant forming taking into account the best process parameters from the analysis carried out in the previous step. As newness, two variants of the incremental forming process, Single (SPIF) and Two-Point (TPIF) Incremental Forming, are used for the same magnesium implant geometry. Different outputs variables, mainly: Ra, Shape accuracy and Thicknesses, besides Force and Temperature were analysed for comparison purposes.

Investigation of Deformation Mechanism and Failure Mode in Two Point Incremental Sheet Forming

In this work, the deformation of material and fracture mechanism during the incremental sheet forming process experimentally investigated. The mechanism of deformation is dependent on the process parameters. The present work experimentally explains how the tool radius, step size, and feed rate affect the failure mode during two-point incremental sheet forming. Experimental work achieved to examine the failure modes and analyses the reasons. The deformation of the material in two-point incremental sheet forming is a compound of stretching, shearing, squeezing and bending of material through a deformation zone. The experimental plan based on eighteen experiments cover all the conditions leading to the appearance of failure. The results showed an increasing tool radius and step size the behaviour of failure changes from crack without previous necking to crack with necking. The result showed four types of failure that were found during the TPIF process and identify the factors that lead to their appearance.

Flexibility improvement in two-point incremental forming by implementing multi-point die

Among various incremental forming methods, two-point incremental forming (TPIF) is superior to single-point incremental forming (SPIF), but nonetheless, its flexibility is lower than SPIF. In this paper, in order to increase the flexibility of TPIF to form parts with free-form surfaces from an aluminum sheet, a supporting structure together with a reconfigurable multi-point die is implemented. The flexibility of TPIF process using the multi-point die is experimentally and numerically studied by forming a set of components comprising a hemisphere and free-form surfaces such as a scaled-down bulbous bow of a ship hull. The results showed that the proposed multi-point die has a high ability and flexibility in manufacturing of various symmetric and asymmetric components with different dimensions and geometries. In this regard, TPIF of a hemisphere using the rigid and presented flexible dies is experimentally and numerically compared. The results showed that the part formed using the multi-point die has an acceptable accuracy, but for improving the surface quality, the use of a rubber pad between pins and the aluminum sheet is inevitable. The effect of three different types of rubber and the influence of a polyurethane pad with three different hardness values on the thickness distribution and the dimensional accuracy were numerically studied. The results showed that the rubber type does not affect the minimum thickness, and the hemisphere produced using the natural and polyurethane rubbers has the highest and lowest dimensional accuracy, respectively. It was numerically shown that by increasing the hardness of the rubber pad, the minimum thickness and the dimensional accuracy are improved.

Incremental sheet metal forming on the example of car exterior skin parts

Abstract In this article, current, application-related investigations in the field of incremental sheet metal forming (ISF) will be presented and discussed. The main focus of the study will be on the chain of conceptual design, experimentation and subsequent work processes, right through to the final assembly of car exterior skin parts of a streamlined vintage concept car. This will be accompanied by a comparison and evaluation of different production technologies with regard to their economic efficiency, their real duration times and the specific boundary conditions for the manufacturing of just one part per geometry. The manufacturing processes at the centre of the study were: deep drawing, hydroforming and ISF (Two Point Incremental Forming (TPIF) and rolling). Following the holistic discussion on the procedure and choice of processes, the TPIF is examined in detail using the example of the rear mudguards.

Applying ultrasonic vibration during single-point and two-point incremental sheet forming

Abstract Ultrasonic assisted (UA) deformation has been studied on a variety of materials in both fundamental tensile and compression tests as well as in relevant industrial processes. Reductions in flow stress are a common observation when applying UA during material plastic deformation. The objective of this work is to study the effects of ultrasonic energy on single-point (SPIF) and two-point (TPIF) incremental forming. A longitudinal ultrasonic vibration is applied to a hemispherical ISF tool at 20kHz oscillating frequency. A series of conical shapes were selected for UA-SPIF and a 45° conical shape backing die is selected for UA-TPIF. Generally, a positive correlation between oscillation amplitude and reduction in forming forces is observed in the investigated conditions. The force reduction in UA-TPIF is much more significant compared with UA-SPIF. It is hypothesized that UA-SPIF allows membrane vibration of the entire sheet, which lowers the effective ultrasonic energy input into the local plastic deformation region. In addition, UA-TPIF shows a local sheet thickness reduction in regions where ultrasonic oscillation is applied.

Development of Elastomer-Based Incremental Sheet Forming Method for Curved Products

Abstract A novel methodology based on the elastomer-based incremental sheet forming method was developed to employ oblique two-point incremental forming. In order to evaluate the effectiveness of the develped method, several experiments have been conducted for curved products. Our experiments with the proposed method reveal that the material displacements do not only occur along the straight projection line, but also arise along the curved projection path.