Statistical Study on Correlation between Design Variables and Shape Errors in Flexible Stretch Forming Process

2013 ◽  
Vol 652-654 ◽  
pp. 1994-2001
Author(s):  
Young Ho Seo ◽  
Jun Seok Yoon ◽  
Beom Soo Kang ◽  
Jeong Kim
Keyword(s):  
Material Behavior ◽  
Radius Of Curvature ◽  
Curvature Radius ◽  
Regression Equations ◽  
Shape Error ◽  
Stretch Forming ◽  
Forming Process ◽  
Tensile Direction ◽  
Design Variables ◽  
Shape Errors

In order to reduce the elastic recovery of a sheet material and eliminate a great number of solid dies used in the forming process of various shapes, a flexible stretch forming process (FSFP) is considered in this study. Especially, the relationship among design variables, such as the punch size, objective radius of curvature, and elastic pad thickness is quantitatively evaluated to find out their respective influences on the shape errors of a formed sheet plate using the statistical method based on the FE simulation result planned by the three-way factorial design. The shape errors are divided into two types based on the material behavior according to the widthwise- and tensile- directions. The correlations of the shape errors and the design variables are estimated through the Pearson correlation analyses. The punch size has a strong positive linear correlation with the widthwise- and tensile- shape errors, and the correlation between the objective curvature radius and tensile-direction shape error is weak and negative. Although the effect of the elastic pad thickness is less than those of the other variables, it prevents effectively surface defects. Subsequently, the mathematical model is assumed to clarify their relationship. Two regression equations are estimated in terms of the design variables regarding the widthwise- and tensile- shape errors. The shape errors could be inferred by the assumed model in the particular combination of the design variables; then, the acceptable punch size and elastic pad thickness can be determined according to the objective curvature radius.

Flexible Stretch Forming Technology for Sheet Metal Based on Discrete-Gripper and Multi-Point Die

2014 ◽  
Vol 556-562 ◽  
pp. 460-463 ◽  
Author(s):  
Xue Chen ◽  
Ming Zhe Li ◽  
Wen Hua Liu ◽  
Zhi Qiang Hou
Keyword(s):  
Sheet Metal ◽  
Experimental Results ◽  
Shape Error ◽  
Stretch Forming ◽  
Forming Process ◽  
Structural Composition ◽  
Forming Technology ◽  
Working Principle ◽  
Material Utilization

To solve the problem of low material utilization in traditional stretch forming process, a flexible stretch forming method was proposed, which can be realized by interaction of the multi-point stretch forming die with discrete-gripper stretch forming machine. The principle and characteristics of sheet metal flexible stretch forming technology was introduced, structural composition and working principle of the multi-point stretch forming die and discrete-gripper stretch forming machine were expounded, and the technology experiments was carried out with a self-designed flexible stretch forming technology equipment for sheet metal. The experimental results indicate that structure of multi-point stretch forming die and discrete-gripper stretch forming machine are reasonable, and flexible stretch forming technology can be realized by above-mentioned die and machine, stretch forming parts has a good quality and its shape error can satisfy requirements of production.

scholarly journals Tool Path Design of the Counter Single Point Incremental Forming Process to Decrease Shape Error

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4719
Author(s):  
Kyu-Seok Jung ◽  
Jae-Hyeong Yu ◽  
Wan-Jin Chung ◽  
Chang-Whan Lee
Keyword(s):  
Sheet Metal ◽  
Tool Path ◽  
Incremental Forming ◽  
Single Point ◽  
Optimization Method ◽  
Single Point Incremental Forming ◽  
Shape Error ◽  
Forming Process ◽  
Two Stage ◽  
Shape Errors

Incremental sheet metal forming can manufacture various sheet metal products without a dedicated punch and die set. In this study, we developed a two-stage incremental forming process to decrease shape errors in the conventional incremental forming process. The forming process was classified into the first single point incremental forming (1st SPIF) process for forming a product and the counter single point incremental forming (counter SPIF) process to decrease shape error. The counter SPIF gives bending deformation in the opposite direction. Furthermore, the counter SPIF compensates for shape errors, such as section deflection, skirt spring-back, final forming height, and round. The tool path of the counter SPIF has been optimized through a relatively simple optimization method by modifying the tool path of the previous step. The tool path of the 1st SPIF depends on the geometry of the product. An experiment was performed to form a circular cup shape to verify the proposed tool path of the 1st and counter SPIF. The result confirmed that the shape error decreased when compared to the conventional SPIF. For the application, the ship-hull geometry was adopted. Experimental results demonstrated the feasibility of the two-stage incremental forming process.

Stretch Forming Process Modeling: The Role of Modern Stretch Forming Machinery Design and Performance

2000 ◽  
Author(s):  
James M. Widmann
Keyword(s):  
Control System ◽  
Process Model ◽  
Local Buckling ◽  
Analytical Models ◽  
Hydraulic Control ◽  
Stretch Forming ◽  
Forming Process ◽  
Tensile Direction ◽  
Non Linear ◽  
Hydraulic Control System

Abstract Extrusion stretch forming is used extensively in the aerospace and architectural industries to add contour to extrusions and roll formed sections. Frame members, stringers, wing spars, curtain tracks and many other important aircraft parts are formed with this process. Forming is achieved by pulling an initially straight part in the tensile direction above the material’s yield point and then wrapping the section around a die to add contour. Local buckling and wrinkling that might appear in a pure bending operation can be avoided. There is current interest in improving the process for greater repeatability and less part rework to reduce cost while achieving tighter tolerances (e.g. [1,2]). The stretch forming die plays a significant role in the process. To this end researchers are interested in quicker die development techniques using non-linear beam theory and non-linear finite element modeling of the forming process. For a complete analytical picture of the process, a close look at the stretch forming machine’s performance must be included in the process model. Two major areas of machine performance are important; machine deflections and hydraulic control system performance. This paper provides a brief overview of the extrusion stretch forming process and then focuses on the structural and control system design of the modern stretch forming machine. Analytical models of the machine deflection as well as its hydraulic control system are developed. A short discussion concerning the difference between traditional “pressure forming” and modern CNC position forming is also included. Insight into the limitations of traditional PID control for the stretch forming machine can be seen from the analysis. It is evident that these machine models must be used to complete the process model to effectively create die designs for close tolerance and highly repetitive part production.

Design and Optimization of Loading Trajectory for S-Skin Stretch Forming Process by Simulation

2011 ◽  
Vol 704-705 ◽  
pp. 1363-1369
Author(s):  
Yan Min Zhang ◽  
Xiao Qiang Li ◽  
Ke Xing Song
Keyword(s):  
Mathematics Model ◽  
Stretch Forming ◽  
Forming Process ◽  
Primary Methods ◽  
Design And Optimization ◽  
Design Variables ◽  
Loading Trajectory ◽  
Set Up ◽  
Skin Stretch Forming ◽  
Thinning Rate

Stretch forming is one of the primary methods in skin forming process. Uniform strain distribution and springback are main factors which affect the precision of air skin. In the article the stretch forming process based on S-skin was analyzed. Firstly the parameters ranges of the loading trajectory were designed through the analytic method. Secondly the initial loading trajectory was optimized through finite element numerical simulation. The optimization processes was performed through FET software integrated with the optimization arithmetic. The motion parameters of jaw and machine’s instructions were selected as design variables. Optimization mathematics model was set up which objective is to reduce springback and improve the strain distributes uniform degree. During optimization the maximum main strain and thickness thinning rate of elements were restricted in permissive range. The forming degree of each stage was rational distributed, and the reasonable loading trajectory was founded. The result shows that the reasonable loading trajectory is including pre-stretch, wrap, press and after stretch. After optimization the strain distributes uniformly and the maximum main strain is between 3％～5％. The maximum stretching rate which appears in the shoulders area is less than 6%. In the concave area in which the insufficiency deforming can be occurred easily the strain achieves about 3%, and the deformation is enough. After optimization the unloading springback is decreased distinctly. The average springback of all elements is 0.47mm which reduces 30% compare with before optimization. The result meets the manufacture requirement.

Closed-Loop Shape Control of the Stretch Forming Process Over a Reconfigurable Tool: Precision Airframe Skin Fabrication

1999 ◽  
Author(s):  
Marko Valjavec ◽  
David E. Hardt
Keyword(s):  
Shape Control ◽  
Closed Loop ◽  
Stretch Forming ◽  
Empirical Estimation ◽  
Forming Process ◽  
Sheet Metal Parts ◽  
Shape Errors ◽  
Tool Shape ◽  
Loop Shape ◽  
Chemical Milling

Abstract The accuracy of stretch formed sheet metal parts in the aerospace industry depends heavily on tool designer and machine operator expertise. In addition, fixed-configuration facilities and rigid tools result in long lead times, high manufacturing costs and insufficient product quality. In response to this, a methodology combining an adaptive closed-loop shape control algorithm and a reconfigurable forming tool has been developed and implemented for stretch forming. This method is based on empirical estimation of the process characteristics using a “Deformation Transfer Function” and is capable of rapidly generating a tool shape that produces the desired final part shape, even when significant process uncertainties exist. The same control system is also used to compensate for shape distortions caused by the downstream manufacturing processes of chemical milling and trimming. Experiments involving various compound curvature skins are presented that validate the effectiveness of this methodology in reducing the shape errors below the forming system error threshold in just one or two closed-loop forming trials regardless of skin shape.

A New Stretch-Forming Process Based on Loading at Discrete Points and its Numerical Investigation

2013 ◽  
Vol 423-426 ◽  
pp. 737-740
Author(s):  
Zhong Yi Cai ◽  
Mi Wang ◽  
Chao Jie Che
Keyword(s):  
Sheet Metal ◽  
Three Dimensional ◽  
Discrete Point ◽  
Stretch Forming ◽  
Sheet Metal Part ◽  
Metal Part ◽  
Forming Process ◽  
Loading Trajectory ◽  
New Process ◽  
Forming Defects

A new stretch-forming process based on discretely loading for three-dimensional sheet metal part is proposed and numerically investigated. The gripping jaw in traditional stretch-forming process is replaced by the discrete array of loading units, and the stretching load is applied at discrete points on the two ends of sheet metal. By controlling the loading trajectory at the each discrete point, an optimal stretch-forming process can be realized. The numerical results on the new stretch-forming process of a saddle-shaped sheet metal part show that the distribution of the deformation on the formed surface of new process is more uniform than that of traditional stretch-forming, and the forming defects can be avoided and better forming quality will be obtained.

The Stress and Deformation in Mild Steel During Axisymmetric Necking

1973 ◽  
Vol 40 (1) ◽  
pp. 271-276 ◽  
Author(s):  
M. A. Kaplan
Keyword(s):  
Mild Steel ◽  
Work Hardening ◽  
Flow Region ◽  
Material Behavior ◽  
Experimental Result ◽  
Radius Of Curvature ◽  
Specific Work ◽  
Flow Equations ◽  
Closed Form Solutions ◽  
Stress And Deformation

Closed-form solutions for the stress and deformation fields near the minimum section of the neck are obtained for a mild steel rod subject to axial extension by tensile loads. The procedure involves the use of an experimental result together with the incompressibility and symmetry conditions to find the deformations independently of the stresses. The stresses are then determined with the Levy-Mises flow equations without the use of a specific work-hardening rule. The solution, because of a simplifying assumption, is not valid throughout the entire plastic flow region. Experimental evidence indicates, however, that the region of validity extends well beyond the fracture region. The results enable the tensile test to be used to provide a complete description of material behavior until fracture. To accomplish this, it is necessary to measure the axial load and the radius and radius of curvature at the minimum section. As an example, the work-hardening characteristics of mild steel are determined under the usual work or strain-hardening hypothesis. The application of the results to ductile metals, other than mild steel, is briefly discussed.

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