1 ,a 2 ,b 3 ,c 4 ,d - HCMUT

A Measure of Optimization of Technological Parameters to Improve the Formability of Stainless-Steel Sheet SUS 304 by SPIF Technology

Vo Tuyen1,a, Nguyen Thanh Nam2,b*, Nguyen Phan Anh3,c, Le Khanh Dien4,d, Tan Ken Nguyen1,e, and Trung Le Tran4

1Ho Chi Minh City University of Food Industry (HUFI) 2Faculty of Mechanical Engineering - HCMUT, VNU-HCM

3PetroVietnam University (PVU) 4Saigon Technology University (STU)

[email protected], [email protected], [email protected], [email protected], [email protected],

Keywords: SPIF, DOF, INOVA, regression function, Optimization, stainless steel

Abstract. The objective of this paper is to select a set of technological forming parameters including vertical feed ∆z, feeding rate of vxy of the tool (a kind of pestle but no-cutting edges), the diameter of tool D and the revolutions per minute of tool n to achieve the highest forming ability of stainless steel sheet SUS304 (according to JIS Japanese standard) when forming metal sheet by Single Point Incremental Forming Technology- SPIF. The content of the article consists of 3 processes: − Pre-design of experiment (Pre-DOE) to select of a set of reasonable limited parameters when

forming SUS304 stainless steel models when forming on the existent specialist SPIF machine in the National Key Laboratory of Digital Control and System Engineering laboratory (DCSELAB);

− Performing SUS304 models on the Pre-DOE to obtain the forming angle values. − Evaluating the experimental results by Analyzing of the variance. − Setting up the regression equation of the angle of deformability with influence parameters − Optimization the regression equation to select an optimal set of forming parameters to gain the

highest deformability of stainless-steel sheet SUS304.

Introduction of Incremental Sheet Forming (ISF) technology The sheet forming without die technology invented by Leszak in 1967[1] under the terminology

of Incremental Forming Sheet (ISF). This forming sheet technology is suitable for single or small batch production, could be categorized into two methods: Single Point Incremental Forming (SPIF) that applies forces on one side of the sheet workpiece and Two Point Incremental Forming (TPIF) that applies forces on both sides of the workpiece as shown in Figure 1.

Different from TPIF, which can form complex convex and concave surfaces on model, SPIF can only create concave surfaces but its feather is simpler: no need of pre-machined replica that is placed under the movable feature with slider sleeve as in figure 1b.

Key Engineering Materials Submitted: 2020-01-10ISSN: 1662-9795, Vol. 863, pp 59-66 Revised: 2020-05-31© 2020 Trans Tech Publications Ltd, Switzerland Accepted: 2020-05-31

Online: 2020-09-15

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TransTech Publications Ltd, www.scientific.net. (#542582317-03/09/20,11:18:57)

Figure 1: Two categories of ISF: (a) SPIF and (b) TPIF [2].

In order to study the deformability of models, almost all researchers have always selected the circular tapered shapes of the model as shown in Figure 2.

Figure 2: The circular tapered shapes of the model is suitable for measuring the deformability angle

α in experiment.

This model can help us to measure the angle α at any random depth z of the model because its lateral profile is a curved cone shape because α is made by the tangent line of curved cone shape and the horizontal line. There is a relationship between depth z and α. Because at the maximum depth z

where the model is torn, we could calculate the angle α according to the formula

−

=R

zRarccosα

[2]. The deeper of depth z, the greater the formability α that could show us the gradual forming angle of this technology and respond the purpose of the article. The forming angle α relates to the 4 above parameters of SPIF technology.

Selection of the affecting deformability parameters The following SPIF forming parameters are considered to have a great influence on the forming

angle: diameter of forming tool D [mm], tooling step ∆z [mm], speed of tooling vxy [mm/min] and the revolution per minute of the tool n [rpm] that are also controllable parameters and have direct influence on the forming angle of SUS304. This is the reason that we need to investigate the mechanical properties of SUS304 and define the limite values of these technology parameters. 1. Mechanical properties of stainless steel SUS304

Stainless steel SUS304 is a relatively soft, deformable and very popular in domestic utensil such as kettle, fork, spoon as well as in industry: centrifugal fan, shielded carter, chassis of elevator ... The properties of SUS304 stainless steel are shown in Table 1.

60 Materials and Processing Technologies

Table 1: Mechanical properties of stainless steel SUS304 [3]. Young’s modulus E

[GPa] Coefficient of

Poisson Yield stress σY

[MPa] Thickness

[mm] 193 0,29 205 0.4

With the mechanical properties mentioned above, the forming modes of stainless-steel SUS 304 are selected to suit the capacity and power of the specialized SPIF machine (Figure 3) that is available at our laboratory. With the combine of practical experience, mechanical properties of stainless-steel SUS 304 and technology systems of specialized SPIF forming machine, we can choose the limited forming parameters suitable for SUS 304 stainless steel as Table 2.

Table 2: Selection of the appropriate forming parameters for SUS304 stainless steel

Thickness of sheet [mm] 0.4

Vertical feed ∆z [mm] Low level : 0.2, high level : 1

Diameter of tool D [mm] Low level : 5, high level : 10

Feeding rate vxy [mm/min] Low level : 800, high level : 3000

Revolution of tool n [rpm] Low level : 400, high level : 800

2. Selection of method of Design of experience (DOE) and suitable regime of forming for SUS304 The selection and distribution of the values of the 4 forming parameters are based on the

capabilities of SPIF machine and the experimental plan of part with 2 boundary values [4]. With the selected Partial DOE of 4 parameters, 2 limited values of each, the number of samples to be performed is 24-1 = 8 samples. With the number of iterations is 3, the total of samples to be formed is 3x8 = 24 samples [5]. The regimes of forming of 1 iteration of experience are presented in the following table 3:

Table 3: Regimes of forming stainless steel SUS304

Run Vertical feed ∆z [mm]

Diameter of tool D [mm]

Feeding rate vxy [mm/min]

Revolution of tool n [rpm]

1 0.2 5 800 400

2 0.2 5 3000 800

3 0.2 10 800 800

4 0.2 10 3000 400

5 1 5 800 800

6 1 5 3000 400

7 1 10 800 400

8 1 10 3000 800

Experimental Forming With the iteration number of 3, total 24 samples of SUS304 stainless-steel are formed successively 3 times according to the selected modes in Table 3 on the SPIF specialized machine at DCSELAB. The specialized SPIF machine, its feather and gauge instrument are shown in Figure 3.

Key Engineering Materials Vol. 863 61

Figure 3: Left: Specialist SPIF machine. Right: feather and accessories were used for experiments

in DCSELAB Right: The torn formed model is measured to find the deepest value or the maximum deformable

angle

− The feather has been analyzed on stresses and displacements by Solidworks to define its stiffness before experiment [6]. The displacement of the feather is so small that can be negligible so it can be considered as a robust rigid technology frame system as shown in Figure 4.

Figure 4: The displacement of the feather is considered almost be zero by Solidworks, proving the rigidity of the technology system before forming SUS 304 stainless steel models.

− Lubrication: Due to the huge heat generated when forming, it is necessary to use emulsion slurry of 5% soluble oil solution to lubricate and cool down heat of the tools and sheet materials (Figure 5).


Figure 5: Cooling and lubricating the pestle by emulsion slurry of 5% soluble oil solution.

− Experimental results for determining the average of forming angle of SUS304 with 3 iterations, number of models to form is 3x8 = 24 (Table 4).

Table 4: Experimental results to get the mean deformable angles of SUS304 stainless steel sheet. Run Vertical Feed

∆z [mm]

Diameter of tool D [mm]

Feeding rate vxy

[mm/ min]

Revolution of tool n [rpm]

Mean formable angle [oC]

1 1 5 800 800 65.36 2 0.2 5 800 400 66.41 3 1 10 800 400 62.44 4 0.2 10 800 800 63.68 5 1 5 3000 400 63.41 6 0.2 5 3000 800 66.27 7 1 10 3000 800 65.84 8 0.2 10 3000 400 64.15

Analysis the results of experiment of 3 set of deformable angle by analysis of variance (ANOVA) Before establishing the regression equation of the deformable angle, it is necessary to analyze the variance (Anova: Analysis of Variance) to see if the experimental results are truthful. Anova is used when studying the truthfulness effect of experimental results of forming angle of SUS 304. Anova results with a very small value of P-value = 6.68E-7 shows that the reliability of experimental

Design of experiment (DOE) to define the regression equation of deformable angle The Minitab software is selected to form the regression equation of angle. In Minitab at / DOE/ Factorial / Create factorial design (Figure 6).


Figure 6: Apply Minitab software to determine the regression equation.

Finally, after eliminating all the trivial and very small coefficients we could gain the regression equation for determining the relations of angle of deformation of SUS304 stainless-steel and influential parameters. α = 63,10–18,163∆z – D – 0,0008vxy -0,0092n + 0,8333∆zD – 0,0015∆zvxy

Analysis of the Regression Equation to Choose a Set of Optimized Forming Parameters The limited values of 4 influential parameters when forming experimental the models to optimize the forming angle are: Vertical Feed ∆z: 0.2 ≤ ∆z ≤ 1 mm Diameter of tool D: 5 ≤ D ≤ 10 mm/min Feeding rate vxy: 800 ≤ vxy ≤ 3000 mm/ph Revolutions of tool n: 400 ≤ n ≤ 800 rpm

The optimal influential parameters for the maximum forming angle α could be performed by software such as Minitab, Microsoft Excel/Solver or even by partial differential. The qualitative influence of these 4 parameters for maximum optimal forming angle are illustrated as in Table 5 Table 5: The qualitative influence of 4 parameters to gain the maximum forming ability of SUS 304.

Optimization of deformed angle α [degree] of SUS 304 for α ⇒ max

∆z [mm] Min D [mm] Min

vxy [mm/min] Min n [rpm] Min


More specifically, we optimize the regression equation of the aforementioned forming angle α in order to gain a specific set of 4 optimal forming parameters along with the maximum value of the forming angle by Microsoft Excel / Solver, a popular software, as shown in the Figure 7:

Figure 7: Results of optimization of forming angles of stainless steel SUS304. The obtained quantitative results from Microsoft Excel/Solver match to the qualitative results as in Table 5. The forming angle can reach to 53.86 degree with a set of forming parameters that are displayed in Table 6 Table 6: Results of the optimal forming angle values with the set of influencing parameters to chose

Maximum optimal forming angle of SUS304: α = 53.86 [degree]

∆z [mm] 0.2 D [mm] 5

vxy [mm/min] 800 n [rpm] 400


However, when application the obtained optimal parameters to form 3 samples of the same specific SUS304 sheet, the biggest average forming angle can only be achieved up to 51,79 degree. This can be explained by the defection of material, uncontrolled random conditions in the experiment, the vibration of the foundation of the workshop via other machines and the differences of ambient and machine temperatures when forming.

Conclusions After optimization of the regression equation of the deformable angle of stainless steel SUS304 to

achieve the optimal set of forming parameters, we can draw conclusions: For stainless steel SUS304, it is necessary to select the minimum values of all the forming

parameters to get maximum angle of deformation. Therefore, the vertical feed ∆z after each cycle, the tool diameter D, the speeding rate of tool vxy and the revolutions of tool or spindle n should be as small as possible. Thus, the productivity of maximum ability of deforming of stainless steel SUS304 will be lowest. In the other hand, forming energy is also low and the longevity of the SPIF machine will be prolonged.

Acknowledgments This work is funded by Petrovietnam University under grand code number GV1913. We highly appreciate the great grant from PVU that contributed to achieve this research.

References [1] Edward Leszak “Apparatus and Process for Incremental Dieless Forming” Patent US3342051, Ser.No. 388.577 10 Claims (Cl. 72- 81)

[2] P.A.F. Martins, N. Bay, M. Skjoedt, M.B. Silva “Theory of single point incremental forming”, CIRP Annals - Manufacturing Technology 57, pp 247–252 (2008)

[3] Stainless Steel Grade 304 Atlas Steels Australia

[4] N. Decultot, V. Velay, L. Robert, G. Bernhart, E. Massoni “Behavior modelling of aluminum alloy sheet for Single Point Incremental Forming”, International Journal of Material Forming1, Supplement 1 (2008) Pages 1151-1154 DOI: 10.1007/s12289-008-0184-z

[5] DOUGLAS C. MONTGOMERY “Design and Analysis of Experiments” Eighth Edition, John Wiley & Sons Inc, ISBN 978-1-118-14692-7, 2013

[6] An Introduction to Stress Analysis, Applications with SolidWorks Simulation, Student Guide. 1995-2010, Dassault System SolidWorks Corporation


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