Proceedings of the 5th International Conference on Integrity-Reliability-Failure, Porto/Portugal 24-28 July 2016

Editors J.F. Silva Gomes and S.A. Meguid

Publ. INEGI/FEUP (2016)

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PAPER REF: 6288

TOOLS EVALUATION FOR A MAXIMUM ANGLE CHARACTERIZA-

TION ON A SINGLE POINT INCREMENTAL STAMPING WITH

ALUMINUM 1100 ALLOY

Daniel de Castro Maciel1, Gilmar Cordeiro da Silva

1(*), Juan Marcos Santos Dutra

1,

Diego Raimundi Corradi1, Norberto Martins

1, Daniel Januário Cordeiro Gomes

2 1Polytechnic Institute of PUC-Minas (IPUC), Pontifical Catholic University of Minas Gerais,

Belo Horizonte, Brazil 2University Center Una, Belo Horizonte, Brazil

(*)Email: gilmarcordeiro@pucminas.br

ABSTRACT

The rising demand on market for personalized pieces production and for low cost production

has made incremental stamping a studying target. This present work explores the single point

incremental stamping process. Two tools were built, one with independent rotating spherical

point applied to a support base, and the other with a spherical point machined directly on a

support base. Both have 12 mm diameter. Results show a last breaking angle variation,

demonstrating that the tool contact on a metal blank has an influence on the stamping

maximum angle formation. The first pieces were stamped without lubrication, and the later

ones used Vaseline based lubrication. Thus a better mechanism attendance on a stamping

process deformation, evaluating a maximum angle with both used tools.

Keywords: Aluminium, incremental stamping, rotating tool, maximum angle.

INTRODUCTION

According to Maciel (2015), fabrication and projects sectors look constantly for productive

and economically viable fabrication processes. Low production of prototypes and pieces are,

in most of the cases, expensive due to the tooling used. A viable solution, with excellent

forming limits for low production scale products and/or of complex geometries, is

incremental stamping (IS).

Jeswiet (2001) highlighted that this process has been used to conform metal sheets on

complex shapes with no die use, having the assistance of a single point tool mounted on a

machining base, with a purpose of deforming plastically the material through the tool

movement, and/or of the tool on the vertical plane. This process is well accepted when is

required a low scale production and a high level of geometrical complex.

According to Patricio (2011), recently, incremental stamping theoretical fundaments have

begun to be an attention target to scientific community, once during the first decade of the

XXI century, the obtained knowledge about this process were basically the ones

experimentally reached. On the present work, from an aluminum sheet with 1.0 mm of initial

thickness, were taken six pieces, three lubricated and three without lubrication. On these

experiments, a 1500 mm/min of forward speed, a forward increment on the Z axis of 0.10

mm/rotation, and a free tool rotation have been used.

Topic_B: Experimental Mechanics

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INCREMENTAL STAMPING PROCESS PRESENTATION

According to Jeswiet (2001), mentioned by Patrício (2011), the process is manly used on

metallic materials stamping without complex dies use, but instead of that is used a single

point metallic tool, constructed on a machining centre or a specific equipment. Aiming to

obtain deformation through piece movement and/or through main tool movement on vertical

plane. Three of the main variables that can be changed due to control on CNC equipment are:

ω (rotation) [RPM], V (velocity) [� ���⁄ ], and I (vertical increment) [mm]. Figure 1

illustrate these variables.

Fig. 1 - Basic elements of incremental sheet forming (AISF). Adapted by J. Jeswiet (2005).

LUBRICATION

Lubricants are every or any liquid or solid material of low shearing resistance, whose function

is to maintain separated the tool surfaces (puncture and matrix) of the conforming materials,

reducing friction.

Dieter (1996), affirm that lubricants reduce friction by introduction of well shearing

interfaces.

Keeler (2001) defines a lubricant barrier as a film capable of completely matrix metal sheet

surface isolation, as showed on Figure 2. Forming this coat efficiently, some properties should

be considered.

Fig. 2 - Scheme of lubricant barrier isolating the surface of the tool surface sheet metal Keeler, (2001).

Under dry conditions, no lubricant is used in the interface, and only oxide coats are present in

matrix and in raw material. In this case, friction is high, desired situation in only few

conforming operations.

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EXPERIMENTAL TESTS

The initial project consists on determining the best possible sequence to obtain both tools.

Parting from the first draws collection (sketches), the best rotating point fixation mode and its

contact region with fixed shaft were defined, as showed on Figure 3a). Then, thermal

treatments was done, such as quenching and tempering in both tools with 12 mm diameter.

These procedures were made at the Catholic Pontifical University of Minas Gerais

Mechanical Construction Materials Laboratory, Contagem Campus, Brazil.

a) Rotating Point Tool b) Rigid Point Tool

Fig. 3 - Scheme of the used Tools

According to Lopes (2013), the procedure to describe the maximum wall angle in a single

pass has to use a frustum cone geometry, designed on a software, because this geometry

passes through minimum and maximum angles (0° and 90°). The used speed is approximately

of 1500 mm/min, vertical increment of 0.1 mm, with and without Vaseline base lubricant.

Three pieces was done by each cited interface, and the measurement equipment used will be a

Mitutoyo brand, QM-messure 353 model, for measuring a piece breaking point depth,

according to Figure 4.

Fig. 4 - Measurement Equipment

Topic_B: Experimental Mechanics

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After the measurement of the depth which the failure occurred, the support of the CAD used

to design de piece was used carried out a cut by a symmetrical plan, as Figure 5 illustrates.

Thus, the maximum angle for this example was 76.27 °

Fig. 5 - Measurement Equipment

The blank sheet holder, the deforming tool and the aluminium sheet can be noticed on Figure

6.

Fig. 6 - Blank Holder Support

This testing process has been divided by two: one using rigid tool and other using a rotating

tool. Both with the same speed parameter (1500 mm/min), increment (0.1 mm), incremental

strategy, frustum cone geometry and 12 mm diameter.. Figure 7 is a rigid tool flowchart.

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Fig. 7 - Rigid Tool Experimental Procedures

Figure 8 illustrate the rotating tool flowchart, using same entrance rigid tool parameters.

Fig. 8 - Rotating Point Experimental Procedures

Incremental stamping has been executed by the machining centre CNC ROMI Discovery 560,

with numerical command Siemens Sinumerik 810D. The machine has a potency of 12,5 CV,

in a rotating range value varying from 10 to 10000 rpm. The table working speed (forward)

adopted was 1500 mm/min and without tool rotating speed. These values are in a process’s

using range, data widely used on literature about this topic. The vertical increment was fixed

as 0.1 mm/pass, and a conforming strategy was incremental circular.

Topic_B: Experimental Mechanics

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RESULTS

Notice in Figure 9 the external and internal stamped pieces surfaces using rigid point, on

which the surface that had no lubricant during process present an external surface with a

defect called as “orange peel”.

(a) Inner region without lubrication

(b) External region without lubrication

(c) Inner region with vaseline lubrication (d) External region with vaseline lubrication

Fig. 9 - Rigid Tool Cone Core

In Figure 10 are shown stamped pieces using rotating tools, internal and external regions. On

which external regions are similar between those with and without lubrication.

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(a) Inner region without lubrication

(b) External region without lubrication

(c) Inner region with vaseline lubrication

(d) External region with vaseline lubrication

Fig. 10 - Rotating Tool Cone Core

Tables 1 and 2 present data information collected by the rigid tool.

Table 1 - Rigid Tool with Vaseline Base Lubricant

Experiment Breaking Depth [mm] Maximum Angle [º]

1 39.9558 78.4113

2 37.3434 75.3371

3 38.9350 77.2146

Average: 76.9877

Standard Deviation: 1.5496

Table 2 - RigidTool without Lubrication

Experiment Breaking Depth [mm] Maximum Angle [º]

4 23.3262 57.7553

5 24.3210 59.0974

6 22.5577 56.7100

Average: 57.85423

Standard Deviation: 1.196771

Tables 3 and 4 present data information collected by rotating point tool.

Table 3 - Rotating Point Tool with Vaseline Base Lubricant

Experiment Breaking Depth [mm] Maximum Angle [º]

7 37.6286 75.6746

8 37.1968 75.1634

9 37.4529 75.4667

Average: 75.4349

Standard Deviation: 0.257079

Topic_B: Experimental Mechanics

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Table 4 - Rotating Point Tool without Lubrication

Experiment Breaking Depth [mm] Maximum Angle [º]

10 34.2869 72.0957

11 34.8511 72.3634

12 33.3115 70.5022

Average: 71.65377

Standard Deviation: 1.006228

CONCLUSION

Through measurements has been possible to prove that tool point and lubricant, in contact to

piece, are directly related to the stamped piece maximum wall angle. The rotating point tool

showed a better superficial finish in piece’s stamping process, and a smaller standard

deviation value (independent if using or not lubrication), showing a more homogeneous

surface. A larger standard deviation value showed up when using rigid point tool, but a larger

limit angle when in use of lubricant, in other hand, it had the worst value of limit angle when

doing without any lubricant. May be concluded that a rotating to rigid point variation, and

vice-versa, influence the limit angle. Once the rigid point, compared to the rotating one, both

without lubrication, divergent results have pop up. When comparing the use or not of

lubrication, is observed on rigid tool that different values were found, thus lubricants

influence on limit angle stipulation.

ACKNOWLEDGMENTS

The authors express their acknowledgments to PUC-MINAS, CNPq and FAPEMIG.

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