ASPECTS OF STAMPING PARALLELEPIPED PARTS WITH

The 6th edition of the
Interdisciplinarity in Engineering International Conference
“Petru Maior” University of Tîrgu Mureş, Romania, 2012 ASPECTS OF STAMPING PARALLELEPIPED PARTS WITH
BIG RADIUSES IN ONE OPERATION
Liviu POP #1, Teodor SOCACIU #2
#Departament of Industrial and Managerial Engineering, “Petru Maior” University of Târgu Mureş,
No.1 N. Iorga St., Tg. Mureş, Romania
1liviu.pop@ing.upm.ro
2teodor.socaciu@ing.upm.ro
ABSTRACT
The pressing of parallelepiped parts represents a complex process of cold plastic
deformation. The internal tension and deformation of the material along the part contour
is uneven, showing big differences from one area to another. The unevenness of
deformations depends of the height of the part and of the radiuses at the corners.The
parallelepiped parts that can be stamped with one operation have the ratio between
height and width smaller than 0.5, parts that are considered short. The present paper
studies the optimal shape and dimensions of the semi-finished part for stamping the
parallelepiped parts that are short with big corner radiuses, so that after the pressing the
height of the walls will be uniform and eliminate the later trimming operations.
Keywords: stamping, parallelepiped parts, big corner radiuses, unevenness of
deformations, optimizing shape
1.Introduction
Determining the shape and dimensions of the
semi-finished parts is realized according to the law of
constant volume. When the pressing is done without
the intentional thinning of the parts wall, the changes
of the thickness are neglected, and the dimensions of
the semi-finished parts result from it's surface that is
equal to the surface of the finished part [8], [9], [10].
If the shape and dimensions of the semi-finished parts
are not properly established, the side walls will result
with uneven height (fig. 1) and will require an extra
cutting operation.
Determining the shape and dimensions of the
plane parts necessary for obtaining the parallelepiped
parts is done with the assumption that in the corner
areas, a pressing process takes place, and in the plane
wall areas the deforming process is similar to a
bending process.[2], [3], [5], [7].
The bigger the relative height of the parts is, the
flowing of the material will be more intense from the
corner areas to the plane wall areas.
That is why, when determining the shape and
dimensions of the semi-finished parts, the distinction
has to be made, between the pressing of the short
parts (5,0
b
h
), which can be realized in the majority
of cases with one single operation, the pressing of the
middle-height parts (7,0
...
5,0
b
h
=) and the tall ones
(7,0
b
h
〉),which are
realized with several operations
[4], [6].
Fig1. – Stamping part with side walls that have an
uneven height
The present paper wants to optimize the shape and
dimensions of the semi-finished parts for pressing the
short parallelepiped parts with big corner radiuses
(domain II, fig. 2), in which case the shape and
dimensions of the plane parts can be determined
e xactly, so that after the pressing, cutting o
f the edges will no longer be necessar. [4], [11].
For simplifying, the bottom radius r will be considered equal to the corner radius r c .
Fig. 2 - The domain of short parts with relatively
big corner radiuses resulted from a single
operation
In this case, the shape and dimensions of the semi-finished parts are determined by the present graph, with the equality of the areas method [4], [6].
When pressing with a single operation of the short
semi-finished parts with relatively big (b
r
c ) radiuses,
the flow of the material from the corner area to the plane walls area is sensitive, with the length of the edges increasing, this resulting in the shortening of the part's height in the corner area. In this case, determining the configuration of the plane semi-finished parts is done this way (fig. 3):
• the total length of the side walls is determined "l", as in the case of the bending, using the equation:
g
215,0r 57,0h l −+= (1)
and parallel lines are drawn for the part's edges at the distance of "l";
• the R radius is calculated, as in the case of pressing the cylindrical part with the diameter of 2 rc and the height h, formed by the four corners of the parallelepiped part, using the equation:
,
g 5,0)r h (g h r 2R 2c c −
−+=
(2)
Fig. 3 - Establishing the contour of the semi-finished parts for the pressing of short parts with
relatively small corner radiuses
• a contour is drawn in steps from the corners to the plane side walls;
• a bigger radius is determined at the corers R1 = x R, for compensating the flown material from the corner to the side walls area. The coefficient x is determined with the equation:
;
982,0g
r 2R
(074,0x 2c ++= (3)
• the width of the strips ha and hb determined, and these are substracted from the side areas, staright and unfolded, beeing compensated by the material that is flowing from the corner areas during the pressing. Dimensions ha and hb are determined by making equal the area of the material added at the corners of the plane part with thee area of the material that has been substracted from the straight edges zone. For this purpose, the following equations are used:
)
g r (2a R y
h c 2
a +−= (4)
)
g r (2b R y
h c 2
b +−= (5)
The y coefficient has values shown in Table 1.
Table 1. Values of “y” coefficient
•the unfolded contour is corrected, by increasing the radius R to R1 and decreasing the
dimensions l with ha and hb resulting:
L a = l-h a and L b = l-h b; (6)
•with the resulted values for the length, width and radius of the unfolded part, a contour is
drawn with the arcs Ra and Rb tangents to the
straight side walls and to the arc with the R1
radius.
This method of determining the shape and dimensions of the semi-finished parts applies to the parallelepiped parts with the relative dimensions a/b=1,5…2 and for parts that have an square shape in the transversal section, with long edges.
2.Optimization calculations
A study has been made of a parallelepiped part with the height of h=80mm, width of b=200mm.The length a=300mm, thickness g=2mm and the round radius varying between r c= 40…65mm. With these values, the part is accordingly to figure 2, in the category of short parts with relative big corner radiuses, that result from a single operation.
The unevenness of the flow is bigger as the difference between the unfolded lengths L a& L b increases (fig. 3), between the plane walls and the R1 (fig. 3). Because of this, the way that the values L a, L b and R1 varies according to the corner radius r c of the part.
In Fig. 4 the variation of the lengths L a, L b and radius R1 can be observed accordingly to the bottom radius of the part.
It can be clearly observed that the corner radius influences significantly difference between the length L a, L b and the radius of the plane semi-finished part R1.The smaller the corner radius is, the bigger the difference between l and R is, meaning that the deformation in the pressing process is more uneven.
Because of this, when designing the short parts with relatively big corner radiuses, resulted from only one operation, it is recommended to choose the relative corner radius r c/b at the upper limit of the domain II from Fig. 2.
Fig. 4 - The variation of La, Lb şi R1 parameters accordingly to the bottom radius rc
3.Experimental results
The experimental check of the theoretical considerations has been made with the stamping die from Fig. 5.
Fig. 5- Stamping die for pressing parallelepiped
parts
The semi-finished parts that have been used have the shape obtained with the equations 1…6, but also the semi-finished parts with simpler shapes, like the oval one. It has been notices that any other shape, even similar to the one obtained by the equations 1…6, will result in the unevenness of the pressed part's walls. If the radius R is bigger than the one calculated, the corners of the part will be taller than
t he side walls (fig. 6.a), and if R is smaller, the resulted corners will be shorter (fig. 6.b)
Fig. 6 - Different shapes of the semi-finished part and the resulted pressed parts
4.Conclusions
After the theoretical and experimental research the following conclusions result:
•the difference between La-Lb increases with the increase of rc but it does not influence the
pressing process and the evenness of the walls
height;
•La, Lb and R1 increases with rc, in order to obtain the same height of the walls;
•the corner radius rc influences significantly the difference between the length of the edges La,
Lb and the radius of the plane semi-finished
part R1. The bigger the corner radius, the the
smaller the difference between R1 and La,, Lb
is, meaning that the resulting walls have a more
uniform height;
•when designing short parts with relatively big corner radiuses, realized from a single
operation, it is recommended to choose the
relative corner radius rc/b at the upper limit of
the domain II from figure 2;
•at the taller pressed parts, because of the anisotropy of the material and the imprecision
of the semi-finished parts positioning, the side
walls do not have an uniform height. If a higher
precision is required, the edge of the part will
be cut, and in this case the dimensions of the
semi-finished part will have to be determined
accordingly also to the necessary material to be
cut.
References
[1]Billigman-Feldman (1977), Modeling and
buckling, Technical Publishing, Budapest, Hungary.
[2]Chen F. K. and Liu J. H., (1995), Analysis of die
designs for the stamping of an automobile rear floor panel, Journal of Materials Processing Technology, vol. 55, pp. 408-416.
[3]Chen W., Liu Z.J., Hou B., Du R.X., (2007),
Study on multi-stage sheet metal forming for automobile structure-pieces, Journal of Materials Processing Technology, vol. 187–188, pp. 113-117.
[4]Ciocârdia, C., et al., (1991), Cold pressing
technology, published by E.D.P, Bucharest, Romania.
[5]Firat M., Livatyali H., Cicek O., Onhon M. F.,
(2009), Improving the accuracy of contact-type drawbead elements in panel stamping analysis, Materials & Design, vol. 30, pp. 4003-4011. [6]Iliescu, C., (1984), Cold pressing technology,
published by E.D.P, Bucharest, Romania.
[7]Levy B.S., Van Tyne C.J., (2009), Predicting
breakage on a die radius with a straight bend axis during sheet forming, Journal of Materials Processing Technology, vol. 209, pp. 2038-
2046.
[8]Romanovski, V.P. (1970), Stamping and cold
stamping,Technical Publishing, Bucharest, Romania.
[9]Rosinger, S., (1987), Processes and cold
forming tool, published by Facla, Timişoara, Romania.
[10]Teodorescu, M., et al., (1987), Processed by
cold deformation, Technical Publishing, Bucharest, Romania.
[11]Teodorescu, M., et al., (1988), Processed by
cold deformation. Processing technologies and equipment design by plastic deformation, Technical Publishing, Bucharest, Romania.。