- Email: [email protected]
Precision cutting of sheets by means of a new shear based on rolling motion
ELSEVIER
Journal of Materials Processing Technology 66 (1997) 232-239
Precision cutting of sheets by means of a new shear rolling motion Masao Murakawa
al*, Uan Lu b
a Nippon Institute of Technology, 4-1 Gakuendai, Miyashiro, Saitama 345, Japan b Amino Corporation,
1132-2
Yodoshi, Fujinomiya, Shizuoka 418, Japan
Received 12 October 1995
Ahstraet
In this paper an improvement is proposed in rolling cut shear which cuts work material using a circular upper blade and a straight lower blade, whereby irregularities found in conventionally sheared products such as bow, twist and camber, can be reduced drastically. In particular, the improvement comprises the inclusion of a straight counter-holding pressurizing bar in conventional rolling cut shear to reduce or eliminate the above-mentioned irregularities, which are unavoidable in a conventional guillotine-type shear, as well as the use of a simplified guide mechanism to ensure a rolling movement of the upper blade along the lower blade. The bar has not been considered for inclusion in conventional rolling cut shears because these shears have been used exclusively for cutting hot slabs of such great thicknesses that irregularities are negligible. The present experimental results, however, show that the bar can effectively eliminate or reduce dramatically the above-mentioned irregularities compared with the guillotine-type shear. Finally, a large prototype rolling cut shear intended for use in actual manufacturing is introduced. 0 1997 Elsevier Science S.A. Keywords: Shear: Rolling motion: Sheet
-
1. Introduction A guillotine-type shear is known to have a pair of straight blades, one of which has a so-called shear angle, the guillotine-type shear usually adopting a shear-angled blade in order to reduce the so-called stationary shearing force [l], where the length of the work material requires extremely great cutting forces. Accordingly, a shear machine with a large shear angle is desired when thicker materials are to be cut. However, a large shear angle generally results in the deterioration of the quality of the products, thus leading to a compromise wheiein the blade angle is made variable so as to enable the use of a smaller shear angle when thinner sheets are to be sheared with the same shear machine. However, even with such technical improvement in conventional guillotine-type shears, it is still impossible to eliminate irregularities such as those shown and
defined in Fig. 1 as (a) bow, (b) twist and (c) camber; these irregularities being known to become worse as the cutting width, B,decreases.
Accordingly, one objective of this study is to manufacture a new shear machine based on a new concept whereby the above-mentioned irregularities can be reduced or eliminated without making the shear structure complicated as compared with guillotine-type shears. Another objective of this study is to investigate the extent of improvement in the precision of sheared products by using i- trial-made new type of rolling cut shear.
(a)
* Corresponding author. 09240136/97/%17.000 1997 Elsevier Science S.A. All rights reserved. PII SO924-0136(96)02529-O
Bow
Fig. 1. Sheared contours comber.
(b) Twist
(c)Camber
with poor precision: (a) bow; (6) twist; (c)
133
y conventional guillotine-type shears are likely to cause poor precision of the sheared products, the conclusion was arrived at that the inclined straight blade of conventional g~~~l~oti~e-ty~eshears woulel continue to push do the already cut product portion, thereby increasing e degree of irregularity. This co elusion led to utilizing a cutting conventional slitters or side trimmer nate the disadvantages of the cutting mode in conventional shears. In particular, the cutting mode in side trimmers, wherein a circular disk cutter is used to shear the material, does not exert the undesirable pushingdown action during shearing. owever, since it is not practical to use a large-diameter cutter so as to yield a sufficiently small (equivalent) shear angle [Z] of about l-3*, similar to that found in conventional precision shears, only an inadequate improvement in shear precision will result when this type of sht;aring arrangement is employed. Thus, an attempt was made to use a rolling cut shear (RCS) [3] which is characterized by a pair consisting of a straight blade and an extremely large-diameter circular blade in place of the pair of circular blades used in the conventional side trimmer. As shown in Fig. 2, the RCS has the following operation principles: a circular-shaped upper blade rolls along a straight lower blade without any slippage between them, thereby achieving a shear action. The RCS is advantageous in that it can reduce dramatically the load exerted with shorter vertical shearing strokes compared with shearing by a pair of a straight and a parallel blade: thus, RCS has been used exclusively to cut extremely thick hot plates, such as 100 mm thick hot slabs, in the field of steel making. However, in order to enable the use of RCS in the sheet metal industry, it is considered essential that the guide mechanism (comprising (1) h(3) in Fig. 2) ensuring a rolling motion be simplified to render RCS cost competitive. Furthermore, a counter-holding pressurizing bar was employed, which was not considered at all for use in the conventional RCS because the latter dealt only with extremely large thicknesses, where the precision of the cut plates is not critical. It should be noted here that this pressurizing bar is extremely simple in structure as compared with the complicated segmented counterholder [4] employed in conventional guillotine-type shears. Fig. 3 shows a prototype RCS machine in which the above-mentioned flat-bar-type counter-holder is included, and the guide that is used to ensure a rolling motion of the upper blade is simplified far more than that used in the conventional RCS for extremely thick
Fig. 7. Structure ofconcentionai rolhng cut shear with a complicated guiding mechanism for the upper R blade [3].
Fig. 3. Structure and qxcitications for a prototype rolling cut shear.
Fig. 4. Definition of the working parameters for the RCS in Fig. 3.
plates, because this RCS machine employs a straight curved guide groove instead of the conventional groove. This RCS machine achieves the rolling motion of a circular-shaped upper blade by a rack and gear mechanism and a pair of cams, as explained below and shown in Fig. 3, instead of a link mechanism. The RCS machine is also characterized by a straight guide, which
234
M. Murakawa, Y. Lu /Journal of Materials Processing Technology 66 (1997) 232-239
Convention;1 ,h& (withcounterholder) onventional shear
Y
I \t Cutting Fig. 5. A comparison
width
B I’ mm
of the precision of sheared contours (A3004, t = 1.2 mm, C = 8%).
has been realized by trial-and-error computation of the particular location of the guide roller (12) which enables the shape of the guide groove (14) to be straight, as shown in Fig. 3. The operation of this new RCS developed by the authors proceeds as follows. The work material or sheet (2) is first subjected to compressive force by a blank holder (l), and then the racks (5) connected with a piston (4) of a hydraulic cylinder (3) cause the movement of cams (7) of curved configuration via gears (6). AE a result, the R blade (11) fixed to the slide (8) is moved by means of upper (9) and lower (10) rollers mounted on the slide (8). During this movement of the R upper blade (11) a pure rolling movement over the lower straight blade (17) is ensured by means of a guide roller (12) fixed to the slide (8) and a straight guide groove (14) fixed to the shear frame (13). It is obvious that the present guide mechanism is simpler than that of the conventional RCS. Although the preferred counter-holding mechanism is hydraulic, a spring-type mechanism can also be used. Fig. 4 shows relevant working parameters for the RCS including the counter-holding pressure bar (15).
3. Investigation of the shear precision of the RCS Here the effects of the new RCS equipped with a spring-type counter-holder on the precision of the sheared products will be demonstrated, by comparing the RCS with conventional guillotine-type shears. As work materials, aluminum sheets (JIS A3004, sheet thickness t = 1.2 mm, tensile strength = 284 N mme2, elongation = 3.2% and hardness = I-IV96) were chosen, which are known to exhibit poor precision when the width of cut (B) (Fig. 4) is small. A constant cutting length I (Fig. 3) of 500 mm was chosen, as were a tool clearance C and a tool overlap L (Fig. 4) of 8% t and 0.8 mm, respectively. A conventional mechanical shear was used for comparison with a shear angle w of about 1.1 degree and a value of C of 8% t. The above-mentioned segment-type counter-holder can be installed optionally in this shear, enabling the performing of experiments with and without the counterholder. It is also noted here that in the case of RCS, an equivalent shear angle uM of about 1.01 degrees is obtained with a value of L of 0.8 mm, since the radius, R, of the RCS circular blade is 12000 mm.
Table 1 Mechanical properties of work materials used in RCS experiment Material
Pure aluminum
Low-carbon steel Stainless steel
JIS symbol
All00 All00 Al 100 All00 SPC su304
Thickness, I (mm)
I 2 3 4 2 2
Mechanical property Tensile strength (N mm-‘)
Elongation (%)
Hardness HV
100 124 95 95 326 672
25 30 24 23.8 51 54
35 45.6 32 30 95.2 178
4fl
60
80
6
sus304
5 Fe
10 P-’
/
15 %
Fig. 6. Effects of RCS counter-holding force F on the precision of products (t = 2 mm. B = IO mm, and C= 15% 1. (In the figure the symbols show the values for conventional shear. The cross symbol (6(c)) in the case of RCS shows that each respective camber value is shown for B = 20 mm instead of i3 = IO mm, since workpieces with B = IO mm render the measurement of camber impossible due to excessive bowing and twisting.)
Fig. 5 presents a comparison of precision in cut products (bow, twist and camber) between the convcntional mechanical guillotine-type shear (with and witkout a counter-holder) and the present RCS (with and without a counter-holder). As shown, RCS can give lower values of bow and twist even without the counter-holder, compared with the mechanical guillotinetype shear with a counter-holder. and almost the same degree of camber. It is evident that RCS with a counter-holder can yield excellent results as compared with guillotine-type shears, with regard to all values of B. Next, detailed experimental results are introduced in order to investigate the effects of the counter-holder in RCS. For this purpose a hydraulic-type counter-holder was employed because it can exert a wider range of counter-holding pressure or force than a spring-type counter-holder. Three kinds of materials were chosen: pure aluminum (Al 100) with thicknesses of 1, 2, 3 and 4 mm; a 2 mm thick carbon steel sheet (SK); and a stainless steel sheet (SUS304). Table 1 shows the mechanical properties of these work materials. B values were chosen to be sma!l (mainly B = 10 mm) so as to make the effects of the counter-holder as clear as possible. A cutting length, I, of 1000 mm was chosen. The values of C between the upper R blade and the
lower linear blade were ckosen to be 8, 10. 15 and 20% I, and L values of 1 mm and 6 mm were chosen. In the case of ‘with counter-holder’. counter-holding force. F. values of 4.9, 9.8, 14.7 and 19.6 kN were chosen with an additional condition of F = 0 kN. For purposes of comparison, experiments using a conventional guillotine-type shear ((1) + 1.Olo, C + 6%) were performed also. Fig. 6 shows product precision vs. F. which is kept constant during shearing. Here camber values for B = IO mm in conventional hydraulic-type shear and RCS are not plotted because work materials with I3 = 10 mm render the measurement of camber impossible due to excessive bowing and twisting. The cross symbol in Fig. 6(c) therefore shows the camber values for B = 20 mm instead of B = 10 mm. As shown in Fig. 6. the general trend is that even a small value of F can reduce the values of bow and twist markedly. For example, in the case of the stainless steel sheet (SUS304), even a value of F ofless than 5% of the shearing load, P, can yield about l/5 of bow and about l/I3 of twist compared with t&se for ,r- 0. it is shown also that further increase in the value of F would bring about only a slight improvement in the reduction of irregularities. For example, in the case of the aluminum
M. Murakawa, Y. Lu / Jotrntal oJ‘Materials Processing Technology 66 (1997) 232-239
236
F= P-’
/
%
t=Zmm
t=3mm
0
11
22
33
44
tJmm
F* P-’
8 0
5
10
15
I
I
20
0
/
%
1 5
10
Counter-hddmg
hurt
15
20
t
1
0
5
llJ
15
20
F / kN
Fig. 7. Effects of RCS counter-holding force F on the precision of sheared products having various thicknesses t (Al 100. C = 15%~. B = IO and L = 1 mm). (The cross symbol shows the values of camber for B = 20 mm instead of B = 10 mm.)
sheet (AllOO), it is shown that the values of bow and twist reach a plateau when F exceeds 4.9 kN (corresponding to 20% of the shearing load, P). Another trend that was observed in Fig. 6, i.e., the trend on how far the product precision will be degraded when L in RCS is increased with the consequent increase of uM so as to reduce the P value, will now be described. As shown in Fig. 6, even when the overlap value is increased from L = 1 mm (o i 1.Ol”) to L = 6 mm (e& + 1.81’), by which P can be decreased by about 44% according to calculation [3], a good level of precision can still be maintained if a relatively large value of F is selected compared with the condition of L = 1 mm and F= 0 (i.e., without counter-holding force). Fig. 7 shows F versus the precision when t is varied. Regardless of t, the values of bow and twist are reduced markedly by a large value of F. Furthermore, in the case of aluminum (AllOO), where the same equivalent shear angle determined by L is applied to different
thicknesses ranging from t = 1 mm to t = 4 mm, it is found that the application of various values of F greater than zero and having the same ratio to P can achieve a greater reduction of bow and twist than when F= 0, and that the reduction becomes more significant as t decreases. In other words, the effect of F on the improvement of product quality decreases as the sheet thickness is increased. An experiment was then performed in which effects of F on the quality of products were investigated when B was varied and the thickness kept constant at t = 2 mm. Additionally, another experiment was performed, for purposes of comparison, to investigate the effects of F on the quality of products using a conventional guillotine-type shear with no counter-holder, with o k 1.01” and C + 6%t, the experimental results being shown in Fig. 8. As seen in this figure, markedly low values of bow and twist can be achieved by using a RCS with a counter-holder compared with a conventional guillotine-type shear (without a counter-holder),
I ‘\
a6 4 2 I '\ a6
Cutting width
B / mm
Fig. 8. Effects of RCS counter-holding force F on the precision of sheared products having various cm widths B (t = 2 mm. C = 15%r, F= 9.8 kN). (Camber values expressed with the cross symbol for conventional guillotine-type shear at 8 = 10 mm (and 20 mm in the case of SUS304) are not plotted due to excessively large bow and twist. rendering measurement impossible.)
even when the RCS equivalent shear angle of wM % 1.8 lo (L = 6 mm), which is greater than the shear angle of w + 1.01” for the conventional shear machine, is used, and materials having a very small cutting width, e.g., of B = 10 mm, are sheared. Fig. 9 shows the relationship between F and the product quality when the blade clearance is varied. It is known that conventional shears will, in general, yield a low value of bow on one hand, and a large value of twist on the other with increasing clearance, C. However, the RCS with a counter-holder reduces the values of both bow and twist when C is increased, whilst no marked change is observed for camber. In other words, by using RCS with a counter-holder, the most appropriate C value that enables all values of bow, twist and camber to be reduced can be chosen, compared with those for conventional shears.
Clearance Fig. 9. EffMs of RCS counter-holding and F = 9.8 kN).
Finally, a prototype RCS manufactured by Amiilo Corporation for practical use is introduced, Fig. 10 showing the structure of the shear, which employs a link mechanism, instead of the cam mechanism in the RCS shown in Fig. 3, to induce a rolling motion of the upper R blade. This is mainly because a cam mechanism cannot be used in the cutting operation of long work materials, which requires a longer blade stroke along the vertical direction. Table 2 shows specifications for the prototype RCS, whilst Fig. 11 presents an external view of the shear. Fig. 12 shows a comparison of cut products obtained by a conventional guillotine-type shear and the prototype RCS machine, demonstrating clearly that RCS can
C /
%t
force F on the precision of products sheared with various clearances C (t = 2 mm, f? = 10 mm. L = 1 mm
M. Murakawa, Y. LII/Journal of Materials Processing Technology 66 (1997) 232-239
238
Fig. 11, External view of the prototype use.
@IBlank holder, cylinder,
@Work material
@Piston,
@Rack,
to be sheared,
@Gear,
@Shaft,
@Hydraulic @Slide,
@Link A, @Link B, @Upper R blade, @Guide roller, @Frame, @Linear groove guide for upper R blade, @Counter-holding
pressrizing
bar, @Cylinder
for counter-
holding pressurizing bar, @Lower linear blade, @Guide for counter-holding pressurizing bar
Fig. 10. Structure of a
prototypeRCS machinefor practicaluse.
significantly reduce twist and/or bow, particularly when the cut width, B, is small.
RCS machine for practical
experimental purposes, whilst the other is of a large size and has prototype features for practical use. These RCSs are characterized by a simplified straight guide mechanism to ensure a pure rolling motion of the upper R blade along the lower linear blade, and a flat-bartype simple counter-holding mechanism; these features being developed to render the RCS suitable for use in the sheet metal industry. Experimental results obtained by the present RCSs have proven that the irregularities involved in cutting or shearing of sheet materials using conventional guillotine-type shears can be reduced drastically.
5. Conclusions
The authors have trial-manufactured two improved rolling cut shears (RCSs): one is of a small size for Table 2 Specifications for prototype RCS machine for practical use 1 2
Slide driving mechanism Hydraulic 2-l cylinder
2-2
system
3-3 2-4
3
Blade
3-l 3-2
4
Maximum 4-l shearing 4-2 ability 4-3 Minimum shearing ability Maximum shearing length Stroke
5 6 7
Two pinion and rack mechanisms, and two linking rods Driving cylinder for upper R blade (1 unit) Holding down cylinder for blank (18 units) Cylinder for counter-holding (IO units) Work material supporting cylinder (1 unit) Upper R blade Lower linear blade IO mm for SPC (mild steel sheet) 6 mm for SU304 (stainless steel sheet) 10 mm for Al 100 (aluminum sheet) 1 mm 4000 mm 15 s.p.m. at a stroke length of 360 mm
Fig. 12. A comparison of sheared stainless steel products having a length of 4000 mm, a thickness of 6 mm and width of: (a) B = 30 mm; (b) B = 80 mm; the upper products in the figure being those from the RCS mackine and the lower products from a conventional guillotinetype shear.
Journal of Materials Processing Technology 66 (1997) 232-239
Precision cutting of sheets by means of a new shear rolling motion Masao Murakawa
al*, Uan Lu b
a Nippon Institute of Technology, 4-1 Gakuendai, Miyashiro, Saitama 345, Japan b Amino Corporation,
1132-2
Yodoshi, Fujinomiya, Shizuoka 418, Japan
Received 12 October 1995
Ahstraet
In this paper an improvement is proposed in rolling cut shear which cuts work material using a circular upper blade and a straight lower blade, whereby irregularities found in conventionally sheared products such as bow, twist and camber, can be reduced drastically. In particular, the improvement comprises the inclusion of a straight counter-holding pressurizing bar in conventional rolling cut shear to reduce or eliminate the above-mentioned irregularities, which are unavoidable in a conventional guillotine-type shear, as well as the use of a simplified guide mechanism to ensure a rolling movement of the upper blade along the lower blade. The bar has not been considered for inclusion in conventional rolling cut shears because these shears have been used exclusively for cutting hot slabs of such great thicknesses that irregularities are negligible. The present experimental results, however, show that the bar can effectively eliminate or reduce dramatically the above-mentioned irregularities compared with the guillotine-type shear. Finally, a large prototype rolling cut shear intended for use in actual manufacturing is introduced. 0 1997 Elsevier Science S.A. Keywords: Shear: Rolling motion: Sheet
-
1. Introduction A guillotine-type shear is known to have a pair of straight blades, one of which has a so-called shear angle, the guillotine-type shear usually adopting a shear-angled blade in order to reduce the so-called stationary shearing force [l], where the length of the work material requires extremely great cutting forces. Accordingly, a shear machine with a large shear angle is desired when thicker materials are to be cut. However, a large shear angle generally results in the deterioration of the quality of the products, thus leading to a compromise wheiein the blade angle is made variable so as to enable the use of a smaller shear angle when thinner sheets are to be sheared with the same shear machine. However, even with such technical improvement in conventional guillotine-type shears, it is still impossible to eliminate irregularities such as those shown and
defined in Fig. 1 as (a) bow, (b) twist and (c) camber; these irregularities being known to become worse as the cutting width, B,decreases.
Accordingly, one objective of this study is to manufacture a new shear machine based on a new concept whereby the above-mentioned irregularities can be reduced or eliminated without making the shear structure complicated as compared with guillotine-type shears. Another objective of this study is to investigate the extent of improvement in the precision of sheared products by using i- trial-made new type of rolling cut shear.
(a)
* Corresponding author. 09240136/97/%17.000 1997 Elsevier Science S.A. All rights reserved. PII SO924-0136(96)02529-O
Bow
Fig. 1. Sheared contours comber.
(b) Twist
(c)Camber
with poor precision: (a) bow; (6) twist; (c)
133
y conventional guillotine-type shears are likely to cause poor precision of the sheared products, the conclusion was arrived at that the inclined straight blade of conventional g~~~l~oti~e-ty~eshears woulel continue to push do the already cut product portion, thereby increasing e degree of irregularity. This co elusion led to utilizing a cutting conventional slitters or side trimmer nate the disadvantages of the cutting mode in conventional shears. In particular, the cutting mode in side trimmers, wherein a circular disk cutter is used to shear the material, does not exert the undesirable pushingdown action during shearing. owever, since it is not practical to use a large-diameter cutter so as to yield a sufficiently small (equivalent) shear angle [Z] of about l-3*, similar to that found in conventional precision shears, only an inadequate improvement in shear precision will result when this type of sht;aring arrangement is employed. Thus, an attempt was made to use a rolling cut shear (RCS) [3] which is characterized by a pair consisting of a straight blade and an extremely large-diameter circular blade in place of the pair of circular blades used in the conventional side trimmer. As shown in Fig. 2, the RCS has the following operation principles: a circular-shaped upper blade rolls along a straight lower blade without any slippage between them, thereby achieving a shear action. The RCS is advantageous in that it can reduce dramatically the load exerted with shorter vertical shearing strokes compared with shearing by a pair of a straight and a parallel blade: thus, RCS has been used exclusively to cut extremely thick hot plates, such as 100 mm thick hot slabs, in the field of steel making. However, in order to enable the use of RCS in the sheet metal industry, it is considered essential that the guide mechanism (comprising (1) h(3) in Fig. 2) ensuring a rolling motion be simplified to render RCS cost competitive. Furthermore, a counter-holding pressurizing bar was employed, which was not considered at all for use in the conventional RCS because the latter dealt only with extremely large thicknesses, where the precision of the cut plates is not critical. It should be noted here that this pressurizing bar is extremely simple in structure as compared with the complicated segmented counterholder [4] employed in conventional guillotine-type shears. Fig. 3 shows a prototype RCS machine in which the above-mentioned flat-bar-type counter-holder is included, and the guide that is used to ensure a rolling motion of the upper blade is simplified far more than that used in the conventional RCS for extremely thick
Fig. 7. Structure ofconcentionai rolhng cut shear with a complicated guiding mechanism for the upper R blade [3].
Fig. 3. Structure and qxcitications for a prototype rolling cut shear.
Fig. 4. Definition of the working parameters for the RCS in Fig. 3.
plates, because this RCS machine employs a straight curved guide groove instead of the conventional groove. This RCS machine achieves the rolling motion of a circular-shaped upper blade by a rack and gear mechanism and a pair of cams, as explained below and shown in Fig. 3, instead of a link mechanism. The RCS machine is also characterized by a straight guide, which
234
M. Murakawa, Y. Lu /Journal of Materials Processing Technology 66 (1997) 232-239
Convention;1 ,h& (withcounterholder) onventional shear
Y
I \t Cutting Fig. 5. A comparison
width
B I’ mm
of the precision of sheared contours (A3004, t = 1.2 mm, C = 8%).
has been realized by trial-and-error computation of the particular location of the guide roller (12) which enables the shape of the guide groove (14) to be straight, as shown in Fig. 3. The operation of this new RCS developed by the authors proceeds as follows. The work material or sheet (2) is first subjected to compressive force by a blank holder (l), and then the racks (5) connected with a piston (4) of a hydraulic cylinder (3) cause the movement of cams (7) of curved configuration via gears (6). AE a result, the R blade (11) fixed to the slide (8) is moved by means of upper (9) and lower (10) rollers mounted on the slide (8). During this movement of the R upper blade (11) a pure rolling movement over the lower straight blade (17) is ensured by means of a guide roller (12) fixed to the slide (8) and a straight guide groove (14) fixed to the shear frame (13). It is obvious that the present guide mechanism is simpler than that of the conventional RCS. Although the preferred counter-holding mechanism is hydraulic, a spring-type mechanism can also be used. Fig. 4 shows relevant working parameters for the RCS including the counter-holding pressure bar (15).
3. Investigation of the shear precision of the RCS Here the effects of the new RCS equipped with a spring-type counter-holder on the precision of the sheared products will be demonstrated, by comparing the RCS with conventional guillotine-type shears. As work materials, aluminum sheets (JIS A3004, sheet thickness t = 1.2 mm, tensile strength = 284 N mme2, elongation = 3.2% and hardness = I-IV96) were chosen, which are known to exhibit poor precision when the width of cut (B) (Fig. 4) is small. A constant cutting length I (Fig. 3) of 500 mm was chosen, as were a tool clearance C and a tool overlap L (Fig. 4) of 8% t and 0.8 mm, respectively. A conventional mechanical shear was used for comparison with a shear angle w of about 1.1 degree and a value of C of 8% t. The above-mentioned segment-type counter-holder can be installed optionally in this shear, enabling the performing of experiments with and without the counterholder. It is also noted here that in the case of RCS, an equivalent shear angle uM of about 1.01 degrees is obtained with a value of L of 0.8 mm, since the radius, R, of the RCS circular blade is 12000 mm.
Table 1 Mechanical properties of work materials used in RCS experiment Material
Pure aluminum
Low-carbon steel Stainless steel
JIS symbol
All00 All00 Al 100 All00 SPC su304
Thickness, I (mm)
I 2 3 4 2 2
Mechanical property Tensile strength (N mm-‘)
Elongation (%)
Hardness HV
100 124 95 95 326 672
25 30 24 23.8 51 54
35 45.6 32 30 95.2 178
4fl
60
80
6
sus304
5 Fe
10 P-’
/
15 %
Fig. 6. Effects of RCS counter-holding force F on the precision of products (t = 2 mm. B = IO mm, and C= 15% 1. (In the figure the symbols show the values for conventional shear. The cross symbol (6(c)) in the case of RCS shows that each respective camber value is shown for B = 20 mm instead of i3 = IO mm, since workpieces with B = IO mm render the measurement of camber impossible due to excessive bowing and twisting.)
Fig. 5 presents a comparison of precision in cut products (bow, twist and camber) between the convcntional mechanical guillotine-type shear (with and witkout a counter-holder) and the present RCS (with and without a counter-holder). As shown, RCS can give lower values of bow and twist even without the counter-holder, compared with the mechanical guillotinetype shear with a counter-holder. and almost the same degree of camber. It is evident that RCS with a counter-holder can yield excellent results as compared with guillotine-type shears, with regard to all values of B. Next, detailed experimental results are introduced in order to investigate the effects of the counter-holder in RCS. For this purpose a hydraulic-type counter-holder was employed because it can exert a wider range of counter-holding pressure or force than a spring-type counter-holder. Three kinds of materials were chosen: pure aluminum (Al 100) with thicknesses of 1, 2, 3 and 4 mm; a 2 mm thick carbon steel sheet (SK); and a stainless steel sheet (SUS304). Table 1 shows the mechanical properties of these work materials. B values were chosen to be sma!l (mainly B = 10 mm) so as to make the effects of the counter-holder as clear as possible. A cutting length, I, of 1000 mm was chosen. The values of C between the upper R blade and the
lower linear blade were ckosen to be 8, 10. 15 and 20% I, and L values of 1 mm and 6 mm were chosen. In the case of ‘with counter-holder’. counter-holding force. F. values of 4.9, 9.8, 14.7 and 19.6 kN were chosen with an additional condition of F = 0 kN. For purposes of comparison, experiments using a conventional guillotine-type shear ((1) + 1.Olo, C + 6%) were performed also. Fig. 6 shows product precision vs. F. which is kept constant during shearing. Here camber values for B = IO mm in conventional hydraulic-type shear and RCS are not plotted because work materials with I3 = 10 mm render the measurement of camber impossible due to excessive bowing and twisting. The cross symbol in Fig. 6(c) therefore shows the camber values for B = 20 mm instead of B = 10 mm. As shown in Fig. 6. the general trend is that even a small value of F can reduce the values of bow and twist markedly. For example, in the case of the stainless steel sheet (SUS304), even a value of F ofless than 5% of the shearing load, P, can yield about l/5 of bow and about l/I3 of twist compared with t&se for ,r- 0. it is shown also that further increase in the value of F would bring about only a slight improvement in the reduction of irregularities. For example, in the case of the aluminum
M. Murakawa, Y. Lu / Jotrntal oJ‘Materials Processing Technology 66 (1997) 232-239
236
F= P-’
/
%
t=Zmm
t=3mm
0
11
22
33
44
tJmm
F* P-’
8 0
5
10
15
I
I
20
0
/
%
1 5
10
Counter-hddmg
hurt
15
20
t
1
0
5
llJ
15
20
F / kN
Fig. 7. Effects of RCS counter-holding force F on the precision of sheared products having various thicknesses t (Al 100. C = 15%~. B = IO and L = 1 mm). (The cross symbol shows the values of camber for B = 20 mm instead of B = 10 mm.)
sheet (AllOO), it is shown that the values of bow and twist reach a plateau when F exceeds 4.9 kN (corresponding to 20% of the shearing load, P). Another trend that was observed in Fig. 6, i.e., the trend on how far the product precision will be degraded when L in RCS is increased with the consequent increase of uM so as to reduce the P value, will now be described. As shown in Fig. 6, even when the overlap value is increased from L = 1 mm (o i 1.Ol”) to L = 6 mm (e& + 1.81’), by which P can be decreased by about 44% according to calculation [3], a good level of precision can still be maintained if a relatively large value of F is selected compared with the condition of L = 1 mm and F= 0 (i.e., without counter-holding force). Fig. 7 shows F versus the precision when t is varied. Regardless of t, the values of bow and twist are reduced markedly by a large value of F. Furthermore, in the case of aluminum (AllOO), where the same equivalent shear angle determined by L is applied to different
thicknesses ranging from t = 1 mm to t = 4 mm, it is found that the application of various values of F greater than zero and having the same ratio to P can achieve a greater reduction of bow and twist than when F= 0, and that the reduction becomes more significant as t decreases. In other words, the effect of F on the improvement of product quality decreases as the sheet thickness is increased. An experiment was then performed in which effects of F on the quality of products were investigated when B was varied and the thickness kept constant at t = 2 mm. Additionally, another experiment was performed, for purposes of comparison, to investigate the effects of F on the quality of products using a conventional guillotine-type shear with no counter-holder, with o k 1.01” and C + 6%t, the experimental results being shown in Fig. 8. As seen in this figure, markedly low values of bow and twist can be achieved by using a RCS with a counter-holder compared with a conventional guillotine-type shear (without a counter-holder),
I ‘\
a6 4 2 I '\ a6
Cutting width
B / mm
Fig. 8. Effects of RCS counter-holding force F on the precision of sheared products having various cm widths B (t = 2 mm. C = 15%r, F= 9.8 kN). (Camber values expressed with the cross symbol for conventional guillotine-type shear at 8 = 10 mm (and 20 mm in the case of SUS304) are not plotted due to excessively large bow and twist. rendering measurement impossible.)
even when the RCS equivalent shear angle of wM % 1.8 lo (L = 6 mm), which is greater than the shear angle of w + 1.01” for the conventional shear machine, is used, and materials having a very small cutting width, e.g., of B = 10 mm, are sheared. Fig. 9 shows the relationship between F and the product quality when the blade clearance is varied. It is known that conventional shears will, in general, yield a low value of bow on one hand, and a large value of twist on the other with increasing clearance, C. However, the RCS with a counter-holder reduces the values of both bow and twist when C is increased, whilst no marked change is observed for camber. In other words, by using RCS with a counter-holder, the most appropriate C value that enables all values of bow, twist and camber to be reduced can be chosen, compared with those for conventional shears.
Clearance Fig. 9. EffMs of RCS counter-holding and F = 9.8 kN).
Finally, a prototype RCS manufactured by Amiilo Corporation for practical use is introduced, Fig. 10 showing the structure of the shear, which employs a link mechanism, instead of the cam mechanism in the RCS shown in Fig. 3, to induce a rolling motion of the upper R blade. This is mainly because a cam mechanism cannot be used in the cutting operation of long work materials, which requires a longer blade stroke along the vertical direction. Table 2 shows specifications for the prototype RCS, whilst Fig. 11 presents an external view of the shear. Fig. 12 shows a comparison of cut products obtained by a conventional guillotine-type shear and the prototype RCS machine, demonstrating clearly that RCS can
C /
%t
force F on the precision of products sheared with various clearances C (t = 2 mm, f? = 10 mm. L = 1 mm
M. Murakawa, Y. LII/Journal of Materials Processing Technology 66 (1997) 232-239
238
Fig. 11, External view of the prototype use.
@IBlank holder, cylinder,
@Work material
@Piston,
@Rack,
to be sheared,
@Gear,
@Shaft,
@Hydraulic @Slide,
@Link A, @Link B, @Upper R blade, @Guide roller, @Frame, @Linear groove guide for upper R blade, @Counter-holding
pressrizing
bar, @Cylinder
for counter-
holding pressurizing bar, @Lower linear blade, @Guide for counter-holding pressurizing bar
Fig. 10. Structure of a
prototypeRCS machinefor practicaluse.
significantly reduce twist and/or bow, particularly when the cut width, B, is small.
RCS machine for practical
experimental purposes, whilst the other is of a large size and has prototype features for practical use. These RCSs are characterized by a simplified straight guide mechanism to ensure a pure rolling motion of the upper R blade along the lower linear blade, and a flat-bartype simple counter-holding mechanism; these features being developed to render the RCS suitable for use in the sheet metal industry. Experimental results obtained by the present RCSs have proven that the irregularities involved in cutting or shearing of sheet materials using conventional guillotine-type shears can be reduced drastically.
5. Conclusions
The authors have trial-manufactured two improved rolling cut shears (RCSs): one is of a small size for Table 2 Specifications for prototype RCS machine for practical use 1 2
Slide driving mechanism Hydraulic 2-l cylinder
2-2
system
3-3 2-4
3
Blade
3-l 3-2
4
Maximum 4-l shearing 4-2 ability 4-3 Minimum shearing ability Maximum shearing length Stroke
5 6 7
Two pinion and rack mechanisms, and two linking rods Driving cylinder for upper R blade (1 unit) Holding down cylinder for blank (18 units) Cylinder for counter-holding (IO units) Work material supporting cylinder (1 unit) Upper R blade Lower linear blade IO mm for SPC (mild steel sheet) 6 mm for SU304 (stainless steel sheet) 10 mm for Al 100 (aluminum sheet) 1 mm 4000 mm 15 s.p.m. at a stroke length of 360 mm
Fig. 12. A comparison of sheared stainless steel products having a length of 4000 mm, a thickness of 6 mm and width of: (a) B = 30 mm; (b) B = 80 mm; the upper products in the figure being those from the RCS mackine and the lower products from a conventional guillotinetype shear.