Deformation by V-bending of Thick Plate Metal 5083

Transcription

1 Proceedings o the 12th International Conerence on Aluminium Alloys, September 5-9, 21, Yokohama, Japan 21 The Japan Institute o Light etals pp Deormation by V-bending o Thick Plate etal 583 Naranbaatar Khamt 1, akoto urata 1, Takashi Kuboki 1, Takahiro Shibata 2 and Yingjun Jin 2, 1 The University o Electro-Communications, Chougaoka, Chou city, Tokyo , Japan 2 AADA Co.,Ltd, 2 Ishida, Isehara city, Kanagawa , Japan This study has been perormed to investigate mechanism in V-bending process in thick plate metal. Purpose o this research is to ind out dierence o mechanism between thick and thin plate metals. As usual V bending process like bottoming and coining uses V type die. In these cases, plate will pressed up between punch and die, so it will bear many complicated eects. Accordingly, this search used U type die to conirm undamental eects o bent plate. For that, this research conducts a series o experiments in V-bending process by changing die-open width. As a result, it is quantitatively clariied that the die width has some amount o eect on the unique phenomena in thick-plate bending such as saddle type deormation, reduction o bending curvature rom the punch radius, and the deduction discrepancy rom theoretical value. Keywords: thick plate, V-bending, deduction, camber, A Introduction Bending is a undamental and common process, which has been applied in industry or hundreds o years. There are many research works [1-5] on bending process or thin plate metal with thickness o 3mm or less, which is used as components or various products. On the other hand, bending process or thick plate metal has also been applied according to the diversity o market needs, only or special usage. Thereore, only a ew research works have been presented and the expertise is still limited. Ogawa shows some examination results o thick-plate-metal bending up to 6mm thickness. In the present research, experimental examination is carried out with emphasis on the eect o the die width on the bending behavior o thick plate metal with 1mm thickness: deormation in the width direction, spring-back and deduction o total length. As a result, it is quantitatively clariied that the die width has some amount o eect on the unique phenomena in thick-plate bending such as saddle type deormation, reduction o bending curvature rom the punch radius, and the deduction discrepancy rom theoretical value. 2. Experiment instruments and plate Fig. 1 shows composition o die, punch and plate (thick plate) at bending process. The plate is hot-rolled 583 aluminum alloy, and it is not subjected to heat treatments. Rolling direction and die-open width direction are set same. echanical properties o thick plate are the ollowing. Tensile strength and total elongation are σ B =315PA, φ=27.4% at rolling direction and σ B =334PA, φ=24.7% in the direction vertical to rolling direction. Size o thick plate is ollowing. Thickness is t=1mm, length is a=2mm, width is b=1mm. V type punch with tip radius R p =1mm and die with R d =1mm shoulder are used in bending process. Bending angle is 9 as shown in same igure. Punch and die are made by S45C. Hardening processed SKD11 shat has been inserted in tip o punch and shoulders o die. Bending process was conducted with 7 kinds o the open width V d ranges rom 4 to 1 mm, so it is 4 to 1 times o thickness t. The number o test pieces or an experiment is one. The position o let end o the plate rom the die-open ing L is constantly set as 5 mm as shown in the igure. An universal tensile test machine is used in this the experiment. Two displacement transducers with

2 62 ±1µm high precision are used or the measurement o bending angle during and ater bending. Plate was bent at room temperature and used petroleum-based lubricating grease. Fig. 2 shows the cross section at A in Fig. 1. Thick plate becomes saddle type shape ater bending process as shown in Fig. 2. As the extrados o plate expands and the intrados contracts in longitudinal direction, the ormer contracts and the latter expands in the ridge direction due to volume constancy. In this paper, examination o the inluence on deormation o thick plate and spring-back o changing die-open width V d was added. L 9 2R p A V d 2R d Punch Plate Plate at initial position Die (a) (b) Cross section A C l i Inside o bending vertical direction die open width direction Fig.1 Schematic illustration o die and punch in plate bending Outside o bending l o =.2 mm ridge line direction Fig.2 Cross section o bent plate 3. Results o experiment 3.1 Punch load at bending process Fig. 3 shows photo o plate at the end o bending. Space is produced between punch and thick plate at bending process. It means plate does not deorm precisely to the shape o punch as shape o punch. Fig. 4 shows relationship between punch stroke and load as a parameter die-open width V d. When the punch load P reaches 15 kn, the plate was released rom the punch and die. Point S indicates the situation whereby plate edge and punch slope starts to contact. On the other hand, point T indicates the situation whereby the clearance between punch slope and die shoulder c is equal to plate thickness t as shown in Fig. 3. Although punch load monotonously increases up to the maximum point due to work hardening, it slightly decreases beore reaching point S. Punch load monotone increases by work hardening, but ater that decreases little bit. It is because the vertical component o orce at the die shoulder decreases with increase o bending angle, while work hardening is small rom a certain punch stroke resulting in a constant moment. This is because o bending moment increases rom the beginning o bending process but ater some time bending process will done almost without increasing moment. The smaller the die-open width, the larger the Punch load is. From point S to T, the gap g between the punch slope and the plate decreases. Ater reaching point T, punch load will increase quickly without increase o stroke.

3 621 c Punch g Punch load P / kn Plate width : b =1.mm Die open width V d / mm point T point S Plate Die Punch stroke S / mm Fig.3 Photograph o bending view Fig.4 Load change during bending 3.2 Deormation o thick plate metal in bending process This research examine bending radius, dent, spring-back, lat length, camber, bending deduction. Fig. 5 shows deormation process o thick plate metal in bending process. Thick plate placed on the die and supported by die shoulders is bent by tip o punch like shown in igure (a). The thick plate is indented between die shoulders and the punch when the punch stoke reaches 4kN as shown in Fig. 5(b), ater that contacting area o thick plate and punch slope is increased. In a word, space between thick plate and punch slope is decreased then bending process will end. As shown in Fig. 5(c), there is still space between thick plate and punch slope, even ater the punch load reaches 15 kn. Although the shape o thick plate its to the punch slope except at the punch tip at the end o bending process as shown in Fig. 6, the thick plate deorms to the shape o dashed line because o spring-back. Bending radius is almost the same as punch tip radius R p, because more plastic deormation is produced around tip o punch. However, the other part o the plate comes apart rom the punch slope due to elastic recovery. φ (a) P=2kN (b) P=4kN T t end o bending ater spring-back (c) P=15kN Fig.5 Process o bending (V d =1 mm) Fig.6 Bending situation at the end o bending (P=15kN) Fig. 7 shows the eect o die-open width V d on inside bending radius ρ i and outside bending radius ρ o ater unloading. At the bending process, inside bending radius ρ i is smaller than tip radius o punch R p in the vicinity o punch tip. Ater unloading and spring-back, inside bending radius ρ i is still smaller than tip radius o punch R p in the case die-open width is under than 7mm. This phenomenon

4 622 is called spring-go [6]. On the other hand, inside bending radius ρ i is bigger than tip radius o punch R p when die-open width V d is bigger than 7mm. It is because spring-back increases with increase o V d as the area o elastic and plastic deormation expands. Outside bending radius ρ o is around 25mm. Fig. 8 shows relationship between dent o plate d and die-open width V d. Dent o plate d is proportional to die-open width V d. It is because deormation area o thick plate increases when die-open width V d gets longer. 5 1 Bending radius ρ / mm Plate width : b =1.mm Punch load : P =15 kn ρ i ρ o ρ o ρ i Dent o plate Δd o / mm Plate width : b =1.mm Δ d o Punch load : P =15 kn Die open width V d /mm Fig.7 Relationship between die open width and bending radius o plate Die open width V d / mm Fig.8 Relationship between die open width and dent o plate 4. Results and examination Spring-back φ b is deined as the dierence between the lange-angle φ and the punch angle 9 as ollows: φ-9 =φ b (1) Fig. 9 shows eect o die-open width on spring-back. Spring-back increases when die-open width increases. The increasing tendency is similar to that o inside-bending radius ρ i in Fig. 7. Further examination was conducted on the plate deormation along the ridge line o bending. Although the similar deormation along the ridge line might occur in thin-sheet bending, the amount o deormation is relatively small compared to the width o the sheet, and it might be able to be ignored. In the case o thick plate bending, the deormation along the ridge line cannot be ignored and the plate signiicantly deorms as shown in Fig. 2. In order to evaluate the deormation, lat length on the bending inside l i and outside l.are deined as shown in Fig. 2. Here the lat part is the area where the warpage is less than.2mm. The shape o the ridge was measured at the interval o.2mm using displacement transducer with high precision o 1μm. Fig. 1 shows the eect o die-open width on lat length along in the ridge line direction. Flat lengths in both inside and outside parts are constant regardless o die-open width because all plates are bent in the same shape. Inside lat part is longer than outside part because inside part o plate will be pressed by tip o punch and straightened.

5 623 Spring-back angle φ b / φ b +9 Plate width : b =1.mm Punch load : P =15 kn 1 Die open width V d / mm Flat length l / mm l i l o Inside l i l o Outside Cross section A =.2 mm Die open width V d / mm Fig.9 Relationship between die open width and spring-back angle Fig.1 Relationship between die open width and lat length o plate Inside the plate contracts in the longitudinal direction and outside expands because o bending moment. However, in the ridge-line direction, inside part o the plate expands in the ridge-line direction and outside part contracts as shown in Fig. 2 due to volume constancy. In this bending process, inside the camber will be around 1mm, outside the camber will be 15mm. Fig. 11 shows the eect o die-open width on camber height h s. Inside the camber o plate monotonously increases when die-open width increases, but outside the camber is not aected by die-open width because inside the plate is pressed by tip o punch and straightened. Decision o length o lange part is industrially important in bending process. For the evaluation o lange length, deduction δ is introduced as ollowing equation: δ=l 11 +l 12 -l (2) Where l 11 l 12 is shown as this Fig. 12, Fig. 12 shows relationship between die-open width and deduction. Short dashed line shows value calculated by ormula or thin plate. In case o thick plate deduction, this ormula is useless because it is given or thin plate. Deduction δ increases when die-open width increases. Because the tensile orce T t shown in Fig. 6 expands the thick plate. The expansion o the plate increases when die-open width increases. 3 3 Camber h s /mm 2 1 Inside Outside h si h so Cross section A h si h so Bend deduction δ / mm 25 2 Plate width : b =1.mm Punch load : P =15 kn Experimental l 11 l 12 Theoretical Die open width V d /mm Fig.11 Relationship between die open width and camber Die open width V d / mm Fig.12 Relationship between die open width and bend deduction

6 Summary Thick plate was bent with 7 kinds o dies rom V d =4mm(4t) to 1mm(1t) open width and used aluminum alloy thick plate (1mm). And result o the examination summary is ollowing. 1. In case o die-open width rom 4mm to 7mm, phenomenon spring-go is produced and in other cases phenomenon spring-back is produced. 2. Dent o plate increases proportionally to die-open width V d. 3. The value o spring-back increases when die-open width increases. aximum value was Flat length in ridge line direction is not aected by die-open width at both sides o plate. 5. The value o camber increases proportionally to die-open width V d outside the plate, and maximum value reached to 7% o thickness o the plate. On the other hand, inside the plate is pressed by tip o punch and straightened and is not aected by die-open width. 6. Bending deduction increases when die-open width increases. Reerences [1] H.oritoki: Transactions o the Japan Society o echanical Engineers (1972) [2] H.Kazama, K.Yagyu and Y.Nagai: Journal o JSTP (24) [3] H.Ogawa, K.Tamura and T.Nakagawa: Journal o JSTP (1984) [4] T.Yamura: Journal o JSTP (1981) [5] H.Ogawa: Journal o JSTP (22) [6] T.aeda: Journal o JSTP. (1972)329-33