FORGING METHOD AND FORGING APPARATUS

Abstract: A forging method and apparatus therefor is provided for forming a product such as a pulley having a cylindrical portion and a flange. In the forging step two metallic flows (A, B) are generated in a metallic blank (100), one is an elongating flow (A) toward the flange portion (T2) and another is an elongating flow (B) toward the cylindrical portion (T1). These metallic flows (A, B) are generated simultaneously. Since the metallic blank (100) elongates toward the cylindrical portion (T1) and the flange portion (T2) at the same time, the metallic structure of the product formed by the present forging method resists the formation of metallic slide surfaces so that a structural weak portion which would otherwise be generated in the product is prevented.

Description: The present invention relates to a method and apparatus for forging a metallic blank in order to form a cup-­ shaped product having a flange at an outer surface thereof. A product made by such a forging method may be a pulley, for example. Conventionally, a cup-shaped product having a flange at an outer surface thereof is formed by forging from a metallic blank. However, in the conventional forging method, the flange portion must be forged as a different step from that of the cup portion. For example, as described in Japanese Patent publication 55-49876, a cup portion is forged first, then a flange portion is formed by another forging step. Such conventional steps are described by reference to Figures 13 to 15. In those Figures, a metallic blank 100 preformed to a shape as shwon in Figure 13 is forged in a first step into a cup-shaped metallic member as shown in Figure 14. Then, in a second step, a thick portion 105 of the metallic member 104 shown in Figure 14 is forged again in order to produce the shape shown in Figure 15. Therefore, as described above, the conventional forging method requires a plurality of forging steps, so that the conventional method is time consuming and expensive. An object of the present invention is to provide a forging method for forming a cup-shaped product having a flange at an outer surface thereof by single forging step. In order to attain the object, the present inventors first tried to form the flange 101 and the cylindrical portion 102 by squeezing the metallic blank 100 as shown in Figure 16. However, the product made by the method shown in Figure 16 has a defect in that, the product has a crack at the flange portion 101. After careful study the present inventors concluded that the crack occured due to the following circumstances. In order to carry out squeezing forging, the metallic blank 100 is positioned within a die portion 200 having an inner diameter which is almost the same as an outer diameter of the metallic blank 100, as shown in Figure 17. One end of the metallic blank 100 faces to a first punch 201 having an outer diameter which is smaller than that of the metallic blank 100 and the other end of the metallic blank 100 faces a second punch 202 having an outer diameter which is almost the same as that of metallic blank 100. The second punch 202 is then moved toward the first punch 201. Since a side surface of the metallic blank 100 is contacted with the inner surface of the die portion 200 as shown, the metallic blank 100 elongates toward the outside of the first punch 201. In this process it should be noted that a plate portion of the metallic blank which becomes flange portion 101 is not deformed during the loading by punch 202, so that the metallic structure in this portion 101 should remain. On the other hand, the metallic structure of the metallic blank elongating toward the outside of the first punch is deformed largely for forming cylindrical portion 102. Therefore, it will be understood that a slide surface 300 occurs at the boundary between the metallic structure of the flange portion 101 and that of cylindrical portion 102. At this slide surface the metallic strength is weaker so that the product has a tendency to crack at this position. The problems of the slide surface 300 can be reduced if the thickness of the flange portion 101 is made large enough, so that the slide surface 300, even if it occurs, does not significantly reduce strength. In other words, if the thickness of the flange portion 101 is large enough, no crack appears at the slide surface 300. Accordingly, the forging method shown in Figures 16 to 18 can be used for a product having thick flange portion. However, this forging method can not be used for a product having the thin flange portion such as a pulley. The present invention provides a forging method which can be used for producing a product having a thin flange portion, whilst preventing cracking at the flange portion. In order to attain the object described above, the forging method of the present invention deforms the metallic blank for elongating two directions, for exampe, when making a pulley, one elongation makes the flange portion and another elongation makes the cylindrical portion. In other words, the forging method of the present invention does not make the flange portion and the cylindrical portion by reducing the outer diameter of the metallic blank. During the forging step of the present invention two metallic flows are generated in the metallic blank, one is an elongating flow toward the flange portion and another is an elongating flow toward the cylindrical portion. These metallic flows are generated simultaneously. Since the metallic blank elongates toward the cylindrical portion and the flange portion at the same time, the metallic structure of the product formed by the present forging method resists the formation of slide surfaces so that a structural weak portion otherwise generated, is prevented. The scope of the invention is defined in the appended claims. The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a sectionalview showing a forging apparatus in accordance with the invention; Figures 2 and 3 are sectional views showing the operation of the forging apparatus shown in Figure 1; Figure 4 is a sectional view explaining the forging method of the present invention; Figure 5 is a sectional view showing a knock out sleeve according to the forging apparatus of the present invention; Figure 6 is a graph explaining scattering of the thickness of the products produced by the apparatus shown in Figure 5 and another apparatus shown in Figure 8; Figure 7 is a schematic view explaining moving power of the apparatus shown in Figure 5; Figure 8 is a sectional view showing a forging apparatus employing an improved knock out sleeve; Figure 9 is a sectional view showing a product prdouced by the forging method of the present invention; Figures 10, 11, and 12 are sectional views showing machining step of the product; Figures 13, 14 and 15 are sectional views explaining conventional forging methods; Figure 16 is a sectional view explaining forging method the present inventors have done on the way to invent the present invention; Figures 17 and 18 are sectional views showing forging apparatus used for the forging method shown in Figure 16. A preferred embodiment of the present invention is illustrated in Figure 1 which shows an apparatus for the present forging method. Numeral 201 indicates a first punch made of high speed steel (SKH 51), and this first punch 201 is fixed on a holding base 230. Numeral 202 indicates a second punch which is operatively aligned with the first punch 201. The second punch 202 includes an inner punch portion 231 and an outer punch portion 232. Both the inner punch portion 231 and the outer punch portion 232 is made of high speed steel (SKH 51). A punch reinforcing ring 233 is provided at an outer surface of the outer punch portion 232, and surrounds the inner and the outer punch portions. A side die portion 200 is provided between the first punch 201 and the second punch 202 and is arranged to receive a metalli blank 100. The side die portion 200 is made of the tool steel (SKD 11) and is surrounded by a reinforcing ring 212. The side die portion 200 is supported by supporting bars 213, and the side die portion 200 and the supporting bars 213 can be moved vertically. The supporting bars 213 pass through holes 240 formed in the holding base 230, and the ends of the supporting bars 213 are connected with a piston 214 located within a cylinder 215 (Figure 2). The piston 214 can be reciprocated vertically by receiving oil pressure so that the supporting bars 213 and the side die portion 200 force the first punch 201 upwardly in order to keep the form of the flange portion formed between the side die portion 200 and the outer punch portion of the second punch uniformly. As shown in Figure 2, the outer diameter L1 of the first punch 201 is smaller than the diameter L of the metallic blank 100, and an outer diameter L2 of the end portion of the second punch 202 which faces the metallic blank 100 is larger than the diameter L of the metallic blank 100. An inner diameter of an inner surface of the side die portion 200 which faces to the metallic blank is almost the same length as the outer diameter L of the metallic blank 100. The inner diameter of the inner surface of the side die portion 200 which the second punch 202 contacts is almost the same length as the outer diameter L2 of the second punch 202. An annular groove 301 is formed at the inner surface facing the second punch 202, and the inner diameter of the deepest portion of the annular groove 301 is almost the same length as the outer diameter L2 of the second punch 202. In this way, a cylindrical die chamber T1 is formed between the first punch 201 and the side die portion 200, and a flange die portion T2 is formed between the annular groove 301 of the side die portion 200 and the second punch 202. The holding method using the apparatus described above will now be explained. A metallic blank 100 is conveyed and set on the first punch 210 by conveying apparatus which is not described with the second punch 202 in an upper position. The metallic blank 100 is so set on the first punch 201 that the metallic blank 100 is fitted in the inner surface 300 of the side die portion 200 as shown in Figure 4 and that the upper side of the metallic blank 100 extends above the annular shoulder defining the groove 301 of the side die portion 200. Then the second punch 202 is forced to move downwardly. During the movement of the second punch 202, the second punch 202 is receiving high forcing power of about 600 - 1000 t. When the second punch 202 is moved downwardly, the second punch 202 is inserted into the annular groove 301 of the side die portion (shown in Figure 2). The second punch 292 is moved further downwardly until the side die portion 200 is attached with the receiving base 216 (shown in Figure 3) so that the side die portion 200 is also moved downwardly with the movement of the second punch 202. The side die portion 200, on the other hand, is forced upwardly by the oil pressure in the cylinder 215 acting as the piston and through the supporting bars 213 in order to contact with the second punch 202. During the movement of the second punch 202, the side die portion 200 is contacted with the second punch by the forcing power from the piston 214 thereby preventing a gap occurring between the second punch 202 and the side die portion 200 and in order to prevent the elongation of the metallic blank toward such gap. During the movement of the second punch 202, there are two metallic flow paths in the metallic blank 100, one is the flow A elongating toward the annular groove 301 and another is flow B elongating toward the cylindrical die portion T1 as shown in Figure 4. As clearly shown from Figure 4, the resistance against the flow A toward the flange shaped die portion T2 is almost the same as that against the flow B toward the cylindrical portion T1. Therefore, the metallic flow in the metallic blank 100 is shared substantially evenly between the flow A toward the flange die portion T1 and the flow B toward the cylindrical die portion T2. Accordingly, the forging method of the present invention can well prevent the situation where the metallic flow is elongated only in one direction T1 (T2) and the other flow toward the other direction T2 (T1) starts after the one flow toward T1 (T2) is terminated. If one die portion T1 (T2) has a much bigger volume that another one T2 (T1), the metallic blank might have a tendency to elongate toward the bigger volume, and the metallic flow toward anothe die chamber having smaller volume will start after the metallic flow toward the one die chamber having the bigger volume terminates. Furthermore, when the metallic flow toward the die chamber with the smaller volume occurs, the reverse flow from the die chamber having the bigger volume to the die chamber with the smaller volume occurs. This reverse flow again results in a slide surface at the boundary between the metallic structure in the smaller die chamber. This surface makes the metallic structure weaken and causes structural damage such as crack. Such damage described above may not occur by the present forging method, because the sectional area of flange shaped die chamber T2 is almost the same a that of the cylindrical die chamber T1. It should be noted that the starting timing of the metallic flow toward the die chambers T1 and T2 does not have to be the same. The metallic flow toward one die chamber T1 (T2) can start after the metallic flow toward another die chamber T2 (T1) starts. The important point in the forging method is the terminating timing, namely that both metallic flows toward the die chambers T1 and T2 should terminate at the same timing. If the metallic flow elongating toward one die chamber T1 (T2) continues after the metallic flow toward the die chamber T2 (T1) is terminated, then the continuing metallic flow creates a slide surface and causes the metallic structure to weaken. It is preferred that a knock out sleeve 217 exists between the first punch 201 and the side die portion 200 during the whole movement of the second punch 202 and the side die portion 200 downwardly. Figure 5 shows a forging apparatus having the knock out sleeve 217 which is not present between the side die portion 200 and the first punch 201 when the forging starts but is positioned between the side die portion 200 and the first punch 201 when the second punch 202 and the side die portion 200 moves downwardly as shown. However, the products made by the forging apparatus shown in Figure 5 have a defect in that the thickness of the product can not be uniform as shown by the dots X1 and X2 in Figure 6. the dot X1 indicates the scattering of the thickness of the product at a portion X1 shown in Figure 9, and the dot X2 indicates the scattering of the thickness of the product at X2 in Figure 9. The present inventors believe that such scattering is caused by the moment M shown in Figure 7. The moment M generated when the second punch 202 moves downwardly makes the metallic blank 100 and the first punch 201 slide horizontally, and makes the thickness of the product lack of uniformity. Therefore, in the preferred arrangement, the forging apparatus of the present invention employs a knock out sleeve 217 which is positioned between the first punch 201 and the side die portion 200 from the start of the forging operation when the second punch 202 and the side die portion 200 moves downwardly as shown in Figure 8 to the termination of the forging. The existence of the knock out sleeve 217 between the first punch 201 and the side die portion 200 during the duration of the forging operation prevents the slide of the first punch 201 mentioned above. The knock out sleeve 217 is forced to move downwardly by deformation of the metallic blank 100. After the second punch 202 is moved down to the predetermined position as shown in Figure 3, the second punch 202 is pulled up by the pulling apparatus which is not shown. When the second punch 202 is pulled up, the product 100 remains between the first punch 201 and the side die portion 200. Then, the product 100 is pushed up from the die portion between the first punch 201 and the side die portion 200 by the knock out sleeve 217 using the knock out pins. After that, the product 100 is conveyed from the forging apparatus toward the next machining step. The product 100 removed from the forging apparatus is annealed, then a pulley hole 401 is stamped at the bottom portion 400 of the product 100 as shown in Figure 10. After that, the cylindrical portion 102 of the product 100 is forged outwardly as shown in Figure 11 in order to make flange 102 at the outer side surface of the product 100. The product having the flanges 101 and 102 is then machining for forming a plurality of grooves 402 about the pulley surface as shown in Figure 12. As described above, the forging method of the present invention can form a cup-shaped product having a flange by elongating the metallic blank toward both the flange portion and the cylindrical portion. Furthermore, the metallic flow toward one direction starts at least before the terminating timing of the metallic flow toward another direction. So that, according to the forging method of the present invention, a slide surface does not occur in both the flange portion and the cylindrical portion of the product, and the occurrence of a metallic structural defect such as a crack is prevented.

Claims: 1. A forging method comprising: a) a first step of providing a metallic blank having an outer diameter which is smaller than maximum outer diameter of a final product on a surface of a first punch having an outer diameter which is smaller than the outer diameter of said metallic blank; providing a second punch having an outer diameter which is greater than the outer diameter of said metallic blank at an opposite position to said first punch so that said first punch and said second punch may cooperate to forge said metallic blank; and providing a side die portion having an inner diameter which is almost the same as the outer diameter of said metallic blank and having a groove at an inner surface thereof; said side die portion being so provided and arranged that a cylindrical die chamber is formed between an outer surface of said first punch and an inner surface of said side die portion on which said groove is not provided and a flangve shaped die chamber is formed between said second punch and said groove of said side die portion; and b) a second step of reducing distance between said first punch and said second punch whilst keeping a shape of said flange shaped die chamber uniformly in order to elongate said metallic blank toward said cylindrical die chamber and said flange shaped die chamber; an elongation toward said cylindrical die chamber and said flange shaped die chamber being carried out in such a manner that the elongation toward one die chamber starts before the elongation toward another die chamber finishes and the elongation toward one die chamber finishes almost the same time when the elongation towards another die chamber finishes. 2. A forging method according to claim 1, wherein: said metallic blank elongates toward said flange shaped die chamber without any reverse flow from said flange shaped die chamber to said metallic blank during said second step for reducing the length between said first punch and said second punch. 3. A forging method according to claim 1, wherein: said metallic blank elongates toward said cylindrical die chamber without any reverse flow from said cylindrical die chamber to said metallic blank during said second step for reducing the length between said first punch and said second punch. 4. Forging apparatus comprising: a first punch having an outer diameter which is smaller than an outer diameter of a metallic blank; a second punch having an outer diameter which is greater than the outer diameter of said metallic blank; a side die portion having an inner diameter which is greater than the outer diamete of said first punch and provided between said first punch and said second punch in such a manner that said side die portion embraces said metallic blank, said side die portion having a groove at an inner surface thereof and said side die portion moving simultaneously with said second punch; pressing means for pressing said second punch toward said first punch; and holding means for holding said side die portion in such a manner that said side die portion slides while keeping contact with said second punch; an end portion of said second punch becoming the same level of said groove of said side die portion for forming a flange shaped die chamber between said second punch and said side die portion and for forming cylindrical die chamber between the inner surface of said side die portion and the outer surface of said first punch. 5. A forging method for forming from a metallic blank a product having forgved extensions of said blank in two transverse directions, the method comprising the steps of: a) providing and positioning said metallic blank within a die portion between first and second forging punches, said die portion and punches defining the shape of the product to be formed and cooperating to form a first and a second die chamber corresponding to said forged extensions; b) applying forging pressure to the blank by effecting relative movement between the first and second forging punches; c) generating by said forging pressure a metallic flow of metal of said blank into the first die chambers; d) generating by said forging pressure a metallic flow of metal of said blank into the second die chamber during the time that the metallic flow is generated to the first die chamber; and e) terminating said metallic flows to the first and second die chambers substantially simultaneously. 6. A forging method according to claim 1 wherein the metallic flows to said first and second die chambers are started at different times during the forging operation. 7. A forging method according to claim 5 or claim 6 including providing a knock-out member and positioning the knock out member between the die portion and the first forging punch throughout the duration of the forging operation. 8. Forging apparatus for forging from a metallic blank a product having forged extensions of said blank in two transverse directions, said apparatus comprising: a die portion for receiving the metallic blank; a first forging punch within said die portion and having a smaller outer dimension that the inner dimension of the die portion to define a first die chamber therebetween; a second forging punch cooperable with the die portion and the first forging punch to forge a blank positioned therebetween, and a second die chamber formed in said die portion laterally of said first die chamber, said second die chamber having an outer dimension greater than the outer dimension of a metallic blank to be received within the die portion whereby, under forging pressure between the first and second forging punches, metallic flows are generated in two transverse directions one to each of said first and second die chambers. 9. A forging apparatus according to claim 8 including a knock out member positioned between the die portion and the first forging punch and being dimensioned to be positioned therebetween throughout the duration ofd a forging operation to prevent lateral movement of the first forging punch.

Inventors: MORITA, KAZUHIRO, SHIRAI, TUKUO
Applicants: NIPPONDENSO CO., LTD.
Application year: 1986
Main classification: B21K23
IPC codes: B21J5, B21K23, B21K1