GB2141063A - Redrawing-ironing apparatus - Google Patents

Abstract

In a redrawing-ironing apparatus provided with a punch 4 fixed on a ram 1, a die means including a redrawing die 12 and ironing dies 15, an annular piston 26 for fastening the die means, a cup retainer pad 53 adapted to push the inner periphery of the bottom of a drawn cup placed on the redrawing die, and pins 39 fixed on the annular piston and extending axially, the free end surface of the pin is engaged with the flange 53a of the cup retainer pad at the end of the redrawing. As a result, the earing portions of the drawn cup can be prevented from being thinned and broken into fragments at the redrawing. A hydrostatic bearing for the ram 1 comprises three sets of oil pockets (Fig. 15(b)). <IMAGE>

Description

SPECIFICATION Redrawing-ironing apparatus This invention relates to a redrawing-ironing apparatus and, more particularly, to an improved redrawing-ironing apparatus in which earing portions can be prevented from being extended too thin into fragments at the end of a redrawing process of a drawn cup.

A drawn-ironed can body which is used extensively of late for carbonated beverage cans, beer cans and the like is usually formed by redrawing and then ironing in two or three steps a drawn cup formed from a metallic blank such as of aluminum alloy sheet or tinplate, on a redrawingironing apparatus. The diameter of the cup after redrawing becomes somewhat smaller (the inside diameter being equal to that of the drawn-ironed can body), and its height becomes somewhat larger by redrawing. So as to prevent wrinkles from arising on the bottom during the forming, the cup is redrawn while the inside periphery of its bottom is pushed under fluid pressure between a retainer pad and the surface of a redrawing die.

At the end of the redrawing process, an excessively high pressure is exerted on earing portions of the cup, which are formed usually at 4 to 6 portions circumferentially during the drawing process due to anisotropy of metallic sheets, and, therefore, the earing portion is extended thin and torn off the cup into fragments. Accordingly, the next coming cup is often redrawn with a tool having the fragments sticking thereon, and in such a case, the fragments are embedded in the sidewall portion of the redrawn cup, and the portion of the sidewall portion where the fragments are embedded becomes extremely thin in the process of ironing. Therefore, the sidewall portion tends to develop small holes therein, or completely rupture circumferentially due to tension incidental to the ironing.

Further, the redrawing-ironing is carried out by means of a punch and a plurality of dies in a cooperative operation with the punch, and the punch is normally fixed on the nose of a ram reciprocating horizontally. The ram has its base fixed on a slide yoke and is supported by bearings, and is driven usually to a high-speed reciprocation by a crank mechanism through the slide yoke. In this case, it is preferable that a hydrostatic bearing device be employed for prevention of heat generation and wear on a sliding zone of the slide yoke and the ram.

However, the hydrostatic bearing device proposed hitherto is not satisfactory, since it involves the problem that a deflection will result on the ram in case of high-speed reciprocation (200 strokes per minute, for example).

A final thickness of the sidewall portion of a redrawn and ironed can body is normally very thin such as to be about 0.10 to 0. 15 mm, and, therefore, a dislocation of the alignment between the punch and the ironing dies due to a slight deflection of the ram may exert an excessive load locally on the sidewall portion of the can body, thereby to incur rupture of the sidewall portion.

Moreover, in a return step of the punch, there tends to arise a problem that the deflection allows the punch and the dies to come in contact with each other to damage the two, thus shortening their life. Further, the can body after ironing is pulled off the punch with a so-called stripper at the punch return step. In case where, however, the alignment between the punch and the stripper is lost by a slight deflection of the ram, an excessive load is applied locally on the open end portion of the can body and, the open end portion is damaged thereby, or the can body is fed as far as to the die means without being pulled off, thus breaking down the dies.

This invention has been made in view of the problems of the prior art as mentioned above.

According to the present invention there is provided a redrawing-ironing apparatus comprising a punch fixed on the nose of a ram; a die means including a redrawing die and a plurality or ironing dies for forming a can body from a drawn cup in a cooperative operation with the punch, a holding ring for the redrawing die and a plurality of holding rings for the ironing dies which are piled with a plurality of spacers therebetween; an annular piston for fastening the die means which is provided circumferentially to abut on the end surface of the redrawing die holding ring; a cup retainer pad adapted to push the inner periphery of the bottom of the drawn cup placed on the redrawing die; and a plurality and predetermined length of pins fixed on the annular piston and extending in the axial direction of die means.

In the apparatus a free end surface of the pin is engaged with a flange of the cup retainer pad at the end of a redrawing process, thereby preventing a clearance between the redrawing die and the cup retainer pad from becoming less than a given value, so that earing portions of the drawn cup is prevented from being thinned and broken into fragments.

The ram in the apparatus reciprocates horizontally, the base thereof is fixed on a slide yoke for driving the ram, each sliding member of the slide yoke is provided with at least two sets of hydrostatic pressure sliding oil pockets in the longitudinal direction thereof, and the ram is supported by a hydrostatic pressure bearing having at least three sets of oil pockets in the longitudinal direction thereof which are spaced with bushings therebetween. Therefore, the deflection of the ram and the oscillation of the punch are small even at a high speed operation.

The above and other objects, features and advantages of the invention will be apparent from the following description when the same is read in conjunction with the accompanying drawings.

Figure 1 is a plan view, partly cut, of a main part of a redrawing-ironing apparatus which is given as an embodiment of this invention; Figure 2 is an inlet side view of a redrawing-ironing die means which is taken on line Il-Il of the apparatus of Fig. 1; Figure 3 is a vertical sectional view taken on the line Ill-Ill of Fig. 2, representing a die means and a retainer pad device; Figure 4 is a vertical sectional view representing a mounted state of the die means which is taken on line IV-IV of Fig. 2; Figure 5 is a vertical sectional view taken on line V-V of Fig. 3, representing the structure of an annular piston; Figure 6 is a transverse sectional view taken on line VI-VI of Fig. 2, representing a redrawing die and its vicinity; Figure 7 is a vertical sectional view taken on line VII-VII of Fig. 1, representing a slide yoke and its sliding member;; Figure 8 is a plan view of the slide yoke of the apparatus of Fig. 1; Figure 9 is a side view of the slide yoke of Fig. 8; Figure 10 is a vertical sectional view taken on line X-X of Fig. 8; Figure ii is an explanatory vertical sectional view taken longitudinally of the sliding member of the slide yoke, wherein Fig. 11 (a) and Fig. 11 (f) are drawings repres#enting the cases of this invention, and Figs. 11(b), (c), (d) and (e) are drawings representing the cases of comparative examples; Figure 12 is a vertical sectional view taken on line Xll-Xll of Fig. 1, representing a bearing system for the ram; Figure 13 is a vertical sectional view taken on line Xlll-Xlll of Fig. 1, representing similarly the bearing system;; Figure 14 is a sectional view taken on line XIX-XIV of Fig. 13, representing oil pockets disposed longitudinally of the ram; Figure 15 is an explanatory sectional view of a main part of the ram running longitudinally of the bearing system, wherein Fig. 15(a) is a drawing representing the case of comparative example, and Fig. 15(b) is a drawing representing the case of this invention; Figure 16 is a block diagram of a deflection measuring apparatus for the ram.

Fig. 1 represents a main part of a redrawing-ironing apparatus given as an embodiment of this invention: a ram 1 has its base fixed on a front end portion of a slide yoke 2. A numeral 3 denotes a hydrostatic bearing system to bear the ram 1, and a redrawing-ironing punch 4 is installed on the nose of the ram 1. A numeral 5 denotes a redrawing-ironing die means, and 6 denotes a stripper for pulling a redrawn and ironed can body 7 off the punch 4.

As shown in Fig. 2 and Fig. 3, the die means 5 consists mainly of a holding ring 13 of a redrawing die 12, a first spacer 14, a holding ring 16 of a first ironing die 15, a second spacer 17, a holding ring 19 of a second ironing die 18, a third spacer 20, and a holding ring 22 of a third ironing die 21. A numeral 23 denotes a nozzle for a cooling lubricant 24, and 25 denotes a discharge hole for the cooling lubricant injected through the nozzle 23.

As shown in Fig. 4, the die means 5 is placed on two pieces'of rails 27 fixed on a housing 26 and pushed by a leaf spring 29 fixed on a cover 28 which is installed hingedly on the housing 26, thus being supported at three points. A base plate 30 which is fixed on the housing 26 receives a stripper 6 having fingers (refer to Fig. 1).

A cylinder plate 33 is fixed on the housing 26 with a bolt 34. There is formed an annular air cylinder 35 in the cylinder plate 33 along a flange 13a of the redrawing die holding ring 13, and as shown in Fig. 3 and Fig. 5, an annular piston 36 with an O-ring 37 is enclosed in the air cylinder 35 so that it comes in contact with an end surface 13a' of the flange 13a.

A pressure air is supplied to the air cylinder 35 through a hole 38 and a piping (not illustrated). The holding rings 13, 16, 19, 22 and the spacers 14, 17, 20 are pushed and so fastened to the base plate 30 by the annular piston 36. Demounting or remounting of the holding rings or the spacers can be done far easily as compared with a conventional case wherein the fastening is done with bolts or the like, by opening the cover 28 and depressurizing the air cylinder 35 to release the annular piston 36 from pushing and fastening.

A given length and a plurality of pins 39 extending axially (3 pieces in case of the drawing) are fixed on the annular piston 36. The function of the pins 39 will be described later.

A cup holder 41 is fixed on the cylinder plate 33 with bolts 45. As shown in Fig. 2 and Fig.

6, the cup holder 41 is of a short cylindrical form with a feed side A open, and its inside diameter is specified to be almost equal to an outside diameter of the drawn cup 42 to be held therein and redrawn. A numeral 43 denotes a nozzle for injecting a cooling lubricant 44 onto the outside of the sidewall portion of the drawn cup 42.

As will be apparent from Fig. 2 and Fig. 6, the outside 33a of the cylinder plate 33 on the feed side A of the drawn cup 42 is formed so as to be of the same plane as the outside 1 3b of the redrawing die holding ring 13 which is on the same plane as the outside 1 2a of the redrawing die 12. The drawn cup 42 can therefore be fed smoothly.

In case the outside 1 2a of the redrawing die and the outside 1 3b of the redrawing die holding ring are aligned with the end surface 1 3a' of the flange 1 3a so as to simplify the structure of the redrawing die holding ring 13, since the drawn cup 42 will be afloat axially when it comes near the redrawing die 12, the drawn cup 42 comes to bounce due to the pressures of the cooling lubricant injected through the nozzle 43 and of air blown out of a hole 52 of the punch 4 which will be described later, the center thereof is dislocated, and thus the drawn cup 42 tends to be crushed by a retainer pad 53 described later. However, such a trouble will not be caused in the case of this embodiment.

Then, the drawn cup 42 is guided by a cage 46 (refer to Fig. 2) to descend on gravity in the direction indicated by an arrow B, and after reaching the position indicated in Fig. 2 and Fig. 6, it is fed in the direction indicated by an arrow C by a shuttle 47 and placed on the redrawing die 12.

The punch 4 is fixed on the nose of the ram 1, and the ram 1 is reciprocated axially by a crank mechanism (not illustrated), as described later, through the slide yoke 2. A hole 52 passes through the punch 4 and the ram 1, and pressure air is blown out of the punch nose at all times through the hole 52. The pressure air is so fed as to make the ironed can body easily come out of the punch 4 in the stripper 6.

A hollow cylindrical retainer pad 53 functions to prevent wrinkles from arising on the drawn cup 42 during redrawing and is specified to have the inside diameter slightly larger than the outside diameter of the punch 4, and the outside diameter a little smaller than the inside diameter of the drawn cup 42. The retainer pad 53 is fixed on a sliding portion 54a of an annular air cylinder 54 via its flange 53a. A supporting portion 54b of the annular air cylinder 54 is fixed on a support wing 55, and the sliding portion 54a is adapted to be slidable along a bushing 56 of the supporting part 54b. The pressure air is supplied into the annular air cylinder 54 through a piping (not illustrated) by way of a hole 57. The support wing 55 is reciprocated axially at a given timing by a cam mechanism (not illustrated) driven by a crank mechanism (not illustrated) which drives the ram 1.

The height of the pin 39 is specified so that the end surface 39a of the pin 39 will be engaged with the flange 53a of the retainer pad 53, when the clearance between the outside surface 1 2a of the redrawing die 12 and the nose surface 53b of the retainer pad 53 is kept preferably at about (0.5#0.9) > < t t (t being a thickness of the bottom of the drawn cup 42), thus leaving the above clearance not less than the above value. Therefore, at the end of the redrawing step, the earings 42a (Fig. 5) of the drawn cup 42 will never be thinner than the value (0.5#0.9) x t or so, and thus the fragments mentioned above can be prevented from generating.Further, with the height of the pin 39 as above, the above clearance will not develop greater than the thickness t of the bottom of the drawn cup 42 due to the engagement of the pin 39 with the flange 53a, and, therefore, the retainer pad 53 will be left powerful enough to suppress occurrence of the wrinkles.

Redrawing-ironing and particularly redrawing are carried out on the above apparatus as follows: First, the drawn cup 42 which have descended on gravity by way of the cage 46 shown in Fig. 2 is placed on the redrawing die 12 by the shuttle 47. At this point of time, the punch 4 and the nose of the retainer pad 53 are positioned rightward from the cup holder 41 so as not to prevent feeding of the drawn cup 42, as shown in Fig. 6. Subsequently, a support wing 55 goes leftward, the nose surface 53b of the retainer pad 53 comes in contact with the inside of the drawn cup 42, and thus the inside is pushed under air pressure by the annular air cylinder 54 (the state given in Fig. 3). At this point of time, there is left a clearance of about (0.1#0.5) Xt between the pin 39 and the flange 53a.The punch 52 then goes leftward to redraw, and at the point of time when the drawn cup (not illustrated) has passed the redrawing die 12, the end surface 39a of the pin 39 is engaged with the flange 53a. The ironing process then ensues.

The advantage that the pin 39 is fixed directly on the annular piston 36 is as follows: The die holding rings 13, 16, 19, 22 and the spacers 14, 17, 20 are often replaced owing to wear and failure of the dies. However, a dimensional accuracy of the thickness of each holding ring and spacer is about 0- + 0.02 mm. Therefore, a dispersion at about + 0.02 x 7 mm maximum (7 being a total number of the holding rings and spacers) = + 0. 14 mm will arise on overall thickness of the die means 5.

In case the pin 39 is fixed on the annular piston 36, the dispersion will not affect the clearance between the outside surface 12a of the redrawing die and the nose surface 53b of the retainer pad when the pin 39 is engaged with the flange 53a. However, in case the pin 39 is fixed on the housing 26, or the cylinder plate 33, or the cup holder 41, the above dispersion will be influential directly to the above clearance.

Since the thickness t of the bottom of the drawn cup 42 is usually about 0.3#0.4 mm, if the above clearance is set at 0.3 mm X 0.5 = 0.15 mm to a specific die means 5 when the thickness t is 0.3 mm, then a replacement of the die means may cause the above clearance to be 0.15 mm - 0.14 mm = 0.01 mm owing to the above dispersion. When the clearance is such small as above, there may arise the trouble that the earings 42a of the drawn cup 42 are extended thin and broken into fragments.

As described above, in case the die means is fastened by the annular piston, the die holding rings and spacers can be replaced very easily. Further, in case the pin for preventing the clearance between the redrawing die and the retainer pad from being less than a given value is fixed on the annular piston, the above earings trouble will not be incurred from a fluctuation of an overall thickness of the die means due to the above replacement.

Next a description will be given of a support means of the ram which is capable of preventing a deflection of the ram reciprocating horizontally at high speed.

As illustrated in Fig. 1, the slide yoke 2 on whose front end portion a base portion of the ram 1 is fixed, has one pair of sliding members 59 adapted to slide along upper and lower hydrostatic pressure sliding surfaces 60a of slide rails 60, by a crank mechanism (not illustrated) including a connecting rod 58, thus reciprocating horizontally (Fig. 7). The slide rails 60 are fixed on a frame 61.

As shown in Fig. 8, Fig. 9 and Fig. 10, there are provided two sets of slender hydrostatic pressure sliding oil pockets 62 in the longitudinal direction, that is, the direction in which the ram 1 moves, one set thereof being provided at positions opposite each other on the upper surface 59a and the lower surface 59b of each sliding member 59.

A primary pressure oil kept at a predetermined hydrostatic pressure (for example, a hydrostatic pressure oil at 100 kg/cm2) is led to the oil pocket 62 from a pressure oil source (not illustrated) by way of a primary conduit hole 63a, an orifice 63b and a secondary conduit hole 63c, decreases in pressure when passing the orifice 63b, so that the oil pressure (secondary pressure) in the oil pocket 62 becomes, for example 50 kg/cm2 (Fig. 10). As shown in Fig.

11(a), a thin pressure oil film layer 64 (0.04 mm thick, for example) is formed between the upper surface 59a and the lower surface 59b, and the hydrostatic pressure sliding surface 60a opposite to each of them, and the sliding member 59 slides to reciprocate in the direction indicated by the arrow along the slide rail 60 with the oil film layer 64 therebetween. Therefore, the sliding member 59 and the slide rail 60 will be prevented from heating and wearing.

It is necessary to provide at least two sets of the oil pockets 62 in the longitudinal direction of each sliding member 59, so as to prevent the sliding member 59 from inclining, that is, ascending leftward and descending leftward, and thus the punch 4 from oscillating vertically.

Namely, as shown in Figs. 1 1 (b) and (d), in case where one set of oil pockets 62' are provided on each sliding member 59', since upper and lower pressure oil film layers 64'a and 64'b corresponding to the upper and lower oil pockets 62' are equal in average thickness, pressures exerting on both pressure oil film layers 64'a and 64'b are also equal (when thought excepting a pressure according to gravity working on the sliding member 59'), and thus restoring force for the inclination of each sliding member 59' as shown in Figs. 6(b) and (d) scarcely functions.

Further, when the sliding member 59' moves at high speed in the direction indicated by arrow A as kept slanting higher leftward, as shown in Fig. 11 (b'), the oil in the clearance between the upper surface 59'a of the sliding member and a slide rail 60a flows relatively in the direction indicated by arrow Va shown in Fig. 11(b). In this case the clearance formed by the upper surface 59'a of the sliding member and the slide rail 60a becomes gradually wider in the oil flowing direction, and, therefore, a pressure working on the pressure oil film layer 64'a on the upper surface of the sliding member slightly drops to P'a.

On the other hand, the oil in the clearance between the lower surface 59'b of the sliding member and a slide rail 60b flows relatively in the direction indicated by arrow Vb shown in Fig.

11(b). In this case, since the clearance formed by the lower surface 59'b of the sliding member and the slide rail 60b becomes gradually narrower in the oil flowing direction, a pressure exerting on the pressure oil film layer 64'b on the lower surface of the sliding member slightly rises to P'b.

Where the pressures exerting on the pressure oil fiim layer 64'a on the upper surface of the sliding member and also exerting on the pressure oil film layer 64'b on the lower surface of the sliding member come to a state P'a < P'b, the sliding member 59' moves upward so that the pressures on the pressure oil film layers 64'a and 64'b come to a state P'a = P'b.

Then, in Fig. 11 (c) where the sliding member 59' moves at high speed in the direction indicated by the arrow B, the pressure exerting on the pressure oil film layer 64'a on the upper surface of the sliding member slightly rises to P"a, and the pressure exerting on the pressure oil film layer 64'b slightly drops to P"b. Therefore, the pressure exerting on both pressure oil film layers on the upper and lower surfaces of the sliding member become P"a > P"b, and thus the sliding member 59' moves downward so that the pressures come to a state P"a = P"b.

As shown in Fig. 11(d), a similar phenomenon will result in case where the inclination of the sliding member 59' is reversed such that it inclines higher rightward; when the sliding member 59' goes at high speed in the direction indicated by the arrow A, the sliding member 59' moves downward, and as shown in Fig. 11(e), on the other hand, when it goes in the direction indicated by the arrow B, the sliding member 59' moves upward. Such behavior of the sliding member 59' is due to a so-called wedge effect, which gets larger as the sliding speed increases.

In case where two oil pockets 62 are provided in the longitudinal direction of each sliding member 59, when the inclination becomes higher leftward, for example, as shown in Fig. 11(f), the thickness of the pressure oil film layer 64a corresponding to the left side upper oil pocket 62a becomes thinner than that of the pressure oil film layer 64b corresponding to the left side lower oil pocket 62b.

Then, since the pressure of a primary pressure oil is constant, the pressure Pa exerting on the upper pressure oil film layer 64a becomes higher than the pressure Pb exerting on the lower pressure oil film layer 64b, and thus a force working downward is exerted on the left end portion of the sliding member 59. Similarly a force working upward is exerted on the right end portion of the sliding member 59, and a restoring force to the inclination operates. As a result, as shown in Fig. 11(a), the upper. surface 59a and the lower surface 59b of the sliding member 59 slide in substantial parallel with the hydrostatic pressure sliding surface 60a.

Fig. 12, Fig. 13 and Fig. 14 represent the hydrostatic pressure bearing system 3 which bears the ram 1. The hydrostatic pressure bearing system 3 is provided with a cylindrical sleeve 65, bushings 66 and oil pockets 67. As shown in Fig. 12 and Fig. 13, one set of the oil pockets 67 consists of 4 pockets, each two pockets being disposed opposite to each other vertically and horizontally, and each oil pocket 67 is spaced with the bushing 66.

As shown in Fig. 14, the oil pockets 67 are provided in three sets in the longitudinal direction (or in the direction in which the ram 1 moves). A primary pressure oil (a hydrostatic pressure oil at, for example, 100 kg/cm2) kept at a predetermined hydrostatic pressure is led to each oil pocket 67 from a pressure oil source (not illustrated) by way of a piping 68a, an orifice 68c (refer to Fig. 10) in a head 71, a piping 68b and a conduit hole 69, and the oil pressure (secondary pressure) in the oil pocket 67 works, for example, at 50 kg/cm2.

There is formed a pressure oil film layer 70 (0.04 mm thick, for example; refer to Fig. 15) between the bushing 66 and the ram 1. Thus the ram 1 and the bushing 66 are prevented from heating and wearing. An inner surface 66a of each bushing 66 is so formed as to position substantially on the same phantom cylindrical surface by a simultaneous grinding. As a result, the inner surface 66a is formed so as to have a radial deviation between each set of about 5 #m or below. It is not desirable that the above deviation exceeds about 5 jum, since a wedge effect becomes too large to impede a deflection of the ram 1. The pressure oil in the oil pocket 67 flows out by way of oil reservoirs 72, and conduit holes 73a, 73b.

An oil groove 74 formed on an outside bushing 66a communicates with the oil reservoir 72 through a conduit hole 74a. The oil groove 74, for example, that on the left side of the drawing, feeds oil to the clearance between an inner surface 66a, of the left side bushing 66a and the ram 1, and thus prevents deterioration of a bearing function due to cavitation which tends to occur as an oil film gets thinner, and also roughening of the inner surface 661, thereby ensuring a long life of the bushing.

It is necessary that the oil pockets 67 are provided in at least 3 sets in the longitudinal direction of the sleeve 65 so as to prevent the ram 1 from deflecting, and the punch 4 from oscillating, particularly during high-speed movement.

The reason is deemed as follows. In case oil pockets 67' are provided in two sets and consequently metal bushings 66' in two sets, a maximum linear speed of the ram 1 during high-speed movement (200 strokes per minute, for example) will be caused about at the middle of the strokes and becomes 8.2 m/sec, for example.

In this case, the ram 1 will be curved upward on its own weight, as shown in Fig. 15(a), in the middle of a right side oil pocket 67'a and a left side oil pocket 67'b, and the portion of the ram 1 positioned at the above middle will be slightly higher (upward in Fig. 15(a)) than the portions thereof positioned along each oil pockets.

Further, the portion of the ram 1 along the right side oil pocket 67'a is inclined slightly lower rightward, and the portion along the left side oil pocket 67'b is inclined slightly to lower leftward. As in the case of the sliding member 59 of the slide yoke, the ram 1 moves slightly downward at the position of the right side oil pocket 67'a at its forward stroke (that is, a stroke moving leftward of the drawing), and slightly upward at the position of the left side oil pocket 67'b at the same stroke. As a result, the left side nose portion of the ram 1 on which the punch is mounted moves upward.

On the other hand, in a return stroke (that is, a stroke moving leftward of the drawing), the ram 1 moves slightly upward at a position of the right side oil pocket 67'a, and also moves slightly downward at a position of the left side oil pocket 67'b.

The left side nose portion of the ram 1 moves downward consequently. Thus the position where the ram is supported at the bearing system is different vertically between at the forward and return strokes of the ram 1, and the difference is enlarged at the nose portion of the ram 1, and, therefore, the punch 4 mounted on the nose of the ram 1 will be subjected to large vertical oscillations.

In an apparatus like redrawing-ironing can body forming machine, wherein a slender ram is supported with its one end fixed on a slide yoke and reciprocated horizontally by a crank mechanism through a connecting rod, the ram itself vibrates in accordance with the vibration of the apparatus. In the prior art therefore, the deflection of the ram consists of a deflection due to vibrations of the apparatus and a deflection due to the above-mentioned wedge effect, thus developing to a big deflection from duplication of both the two deflections.

Under such circumstances, the deflection of the ram usually can be minimized by enlarging the outside diameter of the ram and increasing its rigidity against the deflection of the ram.

However, in the redrawing-ironing can body forming machine the outside diameter of the ram 1 must be smaller than that of the punch 4, namely the outside diameter of the ram is restricted to cope with the size if the sidewall portion of the can body to be formed.

However, the oscillation of the punch 4 can be minimized without enlarging the ram outside diameter under the above condition, by suppressing the vertical movement of the ram due to the above-mentioned wedge effect by the following arrangement wherein, as shown in Fig.

15(b), at least 3 sets of the bushings 66 are provided close to each other in the hydrostatic pressure oil bearing, namely, a bushing of the hydrostatic pressure oil bearing is provided additionally in the middle of two bushings 66' of the hydrostatic pressure oil bearing in the prior art shown in Fig. 15(a).

As described above, in case of two bushings, the ram 1 is curved upward due to flexure from its own weight in the middle of the two bushings of the hydrostatic pressure oil bearing, as shown in Fig. 15(a), and the center portion of the ram comes higher (upward in the drawing) than the portions of the ram in the two bushings of the hydrostatic pressure oil bearing.

Therefore, the portion of the ram positioned high (upward in the drawing) can be pushed down by providing a bushing additionally in the middle of the two bushings of the hydrostatic pressure oil bearing, and thus the ram 1 through the three bushings can be held substantially linearly as shown in Fig. 15(b). The inclination of the ram in each bushing of the hydrostatic pressure oil bearing is improved as a result, the deflection of the ram due to the abovementioned wedge effect is eliminated unlike the prior art, and thus the oscillation of the punch 4 can be improved substantially on -the whole.

As described above, the arrangement wherein at least two sets of hydrostatic pressure sliding oil pockets are provided in the longitudinal direction on each sliding member of the slide yoke, and the ram is supported by the hydrostatic pressure bearing provided with at least 3 sets of oil pockets in the longitudinal direction thereof is advantageous in that it can prevent the ram substantially from heating and wearing, and decrease the deflection of the ram remarkably even in case of its high-speed reciprocation.

Therefore, when the arrangement is applied on a redrawing-ironing can body forming apparatus, rupture in the can body sidewall portion at the die means, damages of the punch and the dies, and further troubles liable to occur when the can body is pulled off with the stripper can be prevented, and a redrawing-ironing can body.forming can be realized even at a highspeed operation which was impossible heretofore.

The ram supporting device will be then described for its operation with reference to an example.

Example: In the redrawing-ironing apparatus of the type shown in Fig. 1, the amplitude of oscillation of the punch 4 at a position of the final die 21 of the die means 5 was measured for combination of the cases where the coil pockets 62 provided in the longitudinal direction of the sliding member 59 were in two sets and one set, and the other cases where the oil pocket 67 provided in the longitudinal direction of the hydrostatic pressure bearing system 3 of the ram 1 were in three sets and two sets.

The constitution of an amplitude measuring apparatus is shown in Fig. 16. A numeral 75 denotes a ring for mounting displacement sensors (of an eddy current type for measuring a distance to the surface portion of the punch 4 opposite thereto; measuring precision being 1 jum) 76a, 76b, 76c and 76d; 77a, 77b, 77c and 77d denote amplifiers; 78 denotes a subtraction circuit, which operates for subtraction between outputs of the amplifiers 77a and 77b and also for subtraction between outputs of the amplifiers 77c and 77d. A numeral 79 denotes an A-D converter, the output of which is inputted to a microcomputer 80. A data obtained through the microcomputer 80 is outputted to a printer 81.

The ring 22 for holding the die 21 (refer to Fig. 1) is demounted, and the ring 75 is installed at the position so that the displacement sensors 76c, 76d will face vertically and the sensors 76a, 76b will face horizontally. Therefore, a subtracted value x1 of the outputs of the amplifiers 77a and 77b indicates the value double of a horizontal displacement of the center of the punch 4 to the center of the ring 75.

Similarly a subtracted value x2 of the outputs of the amplifiers 77c and 77d indicates the value double of a vertical displacement of the center of the punch 4 to the center of the ring 75.

A sampling of data was carried out at every 2 mS, and a MAX value obtained on the microcomputer 80 during the period of measurement (the maximum value including + and of values read therefor, indicating a maximum displacement of the center of the punch 4) was displayed on the printer 81.

The oil pocket 62 provided on the sliding member 59 was standardized at 60 mm in length, 13 mm in width and 8 mm in depth; a primary pressure of the pressure oil was set at 100 kg/cm2 and a secondary pressure was set at 50 kg/cm2.

The oil pocket 67 provided on the hydrostatic pressure bearing system 3 was standardized at 56 mm in length and 22 mm in width, the bushing inner surface 66a at 20 mm in length, and the oil reservoir 72 at 45 mm (in the case of 3 sets) and 185 mm (in the case of 2 sets) in length; a primary pressure of the pressure oil was set at 100 kg/cm2 and a secondary pressure was set at 50 kg/cm2. The diameter of ram 1 was 50 mm, the length from the base of the ram 1 to the leading end of the punch 4 was 1345 mm, and the stroke of the ram 1 was 650 mm.

Results obtained by measuring the displacements in case the number of strokes per minute of the ram 1 was changed, are given in Table 1.

Table 1 120(1) 180( 230(1) Number of Number of sets of oil sets of oil MAX value MAX value MAX value pockets 67 pockets 62 (ym) (ym) (tom) 3 2 108 121 124 2 2 163 234 302 2 1 297 346 435 NOTE: (1) Number of strokes per minute

Claims (6)

1. A redrawing-ironing apparatus comprising a punch fixed on the nose of a ram; a die means including a redrawing die and a plurality of ironing dies for forming a can body from a drawn cup in a cooperative operation with the punch, a holding ring for the redrawing die and a plurality of holding rings for the ironing dies which are piled with a plurality of spacers therebetween; an annular piston for fastening the die means which is provided circumferentially to abut on the end surface of the redrawing die holding ring; a cup retainer pad adapted to push the inner periphery of the bottom of the drawn cup placed on the redrawing die; and a plurality and predetermined length of pins fixed on the annular piston and extending in the axial direction of the die means, wherein a free end surface of the pin is engaged with a flange of the cup retainer pad at the end of a redrawing process, thereby preventing a clearance between the redrawing die and the cup retainer pad from becoming less than a given value.

2. Apparatus as claimed in Claim 1, wherein the given value is (0.5#0.9) > < x t,t, where t is the thickness of the bottom of the drawn cup.

3. Apparatus as claimed in Claim 1, wherein the ram reciprocates horizontally, the base thereof is fixed on a slide yoke for driving the ram, each sliding member of the slide yoke is provided with at least two sets of hydrostatic pressure sliding oil pockets in the longitudinal direction thereof, and the ram is supported by a hydrostatic pressure bearing having at least three sets of oil pockets in the longitudinal direction thereof which are spaced with bushings therebetween.

4. Apparatus as claimed in Claim 3, wherein the inner surface of each bushing of the hydrostatic pressure bearing is formed on the same phantom cylindrical surface by simultaneous grinding.

5. A redrawing-ironing apparatus comprising a punch fixed to the nose of a ram; a die means including a redrawing die and a plurality of ironing dies for forming a can body from a drawn cup in a cooperative operation with the puch, a holding ring for the redrawing die, a plurality of holding rings for the ironing dies which are piled with a plurality of spacers therebetween; an annular piston for fastening the die means the annular piston being arranged to abut against the end surface of the redrawing die holding ring; a cup retainer pad adapted to push the inner periphery of the base of the drawn cup placed on the redrawing die; and a plurality of pins of predetermined length fixed to the annular piston and extending in the axial direction of the die means.

6. A redrawing-ironing apparatus substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.