US3909167A

US3909167A - Apparatus for moulding helical parts by compacting powdered materials

Info

Publication number: US3909167A
Application number: US424700A
Authority: US
Inventors: Maurizio Signora
Original assignee: C Olivetti & C S P A Ufficio B
Current assignee: TECSINTER SpA
Priority date: 1972-12-29
Filing date: 1973-12-14
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30
Also published as: CA1016317A; SU656489A3; JPS4998306A; FR2212199B1; GB1394300A; IT976216B; DE2363948C2; FR2212199A1; DE2363948A1; JPS5716161B2

Abstract

Apparatus for moulding helical parts by compacting powdered materials to be sintered comprising a pair of dies having helical profiles and movable axially one respect to the other and two plungers adapted to compact the powder in the corresponding die. After the compression, a die is axially withdrawn from the other with a rotational movement and the moulded part can be ejected from the other die.

Description

United States Patent Signora Sept. 30, 1975 [54] APPARATUS FOR MOULDING HELICAL 2,767,438 10/1956 Pingel 425/78 PARTS BY COMPACTING POWDERED 3,020,589 2/1962 Maritano 425/78 3,118,183 l/l964 Gex et a1. 425/345 X MATERIALS 3,394,432 7/l968 Laurent 425/78 [75] Invent r; Maurizio Signora Palazzo 3,677,671 7/1972 Martin 1 425/78 Canavese, h l 3,677,672 7/1972 Harrington l 1 425/78 3,694,127 9/1972 Takahashi et al.. 425/78 X [731 Asslgnee: Ing. C. Ohvetti & -p- Uffici 3,773,446 11 1973 130mm 425/78 Brevetti, Ivrea, Italy 22 Filed; 14 973 Primary Examiner-J. Howard Flint, Jr.

Attorney, Agent, or FirmSchuyler, Birch, Swindler, [21] Appl. N03 424,700 McKie & Beckett [30] Foreign Application Priority Data [57] ABSTRACT Dec. 29, 1972 112211) .1 71122/72 Apparatus for moulding helical parts y Compacting powdered materials to be sintered comprising a pair of [52] U.S. Cl. 425/78; 425/352; 425/418 dies having helical profiles and movable axially one respect to the other and two plungers adapted to compact the powder in the corresponding die,

6 Claims, 13 Drawing Figures [58] Field of Search 425/78, 79, 344, 345, 352, 425/353, 354, 355

[56] References Cited UNITED STATES PATENTS 2,767.428 10/1956 Pingel 425/79 -5 73 e l E gen US. Patent Sept. 30,1975 Sheet 1 of7 3,909,167

US Patsnt Sept. 30,1975 Sheet 3 of7 3,909,167

Fig.6

US. Patent Sept. 30,1975 Sheet 4 of7 3,909,167

US. Patent Sept. 30,1975 SheetS 0f7 3,909,167

US. Patent Sept. 30,1975 Sheet 7 of? 3,909,167

Fig.13

APPARATUS FOR MOULDING I'IELICALv PARTS BY COMPACTING POWDERED MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for moulding helical parts by compacting powdered materials to be sintered having two different helical profiles.

2. Description of the Prior Art Apparatus for moulding helical parts such as gear wheels is known. A first known apparatus comprises a die and two punches movable in opposed fashion to compress the powder in the die. With this known appav SUMMARY OF THE INVENTION According to the present invention there is provided an apparatus for moulding helical parts by compacting powdered materials to be sintered comprising a pair of dies having helical profiles and movable axially one with respect to the other, in which one of the dies is rotatable with respect to the other during the axial movement, and two plungers adapted to compact the powder in the corresponding die by axial movement into the die, the compacted parts having two different helical profiles in correspondence with the two dies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a helical part to be moulded;

FIG. 2 is a median section of a first embodiment of the invention in the initial stage of its operation;

FIGS. 3 and 4 show the apparatus of FIG. 2 from which a number of parts have been omitted in two following stages of its operation;

FIG. 5 is a partial section taken on the line V--V of FIG. 2;

FIG. 6 is a median section of a second embodiment of the invention in the initial stage of its operation;

FIGS. 7 and 8 show the apparatus of FIG. 6 from which a number of parts have been omitted in two following stages of its operation; g

FIG. 9 is a partial section take on the line lX-IXof FIG. 6; g 7

FIG. 10 is thesection of FIG. 9 in which the apparatus of FIG. 6 is provided with a modification;

FIG. 11 isa median section of a third embodiment of the invention in the initial stage of its operation;

FIG. 12 shows the apparatus of FIG. 11.. from which a number of parts have been omitted in a following stage of its operation; and

FIG. 13 is a median section of a fourth embodiment in the initial stage of its operation.

DESCRIPTIONOF THE PREFERRED EMBODIMENT According to a first embodiment, the moulding apparatus comprises an upper die 14 (FIG. 2) for moulding the toothing 11 (see also FIG. 1) and a lower die 15 for moulding the toothing 12. The profiles of the

dies

14 and 15 respectively conform with the profiles of the

toothings

11 and 12 of the gear 10 to be moulded. The upper die 14 is fixed in manner known per se to an upper die-bearing plate 17 and is provided on top with two pins 18 perpendicular to the said upper die 14 and fast therewith. Four stop feet 19 (only two thereof are shown in FIG. 2) project from the upper die 14 on the top thereof and have their upper ends disposed in a plane parallel to the plane of the upper die 14. The plate 17 is fixed in known manner to the frame 20 of the press operating the apparatus of the invention, as a result of which the upper die 14 is fixed with respect to this frame 20. Two vertical guide columns 22 project below theplate 17 and are fixed thereto in manner known per se.

The moulding apparatus moreover comprises a vertically disposed cam 23 (see also FIG. 5) the profile of which is constituted by a helical groove 24 of V-shaped cross-section. The cam 23 is fixed to the plate 17 by means of the screws 25. The cam 23 is engaged by a conical end 26 of a cam-following pin 27 disposed radially with respect to the lower die 15 and provided at its other end with a screw 29 by means of which it is fixed to the die 15. The inclination of the helix of the groove 24 is such that when the die 15 is shifted vertically, as 'will be described in the continuation of the present description, the pin 27 turns the die at the same time so that the profile of the die 15 itself describes a helix corresponding to its own helix and therefore corresponding to that of the profile 12.

Thelower die 15 is arranged rotatably on a lower diebearing plate 30, to which it is also linked in the vertical direction, by means of rolling bearings indicated generally by the reference 31 in'FIG. 2. The plate is slidable in the vertical direction on the columns 22 and is provided with a pair of flanges 32 in engagement with a pin 33 of'a lever 35 mounted on a pivot 36. A cam follower 37 of the lever 35 is kept in contact with a cam 38 by a 'spring 39. The cam 38 rotates cyclically through the medium of a shaft 40.

With the lower die 15 there co-operates a hollow lowerplunger 42 having its profile corresponding to the profile 12 of the gear 10 to be moulded. The lower plunger 42 is fixed in known manner to a plunger carrier 43 which is rotatable on a support 44 by means of rolling bearings 45 indicated generally in FIG. 2. The support 44 is fixed by means of screws 47 to a lower mount 48 slidable in the vertical direction in the frame '20. The mount 48 is provided with a pair of flanges 49 in engagement with a pin 50 of a lever 51 mounted on a pivot 52. A cam follower 54 of the lever 51 is normally kept in contact with a cam 55 by a spring 56. The cam-55 is also rotated-by the shaft 40.

A core 59 is housed in the cavity of the plunger 42 and is movable vertically with respect thereto for forming the hole 13. The vertical movement of the core 59 is controlled by cam means not shown in the drawings.

An upper plunger 60 can co-operate with the upper die 14, the upper plunger being internally hollow to permit the passage of the core 59 and having its profile corresponding to the profile 11 of the gear to be moulded. The upper plunger 60 is linked to an upper plunger carrier 61 in the vertical direction and is rotatable on the latter through the medium of rolling bearings indicated generally by the reference 62 in FIG. 2 and disposed between the upper plunger 60 and the upper plunger carrier 61 itself. The plunger carrier 61 is slidable in the vertical direction in the frame and is provided with a pair of flanges 63 in engagement with a pin 64 of a lever 65 mounted on a pivot 66. A cam follower 67 of the lever 65 is normally kept in contact with a cam 68 by a spring 69. The cam 68 is rotated by a shaft 70 in synchronism with the shaft 40.

Always in engagement with the upper plunger 60 is a nut 72 belonging to a plate 73 and having a profile corresponding to the profile of the upper die 14. The plate 73 is connected to the upper plunger carrier 61 by means of two vertical tie rods 74 which are provided with a stop head 75 at the upper end and are fixed to the plate 73 by means of their threaded end. The tie rods 74 can slide in two guide apertures 77 in the plunger carrier 61, while the stop heads 75 are normally kept in contact with one face of the plunger carrier 61 through the medium of two compression springs 78. The plate 73 is moreover provided with two vertical holes 79 into which the two pins 18 of the upper die 14 can insert themselves.

The apparatus shown in FIGS. 2 to 5 operates in the following manner. At the beginning of the working cycle, the lower die 15 is in the highest position with its own top face in contact with the bottom face of the upper die 14. In this position, the cam 23 orients the pin 27 in the angular position in which the profile of the lower die 15 mates with the profile of the upper die 14 in the plane of contact between the aforesaid dies 14 and 15. The lower plunger 42 is within the lower die 15 and the core 59 is substantially level with the top face of the upper die 14. The upper plunger 60 and the plate 73 are in the highest position, so that charging means for the powder (which are known and not shown in the drawings) can be arranged above the upper die 14.

Before conventional means which are not shown in the drawings cause the

shafts

40 and 70 to rotate for one revolution and in synchronism, these charging means charge the powder into the dies 14 and 15, after which they are removed from the apparatus. The

shafts

40 and 70 then rotate the

cams

38, 55 and 68 in the direction indicated by the arrows in FIG. 2. At first the cam 68 actuates the lever 65 in the direction in which the plunger carrier 61 is lowered and this lowers the upper plunger 60 and at the same time the plate 73 through the medium of the springs 78. The plate 73 descends until it is arrested by the feet 19 (FIG. 3) of the upper die 14. At the instant when the plate 73 comes into contact with the feet 19, the profile of the nut 72 is aligned with that of the upper die l4 by means of the pins 18, which are inserted in the holes 79 during the last portion of the stroke of the plate 73.

The feet 19 serve to ensure that at each cycle the position of arrest of the plate 73 with respect to the die 14 is always the same, so as to avoid displacements between the profiles of the said die 14 and the nut 72. In fact, if the plate 73 were to stop against the top face of the die 14, the powder which may have dropped on to this face during the charging stage could change this position of arrest from one cycle to the other.

The upper plunger 60, on the other hand, continues to descend in opposition to the action of the springs 78, being rotated by the nut 72 which is locked angularly by the pins 18, and enters the upper die 14 to compress the powder. Substantially at the instant when the upper plunger comes into line with the top face of the die 14, the cam 55 (FIG. 2) actuates the lever 51 in the direction for raising the lower mount 48. The mount raises the lower plunger 42 (FIG. 3) in the opposite direction to the upper plunger 60 by means of the plunger carrier 43 and the support 44. During the strokes of the

plungers

42 and 60, the core 59 remains stationary.

The gear 10 is therefore moulded, the profile of the toothing 1 1 being formed by the upper die 14, while the profile of the toothing 12 is formed by the lower die 15.

The moulded part must now be extracted from the moulding apparatus. To this end, the core 59 (FIGS. 2 and 4) is first lowered to clear the hole 13. The cam 38 then allows the spring 39' to turn the lever 35 anticlockwise. Through the medium of the plate 30, this lever lowers the lower die 15 below the gear 10 and at the same time the cam 23 rotates the die 15 by means of the pin 27, as a result of which the die 15 releases the toothing 12 without damage. After the lower die 15 has released the profile 12, the cam 55 allows the spring 56 to turn the lever 51 anticlockwise to lower the lower mount 48 and, therefore, the lower plunger 42. When the core 59, the lower die 15 and the lower plunger 42 reach the position shown in FIG. 4, the cam 68 turns the lever in the direction for lowering the upper plunger 60 further to expel the moulded part from the die 14. Conventional means not shown in the drawings collect the gear 10 and remove it from the moulding apparatus.

Completing the rotation of one revolution, the

cams

38, 55 and 68 act on the levers associated with them so as to bring the apparatus back into the beginning-ofcyle position shown in FIG. 2, to receive a fresh charge of powder. More particularly, the pin 27, co-operating with the cam 23, brings the profile of the lower die 15 back to mate with the profile of the upper die 14 in the plane of contact between the dies 14 and 15 themselves.

It is necessary to observe that the groove 24 of the cam 23 is longer than the vertical stroke of the lower die 15, so that this die is always linked to the said groove 24. It is not necessary, however, that the groove 24 be inclined throughout its length, but it is sufficient, in accordance with what has been explained hereinbefore, that it be inclined only in the portion corresponding to the thickness of the toothing l 1. Only in this portion, in fact, it is necessary for the lower die to rotate.

Moreover, a cam of the type described, having a helical profile, may be conveniently replaced, in the case in which it is desired to mould gears the toothing of which is of limited inclination and/or thickness, by a.

plane cam the profile of which is constituted by a simple rectilinear groove. A plane cam is convenient within the limits in which the inclination of the teeth of the gear to be moulded and its thickness are sufficiently small to permit adequate keeping of the cam-following.

pin to the profile of the cam, notwithstanding the tendency of the pin to leave the same because of the rotation imposed thereon by the cam itself.

In a second embodiment, the upper die 14 (FIG. 6) is devoid of the pins 18 and is provided with two vertical holes 100 (see also FIG. 9) symmetrical with respect to the axis of the said die 14 and in which two guide columns 101 are slidably inserted. The upper die 14 is movable in the vertical direction by means of an upper die-bearing plate 102 to which it is rotatably connected by means of the rolling bearings 103 indicated generally in FIG. 6. The plate 102 is slidable in the vertical direction on two columns 104 and is provided with a pair of flanges 105 in engagement with a pin 106 of a lever 107 mounted on a pivot 108. A cam follower 110 of the lever 107 is normally kept in contact with a cam 111 by a spring 112. The cam 111 rotates cyclically through the medium of the shaft 70.

The lower die is fixed in known manner to a plate 113 fixed in turn to the frame and provided with two openings 114 in the form of curved slots (see also FIG. 9) to allow the passage of the columns 101. The columns 104 are moreover fixed to the plate 113. The stroke of the lower plunger 42 is controlled by a cam 115 by means of a lever 116 mounted on a pivot 117 and normally in contact with the cam 115 through the action of a spring 116'. The lever 116 comprises a pin 125 and a cam follower 126.

The cam 23 (see also FIG. 9) and the pin 27 are fixed to the upper die 14 and the frame 20,'respectively. The nut 72 is fixed in conventional manner to a guide plate 118 similar to the plate 73 already described. The plate 118 is secured angularly with respect to the upper die 14 by the two columns 101, the threaded upper ends of which are fixed to the plate 118 itself by means of two nuts 119. In FIG. 6 the columns 101 and the openings 114 are shown for clarity in the median plane of the apparatus. In reality, they are disposed in a plane at 45 with respect to this median plane, as shown in FIG. 9, for the purpose of having a larger space available for charging the powder and for extracting the moulded part. The plate 118 (FIG. 6) is supported by a plate 120, to which it is linked in the vertical direction and on which it is rotatable by means of the rolling bearings 121 indicated generally in FIG. 6. The plate 120 can be shifted vertically by the upper plunger carrier 61 by means of the tie rods 74 and the springs 78. The stroke of the upper plunger carrier 61 is controlled by a cam 121 by means of a lever 122 mounted on a pivot 127 and the spring 123. The lever 122 comprises a pin 128 and a cam follower 129.

The apparatus shown in FIGS. 6 to 9 operates in the following manner. FIG. 6 shows the apparatus at the beginning of the working cycle, when the upper die 14 is in contact with the lower die 15 and its profile mates with the profile of the lower die 15 in the plane of contact between the two dies themselves.

After the charging of the powder has been effected, the cam 121 turns the lever 122'in the direction in which the plunger carrier 61 is lowered, so that the carrier lowers the upper plunger 60 (FIGS. 6 and 7) and the plate 1 18 until the latter is arrested by the feet 19. In this position, the profile of the nut 72 is aligned with that of the upper die 14 through the medium of the columns 101. After the arresting of the plate 118, the upper plunger 60 continues to descend, being rotated by the said plate 1 18, and enters the upper die 14, compressing the powder against the lower plunger 42, which is urged at the same time in the opposite direction by means of the cam 115 and the lever 116.

The moulded part must now be extracted from the moulding apparatus. First, the core 59 (FIGS. 6 and 8) is lowered to clear the hole 13. The cam 111 then allows the spring 112 to turn the lever 107 clockwise and the lever raises the plate 102 and the latter raises the upper die 14 and the plate 118. The upper die 14 and the plate 118 are rotated at the same time by the cam 23, which slides on the pin 27, so that the toothing 11 is disengaged without damage. After the upper die 14 has released the moulded part, the cam 121 allows the spring 123 to turn the lever 122 to raise the upper plunger 60 and the plate 118 to the beginning-of-cycle position (FIG. 6), while the upper die 14 (FIG. 8) is arrested substantially at the height of the pin 27. Beyond this position, the plate 118 moves vertically guided by the columns 101.

The cam then allows the spring 116' to turn the lever 116 in the direction for raising the lower mount 48 and therefore also the lower plunger 42, which expels the moulded part from the lower die 15. Known means (not shown in the drawings) extract the moulded part from the moulding apparatus. The cycle is therefore at an end and the

cams

111, 115, 121 act on the respective levers to bring the apparatus back to the beginning-of-cycle configuration shown in FIG. 6. More particularly, the cam 23, co-operating with the pin 27, brings the profile of the upper die 14 back to match or mate with the profile of the lower die 15 in their plane of contact.

It is necessary to observe that the inclination of the helix of the cam 23 is greater than the inclination of the teeth of the part to be moulded, the distance between the cam 23 and the axis of the dies being always greater than the radius of the part to be moulded. When parts in which the toothing has a considerable inclination are to be moulded, the inclination of the groove 24 may assume very high values, so that the friction between the cam 23 and the pin 27 does not allow the cam 23 to cause the die associated therewith to rotate. To obviate this disadvantage, the apparatus according to the invention comprises a mechanism, indicated generally by the reference in FIG. 10, which is adapted to compensate the friction between the pin 27 and the cam 23 during their relative movement. In FIG. 10, the mechanism 150 is shown fitted to the apparatus in the form illustrated in FIGS. 6 to 9.

The mechanism 150 comprises a double-acting hydraulic (or pneumatic) cylinder 152 which is fixed to the top face of the upper die-bearing plate 102 by known means not shown in the drawings. The cylinder 152 is provided with two inputs'153 and 154 for the pressure oil for producing the movements of a piston 155 in the two directions. Moreover, a connecting rod 157 is disposed between the cam 23 and the rod 158 of the piston 155 to transmit the force exerted by the pressure oil on the piston 155 to the cam 23. The connecting rod 157 is pivoted at one end to a pin 159 projecting from the cam 23 itself and fast therewith and is pivoted at the other end to the end of the rod 158. Known means not shown in FIG. 10 are provided for varying the pressure of the oil in accordance with the force it is intended to exert by means of the piston 155 on the cam 23 and for commanding the admission thereof through one or the other of the

inputs

153 and 154.

At the instant when the cam 111 (FIG. 6) enables the plate 102 to raise the upper die 14 to release the compacted part, oil under pressure is introduced into the cylinder 152 (FIG. 10) through the

input

153 or 154, according to whether the upper die 14 must rotate clockwise or anticlockwise, respectively. The force exerted on the cam 23 by the piston 155 facilitates the sliding of the cam 23 itself on the pin 27 inasmuch as it compensates the friction between these lastmentioned two elements. The pressure of the oil may be predetermined in accordance with the inclination of the groove 24 of the cam 23.

The moulding apparatus in the form shown in FIGS. 2 to may also include the mechanism 150. In this case, the cylinder 152 is fixed to the lower die-bearing plate 30 and produces the rotations of the lower die 15 by rotation of the pin 27.

According to a third embodiment, the moulding apparatus comprises two locking pins 170 and 171 (FIGS. 11 and 12) respectively controlled by two doubleacting and simultaneously and oppositely operated

pneumatic cylinders

172 and 173. The apparatus shown in FIGS. 11 and 12 is substantially the apparatus of FIG. 2, in which the locking pins 170 and 171 have been substituted for the cam 23 and the pin 27. Moreover, the cam 55 has been replaced by another cam 174 of different profile. In FIG. 11, those parts of the apparatus which are not shown are the same as the corresponding parts shown in FIG. 2.

The locking pins 170 and 171 are disposed radially with respect to the dies and plungers and have their ends substantially conical to co-operate respectively with two corresponding

conical seats

175 and 176 in the lower die 15 and the support 44, respectively. The cylinder 172 is fixed to the lower die-bearing plate 30, while the cylinder 173 is fixed to a pillar 177 attached in turn to the lower mount 48, so that the cylinder 173 is connected rigidly to the said lower mount 48. Known means not shown in the drawings are arranged for simultaneous and opposite operation of the

cylinders

172 and 173.

The apparatus shown in FIGS. 11 and 12 operates in the following manner. In FIG. 11 the apparatus is illus-' trated at the beginning of the cycle when thedies 14 and 15 are in contact, the locking pin 170 is engaged in the seat 175, while the locking pin 171 is disengaged from the seat 176. The locking pin 170 is arranged so as to lock the lower die 15 in the angular position in which its profile coincides with the profile of the upper die 14 in the plane of contact between the said two dies. The

cams

174 and 68 actuate the

plungers

42 and 60 in an identical manner to that hereinbefore described with reference to FIGS. 2 to 5, in order to compact the powder.

At the instant when the compression is at an end, the cylinder 172 (FIG. 12) disengages the locking pin 170 and at the same time the other cylinder 173 engages the locking pin 171 in the seat 176. The lower die 15 is now free to rotate, while the lower plunger 42 is rigidly fixed to the lower mount 48.

To effect the extraction of the moulded part, the core 59 is first lowered below the part and then the cam 38 actuates the lower die 15. The latter descends below the moulded part and at the same time is rotated by the lower plunger 42, thus disengaging the profile 12 without damage. Thereafter, the core 59, the plunger 42 and the die descend substantially to the same position which is shown in FIG. 4. The cam 68 (FIGS. 2 and 11) then actuates the upper plunger 60, which expels the moulded part from the upper die 14, similarly to what has already been described with reference to FIGS. 2 to 5.

When the part has been extracted from the moulding apparatus by the above-mentioned known means (not shown in the drawings), the lower die 15, the lower plunger 42 and the core 59 are brought back to the beginning-of-cycle position in the following manner. The plunger42 is enabled by the cam 174 to return to the end-of-compression position shown in FIG. 12, while the lower die 15 is enabled by the cam 38 to bring itself into contact with the upper die 14. When the lower die 15 is arrested against the upper die 14, the profiles of the two dies coincide in their plane of contact, since the lower punch 42 is in the position shown in FIG. 12. The cylinder 173 then disengages the locking pin 171, releasing the lower plunger 42, while the cylinder 172 engages the other locking pin in the seat 175, locking the lower die 15. The cam 174 then allows the lower plunger 42 to return to the beginning-of-cycle position shown in FIG. 11. The powder is charged and the

plungers

42 and 60 effect the compression thereof in the manner already described with reference to FIGS. 2 to 5.

The lockings pins 170 and 171 (FIG. 13) may also be fitted, in substitution for the cam 23 and the pin 27, to the embodiment of the invention described with refer.- ence to FIGS. 6 to 9. The apparatus shown in FIG. 13 is substantially that shown in FIG. 6, from which the cam 23 and the pin 27 have been removed and to which the aforesaid locking pins 170 and 171 have been added. The pneumatic control cylinders 172 and 173 (FIG. 13) are fixed to the upper die-bearing plate 102 and the plate 120, respectively. The locking pin 170 is.

neously unlocks the upper plunger 60. At the instant when the end of the compression is reached, the locking pin 170 unlocks the upper die 17 and at the same time the locking pin 171 locks the upper plunger 60.

Parts different from the herringbone gear of FIG. 1 can also be moulded with the apparatus of the invention. For example, it is possible. to mould drum cams provided with two differently inclined helical profiles. which are off-set and arranged on opposite sides with respect to a plane perpendicular to the axis of the cams.

It is clear that modifications and additions may be made in the apparatus of the invention without departing from the scope of the invention itself. For example, the plungers and the rotatable die may be rotated during their axial movement by means different from those hereinbefore described. For instance, this may be done by means of a worm wheel and worm pair, a rack, or with pairs of helical ring gears. I

Moreover, the apparatus may comprise means for locking the dies during the compression of the powder. For example, this may be done by means of a diepressing plate connected to the plunger co-operating with the movable die through the medium of a flexible coupling so as to be caused to bear resiliently against the movable die during the compression in order to secure it positively.

I claim:

1. Apparatus for moulding helical, gear wheels by compacting powdered materials to be sintered, each wheel including two portions with the teeth inclined in opposite directions, said apparatus comprising:

a machine frame;

a pair of separate dies associated with said two portions each having one helical profile corresponding to the inclination of the associated portion of the helical gear wheel;

means for mounting one of said dies stationary with respect to said frame;

a plate rotatably mounting the other one of said dies;

shifting means for shifting said plate in an axial direction with respect to said dies so as to reciprocate the rotatably mounted die between a first position in which it is in contact with the stationary die to a second position in which it is removed from said stationary die;

a pair of plungers associated with said dies, each one having a helical profile in accordance with the inclination of the helical profile of the associated die;

a pair of supports associated with said plungers, each of said supports rotatably mounting one of the associated plungers;

means for moving said supports in said axial direction to cause said plungers to compact the powder in the associated die, and

cam means for causing said rotatable die to rotate during its said shifting movement in accordance with the helix of its own profile, whereby said rotatable die can be removed after the powder compression from the relevant portion of compacted gear wheel.

2. Apparatus according to claim 1, wherein said stationary die normally contacts said rotatably mounted die in a horizontal plane and is superimposed on said rotatably mounted die, the helical profile of the plunger associated with the rotatably mounted die constantly engaging the helical profile of the rotatably mounted die, and comprising a threaded member constantly in engagement with the helical profile of the plunger associated with the stationarily mounted die and connected to the associated support so as to be reciprocably brought in contact with said stationarily mounted die and removed thereform concomitantly with the associated plunger, and locking means for positively positioning said member in an angular fixed position when said member contacts said stationarily mounted die.

3. Apparatus according to claim 1, wherein the cam means comprise a cam with a helically inclined groove and a cam follower disposed radially with respect to the dies and engaging in the groove.

4. Apparatus according to claim 1, comprising a double acting hydraulic cylinder adapted to transmit to the rotatably mounted die, through intermediate means, a torgue commensurate to the value of the frictional couple between the cam and the cam follower during said shifting, whereby the friction between the cam and the cam follower is reduced.

5. Apparatus according to claim 1 comprising elements engagable for locking respectively the rotatable die and the plunger associated therewith, and a pair of simultaneously and oppositely operated double-acting hydraulic cylinders for alternately actuating said locking elements so as to alternately positively lock and release said rotatable die and said associated plunger.

6. Apparatus according to claim 5, wherein said locking elements are formed by a pair of pins, the first of the locking pins being disposed radially with respect to the dies to introduce itself into a corresponding seat in the rotatable die, the cylinder associated with the first locking pin being fixed to the said plate, the second of the said locking pins being disposed radially with respect to the dies to introduce itself into a corresponding seat of the plunger associated with the rotatable die, the cylinder associated with the second locking pin being fixed to the mount controlling the plunger associ ated with the rotatable die.

Claims

1. Apparatus for moulding helical gear wheels by compacting powdered materials to be sintered, each wheel including two portions with the teeth inclined in opposite directions, said apparatus comprising: a machine frame; a pair of separate dies associated with said two portions each having one helical profile corresponding to the inclination of the associated portion of the helical gear wheel; means for mounting one of said dies stationary with respect to said frame; a plate rotatably mounting the other one of said dies; shifting means for shifting said plate in an axial direction with respect to said dies so as to reciprocate the rotatably mounted die between a first position in which it is in contact with the stationary die to a second position in which it is removed from said stationary die; a pair of plungers associated with said dies, each one having a helical profile in accordance with the inclination of the helical profile of the associated die; a pair of supports associated with said plungers, each of said supports rotatably mounting one of the associated plungers; means for moving said supports in said axial direction to cause said plungers to compact the powder in the associated die, and cam means for causing said rotatable die to rotate during its said shifting movement in accordance with the helix of its own profile, whereby said rotatable die can be removed after the powder compression from the relevant portion of compacted gear wheel.

6. Apparatus according to claim 5, wherein said locking elements are formed by a pair of pins, the first of the locking pins being disposed radially with respect to the dies to introduce itself into a corresponding seat in the rotatable die, the cylinder associated with the first locking pin being fixed to the said plate, the second of the said locking pins being disposed radially with respect to the dies to introduce itself into a corresponding seat of the plunger associated with the rotatable die, the cylinder associated with the second locking pin being fixed to the mount controlling the plunger associated with the rotatable die.