Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
  • B62D—MOTOR VEHICLES; TRAILERS
  • B62D3/00—Steering gears
  • B62D3/02—Steering gears mechanical
  • B62D3/12—Steering gears mechanical of rack-and-pinion type
  • B62D3/126—Steering gears mechanical of rack-and-pinion type characterised by the rack
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
  • B21J13/00—Details of machines for forging, pressing, or hammering
  • B21J13/02—Dies or mountings therefor
  • B21J13/025—Dies with parts moving along auxiliary lateral directions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
  • B21K1/00—Making machine elements
  • B21K1/28—Making machine elements wheels; discs
  • B21K1/30—Making machine elements wheels; discs with gear-teeth
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
  • B21K1/00—Making machine elements
  • B21K1/76—Making machine elements elements not mentioned in one of the preceding groups
  • B21K1/767—Toothed racks

Definitions

• the lower side of the "Y" limbs of such racks must act as guide surfaces in the same manner as the cylindrical surface of conventional racks, and hence must be smooth and accurately related to the pitch line of the teeth opposite within a tolerance of .025 mms or less. Machining of these "Y" faces to such a finish and close relationship to the juxtaposed teeth is difficult by known machining methods.
• Such racks do have the advantage that, in forging, the grain of the steel is caused to flow around the contours of the teeth and transverse to their length, so enhancing the rack tooth fatigue strength, as is well known in the art of gear forging.
• Figure 5 shows that provision is made for the formation of side "ribs” by suitable “gutters” on each side of the longitudinal axis of the main cavities of the die as is well known in the art of forging. Furthermore, the process recognises the impracticability of finish forming such teeth to the required accuracy in such dies, either cold or warm, but rather specifies an initial operation be carried out at the conventional forging temperature (generally over 1000°C) .
• the present invention provides a die suited to the forming of steering rack bars of. the configuration described which fulfils all the above needs. Furthermore the invention makes possible a low cost method of making such steering racks involving fewer steps and wasting less material than the prior art. Finally, the invention makes possible the manufacture of a rack of improved design incapable of being manufactured by any other known technique.
• the present invention consists in a die for forming a Y-form rack portion of a steering rack bar from a blank by forging, the rack section having teeth formed on one face and on the opposite face thereof, at least two longitudinally extending guide faces, the die comprising a group of at least three forming elements relatively movable on application of forging pressure to the die to converge on a blank placed therein, a first of said forming elements having in it cavities the shape of which correspond to the shapes of the teeth to be formed, second and third forming elements having forming faces adapted to form the said longitudinal guide faces, the said three forming elements being shaped and arranged to move in such a manner to inhibit escape of the material of the blank between said first and second or first and third forming elements up to substantially the last instant of closure of the die.
• the present invention further consists in a die as claimed in claim 1 wherein the second and third forming elements are symmetrically disposed about a longitudinal plane corresponding to the plane of symmetry of the rack portion to be formed and have between them a fourth forming element shaped and arranged to guide said second and third elements while converging on the blank and having a face arranged to form the surface of the rack portion lying between said guide faces.
• the present invention still further consists in a Y-form rack bar when made in a die or by a method as defined in the last preceding paragraphs.
• a die according to the invention ensures full containment of the blank material right up to the last instant of closure and forces it into the toothed cavity section of the die from at least two directions simultaneously, so preventing escape of material and focusing and intensifying the forming pressure within the toothed die cavity.
• the die is suited to use in a single-direction impact press and can re-direct the impact in several directions simultaneously without loss due to friction.
• the die preferably includes means to restrain the blank material in a gripper system which provides longitudinal restraint and ensures exact alignment of the formed rack section to the non-worked cylindrical blank section; thereby no further finish machining of the cylindrical end is required, saving material cost and manufacturing operations.
• the die in a preferred form comprises in section a relatively fixed element containing cavities corresponding to the teeth of the rack including the oblique ends of the teeth, and movable elements having symmetrically disposed forming faces which converge towards the relatively fixed element and towards 'each other during the closing of the' die.
• the two principal forming faces are incorporated in rolling die elements having convex, part-cylindrical surfaces on the ends thereof remote from the forming faces, which surfaces bear on concave recesses in the die bolster opposing that which carries the relatively fixed die element containing the teeth.
• Fig. I illustrates a rack made according to the invention
• Fig. II is a cross sectional view of the rack on line - 8 -
• Fig. Ill is a sectional elevation of a die according to the invention, which is cross-hatched for clarity;
• Fig. IV is a sectional view of the die on line C-C of Fig. 5 III, also cross hatched;
• Fig. V is a sectional view of the die on line D-D of Fig. Ill, also cross-hatched;
• Fig. VI is an end view to an enlarged scale of the central part of Fig. IV; 0 Fig. VII, VIII and IX are scrap views to an enlarged scale of a part of Fig. VI showing progressive stages of forming; and
• Fig. X is a view similar to Fig. IV of an alternative form of construction of a die suitable for cold forming racks.
• Fig. 1 shows a typical Y form rack bar made according to the invention comprising toothed portion 1 and cylindrical portion 2.
• the ends of the rack are threaded as at 3 for the attachment of ball joints and tie rods.
• tie rods are fastened to the rack by rubber 0 bushed studs located near the vehicle centre line, for which purpose the cylindrical part may be locally enlarged, drilled and tapped. The method to be described applies also to the manufacture of such racks.
• Fig. II shows the appearance in section of the toothed 5 portion of the Y form rack seen at A-A of Fig. I and by diameter 13, the cylindrical section 2 of the rack bar.
• opposing guide faces 4 and 5 are symmetrically disposed about vertical axis 6 at an included angle 7 of, say, 90 .
• Teeth 8 terminate in oblique faces 9 0 and 10 in order to make optimum use of the space available in the in-side of the steering housing tube, indicated by circle 11, centered at 12.
• Such oblique ends of the teeth of the rack also serve to reduce the chance of breakage of the teeth adjacent their ends.
• the cylindrical portion 2 indicated by 5 line circle 13 is also centred at 12. The diameter is chosen 9 -
• the stem of the "Y", 14 preferably has a slight taper of its opposing flanks as indicated by angle 15, giving it a dovetail shape.
• guide faces, 4 and 5 may be either convex or concave and arranged at an angle 7 other than 90 degrees, and stem 14 may have parallel sides or sides tapered opposite to that shown.
• guide faces 4 and 5 may extend to meet or to form * a flat or radius.
• Figs. Ill, IV and V show a preferred construction of a die for making racks of the type described, as installed in a press (not shown) , having a movable platen 20 and fixed lower platen 21.
• the die comprises an upper-half die 22 and a lower-half die 23 secured to the respective upper and lower platen 20, 21, of the press and in each of the three views are shown in the fully closed position as when rack bar 25 has been fully formed.
• the dies separate along axis 24 of rack 25 and upper platen 20 moves to raised position 20a for removal of the finished rack and insertion of a new blank to be formed.
• the die has two zones along the length of the rack, a gripping zone 38, and a forming zone 39, (Fig. Ill) .
• gripping zone 38 As the upper-half die, 22, descends, gripping zone 38, a section of which is shown in Fig. V, first engages rack bar blank 25 after which the several elements of forming zone 39 shown in section in Fig.. IV form the entire toothed end of the rack in one blow.
• Gripping zone 38 comprises an upper gripper 29 and a lower gripper 40 each having grooves semi-circular in section engaging rack bar blank 25 and loaded respectively by springs 32 and 42.
• Lower gripper 40 is secured to plunger 41 which is urged upwards by spring 42 housed in a chamber of lower bolster 27 of lower-half die 23. Downward movement of plunger 41 is limited to the position shown because its shoulder strikes abutment 53 of the lower bolster, and upwards movement is limited by collar 43 striking a similar abutment. Typically such upward movement is about 6mm and a gripping force is provided by spring 42.
• Upper gripper 29 (Fig. Ill) is secured to plate 28 which is urged downwards by springs 32.
• Plate 28 also carries upper die member 30 and block 31.
• Plate 28 is guided in upper bolster 26 through the action of guide pins 33 slidably journalled in upper bolster 26.
• Springs 32 act on the enlarged heads of guide pin 33.
• Plate 28 is limited in its downward travel by stop blocks 36 and 37 to about 8 mm as indicated by gaps 34 and 35 between plate 28 and respective stop blocks 36 and 37.
• FIG. IV it will be seen that in the fully closed position the rack is contained by four die elements; lower, toothed die 44, hinged dies 47 and 48 and upper die member 30.
• Flank dies 45 and 46 may be made in one part with lower toothed die 44 but are here shown as being made separately for convenience of manufacture and servicing.
• Rolling dies 47 land 48 are supported by fulcrum blocks 49 and 50 secured to upper bolster 26.
• Fig. VI is an enlarged scrap view of part of Fig. IV, showing on the right side the position of the various die elements in the fully closed position as in Figs. Ill, IV and V, and on the left side the position of the elements of the die as the forming in zone 39 commences.
• Half circles centred at 24a and 24 illustrate the corresponding initial and final positions of the cylindrical portion of the rack bar blank 25.
• the rack forming sequence of events is as follows:- The cylindrical blank is loaded lengthwise into the open die resting on lower toothed die 44 and lower gripper 40 in its upper position and axially against end stop 51 which is pivotal about centre 52.
• upper gripper 29 first grips the cylindrical blank, (left-hand side Fig. VI) and as the die continues to close lower gripper 40 moves down (right-hand side Fig. VI) against the holding force of spring 42, until the shoulder of plunger 41 contacts the abutment 53 and the stop block 31, secured to plate 28, contacts end stop 51, thereby its downward motion is arrested.
• Upper die member 30 has now reached its fully closed position relative to lower toothed die 44.
• Figs. VII, VIII and IX The closing of the die is illustrated in Figs. VII, VIII and IX.
• Fig. VII corresponds to that shown on the left side of Fig. VI where the downward motion of plate 28 has been arrested and forming of a blank has just commenced.
• Fig. VIII corresponds to the mid stroke, where the cylindrical blank has been deformed approximately as indicated by the dotted area 56.
• Fig. IX corresponds to the final position to that shown on the right side of Fig. VI where forming is complete including forming of the teeth.
• rolling dies 48 and 47 concentrate or focus the forming pressure in the toothed cavities of lower die 44, the most important area of the die to fill. Because rolling die 48, Fig. IX, is in contact with the flank die 46 for the last part of its travel, there is no place for the metal being formed to escape and hence become entrapped between the two die elements 48 and 46. Thus the highly-desirable, fully contained die cavity is provided.
• upper die member 30 may be shortened (while still acting as a guide for rolling dies 5 47, 48) so that the top of stem 14 remains rounded and is not - 13 -
• rolling die 48 has a convex, part-cylindrical face 62, having a centre 63 engaged with a concave part-cylindrical seat 64 of the fulcrum' block 50, having a centre 65.
• Contact between the face of 48 and seat of 50 must occur where the line joining 63 and 65 intersect them as at 68.
• the corresponding centres for the "up" position of the die are shown on the left side of Fig. VI and are indicated by 66 and 67, and in a similar manner contact between the,seats will occur at 69. Very great loads can be carried between surfaces having nearly the same curvature.
• rolling dies 47 and 48 are maintained in their correct rolling relationship to fulcrum blocks 49 and 50 at all times by gear tooth-like abutments 72 and 73 of fulcrum blocks 49 and 50, which engage corresponding abutments of hinged dies 47 and 48.
• the weight of rolling dies 47 and 48 may tend make them depart from upper die member 30 in the open die position.
• a small spring (not shown) serves to ensure that contact as at 70 is maintained.
• Fig. X of another preferred embodiment is intended for use in the manufacture of racks by cold working.
• die elements 47 and 48 hereinbefore referred to as the rolling dies ' are replaced by oscillatory dies 74 and 75.
• the particular feature of the arrangement is the manner in which the working face of the die does not merely travel along line 57 as represented in Fig. VII, VIII and IX but, in addition, oscillates or rolls from side to side.
• face 55 of the rack be a flat face
• the working face 55 of oscillatory die 75 may be in the form, in section, of part of cylinder, or other appropriate form.
• sliding block 76 In the configuration shown in Fig. X fulcrum blocks 49 and 50 are omitted and in their place is installed a sliding block 76.
• This sliding block is capable of an oscillatory movement of typically around 15mm. as indicated at 77, under the action of hydraulic cylinder 78 whose piston rod is attached to sliding block 76.
• the lower face of sliding block 76 is formed as part of a cylindrical surface 79, having a longitudinal axis centred at 80.
• sliding block 76 On this cylindrical surface is arranged to slide oscillatory die holder 81 to which is secured oscillatory die 75. Both the upper and lower surfaces of sliding block 76 are equipped with pockets into which is forced a fluid at extremely high pressure so that the free motion of the sliding block under the action of cylinder 78 is permitted without excessive friction.
• cylinder 78 oscillates the sliding block over distance 77, so causing the longitudinal axis of cylindrial surface 79 to oscillate over the distance 82 which is of the same magnitude as distance 77.
• oscillatory die 75 oscillates through some angle 83 so that its working face which as stated earlier may be part of a cylinder, having a longitudinal axis centred at 80 rolls cyclically across the longitudinal guide surface of the rack being formed.
• the left hand of the die arrangement which is symmetrical with that just described and provision is made so that the oscillation- of the left hand sliding block is co-ordinated with that of the right sliding block.
• a carbon steel for example 1050 steel
• a die of this construction may be formed in a manner which may not be possible in the die described earlier because of the onset of work hardening typical of such materials- It will be appreciated however that the construction of such a die is significantly more complex and thus more costly than that described in connection with Fig. VI.
• the entire die can be placed in a conventional forging or hydraulic press and the angular motion of the die elements described is obtained by the mechanism of the die itself.
• a special press could be constructed in which the downward and inward travel of the presently rolling die elements is replaced by direct travel of the angled dies along, for example, line 57.
• Such a press might be particularly advantageous if it were of hydraulic operation in that it ' would be very compact and of relatively low cost providing that a number of such presses were to be made.
• a forging press having two angled rams would be complicated and expensive machine.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Transportation (AREA)
• Forging (AREA)
• Gears, Cams (AREA)

Priority Applications (2)

Applications Claiming Priority (3)

Publications (1)

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ID=25616077

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Citations (6)

• 1983
  • 1983-06-02 WO PCT/AU1983/000073 patent/WO1983004197A1/en active IP Right Grant
  • 1983-06-02 JP JP58501806A patent/JPS59501004A/ja active Granted
  • 1983-06-02 AU AU15579/83A patent/AU554157B2/en not_active Expired

Patent Citations (6)

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