MXPA06006262A - Steering rack manufacture - Google Patents

Abstract

A die apparatus and method for performing a flashless forging operation to manufacture the toothed portion of a steering rack. The die apparatus comprising first and second die members and at least one punch member, each having a forming surface shaped substantially as the obverse of a portion of said toothed portion, and at least a portion of the forming surface of said first die member being shaped substantially as the obverse of the teeth of said rack. Said first and second die members being moveable towards each other to a closed position thereby partially forging said toothed portion from a blank placed in said die apparatus and forming a substantially closed cavity defined by said forming surfaces, said punch member being adapted to move into said cavity, once said die members are in said closed position, thereby completing said forging operation.

Description

MANUFACTURE OF STEERING ZIPPER TECHNICAL FIELD The present invention relates to a die for forging a steering rack and in particular to a die for a burrless forging of an automotive steering rack.

BACKGROUND OF THE INVENTION The toothed portions of the automotive steering racks are known to be produced by a process of either machining or forging. Typically, the machining process comprises a reaming through a solid cylindrical bar which causes the cross section of the serrated portion to have a "D" shape and thus these racks are commonly referred to as "D" racks. Steering racks that have machined teeth can only be mass produced inexpensively with teeth with constant pitch. However, zips having forged teeth can also be produced in mass with teeth with constant or variable pitch. The term "burr" when used with respect to forging refers to the surplus material that extends outside the body of a component, a forged component and which must typically be removed by a roughing or machining operation. Burr is a common feature of the open-die forging, in which case the excess material is placed in the die to ensure complete filling of the die cavity. The term "burrless forging" refers to a forging process in which virtually no excess material is allowed to escape from the die cavity. The advantages of non-burring forging include the elimination of waste material, elimination of subsequent operations to remove the flash, and greater control over the precision of the forged component. Burr-free forging is typically achieved using a closed die. U.S. Patents 4,571, 982 (Bishop) and ,862,701 (Bioshop et al) describe a die apparatus for the forging without hot flashing of the toothed portion of a steering rack to a net shape of a solid cylindrical bar. "Net shape" means that forged rack teeth do not require additional machining after forging. This type of die apparatus is limited to the forging of racks wherein the cross section of the toothed portion has a "Y" shape and such racks are commonly referred to as "Y-racks". It is important to note that this type of die apparatus only forms a closed slab cavity at the end of the forging process as can be seen in Figures 7, 8 and 9 of US 4,571, 982, and the substantially dented burrs result from the movement unique of the machining elements and the "Y" shaped cross section of the toothed region, instead of closing the slab cavity prior to the forging operation. A disadvantage of Y-zips is that they require modification of the steering gear to allow reassembly and as such the market has historically preferred D-racks. Several types of die fixtures have been proposed to forge D-racks from a solid bar However, most of these dice produce burr. Figures 3 to 5 of JP 58218339 (Daido Steel Co Ltd) illustrate a basic open die apparatus comprising only two die halves. The surplus material simply escapes from the die cavity as a burr. This die apparatus does not provide a means for controlling the pressure in the cavity and as such the filling of the resulting tooth is likely to be deficient, in particular if the forging operation is carried out at warm forging temperatures instead of hot forging. Figure 5 of JP 58219339 illustrates the process of roughening the burr after its forging. GB 2108026 (Cam Gears Ltd) discloses a die apparatus for forging a D-rack from a solid bar. This is a basic die apparatus having two halves with the addition of directed burr chutes to control the formation of the burr and assist tooth filling. Nevertheless, material can still escape prematurely into these burr chutes, thus limiting the assumed hydrostatic pressure that can be caused by underfilling the die cavity. The burr produced by such die apparatus has a more controlled shape than that produced by a simple open die, but the burr would have to be removed even after forging. A more sophisticated die apparatus using a similar principle is described in US 5,992,205 (Bishop), which is directed to forming the burr chutes to maintain a suitable hydrostatic pressure and with. This will help achieve an adequate tooth filling. The die apparatus for forging solid D-racks is described in JP 58013431 (Jidosha Kiki Co Ltd) and 03138042 (IS Seiki KK et al.). Both dice forge resulting serrated portions that better surround the diameter than the finished rack rod, which is usually the nominal diameter of the bar material. Such zippers have the same assembly problems that Y-zips. Moreover, both sides only comprise two halves and as such in practice it is unlikely to completely close and fill the teeth without forming burrs between die halves. Figures 8 to 12 of JP 58218339 (Daido Steel Co Ltd) illustrate a closed die apparatus for forging a steering rack from a hollow tube. This die is closed before the forging starts and therefore the forging process would be substantially burr-free. The punch 56 of this die arrangement has a shape that forges the teeth of the rack. Punch 56 moves inward to perform the forging operation after the die halves 58 and 50 close around the. hollow tubular preform. The problem with this die arrangement is that the ends of the teeth in the punch 56 are open and as such there is no support between the ends of the teeth, which would cause premature failure of the die. Furthermore, the ends of the forged teeth are perpendicular to the teeth, instead of sloping towards each end, which would interfere with the assembly of the rack. It is an object of the present invention to provide a thin apparatus and a method for forging without steering rack burr which reduces at least some of the problems of the prior art.

BRIEF DESCRIPTION OF THE INVENTION In a first aspect, the present invention consists of a die apparatus for performing a burrless forging operation for manufacturing the toothed portion of a steering rack, said die apparatus comprising first and second die elements and at least one element punch, each with a forming surface substantially formed as the obverse of a portion of said notched portion, and at least a portion of the forming surface of said first die member substantially formed as the obverse of said teeth. rack, characterized in that said first and second die element move towards each other to a closed portion, thus partially forging said toothed portion from a preform placed in said die apparatus and form a substantially closed cavity defined by said surfaces of said die. formation, said punch element being adapted to move within said cavity, a once said die elements are in said closed position, thus completing said forging operation. Preferably, in one embodiment, said punch member moves within said closed cavity through an opening in one of said die elements. Preferably, said opening is in said second die element and said punch element moves with respect to said second die element. Preferably, said punch element is disposed substantially centered and opposite said first die element, and moves towards said first die element. Preferably, said die elements abut against each other in said closed position. Preferably, in another embodiment, said at least one punch element comprises first and second punch pins disposed on opposite sides of said cavity, between said first and second die elements. Preferably, said punch element is moved by a mechanism operated by the movement of said closure of the die apparatus.

Preferably, said mechanism comprises at least one wedge element adapted to urge said punch element into said cavity. Preferably, at least one of said die elements is supported by a pressurized hydraulic cylinder by means of said die apparatus closure.

Preferably, the cross section of said toothed portion is substantially D-shaped. Preferably, said preform is a solid bar. Preferably, said preform is cylindrical. Alternativelysaid preform is a hollow bar and said die apparatus further comprises a mandrel adapted to be inserted into said hollow bar prior to said forging operation. Preferably, said die apparatus further comprises at least one axially movable end punch. Preferably, said end punch is adapted to emphasize one end of said preform. In a second aspect, the present invention is a method for manufacturing a steering rack comprising performing a forging operation in a preform by a die apparatus in accordance with the first aspect of the present invention. Preferably, the teeth of said steering rack are forged to a net shape by said forging operation. Preferably, the cross section of the toothed portion of said steering rack has a substantially D-shape. Preferably, said preform has a first cylindrical portion and a second cylindrical portion of smaller diameter than said first cylindrical portion, said second cylindrical portion being Forging to form the toothed portion of said steering rack, the stem of said steering rack comprises said first cylindrical portion.

Preferably, said preform further comprises a third cylindrical portion, of diameter substantially equal to said first cylindrical portion, said second cylindrical portion being between said first and third cylindrical portions. Preferably, said preform is heated to a warm forging temperature prior to said forging operation.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a first embodiment of a die in accordance with the present invention. Figure 2 is a perspective view of the die shown in Figure 1 partially sectioned along the plane 22. Figures 3a-d are a series of views of the die shown in Figure 1 sectioned along the length of the 24 plan showing the steps to forge a steering rack. Figure 4 is a perspective view of a second embodiment of a die in accordance with the present invention. Figure 5 is a perspective view of the die shown in Figure 4 partially sectioned along the plane 62. Figures 6a-d are a series of views of the die shown in Figure 4 sectioned along the length of the 64 plane showing the steps to forge a steering rack.

Fig. 7 is a perspective view of a steering rack using the die shown in Fig. 4. Fig. 8, 9 and 10 show a schematic arrangement of a complete die apparatus incorporating the die shown in Figs. Figure 4. Figure 11 is a sectioned perspective view of a third embodiment of a die in accordance with the present invention. Figure 12 is a partially sectioned perspective view of a fourth embodiment of a die in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Figures 1 and 2 illustrate a first embodiment of a die 10 in accordance with the present invention. The die 10 comprises a first die element 14, a second die element 16 and a punch element 18. The rack 12 is forged using the die 10 in combination with a suitable forging press, such as that described in US 3,802,248 (Ross et al), in which the die elements 14 and 16 are attached to the platens of the press. The zipper 12 is a D-rack comprising the arrow portion 25 and the toothed portion 26, which may be of the type having gear teeth with constant pitch or of the type having gear teeth with a variable pitch. - "Figures 1 and 2 show the die 10 at the end of the forging process with the first die element 14 abutting the second die element 16 to form a closed cavity 13. The punch element 18 moves with respect to the second element of die 16 through the opening 11 in a second die member 16. The opening 11 allows the punch member 18 to enter the cavity 13. Referring to Figure 3a, the first die member 14 has a forming surface toothed 18 with a shape that is the obverse of the shape of the teeth of the rack 12. The forming surface 19 of the second die member 16 is substantially semicircular in shape and is the obverse of the portion of the toothed portion 26 that is slides in a rack shoe when the rack 12 is assembled in a steering gear The punch element 18 is disposed centrally about the axis of symmetry of the toothed portion 26 and opposite the first track element. 14. The punch element 18 moves towards the first die member 14 and has a forming surface 29 that forms a longitudinal longitudinal mark on the back of the toothed portion 26. The operation of the die 10 is illustrated by the figures 3a to 3d, which are seen in section along the plane 24 (Figure 1) illustrating several steps of the process of forging without burring the toothed portion 16 of the rack 12. Figure 3a shows the die 10 at the beginning of the process forging with the preform 12a seated on the second die member 16 and the first die member 14 moved towards the second die member 16 such that the toothed forming surface 28 touches the preform 12a. The punch element 18 is retracted with respect to the second die element 16 such that its forming surface 29 is substantially flush with the semicircular forming surface 19 of the second die element 16. The preform 12a has the shape of a solid cylindrical bar .

For the assembly of the forged rack 12 in a steering gear, it is desired that the diameter of a circle surrounding the toothed portion 26 is not greater than the diameter of the arrow 25 of the rack 12. This can be achieved by staggering towards down the bar 12a so that the portion thereof that is forged to become the toothed portion 26 is of smaller diameter than the portion that remains as the arrow 25 of the rack 12. The bar 12a may be stepped so that it only has two portions, a larger diameter portion that becomes the arrow 25 of the steering rack and a smaller diameter portion that is forged to become the toothed portion 26. Alternatively, the bar 12a may have three portions, a portion of smaller diameter, which is forged to become the serrated portion 26, between two larger portions that are of a substantially equal diameter. One of the larger diameter portions forms the arrow 25 of the rack and the other forms the opposite coupling bar end. In Figure 3b, the first die member 14 has moved towards the second die member 16 partially forging the toothed portion 26 from the preform 12a. During this step, the semicircular forming surface 19 is substantially filled. In Figure 3c, the first die member 14 has moved more towards the second die member 16, partially and additionally forging the toothed portion 26 until a closed position is reached in which the first die member 14 abuts the second die element 16. This forms a closed cavity 13 defined by the forming surfaces 28, 19 and 29. The teeth of the notched portion 26 is not yet fully formed as indicated by the unfilled portions 30 of the closed cavity 13. During the steps shown in Figures 3b and 3c, the punch element 18 has remained static with respect to the second die element 16. However, in other embodiments that are not shown, the punch element 18 can move with respect to the second die element 16 as the die elements 16 and 14 move towards each other. Figure 3d shows the final step of the forging process, with which the punch element 18 moves up and into the closed cavity 13, creating a high pressure inside the preform 12a such that it fills the forming surface 28. The burr can not be formed during this step because the cavity 13 is already closed. The teeth of the serrated portion 26 are forged to the net shape and no finishing machining is required. The movement of the portion element 18 can be effected by a linkage arrangement connected to the press ram, or an alternative actuation means can be used.

During this step, the die elements 14 and 16 remain static with respect to each other. Die 10, and other embodiments described herein, can be used for hot, warm or cold forging of steering racks. However, the use of the warm forging in which a steel preform is heated to a temperature of the order of 500 ° C to 900 ° C is preferred. Figures 4 and 5 illustrate a second embodiment of a die 50 in accordance with the present invention. The die 50 comprises a first die element 54, a second die element 56 and two punch elements 58. Similar to the first embodiment, the die 50 is used together with a suitable forging press to forge the rack 52 having a toothed portion 66. Die 50 is similar to die 10, except that die 50 has two punch elements 58 instead of a single punch element 18. Having two punch elements 58 that exert slab load instead of only one is convenient because it improves the control of the forging process. The punch elements 58 are disposed on opposite sides of the die 50, between the data elements 56 and 58. The punch elements 58 are adapted to move simultaneously towards the center of the die, with respect to the second die element 56. There is a minimum gap between the punch elements 58 and the second die element 56. Referring to Fig. 6a, the first die member 54 has a tooth-forming surface 78 with a shape which is the obverse of the shape of the teeth of the rack 52. The forming surface 69. of the second die member 56 has a substantially semicircular shape and corresponds to the surface of the toothed portion 66 that slides on a rack shoe when the rack 52 is assembled in a steering gear. Each punch element 58 has a forming surface 79 that forges surface longitudinal marks 72 on either side of the serrated portion 66, as is seen lighter in Figure 7. It is an advantage to have marks 72 on both sides of the serrated portion. , instead of a single mark opposite the teeth as in the rack 12, since it maximizes the contact area between the toothed portion and a rack shoe. The operation of the die 50 is illustrated by FIGS. 6a to 6d, which are seen in section along the plane 64 (FIG. 4) illustrating various stages of the non-burring forging process of the toothed portion 66 of the rack 52. Figures 6a to 6d are similar to Figures 3a to 3d illustrating the operation of the die 10. Figure 6a shows the die 50 at the start of the forging process with the preform 12a seated on the second die member 56 and the first die element. given 54 displaced towards the second, die element 56 such that the toothed forming surface 78 touches the preform 12a. The punch elements 58 are retracted with respect to the second die member 56 such that their forming surface 79 remains substantially flush with the semicircular forming surface 69 of the second die element 56.

In Figure 6b, the first die member 54 has been moved to the second die member 56 by partially forging the toothed portion 66 from the preform 12a. During this step, the semicircular forming surface 69 is substantially filled. In Figure 6c, the first die member 54 has moved further towards the second die member 56 by further partially carving the toothed portion 66 until a closed position is reached in which the gaps between the first die element 54 and the punch elements 58 have been closed. This forms a closed cavity 63, defined by the forming surfaces 78, 69 and 79. The teeth of the notched portion 66 have not yet been fully formed as indicated by the unfilled portions 70 of the closed cavity 63. During the steps that shown in Figures 6b and 6c, the punch elements 58 have remained static with respect to the second die member 56. However, in other embodiments that are not shown, the punch elements 58 can be moved relative to the second die member 56. as the die elements 54 and 56 move towards each other. Figure 6d shows the final step of the forging process, with which the punch elements 58 simultaneously move radially within the closed cavity 63 through the openings formed between the die elements 54, 56, creating a pressure elevated within the preform 12a such that it fills the toothed forming surface 78. No burrs can be formed during this step because the cavity 63 is already closed. During this step, die elements 54 and 56 remain static with respect to each other. The teeth of the serrated portion 66 are forged to the net shape and a finishing machining is not required. Figure 7 shows the rack 52 forged by the die 50. Figures 8, 9 and 10 show a schematic arrangement of a complete die apparatus 81 incorporating the die 50 shown in Figure 4. The die 50 comprises the first die element 54, the second die element 56 and two punch elements 58. The first die element 54 is fixed to the carrier 82 which in turn is attached to the arrow 83 that moves vertically within the first crosspiece 84. carrier 82 is shod by a means that is not shown. The hydraulic piston 85 is attached to the arrow 83 and moves inside a cylinder 86 formed in the first cross member 84. The second die member 56 is joined to the second cross member 87. The punch elements 58 are attached to blocks 88, each one movable horizontally with respect to the second cross member 87. The blocks 88 bump against the wedge elements 89, which move vertically with respect to the second cross member 87 and are deflected upwards by means of springs 90. Figure 8 shows the die apparatus 81 in its open position - with a preform 12a loaded on it. The cylinder 86 is filled with hydraulic fluid 91 through the port 92. The wedge elements 89 extend upwardly by springs 90, which retracts the punch elements 58 to allow sufficient clearance to load the preform 12a.

Figure 9 shows the die apparatus 81 in a position during the forging operation corresponding to the position of the die 50 shown in Figure 6c. As the first cross member 84 moves downward, the gap between the first die element 54 and the punch elements 58 closes to form a closed cavity. In this position, the first die element 54 is supported by stops that are not shown so that the elements of die 58 are not embraced by the die elements 54 and 56. There is a small gap between the die element 54 and the elements Punch 58 can allow the last 58 to move freely. Once the first die element 54 has reached the closed position, it remains in that position for the remainder of the forging operation and an additional downward movement of the spout 84 moves the piston 85 relative to the cylinder 86, which forces the hydraulic fluid 91 outwardly from port 92. Port 92 is connected to a relief valve, carriage valve, accumulator or other device for controlling the hydraulic pressure in cylinder 86 as a function of the flow to Through port 92. By this means sufficient pressure can be generated in the hydraulic fluid 91 to react against the forging loads in the first die element 54 and to maintain the die element 54 in its closed position. As the first cross member 84 moves downward, it contacts the upper surfaces of the wedge members 89, thus pushing the wedge members downwardly relative to the second cross member 87. As the wedge members 89 are pushed downward, they push the members downwardly. blocks 88 and the elements of punch 58 denier of the closed cavity. Figure 10 shows the die apparatus 81 at the end of the forging operation corresponding to the position of the side 50 that is shown in Figure 6d. Enlarge the positions shown in Fig. 9 and Fig. 10, the die element 54 remains skeletal while the first shaft 84 continues to move downward, thus moving the punch elements 58, by means of wedge elements 89, respectively. Closed cavity to complete the forging operation to form the denoted portion 66. Figure 11 illustrates a third embodiment of a die 100 in accordance with the present invention. Unlike the zippers produced in the first and second embodiments, the zipper 112 is not a full length zipper and will need to be attached to a portion of arrows before it is inserted into a steering gear of a vehicle. A method for attaching portions of zip fasteners to arrow portions is described in JP 06207623 (Sekiguchi Sangyo KK). The die 100 differs from the dies of the previous embodiments in that it includes an axial punch element 108 and a mandrel element 110. The axial punch element 108 provides an effective conirol over the forging process as well as a means to control the length of the die. end of the zipper 112.

The axial punch 108 is used in combination with radial punch elements 106 (only one is shown) in the same manner in which the punch elements 18, 58 are used in the first and second embodiments, differing only by the addition of the element of mandrel 110, which is required for a hollow zipper. The mandrel element 110 is inserted into the bore 113 of the zipper 112 before applying any slab load; that is, before any relative movement of the die elements 102, 104 occurs. The mandrel member 110 is removed once the forging process is completed to leave a hollow zipper 112. The hollow zippers are desired in gears of direction of vehicles for its light weight and less consumption of material. Figure 12 illustrates a fourth embodiment of a die 150 in accordance with the present invention. The die 150 comprises the first die element 152, second die element 154 and punch elements 159 corresponding to the members 54, 56 and 58 respectively of the die 50. The die 150 differs from the die 50 of the second embodiment of the invention in which it additionally includes a first axial groove punch 156 and a second axial punch groove 158. The die 150 forges the rack 160, which like the rack 112 is a short rack that must be attached to an arrow element to complete a steering rack. The axial end punches 156 and 158 move in the direction of the longitudinal axis of the rack 160. The axial end punches 156 and "158 can be moved either simultaneously with the die elements 152 and 154 or they can start moving after the die elements 152 and 154 have been moved to a closed position.The axial end punches 156 and 158 move axially within the die to impress the ends of a preform 12a that is being forged, thus increasing the diameter of the forged zipper. 160. It should be understood that forged zippers that are illusive in the above embodiments are shown with their characteristic features, such as the mating faces of their teeth and the punch element, as solid lines suggesting that the die cavity could be completely filled. The practical degree of filling could not be achieved nor is it desirable in a mass production, that is to say, a commercial forged zipper. It would desirably show some degree of under-filling, which is set by the rounded charac- teristics. It should also be understood that for reasons of clarity, various supports, trunnions, bearings and conirol units have been omitted from the figures. Although the present invention has been shown in the present and has been described in four modalities, it is recognized that changes of and combinations of these modalities can be made without departing from the scope of the invention. In addition, the present invention is primarily intended to be used for forging steering racks made of steel but can also be used in a highly effective manner with forging metal heads.

The term "comprising" as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consists solely of".

Claims (27)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A die apparatus for performing a burrless forging operation to fabricate the denoted portion of a steering rack, said die apparatus comprising first and second die elements and at least one punch element, each with one forming surface substantially as the obverse of a portion of said denoted portion, and at least a portion of the forming surface of said first die member formed substantially as the front of the teeth said rack, wherein said first and second die elements move one towards the ear to a closed position, thus partially forging said portion of the die from a preform placed in said die apparatus and forming a closed substantially closed cavity defined by said forming surfaces, said punch element being adapted to move within said cavity, once said die elements are in said p closed position, thus completing the forging operation.
2. 2. The die apparatus according to claim 1, further characterized in that said punch element moves from said closed cavity through an opening in one of said die elements. 3. - The die apparatus according to claim 2, further characterized in that said opening is in said second die element and said punch element moves respecio to the second die element. 4. The die apparatus according to claim 3, further characterized in that said die element is "arranged substantially censed and opposite said first die element and moves towards said first die element. given in accordance with claim 1, further characterized in that said die diameters have one in the said closed position 6. The die apparatus according to claim 1, further characterized in that said at least one punch element It comprises first and second punch elements disposed on opposite sides of said cavity, said first and second die elements. 7.- The die apparatus according to claim 1, further characterized in that said punch element moves by means of a mechanism operated by the movement of said closing of the die apparatus 8. The die apparatus according to the claim n 7, further caracíerizado that said mechanism comprises at least one wedge elemenío insíar adapíado to said punch elemenío Deniro said cavity. 9. - The die apparatus according to claim 1, further characterized in that at least one of said die elements is supported by a pressurized hydraulic cylinder by means of said die apparatus closure. 10. The die apparatus according to claim 1, further characterized in that the transverse section of said toothed portion is substantially in the form of D. 11. The die apparatus according to claim 1, further characterized in that said preform It is a solid bar. 12. The die apparatus according to claim 1, further characterized in that said preform is cylindrical. 13. The die apparatus according to claim 1, further characterized in that said preform is a hollow bar and said die apparatus further comprises a mandrel adapted to be inserted into said hollow bar prior to said forging operation. 14. The die apparatus according to claim 1, further characterized in that said die apparatus further comprises at least one axially movable end punch. 15. The die apparatus according to claim 14, further characterized in that said extrusion punch is adapted to emphasize an eximetry of said preform. 16. A method for manufacturing a steering rack comprising performing a forging operation in a preform by means of a die apparatus according to any of claims 1 to 16. 17.- The method for manufacturing a steering rack in accordance with claim 16, further characterized in that the teeth of said steering rack are forged to a net shape by said forging operation. 18. The method for manufacturing the steering rack according to claim 16, further characterized in that the transverse section of the denoted portion of said steering rack is in the form of a D.sub.lanially. 19. The method for manufacturing the rack of direction according to claim 16, further characterized in that said preform has a first cylindrical portion and a second cylindrical portion smaller in diameter than said first cylindrical portion, said second cylindrical portion is forged to form the toothed portion of said steering rack, the arrow of said steering rack comprises said first cylindrical portion. 20. The method for manufacturing the steering rack according to claim 19, further characterized in that said preform also comprises a cylindrical portion, of diameter substantially equal to said first cylindrical portion, said second cylindrical portion being between said and first and third cylindrical portions. 21. - The method to manufacture the steering rack according to claim 16, further characterized in that said preform is heated to a warm forging lemperairy prior to said forging operation. 22. A steering rack made by the method according to claim 16 wherein the toothed portion of said steering rack has two opposite longitudinal marks on either side thereof, said marks being formed by said forging operation. 23. A steering rack comprising a portion denoted in which said denoted portion has two opposing longitudinal marks on either side thereof. 24. The steering rack according to claim 23, further characterized in that the transverse section of said denoted portion is substantially in the form of D. 25.- The steering rack according to claim 23, further characterized because said portion denoted It is manufactured by a forging process. 26. The steering rack according to claim 25, further characterized in that said marks are formed during said forging process. 27. - The steering rack according to claim 25, further characterized in that the dienis of said toothed portion are forged to a net shape.