Patent Publication Number: US-2012030929-A1

Title: Method for producing a component of a synchronization device for a manual transmission

Description:
The invention relates to a method for producing a component of a synchronization device for a manual transmission according to the preamble of claim  1 , and also to a component of a synchronization device for a manual transmission. 
     Such a method is known from DE 35 19 811 52. Here, a round blank which has been stamped from a metal sheet is subjected to a multiplicity of cold forming steps in succession. In order to produce a specific predefined contour extending merely over a partial portion of the component, e.g. toothing, a plurality of successive cold forming substeps are often additionally required. In this case, firstly preforms of the contour are produced, and the contour is finally produced in a last cold forming substep. For each of the cold forming substeps, it is necessary to provide a complex and expensive forming tool. If the contour changes, it is necessary to change the corresponding forming tools. As a whole, the known method is therefore complex and expensive. 
     A further disadvantage of the known method is that the synchronizer rings produced thereby, for example, subsequently have to be hardened in their functional regions, for example in the case of contours, such as toothed systems, indexing studs, centering studs or driving tabs. 
    
    
     It is an object of the present invention to eradicate the disadvantages according to the prior art. The intention in particular is to specify an extremely simple and cost-effective method for producing a component of a synchronization device for a manual transmission, in particular a synchronizer ring. A further aim of the invention consists in the specification of a component, which is extremely inexpensive and simple to produce, of a synchronization device for a manual transmission, in particular a synchronizer ring. 
     This object is achieved by the features of claims  1  and  12 . Expedient configurations of the invention are apparent from the features of claims  2  to  10  and  13 . 
     In a method for producing a component of a synchronization device for a manual transmission, in particular a synchronizer ring, it is provided according to the invention that at least one of the forming steps is a hot forming step in which the round blank is partially heated to a temperature of more than 600° C. and is then formed in the partially heated forming portion. In a departure from the prior art, the invention provides that the plurality of cold forming substeps for producing a desired contour are replaced in each case by a single hot forming step. In order to carry out the hot forming step according to the invention, the round blank is heated merely in portions, specifically in the region of the forming portion to be formed, to a temperature of more than 600° C., preferably to a temperature in the range of 650° C. to 850° C., and is then formed in this partially heated forming portion. In this case, the formed portion can be cooled at a predefined cooling rate and a specific microstructure can thus be set. 
     According to an advantageous configuration, the round blank is produced by means of stamping. Within the context of the present invention, the term “round blank” is understood in general terms. It is generally a metal sheet with a substantially round outer contour. 
     Within the context of the present invention, a round blank can also be, in particular, an annular body. The proposed method for producing the round blank by means of stamping is particularly cost-effective. It goes without saying that it is also possible to produce the round blank by other common processes, for example sawing, water jet cutting or laser cutting. 
     It is expedient that at least one of the forming steps is a cold forming step, preferably deep drawing. Such a cold forming step, as is known according to the prior art, is retained particularly when it can be carried out in a single step. By way of example, it is possible to give the round blank a conical shape in a cold forming step. 
     The round blank is advantageously produced from steel, preferably from a steel alloy. If the intention is to form, but not harden, a component, micro-alloyed steels, e.g. HC260LA, and low-alloy or unalloyed steels, for example D04, have proved to be particularly suitable. If the intention is to harden a component at least in partial regions, standard heat-treated steels have proved to be particularly suitable, as defined for example in EN 10132. Steels such as C45 are also suitable. Steel alloys, e.g. 22MnB5 or 80CrV2, have also proved to be expedient. 
     According to an advantageous configuration, the round blank is deformed in the forming portion and then at least partially hardened during the hot forming step. For this purpose, the forming portion is heated to a temperature above the austenitization temperature. The austenitization temperature depends on the steel or on the steel alloy. It is usually in the range of 850° C. to 1000° C. The quenching of the forming portion heated to a temperature above the austenitization temperature, which takes place after the forming, hardens said portion. The quenching is preferably effected by at least partial contact between the forming portion (contact hardening) and a heat sink, for example a metal mold matched to the shape of the forming portion. By using the proposed method steps, it is advantageously possible for selected regions of the forming portion to be hardened. 
     According to a particularly advantageous configuration, the round blank is not only deformed but also press-hardened in the forming portion during the hot forming step. For this purpose, the forming portion is heated to a temperature above the austenitization temperature. The austenitization temperature depends on the steel or on the steel alloy. It is usually in the range of 850° C. to 1000° C. The quenching of the forming portion heated to a temperature above the austenitization temperature, which takes place at the same time as forming, hardens said portion. By using the proposed method steps, it is possible to dispense with the hardening method which follows the shaping according to the prior art. Shaping and hardening can be effected at the same time according to the method proposed according to the invention. As a result, the method proposed according to the invention is particularly efficient. 
     According to a further expedient configuration, the round blank is partially heated by means of laser or induction. With the processes mentioned, it is possible to transfer a high thermal energy to the portion of the round blank to be formed particularly quickly. The forming portion of the round blank generally amounts to less than 50%, preferably less than 30%, in particular less than 20%, of the volume thereof. That is to say, during the partial heating of the forming portion which is proposed according to the invention, exclusively this portion is heated to the given temperature. The remaining portions of the round blank are not heated up to this temperature. 
     According to a further advantageous configuration, the thermal energy required for partial heating is supplied to the forming portion in less than three seconds, preferably less than one second. It is thereby possible to keep the introduction of heat limited to the predefined forming portion. In addition, the short heat introduction times proposed make a particularly rapid procedure possible. 
     It has proved to be particularly expedient, in particular in large-scale production, to use a cooled forming tool for quenching. As a result of contact with the forming tool, the forming portion is formed to the desired contour, quenched at the same time and consequently hardened. Here, the formed metal sheet is usually hardened down to a depth of 0.5 to 2 mm. 
     The method according to the invention also makes it possible, in particular, to stamp the round blank after the hot forming step. This also holds true when a forming region of the round blank has been hardened by the hot forming step. In this case, the following stamping step is expediently limited to those regions of the round blank which have not been previously hardened. 
     According to a further advantageous configuration, the hot forming step is carried out as a cycle in a cyclic sequence of forming and/or stamping steps. That is to say, the hot forming step can be implemented in a cyclically working line for the large-scale production of components of a synchronization device. 
     It is also proposed according to the invention that a component of a synchronization device for a manual transmission, in particular a synchronizer ring, has at least one press-hardened forming portion. Here, the press-hardened forming portion can have one of the following configurations: toothing, indexing stud, centering stud, driving tab, driving stud, connecting web. 
     Within the context of the present invention, a “synchronization device” is understood to mean a device which adapts a rotational speed differential between the shaft and the gear wheel to be shifted. In addition to at least one synchronizer ring, the synchronization device can also comprise further components, such as a sliding sleeve, a sleeve carrier and also a gear wheel or loose wheel. By way of example, reference is made to the synchronization device disclosed in DE 10 2005 035 941 B3. The disclosure content of the exemplary embodiment in said document is hereby incorporated. 
     In the text which follows, exemplary embodiments of the invention are explained in more detail, in particular on the basis of the single drawing. 
     The single drawing shows, in a perspective view, a synchronization assembly of a synchronization device (not shown in further detail here). The synchronization assembly comprises an outer ring  1 , an intermediate ring  2  and an inner ring  3 . 
     The outer ring is provided with toothing or gear toothing  4  in portions on its outer circumference. The reference symbol  5  denotes centering studs and the reference symbol  6  denotes indexing studs with indexing stud side faces  6   a , which are fitted between the portions of the toothing  4 . Driving tabs  7  with driving tab side faces  7   a  extend from the inner circumference. An inner circumferential surface of the outer ring  1  forms a first friction surface  8 . 
     The intermediate ring  2  has a second friction surface  9  on its inner circumference and a third friction surface  10  on its outer circumference. The reference symbol  11  denotes driving studs with driving stud side faces  11   a  which extend in the axial direction. 
     The inner ring  3  has a fourth friction surface  12  on its inner circumference and a fifth friction surface  13  on its outer circumference. The reference symbol  14  denotes connecting studs which extend axially in the direction of the outer ring  1 . 
     Production of the Outer Ring 
     In order to produce the outer ring  1 , firstly a round blank of annular form is stamped out from a suitable steel sheet, for example of the steel grade C45 or 80CrV2. Then, a conical geometry is given to the round blank in a conventional deep-drawing step. This is followed by a hot forming and calibration step, in which the conical portion produced is initially heated in portions to a temperature above the austenitization temperature and is then calibrated and press-hardened with a cooled pressing tool. 
     In a further step, the toothing  4  is then preformed by means of stamping. The preformed toothing is partially heated to a temperature above the austenitization temperature and is then formed to its predefined contour in a first hot forming step with a cooled pressing tool. Here, the toothing  4  is press-hardened at the same time. 
     In further hot forming steps, the indexing studs  5  and also the centering studs  6  are then formed. In this case, too, the appropriate forming regions are partially heated to a temperature above the austenitization temperature and are then formed to their predefined contour with a cooled pressing tool, and press-hardened at the same time. 
     In a further stamping step, the driving tabs  7  are preformed. In a further hot forming step, the driving tabs  7  are then partially heated in turn to a temperature above the austenitization temperature and are formed to their predefined contour with a cooled pressing tool. Here, they are press-hardened at the same time. 
     Within the context of the present invention, not every hot forming step has to be accompanied by press-hardening. By way of example, it is also possible to carry out one or more of the hot forming steps at a temperature below the austenitization temperature. 
     If the intention is to harden the forming region to be subjected to hot forming and press-hardening with the forming tool should not suffice for this purpose, it is additionally possible for, e.g. lateral, contact pressure to be applied after repeated heating to a temperature above the austenitization temperature. This is expedient particularly for the production of the indexing stud side faces  2   a , the driving stud side faces  8   a  and also the connecting web side faces  12   a  and the driving tab side faces  3   a.    
     The intermediate ring  2  and the inner ring  3  can be produced in a similar way. Here, too, an annular round blank is firstly stamped out. Then, the round blank is given a conical shape by deep drawing. The cone is calibrated in turn in a hot forming and calibration step. The conical geometry can be set exactly in this case. At the same time, it is thereby possible to achieve press-hardening, in particular of the friction surfaces. 
     This is followed by the production of the driving studs  11  and connecting studs  14 . Just like the centering studs  5  and indexing studs  6 , these can initially be preformed by means of stamping and then be formed to their end contour in a single hot forming step, it being possible for press-hardening to be effected in each case. The driving stud side faces  11   a  and the connecting web side faces  14   a  can be hardened, if necessary, by the lateral application of contact pressure. 
     The method proposed according to the invention simplifies the production process significantly and makes it more cost-effective, in particular in the case of synchronizer rings. To this end, conventional cold forming steps can be combined with hot forming steps. The hot forming steps make it possible to achieve a high degree of forming. It is possible to replace a plurality of the cold forming substeps required for producing the same degree of forming with a single hot forming step. At the same time, it is possible to press-harden the respective functional surfaces with the hot forming step. As a whole, this results in a considerably reduced number of production steps. A costly downstream hardening process can be dispensed with. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Outer ring 
           2  Intermediate ring 
           3  Inner ring 
           4  Toothing 
           5  Indexing stud 
           6   a  Centering stud 
           6   a  Centering stud side face 
           7  Driving tab 
           7   a  Driving tab side face 
           8  First friction surface 
           9  Second friction surface 
           10  Third friction surface 
           11  Driving stud 
           11   a  Driving stud side face 
           12  Fourth friction surface 
           13  Fifth friction surface 
           14  Connecting web 
           14   a  Connecting web side face