Hirth toothing with secondary profile angle

Description

[0001] The invention relates to a method for manufacturing a machine element comprising a Hirth tooth with several centrally symmetrical teeth and intervening tooth gaps. It further relates to a machine element manufactured using this method. Machine elements with Hirth teeth are primarily used to transmit torque from one machine element to another. High-precision positioning and alignment tasks can also be performed repeatably using this method. Hirth teeth are particularly suitable when high torques need to be transmitted in a small installation space and with low weight. They are axially acting, face-mounted, face-cut splined teeth. Furthermore, they are self-centering and, with backlash-free positive locking, also wear-free.

[0002] In DE 102016012947 A1, machine elements with Hirth couplings are described. They are used here for the end-face connection of two shaft sections.

[0003] Further improvements for Hirth gears are known, for example, from DE 102014224355 A1 and from DE 102008057383 A1.

[0004] The teeth of a Hirth gear are subjected to particularly high loads, especially at the transition between the tooth flank and root. Therefore, such machine elements are manufactured from high-strength metallic materials, particularly high-strength steel. Machining high-strength materials is complex and requires numerous machining steps to achieve both the highly precise and dimensionally accurate shape and the desired strength properties of the finished machine element. The associated manufacturing effort for Hirth gears is a disadvantage. The production of Hirth gears differs significantly from the production of simpler gears, such as spur or bevel gears.

[0005] The object of the invention is to develop a method for manufacturing a machine element with Hirth gearing that enables simpler manufacturing and offers high load-bearing capacity of the gearing, as well as to provide a corresponding machine element.

[0006] The problem is solved by a method for manufacturing a machine element according to claim 1. It is further solved by a machine element according to claim 10. Further advantageous features are specified in the respective dependent claims.

[0007] Several steps are necessary in the production of gear teeth. First, the tooth gaps are created in the pre-machining stage, for example by milling, especially using form milling cutters, or by grinding, resulting in the pre-machined blank. The pre-machined blank then usually undergoes heat treatment, which hardens and, if necessary, strengthens the material. Finally, the finishing process, known as hard finishing, takes place, in which the tooth profile is precisely machined to create the finished machine element. This can be achieved by grinding.

[0008] In the inventive method, the pre-machined blank is designed such that each tooth has a tooth flank with a profile angle and a secondary flank with a secondary profile angle, as well as a tooth root region, wherein the secondary flank transitions continuously tangentially into the radius of the tooth root region and wherein the secondary profile angle is smaller than the profile angle. According to the invention, a grinding allowance of material is present on the pre-machined blank in the area of ​​the tooth flank after pre-machining and before final machining, and no grinding allowance is present in the area of ​​the secondary flank after pre-machining and before final machining. Such a blank still has a grinding allowance in the area of ​​the tooth flank, but is otherwise pre-machined according to the finished shape of the gear teeth of the machine element with regard to the production of the gearing and heat treatment.The production of the gear teeth during pre-machining is preferably carried out by milling, in particular using form milling cutters.

[0009] Because the tooth has a secondary flank with a smaller angle than the profile angle between the load-bearing tooth flank and the tooth root, machining during gear manufacturing can be significantly improved. To produce the exact tooth contour, the additional material present in the grinding allowance is removed during finishing, preferably as finish grinding. In contrast, no grinding allowance is present in the area of ​​the secondary flank after roughing and before finish grinding. This area is not machined during finish grinding. This simplifies the entire manufacturing process without reducing strength.

[0010] In state-of-the-art Hirth gearing, the tooth flank typically has only a single profile angle and transitions directly into the radius of the tooth root. To prevent weakening of the tooth by grinding marks during the hard finishing of the tooth flank, the entire tooth root must always be ground out as well. Only in this way can a uniform surface quality be achieved. A disadvantage of this method is that grinding partially releases the residual stresses introduced by the previous heat treatment, resulting in an undesirable decrease in surface strength and deformation.

[0011] A significant advantage of the inventive design is that the precise grinding of the tooth flank can be achieved without completely grinding away the tooth root area, and simultaneously, no grinding marks appear at the end of the grinding area. During grinding, the tool can machine the entire area of ​​the tooth flank, remove the grinding allowance in the tooth flank area, and then run into empty space without coming into contact with the subsequent surface of the secondary flank, since the secondary profile angle is smaller than the profile angle and since there is no grinding allowance on the pre-machined blank in the area of ​​the secondary flank. The residual stresses introduced into the pre-machined blank by heat treatment and any surface hardening processes used, e.g., shot peening, are completely retained in the particularly highly stressed tooth root area. Furthermore, the grinding process can be optimized.

[0012] Additionally, it is advantageous if there is no grinding allowance in the tooth root area after pre-machining and before finish grinding. This area can then also be removed during finish grinding, resulting in the aforementioned improvements.

[0013] In particular, the grinding allowance can advantageously be at least 0.01 mm, preferably at least 0.1 mm. This ensures sufficient material is available to achieve a good surface finish with an exact tooth contour. The upper limit for the grinding allowance is a maximum of 1 mm to avoid unnecessary material removal.

[0014] A particularly advantageous measure for the deviation of the secondary flank from the extended profile of the tooth flank is when the secondary profile angle α2 is at least 5% and at most 30% smaller than the profile angle α1. If the secondary profile angle is too small, i.e., the deviation from the profile angle is too large, the tooth thickness in the tooth root region is reduced too much. This would reduce the strength, especially with regard to the bending stress of the tooth. If the deviation is too small, i.e., the secondary profile angle is too large and thus too close to the profile angle, there is still a risk of residual grinding marks in the transition area to the secondary flank. It is even more advantageous if the secondary profile angle α2 is at least 10% and at most 25% smaller than the profile angle α1.

[0015] In a particularly preferred embodiment according to the invention, the length of the secondary flank along the tooth profile between the end of the tooth flank and the beginning of the radius of the tooth root region is at least 0.05 mm, preferably at least 0.1 mm, and at most 2 mm, preferably at most 0.5 mm. In particular, the length of the secondary flank along the tooth profile is at most 20%, preferably at most 15%, of the length of the tooth flank along the tooth profile. Limiting the length of the secondary flank restricts the reduction in the bearing area of ​​the flank.

[0016] Advantageously, the profile angle α1 lies in the range between 35° and 75°, so that the force transmission takes place via the flank surface.

[0017] In particular, the method according to the invention is carried out such that the secondary flank and the tooth root area are not machined during finish grinding, i.e., during hard finishing. This preserves the residual stresses from pre-machining, heat treatment, and, if applicable, surface hardening processes.

[0018] The smaller secondary profile angle allows the tooth root radius to be increased, which reduces the notch effect in the tooth root area and thus increases the load-bearing capacity. The radius in the tooth root area can be up to 15% larger than it would be in a design with only one profile angle. The absolute dimensions of the radius depend on the diameter and the number of teeth. Preferably, the radius in the tooth root area is between 0.1 mm and 10 mm inclusive.

[0019] Furthermore, advantages arise for a machine element that has been manufactured using a method according to the invention.

[0020] In one embodiment, the teeth are designed such that a mating edge is located in the secondary flank or at the transition to the tooth root when engaging with a second machine element with Hirth toothing. The mating edge is the edge of the tooth head of the meshing tooth. This ensures that the largest possible bearing area is utilized while simultaneously providing sufficient clearance between the mating edge and the tooth root.

[0021] The gearing produced according to the invention is particularly well suited for application to a power-transmitting and / or positioning machine element, which is designed as a toothed ring, as a joint of a drive shaft, as a coupling component, or as a transmission component. The machine element can also be designed as a disc or shaft of pumps, compressors, or turbines.

[0022] Additionally, machine elements manufactured according to the invention can be used in a gear coupling consisting of two machine elements, each with a Hirth tooth, wherein at least one of the two machine elements is manufactured according to the invention. The mating of a machine element manufactured according to the invention with a machine element having a Hirth tooth according to the prior art is possible while maintaining the required center clearance and, in the case of gear rings, the defined assembly dimensions.

[0023] The gear coupling preferably consists of two machine elements manufactured according to the invention, each with a Hirth gear.

[0024] In this context, a tooth coupling refers to the connection of two rotatable machine parts via a non-rotating toothed connection.

[0025] Further advantageous features of the invention are explained using exemplary embodiments with reference to the drawings. Fig. 1 schematic representation of a gear coupling manufactured according to the invention Fig.2 Toothed ring manufactured according to the invention, with sectional view Fig.3 Tooth gap of a Hirth tooth according to the state of the art Fig.4 Tooth gap of a Hirth gear manufactured according to the invention, showing the grinding allowance

[0026] The Fig.1 Figure 1 shows a gear coupling with two machine elements 1 and 2 manufactured according to the invention, each configured here as a toothed ring. Both the first machine element 1 and the second machine element 2 each have teeth 3, 4, which are designed as Hirth teeth with a secondary flank and were manufactured from a blank pre-machined according to the invention. Furthermore, it is possible to pair two machine elements 1 and 2 in which only one of the teeth 3, 4 is designed as a Hirth tooth manufactured according to the invention. The exact contour of the tooth flanks is not visible in this illustration. The two machine elements 1, 2 can be engaged via the first tooth 3 and the second tooth 4, so that a high torque can be transmitted reliably and without backlash.The machine element produced according to the invention can not only be designed as a toothed ring, as shown here by way of example, but can also be a differently designed machine element which has a Hirth toothing 3,4 produced according to the invention.

[0027] Fig.2 The lower section shows the top view, and the upper section shows the sectional view along line CC of a toothed ring 1,2 with Hirth teeth 3,4. A Hirth tooth 3,4 is a face-facing planar splined tooth. It can be seen that the tooth root slopes radially outwards. The tooth thickness and tooth height also increase radially outwards.

[0028] If we now consider a tooth gap in a Hirth occlusion in general, in normal section, that is, perpendicular to the tooth base, as is shown by the vertical in Fig.2 As depicted, there is one variant as it is known from the prior art - see Fig.3 - and once the embodiment produced according to the invention - shown in Fig.4 - as it is implemented in machine elements 1,2.

[0029] Fig.3 For better understanding, the state of the art is first shown. The tooth gap is bounded by the tooth flanks 5 of adjacent teeth. The profile angle α1 is the opening angle of the tooth gap. At the root of the tooth gap, these are connected via the tooth root region 6. The bearing portion of the tooth flank 5 extends between the opposing edges 7 of two adjacent teeth or tooth gaps. The tip clearance 8 is the free space between the opposing edge 7 and the tooth root.

[0030] In Fig.4A normal section view of a Hirth gear manufactured according to the invention is shown. The tooth flanks 12 define the tooth contour, the tooth profile of the finished ground gear, and form the bearing portion of the teeth. The profile angle in this area is α1. From point A, the secondary flank 13 adjoins this tooth flank 12 and then transitions continuously into the radius of the tooth root area 14 at point B. The secondary profile angle α2 is smaller than the profile angle α1, resulting in an edge at point A and subsequently a steeper profile. This is clearly visible in the indicated extension 23 of the secondary flank and the extension 22 of the original tooth flank. Furthermore, it can be seen that the bearing area of ​​the tooth flank 12 is somewhat reduced because the mating edge 20 projects into the area of ​​the secondary flank 13.

[0031] The length of the tooth flank 12 along the tooth profile is the distance between point A and the tooth tip at the upper end of the tooth flank. The length of the secondary flank along the tooth profile is the distance AB.

[0032] In the inventive manufacturing of the gear teeth, the tooth gap is first milled in the pre-machining stage, preferably with an end mill that replicates the corresponding shape. The result is the tooth gap according to the contour 11 + 13 + 14. This provides the necessary grinding allowance 10 in the area of ​​the tooth flank 12. After appropriate heat treatment of the entire machine element or just the gear teeth, the secondary flank 13 and the tooth root area 14 are already finished. Only the tooth flank 12 is then brought to the exact contour by finishing, preferably finish grinding. The tool, the grinding wheel, runs freely from point A onwards, since the secondary flank 13 is steeper than the tooth flank 12. This reliably prevents grinding marks at the end of the grinding area. The maximum grinding wheel radius is indicated by 21.

[0033] Preferred dimensions for the geometry of the tooth contours and for the grinding allowance have already been described. The embodiment according to the invention is well suited for Hirth gears with an outer diameter of 50 mm to 1800 mm and for numbers of teeth from 12 to 1000. This allows for the reliable transmission of torques from 100 Nm up to 100 kNm.

Claims

1. Method for producing a machine element (1, 2) which comprises a Hirth serration (3, 4) having a plurality of centrally symmetrical teeth and intervening tooth gaps, wherein each tooth has a tooth flank (12) with a profile angle (α1), which is provided to support the load, and a secondary flank (13) with a secondary profile angle (α2), and a tooth root region (14), wherein the secondary flank (13) continuously transitions tangentially into the radius of the tooth root region (14), and wherein the secondary profile angle (α2) is smaller than the profile angle (α1), wherein a plurality of sub-steps are carried out: firstly, the tooth gaps are created during premachining by milling or grinding in such a way that a premachined blank is created, wherein a grinding allowance (10) in terms of material is present in the region of the tooth flank (12) after premachining and prior to finishing, and wherein there is no grinding allowance present in the region of the secondary flank (13) after premachining and prior to finishing; finally, finishing is carried out by grinding as a hard fine-machining process in which the profile of the teeth is carved out exactly, wherein the tool machines the entire region of the tooth flank during grinding, removes the grinding allowance in the region of the tooth flank and can then be ineffective without coming into contact with the subsequent area of the secondary flank.

2. Method according to Claim 1, characterized in that there is no grinding allowance present on the premachined blank in the tooth root region (14) after premachining and prior to finishing.

3. Method according to Claim 1 or 2, characterized in that the grinding allowance (10) on the premachined blank is at least 0.01 mm, preferably at least 0.1 mm, but at most 1 mm.

4. Method according to one of the preceding claims, characterized in that the secondary profile angle (α2) is at least 5% and at most 30%, in particular at least 10% and at most 25%, smaller than the profile angle (α1).

5. Method according to one of the preceding claims, characterized in that the secondary flank (13) between the end of the tooth flank (12) and the start of the radius of the tooth root region (14) has a length of at least 0.05 mm, preferably at least 0.1 mm, and of at most 2 mm, preferably at most 0.5 mm.

6. Method according to one of the preceding claims, characterized in that the profile angle (α1) is between 35° and 75° inclusive.

7. Method according to one of the preceding claims, characterized in that the length of the secondary flank (13) along the tooth profile is at most 20%, preferably at most 15%, of the length of the tooth flank (12) along the tooth profile.

8. Method according to one of the preceding claims, characterized in that the radius in the tooth root region (14) is between 0.1 mm and 10 mm inclusive.

9. Method according to one of the preceding claims, characterized in that the premachined blank is subjected to heat treatment and optionally to a surface solidification method, in particular shot peening, prior to finishing.