DE102008036226A1 - Hollow shaft i.e. transmission shaft, manufacturing method for motor vehicle, involves transforming reform into hollow intermediate form and performing rotary swaging of hollow intermediate form - Google Patents

Abstract

The method involves heating a semi-finished material at a temperature of 1000-1200 degree Celsius before forging. A preform is produced from the heated semi-finished material by forging such as die forging which is performed in a forging press whose stroke rate is 80 strokes per minute. The preform is subjected to thermal treatment for transforming the preform into a hollow intermediate form by borehole drilling. Rotary swaging of hollow intermediate form is performed to obtain a hollow shaft (1) with wall thickness which is same in course of the hollow shaft.

Description

The The invention relates to a method for producing a hollow shaft from semi-finished products.

at It is the manufacture of transmissions for motor vehicles desirable, the overall weight of the transmission with increasing Performance of the gearbox as low as possible to keep. A way to save weight can for example, by designing a gear shaft as a hollow shaft be achieved. By using one or more in the transmission existing waves as hollow shafts will be the power of the Gear increases, d. H. with the same transferable Torque decreases the overall weight of the transmission. With it reduced also the total weight of a motor vehicle, in which the Gearbox is installed, which reduces fuel consumption becomes.

The technical need to have one or more shafts in a transmission Form as a hollow shaft, can also constructive reasons to have. An increasing number of waves in a motor vehicle transmission leads to an increase of the transmission weight, so that resource conservation, such as material and fuel saving and environmental compatibility (emission reduction), Measures for weight reduction of the individual transmission shafts must be taken. In a shaft-in-shaft transmission, for example, in a dual-clutch transmission, it is even necessary to make the waves partially or completely hollow.

According to one already known procedure is the hollow shaft by combination made of two process steps. In a first step becomes a massive starting material through a forming process, for example Drop forging, shaped into a basic body. In one subsequent machining process is then used to manufacture the Hollow shaft a hole in the longitudinal direction of the body machined. Through this machining process step a considerable part of the material used is not used. This process, called deep hole drilling, requires special equipment Machines and tools (deep hole drills) and thus brings increased Cost of production with itself. With the procedures described above Furthermore, it is not possible undercuts in the hole, d. H. along the inner surface of the produced To produce hollow shaft. The disadvantage of this method is from today View that the requirement of resource conservation due to the cutting Processing is not fulfilled.

From the EP 1745 870 a method sequence described below is known. First, a cylindrical starting material is converted in a first step by cross wedge rolling into a base body. The stock material is positioned between the two profiled rolls or jaws of a cross wedge rolling apparatus. The existing on these rolls or jaws profiles are transferred during the forming of the starting material. After forming by cross wedge rolling, the base body has a desired outer surface profile. D. h., By the cross-sectional change by means of cross wedge rolling, the main body has a contoured outer peripheral surface with predetermined continuous diameter transitions, at the transition points radii are formed. This avoids notches, which can adversely affect the strength of the shaft. The introduction of an axial bore in the body takes place during the described cross wedge rolling. In addition to the radial and tangential deformation caused by the cross wedge rolling, an axial force in the longitudinal direction of the starting material is exerted on the workpiece via a mandrel. As a result, a bore with a constant diameter can be generated. The mandrel can be performed either axially movable during cross wedge rolling or be arranged stationary.

task The present invention is to develop the known methods and to provide a sequence of process steps that allows a hollow shaft in a mass production in relation to Production time, material and resource usage as well as capital expenditure to produce optimally.

These The object is achieved by a method having the features of the claim 1 solved.

• – Herstellen einer Vorform durch Schmieden;
• – Durchführen einer Wärmebehandlung der Vorform;
• – Umformen der Vorform in eine zumindest teilweise hohle Zwischenform durch Bohrungsdrücken; und
• – Rundkneten der Zwischenform zu einer Hohlwelle mit einer im Verlauf der Hohlwelle im Wesentlichen gleichen Wandstärke.

The method sequence according to the invention for producing a hollow shaft, for example for motor vehicle transmissions from semi-finished products, comprises the following steps:

• - making a preform by forging;
• - performing a heat treatment of the preform;
• - Forming the preform in an at least partially hollow intermediate form by drilling pressures; and
• - Rotary kneading of the intermediate form to a hollow shaft with a substantially uniform in the course of the hollow shaft wall thickness.

In a first step, the production of a preform of a shaft by a forging process takes place. For this purpose, a section or blank required for producing the shaft is separated from a semifinished product and brought by a forging process into a preform required for the further method steps. This preform then becomes a suitable heat treatment for the selected material to prepare them for the further manufacturing process. In an advantageous manner, following the heat treatment, the forming of the preform into an at least partially hollow intermediate form takes place by means of bore pressures as the basis for the further production sequence. Bore Pressing is a partial, incremental pressure forming process for producing an axially symmetric hollow shaft made from solid semi-finished products. The preform is added to a spindle in a clamping device and rotated about its longitudinal axis. The material of the preform is displaced by the force applied by the pressure rollers used and a simultaneously acting thrust stamp force and flows counter to the feed direction of the plunger. The plunger rotates synchronously with the spindle and the preform and performs synchronous axial movement common to the pressure rollers. This creates from the massive preform the at least partially hollow intermediate form.

One significant advantage of the hole pressing opposite the known method of deep hole drilling is the far higher Degree of material utilization through the pure transformation of material. The method can therefore be particularly advantageous for producing a hollow shaft made of cost-intensive materials because of the loss of material during a forming process is very low. Another advantageous feature of this method lies in the fact that the time required to produce a hollow shaft is well below the cost of deep hole drilling. this Advantage comes especially in the context of a production with high quantities great importance too.

To the production of the hollow intermediate form by drilling pressure comes as a further step in the design of the outer Wave contour a rotary swaging used. Even with the rotary swaging it is an incremental forming process in which the Forming is accomplished in many small steps. Across from The advantage of known continuous processes is that that a more homogeneous material transformation takes place. This in turn allows high degrees of deformation, since the deformability of the material in the entire component cross-section evenly is exploited. The swaging allows a continuous Course of the material fibers in the workpiece, what opposite machined shafts leads to better mechanical properties. Furthermore, one, introduced by the forming, increases Hardening of the material, for example, the component strength. The method of rotary kneading is further characterized by a high accuracy out. This makes it possible for the dimensions to maintain a tight tolerance, so that a subsequent machining the hollow shaft is usually unnecessary. In an advantageous way this material can be saved and the process chain shortened, which is advantageous for mass production the unit cost of each component affects.

at play the selection of a semi-finished product for producing a hollow shaft in addition to the availability of the corresponding material in the desired initial form and economic issues a crucial role. Advantageous in the inventive Method is preferably the use of a cylindrical rod material as Output semi-finished product for the hollow shaft. This semi-finished product has compared to other semi-finished products has the advantage that, for example cheaper to obtain than a tubular Workpiece.

Around preparing the material for the forging process is the semi-finished product to a temperature of preferably 1000 ° C. heated to 1200 ° C. After this warming is a shearing a material blank from the bar-shaped semifinished product separated, which then for the further process sequence in the required size available stands. Alternatively, there is the possibility of the material blank from a non-heated semi-finished to the required Shear off size and only then for to heat the following forging process.

is the blank is available in the required size, so is in the process sequence according to the invention the forging process carried out. This takes place in an advantageous manner As a hot forging process, where the material is at a temperature from about 1000 ° C to 1200 ° C. Especially advantageous is a drop forging.

The Drop forging allows the preform to pass through the contour a Gesenkes the essential geometry parameters of the later Apply hollow shaft. In this process step will be the preform already the necessary material accumulations for a later processing molded to this then, for example ready to go to bonds or warehouse seats.

Of the entire forging process advantageously has the main work steps Upsetting, preforming and preforming, with which the blank is converted into the geometry of the preform. if it is necessary, the forging process can still be followed by a burring, around the outer contour of any supernatants, for example, a smithy, to liberate.

During the forging process, it may be necessary to cool to improve the flow properties of the material used Apply lubricant to adapt the material properties to the requirements of the forging process.

The Forging, for example, is done on a horizontal forging press performed, which preferably with a stroke rate up to 80 Strokes per minute can be operated. This embodiment of the Press allows the forging process under optimal Boundary conditions regarding the precision of the product as also perform application of components per unit time.

To the forging process, the preform from the forging heat controlled for further processing to be cooled, depending on the characteristics the starting material certain structure and thus certain Set workpiece properties of the preform. As a variant to Controlled cooling is also a cooling the air conceivable. This variant has but in terms of during the cooling process forming material structure the disadvantage that here may be microstructure arise for further processing in a subsequent Forming process are only partially suitable. The process of forging and subsequent cooling may be followed by a blasting process if necessary, to free the preform from existing scale.

In front the further forming steps is used to improve the material property a heat treatment process in the form of an annealing process carried out. Here are different forms Normalizing be used. Preferably comes Here is a BF glow used. In this annealing process it is a glow to achieve a particular Tensile strenght. It has a heating of the preform at about 850-950 ° C with a subsequent cooling and following Tempering at approx. 500-550 ° C. Advantageous in this type of heat treatment is a low process time, which makes this process particularly economical. As an alternative annealing process, a BG glow can also be used be used. The BG annealing occurs at about 900-1000 ° C followed by controlled cooling to produce a ferrite-pearlitic structure. Finally, too the use of a GKZ annealing with the goal possible to create a structure of spherical carbides, since this Process improves the cold workability of the material.

After this the heat treatment process is completed takes place According to the invention, the forming of the preform into a at least partially hollow intermediate form by drilling pressures. Preferably, the bore pressing is called hot forming process performed with a heated preform. The The temperature of the preform is preferably in a range of about 400 ° C to 800 ° C. It is also an application of the Bohrungsdrückens conceivable as cold forming process. The bore press itself can both from one side as well as from both sides of the Workpiece or the preform be performed. For the decision which process variant to use should come, parameters such as component size, Part shape u. a. Consideration.

to Optimizing the Bohrdrückprozesses it is advantageous Apply a lubricant to the preform and / or the tool. The lubricant makes it possible to improve the surface quality the resulting hole in the intermediate form and leads To increase the tool life, what the process improved in terms of its profitability. The order of this lubricant can be done on the one hand such that the lubricant in liquid Mold during the Bohrdrückprozesses on the workpiece is sprayed on. On the other hand is also an order of the Lubricant on the workpiece before the Bohrungsdrückprozess in the form of diving or the like conceivable. Here is However, be aware that the lubricant will dry after application should be to make sure that it is during the forming process as well is available at the desired locations.

In front The further transformation steps may be to improve the material property be beneficial again in a heat treatment process To perform the form of an annealing process. Here too are the above-mentioned annealing to Selection. The decision whether and which of the methods to use comes is from the material properties and the degree of deformation depends on the intermediate form and can be used for each process be redefined.

The Fertigformen the gear shaft from the intermediate form then takes place by swaging. This process step can be done right after the Bore pressures or after the aforementioned additional Heat treatment process done.

at the process step of the rotary kneading creates a hollow shaft optimal wall thickness, low wall thickness differences and an optimum for the component strength fiber profile. Preferably, the swaging is used to create the hollow shaft as Hot forming process performed with a heated intermediate form. The temperature of the intermediate form is preferably in one Range from about 400 ° C to 800 ° C. Alternatively, the Use of rotary kneading provided as cold forming process.

He follows the round kneading with heated intermediate form, is the finished Cooled component before further processing, cooled depending on the properties of the starting material certain microstructures and thus also certain desired properties of the workpiece adjust. As a process variant for the controlled cooling is a cooling in the air conceivable. This variant can, as explained above, disadvantages in terms of forming during the cooling process Material structure have. The resulting structure is for further processing in the following manufacturing process possibly only conditionally suitable. If necessary acts The structure also disturbs the properties of the finished component.

In The above description will be the inventive Process steps for producing a one-piece gear hollow shaft described. It should be for reasons of geometric requirements be necessary to make a wave two or more pieces, so the process sequence of the invention to join a method step, for example welding, be supplemented. In this process step, two or more partial wave sections connected to a total wave. there For example, the design of the preforms may be such that they are in the Area of the joint with a depression, for example a bore, are provided. These holes form after the joining process an internal cavity in the intermediate form.

Here finds as a joining method preferably a friction welding Application. The use of other joining methods, for example Pressing, soldering or other welding processes is also possible.

following the inventive method is based on a Embodiment with reference to the attached Drawings explained in more detail by example which:

1 : shows a schematic sectional view of a hollow shaft produced by the method according to the invention;

2 Fig. 3 shows a schematic sectional view of an intermediate mold after the bore presses; and

3 : shows a symbolic representation of the procedure.

The 1 shows a hollow shaft 1 which has undergone the entire process sequence according to the invention. The illustration clearly shows that the strength of the wall 2 over the entire length of the hollow shaft 1 is almost constant. Also in the range of changes in diameter, the strength of the wall changes 2 only insignificant. A material accumulation 3 , For example, a covenant is found in the areas in which, for example, a toothing or a bearing seat is applied in the further manufacturing process in order to maintain the necessary material for the further machining mostly. The illustrated hollow shaft is continuous with a bore 4 Mistake.

In 2 becomes an intermediate form 5 shown. This intermediate form 5 has only gone through the process steps to the hole pressures. Shown is the forging contour produced by drop forging 6 and the holes introduced by the bore press 4 ' and 4 '' , In the illustrated intermediate form 5 were the holes 4 ' and 4 '' introduced from both mutually opposite shaft ends. In about the middle of the intermediate form 5 became for example a first material accumulation 7a in the area between the holes 4 ' and 4 '' and a second accumulation of material 7b in the approximately central outer peripheral region of the forging contour 6 left behind. The material accumulation 7a can be removed after the bore pressing by the introduction of an additional axial force and a feed of the plunger in the axial direction.

The 3 shows a symbolic representation of the individual process steps and their sequence. The process starts in a thermal plant 8th for heating a rod-shaped semi-finished product 9 , to which then a shearing device 10 for shearing a blank 11 from the semifinished product 9 followed. Then the blank is 11 a forging press 12 fed where he is in a die 13 forged to preform. After swaging, the preform becomes a first annealing furnace 14a fed, in which a first annealing process takes place. After the annealing process, the preform may be cooled in a controlled manner in a corresponding cooling device (not shown). The heat treatment in the annealing furnace 14a is a machine 15 downstream of the bore press. After drilling press in the appropriate machine 15 becomes an intermediate form thus obtained 5 in a second annealing furnace 14b given and subjected to a second annealing process. At the end of the illustrated process chain is in a suitable plant 16 a rotary swaging of the outer contour carried out to the finished end product, the hollow shaft 1 to obtain. Finally, the hollow shaft 1 be cooled controlled in a corresponding cooling device (not shown).

1

hollow shaft

2

wall

3

material accumulation

4, 4 ', 4' '

drilling

5

intermediate form

6

wrought contour

7a, 7b

material accumulation

8th

heating system

9

Workpiece

10

shearing

11

blank

12

forging press

13

die

14a, 14b

annealing furnace

15

machine for drilling pressure

16

machine for swaging

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1745870 [0005]

Claims (21)

Method for producing a hollow shaft ( 1 ) from semi-finished products ( 9 ) comprising the steps of: - making a preform by forging; - performing a heat treatment of the preform; - Forming the preform into an at least partially hollow intermediate form ( 5 ) by drilling pressure; and - swaging the intermediate form ( 5 ) to a hollow shaft ( 1 ) with one in the course of the hollow shaft ( 1 ) substantially equal wall thickness. Method according to claim 1, characterized in that the semifinished product ( 9 ) is bar-shaped before forging. Method according to claim 1 or 2, characterized in that the semifinished product ( 9 ) is heated to about 1000 ° C to 1200 ° C before forging. Method according to one of the preceding claims, characterized in that the forging is a hot forging. Method according to one of the preceding claims, characterized in that the forging is a drop forging. Method according to one of the preceding claims, characterized in that the forged preform one or more material accumulations ( 3 ) having. Method according to one of the preceding claims, characterized in that the forging process comprises the upsetting, Preforming, finish molding and / or trimming has. Method according to one of the preceding claims, characterized in that during the forging a Coolant is applied. Method according to one of the preceding claims, characterized in that the forging on a forging press ( 12 ) he follows. Method according to claim 9, characterized in that the number of strokes of the forging press ( 12 ) is up to 80 strokes per minute Method according to one of the preceding claims, characterized in that the preform is controlled after forging is cooled. Method according to one of the preceding claims, characterized in that the heat treatment is an annealing process is. Method according to one of the preceding claims, characterized in that two or more preforms to an intermediate form ( 5 ). A method according to claim 13, characterized in that two or more molds are joined with axial bores such that an intermediate form ( 5 ) arises with an internal cavity. Method according to one of the preceding claims, characterized in that the bore pressures when heated Preform takes place. Method according to claim 15, characterized in that that the temperature of the preform when drilling press about 400 ° C to 800 ° C is. Method according to one of the preceding claims, characterized in that when drilling a lubricant is used, the before and / or during the Bohrungsdrückens is applied. Method according to one of the preceding claims, characterized in that after the hole pressing a Heat treatment process is done. Method according to one of the preceding claims, characterized in that the rotary kneading with heated intermediate form ( 5 ) he follows. Process according to claim 19, characterized in that the temperature of the intermediate form ( 5 ) is about 400 ° C to 800 ° C in the rotary swaging. Method according to one of the preceding claims, characterized in that the hollow shaft ( 1 ) is cooled controlled after the rotary kneading.