SK165098A3 - Process and device for producing camshafts - Google Patents

Abstract

In order to be able economically to produce longitudinal hollow body components, especially camshafts, not only with a saving in tooling and working steps but also with increased efficiency, projections or cams (6) from a hollow shaft (5) are made by high internal pressure forming in such a way that the form and/or position of the projections (6) can be shaped in several steps.

Description

Method for producing a camshaft apparatus ¹ ^ tion of the method

Technical field

The invention relates to a method for producing an elongated body, in particular a camshaft, and to an apparatus for carrying out the method.

BACKGROUND OF THE INVENTION

A number of methods for producing camshafts are known. In principle, they can be divided into two groups.

The first group comprises a conventional camshaft, which is either forged or cast as a blank, either as a solid body or as a shell cast from hardened cast iron, after which the two blanks must be further machined, first mechanically by chipping, and then it is necessary to refine their surface by subsequent heat treatment, and finally to grind the bearing parts and cams. The drawbacks of the camshafts thus produced are, in particular, their high weight and, consequently, the high moment of inertia, which have an adverse effect on the bearings, for example in torque variations, and on the high costs associated with machining the workpiece.

The second group consists of coupled cam shafts, in which the cams are manufactured separately and then individually connected to the shaft in different ways. Thus, for example, the cams may be welded, in particular onto the hollow shaft, or may be hot-placed on the tube. In the latter process, it is known to place the tube or hollow shaft with the cams inserted into a correspondingly shaped tool and then open the tube by a method of internal high-pressure forming, whereby the cams are elastically expanded and the tube plastically expanded to achieve hollow shaft.

When the tube is expanded by the internal high-pressure forming method, the molded hollow tubular body is simultaneously loaded with internal pressure and axial force acting on its ends. Liquids or elastomers are suitable as pressure means. The axial force is usually performed by means of rigid tools, such as pistons, punches and the like, which directly or indirectly apply pressure to the ends of the workpiece.

Exemplary embodiments of the shafts or shafts thus connected as described above are known from DE 34 09 541 A1 and DE 35 21 206 A1.

- parts whose production, in particular in the case of cams, is associated with high costs, notwithstanding that the entire process associated with their fixing is expensive.

A method is further known from U.S. Pat. No. 2,222,762 according to which the tubular blanks are first heated and then inserted into a mold. After heating, the easy-forming blank is stabilized from the inside by means of a support medium, gas or liquid. The axial forces exerted either by the movably formed mold or by means of independent punches simultaneously press the blank into the mold, with the support medium ensuring that the heated blank does not collapse. The disadvantage of this method is that it is first necessary to heat the blank to obtain the necessary plasticity and to be pressed into the mold. This heating, in addition to changing the structure, also constitutes another work operation, which increases production costs. Moreover, the working pressure is exerted only by axial forces, which results in an uneven flow of material and thus an uneven stress distribution in the blank.

JP 57 206530 A discloses a method for producing a camshaft according to which a pre-heated hollow body is pressed into a mold in a single operation by means of a pressurized liquid. Here too, the heating must be carried out first; furthermore, in this method no further axial displacement follows, which also leads to uneven flow of material; furthermore, in this method, there is no sequence of forming operations, the method comprising only a single forming operation.

SUMMARY OF THE INVENTION

The problem solved by the present invention is to provide a method and apparatus for carrying out the method by which at reduced production costs, reduced tool costs and reduced work operations it will be possible to produce elongated hollow bodies with an increased degree of efficiency, i. j. at higher productivity and without reducing wall thickness.

This problem is solved in a manner apparent from the features of the main claim, i.e. the high-pressure forming method, unlike the prior art, is not used to extend the hollow shaft in order to achieve a press fit, or, as in the case of DE 35 21 206 A1, additional axial reinforcement, but for one-piece formation of concave parts, preferably cam-shaped, directly from tube or profile material - simplified but not limited to hereinafter referred to as "hollow body" or "hollow shaft" or "shaft" - so by gradually forming concave

-3 parts, i. In this way, the time-saving possibilities of producing a hollow body from a single piece are achieved both in terms of cost and in the manufacturing process.

A further embodiment of the invention is common to the various embodiments in which the hollow shaft is formed in several operations in which the cams are progressively shaped in terms of their shape and / or their position on the shaft. As will be explained in greater detail below, it is meant that, on the one hand, the cams can be gradually formed into the final state, but on the other hand it is also possible to shape them on the shaft successively in the desired order. It goes without saying that both of these options may also overlap.

Thus, in a preferred embodiment of the invention, the cams can be shaped one after the other from the center of the shaft to its ends, which can be performed in a particularly economical manner in pairs. It is also possible to shape the cams from one end of the shaft to the other end. An important advantage of this process is the cost-effective manufacture, especially since the separate production and calibration of the cams is eliminated, and the axial flow of material can flow into the forming zone without hindrance. The supply of material from the pipe ends due to the axial load and displacement of the invention is not limited by the preceding pairs of cams, i.e. the material of the pipe can be unrestrictedly fed into the respective forming zone. The shaping of this zone is followed by the shaping of another pair of cams. Consequently, the advantage is that greater axial deformations of the tube material which are above the elongation degree can be achieved by the axially compressive stresses. In addition, there is a reduction in wall thickness in the deformation region, i. in the area of cam forming, it is considerably reduced, that is, the wall thickness is uniformly formed, thus achieving greater component stability. There are several possibilities for practical use.

Thus, the cams may be purposely formed individually or in groups in response to the pressure of a plurality of slides which can be actuated in reverse or the like.

With respect to the above-mentioned possibility of progressively shaping the cams from the central part of the shaft towards its ends, it is particularly advantageous that in the controlled flow of material into the inner regions, i. to the central part of the shaft, there is no great stretching of the material with a thinning of the wall, since during the forming of the internal cams by axial feeding of material, its flow is not limited by cams that would have been previously formed. In addition, it is thus possible to produce cams

- shafts of lower extensibility materials, with high cam heights as well as a relatively large number of cam pairs and bearings, such as those required for twelve-cylinder engines. In addition, there is less material compression on the components and their wall thickness is more uniform, which provides a further advantageous possibility of a possible overall reduction of the wall thickness.

In the practice of the invention, various cold-forming materials such as custom blanks or custom tubes, or many single-layer materials, can also be used in two-layer materials - for example steel / steel or steel / aluminum combinations, sandwich hollow bodies or coated hollow bodies; for a steel / aluminum combination, it is preferable that the steel forms an outer layer and the aluminum forms an inner layer. This results in significantly better properties of the blank; the steel jacket increases abrasion resistance, improves heat treatment and torque, while the inner aluminum layer is a suitable support material and is advantageous in terms of weight. Combination with a press fit can serve as a multi-layered starting material for forming a product according to the invention, but can also be produced by co-extrusion or by continuous casting.

In the above-mentioned variant, the slides can be subjected to pressure at a desired time, either individually or in pairs. In a preferred embodiment, the slides are both pressurized and retractable by means of the associated hydraulic cylinders, and there is no need for slides when forming from the central part of the shaft towards its ends, for the internal cam or the corresponding recess in the tool, the cams, and during this time the slides in the other recesses are pressed against the outer wall of the hollow shaft so that no deformation can occur at these points; the cams will be created later in these places.

As an alternative to the hydraulic pressure load of the slides, or their pistons or punches, their reversal can also be mechanically controlled by means of a wedge movable substantially parallel to the longitudinal axis of the hollow shaft, which is equipped with a wedge cam directly acting on the punches, that the slides move by moving the wedge accordingly. This means that even with this embodiment it is possible to deliberately achieve an overlap of the currently unusable recesses, or to release those places where no or only one cam is to be formed.

The successive shaping of the cams from the inside and the outside can also be carried out according to a particularly advantageous possibility of the invention in such a way that the individual manufacturing operations are

3 are carried out in different parts of the tool, that is, although it is necessary to vary the placement of the blank in the tool between operations, it is all the more simple and cost-effective to implement the tool; furthermore, no active elements, such as slides and the like, are needed in this case, which are mainly used in cases where there are no spatial problems, because in the production of a six-cam shaft for example and forming it in pairs from the outside. three forming tools in the tool.

Alternatively, locally designed cams may also be provided by means of internal mandrels introduced into the hollow shaft which, once in effect, like the aforementioned slides, initially prevent shaping at certain locations, unlike the slides, however, from the inside of the hollow shaft. The internal pressure is individually loaded only at the points where the cams are to be formed from the inside outwards at a given time, so that only at these points the hollow shaft can be deformed; the other areas are not under pressure and therefore there is no deforming force. That is, the internal pressure is not counteracted by means of slides, but the internal mandrel prevents the internal wall of the hollow shaft from being subjected to pressure in the recess areas into which the respective parts are not yet to be formed. In this way, the mechanically induced axial pressure together with the internal pressure causes the compression and finally the desired shaping only in those places where the inner wall of the hollow shaft is not covered by the inner mandrel against the internal pressure and where one or more recesses are made in the tool.

In a practical embodiment, two internal mandrels are preferably used which are to be inserted from both sides into the hollow shaft and which have an outside diameter allowing their insertion or retraction into the pistons transmitting mechanical axial forces to the end portions of the tube. This in turn makes it possible to advantageously shape the cams starting from the center of the shaft to its ends. Of course, the internal mandrels must be provided with coaxial passageways through which the pressurized environment can enter the shaft cavity.

This embodiment of the invention allows a relatively large number of recesses to be integrated at a relatively low cost.

It should also be noted that it is also within the scope of the invention to start from a blank which has been preformed by, for example, printing and / or cross-rolling the hollow shaft. This procedure allows the hollow shaft where it is to be shaped

- the pouches, to create a buildup of material in order to counteract wall reduction and possible under-expansion of the material.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are shown in the drawings. 1 shows schematically the basic construction of the tool without additional tools, with the intermediate product inserted in its initial and final state, in side and sectional view, FIG. 2 shows the tool with respect to FIG. 1 with details and with the aid of hydraulic cylinders individually controlled by slides in several mold cavities, FIG. 3 shows schematically a wedge strip for operating the slide punches according to FIG. 2, FIG. 4 is a diagrammatic top and cross-sectional view of a tool half with a plurality of receiving locations for progressively forming a blank, which is shown in a respective processing state at each receiving location; FIG. 5 shows a tool half for a further variation of use, with the semi-finished, i.e. hollow shaft, and with inner mandrels partially overlapping the inner wall of the hollow shaft, schematically in cross-section and in a top view, FIG. 6 shows a preformed hollow shaft which can serve as a preform for further shaping, for example, in the tool of FIG. First

DETAILED DESCRIPTION OF THE INVENTION

Before describing the drawings in detail, some basic remarks should be made. Thus, first of all, it should be noted that at the top of FIG. 1 and 2, the semi-finished product is shown in its final shape, while in its lower parts its initial state is shown, optionally in FIG. 6 shows its initial interoperative condition. For FIG. 1 to 5 it is moreover common that they schematically illustrate tools which are fundamentally suitable for the high pressure internal forming method and are preferably divided in a horizontal plane. They are provided with successive recesses, described in more detail below, i.e. the internal cavities of the tool in which the workpiece to be shaped, in this case a hollow shaft, is deposited, which is then subjected to frontally acting forces in the axial direction by means of punches arranged in a manner known from the tool, it presses the pressure environment so that the workpiece is loaded by high internal pressure and axial force acting on the ends of the tube. This results in a desirable bulge in the closed tool. The diameter of the side punches is thus

-Ί large to allow these punches to be inserted into the tool and to push the hollow shaft, provided with coaxial channels through which the pressurized environment can pass into the hollow shaft cavity. The punches are provided at their free end with sealing heads serving to seal the workpiece, i. tubes at both ends and to introduce axial forces into the blank as well as to apply pressure to the inner part thereof. The pressure is preferably applied by means of a multiplier with a structure similar to that of a hydraulic cylinder, and can be increased because the liquid is compressed in the interior of the multiplier, or reduced as the fluid pressure decreases.

For a general idea, FIG. 1 shows in a simplified manner a tool with an upper half 1 and a lower half 2, which in the closed state form a hollow space 3 as a mold for the final shape of the camshaft. It should be noted - and this also applies to further illustrating other preferred exemplary embodiments of the invention - that the individual cams are shown in one plane for ease of understanding; it is obvious that they are generally radially angularly offset. At the places where the cams are to be formed, the hollow space 3 is provided with corresponding recesses 4, in the illustrated embodiment only three recesses 4, because this is a representation of the principle of solution, and these recesses 4 press corresponding parts of the hollow shaft walls. The recesses form part of the total number of internal tool-cavities (form-nest) in which the precursor stock is placed.

In the lower half of FIG. 1 shows the initial state with the hollow shaft 5 mounted, while in the upper half of FIG. 1 shows a finished state with finished cams 6, i.e. a camshaft made according to the invention in one piece of material. The side punches 7 are provided with heads 8 and a transitional coaxial channel 9, in cross-section shown on the left side, through which the pressurized environment enters the interior of the hollow shaft 5.

In this exemplary embodiment, the tube, as a hollow shaft 5, is inserted into a tool 1, 2 having a camshaft geometry and internal high pressure and is formed by axial material feed. That is, the hollow shaft 5 gradually moves from its initial state to its final state, so that the pressure punches 7 engage and exert pressure on the front surfaces of the hollow shaft 5 while supplying the pressure fluid through the channels 9. As a result of the action of the two overlapping of force during the insertion of the pressure punches 7 into the inner part of the tool, the hollow tube is transformed into the final state shown.

In the following embodiments of the invention, the same reference numerals as in FIG. First

As mentioned above, in the exemplary embodiment of FIG. 2, the tool consists of the upper half of the lower half 2, and its hollow space 3 is formed in the geometry required for the camshaft to be produced. In this embodiment, six recesses 4 for the six cams to be produced are arranged in the tool. The ducts 9 for supplying the pressurized medium are not shown in the punches 7/8 for the sake of simplicity. In each case, the recesses 4a, 4b facing the shaft ends facing the shaft ends only have schematically represented slides 11a. eventually 1 lb. which are displaceable with respect to the recess according to the illustrated double arrows in a practically vertical direction, by means of punches 13a and 13b, respectively. connected to the hydraulic cylinders 12a. 12b. This is a slide 11a. 1 lb movable in both directions; in the starting position, they are located with their front face in the position shown in the drawing as the upper position, i.e. in the position in which they engage the outer wall of the hollow shaft 5. The two inner recesses 4 are not provided with a slide.

An exemplary manufacturing method is as follows:

Since there are four slides 11a. 11b are in the extended starting position, they are formed by the axial displacement of the shaft material first inside the lying cam 6 without the flow of the material being limited by the formation of the outer cams, i.e. cams lying closer to the ends of the shaft. After the two inner cams 6 have been formed with the hydraulic cylinders 12b arranged outwardly from the two finished inner cams 6, the slides 11b are retracted. and for this purpose further cams 6b are formed, whereby the axial creep of the material is not reduced, since the cams 6a are not yet formed on the end faces of the shaft. In the last phase of the high pressure internal molding, the slides 11a are displaced and the corresponding cams 6a are formed.

Instead of hydraulic slide 1 la. 11b may be such slides 11a. 11b also mechanically operated. For this purpose, the wedge strip 14 shown in FIG. 3 in which the wedge cams 15a are provided. optionally 15b. in the order corresponding to the position of the punches 13a. 13b. The wedge 14 is in this case arranged in the region of the hydraulic cylinders 12a. 12b and is movable in a direction parallel to the elongate person of the hollow shaft 5, wherein the wedge cams 15a. 15b directly affect the respondents

-9 bumpers 13a. optionally 13b. In this case, only a single hydraulic cylinder (not shown) that moves the wedge bar 14 in the direction shown in FIG. 3 two-way horizontal arrow. In the position shown in FIG. 3 are punches 13a. 13b. on which the wedge cams 15a act directly. 15b. in the retracted state, i.e. in the position in which the inner cams 6 are first formed.

When the wedge bar 14 is moved to the left (FIG. 3), the slides 11a are compressed under the effect of the internal pressure in the hollow shaft 5. 11b below because their punches 13a. optionally 13b may extend along the slope of the wedge cams 15a and 15b, respectively. bend downwards.

The wedge strip 14 described above allows direct control in the sense of the procedure explained above with reference to FIG. 2, because, as also shown in FIG. 3, the inner wedge cams have shorter faces, i.e., when moving to the left, the punches 13b located in front of the punches 13a reach the tapered cam area 15b rather than the punches 13a. so that before the cams 6a are formed, the cams 6b are first formed. The camming of the cams 6a takes place only when the punches 13a have reached the bevel of the wedge cams 15a.

To further improve the creep of the material in forming the inner cams 6, recesses 4 can also be provided with slides, which are correspondingly defined by punches operated by the wedge cams (not shown here) arranged between the wedge cams 15a, 15b.

Fig. 4, in which the side punches 7/8 are not shown, represents a particularly preferred embodiment of the invention. In plan view, there is shown the lower half 2 of the tool with three mold cavities of different geometry, i. a different number of recesses, with a camshaft 5 formed in each cavity in a corresponding operation. The shaping in the individual mold cavities may take place simultaneously or sequentially.

FIG. 4, it is clear that the illustrated production of the six-cam camshaft is performed in three operations, the hollow shaft 5 being subjected to a first shaping operation in the forming cavity shown in the upper part of FIG. 4, in which the two inner cams 6 are formed. The blank thus formed is then transferred to the forming cavity shown below, which is provided with two further recesses 4b. In this second operation, further cams 6b are formed on the hollow shaft 5 by pressing the material into the recesses 4b. Finally, the hollow shaft 5 is transferred to a forming cavity equipped with six recesses 4, 4a, 4b. shown in the lower part of FIG. 4 in which the final shaping is carried out.

- 10Fig. 5 also represents a preferred embodiment of the invention. It shows the lower half 2 of the camshaft production tool with six cams 6 on which the two inner cams 6 have already been formed. Also by means of this tool, the cams 6 are produced progressively from the inside outwards. For this purpose, two internal mandrels 16 are used which, in the illustrated position of the in-process procedure, are inserted into the hollow shaft 5 as far as possible to close and protect against high internal pressure those areas in which the walls have walls only in the next operation. hollow shaft 5 to be pushed into the outer recesses 4a, 4b. For this purpose, the inner mandrels have an outer diameter which allows their telescopic insertion into the hollow shaft 5 by a corresponding play with respect to its inner wall. At their free end lying inwardly, the inner mandrels 16 are provided with a face seal 17 or wedge-sealing rings which seal the tube or hollow shaft 5 as soon as pressure increases in its inner part. The higher the pressure, the greater the sealing force of the wedge seal rings; the sealing force is thus derived from the internal pressure.

The punches 7/8 in this case are designed to have on one side an outer diameter which, as in the exemplary embodiments described so far, permits introduction into the tool recess, i.e. a diameter which approximately corresponds to the outer diameter of the hollow shaft 5, but from the exemplary embodiments described so far, it has an expanded embodiment, and its diameter is so large that the inner mandrels 16 can be bi-directionally moved therein. Thus, punches 7/8 can exert their axial force on the end faces of the hollow shaft 5 while simultaneously moving The coaxial duct 9 for the pressurized medium is now always located in the inner mandrels 16. The details of this process are apparent from the embodiment shown in section on the left of FIG. 5th

According to this concept, it is possible to carry out the following process: First, the inner mandrels 16 from the end portion of the punches 7/8. that engage the hollow shaft, extend to the position shown in FIG. 5 and are inserted into the hollow shaft 5, which can be carried out by means of suitable elements not shown here and not shown at the outer end of the hollow punches 7/8, wherein the inner mandrels 16 can, for example, pass through the punches 7/8 up to their outer end. Upon subsequent application of local internal pressure, both internal cams are formed as shown.

In the next phase, the inner mandrels 16 are moved outwardly until the area of the further recesses 4b is released so that the internal pressure can now act on these areas

11 of the hollow shaft 5 into which further cams 6b can be formed while simultaneously axially moving the material from the end portions of the tube, the inner mandrels 16 being displaced inwardly in order to replenish the necessary amount of material to avoid friction between the wedge front by sealing 17 on the inner mandrels 16 and the inner tube wall.

The formation of this second pair of cams 6b is always followed by a relief of the internal pressure, whereby the sealing force of the wedge-sealing rings of the face seal 17 is minimized while maintaining the elastic intrinsic proportion of the wedge-sealing rings. Thereafter, the inner mandrels 16 are pushed further outwardly to form a further pair of cams 6a.

In this version, too, the optimum material supply can be achieved because, as already mentioned in connection with the exemplary embodiments described above, in each operation where the cams are formed progressively away from the central portion of the hollow shaft towards its end portions, the material must be pushed away from the ends of the pipe without restraint, since it is not yet deformed in these areas not yet under pressure.

Only to supplement these various applications of the method according to the invention, FIG. 6 shows an initial blank for a hollow shaft 5 to be shaped into a six-cam camshaft and in the state shown in FIG. 6, produced by conventional techniques, such as compression, cross-rolling, and the like, where there are accumulations of material 19 at the points where the cams are to be formed to counteract the reduction in wall thickness and possible insufficient material expansion.

«

Such a preform is suitable, for example, for processing in the tool shown in FIG. 1 and 2, wherein the axial flow of the material is also reduced due to the accumulation of material.

Industrial usability

In particular, the invention is for the production of elongated hollow bodies, which are widely used in the automotive industry.

Claims (11)

PATENT CLAIMS Method for producing an elongated body with at least one concave part, in particular a camshaft, by a high pressure internal forming, characterized in that the concave parts are formed individually or sequentially in groups, by progressively feeding the material in the axial direction. Method according to claim 1, characterized in that the shaping process starts from at least one end of the shaft of the arranged feed tool at the furthest distal portion and is progressively carried out further towards the feed tool. Method according to claim 1 or 2, characterized in that the concave parts are shaped against the pressure of a plurality of reciprocating slides either individually or in groups in succession. Method according to claim 1 or 2, characterized in that the individual manufacturing operations are carried out in different parts of the tool. Method according to claim 1 or 2, characterized in that the locally carried out shaping of the concave parts is guided by means of at least one inner mandrel which is introduced into the hollow body, is longitudinally displaceable therein and overlaps positions in which no concave shapes are currently formed. section. Method according to one of claims 1 to 5, characterized in that a multi-walled hollow blank is formed. Device for carrying out the production method according to claim 1, characterized in that it comprises a multi-part tool (1, 2) for receiving and shaping a hollow body (5), which is provided with recesses (4) on the concave parts (6), two opposing and coaxially arranged punches (7/8) with coaxial channels (9) for supplying the pressurized medium to the interior of the hollow body (5) and the punches (7/8) with a longitudinally movable hollow inner mandrel (16) retractable at each end of the hollow housing 13 (5), which at its end extending into the hollow body (5) is provided with a seal (17) abutting the inner wall of the hollow body (5). Device according to claim 7 for carrying out the method according to any one of claims 1 to 3 and 6, characterized in that at least some of the recesses (4) have a movable slide (11a, 11b) perpendicular to the axis of the hollow body (5). Apparatus according to claim 7, in particular for carrying out the method according to any one of claims 1, 2, 4 and 6, characterized in that it comprises at least one tool with a set of forming cavities with different recesses. Apparatus according to claim 9, characterized in that the two-part tool (1, 2) is provided with a set of forming cavities with a gradually increasing number of recesses. Apparatus according to claim 7, characterized in that the coaxial channels (9) of the punches (7/8) have a diameter enabling the inner mandrels (16) to be inserted into these punches (7/8).