CN1222379C - 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 and device for manufacturing a camshaft

The invention relates to a method for producing long hollow parts, in particular camshafts, and a device for carrying out the method.

Many methods of manufacturing camshafts are known. Here, basically divided into two groups.

Belonging to the first group are camshafts produced by conventional methods, which are either forged or cast as blanks, to be precise not only as solid bodies but also as chilled castings, where the two semi-finished products are also processed The other processing steps are firstly mechanical machining, followed by surface conditioning with heat treatment, and finally grinding of bearing bearing points and cams. Disadvantages of camshafts produced in this way are in particular their relatively heavy weight, which also results in high moments of inertia, which can cause damage to the bearings, for example due to torque variations, and involve high costs in the blanking process.

Belonging to the second group are joined camshafts, in which the cams are manufactured as a single piece and then connected to a shaft in various ways. For example, the cam can be welded to a hollow shaft or inserted into a tube and shrunk fit onto the tube. For the latter production method it is known to place the cammed tube or hollow shaft in a correspondingly shaped mold and to expand the tube according to the internal high pressure deformation method (IHU-method), where the cams expand elastically and the tube Plastic expansion, so that the cam is fixedly seated on the tube or hollow shaft by a press fit.

With the IHU method, the tubular hollow part to be deformed is simultaneously subjected to internal pressure and an axial force acting on one end thereof. Liquids or elastomers are suitable as pressure medium. In general, axial force can be transmitted by rigid tools, such as pistons, punches and similar items that can directly or indirectly act on one end of the workpiece.

Examples of engaged or assembled shafts in the above sense are known from DE3409541A1 and DE3521206A1. The two known proposals have in common the costly separate manufacture of the functional parts to be fastened to the shaft, especially in the case of individual cams, and the overall cost associated with the steps required for the joining process. Operating costs are also relatively high.

Furthermore, a method is known from US-PS2222762, in which a tubular blank is first heated and then placed in a mold. The blank, which is easily deformed by heating, is stabilized from the inside by means of a support medium, gas or liquid. At the same time, the blank is pressed into the mold either by moving the designed mold itself or by means of an axial force from a punch independent of the mold, where the support medium is responsible for keeping the heated blank from collapsing. The disadvantage of this method is that in order to obtain the necessary plasticity of the material, the blank must be heated in advance in order to be pressed into the mold. This heating means, in addition to the change of the metallographic structure, an additional work step which makes the method too expensive. Furthermore, the working pressure is only achieved by axial forces, which leads to an inhomogeneous material flow and thus to an inhomogeneous stress distribution in the workpiece.

Known a kind of method of manufacturing camshaft from JP 57206530A, in this method, a hollow part heated in advance is pressed in the mold by means of pressure liquid step. Here too, heating is performed beforehand; moreover, there is no axial push, which likewise leads to inhomogeneous material flow; moreover, the deformation steps cannot be carried out consecutively, but only in one step.

The present invention is based on the problem of creating a method and a method for implementing this that not only saves tools and working steps, but also reduces the outlay for producing longer hollow parts with increased efficiency and avoids a reduction in wall thickness. device for a method.

This problem can be solved by adopting the internal high pressure-deformation method of the present invention, that is, the cams are sequentially formed from the middle of the shaft to the shaft end under the condition of axially pushing in the material, either individually or in pairs. This means that the IHU-method now differs substantially from the prior art in that it is not used for enlarging the hollow shaft in order to create a press-fit seat or, as in the case of DE3521206A1, to create an additional axial fixation, but for the convex The protruding part (cam) is deformed in one piece, especially a cam which is itself made of a tube or profile - hereinafter referred to simply and non-restrictively as "hollow part" or "hollow shaft" or "shaft", whereby in the protruding part The continuous deformation (cam) is not only particularly cost-effective but also saves time during the process for producing the hollow part as a whole.

What is common to the various implementations of the further embodiments of the invention is that the hollow shaft is deformed in several steps, wherein the cam is continuously shaped depending on its configuration and/or its position on the shaft. This means, as also shown in detail in the following embodiments, that on the one hand the cams can reach their final form step by step, but on the other hand can also be successively formed on the shaft in the sequence required for their arrangement. Of course, both possibilities can also be used overlappingly.

In an advantageous embodiment of the invention, the cams are formed successively from the center of the shaft to the ends of the shaft, which can be done in pairs in a particularly economical manner. It is also conceivable that the cam is formed from one end of the shaft to the other end of the shaft. Significant advantages of this process are, inter alia, the relatively low-cost manufacture of the cams without the need for individual manufacture, and the fact that the calibration provides for an unimpeded axial flow of material into the deformation zones. According to the invention, by applying an axial force and a feed movement, the feeding of the pipe end is not blocked by the pair of cams present before, that is to say, the pipe material can be fed unimpeded into the deformation zones. If this pair has been formed, the next pair of cams is formed. The advantage here is that, due to the axially generated compressive stresses, relatively large deformations of the tube material can be achieved which exceed the elongation at break of the material. Furthermore, the thinning of the wall thickness in the deformation zone (cam to be formed) is considerably reduced, that is to say a uniform wall thickness can be obtained, that is to say a high component stability is achieved. There can be many possibilities suitable for practical application.

The cams can thus be formed individually or in groups successively against the pressure of a plurality of slides or similar objects whose return can be controlled, depending on the positional target.

For this and the following embodiment, in combination with the previously described possibility of forming the cams successively from the middle of the shaft to the end of the shaft, a particular advantage is that by controlling the flow of material into the inner region, that is to say, in the middle of the shaft no Higher material tensile stress (thinning deep drawing), because during the forming of the cam located inside, the material flow is not blocked by the cam stored in front of it when pushing the material axially. In addition, this makes it possible to produce camshafts made of less stretchable material, which have a higher cam height and a greater number of cam pairs and bearing supports. Like the camshaft needed for, say, a 12-cylinder engine. There is less material upset (flattening) at the component end and a uniform wall thickness distribution, another advantageous possibility is an overall reduction of the wall thickness if necessary.

In the present invention, various cold forming materials can be used, such as "tailored blanks", "tailored tubes", and double-layer materials, such as steel/steel or steel /aluminum combination materials, sandwich hollow parts or coated hollow parts; for steel/aluminum combination materials, steel is preferentially used as the outer filler and aluminum as the inner filler. A considerable improvement in workpiece properties can be achieved through this; the steel sheath brings better wear properties, heat treatment properties and torque properties, while the inner aluminum layer is a good support material and has advantages in terms of weight. Composite materials that are shrink-fitted can be used as multi-layer raw semi-finished products shaped according to the invention, however, it is also possible to produce such semi-finished products by mutual extrusion or by continuous casting.

In the above-mentioned variants, the slides can be pressed at the desired time, that is, individually or in pairs, depending on the situation of use. In an advantageous embodiment, each slide can be stroke-controlled and force-controlled by means of a hydraulic cylinder assigned to each slide, wherein, during the shaping from the center of the shaft to the end of the shaft, the internal cams or corresponding molds The slide plate is not required for the milling slots of , because the camming starts there, and during this time, in the remaining milling slots, the slide plate is always pressed against the outer wall of the hollow shaft, so that there is no shaft deformation in these places; There, the cam is only formed at a later moment.

In addition to the optional hydraulic pressurization of the slide or its piston or punch, it is also possible to use mechanical stroke control, to be precise, by means of a wedge moving substantially parallel to the longitudinal axis of the hollow shaft, which is fitted directly against the punch. In this way, the stroke of the slide plate can be adjusted through the appropriate movement of the wedge bar, that is to say, with this embodiment, it is possible to purposely cover the milling grooves that do not need to be pressurized or open those that should not be or are being cam-shaped parts.

According to a particularly advantageous implementation possibility of the invention, the camming can be carried out successively from the inside out, that is, the individual production steps are carried out in different mold regions, that is to say, although it is necessary to take over from one of the molds between the individual process steps One piece to another receiving piece to change the workpiece, however, the structure of the mold can be made simpler and the cost is relatively low by this; moreover, in this case, no movable elements such as slide plates or similar objects are provided, and if there are no position problems, the overall Primarily for support, since for example 6 cams and forming in pairs from the inside out require three workpiece receptacles with correspondingly milled grooves in the mold.

As an option, the local targeted shaping of the cam can also be carried out by inserting the inner shaft of the hollow shaft, which can be used in the same way as the slide plate described above, first preventing the shaping of certain parts, of course this is different from the The skateboard inside the hollow shaft is different. Only the cam (from the inside to the outside) to be shaped at that time is exerted pressure (local), like this, only can carry out deformation there; Other ranges do not apply pressure, therefore there is not produced deformation force either, that is to say, here Instead of retaining the sliding plate against the internal pressure, the inner mandrel prevents the pressure on the inner wall of the hollow shaft, which should not yet enter the region of the deformed milling groove. Therefore, the mechanically induced axial pressure together with the internal pressure only upsets (upsets) there and finally produces the desired deformation at the inner wall of the hollow shaft which is not covered by the mandrel against the pressure and which has one or more milled grooves .

In the actual construction, two inner mandrels are advantageously used, which are inserted into the hollow shaft on both sides and have a diameter which enables them to be inserted or entered into the piston which transmits the mechanical axial force to the tube end. This again enables an advantageous, locally continuous camming from the center of the shaft to the shaft ends. Of course, the inner mandrel must be provided with a coaxial through-channel so that the pressure medium can reach the inside of the mandrel.

This embodiment of the invention allows a relatively high number of milled grooves to be concentrated in the tool with relatively low tool outlay.

It should be mentioned that within the scope of the invention it is also possible to start from a semi-finished product which has been preformed by conventional methods, for example by upsetting and/or cross-rolling of the hollow shaft. This makes it possible to provide a material build-up at the region of the hollow shaft where the cam is to be shaped, in order to overcome the reduced wall thickness and possibly insufficient elongation.

Further details and advantages are explained below with the aid of the appended drawings showing an advantageous embodiment of the invention. The accompanying drawings show:

Figure 1: A basic structural mold with the workpiece placed in its original and final state and without additional tools, shown in a cutaway side view;

Figure 2: Compared with the mold shown in Figure 1, it is more detailed, and has a mold with stroke control and force control slides in some modeling nests alone through hydraulic cylinders

Figure 3: The wedge used to control the slide punch of Figure 2, shown schematically;

Figure 4: Die half with the workpiece in its then formed state, shown in cross-section in top view, with multiple jackets for the progressive manufacture of the workpiece;

Fig. 5: The half part of the mold in another use scheme with the inserted, partially completed workpiece (hollow shaft) and the inner mandrel partially covering the inner wall of the hollow shaft, shown in section from the top view;

FIG. 6 : A preformed hollow shaft used as a raw semi-finished product, eg in a mold according to FIG. 1 .

Before discussing the schematic diagram in detail, some basic instructions are in order. It should first be noted that in the upper part of FIGS. 1 and 2 the workpiece in its final shape is shown, whereas in the lower part it shows the original state or in FIG. 6 the initial intermediate state. Furthermore, FIGS. 1 to 5 have in common the fact that they show schematically a tool which is basically suitable for the internal high-pressure forming method, the so-called IHU method, and which is preferably divided into two parts horizontally. They have one or more recesses (cavities in the mold), the shape of which will be explained in more detail below, into which the workpiece to be deformed, in the present case the hollow shaft, is inserted and placed outside the mold A lateral, known-actuated punch exerts an axial force on the end face, wherein the pressure medium is simultaneously pressed into the hollow shaft, so that the workpiece is subjected to high internal pressure and axial forces acting on the tube end. The desired projections (cams) are thus formed in the closed mold. The lateral punches are dimensioned in such a way that they can be inserted into a die and upset (upset) the hollow shaft and have coaxially extending channels through which pressure medium can pass into the hollow shaft. The free ends of the punches are equipped with sealing heads which are used for sealing the semi-finished product (pipe) at the pipe end and for introducing axial forces into the workpiece and pressure into the interior of the workpiece. Preferably, the pressure is generated by a pressure multiplier (structured like a hydraulic ram) and can be increased (fluid inside the pressure multiplier is compressed) or decreased (fluid is unloaded).

In FIG. 1 , a tool with an upper half 1 and a lower half 2 is shown very simply for overall illustration, which in the closed state forms the hollow chamber 3 as the final shape of the camshaft. It should be explained here that the individual cams are shown in one plane only for the sake of clarity; this also applies to the description of the other advantageous embodiments. Of course, in general they are radially staggered. The hollow cavity 3 has some corresponding milling grooves 4 on the position where the cam should be at the end. In the existing embodiment, only three are shown in the schematic diagram, and the corresponding wall regions of the hollow shaft are pressed into the milling grooves. A slot is a part of the cavity (cavity) of the overall mold in which a workpiece is placed.

The original state of the hollow shaft 5 is shown in the lower part of Fig. 1, while the final state of the formed cam 6 is shown in the upper part, that is to say, the camshaft manufactured in one piece according to the invention . A side pressure punch with a pressure punch tip 8 is designated 7 , which according to the left sectional view has a coaxial continuous channel 9 through which the pressure medium enters the hollow shaft 5 .

In this embodiment, the hollow tube 5 is inserted into the mold 1/2 with the geometry of the camshaft to be formed and deformed by the internal high pressure as the material is pushed in axially. This means that an axial force is generated by the pressure punch 7 close to the end face of the hollow shaft 5 and at the same time the pressure medium is fed through the channel 9 and the hollow shaft is deformed during the insertion of the pressure punch into the mold under the influence of the two superimposed forces , until the final state shown, so that the hollow shaft 5 continuously reaches its final state from its original state.

The embodiments shown below use the relevant reference numerals for corresponding parts in FIG. 1 .

In the embodiment according to FIG. 2 , as explained above, the mold consists of an upper half 1 and a lower half 2 , the cavity 3 of which is shaped according to the required geometry of the camshaft. Here, in this exemplary embodiment, six milled grooves 4 are provided in the mold for the six cams to be formed at the time. For the sake of simplicity, the pressure medium supply channel 9 to the plunger 7/8 is not shown. Here, the slides 11a or 11b, shown only in schematic form, are arranged in the outer, that is to say, in the milled grooves 4a and 4b at the shaft end, in which they can be substantially perpendicular to the hollow according to the double arrows shown. The longitudinal axis of the shaft 5 is moved, more precisely, by the punch 13a or 13b connected to the hydraulic cylinder 12a or 12b. The slides 11a and 11b are thus stroke- and force-controllable; in the initial position, their end faces are in the upper position in the figure, that is to say next to the outer wall of the hollow shaft 5 inserted therein. The two inner milling grooves 4 do not have slide plates.

The process is as follows: Since the four slides 11a and 11b are located in their original position at the front, the cam 6 which is first located inside is formed under the axially pushed-in shaft material, the material flow is not caused by the external, that is to say , is hampered by camming closer to the shaft end. After the forming of the two inner cams 6 is completed, the cylinder 12b closest to the formed cam is retracted so that the slide plate 11b is also retracted and the cam 6b is formed as the next one. Here, the axial material flow will not be blocked. , because the cam 6a on the terminal side has not yet been formed. In the last stage of the IHU deformation, the slide 11a retracts and shapes the corresponding cam 6a.

Instead of a hydraulic actuation of the slides 11a and 11b, their control and movement can also be performed mechanically. For this purpose, a wedge 14 is shown in FIG. 3 , which shows an arrangement in which the number of wedge-shaped projections 15 a , 15 b corresponding to the number of slide plates 11 a , 11 b is provided in the respective positions of the slide punches 13 a , 13 b. In this case, the wedge strips 14 are arranged in the region of the hydraulic cylinders 12a and 12b and can move parallel to the longitudinal axis of the hollow shaft 5, where the wedge-shaped projections 15a and 15b act directly on the corresponding punch 13a or 13b . In this case, only a single hydraulic ram, not shown, is required, which pushes the wedge strip in the direction of the horizontal double arrow in FIG. 3 . In the position according to FIG. 3 , the punches 13 a and 13 b , against which the wedge-shaped projections 15 a or 15 b act directly, are in their retracted position, that is to say in the position in which the inner cam 6 is first formed.

By wedge strip 14 moving to the left ( FIG. 3 ), when hollow shaft 5 exerts internal pressure at the same time, slide plates 11a and 11b in FIG. The ramp can be moved downwards to avoid.

Using such a wedge can be directly controlled according to the process described above in conjunction with FIG. 2, also shown in FIG. 3, because the inside wedge has a shorter end face, that is to say, when moving to the left , the punch 13b arrives in the range of the wedge-shaped cam block 15b slope before the punch 13a, so that the cam 6b is first formed before the cam 6a is formed, and the cam 6a is formed when the punch 13a arrives in the range of the slope of the wedge-shaped projection 15a. take shape.

In order to also improve the material flow during the shaping of the inner cam 6, slides can also be placed in the milled groove 4, which are correspondingly pressed by the punch between the wedge-shaped projections 15a and 15b, not shown here. Out of the cam control.

FIG. 4 , which does not show side punches 7 / 8 here, shows a particularly advantageous embodiment of the invention, in which, in the lower mold half 2 shown in plan view, 3 There are three molding nests for workpieces of different geometries (ie different numbers of milling slots), in each of which a workpiece 5 that has been completed at this stage is located here. The shaping in the individual shaping nests can take place simultaneously or successively.

Fig. 4 clearly shows that the camshaft 5 equipped with six cams is completed in three steps, here, in the first process step, the hollow shaft 5 is deformed in the upper molding nest in Fig. 4 until two The cam 6 that is positioned at the inside is formed so far. The semi-finished product shaped in this way is then placed in a molding nest shown below, which has two additional milled grooves 4b, in which the cam 6b is deformed in this second stage. Finally, the hollow shaft 5 is fed into the molding nest in FIG. 4 below, equipped with six milled grooves 4, 4a, 4b, where it is then deformed to its final state.

FIG. 5 —an equally advantageous embodiment—shows the lower mold half 2, where a camshaft with 6 cams is produced, of which the two inner cams have already been produced. The cam 6 can also be produced continuously from the inside out with this mold, for which two inner mandrels 16 are used, which, in the intermediate production state shown, are inserted into the hollow shaft 5 on the end side so far that the They protect the regions within the hollow shaft from internal pressure that are only to be deformed into the outer milled grooves 4 a and 4 b during a further process. For this reason, the outer diameter of the inner shaft allows telescopically inserting the hollow shaft 5 miles with a certain gap with the inner wall. At its free, inner end, the inner shaft 16 is each equipped with a top seal 17 or a wedge-shaped sealing washer, which seals the pipe or the hollow shaft 5 as soon as pressure is generated inside. The higher the pressure, the greater the sealing force of the wedge sealing gasket; thus, the sealing force is generated by the internal pressure.

In this case, the punch 7/8 is designed such that, on the one hand, as in the embodiments described so far, the punch has an outer diameter that allows it to be inserted into the die opening, that is to say, has an approximately equal This outer diameter is different from the outer diameter of the hollow shaft 5, but unlike the previous embodiments it is an enlarged sleeve whose diameter is so large that the inner shaft can be inserted telescopically into the inside and out from the inside. The plunger 7 / 8 therefore exerts its axial force as before on the end side of the hollow shaft 5 , while at the same time the inner mandrel 16 can move inside. The coaxial channels 9 for the pressure medium are now respectively located in the inner mandrel 16 . This can be seen in detail from the section view in the left half of the figure.

With this approach, the following process can be achieved: firstly, the inner mandrel 16 emerges from the punch 7/8 which is next to the hollow shaft on the end side and enters the position shown in FIG. 5 and enters the hollow shaft 5, This can be done by suitable means, not shown here, at the outer end of the hollow punch 7 / 8 , for which purpose the inner mandrel can pass through the punch 7 / 8 to its outer end, for example. Upon subsequent local application of internal pressure, the two inner cams 6 are formed in the manner shown.

As a next step, the inner mandrel 16 is retracted so far outwards that the closest milled groove 4b area is opened, so that the internal pressure can now act on this hollow shaft area, and then, in order to form the cam 6b, this area enters these Milling deformation, to be precise, is at the same time as axially pushing in starting from the pipe end, here the inner mandrel 16 moves inwards with the length of the material pushing inwards, in order to avoid wedge-shaped sealing gaskets on the inner mandrel 16 17 and the friction between the inner wall of the pipe.

The internal pressure decreases each time after the formation of the second pair of cams 6b, so that the sealing force of the wedge-shaped sealing washer 17 drops to a minimum (the own elastic part of the wedge-shaped sealing washer). After this the inner mandrel 16 also continues to move outwards and the next pair of cams 6a is formed.

Even in this case, an optimal insertion of the material can be achieved, because in each process stage the camming can be carried out step by step from the middle of the shaft to its end, as already mentioned several times in the previously described embodiments In , deformation cannot take place in the range where no pressure is applied, so the material can be pushed from the end without hindrance.

Only in order to supplement the various possibilities of use of the method according to the invention, the original semi-finished product of the hollow shaft 5 is shown in FIG. The hollow shaft is pre-formed by upsetting, cross-rolling, etc. to the state shown in FIG. 6, where a material build-up 19 is produced at the point where the cam is to be formed, in order to overcome the reduced wall thickness and possible insufficient elongation of the material. For example, such a semi-finished product is suitable for processing in a mold as shown in Figures 1 and 2, and also reduces the axial material flow due to material accumulation.

The invention is used for the production of preferably relatively long hollow parts which are used in many ways, in particular in the automotive industry.

Claims (11)

1. The method for manufacturing a camshaft by an internal high pressure-deformation method is characterized in that, The cams are formed individually or in pairs from the center of the shaft to the end of the shaft while pushing the material axially. 2. according to the described method of claim 1, is characterized in that, Camming begins at the furthest distance from the push tool arranged at the end of the at least one shaft and progresses progressively towards the push tool. 3. according to the described method of claim 1 or 2, it is characterized in that, The cams are formed individually or in pairs successively against the pressure of a plurality of pressure- and/or stroke-controllable slides. 4. according to the described method of claim 1 or 2, it is characterized in that, The manufacturing steps take place in different mold areas. 5. according to the described method of claim 1 or 2, it is characterized in that, The locally targeted shaping of the cam is controlled by at least one inner mandrel which enters into the shaft, moves longitudinally within it, and covers exactly the position of the cam that is not shaped. 6. according to the described method of claim 1 or 2, it is characterized in that, Processing of multi-walled hollow semi-finished products. 7. A device for manufacturing camshafts using the internal high pressure-deformation method, having - a multi-part tool (1, 2) that clamps the shaft (5) and is provided with a milling slot (4) for the cam (6) to be formed; and - two coaxial punches (7, 8), but facing each other to upset one end of the shaft, - a coaxial channel for the supply of pressure medium to the interior of the shaft, and - at least one hollow inner mandrel (16) which moves longitudinally in the shaft (5) and punches (7, 8) and which is inserted into one end of the shaft respectively, - at least at the end where it is inserted into the shaft (5) is fitted with a seal (17) against the inner wall of the shaft. 8. The device according to claim 7, characterized in that, A slide (11a, 11b) movable perpendicular to the longitudinal axis of the shaft is inserted into at least several milled grooves (4). 9. The device according to claim 7, characterized in that, There are one or more molds which have a plurality of pockets each with a different number of milled slots. 10. The device according to claim 9, characterized in that, A two-part mold (1, 2) has a plurality of profile grooves milled in increasing numbers from one receptacle to the other. 11. The device of claim 7, wherein: The diameter of the coaxial channel (9) of the punch (7,8) allows the inner mandrel (16) to be inserted into the punch (7,8).

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