Patent Application
20050232803
The present invention relates to methods and systems for producing a sintered material/plastic composite component. More particularly, the present invention relates to producing such a composite component using a system having a lower die, an upper die and at least one slide, which together define a mold cavity for placing in a sintered material component.
A sintered material/plastic composite component (hereafter “composite component”) refers to a workpiece in which a sintered material component is made to bond with a plastic molding compound, which is subsequently attached to the sintered material component with interlocking and frictional engagement (after the curing of the plastic). It is at the same time intended to be possible also to include one or more further components of any other material in this process, so that the further component is also incorporated in the composite of the sintered material component and plastic with interlocking and frictional engagement. A sintered material component includes at least one of sintered metal component; a sintered ceramic component or the like.
A typical method for producing a composite component comprises bonding the plastic with the sintered material component (and possibly one or more further components) in a pressureless manner as part of a casting process. Pressureless casting has an advantage that, in spite of the brittleness of the sintered material component, a composite component can be produced without running the risk of the sintered material component being destroyed thereby.
However, such a pressureless casting process has a disadvantage that it is comparatively slow and does not represent great process reliability. Furthermore, the chance of cavities not being completely filled (formation of voids) is not ruled out.
Therefore, the injection-molding method is generally preferred in mass production. However, this method has not so far been used in connection with sintered material components because the pressure prevailing during the injection molding has the tendency to destroy the sintered material component.
If the injection-molding method is applied, a composite component is therefore generally produced by a combination of a non-sintered compact steel component and plastic (and possibly one or more further components).
For example, it is known for the production of injection valves for modern diesel engines to produce a composite component on the basis of this method.
This involves initially producing a magnetic pot from a compact steel with high precision. A grinding step and an eroding step are among the steps thereby performed. On account of the generally inferior magnetic properties of compact steel, it may therefore be necessary to provide complex incisions to improve the magnetic properties of the magnetic pot.
Also produced is a coil component, in which a coil is wound around a plastic coil former, two terminal pins being cast, injection molded or inserted into the coil former with interlocking engagement. The terminal pins are then electrically connected to ends of the wound coil.
This coil component is inserted into an annular opening of the magnetic pot, the terminal pins being led through bushings, so that they protrude from the opposite side.
Subsequently, this arrangement is inserted into an injection mold and the remaining cavities between the coil component and the magnetic pot are filled with injected plastic in order to enclose the coil component captively in the magnetic pot. Subsequently, finishing (flash removal, possibly grinding, etc.) may also be performed if need be.
A compact steel/plastic composite component of this type can be used as a stator for a solenoid valve which is, for example, part of a unit-injector system for modern diesel engines. In this case, a solenoid valve needle is led through a central clearance in the magnetic pot and can be adjusted in the axial direction when current is supplied to the coil component.
The magnetic pot made of compact steel is comparatively expensive to produce.
It is accordingly the object of the present invention to provide methods and systems for producing a composite component with which the composite component can be produced at lower cost.
This object is achieved by a method for producing a sintered material/plastic composite component. The method includes: (a) placing a sintered material component in an injection-molding device which has a lower die, an upper die and at least one slide; (b) elastically pressing the slide against the placed-in sintered material component; (d) moving the lower die and upper die together, the elastically pressed slide being clamped in between in order to fix the position of the slide, and a mold cavity being formed, in which the sintered material component is arranged; and (e) injecting plastic into the mold cavity, so that the sintered material/plastic composite component is formed.
The above object is also achieved by the device mentioned at the beginning for producing a sintered material/plastic composite component, the device being an injection-molding device and the slide being elastically prestressed in the direction of the mold cavity and mounted with respect to the lower die and the upper die in such a way that the position of the slide can be fixed such that it lies against the sintered material component by pressing the dies together.
With the method according to the invention or the injection-molding device according to the invention it is possible to produce a composite component at low cost.
On the one hand, a sintered material component is less expensive than a compact steel component, which only obtains the correct shaping by means of complex working steps. Furthermore, a sintered material component generally has much better magnetic properties than a compact steel component, so that composite components with favorable magnetic properties can be produced.
The measure of elastically pressing the slide against the sintered material component placed into the mold cavity achieves the effect of compensating in each case for the relatively great tolerances of sintered material components. The position of the slide optimally lying directly against the sintered material component is subsequently fixed by moving the lower die and the upper die together. Only after that is the actual injection-molding operation carried out.
The fact that the slide lies directly against the sintered material component and is fixed in this position by the upper die and the lower die means that, in spite of the comparatively high injection-molding pressure, there is no risk of the sintered material component being damaged in this process.
This is so because it has been found that previous attempts to produce a sintered material/plastic composite component failed for the following reasons. Until now, injection-molding devices have been constructed in such a way that, for the lateral delimitation of the mold cavity, a slide is displaced into a fixed position, defined by a stop, to form the mold cavity. On account of the comparatively great tolerances of sintered material components, there is the risk of the mold cavity formed in this way either being too small (the sintered material component is then damaged by the slide), or too large (the sintered material component is then destroyed by the pressure of the injected plastic molding compound).
The measure of elastically “docking” the slide such that it lies directly against the sintered material component achieves the effect of compensating for these tolerance problems. The risk of the sintered material component being destroyed is avoided.
The object is accordingly achieved completely.
It goes without saying that, whenever a sintered material component is referred to in the present context, either a sintered material component on its own or (as in the aforementioned example of the solenoid valve) an arrangement comprising a sintered material component and a further component is to be understood.
It is of particular benefit in the case of the method according to the invention if, during the elastic pressing operation, the slide is guided by a control surface until contact is made with the sintered material component or shortly before, so that the slide is brought up to the placed-in sintered material component at low speed.
This measure avoids the slide colliding at excessive speed with the placed-in sintered material component on account of the elastic prestressing. As a result, damage to the sintered material component is avoided in this phase of the method according to the invention.
It is at the same time of particular benefit if the slow approach of the slide takes place simultaneously with the moving together of the lower die and the upper die.
As a result, the process can be carried out in an optimized way in terms of timing. It is also possible to mechanically couple the approach of the slide and the moving together of the dies.
According to a further preferred embodiment, the slide is kept latched in a retracted position before the sintered material component is placed in.
This sets up a defined position of the slide, in which the slide is at an adequate distance from the mold cavity to place in the sintered material component.
It is also preferred if the slide is pressed by the upper die or the lower die against a portion of the other die.
This brings about direct fixing of the slide between the lower die and the upper die. The slide can consequently be securely kept in the position in which it is lying against the sintered material component.
At the same time, it is of particular benefit if the mating portion of the other die is formed by an insert which is fixed on the die concerned and is made of a more elastic material than the material of the upper die or the lower die.
While the dies are generally produced from a high strength steel alloy, the insert is produced from a somewhat more elastic material. However, the insert also generally consists of a metal, for example a steel alloy with a hardness or elasticity which is comparable to that of copper. This achieves the effect that no excessive stresses, which may for example lead to bearing damage or the like, occur during the pressing together of the upper die and the lower die and the accompanying fixing of the slide.
According to a further preferred embodiment, the material pairing of the mating portion and the slide is chosen such that high static friction is achieved.
Accordingly, secure positional fixing of the elastically pressed slide can be achieved even with a comparatively low contact pressure of the lower or upper die.
Furthermore, it is advantageous if the mating portion is inclined in the direction of the mold cavity at an angle of less than 10°, in particular less than 7°, and if the slide is formed with a corresponding slope on its corresponding contact surface.
This measure achieves the effect that a kind of self-locking occurs between the mating portion and the contact surface of the slide as soon as the slide is pressed between the upper die and the lower die even with a comparatively small force. Even when very high injection-molding pressures occur in the interior of the mold cavity (greater than 1000 bar), it can be reliably ensured in this way that the slide is fixed in its position.
Such a high operating pressure in the injection-molding method is required in the case of parts that are subjected to particularly high loading, in order to set up a reliable process.
Furthermore, it is advantageous if the slide is displaceably mounted on one of the two dies.
In this case it is possible to dispense with mounting it independently of the upper die and the lower die, which would generally lead to a much more complex construction. It is particularly preferred at the same time if the slide is displaceably mounted on the die, which for its part is formed in such a way that it is movable with respect to the other die.
As a result, the mold cavity is largely exposed when the dies are open, so that automated placement of the sintered material component is possible in a simple way.
It is of particular benefit furthermore if the slide has a clearance through which a control pin can be led.
This measure makes it possible for the slide to be kept in a retracted position by the control pin when the dies are open.
It is of particular benefit in this case if a relative movement between the control pin and the slide takes place in dependence on the relative movement between the upper die and the lower die.
This makes it possible for the relative movements to overlap in terms of timing. In this way, short cycle times can be achieved.
Furthermore, it is advantageous if the control pin is elastically prestressed and is displaced against the prestressing direction by a push rod during the moving together of the dies.
The push rod may be provided for example on the die on which the slide is not mounted. When the dies are moved together, the push rod keeps the control pin almost fixed as it were while the dies move toward each other. As a result, at the same time a relative movement between the control pin and the slide is set up.
According to a further preferred embodiment, the slide is kept in a retracted position by a latching engagement of the control pin on one edge of the clearance.
The latching engagement is in this case designed in such a way that it cannot be released either during the elastic prestressing of the slide or by the prestressing of the control pin.
The release of the latching connection may take place for example by the push rod mentioned above.
Furthermore, it is advantageous if the speed of the inward movement of the slide in the direction of the mold cavity is set up by a control surface of the control pin.
To be more precise, the speed setting takes place by the interaction between the surfaces of the control pin on the one hand and of the slide (or a clearance of the slide) on the other hand.
This measure makes it possible to avoid the slide advancing too quickly in the direction of the mold cavity when the latching is released, on account of the elastic prestressing, which could have the consequence of destroying the sintered material component or jamming the injection-molding device.
Overall, it is also advantageous if the mold cavity for forming the sintered material/plastic composite component is defined in the lateral direction by a plurality of slides which are all elastically prestressed in the direction of the mold cavity.
This makes it possible to create a largely freely definable mold cavity in the direction of the direction of movement of the slides. Furthermore, a greater number of slides makes it possible to avoid stress peaks or notch stresses occurring in the region between the contact surface between the respective slide and the sintered material component.
It goes without saying that the features mentioned above and still to be explained below can be used not only in the combination respectively specified but also in other combinations or on their own without departing from the scope of the present invention.
Exemplary embodiments of the invention are explained in more detail in the description which follows and are represented in the drawing, in which:
In
The injection-molding device 10 has a lower die 12 and an upper die 14. In the case of this embodiment, the lower die 12 is immovably formed and is for example firmly anchored to the floor.
The upper die 14 is mounted movably in the vertical direction in relation to the lower die 12.
The injection-molding device 10 also has a slide 16 movably mounted in the horizontal direction.
The lower die 12, the upper die 14 and the slide 16 together form a mold cavity 20, which in the present exemplary embodiment is approximately cylindrically formed.
As
The injection-molding device 10 serves for producing a sintered material/plastic composite component (hereafter “composite component” for short). A composite component of this type is to be understood as meaning a component which is created by making a sintered material component bond with plastic with interlocking and/or frictional engagement. In the present case, the plastic is bonded with the sintered material component by means of the injection-molding method. Furthermore, the composite component may have a further component, which is bonded with the sintered material component or the plastic with interlocking and/or frictional engagement by means of the injection-molding method. The additional component may itself in turn be a composite component.
The slide 16 is elastically prestressed in the horizontal direction, in the direction of the mold cavity 20, by means of a spring 24 (or some other elastic device).
This elastic prestressing causes the slide 16 to place itself against a sintered material component 22 placed into the cavity 20, to be precise with a specific pressing force 26. The pressing force 26 is to be chosen such that the slide 16 is pressed against the sintered material component 22, so that a compensation for tolerance takes place. On the other hand, the pressing force 26 is to be chosen such that the relatively brittle sintered material component 22 is not destroyed.
As soon as the slide 16 is pressed elastically against the sintered material component 22 placed into the mold cavity 20, the upper die 14 is lowered onto the lower die 12. As a result, the mold cavity 20 is also closed off in the upward direction. On the other hand, the slide 16 is clamped in between the lower die 12 and the upper die 14 and in this way is fixed in its position.
In this case, the upper die 14 exerts a specific pressing force 28 on the slide 16. The pressing force 28 is adequate to avoid the slide 16 being displaced into the mold cavity 20 on account of the injection-molding pressure during the injection of the plastic.
This ensures that the slide 16 “supports” the sintered material component 22 during the actual injection-molding operation. This avoids deformations of the sintered material component 22, which could lead to rupture on account of the brittle material properties.
It should be noted that the pressure in the interior of the mold cavity 20 during the injection-molding operation may lie in the range of 1000 bar or more. The pressing force 28 must accordingly be significant, in order to ensure that the slide 16 does not change its position on account of this operating pressure. This can be backed up by measures such as suitable selection of the material pairings, by surface treatment at the contact points between the dies 12, 14 and the slide 16, etc.
In the case of the embodiment of
In
Represented in
The composite component has on the one hand a sintered material component 22′, which is represented in
The sintered material component 22′ also has an annular clearance 34, which is aligned concentrically in relation to the central clearance 32. The annular clearance does not extend over the entire axial length of the magnetic pot 30.
Also provided in the magnetic pot 30 are two bushings 35, which extend from the bottom of the annular recess 34 to the opposite extreme end of the magnetic pot 30. Of the two bushings 35, only one is represented in
It is evident from joint consideration of
In order to fasten the coil element 36 securely and captively on the magnetic pot 30, the coil element 36 is injection-molded in the magnetic pot 30 by means of the method according to the invention.
In other words, the arrangement comprising the magnetic pot 30 (sintered material component 22′) and the coil element 36 inserted in it is inserted into the mold cavity 20 of an injection-molding device according to the invention (for example according to
The composite component produced in this way then serves as a stator for a solenoid valve. In this case, the coil arrangement 36 is fixed on the magnetic pot 30 in an operationally secure manner for a long service life (even if there are great vibrations).
In
The injection-molding device 50 is constructed in principle in a way similar to the injection-molding device 10 of
The injection-molding device 50 has a static lower die 12 and, vertically movable with respect to it, an upper die 14. The upper die 14 is movable in relation to the lower die 12 along guiding axes, which are schematically designated in
As can be seen in particular in
The four slides 16A to 16D are mounted movably in the horizontal direction on the upper die 14. Furthermore, the four slides 16A to 16D are in each case elastically prestressed by a spring 24A to 24D on the upper die 14.
The slides 16A to 16D also have in each case a clearance 54 passing vertically through them.
Fastened on the lower die 12 are push rods 56, which protrude upward with respect to a surface on which the slides 16 rest when the mold cavity 20′ is closed. This state is represented in
The push rods 56 pass through the clearances 54 and extend to slightly above an upper side of the respective slides 16. In the horizontal direction, however, the push rods 56 do not touch the slides 16. Accordingly, it is ensured in the state shown in
Aligned with the push rods 56 in the horizontal direction, control pins 58A to 58D are mounted on the upper die 14 (only the control pins 58A and 58B are represented in
In the injection-molding position represented in
In the injection-molding position represented in
In
In the opened state of the injection-molding device 50, that is when the upper die 14 is lifted off from the lower die 12, the control pin 58 has penetrated into the clearance 54 of the slide 16.
A beveled control surface 62 is provided on the radially outer surface of the clearance 54. The control surface ends in a control edge 64 lying in the vertically mid-way region of the clearance 54. The clearance 54 is offset underneath the control edge 64.
On the side facing the control surface 62, the control pin 58 is provided with a correspondingly beveled control surface 66. A clearance is formed in the control surface 66, so that a detent 68 is formed. In this state represented in
The upper die 14 can be lifted off to the extent that the end edge of the control pin 58 comes away from the oppositely lying end edge of the push rod 56. The upper die 14 is lowered onto the lower die 12, as is represented by an arrow 78. When this happens, at a certain point in time the control pin 58 strikes the push rod 56 (cf.
When the injection-molding device 50 is opened (arrow 76 in
In
Also provided in the upper die 14 is a central insert 72, which delimits the mold cavity 22′ from the upper side. For similar reasons, the central insert 72 may be produced from a material other than that of the dies 12, 14.
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 008 450.5 | Feb 2004 | DE | national |
