FR2661343A1 - Method and machine for manufacturing a sintered product with continuous adjustment of the parameters - Google Patents

Abstract

- Sintered product. - The machine comprises: . a station (P1) for precompression of the pulverulent composition in the compression die, in order to obtain a precompacted shaped body (20), . a station (P3) for reducing the volume of the precompacted shaped body, . a compression station (P5) with adjustable and automatically controlled pressure. - Application to the production of permanent magnets.

Description

PROCESS AND MACHINE FOR THE MANUFACTURE OF A SINTERED PRODUCT WITH
SETTING CONTINUOUS PARAMETERS
The invention relates to the field of the production of sintered products from pulverulent compositions, of defined particle size and mixture, which are pressed, compressed or compacted, so as to form bodies of defined volume, of coherent shape, which can be used as such or after heat treatment.

 As an industrial application, mention should be made of the production of permanent magnets, ceramic parts, mechanical parts for heat engines, wearing parts, such as extruder dies, molding parts, pellets. nuclear fuel or, even, electronic substrates or components.

 The manufacture of sintered products can be considered as falling within a generally known technique. If such a technique does not actually experience real development, the reason is to be found in the reliability problems that the parts produced by such a technique reveal.

 It has been found, in fact, that the sintering manufacturing technique makes it possible to obtain parts having excellent mechanical strength at high pressures and under high temperatures. Such parts are, however, very often penalized by impact fragility, which comes from the presence of micro-primers of rupture in their structure.

Furthermore, such parts are also, sometimes, penalized by distortions of shape which it becomes impossible or difficult or, again, long and expensive to resume by machining involving, necessarily, tools of very high characteristics and qualities, as well that a delicate process to continue.

The above drawbacks can be considered
Linked to the very nature of the pulverulent compositions used to obtain such products. In fact, the industrial development of powder compositions or components is not very precise for reasons related to the cost price, the purity of the raw materials used or, again, the uncertainty of the dosages carried out.

 This results in an inconsistent particle size and a variable density of the pulverulent compositions which obviously provide products having imprecise and not certain characteristics.

 To obtain products or parts of a reproducible nature by industrial development and manufacture by sintering from pulverulent compositions, themselves manufactured industrially with the constraints which are necessarily attached to the cost price, it would be necessary to have technical means making it possible to control permanently the following parameters.

- The density
It can be considered that the powders produced
industrially can have densities varying from 1 to 2
for the same volume. Such a variation is linked to obtaining
powders and their propensity to more or less amalgam
important, depending on the size of the elementary grains
component. Such products, which may also have
tendency to agglomerate in an anarchic way according to
environmental conditions, cannot, therefore,
have the same density for a given volume.

- The dosage
To obtain a good sintering result, the initial weight of the
pulverulent composition is an important criterion to be respected.

However, the dosage is linked to the density of the composition and to the
volume occupied at the time of sintering. As the density is
uncertain and imprecise and that in addition the installations
manufacturers do not have precise weighing means,
fast, able to follow high weighing rates for
very small quantities possibly, it does not appear
possible, by this only means, to have a weight criterion
initial precise.

- Sintering pressure
Obtaining parts with reproducible characteristics is
largely dependent on the compression pressure or
compaction which is imposed on the pulverulent composition. The
results of such pressure are, however, essentially
variables, depending on the precision of the particle size of the
powders used.

- The speed of application of the sintering pressure
Because of the uncertain and imprecise particle size, we
found that the application of sintering pressure
punctual and rapid, for example in the form of a shock, does not
failed to provide consistent and repetitive results
for the same series of parts.

 The object of the invention is to propose a new process and a new machine for the production of sintered products or parts which have precise technological characteristics and which can be produced repeatedly and at acceptable economic conditions, from powdery base materials which are industrially produced to date.

In other words, the process and the machine according to
The invention is designed to allow the obtaining of parts or products meeting the requirements set out above, by being prepared from industrially manufactured powders with, as a manufacturing criterion, the search for acceptable economic conditions providing density raw materials. and of variable particle size.

To achieve the above objectives, the process for manufacturing a sintered product, of the type consisting in filling a compression matrix with an appropriate pulverulent composition, in compressing this composition in the matrix and in ejecting the product obtained out of the matrix , is characterized by
what it consists of
- submit the powder composition
filling the compression matrix to a
compression action with a punch
compressive strength precompression
limited, to obtain a conformed body
precompressed,
- reduce the precompacted body to a volume
determined known,
- submit the precompacted body of reduced volume,
by adjustable speed approach to the punch, at
a defined compression pressure of their,
maintained for a fixed period,
- release the compression pressure by return of the
punch and eject the sintered body thus obtained.

The invention also relates to a machine for manufacturing sintered products, of the type comprising a transporter comprising at least one compression matrix and capable of sequentially moving this matrix in succession with a station for dispensing a dose of a composition determined pulverulent, a station for compressing this dose in the matrix and a station for ejecting the sintered product obtained, characterized in that it comprises
- a composition precompression station
pulverulent in the compression matrix for
obtain a pre-compacted conformed body,
- a station for reducing the volume of the shaped body
precompressed,
- a compression station with adjustable pressure,
enslaved.

 Various other characteristics will emerge from the description given below with reference to the appended drawings which show, by way of nonlimiting example, an embodiment of the object of the invention.

 Fig. 1 is a schematic plan view of a manufacturing installation according to the invention.

 Fig. 2 is a sectional elevation taken, on a larger scale, along the line Il-Il of FIG. 1.

 Fig. 3 is a sectional elevation, similar to FIG. 2, but illustrating another phase of the method of the invention.

 Fig. 4 is a sectional elevation taken, on a larger scale, along the line IV-IV of FIG. 1.

 Fig. 5 is a sectional elevation taken, on a larger scale, along the line V-V of FIG. 1.

 Figs 6 and 7 are sections taken, respectively, on a larger scale, along the lines VI-VI and VIl-VIl of fig 1.

 Fig. 1 shows, by way of example, a machine for implementing the invention. This machine comprises a conveyor 1 which is, preferably but not exclusively, produced in the form of a plate capable of being driven on an axis of rotation 2 in the direction of the arrow f1 by a not shown drive member.

 Such a turntable must be appreciated as falling within the known technique of building transfer machines of the carousel type for example. A more detailed description of the support, guiding and rotational drive means is therefore not to be considered further.

 The turntable 1 is designed to include compression dies 3 which are preferably arranged equidistant angularly. The dies 3, in any suitable number, for example eight in number, are preferably located close to the periphery of the turntable 1. In a form which is particularly suitable for implementing the invention, the dies compression 3 are formed by through holes made in the same circular geometric location on the turntable 1. The through holes can be, in cross section, of different shapes suitable for the structure of the parts to be produced. The example given in the form of through cylindrical holes, of axis x-x 'perpendicular to the plane of the plate 1, therefore only represents an indication of a possibility of realization.

 The turntable 1 is intended to ensure the transfer of each compression die 3 in front of different successive intervention stations, designated by the references P1 to P8.

 The station P1 constitutes a station for metering and distributing a pulverulent composition, from a hopper 4 which can be fed, sequentially or continuously, by a conveyor 5. The hopper 4 has, as is known , a supply nozzle arranged at a fixed station and under which each compression die 3 can be immobilized by the plate 1. The nozzle can be at free outlet or, furthermore, be equipped with a valve, a valve or any other means capable of allowing a sequential distribution of an adjustable dose of pulverulent composition.

Without it being a compulsory provision within the meaning of
The invention, the station P1 is also designed to assume a function of precompression of the dose of pulverulent composition distributed by the hopper 4. For this purpose, as can be seen in FIG. 2, the station P1 comprises a filling guillotine 6 constituted by a plate or a plate arranged over the turntable 1 on which it is guided by any appropriate means. The plate 6 is associated with a motor member 6a, such as a double-acting cylinder, capable of moving it in the direction of the arrow f2. The amplitude of movement of the filling guillotine 6 is defined between a first position, in which a funnel 7 which it delimits is placed exactly in alignment and coincidence with the nozzle 8 of the hopper 4 and a compression die 3, and a second position, as illustrated in FIG. 2, in which the funnel 7 is offset radially by a measure such that the guillotine closes the communication between the nozzle 8 and the matrix 3. The drive member 6a and the guillotine 6 are assigned to station 1 and are therefore mounted independently to the plate 1 which can therefore rotate freely and independently.

 The station P1 also includes a precompression assembly 10 composed of a punch 11 extending vertically under the plate, so that it can be placed in alignment with the axis x-x '. The cross section of the punch 11 is the same as that of the die 3 into which such a punch can penetrate with minimal play. The punch 11 is mounted movable on its axis, in a slide 12 which is itself mounted, movable in the same direction, on guides 13 presented by a support body 14. In a preferred embodiment, the body 14 is independent of the plate 1 and is carried by a motor member 15, for example of the jack type, the piston rod 16 of which is able to control the sliding of the slide 12 on the guides 13.

 The punch 11 is mounted in the slide 12 by means of a cartridge 17 with limited compressive strength, adjustable. Such a cartridge comprises a spring 18, for example of the helical type working under compression, interposed between the punch 11 and a member 19 for adjusting its tension. The member 19 may, for example, be constituted by a threaded plug screwed into the slide 12.

 In a stable position of rest, the driving member 15 maintains the slider 12 in a low position in which, under the permanent action of the elastic member 18, the precompression punch protrudes from the slider 12 and is flush its head, the underside of the plate 1 constituting, due to the coincidence, the bottom of the compression die 3.

 The P1 station operates as follows.

When a compression die 3 is brought into line with the nozzle 8 by the rotation of the turntable 1 immobilized in a position of coincidence and coaxiality,
The drive member 6a is controlled to arrange the funnel 7 in alignment with the nozzle 8 and the matrix 3. The hopper 4 is then controlled to dispense a dose of powdered product which falls, by gravity, through the funnel 7 into the matrix 3 which it completely fills. The guillotine 6 is then controlled in reverse displacement to close the matrix 3 and release any excess powdery product which remains
contained in the funnel 7. FIG. 2 illustrates this phase of implementation of the object of the invention.

 After filling the matrix 3, as described above, and without the plate 1 having been rotated, the assembly 10 is controlled so that the driving member 15 lifts the slider 12 in the direction of the arrow f3 . The punch 11 is thus brought into the interior of the compression matrix 3, the top of which is closed by the guillotine 6. The displacement of the slider 12 results in an action of precompression of the dose of pulverulent product contained in the compression matrix 3, up to a limit which corresponds to the prestress adjustment imposed on the spring 18 by the plug 19. This adjustment is made so that the precompression pressure is between 10 and 20% of the final filtering compression pressure.

When this threshold is reached, the punch It is immobilized, so that the displacement of the slide 12 takes place without any other precompression action.

 By the above method, a precompression of the initial dose of pulverulent product is established, so as to have a pre-compacted shaped body 20 whose density is made more precise, despite variations in particle size, agglomeration and filling the compression die 3.

 Since the sensitivity of the cartridge 17 to stress is defined by the preload adjustment imposed on the spring 18, the action of the punch 11 can be considered to be a source of substantially constant precompression, whatever the variations in particle size and agglomeration of the dose of product distributed, as well as the filling conditions.

 After the above precompression phase, the punch 11 is released from the compression die 3. Depending on the case, this rotation, which has the effect of clearing the lower opening of the compression die 3, can involve the presence , with a fixed or adjustable station, of an annular plate capable of reconstituting the bottom of the matrix between the stations P1 and P2 to avoid, if necessary, the unexpected fall of the body 20 when the assembly 10 is not integral of tray 1.

 The plate 1 is driven sequentially over a new angular range, to pass the compression matrix containing the body 20 from the station P1 to the station P2, the function of which is provided to ensure cleaning of the plate 1 around the compression matrix 3 containing the body 20. To this end, the station P2 includes means 21 capable of ensuring cleaning by suction, by blowing, by sweeping or by any other method suitable for the nature of the pulverulent composition distributed.

According to another step of the method, the plate 1 is again entrained in rotation in the direction of the arrow f1 to pass the compression die 3 and the body 20 of the station
P2 at station P3, the function of which is to calibrate the body in volume 20. To this end, as shown in FIG. 4, the station P3 comprises a pusher 25 composed of a motor member 26, for example of the type with an alternative rectilinear stroke, such as a jack. The drive member 26 comprises a removable pin 28 whose shape is chosen to correspond exactly to that of the punch 11.

The drive member 26 is arranged so as to be able to move the spindle 28 in the double direction of the arrow f4, along an axis coinciding with the axis xx 'of the matrix 3 immobilized in the stopped position by any indexing means of the plate 1. The pusher 25 is arranged below the plate 1, so as to be able to be engaged in the die 3 on an adjustable penetration stroke by means of a wedge 29. As illustrated by FIG. 4, the penetration of the spindle 28 into the die 30 pushes the shaped body 20 partially out of the die, on a measurement corresponding to the difference in height between that of the spindle 28 and that of the shim 29.

 The station P3 further comprises a means 30 for reducing the volume of the body 20. Such a means 30 is preferably constituted by a leveling knife 31 arranged, preferably, in contact with the upper surface of the plate 1 on which this knife is mounted movable in the direction of arrow f5, by means of a drive member, such as a jack 32.

 In the position illustrated in FIG. 4, the leveling knife is controlled in the direction of the arrow f5 to level the protruding part of the body 20 and give the latter the desired volumetric calibration corresponding to the penetration adjustment of the spindle 28, as a function of the thickness of wedge 29.

 Thus, after having controlled the density parameter initiated by an action of precompression of the dose of powder poured or distributed, the method of the invention controls the volume of the body 20 in a rigorous manner, so that the acquisition of these two essential parameters allow to proceed to the final stages of the manufacturing process of a sintered product with reproducible characteristics.

 IT must be considered that the pusher 25 can be constituted by a set of means occupying, at a fixed position, the orientation suitable for cooperating with each of the successive compression dies occurring by the rotation of the plate 1.

However, in certain cases, such a partial extraction function from the body 20 can be assumed by the means described above and constituting the assembly 10, insofar as such an assembly is carried by the plate 1 and has, by the cartridge 17, an erasure resistance sufficient to cause
The partial extraction of the body 20 relative to the matrix 3.

 Examination of fig. 1 and fig. 4 shows that the leveling waste is recovered by falling by gravity, in particular beyond the peripheral edge of the turntable 1, in a container or transporter 33 responsible for discharging this waste to a possible reprocessing station, since the only intervention that has been suffered is limited to precompression.

 A next step of the method of the invention then consists in again controlling the rotation of the turntable 1 in the direction of the arrow f1 to bring the compression matrix 3 provided with a pellet 20a calibrated in volume to the station P4 which is more particularly charged, although its presence is not absolutely obligatory, to control, as illustrated by fig. 5, on the one hand, the presence of the tablet 20a, but also, by means of a sensor 35 of any suitable type, the actual height of the tablet 20a brought back, by means of the sensor, in the low position , pressing against a stop 36 specific to station P4 for example and defining the bottom of the compression matrix 3. To this end, the sensor 35 preferably has a mechanical type feeler 37 capable of assuming both above functions of moving the pellet 20a and assessing the actual height it presents. The probe 35 is therefore formed by a support bracket 38 mounted on a fulcrum 39, so as to extend, at least in part, above the upper surface of the turntable 1.

 A subsequent step of the method of the invention consists in re-controlling the rotation of the plate 1, in the direction of the arrow f1, in order to pass the compression matrix 3 containing the pellet 20a from station P4 to station P5 responsible for the phase proper manufacturing of a sintered product.

 The post Pg, illustrated in more detail in FIG. 6, comprises a console 40, the ploughshare 41 of which is provided with an anvil 42 intended to adjoin the underside of the turntable 1.

The anvil 42 has a pile 43 intended to be aligned coaxially with the matrix 3 in the indexing position of the plate 1 and movable relatively in the axial direction x-x ', while being supported on a force sensor 44. preferably, a piezoelectric gauge system 45 is provided at the interface of the anvil 42 and the turntable 1 for reasons which emerge from the following.

 The upper part of the encLume 40 carries a motor member 46, of the electrical type with direct current and at variable speed, the output shaft 46a of which attacks, directly or via a transmission, a micrometric screw 47 carried by guides 48 adapted on the bracket 40. The screw 47 cooperates with a fixed nut 49 which is also secured to the bracket 40.

The free end of the screw 47 is provided with assembly means 50 allowing the mounting and dismounting of a compression punch 51 overhanging the upper face of the plate 3 and occupying a position coaxial with the compression die 1 in the position for indexing the turntable 1. The compression punch 51 has, in cross-section, a shape identical to that of the precompression punch 11.

After stopping in the indexing position at post P5,
The drive member 45 is controlled so as to bring down the screw 47 which pushes the compression punch inside the compression matrix 3. The punch 51 compresses the pellet 20a against the pile 43, so as to produce the elaboration of the final sintered product which is obtained when the suitable compression pressure is detected by the force sensor 44. The pressure control, which is exerted progressively by the lowering action of the screw 47, is simultaneously compared to the signal emitted by the gauge 45 which makes it possible to take into account the elastic deformation factor of the compression assembly to assess whether the necessary compression force has been effectively applied to the actual and desired dimensional characteristics of the pad 20a which, after compression final, is immobilized in the lower part of the molding footprint, after raising the punch 51 by the reverse supply of
The drive member 45. Otherwise, the pellet 20a is estimated not to meet the requirements for volumetric calibration. The compression phase ends with a release of pressure occurring by return of the punch 11.

 Another phase of the process then consists in rotating the plate 1 again in the direction of the arrow f1 in order to bring the matrix 3 from station P5 to station P6 responsible for ensuring the ejection of the sintered product produced 20b.

 As shown in fig. 7, the station P6 comprises an ejector 52 which can be moved in the direction of the arrow f5, in order to penetrate into the matrix 3 in the indexing position of the plate 1. The ejector 52 pushes the sintered product obtained 20b out of the matrix 3 to bring it substantially in the plane of the upper face of the plate 1. An actuator 53, of any suitable type, pushes the sintered product 20b out of the plate 1, for example on a conveyor belt 54.

Fig. 1 shows that the method of
The invention provides a station P7, identical to the station P6, but intended to ensure the evacuation of the pellets 20a having been detected at the station P4 as not meeting the desired volumetric definition criterion. In such a case, the plate 1 is controlled in rotation to pass the compression matrix containing such a pellet 20a directly from the station
P4 at post P7.

The method of the invention provides, in addition, a station P8, said to be cleaning, analogous to station P2, in order to eliminate any trace of pulverulent composition around the compression matrix 3, or even in the latter, prior to
The supply under the distribution station P1 at which a new sequential operating cycle, of the type described above, occurs automatically.

 The means according to the invention therefore make it possible to control the uncertainties or variations in density of the pulverulent composition distributed and to take into account a specific density factor, in relation to well-defined dimensional characteristics which arise from the calibration phase. of the pellet 20a at station P3 prior to the application of the effective sintering pressure occurring at station P5.

 The invention is not limited to the example described and shown, since various modifications can be made without departing from its scope.

Claims (15)

CLAIMS:  1 - Process for manufacturing a sintered product with continuous parameter adjustment, of the type consisting in filling a compression matrix with an appropriate pulverulent composition, in compressing this composition in the matrix and in ejecting the product obtained out of the matrix,  characterized in that it consists of  - submit the filling powder composition  The compression matrix has an action of  precompression by a precompression punch to  limited compressive strength, for  obtain a pre-compacted conformed body,  - reduce the precompacted body to a volume  determined known,  - submit the pre-compacted body of reduced volume,  by approaching the punch with adjustable speed, a  a defined compression pressure of their,  maintained for a fixed period,  - release the compression pressure by return  of the punch and eject the sintered body as well  got.  2 - Method according to claim 1, characterized in that it consists in exerting a precompression action in the same direction as the subsequent compression action.  3 - Method according to claim 1, characterized in that it consists in reducing the volume of the pre-compacted body by a leveling action.  4 - Process according to claim 1 or 2, characterized in that it consists in exerting, on the pulverulent composition, a precompression action by applying a pressure between  10 and 20% of the compression pressure.  5 - Method according to one of claims 1 to 4,  characterized in that it consists in carrying out the stages of  precompression, volume reduction and compression by means of a multi-cavity turntable transfer machine.  6 - Method according to claim 1, characterized in that the compression pressure is applied via a motor member whose power is placed under the double dependence of a force sensor associated with the precompacted body and a displacement sensor appreciating the elastic deformation of the compression installation.  7 - Machine for manufacturing a sintered product with continuous parameter adjustment, of the type comprising a transporter (1) comprising at least one compression die (3) and capable of sequentially moving this die in succession with a station (h ) dispensing a dose of a determined pulverulent composition, a station (P5) for compressing this dose in the matrix and a station (P6) for ejecting the sintered product obtained,  characterized in that it includes  - a precompression station (P1) for La  powder composition in the matrix of  compression to obtain a shaped body (20)  precompressed,  - a post (P3) for reducing the volume of the body  conformed pre-compacted,  - a pressure compression station (P5)  adjustable, controlled.  8 - Machine according to claim 7, characterized in that the conveyor (1) consists of a turntable delimiting through impressions (3) defining the compression dies.  9 - Machine according to claim 7, characterized in that the dispensing station (P1) is combined with the precompression station.  10 - Machine according to claim 7 or 9, characterized in that the precompression station comprises a precompression punch (11) carried by a drive member (15) with interposition of an elastic cartridge (17) of limited compressive strength and adjustable to precompression pressure.  11 - Machine according to claim 10, characterized in that the precompression punch (11) is disposed under the plate and constitutes the bottom of the compression die placed in relation to the precompression station.  12 - Machine according to claim 11, characterized in that the precompression punch (11) is mounted movable, against The action of an adjustable elastic member (18), in a slide (12) associated with the motor member (15) and movable, in the direction of penetration of the punch into the die, on a support body (14) and guidance.  13 - Machine according to claim 7, characterized in that the volume reduction station (P3) comprises a spindle (28) of partial extraction of the body (20a) shaped precompacted, out of the die, and a leveling knife (31).  14 - Machine according to claim 7, characterized in that the compression station (P5) comprises, above the plate, a compression punch (51) mounted at the end of a motorized screw (47) rotating in a fixed nut (49) carried by a chassis (40) whose base supports, under the plate, a recovery anvil (42) provided with a compression sensor (43).  15 - Machine according to claim 14, characterized in that the turntable (1) and the anvil (42) are separated, to the right of the compression station, by a sensor (45) of relative movement in the direction of compression.