DE2036284A1 - Method and device for testing pressed parts made of powdered material - Google Patents

Description

DR.-INO. DIPL.-INS. M.SC. OICl.-PHYS. OR. 3TL-PMYS.

HÖGER - LEGAL RIGHTS - GRiESSBACH - HAECKER

PATENT LAWYERS IN STUTTGART

1.7.1970 ■

C reare, Inc.

Box 71

Hanover, New Hampshire, U.S.A.

Method and device for testing from powdery Material manufactured pressed parts

The invention relates to a method for testing from pressed parts made of powdered material for structural defects and a device 'for' implementation this procedure. In particular, the invention is concerned with the testing of pressed parts made of metallic powder are made.

The! Guidelines for determining whether an unsintered pressed part or a sintered article made from it meet the requirements to be placed on it, depend on the "intended use" of the sintered article and the guidelines for the appearance and resilience of the gusintereen Article at &. (ίοrauch -ab. Dementupreohend bind the in Description of the present invention used Aua-.

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express "structural defects ¹ '", "faulty" and "faultless" to be understood relatively and not absolutely and depend on the usefulness of the article for the intended purpose.

To produce stable sintered articles from metallic powder, the powder is first pressed into the shape of the end product and, after pressing, sintered by a heat treatment. In order to avoid structural defects such as cracks or surfaces with high porosity in the sintered parts, the unsintered pressed parts must be free from structural defects. Structural defects in the pressed parts usually occur in the form of areas of high porosity or in the form of sliding surfaces. Furthermore, it has been shown that these structural defects are generally retained even after the pressed part has been sintered. If the structural defects are in the form of an area of high local porosity, then per unit area is the number of contact points between the metal particles and the size of these contact areas less than in the rest of the press part. For a given load thus the load on the contacts between the metal particles in the high porosity is higher than in the remaining areas of the press part, and a fracture occurs therefore in these areas at a lower load, a "If the structural defects, however, _s then be in the form of thrust surfaces the tensile strength of the pressed part transversely to the sliding surface is practically equal to gauze, due to the physical

in the

Separation of the / area of contact between the metal particles during the creation of the sliding surfaces occurs ο Under these circumstances, a relatively low tensile load on the sintered article causes breakage Episode"

The misfitting in the pressed parts can come from different

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Causes arise, but are mainly a consequence of the inability of the powder to flow freely during the pressing or compaction process. The mechanics of the mold movement and the compaction of the powder i ^s t fairly well known, and it can be shown that occur, for example in press parts with stepped form areas of increased porosity or thrust surfaces mainly in the neighborhood of * inner edges where the Quersehnittflache changes abruptly . In practice, joining errors often arise as a result of changes in the optimal movement of the molded parts relative to one another and as a result of slight changes in the homogeneity of the powdery material. At the present time, there are no practically applicable methods for testing the tensile strength of unsintered pressed parts made from powdered material. The usual mechanical strength tests, as specified in MPIF standards 35 - 65, are used to evaluate the powder mixtures and the compression pressure and are not suitable for testing the strength of pressed parts at special predetermined points. It would be highly desirable, however, to improve a reliable method of testing the strength of pressed parts made from powdered material in order to avoid structural defects in the sintered articles made therefrom.

In particular, the present invention has the task the basis of proposing a method by which it is possible to subject the parts of an unsintered pressed part to an examination, in which the presence of structural irregularities is to be suspected ;.

This object is achieved according to the invention in that a liquid or gaseous medium such areas

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of the unsintered pressed parts ₉ in which there is a suspicion of structural defects _{s is} supplied under a pressure that is high enough to cause stresses in the area of the structural defects, * which lead to breakage of the defective pressed part. So will it be a medium ^ be it gas? be it a liquid introduced under pressure into the pressed part, namely in those areas ₉ in which theoretically and practically structural defects arise when the pressed part is sintered *

Me determination of these areas can be based on the knowledge of the production of such pressed parts, as for example by H _β G- »Taylor in the article" The influence of tool design on the dense distribution in complicated

Powder Metallpulverteilen "published in / iletallurgy 1960s, Ur.-6, Pages 87-124 is described # done ^

Another way to determine these areas is that the gesinterten- stampings in terms of their physical quality and in terms of their Schnit.tbilder be examined ₉ if solcne are available to determine to type and location of structural defects ₉ "If the region or regions _s in which or which structural defects occur, for a given pressed part and a given pressing technique, is determined or is _{0 9} . is the medium with a constant standard pressure or with / t ßinem pressure - which changes and up to. Liorm pressure can increase _{9 introduced} into the pressed part in order to exert tensile stresses in the area of the suspected structural defects due to the high internal pressure β Under the exerted pressure, pressed parts with structural defects are destroyed ₉ while pressed parts without structural defects are not damaged ₀

The printing medium is in the press part in such a. Eingefünrtj sighting is that a differential pressure in the zones _s results in which structural defects are most likely

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are, and this causes a tensile stress in the area of the structural flaw, which acts essentially perpendicular to this structural flaw. To carry out the method according to the invention, a device is used which is characterized in that it is designed as a clamping device with an inner chamber for receiving a press part to be examined, that it has devices for introducing the medium under pressure into the inner chamber that it is provided with seals in order to delimit the area in which the medium acts on the pressed part in the inner chamber and that it is otherwise designed so that the internal pressure generated by the medium does not exert any external force in the area of the structural defects counteracts. The clamping device according to the invention thus enables the pressure medium to only act on a limited area that includes the zones of likely structural defects and also allows the pressed parts with structural defects to break under the influence of the forces caused by the pressure medium. The clamping device therefore does not generate any compressive force that counteracts the tensile stress that is generated by the pressure medium and consequently does not prevent the pressed part, which is afflicted with structural defects, from breaking. Under certain circumstances it may be necessary to clamp an area of the pressed part in which there are no structural defects, but which is nevertheless fragile or has a relatively small cross-section, in order to prevent this area from being revealed when the other areas of the pressed part are checked Structural defects are destroyed when the pressure medium flows through the pressed part, pressure and force gradients form, the size of which depends on the flow resistance. If, now, the medium enters an area with a structural defect, the pressure drop in this area is low because the structural defect offers little or no flow resistance. The greatest force gradient within dos presotcils

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thus occurs perpendicular to the plane of the structural defect area in which the weakest contacts between the particles exist and consequently it comes to an essential here lower pressure of the medium on a fracture than in similar pressed parts without a feeler. Have attempts shown that the pressure that is needed to break a to cause structural defects in pressed parts between

ρ ρ

0.7 kg / cm and 35 »2 kg / cm, depending on of the dimensions and the composition of the pressed part. In general, the pressure is what is required; a breakage of one with structural defects. Pressed part cause j, below $ 50 of the pressure, which is necessary to destroy a pressed part without structural defects.

The standard pressure for a given batch of pressed parts is the lowest pressure _s at which all pressed parts that were subjected to the investigation prove to be free of structural defects after the subsequent sintering. In practice, the standard pressure must be determined for a given powder composition, the compression of which takes place in a certain pressing process, since the value obtained in this way cannot be used for other types of pressed parts. In addition, different standard pressures must be determined for different areas of the pressed part in which structural defects are suspected, since the pressure at which an area of the pressed part not affected by structural defects breaks depends on the size and shape of this area for a certain test procedure can be very closely approximated to the theoretical standard pressure using a number of optionally available methods.

For example, the standard pressure for a given Type of a pressed part empirically depending on the

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Determines the maximum pressure that is required to destroy a pressed part without structural defects. The maximum pressure can be determined by means of a batch of pressed parts taken from ongoing production, for which all variables during the pressing process were checked as precisely as possible. One half of the batch can be tested in order to determine the maximum pressure which will result in a break in the area of the suspected structural defects. The remaining pressed parts are sintered and then carefully examined by examining their exterior and making cuts to determine whether or not they have misfitting. If the powder mixture "different pressing movements" the pressing pressure and the sintering cycle all meet the requirements, then all sintered bearings should be satisfactory. If not, the required settings should be made during the pressing process and the entire process, including the pressure test of the pressed parts, should be repeated. The present invention is therefore primarily useful in the study of pressed parts produced in a process of compression which has deviated from the optimum. '' Once it has been established that all of the pressed parts in the batch are statistically satisfactory, the highest pressure required to destroy a pressed part can be assumed to be the maximum pressure and the spread of the pressure measurements can be used as the measuring range. The relationship between the standard test pressure and the maximum pressure is determined statistically and experimentally, but becomes larger. Extent controlled by the spread of the pressure measurements carried out in the test section. The original pressure can, for example, be 2 or 3 $ below the lowest pressure measurement of the test section if the pressure measurements do not vary by more than 5% . If numerous pressed parts are destroyed at Normdruok during the subsequent production cycles, the entire process can be repeated to determine whether the

-8th-

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Pressure was originally set too high

Another possibility for empirical determination of the standard pressure is that the pressed parts are exposed to changing pressures and that the pressed parts that remain undamaged are then sintered in order to determine which of them turn out to be free of structural defects after sintering. "After the pressure of the pressure medium , which was used in a first step to test the pressed parts is known and after the proportion of pressed parts is also known which proved to be free of structural defects after sintering, a second batch of pressed parts, which are made from the same powder mixture and in the same pressing process were produced, either subjected to a higher or lower pressure of the printing medium than before. ”A lower pressure is used if all pressed parts after the sintering process prove to be free of structural defects, as there is then a high probability that the initially used print ck of the medium over the required for testing pressure went and that a large number of press parts would thus be able to come, which had proved to be error-free following the sintering process, "On the other hand, the proportion of affected with structural defects pressed parts following the Sintering process is excessively high, then this shows that the pressure initially imparted to the medium was too low to be able to take it as a standard pressure. In this case, the pressure of the medium is increased during the second series of tests.The successive application of different pressures of the medium and the subsequent sintering is carried out until a minimum pressure has been found for the medium at which all pressed parts that remain intact during the pressure test, also prove to be free of structural defects after sintering.

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There is also the option of setting the standard pressure for a specific Thickening method and a certain powder composition to change within relatively small limits. An initial value for the standard pressure can be determined are »as described above, for pressed parts that were produced in a pressing process, which works under the optimal target conditions. As a result of minor changes in the conditions of the pressing process that but are still within specified limits, the standard pressure can now change slightly. It now exists Possibility of a trend of prints necessary for the destruction of the pressed parts. .... determine if a such is available and to increase or decrease the standard pressure according to this trend. This approach makes take advantage of the fact that there is a large change in one pressing process and still within the specified allowed limits.

The comparative procedure for testing pressed parts according to The invention rather than an absolute test method is highly desirable because the strength and porosity of compacted powder is related to the shape of the pressed part alternate between different compositions and with the specific compression method used.

Further details and advantages are referenced below explained in more detail by embodiments shown in the drawing. Show it"

1 shows a perspective illustration of a typical pressed part with abruptly alternating cross-section made of powdery material}

FIG. 1A shows a part of a cross section through a pressed part according to FIG. 1 with a structural defect in the form of an area higher

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Porosity!

Mg.1B a part of a cross-section through'ein Pressed part according to Pig "1 with a structural defect in lorm one protruding into the pool Viewing area;

1C shows a part of a cross section through a Pressed part according to Figure 1 with an O-efügefehler in the form of a sliding surface projecting into the main body5

2, 3 and 4 are schematic views of different embodiments of gate directions to carry out the fiction. according to the procedure »

Before then I went into the details will ^ should "first the gate direction for implementation of the inventive method "will be discussed.

The device according to the present invention comprises means for pressure generation, whereby air or another gas is usually used as the pressure medium * It also includes Means for controlling and measuring the pressure medium pressure including the pressure at which the destruction of the Press body, if any, takes place. The device also functions as a jig and is so designed so that it holds the pressed part} without doing it In the areas of interest forces were effective that the tensile forces acting perpendicular to the (joining defects, which are generated by the pressure medium, would counteract. _

The structural design used in the individual case Jig depends on the direction in which the feeling flaw expands »In every pail is the jig but so constructed »- that no holding forces

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that counteract the stresses generated by the print medium, unless that is necessary in order to prevent the special construction of the pressed part from breaking in an area in which there are no structural defects. The jig comprises a component with an inner chamber, the cross section of which is adapted to the shape of the pressed part. The jig has at least one feed that the

Pressure- ■■■■ _ ■■ the medium is fed through an opening into the inner chamber at a point where the pressure is to be exerted on the pressed part. For example, if a pressed part with a rapidly changing cross-section is to be examined, in which the area of the suspected structural defects is near the inner corner, then one of the openings can be at the point where the smaller diameter of the inner chamber merges into the larger one. Seals are provided around the opening to prevent the pressure medium from escaping between the surfaces of the press member and the walls of the inner chamber. When examining rotationally symmetrical pressed parts, the seals form an annular chamber around the pressed part. The clamping device can also be constructed in such a way that it is possible to examine a pressed part for structural defects in different ways by supplying the pressure medium to different areas of the pressed part. For example, a structural defect in a rotationally symmetrical pressed part with a flange, that is, in a pressed part with abruptly changing cross-section, can either extend into the main body (PigdC) or into the splash (Pig. 1B), which in both cases depends on the area of Inside edge takes place. When checking whether there is a structural defect which extends into the main body of the pressed part, the pressed part is clamped in the jig between the upper surface of the jig and the sill so that the underside of the main body is exposed, as shown in FIG. A print medium that is like

-12-

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in the embodiment according to Figure 2 under pressure The area around the inner edge is fed, has a pressure gradient between the inner edge and the bore of the pressed part result.

If, on the other hand, the aim is to check the pressed part for structural defects in the region of the flange, the clamping device can be constructed in such a way that it encloses the entire outer surface of the pressed part, with the exception of the bottom and the side surfaces of the flange part. Since there are no forces acting in the area of the flange that counteract the tensile force generated by the pressure medium, a flange part with structural defects breaks off after the pressure medium has been introduced. This design of the clamping device is preferred when a test for structural defects in the flange part is carried out, since there are minimal frictional forces due to the contact between the clamping device and the lower flange surface »The flange only needs to be lifted a few hundredths of a millimeter from the surface of the clamping device«, Die The position of the underside of the flange relative to the upper side of the clamping device is secured by an adjusting element 33 (FIG. 2). The seal is achieved by gently squeezing an O-ring or other sealing element »'■' ■ - ■ '· ■'"'· - · -' * ■ '-''·"■ - -' ■

■■ /. ■■ · - % ίϋί'Άχ

As FIG. 1 shows, a typical press part can consist of a 'Flange part 2 and a main body 3 exist, which has a channel 4 in its center · Structural defects occur in a such pressed part with the greatest probability in Area 5, namely at the joint -voii flanges part 2- and main body 3 »As FIGS. 1, A, 1B and 1C show, can the structural defects belong to one of three basic forms. As Figi ^ iA shows, the structural defect x 6 'on the ram of Flange part 2 and main body 3 by an area · higher

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Porosity formed. Like Pig. IB shows, the structure defect 7 at the joint of the plan circ eiles 2 and the main body

2 formed by a _{sliding plane f} which protrudes into the planar part 2. As Pig.1C shows, the structural defect 8 at the joint between the planar part 2 and the main body 3 is formed by a plane of sight that extends into the main body

3 protrudes. .

When examining for any sensory defects in the main body 3 reach in (as in Pig.iA and 10), the pressed part becomes 1 as shown in Pig. 2 with its main body inserted into the inner chamber 9 of a clamping device 10, in such a way that the underside 11 of the pressed part and the sides 12 of the paddling part 2 not in contact with the jig 10 are available. So the main body 3 is not subjected to compressive forces, the tensile stresses could counteract to which the pressing part is exposed, while the splash part 2 only has a low compression force is exposed, which is caused by the friction between the jig and the plane 15 ■■.

A medium is introduced under pressure through the lines 13 and H to the opening 16 and from there into the region 5 of the pressed part 1. The gas supplied via the line 13 is retained in the space 17, which is formed by seals 18 which surround the opening 16 and forms the shape of an annular channel between the clamping device 10 and the main body 3, which is used to convey the gas to be introduced into the pressed part, while the gas would escape without the use of seals between the pressed part and 4er Innenkanjmerwandung of Einspannvorriohuung 10. Press part is in the jig 10 by the. 1 | maintained, which is acted upon by a pressure force _t her perausschleudern under the influence of Druokverhindert. A pressure gauge 21 measures the pressure of the

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on the press part acting pressure medium in the line 131 while a valve 22 and a regulator 23 control the flow and the pressure of the pressure medium, the valve 22 also serves to limit the gas flow, so that if the press part breaks, the pressure on the Press part which is indicated by the pressure gauge 21, suddenly about to ^"1 O ^ of the value shown before breakage of the pressing member is lowered.

The clamping device according to Pig.2 is primarily used for examinations relating to the main body 3

* refer to urgent structural defects. The total gas pressure that acts on a structural defect in this area depends on • its orientation and on the pressure drop between the Surfaces 30 and 31 on the inside and outside of the pressed part 1. When the pressure difference across the press part 1 is increased to a point where the compact is broken, then the break occurs in the area of the main body 3. The jig 10 according to Pig. 2 can also be used to determine structural defects in the form of displacement surfaces that are affected by the Penetrate the inside edge in area 5 into the paddling part. the However, the latter sliding surfaces can best be used with

^ that in Pig. 3 illustrated embodiment of a front; direction for carrying out the method according to the invention be determined.

In Pig. 3, a jig 32 is shown, with a base plate 33 adjustable in the vertical direction is provided, which on the bottom surface 34 of the pressed part 1 is present. A compressive force on the plate 19 secures the pressed part 1 in the inner chamber 35 of the jig 32 and together with the pressing force of the bottom plate 33 exerts a Pressure force from each evoked by the printing medium Tension in the main body 3 counteracts. This

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Feature is only necessary if the one leading to a break The pore pressure of the main body 3 is lower than that of the flange part 2, either due to a structural defect or as a result of the originally lower strength. The print medium "is through the line 36 via the opening 37 in a Room 38 introduced. In the tree 38, the print medium is through Seals 39 -mier pressure held, which are in the area of the surfaces 40 and 41. The flange part 2 of the pressing part 1 does not touch the surface 41 of the jig 32. Only a minimal compression force acts there on the flange part 2 and thus only a minimal shear-resisting force that is exerted by the pressure medium exerted forces could counteract, so that with structural defects affected flange parts under the influence of forces exerted by the print medium break.

In the embodiment of a device for carrying out the method according to the invention according to FIG Refinements of the gas supply compared to the embodiment according to iig. 2 shown, which have the purpose that To speed up examinations, to provide a permanent record of the fracture pressure and to provide an electrical signal that indicates a low strength pressed part. The pressure regulator 25 », which is parallel to the flow valve 22, is used to deliver a hormonal pressure whose value is like as set out above, is determined empirically. That under standard pressure medium is via line 26 to the Press part 1 supplied. The pressure can be set in such a way that only those with structural defects prone to pressing

to

parts are destroyed that have a / low tensile strength. When the shut-off valve 27, which is in series with the pressure regulator 25, is closed, the pressure on the falls the side of the valve 22 facing the pressed part or is retained, which depends on the one hand on how strong the blocking effect of the pressure regulator 25 is and on the other hand on whether

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the pressed part was destroyed or not. A pressure switch 28 which is set so that it switches at.Uormdruck ^; and which is actuated when the shut-off valve 27 is closed, is suitable for supplying an electrical signal which indicates whether a pressed part has been destroyed or not of the medium fed to the press part can be varied up to a fixed upper limit and the pressure can be recorded by means of a strip chart recorder 29 or other suitable recording device medium supplied can be determined in a simple Yfeise by a sudden drop in pressure, which is indicated by the pressure switch 28.

To maintain the pressure of the medium in the area of the pressed part, in which & efitting error is most likely any sealant can be used « For example, O singles can be used, or * inflated ones Seals or the like.

When testing pressed parts according to the present invention, different ropes of the pressed part, such as a splash part and a main body, can be examined one after the other for the presence of joining errors. to direct the pressure on different areas of the press part, as is the case, for example, in the embodiments according to Pig.2 and 3 of the Pail, used and there exposed to ^{the Borm pressure 1 '. About it ;;} In addition, the method ^{according to the invention is suitable for examining 1} pressed parts of any shape, including those that have more than two different ones -dem ' ^: - "' ~ a ^ jig; voti'gesetien-iwlLrdj ^ the" eiine · inner chamber

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which is designed so that it follows the shapes of the pressing part adapts · These clamping devices have a number of supply lines for the pressure medium and from Seals, each with a certain feed and certain seals forming a tree from which the medium can be supplied under pressure s ^ lc ^ en areas in which Joining errors are suspected.

While the invention above in connection with pressed parts from metal powder has been described, which have an abrupt, changing cross-section, it goes without saying that the invention is not limited to this application is. The invention is namely for pressed parts from any powdery substances applicable, the composition of the powder and the shape are irrelevant. Accordingly, the invention works as well with ceramic powders, for example Applicable as with metallic powders and it is applicable to symmetrical pressed parts including cylindrical ones Pressed parts can be used or for irregularly shaped pressed parts including those with irregular shapes such as gears or those with perforations. The pressed parts can also be hollow or solid be. The only requirement on a device for Implementation of the method according to the invention must be provided, is that the clamping device a Must have inner chamber that is suitable for the pressed part which is also suitable for those areas of the pressed part that are not tested to be supported in order to prevent areas free of structural defects from being destroyed, which furthermore does not put any pressure on the pressed part in the test area exerts, which counteracts the forces generated by the pressure medium and which ultimately has one or more devices namely leads and seals to keep the liedium under pressure in the areas that are being tested should, zuzuführn · To meet these demands, can

♦ J8-109B13 / i08'5

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the jig adjustable or non-adjustable either vertically or horizontally Direction to the shape and dimensions of the inner chamber change. This ultimately depends on the shape of the pressed part to be tested .. ·

Furthermore, it understands »see that the discovery, although you above in connection with de? Application © ines Normdrueks has been described on the pressed parts to be examined, can also be realized in such a way that a variable Pressure is used to inspect the pressed parts. When applying a standard pressure, the pressed part is either destroyed or remains fs under the influence of the forces exerted intact and the usability of the pressed part can thus be easily determined. On the other hand, a variable pressure can also be used can be used, which rises up to the standard pressure and the pressure at which the breakage occurs, if at all determined and compared with the standard pressure in order to determine the usability of the pressed part. With another Embodiment, the pressed part is subjected to a variable pressure, which can exceed the standard pressure, in order to bring about a break of all pressed parts examined and the pressure at which the break occurs with the Compare standard pressure to determine the usability of the preassembly. Since with the latter method all examined parts are destroyed, of course only a fraction of the pressed parts is examined, whereby this fraction is determined using known statistical methods.

109813/1081

Claims (8)

1.7.1970 - ^ - P at ent ans ρ r ü c ^; hey 1. Procedure for testing of powdered material - Manufactured unsintered pressed parts for structural defects, characterized in that a liquid or gaseous medium is supplied to those areas (5) of the pressed parts (1), in which there is a suspicion of structural defects, under a pressure that is high enough to be in the area (5) the structural defects cause stresses that lead to breakage of the defective pressed part (1), _etc. 2. The method according to claim 1, characterized in that the medium is fed with a constant mold pressure » 3. The method according to claim 1, characterized in that the medium with a variable pressure until it is reached a pressure that is less than or equal to the Uorm » pressure is supplied. ■ ■ 4 «Method according to claim 1, characterized in that the medium is fed at a pressure that is high enough is to destroy the pressed part and that the pressure at which the break occurs is measured « 5. The method according to one or more of the preceding claims, characterized in that the pressed part is checked one after the other in different areas in which structural defects are suspected, 6. The method according to claim 1 to 4 »characterized in that that the pressed part is checked simultaneously in different areas in which structural defects are suspected. -2- 109813 / 1Π85 1.7.1970 - ^ - 7 · The method according to one or more of the preceding claims, characterized in that with pressed parts with areas that, even if they were error-free, earlier would be destroyed than the areas to be examined if they were afflicted with structural defects, the first mentioned Areas not to be examined supported in a suitable manner and thus protected against the pressure forces of the medium will. 8. Device for performing the method according to one or more of claims 1 to 7 »characterized in that that it is used as a clamping device (10) with an inner chamber (11). to record a subject to be examined Press part (1) is designed to have means (14, 16) for introducing the medium under pressure into the Inner chamber (11) has that it is provided with seals (18) to the area in which the medium on the pressed part (1) acts in the inner chamber (11) to delimit , and that it is designed in such a way that in the area (5) the structural defect corresponds to that caused by the medium generated internal pressure does not counteract any external force 9 · Device according to claim 8, characterized in that at least one surface of the inner chamber (11) is movable is to change their size or shape «. 10 "Device according to claim 8 and 9» characterized in that that several devices for introducing the medium under pressure into the inner chamber are provided, which together with their assigned seals delimit several areas in which the medium on the pressed part in the Acts inside chamber. 109813/1085 Blank page