DE102020000978A1 - Method and device suitable for increasing the strength of a joined or additive manufactured component - Google Patents

Abstract

The invention relates to a method and a device for increasing the strength of a joined or additively manufactured component by means of the combination of an application of isostatic pressure and ultrasound. For this purpose, the device has a chamber suitable for receiving the component, which is designed for a pressure of up to 1000 MPa and for a temperature of up to 500 ° C. and which is filled with a liquid suitable for imparting the isostatic pressure on the component; In addition, the device comprises a device for introducing the pressure and additionally a device for introducing ultrasound into the chamber.

Description

The invention relates to a method and a device for increasing the strength of a component. Such a method is, for example, from DE 000068906698 T2 famous.

The strength of a material or a component made of such a material describes the ability to withstand mechanical loads before failure (e.g. deformation or breakage) occurs, and is specified as mechanical stress. The strength depends on the type of material as well as the type and duration of stress.

If the strains on a component are measured as a function of differently acting stresses, stress-strain diagrams are obtained from which its strength parameters can be determined. In the case of static loading, the strength characteristics of the yield point R _e (up to which a material shows no permanent plastic deformation under tensile stress) and the tensile strength R _m (at which a test specimen made of this material begins to constrict under tensile stress) are usually mentioned. In the case of dynamic loading (load changes that reduce the load-bearing capacity of the material or component), on the other hand, the short-term, operational and fatigue strength are used as strength parameters, which can be determined in so-called Wöhler diagrams.

The strength theoretically achievable from a material or a component made from it is usually well below the limit in practice. These deviations are based, among other things, on the type of manufacturing process. A distinction is made (e.g. according to DIN 8580) into primary forming, reshaping, cutting (e.g. machining), joining (e.g. welding) and changing material properties. As a rule, the strength of a component made from the same material increases from joining to machining to forming, which can be attributed to defects in the surface and structure of the component. One way of changing this material property is to introduce residual compressive stresses, by means of which the effects of the imperfections can be bridged locally.

In order to increase the component strength by introducing internal compressive stresses, the methods of isostatic pressing, rolling or shot peening are already known, among others, each of which has different advantages and disadvantages.

Usually joined components have comparatively low strengths and consequently components that are manufactured from powder using modern additive manufacturing processes (e.g. laser sintering or 3D printing) have only low strengths due to their large number of joining zones. To increase the strength, for example, in the DE 000068906698 T2 the post-treatment of a sintered component by hot isostatic pressing is proposed. However, the high temperatures required for this can lead to a reduction in other material properties.

It is therefore the object of the invention to provide a method and a device with which the strength of a component, in particular an additively manufactured component, can be increased without reducing its other properties.

The object is achieved with regard to a method by means of the action of an isostatic pressure that is suitable for increasing the strength of a component, in particular a joined or additively manufactured component, in that the component is introduced into a chamber filled with a liquid and this is subjected to an isostatic pressure of more than 200 MPa is applied, the temperature of the liquid being between 0 ° C and 200 ° C, and the liquid is additionally acted upon with ultrasound.

Such a method according to the invention has on the one hand (in contrast to hot isostatic pressing) a temperature stress at which most of the materials that are usually processed in a satisfactory manner do not experience any temperature-related impairment of their material properties, while at the same time a large number of liquids are known that are in this temperature range have suitable properties to convey an ultrasound exposure to the component. On the other hand, the superposition of the effect of the isostatic pressure and the effect of the ultrasonic pressure acting on the surface of the component causes a local pressure increase and therefore acts more deeply on the component than the individual effects. This also creates compressive residual stresses below the surface of the component and increases its strength. This makes the method according to the invention particularly suitable for increasing the strength of joined or additively manufactured components and in particular for components that can withstand thermal loads.

The method according to the invention proves to be particularly advantageous if the isostatic pressure is more than 500 MPa, preferably more than 700 MPa and / or the temperature of the liquid is between 50 ° C. and 120 ° C. and / or the kinematic viscosity of the Liquid in this pressure range and in this temperature range between 10 and 60 mm ² / s and / or the ultrasound has a frequency between 10 and 100 kHz and / or the application of ultrasound for a period of more than 2 minutes, preferably more than 10 minutes, particularly preferably more than 30 minutes is carried out.

These process features allow individually suitable local pressures to be applied to the component surface, but they also work together in an advantageous manner. Therefore, they can be used both alternatively and additionally. For example, an isostatic pressure of 500 MPa causes the component surface to be pressurized, which for many materials is already above their yield point. The specified range of viscosity ensures, on the one hand, that the system remains tight even under high pressure, i.e. no liquid escapes, and, on the other hand, that the applied ultrasound is not attenuated too much in order to achieve the required local increase in pressure on the component surface. The duration of the pressurization also allows the support of longer-lasting processes in the component surface and underlying zones such as e.g. B. structural densification or recrystallization.

The object is achieved with regard to a device suitable for increasing the strength of a joined or additively manufactured component by means of the action of an isostatic pressure in that the device comprises a chamber suitable for receiving the component, which is suitable for a pressure of up to 1000 MPa and for a temperature of up to is designed to 500 ° C and is filled with a liquid suitable for imparting the isostatic pressure on the component, and the device comprises a device for introducing the pressure, and according to the invention additionally has a device for introducing ultrasound into the chamber. The device for introducing the pressure can be designed, for example, as a plunger that moves into the chamber and reduces its volume with the same amount of liquid, or as a pump that additionally introduces liquid into the constant chamber volume or by a combination of these or other configurations . The device for introducing ultrasound can be designed piezoelectrically (sonotrode), capacitive or also magnetostrictive.

Such a device according to the invention is distinguished in comparison to a device for hot isostatic pressing with a comparable area of application by lower safety requirements, since on the one hand lower static pressures and on the other hand lower temperatures are used.

The device according to the invention proves to be particularly advantageous if it contains a liquid which has a kinematic viscosity between 10 and 60 mm ² / s in the aforementioned pressure range and in the aforementioned temperature range, and / or if the device for introducing ultrasound is used as a Sonotrode is designed, the natural frequency of which is between 10 and 100 kHz, and / or if the device additionally has a device for measuring the pressure in the chamber.

These device features already individually bring about improvements in the efficiency of the device, but they also work together in an advantageous manner. Therefore, they can be used both alternatively and additionally.

A liquid with a viscosity in the specified range ensures, on the one hand, that the device remains tight even under high pressure, i.e. no liquid escapes, and, on the other hand, that the applied ultrasound is not dampened too much in order to achieve the required local increase in pressure on the component surface. A device for measuring the pressure enables an advantageous process control. A configuration of the device for introducing ultrasound as a sonotrode allows access to a large number of commercially available and inexpensive piezoelectrically operating ultrasound generators.

A device according to the invention equipped with a sonotrode proves to be particularly advantageous if it comprises a device for the defined setting of the distance between the tip of the sonotrode and the component surface and additionally a device for the defined alignment of the sonotrode relative to the component surface such that the longitudinal axis of the sonotrode can be aligned with the component surface at a predeterminable angle. During operation of the device, this leads to a sound wave emitted by the sonotrode tip impinging on the component surface at a predeterminable angle. Our own tests show that different distances and orientations of the sonotrode are advantageous for the desired increase in strength for different materials.

The device according to the invention can be further improved if it comprises means for focusing the ultrasonic wave emitted by the sonotrode (for example by means of a concave design of the sonotrode tip or by acoustic lenses) and / or means for amplifying the ultrasonic wave (by means of a suitable structural design of the sonotrode, in particular the length-width ratio).

The device according to the invention proves to be particularly advantageous if the chamber is designed as a cylindrical cavity with a plunger that can be inserted into the chamber is closable, which rests slidingly on the inner wall of the cavity, wherein the punch has an axially symmetrical bore at its end facing the cavity, which is designed so that an annular wall remains, which has a smaller extent perpendicular to the inner wall of the chamber than parallel to this.

Such a configuration of the device for applying the pressure as a stamp that moves into the chamber and reduces its volume while the amount of liquid remains the same is technically particularly simple and therefore inexpensive. Because the plunger rests on the inner wall of the cavity in a sliding manner, the chamber is sufficiently sealed at the beginning of the pressure build-up to prevent the liquid from escaping. With increasing pressure, the annular wall of the stamp is pressed by the liquid against the inner wall of the cavity and thus seals the chamber even at high pressure. A wall thickness of less than 3 mm, preferably 2 mm or less, with a wall height of less than 15 mm, preferably 10 mm or less, has proven particularly suitable. Such a thickness-height ratio allows a good sealing of the chamber by elastic deformation of the wall when pressure is applied and likewise after the end of the pressure application a return of the wall to its original shape and thus an easy extension of the stamp from the chamber. A further improvement of the seal can be achieved by using further commercially available seals (metallic seal, in particular copper seal and / or fiber-reinforced plastic seal, in particular glass or carbon fiber reinforced) in the area of entry of the stamp into the cylindrical cavity of the chamber.

It is particularly advantageous in such a configuration of the device that the sonotrode is arranged laterally in the chamber or in the chamber wall outside the entry area of the punch. As a result, both can exert their respective effects independently of one another and be sealed off from the chamber independently of one another. The same applies to the arrangement of the device for measuring the pressure.

It is also advantageous for the device according to the invention if the punch has a further bore which extends from its end facing the cavity to out of the chamber and is designed to be closable with a closure.

This bore is closed during the pressure build-up and, through its opening, enables pressure to be released in the chamber and thereby a regression of the elastic deformation of the ring-shaped wall of the punch, so that the punch can be pulled out without wearing out the chamber wall and the ring-shaped wall of the punch.

• Figur: Einen schematischen und nicht-maßstabsgerechten Querschnitt der Vorrichtung umfassend eine mit einer Flüssigkeit 2 gefüllte Kammer 1, einen in die Kammer 1 einfahrbaren Stempel 3, und eine Einrichtung zur Einbringung von Ultraschall 4.

The method according to the invention and the device according to the invention suitable for increasing the strength of a joined or additively manufactured component are explained in more detail below with reference to the figure and an exemplary embodiment. The figure shows:

• Figure: A schematic and not to scale cross-section of the device comprising one with a liquid 2 filled chamber 1 , one in the chamber 1 retractable stamp 3 , and a device for introducing ultrasound 4th .

According to the exemplary embodiment, a component made of laser-sintered austenitic steel 1.4404 is inserted into the liquid 2 filled chamber 1 introduced and applied therein with an isostatic pressure and additionally with ultrasound.

The fluid is a heavy-duty hydraulic oil (AVIA SYNTOFLUID PE-B 50). It has a kinematic viscosity which is less than 60 mm ^{2 / s at a temperature of 40 ° C. and still more than 10 mm 2} / s at a temperature of 110 ° C. In such a liquid, ultrasonic waves are only slightly attenuated, even at low temperatures. In addition, such a liquid is sufficiently viscous even at a high temperature so that it does not leak through the seals of the chamber even at high pressure. In addition, the liquid is difficult to compress (7% at 100 MPa isostatic pressure, 23% at 700 MPa), resistant to aging, has good lubricating properties (which makes it easier for a stamp to slide into the chamber) and is not aggressive towards conventional sealing materials.

To increase the strength, after the component has been introduced into the chamber 1 First the chamber is vented and then the isostatic pressure is increased to around 30 MPa and then the ultrasound application started at a frequency of 20 kHz. The isostatic pressure is then increased further up to 500 MPa and this pressure is maintained for 4 minutes. The liquid reaches a temperature of around 100 ° C.

A method according to this embodiment has on the one hand (in contrast to hot isostatic pressing) a temperature stress from the liquid, through which the examined laser-sintered component (made of austenitic steel 1.4404) does not experience any temperature-related impairment of its material properties.

On the other hand, the effect of the isostatic pressure and the effect of the ultrasonic pressure acting on the surface of the component are individually too small to impair the material properties (the pressure is below the tensile strength) but in their interaction they also cause a local pressure increase on the component surface Pressure load peaks of up to 1000 MPa and therefore act more deeply on the component than the individual influences. As a result, residual compressive stresses are also generated below the surface of the component and its strength is increased by bridging defects that reduce the strength. This is also achieved through the duration of the application of pressure, which supports longer-lasting processes in the component surface and in the zones below it, e.g. B. structural densification or recrystallization.

For the laser-sintered component made of austenitic steel 1.4404 and subjected to pressure and ultrasound for 4 minutes according to this exemplary embodiment, there is an increase in strength against dynamic stress, which almost doubles the load changes until breakage. If the otherwise constant loading is increased to 12 minutes, this results in a four-fold increase in the load changes until breakage. If the otherwise constant loading is increased to 40 minutes, this causes a sevenfold increase in the load changes up to breakage.

According to a further exemplary embodiment of the process with an application time of 40 minutes and otherwise the same process parameters, a rotated component of the same geometry and made of the same material (steel 1.4404) even increases the load changes by a factor of ten until it breaks. This is attributed to the fact that the finely turned surface of the component is significantly smoother than that of the powder-sintered comparative component and therefore has fewer defects in the surface where the incident ultrasonic waves can be scattered.

In this exemplary embodiment, the device has, in addition to a chamber suitable for receiving the component 1 which is designed for a pressure up to 1000 MPa and for a temperature up to 500 ° C, and with a suitable liquid 2 is filled in the form of the hydraulic oil mentioned above, a device for introducing the pressure and additionally a device for introducing ultrasound 4th into the chamber 1 on.

The device according to the exemplary embodiment is designed with a device for applying the pressure in such a way that the chamber 1 as a cylindrical cavity 1.1 is designed with one in the chamber 1 insertable stamp 3 is lockable, the one on the inner wall 1.2 of the cavity 1.1 rests slidably, with the stamp 3 at his the cavity 1.1 facing end an axially symmetrical hole 3.1 has, which is designed so that an annular wall 3.2 remains, which is perpendicular to the inner wall 1.2 the chamber 1 has a smaller extent than parallel to this, that is, has a greater thickness than height.

Such a configuration of the device for applying the pressure as a stamp 3 that in the chamber 1 retracts and their volume with the same amount of liquid 2 reduced, is technically particularly simple and therefore inexpensive. Because the stamp 3 on the inside wall 1.2 of the cavity 1.1 is sliding, the chamber 1 Sufficiently sealed at the beginning of the pressure build-up to prevent the liquid from escaping 2 to prevent. With increasing pressure, the ring-shaped wall becomes 3.2 of the stamp from the liquid 2 against the inner wall 1.2 of the cavity 1.1 pressed and seals the chamber 1 so even at high pressure. (The effect of pressure on the annular wall 3.2 is shown in the figure by arrows.)

In this embodiment, the annular wall 3.2 a thickness of 2 mm with a height of the wall 3.2 of 10 mm. Such a thickness-height ratio allows a good seal of the chamber 1 by elastic deformation of the wall 3.2 a return of the wall when the pressure is applied and likewise after the end of the pressure application 3.2 to their original shape and thus an easy extension of the stamp 3 out of the chamber 1 . To further improve the seal, the chamber 1 Entry area of the stamp 3 into the cylindrical cavity 1.1 an additional glass fiber reinforced plastic seal and an additional copper seal.

According to the design, the stamp 3 another hole 3.3 on that of its the cavity 1.1 the chamber 1 facing end up out of the chamber 1 reaches out, and with a clasp 3.4 is designed lockable.

This hole 3.3 is with a lock during pressure build-up 3.4 closed and, after the required pressurization has been carried out, allows the chamber to be depressurized through its opening 1 and thereby a regression of the elastic deformation of the annular wall 3.2 of the stamp 3 so that one pulling out the stamp 3 out of the chamber 1 without wear to the inner wall 1.2 the chamber 1 and the annular wall 3.2 of the stamp 3 is facilitated.

The device according to the exemplary embodiment has a device for introducing ultrasound 4th equipped in the form of a sonotrode, which has a natural frequency of 20 kHzkHz. In addition, the device also has a device for measuring the pressure in the form of a commercially available high-pressure sensor in the chamber 1 on. The sonotrode is outside the entry area of the punch 3 on one side of the cavity 1.1 in the chamber 1 arranged. This allows the sonotrode and stamp 3 both exert their respective effects independently of one another and independently of one another in relation to the chamber 1 be sealed. The same applies to the arrangement of the high pressure sensor opposite the sonotrode, which is used for process monitoring.

According to the exemplary embodiment, the sonotrode is provided with a device for the defined setting of the distance between the tip of the sonotrode and the component surface, and also with a device for the defined alignment of the sonotrode relative to the component surface, such that the longitudinal axis of the sonotrode at a predeterminable angle to the Component surface can be aligned. During operation of the device, this leads to a sound wave emitted by the sonotrode tip impinging on the component surface at a predeterminable angle.

Our own tests show that different distances and orientations of the sonotrode are advantageous for the desired increase in strength for different materials.

In this exemplary embodiment, the tip of the sonotrode is designed to be concave, as a result of which the ultrasonic wave emitted by the sonotrode is focused.

The method according to the invention and the device according to the invention are particularly suitable for increasing the strength of a joined, in particular additively manufactured, component due to their comparatively low temperature load. However, they also enable very good improvements in strength in turned, i.e. machined, components.

Preferred applications are to increase the strength of laser-sintered components due to their large number of sintered joints, but also for other joined, in particular welded, components. However, the method and the device are also suitable for increasing the strength of components produced in other ways, for example in the case of components produced by means of separating, in particular by machining, or also by forming.

List of reference symbols

1

chamber

1.1

Cavity [in the chamber]

1.2

Inner wall [of the chamber]

2

liquid

3

rubber stamp

3.1

drilling

3.2

annular wall [of the bore 3.1 ]

3.3

drilling

3.4

Closure [of the bore 3.3 ]

4th

Device for introducing ultrasound

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 000068906698 T2 [0001, 0006]

Claims (6)

Process suitable for increasing the strength of a joined or additively manufactured component by means of the action of an isostatic pressure, in which the component is introduced into a chamber (1) filled with a liquid (2) and this is subjected to an isostatic pressure of more than 200 MPa, wherein the temperature of the liquid is between 0 ° C and 200 ° C, characterized in that the liquid (2) is additionally acted upon with ultrasound. Procedure according to Claim 1 characterized in that the isostatic pressure is more than 500 MPa, preferably more than 700 MPa and / or that the temperature of the liquid (2) is between 50 ° C and 120 ° C and / or that the kinematic viscosity of the liquid ( 2) in this pressure range and this temperature range of the liquid between 10 and 60 mm ² / s and / or that the ultrasound has a frequency between 10 and 100 kHz and / or that the ultrasound exposure for a period of more than 2 min, preferably more than 10 min. Device suitable for increasing the strength of a joined or additively manufactured component by means of the action of an isostatic pressure, with a chamber (1) suitable for receiving the component, which is designed for a pressure of up to 1000 MPa and for a temperature of up to 500 ° C and which is filled with a liquid (2) suitable for imparting the isostatic pressure on the component, and with a device for introducing the pressure, characterized in that it additionally has a device for introducing ultrasound (4) into the chamber (1). Device according to Claim 3 characterized in that the liquid (2) in this pressure range and in this temperature range has a kinematic viscosity between 10 and 60 mm ² / s, and / or that the device for introducing ultrasound (4) is designed as a sonotrode whose natural frequency is between 10 and 100 kHz, and / or that the device additionally has a device for measuring the pressure in the chamber (1). Device according to Claim 3 or 4th characterized in that the chamber (1) is designed as a cylindrical cavity (1.1) which can be closed with a plunger (3) which can be introduced into the chamber and which rests slidingly on the inner wall (1.2) of the cavity (1.1), the plunger (3) at its end facing the cavity (1.1) has an axially symmetrical bore (3.1) which is designed so that an annular wall (3.2) remains, which has a smaller dimension perpendicular to the inner wall (1.2) of the chamber (1) than parallel to this. Device according to Claim 5 characterized in that the punch (3) has a further bore (3.3) which extends from its end facing the cavity (1.1) out of the chamber (1) and is designed to be closable with a closure (3.4).

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