Patent Application
20200261964
The present disclosure relates to a method for producing a structural component, which has different component sections, from a high-strength alloy material.
Structural components with different component sections are parts that are structured in themselves and as such are or can be involved in the construction of a larger structure. Structural components of this type are designed as one piece and are used, for example, in aerospace technology, for example, as ribs, frames, guide rails for wing flaps, and the like. For this purpose, high-strength alloy materials, such as high-strength aluminum materials or titanium materials, are used. Structural components made of titanium materials are increasingly replacing components made of high-strength aluminum alloys because they tend to corrode when coming into contact with carbon fiber-reinforced plastic components. Carbon fiber-reinforced plastic components are increasingly being used in aircraft. Such a structural component made from a titanium material is produced by machining a forged preform. Forging in the (α+β) region is preferred to precision isothermal forging in the β region of the alloy due to the lower process temperatures and lower system expenditure. Due to the high deformation resistance of this material—the same basically also applies to other high-strength alloy materials, such as nickel-based alloys and cobalt-based alloys—a very large allowance is often required because the forging process affects the workpiece globally. Against the background of structural components designed with increasing complexity, the tool costs, tool wear, and the susceptibility to errors increase in the production of such structured structural components. For this reason, the forming of the net-shape is shifted to subsequent machining processes, which in turn leads to the fact that the material utilization is sometimes only 40% or less, and for some components only about 10% of the material originally used. In addition to the high machining costs, the low material utilization increases the cost of the manufactured structural components.
Generative methods for producing specific objects are known. Compared to the method described above for producing structural components, the material usage can be optimized by producing such structural components using a generative production method. However, it is problematic that in many cases the mechanical resilience of objects manufactured by generative methods does not meet the desired load requirements. DE 10 2014 012 480 B4 discloses a method for producing blading of a turbomachine. In this method, the individual blades are formed on a pre-manufactured blade carrier by a generative production method. The blade carrier is a conventional type with a circular base area and an axial bearing bore. In this previously known method, the generative production method is used in order to be able to produce the sometimes complicated geometry of the blades of the blading.
A similar method is known from DE 10 2006 049 216 A1. The method disclosed in this prior art is used to produce a turbine rotor, wherein the turbine rotor has an internal channel system for air cooling. In this method, at least one section of the turbine rotor has been generated by a generative production method. According to a preferred embodiment, the entire turbine rotor has been produced by a generative production method.
Generative production methods are also used, for example, to reinforce parts of a component that are subject to higher loads by applying a material. This reinforcement can be carried out in the form of ribs, a mesh, or flat elements of different thicknesses over the surface. These generatively produced component sections are used exclusively for reinforcement purposes.
In these previously known methods, a generative production method is used for producing specific components, particularly with geometries that would not be possible to be produced or could only be produced with greater expenditure using other production methods, and which are also suitable for producing individual pieces or small serial parts. In this case, only those component sections are produced generatively that either could not be produced with conventional production steps or could only be produced with unacceptable expenditure.
Proceeding from this background, an aspect of the present disclosure is to propose a method for producing a structural component, which has different structures, from a high-strength alloy material, for example, a titanium alloy, with which such a structural component can not only be produced using a forging step, but also at least largely avoids the disadvantages indicated above with regard to the prior art.
According to the present disclosure, this aspect is provided by an initially described method of the type in question, in which
The term “structural component” used in the context of this embodiment refers to any component that has a plurality of, particularly different, structures in the form of component sections and thus combines them. Such a structural component has received its final structure from the sum of the individual component sections. At least one structure of such a structural component referred to as a component section or core segment has been formed by massive forming. The at least one other component section is either produced separately and connected to the component section produced by massive forming by means of a bonded joint connection, or said other component section is applied to the massive-formed component section by means of a generative production method and is thus molded onto it. Therefore, the term “structural component” refers to those components which are structural components in the narrower sense and are thus involved or can be involved in the construction of larger structures, such as ribs, profiles or frames, or other components as parts of airplanes, or also structured structural components that are not used for the construction of a larger structure, such as rotation bodies, e.g., blade wheels for turbines or the like.
The structural component produced in accordance with a method according to the present disclosure is ultimately in one piece, as is desired for highly loaded structural components, but certain component sections—individual structures (component sections) of the structural component—are basically manufactured independently of one another. Each component section can thus be produced with a method, with which the requirements imposed on said component section can be realized, according to circumstances, particularly cost-effectively or also with regard to their properties. This does not mean that each component section must necessarily be produced using the production method which provides an optimum of desired properties. Instead, the focus is on the fact that, due to the multi-part production, in contrast to structural components of this type produced as one piece, individual component sections only have to meet lower requirements and can therefore be produced using other, usually more cost-effective or more easily executed production methods. Thus, these further component sections produced separately from the first component section—the core segment—can be castings, forgings, parts produced by a generative method, or the like. In addition, there is the option of producing one or more of these further component sections using a generative production method, specifically using the first component section as a substrate, on which the additional component section(s) is/are directly generated by such a generative production method.
Therefore, this structural component structured by different component sections is divided into its component sections, wherein at least the requirements for the core segment differ from those of the further component sections for the intended use of the structural component. The interface between two component sections is therefore fundamentally not formed by the geometry of the individual structures of the structural component to be produced, but rather by the different requirements imposed on different component sections.
The first component section—the core segment—is produced by massive forming. A core segment with high dynamic and static strength properties can be produced by massive forming. Possible massive forming processes are basically extrusion, ring rolling, or forging. Massive forming is typically carried out at elevated temperatures.
The structural component produced in this manner and having different component sections is typically the result of different production or forming processes, wherein different component sections of the structural component are basically produced using different process routes, so that such a structured structural component can be called a hybrid structural component with regard to its production. It is important that, prior to the actual production of such a structural component, the different component sections are first defined, wherein the component sections differ with respect to the requirement profile imposed on them, for example, with respect to the mechanical requirement profile imposed on individual component sections. Such a requirement profile for a component section when the structural component is applied or used primarily relates to the requirement profile with regard to mechanical loads, such as strengths, hardness, fatigue strength, and the like. In the case of a structural component, it can be provided that a central component section—the core segment—has to withstand a higher mechanical load, while other component sections molded onto it only have to meet a lower mechanical requirement profile. The component sections which must meet a higher, particularly mechanical, requirement profile are brought to near-net-shape or net-shape by means of massive forming, such as forging, at least to the extent that as little material as possible, if necessary, has to be removed by machining to adjust the net-shape. In said structural components, these component sections typically represent the core segment. At least one component section is molded onto this core segment formed by massive forming; typically, a plurality of component sections, on which only a lower mechanical load acts when the structural component is later used, is molded onto such a core segment. Therefore, these component sections only have to meet a lower requirement profile. Said one or more additional component sections can be applied or molded onto a region of the lateral surface of the core segment by means of a generative production method. These can be extensions, such as connection points, ribs, seats for components, e.g., sensors or the like. These component sections generated, for example, by a generative production method can have a local extension or can be shaped circumferentially both in the transverse direction and in the longitudinal direction of the core segment over the entire or part of said extension. These component sections are mostly responsible for the shape complexity of such structural components. For example, by generative application of a high-strength alloy material, even complicated geometries can be produced without a large allowance, especially those geometries that cannot be formed as a whole by forging as an exemplary massive forming process of the structural component, for example, undercut sections. In this respect, specific regions of the lateral surface of the forged component section form the substrate, on which the additively manufactured component sections are produced.
Said one or more further component sections can also be produced individually and thus separately from the core segment and in a further step are bonded to said core segment to form the desired one-piece structural component. A mechanical connection between the core segment and such a further component section is also possible without the additional use of fasteners, especially if the two parts are at least partially cold-welded to one another by the connection process.
If, in addition to the core segment, different component sections are provided in such a structural component, they can also be produced on different process routes and connected to the core segment. For example, depending on the structure to be formed as a component section and its requirements to be met, it is possible to produce one or more component sections molded onto the core segment by means of a generative production method, while other component sections connected to the core segment are produced separately and bonded to the core segment.
When defining the component sections to be molded onto the core segment, the interface between the core segment and such a component section will be determined at a position of the structural component, in which the core segment is not adversely affected by the connection of the component section with regard to the requirements to be met by the core segment. For this purpose, the core segment can have transition zones protruding therefrom, for example, in the form of connection bases, to which a separately produced component section is then connected or, in the case of generative manufacturing of such a component section, is applied by using the core segment as a substrate. The height of such a connection base is designed such that the thermal energy used for connecting or applying a component section influences the structure in the connection base, but not the other components of the core segment. The core segment therefore does not need to be oversized for the structural change to be factored in otherwise in the connection region of a component section to be molded to said core segment. This reduces the material usage.
It is assumed that in the context of these explanations, different component sections are defined in the case of a structural component for the first time prior to its production with respect to the requirement profiles acting on it when it is used in different regions, wherein said component sections are then produced using different production methods. In this way, the method according to the present disclosure differs from the prior art, which only focused on the producibility of component sections in order to decide whether these are produced generatively or conventionally.
This structural component division also provides the option of producing different variations of a core segment and at least one structural component having a molded-on component section, wherein the massive-formed, for example, forged core segment is the same part in the different variations, and the differentiation is made by the component section(s) connected thereto. A method designed in this manner will be further described below.
In the case of a generative production method for producing the at least one further component section, especially if produced directly on the core segment, a generative production method is used, in which metal powder or metal wire is melted by supplying energy. In order to create the raw form for these regions using the generative production method, it is typically made from an alloy powder or wire that corresponds to that of the core segment. Alloy variations or another metal alloy can also be used to construct the component sections formed by a generative production method. In such case, care must be taken to ensure that there is an intended joint connection between the substrate and the material applied to it by the generative method. The generative production method can be carried out, for example, as laser deposition welding, arc deposition welding, or also by electron beam deposition welding, just to name a few of the possible methods. By means of one or more such steps, the component sections, which have not yet been brought to near-net-shape or net-shape by means of the massive forming process, are constructed to near-net-shape. In a subsequent processing step carried out in one or more steps, these generatively constructed component sections can be brought to their net-shape. In the same processing step, the component section(s) brought to near-net-shape by means of the massive forming process can also be brought to their net-shape. These processing steps can be, for example, a forging step, with which the generatively produced regions are formed to a certain extent, and/or machining. The structure of the generatively produced component section is optimized for a subsequent heat treatment to homogenize the structure by means of a forming step with only a low degree of deformation. Such a step also improves the tension absorption of this component section. Depending on the design of the semi-finished component or of the component section(s) to be brought to net-shape, the machining can involve, for example, form milling, lathing, drilling, or the like. A combination of these measures is also possible, as is the subsequent introduction of a low degree of deformation.
The production method described above can be followed by a heat treatment for the purpose of homogenizing the structure of the massive-formed, for example, forged component section and those component sections which have been produced using a generative production method, and/or cold forming, for example, stretching or compressing of the structural component brought to net-shape.
In the case of such one-piece structural components, which have different component sections and are used primarily in aerospace technology, such a structural component combines the positive properties of a massive-formed blank with the properties of a component produced by a generative or a separate production method with respect to the complex geometries producible with such a method. If said further component section is produced particularly with a generative production method, geometries can be formed which cannot be produced even by forging as a massive forming process, or also by multiple forging, for example, due to relatively long flow paths or because these geometries, such as undercuts, simply cannot be produced by forging. With regard to the division of the regions, such a structural component will be typically divided in terms of the regions formed by massive forming, such as forging, and those constructed by another production method such that the regions of the structural component, which are subjected to greater, especially dynamic loads, are massive-formed component sections or at least have such a core when the structural component is used. For this purpose, the massive forming structure, which is particularly resistant to such loads, is used. In such case, forging is particularly suitable as a massive forming process because the structures thus achievable can withstand particularly high, particularly dynamic, loads.
During the studies that led to the subject matter of this present disclosure, it was first necessary to ignore the prevailing teaching that such a structural component structured by specific geometries must be produced from a single piece in order to meet the requirements placed on the structural component. Only the rejection of said teaching opened the way to a division of the structural component into component sections with different requirement profiles, thus into a core segment and one or more component sections to be molded on, and to the subject of the claimed method. For example, in the case of a structural component with one or more stiffening ribs to achieve the desired strength properties, it is sufficient if the base surface or the root of such a rib is formed together with the adjacent core segment by massive forming, for example, by forging. This also represents a connection base as a transition zone, as already outlined above. The actual rib formation in terms of its height is then realized by the component section to be connected, for example, by a generative production method, typically applied to the base surface or the root. The same applies, for example, to a geometry specified to form connection points, which such a structural component can have. Numerous other configurations are conceivable.
In the case of the structural component produced according to said method and having a plurality of component sections, it is brought to its net-shape only after the at least one component section has been connected to the core segment, which then represents a completed preform. This can be done in one or more steps. Bringing the completed preform to its net-shape can only affect a few sections of the completed preform, typically the component sections connected to a core segment, thus ensuring the dimensional accuracy of the component sections molded onto the core segment and also their transition into the core segment while adhering to very narrow tolerance limits.
A component section produced by a generative production method can be connected to a base formed by the preceding massive forming step, the upper side of said base forming the substrate surface. By means of such a base molded onto the core segment, the actual core segment as a component section, which is intended to meet the requirements of a higher requirement profile, is protected from thermal influence or near-surface material mixing as a result of the generative production method, so that the material and structural properties set by forging in the actual core segment cannot be changed or at least not significantly changed by the typically locally performed generative production step. In this respect, the generative production step will be monitored with regard to its heat input into the forged core segment, wherein bases molded onto the core segment can contribute thereto, as described above. In addition, the notch sensitivity in the transition region is reduced by such a base.
In the case of a forging process for producing the component section serving as the core segment, the forging step is typically carried out in one step. This includes a subsequent pressing after a brief air venting of the die. In this context, “in one step” means that the forming is carried out in a single die. A forging step carried out in more steps is also possible, but can often be avoided by a skillful design of the structural component with regard to the component sections formed by forging and the use of a different production method for producing the at least one further component section. Since this does not result in the entire shaping of the structural component, the dies used for forging are not subjected to an excessive load (washout), so that the service life of the dies is correspondingly longer. In series production, this also has a positive effect on the tolerances to be observed when producing such structural components.
This method provides the option of designing different variations of a structural component. The common part of the different variations is produced by the massive forming step, for example, a forging process. The forged semi-finished product, for example, is therefore the common part in all variations of such a structural component, to which a component section corresponding to the desired variation is connected by a generative production method in the sections which are not yet brought to near-net-shape or net-shape. Both the arrangement of the interfaces for connecting a component section and the shaping of the component sections to be connected can differ in the individual variations. As a result, not only can the material usage be reduced, but the entire production chain can also be carried out more cost-effectively.
In the case of such production hybrid structural components, the one or more less loaded component sections produced, for example, by a generative production method, can be optimized in order to reduce weight in a manner that could not be achieved in the conventional manner or only at a disproportionately high expenditure. An example thereto is the formation of a hollow structure. Such a hollow structure can be made without losses with regard to the load-bearing capacity of this component section due to the requirements it is supposed to meet. The result is a reduced material usage and a reduced weight of the finished structural component. A lower material usage is a particular advantage, especially for structural components with relatively high material costs.
The hybrid production method also allows for the component sections to be formed on the core segment with an alloy different from the alloy of the core segment. This can be an alloy with a different composition of its alloying elements. In this respect, the material used for the component sections to be connected to the core segment can be selected specifically in relation to the requirements to be met by these regions of the structural component in the intended application. Such a configuration is also possible if the component section or sections to be connected to the core segment are formed directly on the core segment as a substrate by a generative production method.
By using different material compositions in the construction of a component section to be produced by a generative production method, material gradients and thus gradients with respect to one or more strength parameters can also be produced within the same. Such a component can also be referred to as a hybrid material component.
The use of a generative production method for producing a component section on the forged semi-finished product, or which is else produced separately, also allows for powder particles or grains made of a material to be built into it, which have special properties that are independent of the alloy to be produced. For example, this material can be a material that evaporates at the melting temperature for fusing the powder particles in order to produce a certain porosity in a component section of the structural component thus constructed. In this manner, solid lubricants can also be embedded in the component section produced by the generative production method if the component section to be produced is, for example, a component section that is supposed to form part of a bearing, for example, a bearing bush.
If the additional component section or sections are generatively formed on the core segment as a substrate, it is considered advantageous if those regions of the typically forged core segment—of the substrate—are pretreated with respect to the at least one component section to be produced by means of a generative production method and are prepared for the generative production method. For example, this can be a mechanical pretreatment, for example, in order to enlarge the contact surface of the substrate with the material to be applied thereto. According to one embodiment, the generative production method is a laser or electron beam deposition welding. In such a case, the substrate surface can be subjected to a beam treatment prior to the first application of the particles to be fused by the laser or electron beam in order to roughen this surface region, thus enlarging the connection surface. Such a step is preferably carried out immediately before the start of the deposition welding for producing the regions to be applied to the substrate surface because this region is also preheated as a preparation for the generative production step. A corresponding heating of the surface region of the substrate can also be used as a preparatory measure for the near-net-shape construction of such a region by means of a generative production method. In isolation or in combination with one of the two aforementioned pretreatment measures, the substrate surface can also be chemically pretreated, for example, in order to remove surface contaminants or a lubricant carried along from the forging die.
If, after the near-net-shape forming of the component section(s) produced by a generative production method on the forged semi-finished product, said component sections are supposed to be brought into their net-shape or nearer-net-shape by forging, the surface irregularities caused by laser deposition welding as well as electron beam welding or arc welding as a generative production method, can be used as lubrication pockets to control the material flow.
In another production of the further component section(s), the connection surface on the core segment side and/or the connection surface of the further component section can be pretreated and/or pre-contoured to support the connection process. The latter is possible, for example, by forming grooves for producing a larger connection surface in order to support a bonded joining process, for example, by means of electron beam welding or friction welding.
The adjustment of the net-shape of the structural component, which follows the forming of the completed preform, can be carried out in one or more steps, typically by machining.
A titanium alloy, particularly an (α+β) titanium alloy, for example, a Ti-6Al-4V alloy, is used for the massive-formed blank, for example, a forged blank according to one embodiment.
The following description utilizes example embodiments with reference to the attached drawings, wherein:
The sequence of drawings of
For preparing the forging of this forging blank 2, it is heated to its forging temperature, placed in a die and forged into the preform 3 shown in (3). Through the forging process, the shorter leg 4 of the forging blank 2 has been brought into a square shape 5. This adjoins the arch section with the interposition of transition regions. In the longer leg of the forging blank 2, two constrictions 6, 6.1 have been introduced by the forging step by extending its length. The preform 3 created by forging has in some sections already been brought to near-net-shape. In the embodiment shown, this preform represents the core segment of the eventual structural component. This core segment is the component section that has to meet a higher mechanical requirement profile than the other component sections described below. In the embodiment shown, this applies particularly with regard to its dynamic resilience.
The structural component to be produced from the blank 1 has a significantly more complex shape than the preform 3. In order to create this more complex shape, rough shapes are constructed by generative laser deposition welding in the regions of the preform 3 which are supposed to carry the further structures in the depicted embodiment. It goes without saying that other deposition welding methods can also be used. With regard to the heat introduced, the deposition welding has been carried out such that the heat input into the core segment is locally only very low, and a material mixing is also limited only to a surface edge zone of the substrate. The preform 7 completed by the generative production method is shown in step (4) of
In the depicted embodiment, the final contouring of the completed preform 7 with its component sections 8 constructed by the described generative production method takes place by machining (see step (5)). The rough shapes forming the component sections 8 are brought into their net-shape shown in (5) by shape milling. In this processing step, the regions of the completed preform 7, which are not brought to net-shape by the forging step, are also brought into their net-shape.
The structural component 9 is a fictitious structural component. In this structural component 9, it is essential that the core segment formed by the forged preform 3 can be exposed to increased mechanical stress as a component section. Since the L-shape of the structural component 9 is formed by forging, this core segment of the structural component 9 also readily meets the high requirements imposed on it. This is also the case due to the requirement profile imposed on the core segment. The component sections 8 produced by the generative production method and the extensions brought into net-shape therefrom by shape milling do not have to meet these requirements when the structural component 9 is used. They can also be subjected to higher loads, but do not have to meet the load requirements that the structural component 9 has to meet in the sections of its L-shaped preform. If, as is the case with previously known methods, the structural component 9 were to be produced by forging a preform and subsequent machining, it would only be possible with a low material utilization, which would not only be more elaborate but also cost-intensive.
The above-described production steps are preceded by a division of the structural component 9 into component sections that differ in terms of their mechanical requirement profile, namely the core segment formed by the preform 3 as a first component section that must meet a higher requirement profile, and the second component sections 8 molded thereto, which do not have to meet said high requirement profile.
After the structural component 9 has been brought into its net-shape, it is subjected to a heat treatment in order to homogenize the structure.
The structural component 9 of the depicted embodiment is one of several variations which differ in the number of component sections 8 constructed by the generative production method. The depicted structural component 9 is the one of the several variations which combines all of the possible variations which differ in terms of the number of extensions. Thus, a further variation, not shown in the drawings, has only a single component section 8 applied by the generative method to the square shape 5 of the shorter leg and an extension brought into net-shape by shape milling. In a further variation, this leg of the structural component 9 has no extensions. In a different design, other variations consist of projections molded onto the longer leg.
A particular advantage of this concept is that all variations can be produced on one and the same production line with one and the same tools.
In this embodiment, the component section 8.2 is designed as a hollow body, as shown by the sectional depictions of this component section 8.2 in steps (4) and (5) of
After the structural component 9.1 has been brought into its net-shape, it is also heat-treated and formed with a low degree of deformation.
In an alternative process sequence, the structural component shown in
The example embodiments described above are provided for illustrative purposes to help explain the invention. Without departing from the scope of the claims, there are numerous other options for a person skilled in the art to implement the invention without the necessity of having to describe or depict such options in detail within the framework of this description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102018102903.9 | Feb 2018 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/053082 | 2/8/2019 | WO | 00 |
