DE102005027259A1 - Producing metal components by semi-hot forming of blanks made of an alloy with a superplastic structure comprises employing high strain rates at low pressures - Google Patents

Abstract

Producing metal components by semi-hot forming of blanks made of an alloy with a superplastic structure comprises applying a pressure that is at least 20% below that required to forge a corresponding alloy without a superplastic structure and adjusting the strain rate to a value above 0.1/second, or by limiting the elongation of the blank to less than 50% of that achievable by superplastic deformation and employing strain rates that are at least 100 times those for superplastic deformation. An independent claim is also included for drive shafts, toothed wheels, pinions or profiles produced by a process as above.

Description

The The invention relates to a process for the production of metallic Components by semi-hot forming of blanks from alloys with superplastic structure, in particular of UHC steels, steels, Al or Ti alloys at high strain rates, according to the features of claims 1 and Second

in the Mechanical engineering but also in the automotive industry are very different Forming process for the production of complex shaped components made of metals known. These include including extrusion, the cross rolling, the hole pressing, the rotary swaging, the gear rolling, the swaging or the Hydroforming, as well as forging.

Become this shaping process carried out at low temperatures, so Sometimes only very slow forming speeds are achievable. If it is formed faster, it must the forming pressures be raised to very high levels at the expense of tool wear and the general tooling costs go. Be the molding process in contrast, carried out in the high temperature range, especially at forging temperature, then The tool costs increase significantly, since only expensive high-temperature tools, in certain circumstances made of ceramic, can be used. Where appropriate, multi-step procedures are required. Furthermore The reshaped blanks are usually without any special precautions oxidatively damaged. this leads to for example, for the scaling of steels or too strong oxidation of titanium alloys. Before the further processing of the components produced thereby must be at least on the surface be reworked.

From more important for The economy of the molding process is one of the best possible high degree of deformation corresponding to a high elongation (ε) to realize. Only then are even complex shaped components in a single Forming step available made.

Superplastic metals offer a high potential in mechanical engineering and the automotive industry to produce components with high degrees of deformation. Superplastic alloys are for example from the FR 274 1360 A1 . US 567 2315 . EP 1 252 352 A1 , or the US 2001 020 502 known.

Under superplasticity becomes the ability understood a material, when applying only very small Teflon tensions without constriction and Virtually no strain hardening to endure deformation, which compared to the usually about 10 to 40% in normal plastic materials some 100 to over 1000%. There is an extremely high Gleichmaßdehung on. An essential feature of the superplastic behavior of Materials is the strong dependence the flow stress of the strain rate or strain rate (Ε ').

The superplastic deformation takes place over time controlled diffusion processes in which the very fine and uniform, often also roundish Slide Crystal Lite past each other and rotate. Therefore, one is only narrow process window of temperature and strain rate (strain rate (ε ')) given to the Elongation values of superplastic forming at some 100 to 1000 to reach. Typical here are an elevated forming temperature above about 50% of the melting temperature and a very low forming speed from about 10-2 to 10-5 to call s-1.

For aerospace applications, superplastic titanium alloys are of particular interest. For example, titanium alloys TiAl6V4 are transformed at about 925 ° C and TiAl5Fe2.5 at 870 ° C. In this case, pressures of about 10 bar, or 1 N / mm ² are used. The temperatures required for superplastic forming necessitate forming tools with good creep resistance at high forming temperatures. Due to the very high reactivity of titanium alloys at high temperatures, the forming must be carried out in vacuo or under protective gas. Since the risk of welding the workpiece with the tool is very large, the tools must be protected.

in the Difference to the aerospace industry are in mechanical engineering and the automotive industry mass-produced components, in particular made of steels of great Interest. In mass production plays a high process speed an essential role to minimize the cost of mass production to keep. The forming rates of superplastic forming are for the Series production of components usually unacceptable.

It is therefore an object of the invention, cost-effective method for mass production of highly formed metallic components.

The object is achieved according to the invention by a method for the production of metallic components by means of semi-hot forming of blanks from alloys with a superplastic structure, wherein the forming pressure in the forming tool is kept at least 20% below the forming pressure of the corresponding alloy required for forging, and the strain rate (ε ') of the semi-hot forming is set to values above 0.1 / s,
and a method for the production of metallic components by semi-hot forming of blanks of alloys with superplastic structure, wherein the elongation (ε) of the blank in the half-warm forming below 50% of the achievable by a superplastic forming strain values and at strain rates (ε ' ) which is at least 100 times that for superplastic forming. The forming pressure is often referred to as the corresponding yield stress.

By the inventive method thus becomes the superplastic structure of metallic alloys used at opposite the maximum values of the superplastic forming comparatively low strains to use high forming speeds. On the high strains that would be possible in forming in the superplastic area in favor of the invention dispensed with a high process speed.

In Often the metallic alloys are after their metallurgical Production not in a structural state, which would have superplastic properties. Only through a special Thermo-mechanical treatment is a microstructure that is superplastic Has properties, hereinafter referred to as superplastic structure. For example, to reach the ultrafine crystal lites, or grains, the for the superplasticity of UHC steels are required two phases are formed, which prevent grain growth. The corresponding phases are ferrite and cementite or more carbon-rich phases. To set this structure is initially relatively homogeneous Material made of pearlite, which is a lamellar mixture Ferrite and cementite is. In a second step, this perlite structure becomes converted into the superplastic microstructure in which the Carbides predominantly shäroidisch (Spherical) and the ferrite ultrafine-grained is present.

The inventive method thus offers the advantage that, for a large number of alloys, in particular of high-strength steels, achieves a significant reduction of the forming steps.

The Forming can already be done at the middle temperatures of the semi-warm forming carried out become. These are temperatures well below the forging temperature the respective alloy, which for example in steels the Difference between approx. 600-900 ° C and about 1200-1400 ° C accounts. These lower temperatures have a significant advantage for the forming tools, since now usually with simpler steel tools and not only with high-temperature-resistant steels or even ceramic tools can be worked.

The Lower temperatures also cause even less Scaling, or oxidation of the metallic surfaces at the components to be produced. This can be a whole depending on the alloy be a significant advantage.

In The rule with the inventive method for complex Components no or at least substantially reduced cutting another Process steps required, which also means a better material utilization Likewise, if appropriate, can be as several separate one after the other stored forming processes to a single forming process according to the invention fold. The process chain for the production of the finished components is shortened in an advantageous manner.

One Another advantage of the method is in the comparatively low forming pressure in the forming tool. This leads to essential improved service life of the tools. Likewise, the space requirement reduced the forming.

It is according to the invention provided the forming pressure well below that for forging required Forming pressure of the corresponding alloy to hold, being explicit outside the superplastic area is worked. The temperature of the Although semi-hot forming usually corresponds to the temperature range in what superplasticity is observed, however, the inventively chosen strain rate is clearly outside the superplastic area. According to the invention, the strain rate (ε ') of the semi-hot forming set to values above 0.1 / s and the forming pressure in the forming tool set at least 20% below the forming pressure required for forging. The pressure for forging refers to the corresponding one Alloy composition that does not have a superplastic structure. The temperature and pressure conditions of forging correspond usually those of hot forming.

Surprisingly, the superplastic structure of the alloys can be formed at relatively low process pressure even at high speeds of deformation. The process pressure required for forming is dependent on the respective alloy, the exact Ge adjustment and in particular also of the forming speed. Process pressure and forming speed are in opposite directions.

For UHC steels with superplastic structure is preferred at a process pressure below 150 to 180 MPa and a forming rate (strain rate (ε ')) worked above 0.1 / s. Especially a process pressure of the transformation below 100 to is preferred 150 MPa chosen. The design of the process can be based on low process pressure or be optimized for high forming speeds. Especially preferred Forming speeds are above 0.5 / s. For Al alloys with superplastic structure the strain rate is much higher at lower pressures. Prefers is pressed here at below 80 MPa and strain rates above 1 / s worked.

In Another embodiment of the invention is provided, the elongation of the blank during the half-warm forming below of 50% of the elongation values obtainable by superplastic forming and at strain rates (ε) perform, at least 100 times that of superplastic forming be. This is explicitly based on the high achievable superplastic Elongated, in favor of a high strain rate, this corresponds the very advantageous short process times. Surprisingly, with the very high strain rates a degree of deformation can be achieved with the Even complex component geometries can be achieved.

at toughen becomes superplastic structure preferably worked at strains (degrees of deformation) above 100% and more preferably in the range of 100 to 500. Below the indicated values are over to understand the component geometry averaged values. The preferred ones Strain rates are in the range of 100 to 1000 times that for the superplastic Forming required low strain rates.

In a particularly preferred embodiment of inventive method the semi-warm forming takes place in a temperature range, the the process window for which corresponds to superplastic forming. The process window is essentially by the parameters temperature, strain and strain rate given. For steels, in particular UHC steels the preferred temperature range is 600-900 ° C, especially preferably at 750 to 850 ° C. UHC steels with Al content above 2% are particularly preferably at 800-950 ° C transformed. The Al alloys are preferably formed in a temperature range of 300-400 ° C.

Prefers Alloys are used for the corresponding superplastic Forming a strain rate sensitivity (m) above 0.4. Particularly preferred are alloys with m> 0.7.

To the preferred alloys include those their maximum superplastic elongation is above 500. Especially Alloys are preferably used with strains above 800%. This ensures that during the forming of the blank Strains in the range of 100 to 400% can be achieved without problems. With this degree of deformation leaves already a very big one Cover the area of technically relevant components.

In Preferred embodiment of the invention, the process time of Forming set to values below 10 s. Depending on the chosen forming process the preferred range is between 1 and 5 s. Here are the process parameters how to adapt forming temperature and process pressure accordingly. lower Forming times are also possible but not absolutely necessary, since the setup times for the forming tool to the speed - determining quantities of Total process time.

at the invention preferred Alloys are steels, Al and Ti alloys.

Especially preferred are the steels selected from the UHC steels (Ultra High carbon steels). The C content of the steels is above 0.9 wt .-% and more preferably in the range from 1.2 to 2%.

• – C: 0,9-2,2; Al: 1,5-10; Cr: 0,5-7; Mn 1-10; Rest Fe und Verunreinigungen
• – C: 0,9-2,2; Al: 1,5-10; Cr: 1-16; Mn 0-2,2; Rest Fe und Verunreinigungen
• – C: 0,9-2,2; Al: 1,5-10; Cr: 0,25-5; 0,5-5 Mo; Mn: 0-2; Rest Fe und Verunreinigungen
• – C: 0,9-2,2; Al: 1,5-3; Cr: 1-7; Si: 0,5-5%; Mn 0-2,2; Rest Fe und Verunreinigungen
• – C: 0,9-2,2; Al: 1,5-10; Cr: 1-7; Ni:0,25-5; Mn 0-2,2; Rest Fe und Verunreinigungen

Particularly suitable UHC steels have the following compositions, the data being in% by weight:

• - C: 0.9-2.2; Al: 1.5-10; Cr: 0.5-7; Mn 1-10; Residual Fe and impurities
• - C: 0.9-2.2; Al: 1.5-10; Cr: 1-16; Mn 0-2.2; Residual Fe and impurities
• - C: 0.9-2.2; Al: 1.5-10; Cr: 0.25-5; 0.5-5 Mo; Mn: 0-2; Residual Fe and impurities
• - C: 0.9-2.2; Al: 1.5-3; Cr: 1-7; Si: 0.5-5%; Mn 0-2.2; Residual Fe and impurities
• - C: 0.9-2.2; Al: 1.5-10; Cr: 1-7; Ni: 0.25-5; Mn 0-2.2; Residual Fe and impurities

Typical representatives of the corresponding group are:
1.3 C, 1.5 Al, 7 Cr, 0.5 Mn, balance Fe,
1.3 C, 1.5 Al, 1 Cr, 2 Mo, 0.5 Mn, balance Fe;
1.3 C, 1 Al, 3 Cr, 2 Si, 0.5 Mn, balance Fe;
1.3 C, 1.5 Al, 4 Cr, 1 Ni, 0.5 Mn, balance Fe;
1.3 C, 3 Al, 1.5 Cr, 2 Mn, balance Fe;
1.3 C, 7 Al, 3 Cr, 3 Mn, balance Fe.

Another well-suited UHC steel, in addition to iron and common steel-accompanying impurities, the following alloy components in wt .-%:
0.8 to 2.5% C,
0.1 to 0.85 Sn,
3.5 to 15% Al,
0.5 to 4% Cr,
0.01 to 4% Si,
up to 4% Ni, Mn, Mo, Nb, Ta, V, and / or W, and
up to 3% of Ti, Be and / or Ga.

Prefers becomes an Al / C ratio chosen above 2/1. This ratio is particularly preferably above 3/1.

a Another advantage is the UHC steels with a high Al content. there Al contents above 3% are to be understood. By the Al will the scaling of the steel pushed further back. When warm-forming finds in these steels in usually so little surface oxidation or scaling instead of that on a surface aftertreatment can be dispensed with to remove the scale layer. The after available for forming surface is essentially the ready to use state.

by virtue of their Al content, the listed UHC steels are not rely on a special protective gas atmosphere. The half-warm forming Therefore, preferably takes place under air access.

The Conversion of the Ti alloys, however, is typically under protective gas, especially under Ar.

When Another low-carbon steel and Al-free steel can be used for the process according to the invention the following composition will be chosen (In% by weight): C <0.05%, Si <1.2%, Mn <2.8%, Cr: 15-23%, Ni: 3-9%, Mo: 1-1.9%, N: 0.09-0.25%, remainder Fe and impurities.

• – 70-79 Zn, Rest Al;
• – 6-8 Al, 4-6 V, Rest Ti;
• – 4-6 Al, 2-3 Fe, Rest Ti.

Particularly suitable Al or Ti alloys include the following compositions in wt%:

• - 70-79 Zn, balance Al;
• 6-8 Al, 4-6 V, balance Ti;
• - 4-6 Al, 2-3 Fe, balance Ti.

The inventive method is preferably performed as a near-net-shape method, so that the component after the forming in as ready as possible state accrues and only if necessary post-processed on special functional surfaces must become. Furthermore, it is expedient the process heat of Use semi-hot forming to create the appropriate microstructure of the component adjust. The component is regulated after forming cooled. steels and Al alloys are cured in a known manner during cooling. Because of the warm-warming transformation no further shaping process step will follow this approach is possible. In comparison, this procedure is the conventional procedure unsuitable because shaping steps, for example by turning or drilling, conveniently only on the unhardened Component performed become; the hardening will after the final Shaping performed by a further thermal process step.

To the preferred process variants of the semi-warm forming include the Extrusion, the Cross rolling, the hole pressing, rotary swaging, gear rolling, swaging, forging or hydroforming, which is essentially in terms of the process temperature and the process pressure on the inventive method be adjusted.

By the combination of the invention warm forming with the known shaping method can be gear shafts, extrusions, Make forgings or drop forged parts, as otherwise only in several process steps, with higher investment or operating costs are accessible.

By the inventive semi-hot extrusion are preferred most diverse mass components of mechanical engineering manufactured. These include for example gears, Pinion, short profile parts and so on.

in the Following are the different methods of semi-warm forming be explained by way of example of transmission hollow shafts example.

Among the most suitable methods is transverse rolling. The known methods are merely adapted to the process parameters of the semi-warm process according to the invention. For example, in the DE 199 05038 A1 a transverse rolling process is described in which in the direction of a workpiece axis of rotation, a movable profiled mandrel is arranged, which has a defined geometry. This is acted upon by a coupled to the mandrel mandrel feed device for guided movement of the mandrel along the workpiece axis of rotation with an axial force. The relative movement of the mandrel is matched to the movement of the cross rolling tool. Further cross rolling methods are for example from DE DE10066177 known in which a rotationally symmetric blank, for example For example, a round bar is unidirectionally rolled or reciprocated between two or more tools until the tooth structure formed on the tools has been transferred to the shell surface of the blank.

By the inventive semi-hot extrusion Solid waves can be more demanding with ready-to-use surfaces surface geometry produce. So it is possible already gears on the surface provided. In particular, you can in this process step, several gear rings independently be introduced. In a subsequent process step this is Boring the solid shaft to the hollow shaft required.

The Cross rolling of transmission shafts made of steel can be by the method according to the invention with very productive cycle times of 1 to 5 s take place. The temperature the semi-warm forming possible to reshape the steel shafts using steel tools. Prefers hollow gear shafts are manufactured; either from full waves with afterthought Drilling or pipes. It is necessary that the inner contour of the pipe during cross rolling becomes. This can be done through mandrels, in particular movable mandrels. Due to the low process temperature, the mandrels can also be made from low-cost toughen getting produced. Compared to the usual cross rollers can significantly thicker-walled tubes are used as starting material. Especially in the transverse rolling according to the invention, the whole is preferred outer contour the gear shaft inserted ready for use. The outer contour for example, gears wear that while the semi-warm cross rolling be introduced.

Possibly when cross rolling is not yet the finished surface structure the outside of the pipe but only in a subsequent process step of warm-water radial forging. This allows greater geometric degrees of freedom especially in the shaft inner contour realize.

For the production of gear shafts with wall thickness increase in Range of flanges is conventionally a combination method from rotary swaging and upset kneading used at room temperature.

At the inventive semi-hot upset kneading (or axial-radial forming) can the transmission shaft in a single process step with high precision and manufactured with complex geometric design. While In the conventional process, heated several times and compressed to the flange must be, or repeated clamping to reduce of the long and short shaft shaft may be required in the inventive semi-hot rotary swaging / upset kneading in one process step, the entire transformation takes place. Possibly can in the same or a subsequent semi-warm forming step By suitable tools still gears are introduced.

The Forming degrees of the method according to the invention Usually enough, already on the gear shafts Teeth of the usual Geometry and depth to bring.

at highest geometric claims can but it also be appropriate gears or other surface structures by machining, such as turning or milling or by electrochemical methods, such as the PECM method applied. A coarse contour can in any case by means of the semi-warm forming already be provided and the workload of fine machining considerably easier.

A Another variant of the method is the half-warm hydroforming. For the production a hollow shaft is applied to the output tube an internal pressure and the material tracked in the direction of the tube length. In the conventional method for typical Transmission shafts are pressure conditions required up to 10,000 bar, which is a cost-effective mass production not possible. With the method according to the invention rich against it for Transmission shafts already process pressures around 1000 to 3000 bar. As a rule, gears have to be in a further process step be introduced.

For the inventive semi-warm forming can the known basic method also combined in a suitable manner or be executed sequentially. In particular, show the already formed components still have considerable expansion reserves on, since in each of the forming steps according to the invention only one Fraction of the maximum possible Stretching performed becomes. Only after several forming steps is the maximum superplastic Elongation reached. Depending on the alloy used, it is required Process steps to follow each other directly so that no recrystallization of the superplastic structure by cooling and Reheating can be done.

For example, it may be expedient first to produce a blank of a gear shaft by means of semi-hot extrusion of solid material and then to convert this by means of semi-hot bore pressures into a hollow shaft with fine inner and outer contours. In particular, the In nenkontur already be the ready-to-use contour, eliminating otherwise elaborate or even impossible post-processing inside.

Claims (19)

Process for the production of metallic components by semi-hot forming of blanks of alloys with superplastic structure, characterized in that the forming pressure in the forming tool is kept at least 20% below the forming pressure required for forging the respective alloy without superplastic structure, and the Density rate (ε ') of the warm transformation is set to values above 0.1 / s. Process for the production of metallic components by semi-hot forming of blanks from alloys with superplastic Structure, by characterized in that the elongation of the blank in the semi-warm forming below 50% of that achievable by superplastic forming Elongation values and at strain rates (ε) is performed, at least 100 times that of superplastic forming be. Method according to claim 1 or 2, characterized in that the half-warm forming is carried out in a temperature range, which corresponds to the process window of the superplastic forming. Method according to one of the preceding claims, characterized characterized in that the semi-warm forming below the forging temperature the alloy takes place. Method according to one of the preceding claims, characterized characterized in that alloys are used when present a superplastic structure a strain rate sensitivity (m) above 0.4. Method according to claim 1, 2 or 3, characterized that an alloy is selected, their maximum superplastic elongation is above 500. Method according to claim 1, 2 or 3, characterized that the deformation to an elongation of the blank in the range of 100 to 400 leads. Method according to one of the preceding claims, characterized characterized in that the semi-warm forming on a process time is set below 10 s. Method according to one of the preceding claims, thereby marked that as alloys UHC steels are used in the essentially the following compositions (% by weight): - C: 0.9-2.2; Al: 1.5-10; Cr: 0.5-7; Mn 1-10; Residual Fe and impurities - C: 0.9-2.2; Al: 1.5-10; Cr: 1-16; Mn 0-2.2; Residual Fe and impurities - C: 0.9-2.2; Al: 1.5-10; Cr: 0.25-5; 0.5-5 Mo; Mn: 0-2; Residual Fe and impurities - C: 0.9-2.2; Al: 1.5-3; Cr: 1-7; Si: 0.5-5; Mn 0-2.2; Residual Fe and impurities - C: 0.9-2.2; Al: 1.5-10; Cr: 1-7; Ni: 0.25-5; Mn 0-2.2; Residual Fe and impurities - 0.8 to 2.5 C; 0.1 to 0.85 Sn; 3.5 to 15 Al; 0.5 to 4 Cr; 0.01 to 4 Si; up to 4Ni, Mn, Mo, Nb, Ta, V, and / or W, and up to 3 Ti, Be and / or Ga; Residual Fe and impurities. Method according to claim 9, characterized in that that the warm transformation takes place under air admission. Method according to claim 7 or 8, characterized that the process heat is used to cool the component regulated. Method according to claim 7, 8 or 9, characterized that when cooling is remunerated. Method according to one of claims 1 to 8, characterized, that Al alloys are used, which are essentially the have the following compositions (in% by weight): - 70-79% Zn, balance Al; - 6-8% Al, 4-6% V, balance Ti; - 4-6% Al, 2-3% Fe, balance Ti. Method according to one of claims 1 to 8, characterized, that as alloy, a steel of the following composition is chosen: C <0.05%, Si <1.2%, Mn <2.8%, Cr: 15-23%, Ni: 3-9%, Mo: 1-1.9%, N: 0.09-0.25%, remainder Fe and impurities. Method according to one of the preceding claims, characterized characterized in that the semi-warm forming as extrusion, Cross rolls, bore pressures, Rotary swaging, toothed rollers, swaging, hydroforming or combinations thereof. Method according to one of the preceding claims, characterized characterized in that several semi-warm transformations on the same component executed in succession become. Gear shafts, gears, pinions or profile parts available according to one of the preceding methods. Gear shafts, gears, pinions or profile parts according to claim 17, characterized in that it consists of UHC steels a superplastic structure are formed. Gear shafts, gears, pinions or profile parts according to claim 18 for the use in a process of claims 1 to 15.