Complex cast component and casting method therefor

Abstract

A complex cast component of an internal combustion engine, in particular a crankshaft or a camshaft, has a longitudinal axis, a plurality of regions, along the longitudinal axis, and a first cavity. Each of the plurality of regions has a certain cool-down rate during a solidification process of a casting process. The first cavity is arranged in a first region of the plurality of regions and has a volume that depends on a first cool-down rate of the first region. In this way, a material thickness in the first region likewise depends on the first cool-down rate.

Claims

1. A casting method for producing a complex cast component of an internal combustion engine, the method comprising the acts of: providing a casting mold; providing a multiplicity of cores in a multiplicity of regions of the cast component during a solidification process, the multiplicity of cores are arranged in the casting mold such that a volume of each core of the multiplicity of cores is dependent on a specific cooling rate relative to a respective region of the multiplicity of regions in which it is arranged, the respective volume increases along a longitudinal axis of the cast component which is to be cast, wherein the multiplicity of regions comprises more than two regions, and wherein each region of the multiplicity of regions at least partially comprises either a main bearing or a pin bearing; introducing a casting material into the casting mold; and removing a finished cast component from the casting mold after the solidification process is complete.

2. The casting method according to claim 1, wherein a ratio of the volume of each core in relation to the respective region lies between 25% and 75%.

3. The casting method according to claim 2, wherein the respective regions take up equal volumes in relation to the component as a whole.

4. The casting method according to claim 2, wherein a material of each core is selected from materials which have a better heat abstraction rate than the heat abstraction rate of quartz sand.

5. The casting method according to claim 4, wherein the material of each core is chromium ore sand.

6. The casting method according to claim 1, wherein the casting method is a shell mold casting method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a sectional view through a crankshaft according to an embodiment of the invention;

(2) FIG. 2 is a sectional view through a portion of a crankshaft without cavity;

(3) FIG. 3 is a sectional view through a portion of a crankshaft, with the region under consideration marked;

(4) FIG. 4 is a sectional view through a portion of a crankshaft with the region and cavity under consideration marked;

(5) FIG. 5 illustrates a half of a shell casting mold; and

(6) FIG. 6 is a schematic flow chart of the method sequence of a casting method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) The present invention will be described in detail on the basis of a crankshaft as a complex cast component, wherein other complex cast components of an internal combustion engine, such as a camshaft, can be produced using the same production method. In addition to a cast crankshaft or camshaft, a complex cast component of an internal combustion engine may also be understood to mean some other cast constituent part of the internal combustion engine which, in relation to a simple shaft or a simple smooth surface, has an outer structure which has projections and recesses.

(8) FIG. 1 shows a sectional view through an exemplary complex cast component according to the invention in the form of a crankshaft 1. The crankshaft 1 has a longitudinal axis 3 and has four pin bearings 10, 12, 14 and 16 and five main bearings 20, 22, 24, 26 and 28. Also shown, for each of the four pin bearings 10, 12, 14 and 16 and for four of the five main bearings 20, 22, 24, 26 and 28, is a respective axis 50, 52, 54, 56, 58, 60, 62 which runs transversely with respect to the longitudinal axis 3 of the crankshaft 1. For example, the first pin bearing 10 has the axis 50, and the fourth pin bearing 16 has the axis 62. The fifth main bearing 28 constitutes the gearbox side or the gearbox end, and a first axial end of the crankshaft 1. Accordingly, the first main bearing 20 constitutes the second axial end.

(9) The crankshaft 1 furthermore comprises eight regions, of which only seven regions 70, 72, 74, 76, 78, 80 and 82 are marked. In the present case, the eight regions 70, 72, 74, 76, 78, 80 and 82 comprise in each case one bearing, wherein the first main bearing 20 is not assigned to a region. For example, the first region 70 comprises the fourth pin bearing 16 and the eighth region 82 comprises the first pin bearing 10.

(10) In the interior of the crankshaft 1, eight cavities 30, 32, 34, 36, 38, 40, 42 and 44 are provided in the region of the respective main bearings 20, 22, 24, 26 and 28 and pin bearings 10, 12, 14 and 16. For better comprehensibility, ducts that may be present in reality owing to a supporting structure, which ducts connect two or more cavities 30, 32, 34, 36, 38, 40, 42 and 44 to one another or constitute an opening to the surface of the crankshaft 1, have not been illustrated. For a volume of the cavities, it is the case that the volume is selected in a manner dependent on the cooling rate in the respective region of the crankshaft 1. In this regard, for better comprehensibility, the production method according to the invention will firstly be discussed.

(11) The crankshaft, as a complex cast component, is produced by way of a preferably vertical shell mold casting method, the method sequence of which is schematically illustrated in FIG. 6. Firstly, in step A, a casting mold is provided. An example of a shell half 100 for a crankshaft 1 is shown in FIG. 5.

(12) In the exemplary vertical shell mold casting method, the introduction of the casting material during the subsequent casting process is performed from below. Referring to FIG. 5, there is a longitudinal axis 103, the filling direction is indicated by the arrow 105, wherein, by contrast to conventional shell mold casting methods, the gearbox side of the finished crankshaft 1 with the fifth main bearing 28 is arranged at the bottom after the casting process.

(13) The shell mold as a whole is, as will be explained below, filled with the casting material, preferably with cast iron, from below, with the casting material rising upward. During the subsequent material solidification, a feeder 107 performs the task of compensating for material shrinkage. Analogously to the crankshaft 1, the four pin bearing regions 110, 112, 114 and 116 and the five main bearing regions 120, 122, 124, 126 and 128 have also been indicated. The axes 150, 152, 154, 156, 158, 160, 162 of the respective resulting bearings are likewise shown.

(14) In the conventional casting process, the two halves of the shell casting mold would now be placed together, and would be filled with casting material without the cores for forming cavities being provided therein. With regard to cooling rates, the distribution discussed in the introduction would arise, with the highest cooling rate prevailing at the lower end, that is to say at the gearbox end in the situation illustrated, and the lowest cooling rate prevailing at the opposite axial end. At four exemplary measurement points 170, 172, 174 and 176, the resulting tensile strength would then be such that the tensile strength at the second measurement point 172 would be lower than that at the first measurement point 170, and the tensile strength at the third measurement point 174 would be lower than that at the second measurement point 172.

(15) Therefore, in step B, at least one core is provided. It is, however, preferable for two cores, and particularly preferably a multiplicity of cores, for example eight cores, to be provided. The design of the cores, that is to say the shape and volume thereof, is dependent on the region in which they are to be arranged in the casting mold or in the cast component. In this regard, for better comprehensibility, FIGS. 2 to 4 will be discussed.

(16) Here, FIG. 2 shows a portion of a conventional crankshaft, which comprises, for example, a pin bearing 90. In FIG. 3, the pin bearing 90 has been labeled with a marked region 92, on which the volume of the core for the casting process, and thus the subsequent cavity, is dependent. Transferred to the crankshaft 1 according to the invention, the region 92 symbolizes the regions 70, 72, 74, 76, 78, 80 and 82. For the exemplary region 92, the cooling rate during the solidification process is known, for example from simulation, tests or the like. Owing to the known cooling rate, it is now the case that a volume of a core, and thus a volume of the subsequent cavity 96 in the portion 94 according to the invention, see FIG. 4, is selected such that the subsequently resulting cooling rate corresponds to a desired cooling rate, that is to say lies for example as close as possible to the maximum cooling rate of the cast component or is based on a desired material characteristic in the marked region. The ratio of the volume of the resulting cavity 96 in relation to the region 92 will hereinafter be referred to as relative volume. This applies analogously to the cavities 32, 34, 36, 38, 40, 42 and 44 in relation to the regions 70, 72, 74, 76, 78, 80 and 82. Depending on the cooling rates, the relative volume preferably lies between 25 and 75%. In a particularly preferred embodiment, it is possible, in the configuration of the relative volume of the cavity 96, for consideration to be given not only to the cooling rate but also to a subsequent load that is expected to be exerted on the component in the respective region 92.

(17) Referring again to the casting method according to the invention, the first core refers to the core which has the smallest volume in relation to its region, that is to say the smallest relative volume. The second core refers to the core which has the greatest relative volume. The first core thus has a smaller relative volume than the second core. The remaining six cores have a relative volume which lies between the first relative volume and the second relative volume.

(18) The eight cores are arranged in the interior of the casting mold in step C. Here, the eight cores are arranged in the interior of the casting mold such that the first core is situated in a region with a first cooling rate. In relation to a conventional cast component, the first cooling rate in the first region is higher than a second cooling rate in a second region, in which the second core is arranged. The first core serves for forming the first cavity 30, wherein the second core forms the second cavity 44. Furthermore, the eight cores are preferably arranged in the interior of the casting mold so as to be situated in regions which, individually or collectively, have a large volume in relation to the cast component as a whole. In a cast component according to prior art, said regions would also be referred to as regions with material accumulations.

(19) The eight cores are arranged in the shell casting mold 100 by way of supporting points or a supporting structure. By means of the supporting structure, it is possible for two or more cores to be connected to one another such that, in the subsequent cast component, corresponding connecting ducts are formed between the two or more cores and/or the surface of the resulting cast component. Chromium ore sand is used as material for the eight cores and preferably also for the respective supporting structure.

(20) After the eight cores have been arranged in the first half of the shell casting mold 100 by way of the supporting structure, the second half of the shell casting mold is connected to the first half of the shell casting mold 100, for example by way of adhesive bonding. The shell casting mold is then arranged in a casting tub and fixed there by way of steel balls, in a manner already known from the prior art. Subsequently, in step D, the casting material, preferably cast iron, is introduced from below.

(21) After the complete solidification of the material in the casting mold, the finished cast component is removed from the casting mold in step E. The eight cores that are provided, and the supporting structure, can be removed in the manner known from the prior art. This will therefore not be discussed in any more detail.

(22) It can be clearly seen in FIG. 1 that the volume of the cavities 30, 32, 34, 36, 38, 40, 42 and 44 in relation to the respective region 70, 72, 74, 76, 78, 80 and 82 increases along the longitudinal axis 3 of the crankshaft 1 proceeding from the gearbox side. As a consequence, the relative material thickness in the respective regions 70, 72, 74, 76, 78, 80 and 82 with material accumulations, that is to say at the locations at which the cores are arranged, decreases with advancing filling direction. The cores are arranged in particular in the region of the main bearings 20, 22, 24, 26 and 28 and/or pin bearings 10, 12, 14 and 16, because it is there, in the case of a cast crankshaft 1, that the lowest cooling rates normally prevail owing to material accumulations.

(23) The crankshaft 1 according to the invention produced in this way has, in the region of a main bearing 28, a cavity 30 formed by way of the first core. Further cavities 32, 36, 40 and 44 are formed in the pin bearings 10, 12, 14 and 16. Furthermore, along the longitudinal axis 3 of the crankshaft 1, the cavities 34, 38 and 42 are provided at the main bearings 22, 24 and 26, that is to say in regions with material accumulations. In this way, at the corresponding locations, the material thickness of the crankshaft 1 can be optimized with regard to the cooling rates during the solidification process during the course of a casting process. This, in turn, leads to a higher cooling speed, and thus to higher strength characteristic values in the corresponding regions, which is advantageous.

(24) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.