Patent Application
20110030214
The present disclosure relates to a multiple step forming process for producing a piston.
Pistons, and in particular piston crowns, are typically manufactured either by casting or forging. Forged piston crowns include different material properties when compared to cast piston crowns. For example, forged piston crowns tend to have a greater material density than cast piston crowns, making forged piston crowns more desirable than cast piston crowns in at least some applications. However, forging a piston crown can be more time consuming and costly to manufacture than utilizing a casting operation. In one type of forging process, a billet is placed in a press and forged by a die into an approximate shape of the piston crown in a single stroke. After forging, the piston crown may be machined to create features such as the cooling gallery, ring grooves and the drain passages, and then finish machined to the final dimensions. In another type of forging process, the billet is placed in a press and is formed into a final shape by exerting multiple strokes on the billet using the same die. However, the final shape may not be accurate enough for production, and the piston crown may still need extensive machining.
Machining can be a labor intensive process that may become costly. It may also be difficult to produce forged piston crowns at high volumes, as machining can become time-consuming. Finally, machining results in wasted material. Producing a near net shaped part reduces the amount of machining necessary to achieve the final dimensions of the piston crown.
Therefore, there exists a need to provide a method of producing a near net shaped piston crown utilizing a forging process and then utilizing the piston crown to complete a piston assembly.
Referring now to the discussion that follows and also to the drawings, illustrative approaches to the disclosed systems and methods are shown in detail. Although the drawings represent some possible approaches, the drawings are not necessarily to scale and certain features may be exaggerated, removed, or partially sectioned to better illustrate and explain the present disclosure. Further, the descriptions set forth herein are not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms and configurations shown in the drawings and disclosed in the following detailed description.
Moreover, a number of constants may be introduced in the discussion that follows. In some cases illustrative values of the constants are provided. In other cases, no specific values are given. The values of the constants will depend on characteristics of the associated hardware and the interrelationship of such characteristics with one another as well as environmental conditions and the operational conditions associated with the disclosed system.
The cooling gallery 44 may be located within the piston assembly 20, and may include a cooling gallery surface 60, where the cooling gallery surface is defined at least in part by an inner wall 62 of the piston crown 30 and an inner wall 64 of the piston skirt 32. The cooling gallery 44 may also include one or more fluid inlet apertures 70 and one or more fluid outlet apertures 72.
In one exemplary illustration, the piston crown 30 and the piston skirt 32 may be constructed from different materials. For example, the piston crown 30 may be constructed from a different grade steel material than the piston skirt 32. More specifically, the steel used for the piston crown 30 may include different mechanical properties, such as yield point, tensile strength, or notch toughness, than the piston skirt 32. The piston crown 30 also includes an outer diameter D, where the finished diameter D is usually less than about 200 mm (about 7.87 inches). This is because the multiple step forging process used to produce the piston crown 30 and discussed in more detail below may have a limited amount of force and energy that can be exerted on the piston crown 30. Therefore, the diameter D of the piston crown 30 produced by the process illustrated in
The piston crown 30 may be created by a multiple step forging process that utilizes at least two different forming stations, which is illustrated in an exemplary manner generally in
While three stations are illustrated, there may be fewer or more stations depending on the nature of the piston crown. Further, while the stations represent discrete hot forging operations, the stations may be part of an overall forming mechanism assembly. In another illustration of the multiple step forging process, the billet 130 can be heated to a warm forging temperature as well. Alternatively, the billet 130 can be cold forged as well too, without the need to heat the metal alloy prior to forming.
As illustrated in
If a hot forging process is used then prior to creating the billet 130 the bar of stock may be heated to a predetermined forging temperature before it is shorn to length L. Alternatively, the billet 130 itself may be heated to the desired forging temperature after being shorn at a lower temperature. In either case, the hot forging temperature is typically a temperature above the recrystallization temperature of a specified metal. For example, a type of steel based metal alloy may have a hot forging temperature of about 1095° C. to about 1150° C. (2003° F. to about 2102° F.). However, other types of metal alloys, such as an aluminum alloy, may be used as well.
The billet 130 may be carried from the shearing station to a first station illustrated in
Turning to
The pre-forming of the piston crown 330 may be performed by a closed set of second dies 390 with a sealing line 394. Similar to
Then, referring to
In one exemplary illustration of the piston crown 430, the cooling gallery 456 may be created by a coining operation. In one illustration, the coining operation may be performed while the piston crown 430 is still heated to near the hot forging temperature. The coining may also be performed on any surface of the piston crown 430 that is generally parallel to the sealing line 494 that is created by the closed third dies 490 of the third forming station.
In the illustration of
The near net shaped part 530 is then machined. The machined net shaped part 530 is then fixedly joined to the piston skirt 32 using any one of a number of known approaches discussed above. The piston assembly may then potentially undergo a finish machining operation to produce the piston assembly 20 illustrated in
As previously noted, in the illustrations of
In one exemplary illustration of the multiple step forging process illustrated in
Producing the piston crown 30 using a multiple step forming process to produce a near net shaped part 530 may be advantageous for several reasons. Multi-stage forming processes using more than one die tend to result in parts that have tighter tolerance ranges as well as improved reproducibility when compared to parts produced with a single stage cavity using multiple strokes to create a finished part. At least some forged piston crowns that are currently available are produced using a single stage die. These types of forged piston crowns may need extensive machining to produce a finished piston crown. Moreover, piston crowns produced by single stage cavities do not generally allow for more complex forming processes, such as, for example, coining operations. This means that a single stage die can not form certain features of the piston crown, such as the cooling gallery, and these features may need to be machined. Single stage forming in the same die using multiple strokes may also require longer cycle times than multi stage forming processes using different dies. Therefore, parts produced by multiple step forming processes may result in higher volumes than parts produced by a single stage die, due to decreased cycle times.
In one preferred illustration, the near net shaped piston crown 530 may be produced by a type of automatic hot forging machine that is a Hatebur type forging machine. A Hatebur type forging machine is a multi-stage metal working machine that automatically transfers parts from one metal forging station to the next. That is, the Hatebur type forging machine transfers parts without the need for an operator to manually remove the parts from one station and place them in the next station. Automatically transferring parts from one station to the next reduces cycle time. Thus, parts produced by a Hatebur type forging machine tend to include reduced cycle times when compared to forged parts produced by other types of forging processes.
The multi stage forming process illustrated in
With specific reference to
In step 304, the billet 130 can be heated to a predetermined forging temperature. For example, the predetermined forging temperature may be the hot forging temperature of a metal. Moreover, the billet 130 can be cold forged as well too, without the need to heat the metal alloy prior to forming. Therefore, step 304 may be optional. Process 300 may then continue to step 306.
In step 306, the billet 130 is upset in a first station using a set of first dies 290 as discussed above, to generally decrease the length L to a second length L′, and to decrease the cross section C to a second cross section C′. Next, in step 308, the billet 230 is pre-formed in a second station using a set of second dies 390 into an intermediate configuration of a piston crown 330. Process 300 may then proceed to step 310.
In step 310, the piston crown 330 is formed into a generally final shape of the piston crown 430. In step 312, a cooling gallery 456 may be created by a coining operation, where the coining operation is part of the forming to create the final shape of the piston crown 430. Process 300 may then proceed to step 314. In step 314, the piston crown 430 is precision forged into a near net shaped piston crown 530. Process 300 may then proceed to step 316. In step 316, the near net shaped piston crown 530 may be machined. That is, the piston crown may be machined to prepare the piston crown 530 for joining to a piston skirt. Process 300 may then proceed to step 318.
In step 318, the piston crown 530 is fixedly joined to a piston skirt, such as the piston skirt 32 illustrated in
Although the steps of the method of process 300 are listed in an exemplary order, the steps may be performed in differing orders. Furthermore, as noted above, one or more steps may be eliminated and other exemplary forging steps may be added between the initial stage and the final stage.
The present disclosure has been particularly shown and described with reference to the foregoing illustrations, which are merely illustrative of the best modes for carrying out the disclosure. It should be understood by those skilled in the art that various alternatives to the illustrations of the disclosure described herein may be employed in practicing the disclosure without departing from the spirit and scope of the disclosure as defined in the following claims. It is intended that the following claims define the scope of the disclosure and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the disclosure should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Moreover, the foregoing illustrations are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.
