Patent Grant
10467359
The invention generally relates to computer aided engineering analysis for simulating sheet metal forming process, more particularly to a special-purpose programmed computer system for conducting simulations of obtaining numerical physical behaviors of workpiece sheet metal during a metal forming process having a predefined load path with corresponding mesh adjustment scheme.
Sheet metal forming has been used in the industry for years for creating metal parts from a blank sheet metal, for example, automobile manufacturers and their suppliers produce many of the parts using sheet metal forming. There are many steps in sheet metal forming, one of the steps is referred to as hemming. Hems are commonly used to reinforce an edge, hide burrs and rough edges, and improve appearance. One example usage of hemming is to manufacture door panel. During a hemming process, a sheet metal edge is rolled flush to itself. In recent years, one particular type of sheet metal forming is referred to as incremental sheet metal forming. A sheet metal is formed into the final workpiece by a series of small incremental deformations. Generally, incremental sheet metal forming is conducted by connecting a forming tool to a CNC (Computer Numerical Control) machine, a robot or the likes. A load path of the forming tool is therefore predefined.
One example usage of incremental sheet metal forming is for production improvements of parts used in a prototyping or concept vehicle. Due limited quantity of the concept vehicles (sometimes one), it is impractical to create stamping tools for various parts. Incremental sheet metal forming is generally used.
With advent of computer technology, computer aided engineering analysis (e.g., time-marching simulation based on finite element analysis (FEA) technique) have been used for assisting engineers/scientists to design products and manufacturing procedures, for example, sheet metal forming process. In order to capture detailed physical behaviors in vicinity of drastic changes, finer finite element mesh is required. One prior approach is to have a finer FEA mesh for the entire model. However, this technique requires unrealistic long computation time and much larger computational resources due to huge size of the FEA mesh model. Incremental metal forming process is very a very slow procedure, to numerically simulate such as a process sometimes requires many hours of computation time. As a result, prior art approaches are not adequate. It would, therefore, be desirable to have improved methods and systems for conducting a time-marching simulation for obtaining numerical physical behaviors of sheet metal during a sheet metal forming process having a predefined load path.
This section is for the purpose of summarizing some aspects of the invention and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract and the title herein may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the invention.
Systems and methods of obtaining numerically-simulated physical behaviors of a workpiece sheet metal during a metal forming process having a predefined load path using a mesh adjustment scheme in a special-purpose programmed computer system are disclosed.
According to one aspect of the invention, a FEA mesh model is received in a special-purpose programmed computer system having a special-purpose finite element analysis (FEA) based application module installed thereon. The FEA mesh model contains a number of finite elements to represent a workpiece sheet metal in a time-marching simulation of obtaining numerical physical behaviors of the workpiece sheet metal during a metal forming process having a predefined load path (e.g., incremental metal forming, hemming, etc.). Also received in the special-purpose programmed computer system are the total simulation time period, the predefined load path, a set of mesh refinement criteria and a mesh coarsening criterion. The predefined load path contains a three-dimensional continuous path of a forming tool in the total simulation period. The set of mesh refinement criteria includes a series of predetermined mesh adjustment times during the time-marching simulation, a characteristic length for establishing a three-dimensional (3-D) mesh refinement zone and a desired mesh refinement level. The mesh coarsening criterion includes a scheme to determine respective element strain gradients of a cluster of four finite elements that share a common corner node. With the special-purpose FEA based application module, the following actions are performed: (a) setting a current simulation time to an initial value; (b) determining current simulation period from the current simulation time and a subsequent next mesh adjustment time in the series of mesh adjustment times; (c) using the characteristic length to establish the 3-D mesh refinement zone that contains a space encompassing a section of the predefined load path corresponding to the current simulation period; (d) updating the FEA mesh model by refining those finite elements deemed to be located within the 3-D mesh refinement zone to the desired mesh refinement level; (e) further updating the FEA mesh model by coarsening certain finite elements located outside of the 3-D mesh refinement zone in accordance with the mesh coarsening criterion; (f) conducting a corresponding portion of the time-marching simulation using the updated FEA mesh model for the current simulation period until the current simulation time has reached the subsequent next mesh adjustment time; and (g) repeating (b)-(f) until the current simulation time has passed the total simulation time period.
Objects, features, and advantages of the invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings.
These and other features, aspects, and advantages of the invention will be better understood with regard to the following description, appended claims, and accompanying drawings as follows:
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will become obvious to those skilled in the art that the invention may be practiced without these specific details. The descriptions and representations herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, and components have not been described in detail to avoid unnecessarily obscuring aspects of the invention.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Additionally, used herein, the terms “horizontal”, “vertical”, “upper”, “lower”, “top”, “bottom”, “right”, “left”, “front”, “back”, “rear”, “side”, “middle”, “upwards”, and “downwards” are intended to provide relative positions for the purposes of description, and are not intended to designate an absolute frame of reference. Further, the order of blocks in process flowcharts or diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention.
Embodiments of the invention are discussed herein with reference to
According to one aspect, the invention is directed towards one or more special-purpose programmed computer systems capable of carrying out the functionality described herein. An example of a computer system 100 is shown in FIG. 1. The computer system 100 includes one or more processors, such as processor 104. The processor 104 is connected to a computer system internal communication bus 102. Various software embodiments are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the invention using other computer systems and/or computer architectures.
Computer system 100 also includes a main memory 108, preferably random access memory (RAM), and may also include a secondary memory 110. The secondary memory 110 may include, for example, one or more hard disk drives 112 and/or one or more removable storage drives 114, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive 114 reads from and/or writes to a removable storage unit 118 in a well-known manner. Removable storage unit 118, represents a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive 114. As will be appreciated, the removable storage unit 118 includes a computer readable storage medium having stored therein computer software and/or data.
In alternative embodiments, secondary memory 110 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 100. Such means may include, for example, a removable storage unit 122 and an interface 120. Examples of such may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an Erasable Programmable Read-Only Memory (EPROM), Universal Serial Bus (USB) flash memory, or PROM) and associated socket, and other removable storage units 122 and interfaces 120 which allow software and data to be transferred from the removable storage unit 122 to computer system 100. In general, Computer system 100 is controlled and coordinated by operating system (OS) software, which performs tasks such as process scheduling, memory management, networking and I/O services.
There may also be a communications interface 124 connecting to the bus 102. Communications interface 124 allows software and data to be transferred between computer system 100 and external devices. Examples of communications interface 124 may include a modem, a network interface (such as an Ethernet card), a communications port, a Personal Computer Memory Card International Association (PCMCIA) slot and card, etc. Software and data transferred via communications interface 124. The computer 100 communicates with other computing devices over a data network based on a special set of rules (i.e., a protocol). One of the common protocols is TCP/IP (Transmission Control Protocol/Internet Protocol) commonly used in the Internet. In general, the communication interface 124 manages the assembling of a data file into smaller packets that are transmitted over the data network or reassembles received packets into the original data file. In addition, the communication interface 124 handles the address part of each packet so that it gets to the right destination or intercepts packets destined for the computer 100. In this document, the terms “computer program medium”, “computer readable medium”, “computer recordable medium” and “computer usable medium” are used to generally refer to media such as removable storage drive 114 (e.g., flash storage drive), and/or a hard disk installed in hard disk drive 112. These computer program products are means for providing software to computer system 100. The invention is directed to such computer program products.
The computer system 100 may also include an input/output (I/O) interface 130, which provides the computer system 100 to access monitor, keyboard, mouse, printer, scanner, plotter, and the likes.
Computer programs (also called computer control logic) are stored as application modules 106 in main memory 108 and/or secondary memory 110. Computer programs may also be received via communications interface 124. Such computer programs, when executed, enable the computer system 100 to perform the features of the invention as discussed herein. In particular, the computer programs, when executed, enable the processor 104 to perform features of the invention. Accordingly, such computer programs represent controllers of the computer system 100.
In an embodiment where the invention is implemented using software, the software may be stored in a computer program product and loaded into computer system 100 using removable storage drive 114, hard drive 112, or communications interface 124. The application module 106, when executed by the processor 104, causes the processor 104 to perform the functions of the invention as described herein.
The main memory 108 may be loaded with one or more application modules 106 that can be executed by one or more processors 104 with or without a user input through the I/O interface 130 to achieve desired tasks. In operation, when at least one processor 104 executes one of the application modules 106, the results are computed and stored in the secondary memory 110 (i.e., hard disk drive 112). Results of the analysis (e.g., updated FEA mesh model after mesh refinement) are reported to the user via the I/O interface 130 either in a text or in a graphical representation upon user's instructions.
Referring to
Process 400 starts at action 401 by receiving a finite element analysis (FEA) mesh model in a special-purpose programmed computer system (e.g., computer system 100 of
Next, at action 402, a total simulation time period, the predefined load path and a set of mesh refinement criteria are also received in the computer system. The predefined load path contains a three-dimensional (3-D) continuous path of a forming tool (e.g., a punch) in the total simulation time period. The total simulation time period may correspond to the time required to perform the task (e.g., hemming, incremental forming, etc.) in a real world forming process. The set of mesh refinement criteria includes a series of mesh adjustment times during the time-marching simulation, a characteristic length for establishing a three-dimensional (3-D) mesh refinement zone, and a desired mesh refinement level.
Referring now to
Then, at action 406, a 3-D mesh refinement zone is established using the characteristic length. The 3-D mesh refinement zone comprises a space encompassing the corresponding section of the predefined load path of the current simulation period. At action 408, the FEA mesh model is updated by refining those finite elements deemed to be located within the 3-D mesh refinement zone to the desired mesh refinement level. At action 409, the FEA mesh model is further updated by coarsening certain finite elements located outside of the 3-D mesh refinement zone in accordance with a predefined mesh coarsening criterion. In one embodiment, mesh coarsening criterion is used for determining respective strain gradients of a cluster of four finite elements that share a common corner node. Updating the finite element mesh model requires mapping of the element states (e.g., stress, strain, etc.) from the original model to the updated model. The mapping of the element states can be done with a number of well-known procedures.
At action 410, a corresponding portion of the time-marching simulation is conducted using the updated FEA mesh model for the current simulation time period until the current simulation time has reached the subsequent next mesh adjustment time. Next, at test 412, it is determined whether the current simulation time has passed the total simulation time period. If test 412 is false, process 400 follows the ‘no’ branch to action 404 to repeat actions 404, 406, 408 and 410 until the test 412 becomes true. Process 400 ends thereafter.
The predefined load path 510 is partitioned to a number of sections (e.g., sections 521-525 are shown) with the series of mesh adjustment times. In other words, each mesh adjustment time and its subsequent mesh adjustment time define a section. The series of predetermined mesh adjustment times can be defined with many well known techniques, for example, equally dividing the entire predefined load path, different times defined by a user of the time-marching simulation, etc.
The predefined load path 510 is an arbitrary path in three-dimension.
Refined finite elements shown in both example FEA mesh models 501-502 are for illustration purpose only. Desired mesh refinement level may require additional refinement to a finer mesh (not shown).
A mesh coarsening criterion is used for determining whether these four finite elements 571-574 can be coarsened back to one finite element. For example, relative angle between any two of the four normal vectors 576-579 must be within a threshold value (e.g., two degrees). In this example, relative angle θ 570 is between element normal vectors N1 576 and N2 577.
Although the invention has been described with reference to specific embodiments thereof, these embodiments are merely illustrative, and not restrictive of, the invention. Various modifications or changes to the specifically disclosed exemplary embodiments will be suggested to persons skilled in the art. Whereas most of the illustrations are shown in two-dimension, the invention comprises a predefined load path in three-dimension. Additionally, whereas only few points are shown in
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