Patent Application
20060112753
Not Applicable
1. Field of the Invention
The present invention relates generally to a system and method for superplastic forming a workpiece; and, more specifically, to an automated system including a plurality of modules forming a superplastic forming cell.
2. Description of Related Art
Superplastic forming (SPF) takes advantage of a material's superplasticity or ability to be strained past its rupture point under certain elevated temperature conditions. Superplasticity in metals is defined by very high tensile elongations, ranging from two hundred to several thousand percent. Superplasticity is the ability of certain materials to undergo extreme elongation at the proper temperature and strain rate. SPF is a process used to produce parts that are difficult to form using conventional fabrication techniques.
SPF typically includes the steps of heating a sheet of material to a point of superplasticity, clamping the material within a sealed die and then using inert gas pressure applied to one side of the sheet of material to force the material to stretch and take the shape of the die cavity. Accordingly, SPF takes advantage of certain material characteristics, specifically increased elongation at higher temperatures or the ability to stretch a material by several times its initial length without breaking.
Standard SPF applications have advantages over conventional stamping techniques, including increased forming strains, reduced spring back and low tooling costs; however, they have disadvantages in that they are limited to low volumes as they normally require relatively long forming cycle times. Specifically, a conventional SPF processes used to manufacture a complex part can require a forming cycle time as high as 30 minutes.
Further, conventional SPF systems require that the forming die is cooled prior to removal. Once cooled the die is removed a new room temperature die is inserted into the press. Before production can resume, the new room temperature die must be heated to suitable SPF temperature. This causes a significant loss of production time and cooling down and heating up of the dies. Cool down and heat up can take anywhere from 24 to 48 hours each.
Reduced cycle times are necessary in order to use SPF for the high production requirements of the automotive industry. Accordingly, there is a need for a superplastic forming system that decreases cycle time and correspondingly increases production volume.
The present invention is a system and method for raising the production volume of a superplastic forming process. The system including a superplastic forming cell used to form a workpiece. The forming cell includes a plurality of individual stations or modules, each one performing a specific manufacturing step or process on the workpiece. A plurality of transfer devices, positioned adjacent the individual stations or modules move the workpiece from one station to another.
The present invention further provides a method for forming a workpiece using a superplastic forming process. The method includes the steps of heating the workpiece, providing a forming die, placing the heated workpiece in the forming die, performing a superplastic forming process on the workpiece. Upon completion of the forming process, the method further includes the steps of removing the workpiece from the forming die, providing a cooling station and cooling the workpiece, providing a cleaning station and cleaning the workpiece and providing a trimming station and trimming the workpiece. The steps are typically performed individually; however, they may be performed or combined into a lesser amount of steps. The method further includes the steps of applying a lubricant to the workpiece prior to the forming step and providing an inspection station and inspecting the workpiece.
The present invention also provides a method and apparatus for installing and removing a heated forming die from the forming press. The method includes placing a heated forming die at a loading station, inserting the heated forming die into the forming press and clamping the forming die within the forming press. The method and apparatus further allows removal of a heated forming die in a reverse order, by unclamping the forming die within the forming press and withdrawing or pulling the heated forming die from the forming press to a loading station. Thus, the heated forming die is removed and a new preheated forming die may be installed.
A plurality of workpieces 12, normally located or stored on a rack 14, is placed nearby the superplastic forming cell 10. The workpieces 12 are typically flat sheets of metal or as they are commonly referred to blanks. In the first or lubrication module 16, an operator, seen generally at 20, using manual labor, or in the alternative a type of robot or machine, lifts a workpiece 12 from the rack 14 and places it on the conveyor 18. The conveyor 18 transports the workpiece 12 to a lubrication dispenser 22.
As with other forming operations, it is important to minimize frictional effects between the workpiece 12 or blank and the die surface. Oil-based or waxy lubricants, typically used in conventional stamping operations, cannot withstand the high forming temperatures associated with superplastic forming. Accordingly, a solid lubricant, such as graphite or boron nitride, is often used in superplastic forming because of its ability to withstand the high temperature environment.
The lubrication dispenser 22 applies lubricant to the workpiece 12 using any of several known procedures, including a roll coater or a spray booth. A dryer 24 dries the lubricant so it remains on the workpiece 12. Depending upon the type of lubricant used, a dryer 24 may not be necessary. Further, given that various types of lubricants exist that are suitable for use with superplastic forming, various lubrication dispensers or processes for applying a lubricant to the workpiece 12 are also suitable for use with the present invention.
In the second or preheat module 26, a conveyor 28 transfers the lubricated workpiece 12 from the dryer 24 to a pre-heater 30. Preheating the workpiece 12 helps to reduce overall part-to-part cycle time. Thus, a preheated workpiece 12 is loaded into a superplastic forming press 32, that forms a part of the third or forming module 34. This is in contrast to conventional superplastic forming processes where a room temperature workpiece is loaded into the forming press and which delays the forming process until the workpiece reaches a predetermined or target forming temperature. Different types of pre-heaters 30 such as conduction, induction or convection heaters are suitable for preheating the workpiece 12. One type of pre-heater 28 suitable for use with the present invention is a contact heater where the workpiece 12 is sandwiched between two heated platens that transfer heat to the workpiece 12 by conduction. A shuttle system 36, which may include a conveyor 38, transfers the heated workpiece from the pre-heater 30 to the forming press 32. One example of a pre-heater and shuttle system for use with a superplastic forming process of the present invention is disclosed in co-pending application Ser. No. ______.
The preheat module 26 may also include a temperature monitor such as a duel wavelength infrared camera 37. The infrared camera 37 monitors the workpiece 12 temperature when it exits the pre-heater 28 and prior to being transferred into the forming press 32. The infrared camera 37 is mounted over the shuttle system 36 such that as the shuttle system 36 transfers the preheated or hot workpiece 12 into the forming press 32, the workpiece 12 passes under the camera 37 which detects the surface temperature of the workpiece 12. The workpiece 12 temperature data is recorded by a computer data acquisition system and is processed to produce a two dimensional map of the surface temperature of the workpiece 12. The surface temperature map may be shown visually on a computer screen using color to identify the temperatures. This monitoring system helps to ensure good process control and can help quickly identify any issues related to pre-heating of the workpiece 12, such as low temperature or temperature inhomogeneity throughout the sheet. Additionally, the system can be used for closed-loop control over workpiece 12 temperatures.
In the third or forming module 34, the conveyor 38 transfers the preheated workpiece 12 from the preheat module 26 to the forming module 34. A forming die 40 located in the forming press 32 receives and forms the workpiece 12. A removal system 44 operates to remove the formed workpiece 12 from the forming press 32.
The forming press 32 is suitable for use with a plurality of forming dies 40. It is advantageous to change the forming dies 40 such that a preheated or hot forming die is installed in the forming press 32. Accordingly, to change or install a preheated forming die 40 in the forming press 32, the preheated forming die 40 is placed on or at a loading station 42 located adjacent the forming press 32. The loading station 42 includes a plurality of a rollers 43 secured to a load table 45. The loading station 42 may be sized such that it supports or holds more than one forming die 40. Specifically, the loading station 42 may support both the forming die 40 being removed from the forming press 32 and the new or preheated forming die 40 ready for insertion into the forming press 32.
As shown in
Die clamps, seen generally at 108, secure the forming die 40 to the lower platen 100. The die clamps 108 are shown as swing-in die clamps situated within the forming press 32 and connected to a power source or driver for remote actuation. The actuation can be accomplished by a simple mechanical connection that enables movement of the die clamps 108 from outside of the heated area of the forming press 40. Further, it is contemplated that other power sources may be used to actuate the die clamps 108, including use of the hydraulic power of the press 32 to actuate the die clamps 108.
Accordingly, the present invention includes a method for changing a hot forming die 40. Specifically, a preheated forming die 40 is placed on or at a load station 42. The preheated die 40 is then inserted and properly secured within the forming press 32. Inserting a preheated forming die 40 into the forming press 32 significantly reduces the loss of production time resulting from having to heat the forming die 42 within the forming press 32. In addition, being able to remove a heated forming die 40 from the forming press 32 reduces the loss of production time resulting from having to wait for the forming die 42 cool to a suitable temperature at which it can be removed from the forming press 32.
In the fourth or cooling module 46, a part extractor 48, which may include a robot 50, operates to transfer the formed workpiece 12 from the forming press 32 to different locations depending upon the particular workpiece 12 and processing parameters. In one instance or path, the workpiece 12 is placed on a cooling rack 52 for a suitable period until the workpiece 12 cools to a predetermined temperature. The robot 50 then transfers the workpiece 12 from the cooling rack 52 to a conveyor 54 that transports the workpiece 12 to the fifth or cleaning module 56. The term rack as used throughout is generic and means any type of storage structure or means for holding or storing the workpieces including placing the workpieces on the floor or on a pallet. In the second instance or path, the robot 50 transfers the workpiece 12 directly to the conveyor 54, which transports the workpiece 12 to the cleaning module 56. Depending upon the particular processing parameters used with the workpiece 12, the workpiece 12 may cool sufficiently on the conveyor 54. In addition, the cleaning module 56 may provide a mechanism to perform any necessary cooling prior to cleaning the workpiece 12.
In the fifth or cleaning module 56, a cleaning mechanism 58, including a throughput cleaning/washing system, cleans the workpiece 12 after the workpiece 12 cools. Various types of cleaning or washing systems are available for cleaning the workpiece 12; these include those using spray nozzles or brushes.
It in the sixth or trimming module, a conveyor 62 transports the workpiece 12 from the cleaning mechanism 58. A material handler 64 connected to a robot 66 is used to transfer the workpiece 12 from the conveyor 62 to a trim press 68 that trims the excess material from the workpiece 12. An automatic or manually operated trim press 68 performs the trim operation. Depending upon the volume, various ways exist to trim the workpiece 12. For low volumes, a flexible system such as a CNC or laser is used. For increased volumes, press-action trimming is used.
In the seventh or inspection module 70 an operator 72, utilizing inspection fixtures 74, inspects the workpieces 12 for part geometry and surface finish. Once inspected, the finished workpiece 12 is placed on a rack 76 for transfer to its ultimate destination.
Accordingly, a superplastic forming cell 10 including a plurality of individual modules, that cooperate or work together as part of an overall forming procedure, used to form a workpiece. The present invention links together these modules and in addition, provides a method for superplastic forming a workplace in an efficiently and expeditiously manner. While disclosed herein as including seven distinct modules, this is for illustration purposes only, the superplastic cell 10 may include a lesser or greater amount or several modules may be combined together.
The overall method of the present invention provides a plurality of steps for raising the production volume for superplastic forming. These steps provide an efficient method for reducing the overall forming or cycle times necessary in order for a superplastic forming process to attain the high production requirements of the automotive or other high volume manufacturing industry.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
