Real-time draw-in sensors and methods of fabrication

Details Real-time draw-in sensors and methods of fabrication Real-time draw-in sensors and methods of fabrication

2002-05-07

2004-08-03

Larson, Lowell A. (Department: 3725)

Metal deforming

With use of control means energized in response to activator...

Sensing work or product

C072S347000, C072S350000

Reexamination Certificate

active

06769280

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to sheet metal forming processes, and more particularly, to a sensor system and sensing element for detecting draw-in of a metal blank during metal forming operations.
Sheet metal forming is one of the predominant processes in the manufacture of automobiles (about 300 parts per vehicle), and also is widely employed in the manufacture of aircraft, appliances, beverage cans and many other products. The popularity of this type of metal-forming/stamping is mainly due to the high degree of design flexibility and its low cost, both in the stamping and in subsequent assembly. It is especially attractive for the manufacture of high strength, low-weight components.
In a typical sheet metal forming process of the prior art, as shown in
FIG. 1
, a blank sheet
12
is placed between a blank holder
14
and a die
16
. During the forming process, the sheet
12
under the blank holder
14
is drawn into the deformation zone
18
by a punch
20
. The draw-in amount “d” is the translation of the edge(s) of the sheet
12
from an initial positions(s)
22
to the draw-in position
24
. The success of a forming process depends entirely on how one designs the tooling geometry and forming parameters for a specific sheet material. The binder acts to provide a tangential restraining force to the sheet to determine how much material flows into the deformation cavity, the draw-in amount at each cross section. This restraining force is generated either through the frictional force between the flat binder and the sheet material or through a combination of the frictional force and the bending/unbending effect of material going through a drawbead
26
(see FIG.
1
).
Excessive material draw-in leads to the occurrence of wrinkling, which is usually undesired in final sheet metal parts for functional reasons. Wrinkling is also unacceptable for aesthetic reasons in the outer skin panels where the final part appearance is crucial. Wrinkling on mating surfaces can adversely affect subsequent part assembly use and function, such as sealing and welding. In addition, severe wrinkles may damage or even destroy dies. On the other hand, an unduly limited material draw-in amount leads to tearing failure in the sheet metal, a result which is just as undesirable. Therefore, proper material flow and draw-in amount are critical to the ultimate success of a metal-forming process.
Another concern of the prior art is that draw-in amounts around the periphery of a sheet metal piece or product are usually uneven due to a combination of complex piece geometry and material anisotropy. An existing method to monitor a forming process uses punch forces at four tooling corners, but is not sophisticated enough for use with formation of irregular shapes. Local sensors currently used in such applications include a mechanically based linear transducer (LVDT type) for sensing the material draw-in, a mouse-like draw-in sensor and a local friction force sensor. The installation of such sensors requires either additional setup time with each forming or intricate tooling modification. The lack of effective and affordable local measurement tools has hampered the implementation of active control systems for industrial metal-forming processes, a state which in turn has resulted in long development time and inconsistent final sheet metal products.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide a sensor device and/or element, together with methods for its production and/or assembly, thereby overcoming various deficiencies and shortcomings of the prior art, including those outlined above. It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all its respects, to every aspect of this invention. As such, the following objects can be viewed in the alternative with respect to any one aspect of this invention.
It can also be an object of the present invention to provide a sensor device and/or system utilizing sensing elements useful in the formation of complex metal piece geometries, such use without excessive tooling modification or set-up time.
It can also be an object of the present invention to provide a sensor device and/or sensing element which can, during the die try-out period, measure and monitor the amount of draw-in, thereby, assisting tooling modification and the determination of process parameters to delay/avoid tearing or wrinkling failure and to keep springback under control.
It can also be an object of the present invention to provide a sensor device and/or sensing element which can provide quantitative measurements of local material movements, to which can be compared with numerical simulations.
It can also be an object of the present invention to provide a sensor device and/or sensing element which can, during a metal-forming process, measure, control and monitor the amount of draw-in material, thereby reducing the incidence of material wrinkling or tearing failure.
It can also be an object of the present invention to provide a sensor device and/or sensing element which produces an output indicative of real-time measurement of the draw-in movement of a metal sheet/plate, such measurement as can be utilized for closed-loop control of a metal-forming process to achieve the optimal (or predetermined) forming condition regardless of variations in incoming material, working environment, operators and process variables. The sensor can be used to provide an indication at the beginning of the forming process to indicate whether the blank is placed correctly at the desired initial position.
It can be another object of the present invention to provide a durable, robust sensing element for use in a variety of metal-forming systems and operations, such as for the measurement of the retreat or movement of the edge of a metal sheet into a mold or toward a deformation zone during a forming operation.
Other objects, features, benefits and advantages of the present invention will be apparent from this summary and the following descriptions of various preferred embodiments, and will be readily apparent to those skilled in the art having knowledge of various metal-forming operations and/or control techniques. Such objects, features, benefits and advantages will be apparent from the above as taken into conjunction with the accompanying examples, data, figures and all reasonable inferences to be drawn therefrom.
In part, the present invention includes a system for sensing the draw-in amount of metal during a forming process, thereby effecting related elements of monitoring and control. A sensor of this invention can include a sensing element and an electronic circuit, which provides a signal, indicative of draw-in amount, to a computer (or a processor) which, in turn, can control aspects of the forming operation (such as, pressure on the binder at different places, drawbead penetration height, etc.). Benefits of such a sensor system/sensing element include provisions of 1) a tool for process optimization during the development stage; 2) control over the forming process to significantly reduce part-to-part variations and compensate for any incoming material variations; and 3) a device for quick process diagnosis during production.
In one embodiment, the sensing element comprises a pair of coils disposed in signal coupling relationship such that an excitation signal applied to one coil produces a signal in the other coil. The presence of a ferrous or non-ferrous metal, such as a metal plate, in the proximity of the coils affects the magnetic field lines, changing the degree of mutual inductance, or magnetic coupling, between the coils in correspondence with the amount of movement of the metal plate relative to the sensing element. Thus, the response signal, or signal output of the sensing element, provides a real-time measurement of the extent of overla

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