A reconfigurable variable blank-holder force system (and method) for producing sheet metal stamping comprises a portable hydraulic unit, controlled by a digital control system and a knowledge-based expert system to enable reconfigurability and an easy transition from the try-out stage to production.
The knowledge-base has a hierarchical structure and includes stored information about part geometry, material properties and press parameters. The expert system enables an operator to determine optimal blank-holder forces, and to fine-tune through a graphical interface unit. The optimal blank-holder forces are generated by hydraulic force actuators, using a controller running a nonlinear algorithm that accounts for valve nonlinearities, variable flow-rate and numbers of operational cylinders.
The portable hydraulic unit preferably comprises hydraulic cylinders with quick disconnect hoses, a manifold, servo-valves and a pump unit. A structured method to utilize this system to produce sheet metal stampings is also described. An article embodying the method is included.
Method of achieving reconfigurability in a blank-holder variable force system for producing stampings from sheet metal blanks, comprising: using movableblank-holder force actuators and variable blank-holder forces to hold and support said sheet metal blank at a first set of blank-holder force actuator locations; monitoring a first set of parameters selectively including punch force, blank-holder forceactuator numbers and locations, and blank-holder force magnitudes at said movable blank-holder force actuators; inspecting a sheet metal stamping work piece produced using said first set of parameters; noting differences between characteristics of asample work piece fabricated using said first set of parameters, and requirements of an acceptable sheet metal stamping work piece; and, using said differences and knowledge-based inputs from an expert system to arrive at a second set of newreconfigurable parameters.
A variable blank-holder force system for performing sheet metal stamping operations, comprising: movable blank-holder force actuators to hold and support said sheet metal stamping at a first set of locations; sensors associated with saidmovable blank-holder force actuators for monitoring parameters associated with the blank-holder force actuators including blank-holder force actuator locations and force magnitudes at the blank-holder force actuator locations; a user interface forviewing and using a first set of parameters for a trial run and for recording differences between a stamped sheet metal from a trial run compared with requirements in an acceptable stamped sheet metal work piece; and, a controllable arrangement forarriving at a second set of parameters based on said differences, knowledge-based software controlled by an expert system and knowledge-based hierarchy.
Sheet metal stamping is an indispensable and significant process because it is well suited to mass production of a wide variety of parts. In the automotive industry, it is used to make several body parts such as doors, hoods and lift-gates. Several other industries such as the consumer appliance industry and the aerospace industry use sheet metal stamping extensively. It is highly desirable to ensure high quality standards for sheet metal stampings so as to avoid problems during subsequentassembly stages and to ensure that the form and finish meet requirements.
A publication by Ananthakrishnan S., Agrawal S., Venugopal R., and Demeri M., entitled "RCS Based Hardware-in-the-loop Intelligent System Design and Performance Measurement," inProceedings of PerMIS 2002, NIST, Gaithersburg, Md., 2002, teaches design of an intelligent system with applications to manufacturing, based on a Real Time Control System (RCS) architecture. The Ananthakrishnan publication describes case studies on howthe RCS architecture can be used in a flexible automation scenario, where traditional industrial control cards (hardware) do not provide adequate measures of performance.
In addition, certain tooling concepts and blank-holder force actuator controlunits with individually controlled hydraulic cylinders have been developed to allow local control of metal flow into the die cavity during a stamping operation. Forces are applied on the sheet metal blank using hydraulic cylinders which are mounted onthe lower bolster of a hydraulic press.
In the known type of hydraulic or mechanical press, a ram depresses the piston of each of the hydraulic cylinders via the blank and tooling in a blank-holder force actuator area to raise the pressure inside thecylinders. The pressure is transferred to the blank. A closed-loop control system modulates the flow of hydraulic fluid from the cylinder. In known arrangements, pressure within the cylinder is difficult to control using commercially available PID(Proportional-Integral-Derivative) control cards.
The few systems that are available presently are systems of hydraulic cylinders installed in the bed of the press (under the die). The hydraulic cylinders used to provide force actuation in knownsystems are placed in fixed locations in the bed of one particular press, and the force actuators are configured for operation in that press. In essence, these systems are not flexible and are customized for one particular press and thus tend to be veryexpensive.
The production of sheet metal stamping parts involves two distinct phases, namely, try-out and production. In the try-out phase, the die design is validated, and required process parameters (blank-holder force actuator forces, punch force etc.)are determined. Try-out is conducted by attempting to make the part and modifying the die and process parameters, until a part is consistently made within the required design tolerances. After successful try-out, the final die design and processparameters are transferred to a production unit that mass produces the part. In practice, try-out and production are typically conducted by different companies in different locations.
It is desirable to provide a system and method for sheet metal stamping that would offer reconfigurability utilizing a knowledge-base, as well as the most economy and flexibility in design, and in doing so, address the needs of both try-out andproduction.
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