Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2002-08-14
2004-07-06
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06759620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention at hand relates to a method for controlling a number of machining processes on a die-sink erosion machine and a device suitable for this purpose.
2. Description of Related Art
Such a die-sink erosion machine is used, among other purposes, for manufacturing casting molds with extremely high machining precision. Hereby a number of machining processes which themselves are divided into several working steps and working cycles of different machining stages or phases are performed on one or more workpieces. Depending on the machining phase, such as roughing or finishing, often different electrode categories, such as, for example, roughing or smoothing electrodes, are used for performing these machining processes. If, in addition, the geometry of the performed machining job changes, the electrode must be exchanged in most cases also. This means that depending on the number, versatility, and quality requirements of the machining processes to be performed in a modern die-sink erosion machine, the order of the work steps to be performed and the electrodes required in each case requires an exact specification that is stored in a control program of a numerical control of the die-sink erosion machine.
When setting up the die-sink erosion machine for such a complex machining job, the machine operator must set the control inputs in the control device that determine which work-steps of a machining process must be performed in which sequence with which electrode on which workpiece. Standard, state-of-the-art control processes of the initially mentioned type require control inputs in the form of closed “programs”, so-called sequential control programs, for this purpose. Such a control program specifies all control data in respect to machining, machining frequency, and electrode used for each point in time during the overall machining. Given the multiple work steps in a complex machining of several workpieces that must be performed and the different electrodes necessary for this purpose, the machine operator easily loses track, so that setup errors could occur that would result in an improper, but at least uneconomical execution of the machining.
The state of the art indeed knows of methods for the so-called object-oriented programming of machine tools, for example from Prof. Dr. Ing. Eversheim, Dipl.-Ing. Lenhart, Objektorientiert Programmieren, in: Industrie-Anzeiger 82/1991, p. 38-40. In contrast to sequential control programs, program components are used here that can be reused over and over again for changing the control program. Hereby only an object-oriented structure of the source program is suggested. But no tool for creating certain machining sequences is made available to the machine operator.
OBJECTS AND SUMMARY
The invention at hand attempts to improve die-sink erosion machines in respect to their user friendliness where the creation of new machining sequences is concerned.
According to one aspect of the present invention, a method controls multiple machining processes in a die-sink erosion machine with several identical or different electrodes, whereby the machining sequence of the machining processes and the electrode used for each machining process are determined with consideration of the following predefined criteria: a) predefining priorities of workpieces to be machined, of a group of machining jobs, of individual machining jobs, of work cycles and/or work steps of a machining job; and/or (b) predefining the life span or wear limit of the electrodes used for the individual machining jobs, work cycles or work steps. The overall machining on the die-sink erosion machine is performed with consideration of the determined machining sequence. To create the machining sequences, a device according to one aspect of the invention for controlling the die-sink erosion machine has, for example, a CNC controller: at least one data memory for the permanent storing of data describing the electrodes required for the respective machining processes; a user interface for inputting the previously mentioned criteria for determining the machining sequence into the control device; and a sequence generator that automatically generates the suitable machining sequence for the performing the multiple machining processes based on said criteria and electrode data.
The invention therefore offers the machine operator a proven tool for setting even complicated machining sequences on a die-sink erosion machine in a relatively simple manner and short time. The creation of the sequence and therefore also of the control program and the subsequent machining also takes into account tool wear, for example, by predefining the tool life span as the maximum number of possible work cycles for each machining type, for example for roughing and smoothing cycles. Once the predefined wear limit of a tool is reached, a tool administration or management system according to one aspect of the invention preferably excludes the tool from further machining or downgrades it to a different tool category, as will be described in more detail below. In this way, the selection of the favorable machining sequence according to the invention is based on the fact that the available electrode material is optimally used, i.e., each electrode is used for several machining processes with or without interruption until its individual life span expires. Another outcome of predefining suitable machining priorities is also that a certain object will be machined before another object is completed. It would be possible, for example, that a certain workpiece would need to be machined with a higher priority because a customer needs this workpiece immediately, or a specific, complicated machining job is moved ahead so that in the case of a failure a workpiece which was already machined with great effort is not lost. A specific predefining of priorities also makes it possible to perform several machining jobs in as little time as possible, and to minimize any traveling distances between machining jobs during which no erosion is possible as much as possible.
The method according to one aspect of the invention and the corresponding device naturally can be transferred to other types of machine tools in which comparable wear symptoms of the used tools occur and/or similar machining priorities can be used.
The term “machining process” has been used in this document as a general term comprising all parts of the work performed on a die-sink erosion machine. This includes the execution of a particular die-sink with a predefined die-sink geometry which is called a “machining job”. Each machining job is performed in several machining steps or phases, for example, in consecutive order, roughing, pre-smoothing, smoothing, and finishing. In each machining phase, a machining job again consists of several work steps that may be combined into so-called work cycles. The term “machining sequence” therefore in general relates to the order of the consecutively performed machining processes which, depending on the type of machining process, may be the order of consecutively performed machining jobs, work cycles of several machining jobs and/or work steps in a work cycle of a certain machining job or combinations of these sequences.
An especially preferred embodiment of the method uses the so-called wear distribution strategy as a selection criterion for performing several identical machining jobs. The individual machining jobs are hereby not completed in their respective entirety, one after the other, but the consecutively performed machining processes are instead distributed in such a way over several machining jobs that an even distribution of the electrode wear over a certain number of work cycles and/or work steps of the multiple machining jobs is obtained. It is known that a sinker electrode experiences electrode wear during the machining, which can be attributed to the electrophysical nature of the erosion process so that the sinker electrode wears after performing a certain number of work steps. Theref
Marchesi Alberto
Riva Luciano
Agie S.A.
Dunn Tom
Johnson Jonathan
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