Electric heating – Metal heating – Cutting or disintegrating
Patent
1982-09-02
1985-08-06
Paschall, M. H.
Electric heating
Metal heating
Cutting or disintegrating
219 69C, 219 69G, B23P 108
Patent
active
045338116
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for automatic process control in spark erosive machining under widely varying process conditions caused by large machining surface changes. The method and the means used for it can be used in all fields of spark erosive machining. They are of particular interest in connection with spark erosive countersinking of three-dimensional shapes with superimposed planetary movement, as well as in the spark erosive taper or conical cutting and spark erosive cutting of workpieces with considerable thickness variations.
The aforementioned uses are all characterized by considerable variations in the erosion process, due to great changes in the workpiece surfaces to be machined. These surface changes can extend over more than two levels and, without action on the part of the operator, necessarily lead to very long machining times or to damage to the electrode and workpiece through overloading. The purpose of the invention is to free the operator from continuous interventions in the process, whilst ensuring minimum machining times and optimum machining results.
It is known to control the spark erosive process as a function of machining surface changes. As early as 1969 Kondo found a possibility of drawing conclusions on the surface being machined during the process by measuring the discharge frequency and the division thereof by the length of feed. This method was published in Swiss Pat. No. 525,061. The control device used by Kondo encountered difficulties, which can only be overcome by periodic withdrawal motions of the sleeve and consequently efficiency reductions (column 26, lines 27 to 36 of Swiss Pat. No. 525,061).
In 1975, Languepin (DAS No. 2,505,944) proposed regulating the feed rate of the servo-system to a constant value of 0.3 to 0.4 mm/min by means of the generator power.
The Languepin constant feed rate control method is based on the assumption that erosion must take place with the same current density for large and small machining surfaces. However, in the case of large surface changes, this is just as incorrect as eroding at constant power, as in conventional erosion plants.
In 1977, Saito of Mitsubishi disclosed in Japanese Patent Application JP-OS No. 53-131.598/74 an erosion machine based on the wire cutting principle in which the electrical parameters can be set on the pulse generator as a function of the workpiece height by means of digital path control. Saito came up with the already known finding that within certain limits, there is a linear relationship between the power applied to the spark gap and the feed rate and that conclusions regarding the depth of cut can be drawn from this.
U.S. Pat. No. 4,071,729 describes a process control system which, in conventional manner, links the input data from an operator with the values at the working gap and carries out processing in accordance with a given programme. The function of this process control system is to maintain the machining state defined by the programme or the operator. However, there is no power adaptation in the case of changing machining surfaces of the workpiece and different machining conditions in the work gap.
None of the four publications refers to power adaptation, either in the case of changing machining surfaces or different machining types. However, without knowledge of these bases, it is impossible to realise a generally valid strategy for the automatic process control in the case of varying machining surfaces. Thus, machines controlled in accordance with these four publications would not be universally usable or adaptable to the process conditions. This is probably why such machines have not hitherto been widely commercially used.
The problem of the invention is to control the process in an optimum and automatic manner for any conceivable erosive machining type and in the case of varying machining surfaces on the basis of a generally valid control strategy.
According to the invention, this problem is solved in that the power p applied to the spark gap 10 is determined and is linked with the fee
REFERENCES:
patent: 3987269 (1976-10-01), Inoue et al.
patent: 4071729 (1978-01-01), Bell
patent: 4296302 (1981-10-01), Bell, Jr. et al.
patent: 4361745 (1982-11-01), Rupert et al.
AG fur Industrielle Elektronik AGIE Losone b. Locarno
Paschall M. H.
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