GB2270646A

GB2270646A - Process for regulating the cutting quality in thermal flame cutting

Info

Publication number: GB2270646A
Application number: GB9318713A
Authority: GB
Inventors: Reinhard Henrici; Joachim Klisch
Original assignee: Messer Griesheim GmbH
Current assignee: Messer Griesheim GmbH
Priority date: 1992-09-21
Filing date: 1993-09-09
Publication date: 1994-03-23
Also published as: ITMI931948A0; ITMI931948A1; DE4231486C1; FR2695852A1; GB9318713D0; IT1272604B

Description

2270646 Process for recrulatincr the cuttincr cruality in thermal flame

cutti The invention relates to a process for regulating the cutting quality in thermal flame cutting.

In the course of flame cutting, the workpiece is locally heated to ignition temperature and is there burnt in the cutting oxygen stream. The heat given off by the heating flame and the heat arising at the cutting position in the course of the burning of the workpiece permit, in this case, continuous burning in the cutting is oxygen stream. Along with the cutting oxygen stream, the burning process propagates in depth and in the direction of advance. The dross which is formed in the course of burning is driven out by the cutting oxygen stream, whereby the cutting seam is formed.

In order, in this case, to achieve an optimal cutting quality, in which incipient edge meltings, convergent or divergent cutting seams, undulating cutting surface profiles, excessive lag or lead of cutting furrows, squeezing and the like do not occur, it is necessary for the operator to undertake a manual fine adjustment of the flame cutting parameters, since the set parameters fluctuate ahead. of and during the flame cutting. The reasons for this include, by way of example, the heating phases of the burners, the burner tolerances, differing sheet metal temperatures, heat sinks and temperature distribution within the sheet metal, removal of heat from the sheet metal onto the supporting table, convectional heat transfer to the environment, differing cutting contours and introduction of heat, alterations of the gas pressures, fluctuations of burner power and the 2 like.

it is known from DE 22 03 194 Cl to detect alterations in the brightness of the part of the gas cutting by oxidizing reaction, by means of a photocell disposed at the upper end of the burner and, as a function thereof, to control automatically conditions of the flame cutting process, such as rate of cutting, the termination of the cutting process, failures of ignition of the cutting flame etc. In this case, according to column 6, lines 38-41, it has emerged in practice that the alterations of the quantity of light which arise in the case of alterations of the rate of cutting can be left out of account.

According to DE 38 03 444 Cl, in place of the photocell disposed at the upper end of the burner the intention is to dispose an optical waveguide within the cutting oxygen tube, and specifically in the immediate vicinity of the nozzle, since as a result of this the detected signal strengths increase substantially and signal fluctuations are avoided. in this case, the optical waveguide is connected to a photoelectric transducer.

According to EP 04 08 846 Al, the fuel gas/oxygen - or air mixture is to be adjusted by this light-sensitive sensor.

Proceeding from the initially mentioned prior art, the object of the invention is to optimize the cutting quality in flame cutting.

This object is achieved by the characterizing

Claims

features of Claim 1.

Advantageous further developments of the invention are indicated in the subclaims.

Surprisingly, an enhancement of the cutting quality with an additional increase in the rate of cutting has been the result of the invention. The optimization of the cutting quality, i.e. the avoidance of flame cutting defects, such as cutting seam enlargements or contractions, undulating cutting surface profiles, squeezings, non-uniform or excessively deep 3 cutting furrows and the like, is achieved by maintaining constant a determined value for the cutting quality, which value describes the cutting quality factor and the accuracy of the shaped part. This value is determined in the form of yellow and/or orange and/or red and/or infrared intensities during the flame cutting on a specimen for each sheet metal thickness/nozzle combination, which is cut using optimized adjustment data. Yellow and/or orange and/or red and/or infrared inten- sities correspond to a wavelength range of 400 to 1000 nm (nm = nanometre). Preferably, the process is carried out within a wavelength range of 500 to 800 =, especially within the wavelength range of infrared intensities, since within that range disturbance effects due to the is flame and resulting from splashes are to a large extent suppressed. The determined yellow and/or orange and/or red and/or infrared value is then filed, in the case of the automatic process, as theoretical value for optimal cutting quality, in a technological data bank, and, during the flame cutting, said value is taken from the technological data bank. Throughout the entire cutting sequence, the quality impairments of the flame cutting which arise on account of differing burner and sheet metal temperatures and differing gas streams and/or pressures are automatically balanced by fine corrections, by altering the rate of cutting. Using an optical waveguide which is disposed in the cutting oxygen tube of an autogenous flame cutter, and which is connected to a transducer which is sensitive 30 within the wavelength range of 400 to 1000 =, the high yellow and/or orange and/or red and/or infrared intensities during the flame cutting are resolved and are evaluated in an evaluating unit. Using the voltage values present at the output of the evaluating unit, the advanc- ing motors of the guiding machine are readjusted.

In this case, higher voltages than the ideal values are present at the output in the case of an excessively high rate of cutting and lower voltages than the ideal values are present at the output in the case of 4 an excessively low rate of cutting. In the case of an excessively high rate of cutting, higher yellow and/or orange and/or red and/or infrared intensities impinge upon the optical system of the optical waveguide, since the cutting oxygen stream is conducted too fast in consequence of the mass moment of inertia and of the required time constants of the liquid metal, and in consequence of this a furrow lag arises. In the case of an excessively low rate of cutting, the yellow and/or orange and/or red and/or infrared intensity at the optical system falls, since the excess oxygen leads to washouts or the field of view of the optical system is blown free of liquid material. The time constant for optimal cutting alters with the temperature of the cutting location ahead of the cut.

As a result of the invention, higher rates are achieved with improved cutting quality, since in the event of conditions of heating of the sheet metal and tolerances of burner, nozzles and machine, appropriate setting to optimal cutting quality takes place, e.g.

rectangle 20 x 20 mm with V. = 600 mm/min and VEd = 750 mm/min or circle of diameter 20 = with V. = 600 mm/min and VEd = 2000 mm/min with a sheet metal thickness of 8 =m.

By a further refinement of the invention, the nozzle wear of the flame cutting nozzle can be detected.

Tests have shown that in the case of defective nozzles in consequence of splashes of dross, nozzle-washouts in the heating channels and/or oxygen channels, a regulation to the value of the cutting quality, i.e. a regulation to the determined theoretical value, is no longer possible. The theoretical value then migrates to predetermined limiting values which are filed in the evaluating unit, in the event of the attainment or exceeding of which limiting values a signal for the exchange of the nozzle is generated.

claims 1. Process for regulating the cutting quality in thermal flame cutting, characterized in that the yellow and/or orange and/or red and/or infrared intensities are detected during the flame cutting within a wavelength range of 400 to 1000 =, preferably within a wavelength range of 500 to 800 nm, and are kept to a constant cutting quality value.
2. Process according to Claim 1, characterized in that the infrared intensities are detected during the flame cutting and are kept to a constant infrared cutting quality value.
3. Process according to Claim 1 or 2, characterized in that the intensities, preferably infrared iiitensities, are detected using an optical waveguide disposed within the cutting oxygen tube and are fed to a photoelectric transducer which is connected -to the optical waveguide and which generates voltage signals as a function of the intensities, preferably the infrared intensities, which voltage signals represent values for the cutting quality.
4. Process according to Claims 1 to 3, characterized in that in the event of the exceeding of a predetermined value for the cutting quality the rate of cutting is reduced and in the event of falling below a predetermined value for the cutting quality the rate of cutting is increased.
5. Process according to one of Claims 1 to 4, characterized in that the values for the cutting quality are determined on a specimen.
6. Process according to one of Claims 1 to 5, characterized in that the determined values for the cutting quality are filed in a technological data bank and are automatically called up in the course of the flame cutting.
7. Process according to one of Claims 1 to 6, 3 characterized in that in the event of deviations of the cutting quality value from predetermined limiting values, a signal for the exchange of the nozzle is generated.

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