Metal deforming – With randomly-actuated stopping – Responsive to condition of work or product
Reexamination Certificate
2000-04-28
2003-01-28
Crane, Daniel C. (Department: 3725)
Metal deforming
With randomly-actuated stopping
Responsive to condition of work or product
C072S020100, C072S031110, C072S416000, C072S453160, C029S720000
Reexamination Certificate
active
06510719
ABSTRACT:
The invention relates to a pressing tool for jointing clamps of various sizes.
Pressing tools for pressing casing-like press fittings home on pipe ends must guarantee that the jointing clamps always press the press fitting home properly. For the common press fitting diameters, appropriate jointing clamps are insertable in any given case into the pressing tool. Because great forces are required for pressing home, a hydraulic cylinder is used for actuating the jointing clamps in various known pressing tools. Embodiments are known from U.S. Pat. No. 5,125,324 where an electric motor drives a hydraulic cylinder. The fluid acted upon by pressure is guided into a hollow cylinder to activate a piston which activates the pressing tool or the jointing clamp. A compact activation unit arises through the pump with electric motor arranged directly on the lifting cylinder. At the end of the pressing process, excessive pressure arises in the cylinder, which leads to opening the excess pressure valve and therewith to ending the pressing process. The piston is reset by a return spring while recirculating the liquid into a collection area. Monitoring complete pressing home takes place through the threshold pressure which is necessary for opening the excess pressure valve. Different forces of pressure are needed for optimal pressing home of various press fittings in any given case. With a pressing tool which generates a force which goes beyond the necessary pressing force due to a fixed threshold pressure for all pressing processes between the open dies, a large proportion of the force is absorbed by the open dies. These must correspondingly be constructed with excessive dimensions and are subject to increased abrasion. If the open dies jam, then the threshold pressure, and consequently the end of the pressing process, can be reached without the press fitting being pressed home correctly.
From DE 297 14 753 U1, a pressing tool with two interacting open dies is known where a spacing receiver is constructed between the open dies. Here a relocatably mounted plastic stop pin pressed from the outside by a spring from the first open die projects against a stop face of the second open die. If the open dies are moved toward one another, the pin is pressed into the first open die by the stop face. A metal casing fixed upon the pin is moved over the area of two sensors when the bolt is moved. The oscillating circuits of the sensors are detuned on the basis of an eddy current induction when a metal casing is placed significantly close. Three different fastening bolt position ranges can be recorded. In a first position range, the casing is only in the vicinity of the first sensor. In a second position range, casing segments are in the vicinity of both sensors. In a third position range, the casing is only in the proximity of the second sensor. The casing and the sensors are now dimensioned or set at a distance such that the first position range is allocated to bringing the open dies together before the pressing process. The second position range is allocated to the pressing process and reaching the third position range corresponds to the end of the pressing process.
This spacing receiver can consequently be used for ending the pressing process. Here, entering into a specified position range is recorded for ending the pressing process between the open dies. All usable jointing clamps must consequently have a spacing receiver. After inserting a jointing clamp, the spacing receiver must be connected with the control unit of the pressing tool. The advantage of a jointing clamp position recording is associated with the disadvantage of the expensive construction of the jointing clamp and the expense of a separate electrical connection of the jointing clamp to the pressing tool.
A crimping tool for pressing home electrical cables with connections is known from U.S. Pat. No. 5,113,679 which supplies the activation pressure when two grips are pressed together with a pump cylinder. During extrusion, a tamping tool connected to the press plunger is moved against a crimp anvil by the press plunger In order to be able to measure the position of the stamping tool, an electrical resistor strip is provided on the crimping tool and contact elements which can be slid over it are provided on the press cylinder. Owing to contamination or oxidation of the resistor strips, false positional values can be recorded. With false positional values, even the quality of the pressure can be falsely indicated, which impairs an efficient operation with the crimping tool. Moreover, no casings can be pressed home.
Underlying the invention is the objective of finding a safely operating pressing tool. In addition, a pressing process with such a pressing tool should guarantee that the pressing can be safely implemented with all insertable jointing clamps.
In accomplishing the objective, it was recognized that with a contact-free or contactless measuring position measuring device which makes the piston position continuously recordable over a positioning range. The current piston position can be determined with certainty at least at one point in time. It thus does not need to be fixed in advance at which position a jointing clamp present check should be conducted by the positioning of a presence sensor. Any desired piston position can be recorded within the positioning range. Because the position recording takes place contact-free or without contacts, no disturbances can occur owing to contaminated sliding contacts. The at least one point in time in which the position should be measured depends upon the activation process. In extruding a press fitting, the piston position is preferably recorded when the threshold pressure is reached, directly before a return valve is opened, or forwarded to a control unit or comparison unit. This piston position is a measure for the quality of the extrusion because the maximal feed obtained is associated with most narrow open die position derivable from the open die shape or mounting or by the open die parameters. If the threshold pressure is reached before complete extrusion, then in this way a piston position is detected which does not correspond to a specified piston position range value, or which does not lie in a tolerance range around the piston position range value. On the basis of the comparison of the piston position recorded with at least one lower range threshold, the quality of the extrusion can be characterized.
With the preferred embodiment of the pressing tool, the result of the comparison is used to initiate a two-valued indication. With a complete extrusion, for example, a green signal is turned on and/or with an incomplete extrusion, for example, a red signal is turned on. It is obvious that, instead of an indication, a signal tone can also be provided. If attaining an effective open die position is being examined, errors which arise in connection with a pressure monitoring can be ruled out. The jointing clamps require no spacing receiver. Any number of standard jointing clamps can be used. The pressing process can be conducted independently of position monitoring whereby, however, position recording serves to monitor the quality of extrusion.
If need be, however, the position measuring device is connected with the control unit of the pressing tool. Then the drive of the fluid pump and/or at least one valve of the fluid conduit system can be controlled independently of a recorded piston position. Preferably, the pressing process is ended upon reaching a piston position necessary for complete extrusion. In this way, building up a standard threshold pressure can be dispensed with. In addition to process control on the basis of continuous monitoring to the piston position, and in particular current open die parameters, a magnitude derived from piston positions, such as piston speed or piston acceleration, can be used to influence the course of the process.
The pressing tools in accordance with the state of the art can be used with many different interchangeable jointing clamps. The various jointi
Crane Daniel C.
Novartec @ AG
Rothwell Figg Ernst & Manbeck
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