DE2437256A1 - CIRCUIT ARRANGEMENT FOR TOOL BREAKAGE CONTROL - Google Patents

Description

Circuit arrangement for tool breakage control The invention relates to a circuit arrangement for tool breakage control on lathes with a measuring system for the cutting force, using one in conjunction with the main spindle standing pulse generator, especially for numerically controlled lathes with adaptive cutting value control.

When machining on numerically controlled lathes Tool breakages not only cause damage to the tool itself, but also on the workpiece.

This is especially true if the broken tool is not recognized in time and then continue working with a broken tool.

It is therefore necessary to repair the tool breakage or

also to recognize the breaking out of the cutting edge as it arises and from it to interrupt the machining process immediately.

If one investigates the cause of the tool breakage, one finds how versatile they are. In a few cases, these are not at all to investigate.

Some causes of tool breakage are: - Incorrect cutting values; - errors in the material; - too large; - error in the ~ tool; - wrong preset V tool.

Avoiding tool breakage from the outset is difficult because the causes cannot be determined without further ado. So it just remains the possibility of breaking out the tool cutting edge for the first time if possible fast to recognize. This means that the tool has become unusable, but most of the time serious consequential damage can be prevented.

It is therefore known that the cutting edge of the tool when turning Visually check for their wear mark width (workshop and factory 103 (1970) 9, pp.

627-637).

The turning tool is out of cut at time intervals taken, pivoted and fed to a measuring device. This method is suitable only for recording the continuous wear of the tool cutting edge and is not suitable for the detection of tool breakage because the measurement is only can be carried out at intervals. Another well-known method of measurement the flank wear mark width during the cut is also for the Tool breakage display (spontaneous change in the flank wear mark width) suitable, but requires very complicated, expensive and therefore prone to failure facilities, to optically capture the image between the minor cutting edge of the tool and the workpiece Via an evaluation circuit (television camera with image scanning device) of the measurement feed (DDR-X2P GOlb / 165334).

Another known arrangement is used for tool breakage control when turning the back force (BRD-OS 1948013).

If a predetermined value of the back force is exceeded, a Signal to interrupt the machining process is output. This facility but has the disadvantage that the clamping force only turns a few revolutions afterwards Tool breakage increases to the abnormally high ert, which already causes consequential damage may have occurred on the workpiece before the interruption of the machining process is initiated at all. On the other hand, the measurement of the compressive force requires a additional Measuring system, assuming that numerically controlled Lathes with adaptive cutting value control for recording the cutting parameters have a different measuring system - namely one for recording the cutting force.

Another known simplified device for checking four-tool breakage is based on the increase in the cutting force to a certain predetermined maximum value from (company publication VEB Werkzeugmaschinenkombinat "Fritz Hecker", ACEMA - a universal adaptive control system for cutting machine tools, 1970, p. 7).

With this method, only the slight breaking out of the tool cutting edge is possible detectable which usually precedes another major break. So is but only a part of the tool breaks can be recorded, because experience has shown that in most of them Cases the tool breaks run in such a way that the initially minor breakout the Erkeeugschneide does not enter. This is through the simplified monitoring With the cutting force, only a small percentage of the possible tool breakages can be controlled.

There are two typical forms of the cutting force: a) The tool breaks, causing the tool to lose its cut. The cutting force drops sharply.

This steep sloping edge is typical of a tool break.

b) The tool cutting edge only breaks out slightly.

There is no waste flank because the tool continues to cut remain. This dull or undefined tool cutting edge increases the cutting force exceeds its normal value during further machining. the The consequence of this is that the tool then breaks out further and now comes out of cut. The cutting force now runs as described under a).

The aim of the invention is to ensure that breaches are made with certainty to detect and thus to protect the workpiece and the machine from consequential damage, This invention is based on the object of a circuit arrangement for tool breakage control to create on lathes with a measuring system for the cutting force, with which from the course of the cutting force, which is used as a measured variable for the cutting value control Is available, a criterion for the rapid signaling of a tool breakage can be derived.

According to the invention, the task is solved in that a dynamic, Trigger that responds to steep falling edges and a static trigger that reacts to underflows the target value responding triggers in parallel at the output of the cutting force meter are connected, the output of the static trigger via a monostable Multivibrator and the output of the dynamic trigger is directly connected to an AND element, whose output is switched to a memory, which in turn has an AND element, the pulse generator is connected to the second input, and one to the start input The last counting stage is a signal to interrupt the feed drive outputs, the output of the static trigger also via a negation element parallel with the clear input of the memory and the reset input of the counter connected is.

This circuit arrangement ensures that all the tool breakages, which were not caused by a sudden increase in the cutting force to a relative high values occur, can also be recognized in time. The steep slope the cutting force in the range of the setpoint within one revolution of the main spindle is suitable as a criterion for tool breakage.

With this criterion it is possible to avoid serious consequential damage occur on the workpiece and the machine, the machining process through immediate Shutdown of the feed drive can be interrupted.

The invention is explained using an exemplary embodiment: The drawing shows a circuit arrangement for tool breakage control. It will Assumed a numerically controlled lathe with an adaptive Cutting value control is equipped and the cutting force is used as a measured variable.

A measuring system 1 for the cutting force is with one of its outputs connected to a dynamic trigger 2 and parallel to it to a static trigger 3. Furthermore, an overload trigger 4 is connected to the output of the measuring system 1. Of the Output of dynamic trigger 2 and the output of static trigger 3 with the interposition of a monostable multivibrator 5, an AND element 6 switched to a memory 7. The output of the memory 7 is connected to an AND element 8, at the second input via a pulse shaper 9 a spindle pulse generator (not drawn) is connected. The output of the AND gate 8 is at the start input a counter 10 which has, for example, four counting stages. The exit from the fourth counting stage of the counter 10 and the output from the overload trigger 4 are via an OR gate 11 to a signal line for triggering the interruption of the feed drive are brought together. The output of the static trigger is 3 also via a negation element 12 to the clear input of the memory 7 and in parallel switched to the reset input of counter 10 for this purpose.

In the return line coming from the negation element 12 there is an OR element 13 interposed, the second input of which with a button 14 with interposition a pulse shaper 15 is connected.

The circuit arrangement works as follows: The cutting force is measured continuously by the measuring system 1. Depending on the changes in the cutting force the adaptive cutting value control changes the feed rate and / or the Depth of cut so that a predetermined target value for the cutting force is maintained.

Now breaks the cutting edge of the "tool" during the machining process off, the cutting force drops steeply until the broken cutting edge of the tool comes back into cut. In some cases the tool cutting edge breaks out also a sudden increase in cutting force ahead. This increase is well known with overload trigger 4, which responds to 1.4 times the setpoint and used to interrupt the feed drive via the OR gate 11. the Most tool breakages begin with the partial breaking out of the cutting edge and only the oil incision coming of those who have broken out and thus become undefined The tool cutting edge leads to a complete breakage of the tool, which is in the Usually also leads to serious consequential damage.

The partial breaking out of the tool cutting edge is already on the way When the tool is re-incised, there is a brief, steep drop in the cutting force to be recorded. This steep drop is recognized by the dynamic trigger 2, which conducts an L signal to AND gate 8. If the cutting force falls below the nominal value the static trigger 3 outputs a signal, which is triggered by the downstream monostable flip-flop 5 only hits the AND element 8 for a defined time.

If both conditions now fall, namely falling below the setpoint value the cutting force and the steep slope that follows at the same time or shortly thereafter If the cut edges fall together over time, the AND element 6 becomes permeable and the signal is shifted into the memory 7. The output of the memory 7 is now on AND gate 8 effective as an L signal, which is then indicated by ~ It becomes permissable if 9 additional pulses are received from the spindle pulse generator via the pulse shaper get to the AND gate 8. The spindle pulse generator connected to the main spindle emits four pulses with one revolution of the main spindle, which are transmitted via the Impulsform mer 9 are passed.

After the signal from the memory 7 has been applied to the AND gate 8 and it has arrived of the first spindle pulse, the counter 10 is started, after a maximum of one Rotation of the main spindle, d. H. four spindle pulses emitted his fourth Has reached the counting level and the switch-off signal for the feed drive via the OR element 11 issues. If the main spindle has completed one revolution, i.e. before the fourth Impulse has reached the counter 10, the target value of the cutting force is already again exceeded, then there is again an O signal and at the output of the static trigger 3 Via the negation element 12 and the OR element 13 at the clear input of the memory 7 and at the reset input of the counter 10 L signal, so that the memory 7 is cleared and the counter 10 is reset.

An interruption of the machining process is therefore not triggered. These short-term undershoots of the nominal value of the cutting force, which after less than one revolution of the main spindle have reached their initial value again due to out-of-roundness4 In these cases there is no tool breakage situation before, which is why the initial state of the memory 7 and the counter 10 is restored will. For a break situation, the signal is retained in memory 7 and the counter 10 gives the switch-off signal with the fourth incoming pulse from the pulse generator Interruption of the processing process.

Before further processing with an exchanged cutter 'Tool is to press the button 14, which is via the pulse shaper 15 and the OR element 13 also clears the memory 7 and at the same time resets the counter 10 to zero

Claims (1)

Circuit arrangement for tool breakage control on lathes with a measuring system for the cutting force, using one with the main spindle related pulse generator, especially for numerically controlled lathes with adaptive cutting value control, characterized in that a dynamic, Trigger (2) that responds to steep falling edges and a static trigger that reacts to underexciting Trigger (3) responding to the setpoint in parallel at the output of the measuring system (1) for the cutting force are connected, the output of the static trigger (3) via a monostable multivibrator (5) and the output of the dynamic trigger (2) lie directly on an AND element (6), the output of which goes to a memory (7) is switched, which in turn via an AND gate (8), at its second input the pulse generator is connected, is at the start input of a counter (10) whose last counting stage outputs a signal to interrupt the feed drive, whereby the output of the static trigger (3) also via a negation element (12) in parallel with the clear input of the memory (7) and the reset input of the counter - (TO) connected is. Blank page