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PDA.Dyn_Limits_Force.1403.GB
Operator's favorite.
always in use –
never switched off! Operator's favorite.
always in use –
never switched off!
Lightning-Fast, ReliableTool Breakage Detectionfor Turning of cast and forged partsin initial cut and more
PDA.Dyn_Limits_Force.1403.GB
Introduction
Unequaled reliability in breakage detection!
Very fast reaction = maximum reduction of secondary damage
Continuous and automatic limit adaptation during the cut
Very low operator expense
• formassproduction
• forsmallbatches
• forlargepartswithAGC
• No input of limit values needed
• No danger of setting limits too high or too low
• No stress for the operator
• No switch-off of the system – it will be in use all the time!
PDA.Dyn_Limits_Force.1403.GB
Description
Task and functionThe cast or forged part to be machined is out-of-roundness, has an
undulating material surface with pronounced hardness fluctuations in its outer surface and can only be clamped off-center. So the load on the lathe tool will extremely fluctuate already within a single work piece rotation. There will be additional load variations from rotation to ratation, from part to part, and from batch to batch. Even near net shape cast or forged parts will pronouncedly display these fluctuations.
Pronounced signal fluctuations
The diagram shows pronounced but normal fluc-tuations in the force signal (black line) of a turning operation for about three work piece rotations:
Where should the alarm (and therefore the feed stop limit) be placed?
Static Limit: faulty breakage detection
If a Static Limit for breakage detection (purple line) is placed at for e.g. 160%, this could cause false alarms and unwanted switch-off of the workpiece feed due to the natural signal fluctuations:
Where should the limit be placed now? Higher? This would render the breakage detection unusable. Lower? This would create even more false alarms.
Please turn the page …
The best solution for tool breakage detection in turning of cast and forged parts
specified size
initial form of casting
Example:Cross-section of forged joint fork
lowest distance fromspecified size
greatest distance fromspecified size
PDA.Dyn_Limits_Force.1403.GB
Description
The perfect solution: Dynamic Limits
Dynamic Limits (yellow lines) are continuously adjusting to the measured signal and therefore tol-erate dynamic signal changes. Adjustment of the Dynamic Limits takes place within cycles of millisec-onds and thus several times within a single workpiece rotation.
The unexpected extreme signal peak (see arrow) is tolerated and no false alarms are generated.
The machining process is not interrupted!
Dynamic Limit in case of breakage
What will happen when an actual breakage occurs? A sudden signal change, typical for breakage (inde-pendently of its absolute level, see diagram below), changes the behavior of the Dynamic Limits - they are are violated and „freeze“ immediately - right where they were:
A fast analysis for atypical breakage signal profile occurs: only if an actual tool breakage happened, the workpiece feed of the machine is stopped, a different analysis(like hard spots, cut interruption etc.) will not stop the machin-ing!
Signal peak will not trigger the limit
an abrupt signal change (typical for breakage) is detected by the limit and the machine is stopped within 5 milliseconds
these fast signal changes are detected independently of their actual level
PDA.Dyn_Limits_Force.1403.GB
Description
ConclusionDynamic Limits are automatically extremely close to the force
signal, regardless of fluctuations of the cast or forged part in allowance and hardness from batch to batch, from part to part or even from work piece rotation to work piece rotation.They adjust very fast in a wide array of 1 : 4 (scale between smallest to largest force) automatically, without generating false break-age alarms. This tracking resp. dynamic range is completely suf-ficient for the machining of part mass production.
Dynamic Limits need minor operating expense only, more than 95% of the breakage events in turning of cast or forged parts are detected. Extremely few false alarms (typical: 1 per shift/week) are generated.
The very short reaction time of 5 milliseconds enables a feed hold within a single revolution of the workpiece after a break-age occurred, which protects the tool holder.
Dynamic Limits need force sensors with very short reaction times below 1 Millisecond, to safely differentiate between fast signal changes in cutting start and cutting end, load changes within a single work piece rotation as compared to those
changes caused by tool breakage. Signals from the power drives, like torque, current, or effective power are much too slow for this task.
Ideally suited are our piezoelectric force sensors – Measuring Wedges, Measuring Cells, or Measuring Dowels, which are installed in the secondary force flow (in suitable bore holes or pockets of lathe turrets respectively between turret/tool holder and slide). For retrofitting our piezoelectric Bolt Sensors can be used. Together with the PROMOS Monitoring System they form the basis for the Dynamic Limits.
Further information can be found in our data sheets for PROMOS and our piezoelectric force sensors.
PDA.Dyn_Limits_Force.1403.GB
Comparison
Dynamic LimitsType MDL
Static LimitsType MSL
Principle
2 Dynamic Limits, an upper and a lower one, follow automatically and very close to the sensor signal every revolution.
2 or more Static Limits, have to be located above and below more or less close to the expected sensor signal
Operator effort very little, only ± 2 levels of sensitivity have to be selected
high, limits need adaptation to hard-ness fluctuation and depth of cut
Setting of Limit Level automaticallymanually by the operator with Teach-In aid
Reaction time to begin feed stop 5 Milliseconds
one or more spindle revolutions, until signal reaches upper limit, plus the system response time
Feed full stop (at max 3000 rpm)
within of one workpiece revolution after a total breakage of the tool
more than 3 workpiece revolutions after a total breakage of the tool
Protection of tool holder very high cannot be guaranteed
Monitoring of Interrupted cuts
simple and effective, very few false alarms only
difficult, too many false alarms
Detection of Chippings possible not possible
Adaptation to process variation(e.g. hardness of the workpiece)
automatically, very few false alarmsnot possible. Every slight process variation needs new “Teach-In”. Many false alarms.
Number of False Alarmsvery few, typical 1 per shift and week (with turning pieces, mass-produced by the automotive industry)
high, depends on level of limit, hard-ness and depth of cut fluctuation of the workpiece
Reliability of Breakage Detection
> 95 % bei zuvor genannter Anwendung
<< 80 %, depending on level of limit
Costs of Systemhigh, needs force sensors in the machine and more hardware and software effort
low, mostly by reading of the drive current values resp. effective power from the drives
Profit from in practical use high and effective!
low, because of high operator effort or system even being switched off!
Customer satisfaction level Dynamic Limits + Static Limits –
Tool Breakage Detection at Turning of of castings and forgings in first cut Comparison Dynamic and Static Limits
PDA.Dyn_Limits_Force.1403.GB
AGC
AGCAutomatic Gain ControlAGC (Automatic Gain Control), is an automatic and limited amplification control of a piezoelectric force sensor’s signal char-acteristic. AGC allows for a very reliable breakage detection even under extreme conditions when machining large parts, like e.g. train wheels or parts for wind turbines.
In all these applications with extreme fluctuations in allowance and hardness of the work piece the 1 : 4 default tracking range of the Dynamic Limits will be increased to 1 : 160 by AGC.
Additional to the adjustment of the upper and lower Dynamic Limit to the sensor signal, AGC adjusts the signal amplification by adaptive control. Similar to the calculation of the Dynamic Limits, this signal amplification control is designed in such a way that very fast sensor signal changes (which occur in the instant of a breakage event) will not be compensated.
Easy monitoringAn additional advantage of this option is the possibility to moni-tor even most complex machining tasks in a single cycle.
For the AGC option the software for Dynamic Limits for the PROMOS 2 RTM is needed, as well as a DSP Card (Digital Signal Processor) for the RTM.
Tool breakage detection for turning of very large cast and forged parts und starting at batch size 1Optional for breakage detection with Dynamic Limits (MDL)
Example: turning of railway train wheels
PDA.Text.0910.GBSubject to technical modifications ©2014 PROMETEC
Overview
Monitoring of Machines, Processes, Tools and Lasers Subsidiary companies and representations in Europe, South-America and Asia
www.prometec.com Germany (Headquarters)PROMETEC GmbH
Jülicher Str. 33852070 Aachen
Phone: +49 241 16609-0Fax: +49 241 16609-50prometec-de@prometec.com
USAPROMETEC Inc.47711 Clipper StreetSuite 200Plymouth, MI 48170
Phone: +1 (734) 455 0100 Fax: +1 (734) 451 4654prometec-us@prometec.com
EnglandPROMETEC Ltd.41 Church StreetBirmingham West MidlandsB3 2RT
Phone: +44 7971 475134
prometec-uk@prometec.com
ItalyPROMETEC S.r.l.
Viale Ticino, 5421026 Gavirate (VA)
Phone: +39 0332-1950049Fax: +39 0332-744952prometec-it@prometec.com
Eastern EuropePROMETEC BratislavaŠustekova 12SK 851 04 BratislavaSlovakia
Phone: +42 1263 531211 Fax: +42 1263 531212prometec-sk@prometec.com
IndiaPROMETEC GmbH IndiaBranch Office#1066, 15th Cross, 25th MainBanashankari-2nd stageBangalore-560 070Phone: +91 (0)80 2671 2220Fax: +91 (0)80 2671 2199prometec-in@prometec.com
KoreaPROMETEC GmbH Korea Branch Office#C-607, SK-Technopark60 Haan-roGyeonggi-doGwangmyeong-si, 423-795South Koreaprometec-ko@prometec.com
PDA.Dyn_Limits_Force.1403.GB
• alwaysandautomaticallyperfectlyclosetothesensorsignal
• willfollowevenmultipleloadchangeswithinasingleworkpiecerotation without any problems (solid minimization of false alarms)
• fastsignalchangeswhicharetypicalforbreakage will trigger an alarm
• loadchangesbecauseofvaryingcutdepthorfluctuatinghardnessin the skin of cast and forged parts make it impossible to be moni-tored with static limits – only Dynamic Limits are able to safely separate normal load fluctuations and breakage
• toolbreakagedetectionwithin5Milliseconds Stand still of the feed drive witin a single work piece rotationa after breakage
• secondarydamagecausedbytoolbreakageiseffectivelymiimized
• toolbreakagedetectionfrombatchsize1!
• extremefluctuationofallowanceandhard-ness of the work piece are tolerated
additional option: AGC for
a u t o m a t i c
signal adaptation
for machining of
l a r g e p a r t s
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