Lightning-Fast, Reliable Tool Breakage Detection …. always in use – never switched off!never...

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


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!


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


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


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.


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


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 [email protected]

USAPROMETEC Inc.47711 Clipper StreetSuite 200Plymouth, MI 48170

Phone: +1 (734) 455 0100 Fax: +1 (734) 451 [email protected]

EnglandPROMETEC Ltd.41 Church StreetBirmingham West MidlandsB3 2RT

Phone: +44 7971 475134

[email protected]

ItalyPROMETEC S.r.l.

Viale Ticino, 5421026 Gavirate (VA)

Phone: +39 0332-1950049Fax: +39 [email protected]

Eastern EuropePROMETEC BratislavaŠustekova 12SK 851 04 BratislavaSlovakia

Phone: +42 1263 531211 Fax: +42 1263 [email protected]

IndiaPROMETEC GmbH IndiaBranch Office#1066, 15th Cross, 25th MainBanashankari-2nd stageBangalore-560 070Phone: +91 (0)80 2671 2220Fax: +91 (0)80 2671 [email protected]

KoreaPROMETEC GmbH Korea Branch Office#C-607, SK-Technopark60 Haan-roGyeonggi-doGwangmyeong-si, 423-795South [email protected]


• 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

Lightning-Fast, Reliable Tool Breakage Detection …. always in use – never switched off!never...

Documents

Transcript of Lightning-Fast, Reliable Tool Breakage Detection …. always in use – never switched off!never...