proplast 2009 / srr 24 sept 09 29. september 2009kistler ... · kistler group measuring technology...

Proplast 2009 / Srr 24 Sept 09 29. September 2009 1Kistler / Bt / 14th April 2008 1

Zero Defect Manufacturing and Hot Runner Balancing based on Cavity Pressure Measurements

Dr.-Ing Oliver Schnerr

Proplast 2009 / Srr 24 Sept 09 29. September 2009 2

Dr.-Ing Oliver Schnerr

Head of Business Unit Plastics

Kistler Instrumente AG

Switzerland

Overview

� Introduction

� Influences in Plastic Injection Molding

� Cavity Pressure Curve – The Fingerprint of Injection Molding

� Zero Defect Manufacturing based on Cavity Pressure


� Zero Defect Manufacturing based on Cavity Pressure

� Automatic Hot Runner Balancing with Cavity Pressure –Controlling Temperatures of Hot Runners Tools

� Summary

Kistler Group

Measuring technology company

Development and production

of sensors, electronics

and systems for measuring


� pressure

� force

� torque

� acceleration

Kistler Group

� International headquarters

Winterthur, founded in 1959

� Production in Switzerland, USA

and Germany

� Active in over 50 countries

worldwide


worldwide

� 1000 employees around the

world, 420 of whom are based

in Switzerland

� Collaboration with over 50

universities

� Turnover 2008: 218 million

Swiss Francs

Kistler Group

Stuttgart (Germany)Kistler-IGeL

35 employees

Stuttgart (Germany)Kistler Instrumente GmbH

50 employees

Lorch (Germany)Kistler Staiger Mohilo

80 employees


Winterthur (Switzerland)

450 employees

Buffalo NY (USA)

85 employees

Kistler Japan

32 employees

Sales Centers

Applications and Markets

Proplast 2009 / Srr 24 Sept 09 720

Engines Vehicles Manu-facturing

Plastics Bio-

mechanics

Kistler Group – Key Figures

� Turnover 2008: 218

million Swiss Francs

� Long-term average annual

growth of 6 %

� 10 % of turnover


� 10 % of turnover

reinvested in research

and development

Influences in Injection Molding

Material DeviationsController Deviations


Operator

Temperature

Abrasion

Environmental

conditions

(Day/Night/

Humidity)

Where to Measure in Injection Molding ?

Part related (p,v,T) Machine related

P far from

the gate

P near

the gate

P gate P in front

of the screwP hydraulic


frozen plastic plastic melt hydraulic

oil

dimensions, weight, shrinkage ... Viscosity changes

Injection workMachine

Control

Injection Molding Parameters and Quality

1: highest influence on part quality / 9: lowest influence on part quality

Cycle Time

Injection Speed

Metering Time

Melt Cushion

Cavity Pressure Integral

Maximum Cavity Pressure

Melt Temperature


Melt Temperature

Mold Temperature Fixed Half

Mold Temperature Moving Half

Technical Precision Parts: Connectors ... (Thinwalled)

Optical Parts: Lenses, Brake Lights, Mirrors ...

Fast Cycle Precision Parts: One-Way Shavers ...

Technical Parts: Gear Wheels ... (Thickwalled)

Medical Parts: One-Way Syringes, Pipettes ...

Technical Packing Material: Tape Cassettes, CD-Covers ...

Office Appliances: Rulers, Squares, Stencils ...

General Parts: Housings, Covers, Vacuum Cleaners ...

Unplasticised PVC Parts: Pipe Connections, Fittings ...

[Source Demag]

The Cavity Pressure Curve

Volume change due to cooling of melt; compensated by holding pressure

Gate freezes

Pre

ssure


Cavity is volumetricallyfilled (switch-over point)

Atmospheric

pressure start of

shrinkageStart injectionMelt reaches sensor

Time

Injection Compression Holding

Qu

ality

Surface,

warpage,

cristallinity,

orientation

Forming of

contour, flash

formation,

weight,

Weight, dimensions, warpage, shrinkage, blow holes,

sink marks, orientation inner layers

Cavity Pressure and Quality


orientation

outer layer

weight,

dimensions

Maximum pressure

Switch-over

sealing point

Cavity Pressure For Three Important Processes

� Production Monitoring� Measure pressure for complete cycle; then decide if part is Good

or Bad

� Real-time Process Signals


� Immediate outputs to activate Alarms, Switch-over or open/close

valve gates

� Process Control� After cycle signals to optimize hot runner temperatures

Production Monitoring with CoMo Injection System

Good / Bad


AnalysisProcess dataGood / Bad

signal

Data

storage

statistics

Quality report

Data processing

system

Mould with sensors

(Cavity pressure)

CPSScrap

separation

Production MonitoringShort Shot Problem

� Detection and Sorting of Short Shots


Production Monitoring: Short ShotMonitoring Maximum Pressure

Short Shot Good Part


Production MonitoringExample Short Shot


Realtime Process Control


Controlsystem

System

Tool with CavityPressure Sensors

Process Data

Set parameter

During Cycle

Parameter

Real-Time Control: Examples

� Cascade control in sequential

injection molding

� Open & close needle gates using a

pressure threshold

� Fluid Injection Molding

(GIT gas-assisted molding &


(GIT gas-assisted molding &

WIT water-assisted)

� Open fluid valve using a pressure

threshold

� Control Injection Compression /

Embossing Molding

� Start compression phase with

pressure threshold

Real-Time Control: Switch-Over with Cavity Pressure

Holding pressure used to

compensate for shrinkage

Gate freezes

Cavity

volumetrically

filled (switch-

over)


Athospheric pressure

reached;

Shrinkage continues..

Injection starts

Melt at Sensor

Note: In most applications the sensor position is not critical.

Pressure

Threshold

Continuous Process Control


Controlsystem

System

Tool with CavityPressure Sensors

Process Data

Set parameter

After Cycle

Parameter

Hot Runner BalancingOptimization of Tip Temperatures


Hotrunner Control: Setting The Correct Temperatures

285°C

285°C

Cavities/ Part


285°C

285°C

285°C

Hot Runner Tips Cavity Pressure

Sensors

Optimization of Hot Runner Tip Temperatures

Cavity P

ressure

Cavity P

ressure

Unbalanced Mold Balanced Mold


Cavity P

ressure

Time

Cavity P

ressure

Time

Optimization of Hot Runner Tip Temperatures

� Unique filling pattern during

injection and start of compression

Cavity P

ressure

Unbalanced Mold


Cavity P

ressure

Time

Region of interest

Goal

� Simultaneous filling of all

cavities

Balancing of Hot Runner Tip Temperatures

Ca

vity P

ressu

re


Cavity Pressure

� Correlation of fill in each cavity

� No partial filling necessary

� All changes can be detected

Ca

vity P

ressu

re

Time

Time

Optimizing Hot Runner Tip Temperatures

Pressure rise too early Pressure rise too late

Cavity P

ressure

Cavity P

ressure


Changes on the process

Cavity pressure rises too early

Cavity fills quicker

Cavity pressure rises too late

Cavity fills slower

� Reduce nozzle temperature � Increase nozzle temperature

Time

Cavity P

ressure

Time

Cavity P

ressure

Optimizing Hot Runner Tip Temperatures

Unbalanced Mold Balanced Mold


Hot Runner BalancingOptimization of Tip Temperatures


Example: Balancing of Hot Runner Tip Temperature

� Automatic hot runner balancing using Kistler Multiflow� Adjustment of hot runner nozzle temperatures using cavity pressure

� Mold / part:� 16 Cavities


� 16 Cavity pressure sensors

� 8 Hot runner tips with

2 Cavities / Tip

� Material: PA 6

� Part weight: 0,17 g

� Shot weight: 6,65 g

Unbalanced Process

1

2

3

4

5

6

Cavity Filling


∆t

6

7

8

Unbalanced Process

1

2

3

4

5

6

Cavity Filling


6

7

8

∆t

Balanced Process with Multiflow

1

2

3

4

5

6

Cavity Filling


6

7

8


1

2

3

4

5

6

Cavity Filling


6

7

8

Without MultiflowTi=const=285°C; ∆∆∆∆t = 140,2 ms


Correlation Level:

300bar

∆t

Balancing with Multiflow: Overview

Cycle 1 Cycle 5 Cycle 15


Cycle 40Cycle 25 Cycle 55

Balanced with Multiflow∆∆∆∆t = 8,4 ms


∆tCorrelation Level:

300bar

Results: Different Balancing Methods

Method Time / Cycles needed ∆t [s]

Manual Balancing without

Cavity Pressure

½ Day 0,126


Manual Balancing using

Cavity Pressure Curve

60 Cycles 0,069

Automatic Balancing with

Multiflow

20 Cycles

50 Cycles

0,0431

0,0019

Long Time Measurement: No Control vs. MultiFlow Method

0.080

0.100

0.120

0.140

Diffe

rence T

ime [

s]

Manuell

Multiflow

No control


0.000

0.020

0.040

0.060

0.080

1 400 1200 2000Cycle

Diffe

rence T

ime [

s]

Kistler Multiflow

Results: Long Run

� Without Multiflow: 30% Change in Filling Time Difference

� With Multiflow:


� With Multiflow: � Reduced Fill Time Difference

� Constant Fill Time Difference over 2500 Cycles

Summary

� Cavity pressure is the most important

aspect of the molding process,

ensuring:

� 100% Quality control

� Zero-Defect molding


� Automatically balancing of hot runner

tools based on cavity pressure

measurements stabilizes production

processes and quality and reduces

setup times

Thank You Very Much For Your Attention !


proplast 2009 / srr 24 sept 09 29. september 2009kistler ... · kistler group measuring technology...

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