precision dispensing webinar peter swanson & paul whitehead intertronics wednesday may 2, 2012...

Precision DispensingWebinar

Peter Swanson & Paul WhiteheadINTERTRONICS

Wednesday May 2, 2012

11:00 AM

You are familiar with dispensing!

Success! Failure!

Ideal application process

Pre-determined volume Applied to the same location

Accurately Repeatedly

Medical device manufacturingValidated repeatability

Micro-electronicsPrecision

But all engineers want to remove variability in their process

Material examples

Adhesives2 partsThermally or electrically conductive

Coatings Oils Inks Paint Greases Solder paste Enzymes or catalysts

Part of the design process

The process of material or adhesive specification must include consultation with manufacturing & processing engineers

How will it be dispensed/applied?Can it be dispensed/applied?

How the material is purchased makes a difference

Why use a dispensing system?

Measured amount No more, no less

Consistency & repeatability Fewer rejects

Speed Faster than a human

Removes skill factor Reduces waste & mess Health & safety

Reduced exposure to chemicals Operator fatigue, RSI

Can’t be done manually Precision, gaskets

Result?

Quality Economy Throughput

Factors affecting dispensing technique

Packaging 1 part, 2 part, multi-part

Mix ratio Viscosity Thixotropy Fillers

Abrasiveness Settling Compressibility

Behaviour with temperature Hot melt

Stability & reactivity Cure mechanism

Pot life or working life

Dispense pattern Corrosiveness

Metal parts Solvents

Seals? Hazards

Toxicity Flammability

2k – two or multi-part systems

Complex subject!

Time/pressure dispensing

Simple time/pressure dispensing from barrel (syringe) Few £100s Very popular

Control of time/pressure

Pressure of air pulse Time of air pulse Size of needle

Diameter of 0.25mm up 0.06 possible

Rheology of material

Suitable for manual use or as part of automation

Reasonably accurate +/- 1-10%? Digital timers

Issues with time/pressure

Air is compressible, liquid is not Repeated compression of air (pulsing) causes heat

Issues with time/pressure

Delay in dispense whilst waiting for air compression As barrel empties

Less liquid, more air More compression time needed Dot size decreases

Issues with time/pressure

Material viscosity can changeWith temperature

Pulsing Ambient temperature

With time Cure

Dispensing valves

Why use a dispensing valve?

Accuracy Remove the variable of air volume increase as the dispensing

barrel empties Mitigate the effects of temperature induced viscosity changes

Challenging materials Liquids with characteristics at the extremes

Cyanoacrylate adhesives(very low viscosity) Thermally conductive RTV silicone adhesives (very high viscosity)

Why use a dispensing valve?

Volume Largest dispensing barrel typically 55ml Dispensing cartridges available with a capacity of 400ml or more

Not suitable for handheld use? Barrels and cartridges need to be filled off-line, and changed

when empty. For higher daily volumes some form of larger reservoir is needed

Automation Valves can be fixtured to a robot and provide better stability than

a dispensing barrel

Valves – material feed

ReservoirPressurisedGravity feedExtrusion pumpCartridges and barrels

Valves - types

Pneumatic control most popular Robust Accurate Can be cycled quickly Often implemented at low cost

Pinch tube Diaphragm Spool Needle Poppet

and Spray!

Valves - operation

True volumetric dispensing

True, volumetric dispense has led to the development of valves which work on a “positive displacement” principle

1) Within the valve, a cavity of the desired volume is filled with the liquid, and then this volume is ejected – mechanically or pneumatically

2) Auger screw inside a tube which can be driven by a motor

These valves are usually specific to a limited range of deposit size or to certain viscosities

Positive displacement valve

Progressive cavity pump

Single-helix metal rotor and a double-helix hole in an elastomeric stator

Rotor seals against the stator, forming a series of spaces or pockets, which translate along as the rotor rotates, keeping their form and volume

Pumped material is moved inside the pockets Pockets are shaped such that they taper and overlap The output is

ContinuousEvenNon-pulsing

Progressive cavity pump

Endless-Piston-Principle®

Imagine a piston pushing on a liquid

Or several pistons in sequence

Make the piston thickness zero

Change the piston shape

A continuous or “endless” piston

Positive displacement dispensing

Flow rate is directly proportional to the rate of rotationCan be reversed

Volumetric output of the pump is directly proportional to the number of rotations

Due to the rotor/stator seal, input pressure has no effect on the pump

Able to pump at very low rates Low levels of shear are applied to the pumped fluid True positive displacement dispensing/dosing

Practical application

Controller allows programing of the motor Speed and number of rotations Dots or deposits of specific volumes, or

continuous beads Motor can be reversed briefly to prevent

stringing or dripping Dispensing needle is fitted to the end of

the pen using a standard luer fitting

Practical application

Once material characterised - desired volume can be selected on the controller

Dispensed regardless of material viscosity changes

Independent of ambient temperature Viscosities from water up to very high

viscosity pastesIncluding abrasive, filled or shear-sensitive

media Flow rates range from ~ 0.1 to 60

ml/minute Can be hand-held or fitted to automation

Capabilities

Highest precision of at least ± 1% and reproducibility over 99% of the medium

With automated handling Dispensing a bead is accomplished by setting one parameter -

the volume flow; matched to the speed of a robot or other automation, possible to dose coherent beads down to a width of 250 µm and at traverse speeds of up to 300 mm/s

Metering & mixing

Metering and mixing two component materials

Two pumps supply the components to a static mixing nozzle in the correct volumetric ratio

Contact dispensing

Practical limitationsSpeedVolume - 0.1 µl minimum?Release of material from needle

Have to touch material to receiving surface

Leads us to non-contact dispensingStamping or pin-transfer

Jetting dispense valves

Fast-pneumatic or piezo driven From ~1nL Up to ~1000Hz dispensing frequency Up to ~2,000,000 mPa.s viscosity

Material dependentValve technology used

A word on needles

Smooth flow for filled materials Avoids agglomerations Thin rigid metal construction Accuracy ID from 0.06mm to 1mm

Summary

Many applications are relatively simpleSingle partNot extreme viscosityNon-curing, only cure with outside energy or catalyst, long pot lifeNot hazardous, corrosiveModest outputs

Volumes, speeds

BUT many applications fall outside thisCan get quite complicatedConsult with both your material supplier and your dispensing

supplier

Our Products

Adhesives Dispensing Robotics UV & Light Curing

GasketsPottingSealants Metering & Mixing

Coatings Masking Cleaning

Thank you

Contactinfo@intertronics.co.uk

+44 1865 842842www.intertronics.co.uk

Version 1.0April 30 2012