Micromoulding: process repeatability + product quality issues In Process Measurement Meeting 3 rd September 2003 Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates, IRC in Polymer Engineering, Dept. Mechanical & Medical Engineering, University of Bradford, Bradford UK Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates, IRC in Polymer Engineering, Dept. Mechanical & Medical Engineering, University of Bradford, Bradford UK

Contents Introduction Equipment Process Interrogation Investigation Micromoulding Product Property Assessment Final Comments Introduction Equipment Process Interrogation Investigation Micromoulding Product Property Assessment Final Comments

Part weight 0,0008 g courtesy: Battenfeld Introduction

Battenfeld Microsystem50 Specifically designed for moulding of products <1g Accurate shot dosing and high injection speed with little material wastage Incorporation of clean room conditions and sealing/ packaging systems Specifically designed for moulding of products <1g Accurate shot dosing and high injection speed with little material wastage Incorporation of clean room conditions and sealing/ packaging systems

Battenfeld Microsystem 50

Conventional vs. Micromoulding Conventional Injection control switch-over to avoid pressure spike Feed system vol << part volume Heat to be removed from product using cooling system – cycle times ~tens of seconds Conventional Injection control switch-over to avoid pressure spike Feed system vol << part volume Heat to be removed from product using cooling system – cycle times ~tens of seconds Micromoulding High speed injection without switchover and corresponding pressure spike – material compression Feed system volume > part volume Very rapid freezing of material allows very low cycle times BUT smaller processing window

Dynisco PCI 4011 Piezo load transducer Dynisco PCI 4006 piezo load transducer The Data Acquisition Setup Temposonics R series displacement transducer J-type thermocouples

Process Interrogation What can we measure to give an accurate representation of process/product quality?

Process Interrogation How? Process characteristic? Peak injection pressure? How? Process characteristic? Peak injection pressure?

Process Interrogation How? Process characteristic? Peak cavity pressure? How? Process characteristic? Peak cavity pressure?

Process Interrogation How? Process characteristic? Pressure/time integral? How? Process characteristic? Pressure/time integral?

Process Interrogation How? Process characteristic? Pressure/time integral? How? Process characteristic? Pressure/time integral?

Typical Micromoulding Process Data Mean = S.D. = 6.88 Mean = S.D. = 3.55

Typical Process Data Mean = 78.9 S.D. = 4.42 Mean = S.D. = 4.86 Nylon6 NC – Step Plaque Mould

Experimental Test response of process data to change in process conditions Use three different mould temperature settings during a production run Test response of process data to change in process conditions Use three different mould temperature settings during a production run

Experimental - step plaque moulding Material: HAPEX (40% sintered hydroxyapatite HDPE matrix) Produced by IRC in Biomaterial Science Queen Mary and Westfield College, London Material: HAPEX (40% sintered hydroxyapatite HDPE matrix) Produced by IRC in Biomaterial Science Queen Mary and Westfield College, London

Process Conditions Screw Speed30rpm Back Pressure150Bar Shot Size220mm3 Injection Speed500mm/s Melt Temperature200C Mould Temperature20C50C80C

Process Data

Injection Pressure Curves

Cavity Pressure Curves

Product Mass – Hapex, step plaque 0.12% variation

Observations Process measurements required in the cavity itself for accurate process monitoring Challenges Size! Techniques Solutions Indirect measurements Ejector pins Ultrasound

Product Property Assessment

Conventional Part mass Balance Dimension testing Custom Rig Scanner Mechanical testing Instron Conventional Part mass Balance Dimension testing Custom Rig Scanner Mechanical testing Instron Micromoulding Part Mass ? Dimension testing Machine Vision Atomic Force Microscopy Mechanical Testing Nano-Indenting

Machine Vision Systems Allow in-process quality control Fully automated – removes the need for visual inspection Ideal for micro-scale products Allow in-process quality control Fully automated – removes the need for visual inspection Ideal for micro-scale products

Machine Vision Allows detection of flawed products during the process and suitable action can be taken

Atomic Force Microscopy

AFM – surface feature measurement AFM scan size 75 µm x 75 µm Pitch of scroll marks ~ 6µm AFM scan size 75 µm x 75 µm Pitch of scroll marks ~ 6µm Cavity Product

Surface feature replication -downstream AFM scan size 75 µm x 75 µm Pitch of scroll marks ~ 6µm AFM scan size 75 µm x 75 µm Pitch of scroll marks ~ 6µm Cavity Product

AFM - Morphology Measurement Component sectioned using glass-knife microtomy Surface is etched using potassium permanganate solution to produce representative surface Surface imaged using AFM Component sectioned using glass-knife microtomy Surface is etched using potassium permanganate solution to produce representative surface Surface imaged using AFM Surface following microtomySurface following etching

Morphology Measurements – Spherulite size

Morphology - experimental Line of indents 25µm separation 800 µm Material: BP Rigidex 5050 HDPE Melt temp: 190C Mould temp 50C Injection speed 500mm/s Material: BP Rigidex 5050 HDPE Melt temp: 190C Mould temp 50C Injection speed 500mm/s 250µm

Morphology Measurements

Nano-Indenting

Properties of POMC mm test bar A B C Gate end Position

Results

Comments AFM and nano-indenting very powerful techniques + Allow direct evaluation of influence process conditions on product properties - Time consuming - Sample preparation issues Machine Vision Systems + Well suited for micromoulding assessment + Performed during processing - Cannot determine morphology/mechanical properties AFM and nano-indenting very powerful techniques + Allow direct evaluation of influence process conditions on product properties - Time consuming - Sample preparation issues Machine Vision Systems + Well suited for micromoulding assessment + Performed during processing - Cannot determine morphology/mechanical properties

Future experiments Longer runs with smaller (top hat) cavity Individual sample collection Assessment Longer runs with smaller (top hat) cavity Individual sample collection Assessment

Fin