MANUFACTURING WITH COMPOSITES 1

Transcription

1 MANUFACTURING WITH COMPOSITES 1 WCC WEBINAR 3 rd June

2 AIMS OF WEBINAR To give an overview of the most important manufacturing methods for composite materials Covering suitable materials, typical products produced Overview of main advantages and drawbacks of each method 2

3 Today s Webinar Lower cost and more mass-produced methods Hand lay-up, Vacuum bagging, Spray-up, Resin Transfer Moulding Resin Infusion Moulding Compounds 3

4 Next Week Higher cost and more quality-critical methods Pre-pregs and autoclave, Quickstep process, Pultrusion, Filament Winding, Automatic Tape Laying Processing of Thermoplastic Composites 4

5 Hand Laminating 5

6 Hand Lay-Up Simplest process Positive former or negative mould made Wood, thermoplastics, aluminium, steel

7 Hand Lay-Up Mould release agent / layer applied Gel-coat applied to give smooth and impermeable surface Resin applied and allowed to partially-cure

8 Hand Lay-Up Then layers of fibre mould fabric placed on Most commonly woven rovings, but stitchbonded and chopped strand mat used Resin applied onto fabric using brush

9 Hand Lay-Up Roller used to (try to) remove trapped air-bubbles Next layer applied

10 Hand Lay-Up Layers built up to give desired thickness Cured in air normally at room temperature Elevated temperatures can be used to give faster / more complete cure (post-cure) Low equipment and mould costs Slow, labour intensive, fibre volume fraction limited, voids a problem

11 Hand Lay-Up Most commonly used with glassreinforced polyesters (though not limited to this) Typically for small numbers of components Quality depends on skill of operator

12 Hand lay-up of relatively small part using chopped strand mat for reinforcement and a tinted polyester resin 12 Hand lay-up of a large part using a range of reinforcing fabrics, a clear resin and a gelcoated mould

13 Hand Lay-Up using PREFORMS Dry lay-up can be used with all reinforcement laid into mould Preforms can be used made of chopped glass sprayed onto a mould and held together with a binder. Resin then applied by hand or by spray. 13

14 Hand lamination Lay-up should be continuous no break of >24 hours for polyester resin as the resin surface is still chemically active and a good bond between subsequent layers guaranteed. Peel ply can be used for epoxies extended breaks may necessitate cleaning and/or roughening the surface before continuing. 14

15 Hand Lamination Disadvantages H&S issues Cost of extraction and treatment of VOCs. High labour content. Product quality and variability dependent on operator expertise 15

16 Hand Laminating Void Content 360 g/m 2 non crimp ±45 carbon & epoxy 3 mm HAND LAYUP 40% fibre by volume

17 Hand Lamination Disadvantages Potential for resin mixing errors. Dimensional inconsistency with high shrinkage. Generally lower fibre volume fraction and voids leads to poorer mechanical properties than other methods 17

18 Hand Lamination Disadvantages Draining of resin from vertical surfaces: May require addition of thixotropic agents. Overhead work almost impossible Only one moulded surface. Low production rates due to cure times of room temperature resins. 18 High levels of waste.

19 Attention!!! The last video clip had an example of very poor practice. The core material should be tapered at the edges to prevent bridging 19

20 Spray Up 20

21 Spray Lay-up As in hand lay-up, a gelcoat is applied to the mould surface, either by hand or spray, after release agents have been applied. 21

22 Spray Techniques Hand-held gun feeds a stream of chopped fibres into a spray of catalysed liquid resin. Stream projected onto the mould tool. Deposited materials left to cure under standard atmospheric conditions. 22

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24 Spray-Up Pros & Cons Fast production rates with automation possible. Inexpensive tooling. Most airborne emissions. Difficult to avoid trapped air. Poor control of thickness. Only suitable for short fibres so mechanical properties limited. 24

25 Vacuum Bagging 25

26 Vacuum / Pressure Bag A method to improve quality of hand lay-up Method almost the same Membrane placed over component and pressure applied above, or vacuum below Sucks or pushes entrapped air out Allows higher fibre volume fraction

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28 Vacuum / Pressure Bag Even slower than hand lay-up Cost increases somewhat more consumables and waste Quality is improved

29 Resin Infusion Techniques 29

30 Resin Infusion Techniques Differ significantly from previous methods as reinforcement is laid into the mould DRY. This has enormous implications for the workforce and environment. Resin is introduced to the mould by either: Pressure (Resin Transfer Moulding RTM) Suction (Vacuum Infusion) A combination (RTM Lite) Resin film 30

31 Materials Resins typically Polyester (orthophthalic & isophthalic) Vinyl ester Epoxy Fibres may be of any material aramid, carbon or glass chopped strand mat, woven-, knitted-, stitched- or bonded-fabrics, singly or in combination. 31

32 Resin Transfer Moulding (RTM) The Basics Two moulded surfaces Most thermoset resins and fabrics Inserts, fixing points and lightweight core materials incorporated at moulding stage. Mould is closed, then resin injected to fill porespace. Once resin is cured, the component is removed from the mould. Superior dimensional tolerances to handlay/autoclave products Reduced emissions of VOCs. 32

33 Resin Transfer Moulding (RTM) 33

34 RTM The Mould High injection pressure requires a robust structure and clamping. The mould must not distort under loads applied. Very high quality finish on all surfaces. Minimal post moulding finishing 34

35 Resin Transfer Moulding (RTM) 35 Minimal void content

36 RTM Light Similar to RTM except: Both suction and injection used Less substantial moulds required Lower injection and clamping pressures May be a quicker process 36

37 Light RTM (VARTM) RTM light 37 Vacuum used both for mould clamping and resin injection into cavity. May also use up to 0.5 bar positive injection pressure.

38 Resin Infusion Closed mould process, using one rigid tool face and one flexible (polymer film, rubber membrane). Dry reinforcement and cores. Liquid thermosetting resin introduced under full or partial vacuum. Various techniques to control resin distribution. Surface mesh Flow channels in core 38 Interlaminate flow fabrics

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40 Infusion flow strategies uniaxial (slow) radial convergent (fast) inlet vent

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42 Resin Film Infusion Reinforcement fibres interleaved with partially cured epoxy film May be laid-up as individual sheets or purchased as a pre-laid-up stack Vacuum bagged and heated in oven or Autoclave Resin softens, flows to wet-out the fibres Cure continues with heat. 42

43 Resin Film Infusion (RFI) 43

44 Moulding Compounds 44

45 Moulding Compounds To make larger numbers of complex mouldings, we can use moulding compounds Sheet Moulding Compound (SMC) Up to 30mm thick Bulk (or Dough) Moulding Compound (BMC / DMC) Thicker Combination of chopped glass fibres, uncured resin, fillers and catalyst 30 to 50% Fibres 30% Resin (Polyester / Poly vinyl ester) 20 to 40% Filler (Calcium Carbonate)

46 Sheet Moulding Compound

47 Moulding Compounds Placed into matched mould High pressure applied Mould heated to cure BMC can be injection-moulded Faster cycle times Automated and reproducible Capital costs higher Moulds need to be robust (tool steel / Cr plated)

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49 Moulding Compounds Used for larger numbers of components Moderate stiffness (much higher than thermoplastics) Reasonable strength Competes with pressed steel Widely used in automotive / domestic goods markets

50 SUMMARY A wide range of process methods. Considerable scope for combining elements of different methods. Always a balance between speed and cost of production, quality of part, capital equipment requirements. In all cases, considerable control required. 50

51 Thank you for your attention Any questions???