Swedish national arena for lightweight innovations

Cost-efficient structural composite parts combiningunidirectional tape reinforcements and injection

molding processes

Dominik StapfDeputy Head Composites & Joining Technologies, IWK Rapperswil

Agenda

◼ Introduction Institute for Materials Technology and Plastics Processing (IWK)

◼ Process Injection molded components with UD-tape reinforcement

◼ Challenge Part

High-Performance ring shaped Element

◼ Challenge 50% lighter

Fiber reinforcement why - and why not ? (https://www.duden.de/rechtschreibung/Feder)

◼ Challenge 50% costs

Efficiency and Performance by combining two processes (https://www.wjtv.com/top-stories)

2

HSR Hochschule für Technik Rapperswil

3

https://de.wikipedia.org/wiki/Datei:Switzerland_in_Europe.svg https://www.google.com/maps

IWK Institute for Materials Technology and Plastics Processing

4

Interfaces and surfacesPolymer engineering

Light weight

design

Hybrid technologyIntegration of

functions and

processes

Simulation

Biobased plastics

Mechanics/

Kinematics

(2005)

Metal Processing

(2016)

Compounding/

Extrusion (2010)

Joining

technologies

(2015)

Composites/

Light weight

design (2015)

Fields of InnovationAdditive Manufacturing

Injection

Moulding/

Polyurethane

(2005)

IWK Institute for Materials Technology and Plastics Processing

5

6

Challenge

Challenge – High Performance parts

Efficiency

Ressources

Performance

Costs

Automotive

Consumer

Sports

Public transport

Industry

Medical

Complexity of the parts

Performance

Weight

Costs

Lightweight structural parts

https://www.juraprofi.de

7

HYX Mold

Challenge – High Performance parts

◼ Challenges of a thin-walled part for automotive application

◼ Static pressure-loaded

◼ Very high reliability

◼ Long lifecycle

◼ 100 % tightness against fluids is essential

◼ Hot/wet conditions in service

◼ Efficiency and function – big lot size, easy to mount

◼ Integration of functions

◼ Corrosion resistance

8

9

Challenge 50 % Lighter

Metals

NonreinforcedPlastics

Short-fiberreinforcedPlastics

ContinousreinforcedPlastics

Weight Mechanical Performance

Challenge 50% LIGHTER

10

Aluminum 2.7 g/cm3

Fiber reinforced plastics (50 % FVC) 1.4 g/cm3

50 % LIGHTER

Challenge 50% LIGHTER

Shaping Plastics

◼ geometric requirements

◼ Integration of functions

Long fiber reinforcement

◼ mechanical requirements

11

https://www.easycomposites.co.uk

Aluminum

Challenge 50% LIGHTER

◼ High strength of glass or carbon fibers: 1.7-7 Gpa(high-alloyed steel max. 2.0 GPa)

◼ High stiffness of carbon fibers: 230-700 GPa (steel 210 GPa)

◼ Low density of composites materials: 1.5-2.0 gr./cm3

(steel 7.5 gr./cm3)

◼ High potential with regard to integration of functions/geometry in a broad variety of production processes

◼ Very good fatigue behavior

◼ Corrosion resistance of composite materials

◼ Specific strength:

◼ Specific stiffness:

12

3

B

cm/g

MPa=

3cm/g

GPaE=

Exemplary calculation for different layer sequences

(Assumptions: Young’s Modulus fiber: 230GPa; approx. 60% fiber volume content)

Layer sequence

Young’s Modulus

in 0°

[GPa]

Density

[g/cm3]

Spec. Young’s

Modulus

[GPa/g cm-3]

Cross section view

CFK-UD (0°) 142 1.5 94

CFK-biax. (0/90°) 76 1.5 51

CFK-quasi-iso. (0/60/-60°) 54 1.5 36

Aluminium 72 2.7 26

Challenge 50% LIGHTER

13

100%

54%

38%

100%

51%

54%

38%

28% Composite: 10% weight savings

Challenge 50% LIGHTER

◼ The appropriate uniaxial (or

even biaxial) stresses seem

very limiting.

◼ In fact, a lot of suitable

applications exists.

◼ The fibers have to be oriented

in a way taking into account

the flow of forces.

◼ However, 3-axial, fast

changing stress states are

not suited in general.

14

FF

MM+

-

Challenge 50% LIGHTER

15

Strength

Stiffness

Impact

Weight

DesignFreedom

Lot size

Continous-fiberreinforcement

Thermoplastics

Thermoplastic Materials

+ High mechanical performance

+ Low weight

+ Great design freedom

+ Fast processing times

Challenge 50% LIGHTER

Short fibre reinforced Long fibre reinforced Continuous fibre reinforced

Fibre length 0.3-2mm, random 5-50mm, random >50mm, oriented

Typical stiffness <20GPa <30GPa <380GPa

Typical strength <220MPa <350MPa <2200MPa

Geometry Complex parts Shell like parts Depending on process

Process • Injection molding

• Low material costs

• High lot sizes

• Automated

• Press processes

• Low material costs

• Medium lot sizes

• Automated

• Various processes

• High material costs

• Small lot sized

• Labour-intensive

16

Challenge 50% LIGHTER

◼ The combination of

excellent mechanical

properties and high

lot sizes is still

challenging with

composites

◼ In general, cycle times

remain relatively high

towards the top end of

the mechanical

properties

17

Me

ch

. p

rop

ert

ies

Lot size

Prepreg-

Autoclave

Infusion

RTM

Hand

laminationSMC

GMT

Pultrusion

Injection

moldinglow

me

diu

mh

igh

Up to 1’000 approx. 10’000 from 100’000

BMCExtrusion

Winding

Casting

Structural components

?

18

Challenge 50 % costs

Challenge 50% Costs

◼ The combination of

excellent mechanical

properties and high

lot sizes is still

challenging with

composites

◼ In general, cycle times

remain relatively high

towards the top end of

the mechanical

properties

19

Me

ch

. p

rop

ert

ies

Lot size

Prepreg-

Autoclave

Infusion

RTM

Hand

laminationSMC

GMT

Pultrusion

Injection

moldinglow

me

diu

mh

igh

Up to 1’000 approx. 10’000 from 100’000

BMCExtrusion

Winding

Casting

Structural components

Injection

molding

(short fibres)

Injection

molding (UD-

Tapes)

Challenge 50% Costs

20

1. Pick up insert

2. (Preheat insert)

3. Transfer to mold

4. (Thermoforming)

5. Back injection

6. Remove from mold

1 2

3

45

6

GranulesUD-Tape

https://www.kraussmaffei.com/imm-en/fiberform.html

Challenge 50% Costs

21

◼ Mechanical Testing with specialized tools

◼ Application of inner pressure by conical punching tool

→ Compression strength of the part

→ Strength at the joining of the circular tape

→ Comparison with results from simulation and optimization

Challenge 50% Costs

22

◼ Optimization of tape joint is

done by FEA

◼ The manufactured samples

are tested in a quasi-static

setup (punching tool)

◼ Dependent on the joint

design, the failure mode

changes from delamination

to fiber fracture

◼ Hydrolysis effects have to be

taken into account

Bu

rst p

ressu

rein

[b

ar]

Delamination vs. fiber fracture

0

50

100

150

200

0 5

str

ess in N

/mm

2

stroke in mm

INFLUENCE OF HYDROLYSIS EFFECTS ON TENSILE STRENGTH

effected byhydrolysis

no hydrolysiseffects

Challenge 50% Costs

23

◼ The adhesion between tape and thermoplast

depends on several process parameters:

◼ Combination of materials

◼ Tool and material temperature

◼ Flow path and mold design

◼ A perfect bond has to be achieved for optimal

mechanical properties

injection Surface next to injection point

cohesive fracture in thermoplast

Surface far away from injection point

adhesive fracture between tape and

thermoplast

Inner layer

THERMOPLASTIC

POLYMER

Outer layer

UD-TAPE

Challenge 50% Costs

24

BACK-INJECTION OF UD-TAPES RESIN-TRANSFER-MOULDING

resinhardener

Moulding

injection

curing/

cross-linking

upper die

lower die

finish: grinding,

polishing, painting

demoulding

tempering

preheating

cutting to sizefibre

material

layer

lay-up

scrap

assembling

preforming

trimming

upper die

lower diehold-down

dry preforms

thermoplastic

resin

TP-UD-Tape

cutting to size

fixed mould half

ejector mould half

UD-Tape-pre-

cut placing

back-injection

of the UD-

Tape /cooling

ejection

sprue

removal

Not necessary

Some seconds

Some minutes

Not necessary

cleaning

Challenge 50% Costs

◼ Back-injection of UD-Tapes combines the excellent

mechanical properties of the tape with the short cycles

times of injection molding

◼ Structural components become feasible (overcome

limitation of injection molding material)

◼ High lot sizes and reasonable costs become feasible

(overcome limitation of typical composites)

◼ Complex parts are feasible

◼ The unidirectional properties have to be considered when

designing a component

◼ There is a wide variety of materials and applications

◼ Fatigue life and ageing is limiting some applications

◼ Due to the automation potential, a production of such

components is possible in Switzerland

25

Strength

Stiffness

ImpactWeight

DesignFreedom

Metals

Continous fiber reinforced plastics

Thermoplastics

Challenge 50% Costs

26

◼50% Lighter

◼ Replacement of Metals by continous fiber

reinforcement

50% Costs

Replacement of RTM process by injection

moulding + Long fiber reinforcement

Challenge 50% Costs

13. Rapperswiler Kunststoff Forum

27

Swedish national arena for lightweight innovations

Thank you for your attention !

Dominik Stapf

Institute for Materials Technology and Plastics Processing (IWK)

dominik.stapf@hsr.ch

+41 (0) 55 222 4766