1. Manufacturing Processes
Plastics & FRP
Professor Su-Jin Kim
Mechanical Engineering
Gyeongsang National University 1

2. Contents 1. Plastic Process Injection molding (사출금형) Blow molding
Thermo forming
Extrusion (압출)
2. Composite (복합재료/강화플라스틱)
Composite process
3. Rapid prototyping (쾌속조형)

3. Processing of Plastics
Injection molding (사출)
Blow molding
Thermo forming
Extrusion (압출)

4. Plastic Injection molding
Molten plastic is injected into a mold by hydraulic plunger
Good dimensional accuracy as die-casting
Hopper
Mold
Barrel
Plastic injection molding:

5. Injection mold Mold structure
Sprue busing
Guard busing
Ejection pin
Injection Mold
JY-Solutec

6. Injection Mold

7. Flow analysis MAPS-3D Plastic injection process analysis
VMTech:

8. Design for Injection Molding
Parting line is flat or simple-curved surface
Flow path ratio (length/thickness < 200)
Clamping force = Pressure x Area
Draft angle 1~2˚
Shrinkage PE(1.5~6), PP(1~3), PS(.2~.6), PVC(0.1~0.5)
Reinforcements (ribs and bosses)
Defects : Sink mark, Weld line, Air traps, Deflection

9. Blow molding Blow up a plastic balloon to fill the mold.
Hollow thin-wall parts; beverage and food containers.

10. Thermo (Vacuum) forming
The thermoplastic sheet is heated, pressed into the mold using vacuum pressure
Medium production rates, low tooling cost
Vacuum

11. Plastic Extrusion
The molten plastic is forced through a die and cooled.
Long products with constant cross-section
High production rates, low tooling cost
Throat
Barrel
Gear reducer
Box
Thermocouples
Feed section
Barrel heater/cooler
liner
Melt thermocouple
Melt section
Adapter
Breaker
plate
Melt-pumping section
Screw
Die
Wire filter
screen
Hopper
Motor
©갈창우, GNU

12. Blown Film Extrusion
A thin-walled tube is extruded and expanded into a balloon shape by blowing air until the desired film thickness is reached.

13. Economics of Processing Plastics
Design and manufacturing decisions are based on costs of equipment, tooling and production volume.
Extrusion
Injection molding
Blow molding
Production rate
Thermo forming
Machining
Number of parts

14. Reference Wook-Ryol Hwang, GNU : http://rmp.gnu.ac.kr
Plastic injection molding process analysis, VM Tech:
Mold:
Mold:
Mold
Injection machine :
Plastic :

15. Fiber Reinforced Polymer, FRP (Composites)
FRP (복합재료) Fiber(섬유) + Plastic matrix (모재)
Fiber: Kevlar, Glass fiber, Graphite fiber, Boron
Plastic matrix: Epoxy, Polyester
Process
Impregnation: fiber+resin
Molding
Compression molding
Vacuum bag molding
Open molding
Resin transfer molding

16. Molding Reinforced Plastics
Prepreg & Autoclave
Vacuum bag molding
Open molding (Contact molding)
Resin transfer molding (RTM)
Filament winding

17. Prepreg
Prepreg is a term for "pre-impregnated" composite fibers containing polymer matrix.
The pre-preg are mostly stored in cooled areas since activation is most commonly done by heat.

18. Vacuum-bag molding
Prepregs lay in mold and apply pressure in a vacuum.
Atmospheric pressure
Clamping bar
Vaccum trap
Gel
coat
Gasket
Vacuum trap
Flexible bag
Room temperature or oven cure
hand or spray lay-up
Mold release
Resin and glass
Mold
©갈창우, GNU

19. Autoclave
Hence, composite structures built of pre-pregs will mostly require an oven or autoclave to cure out.
Temperature 180 °C, Pressure 600kPa, Time 3 h

20. Sheet molding compound (SMC) & Compression Molding
Compression molding: SMC is placed between two molds and pressure is applied.
Compression Molded Composite
Sheet molding compound

21. Open-molding
Open-molding process use single male or female mold and also called contact-molding
Used in making products with high surface-area-to-thickness ratios.
Hand lay-up
Spray lay-up

22. Resin Transfer Molding (RTM)
Resin Transfer Molding (RTM) allows the molding of components with complex shapes and large surface areas with a good surface finish on both sides.

23. Filament winding
Glass fibers are embedded in thermosetting resin matrix materials and winded around a pipe.
FRP pipe
CNG tank

24. Composite Machining & Joining

25. Rapid prototyping
3d CAD  Real part

26. Rapid prototyping
Making a physical prototype directly from 3D CAD drawing.
CAD solid model
Translation to STL format
Slice the model into layers
Send data to RP machine
Curing each layer by laser

27. Rapid Prototyping Usage

28. Rapid Prototyping Usage

29. 3D Printing Roller spreads powder
Inkjet traces the shape of each section

30. SLA (Stereo Lithography Apparatus)
Vat filled with photo-curable liquid resin
Laser beam solidifies liquid resin of 2d cross-section
Elevator drops enough to cover the solid polymer with another layer of liquid
Cured
Resin
XY Scanning
UV Laser Beam
Photo-curable
Resin (Liquid)
Top of the Liquid
Elevator
Vat

31. SLS (Selective Laser Sintering)
Roller spreads powder across the top of the elevator
Laser traces the shape of each cross-section, fusing powder in the thin layer

32. FDM (Fused Deposition Manufacturing)
Dispenser heats the plastic and extrudes it at the desired position. Deposited plastic solidifies to form a hardened layer.

33. Reference Polymer Mixing (W. R. Whang) : http://rmp.gnu.ac.kr/
Mechanical Properties of Composite (J. H. Choei):

34. Injection molding
insert label in pet mold

35. Multiple injection molding (복합사출)
Product with hard and soft plastics.
Sliding split mold
S778T + TPE
Turn table mold