InjectionMolding1

“Shear Thinning”
Calendering
10~102
Injection molding 103~104
~ 1 sec-1 for PE
Comp. Molding 1~10
Viscous Heating
Rate of Heating = Rate of Viscous Work
P FvFvv2
130Nsm2
Re104
Fitlilme1s
For Die casting
R e310 3110 0 3110 3 300
* Source: /proc/plastic/injection/injection_process.htm
Viscous Shearing of Fluids
Tadmore and Gogos
Molding and Casting pp584 -610
Boothroyd Dewhurst
Design for Injection Molding pp 319 - 359
Kalpakjian see Ch 18 Injection molding case study;Washing machine augers; see on web page
Fountain Flow
*
**
* Source: /trp/inj/flw_froz.html ; ** Z. Tadmore and C. Gogos, “Principles of Polymer Processing”
Shrinkage distributions
Gate Location and Warping
Sprue
2.0
60
Shrinkage
Direction of flow – 0.020 in/in
1.96
60.32
Perpendicular to flow – 0.012
பைடு நூலகம்2.0
Before shrinkage
1.976
After shrinkage
Tii Let Lch = H/2 (half thickness) = L ; tch = L2/ ;
t
Tch = Ti – TW (initial temp. – wall temp.)
-L
x
TW +L
Non-dimensionalize: TT W;
T iT W
x1;
L
F OL 2t
Dimensionless equation:
qx
qx + qx
Fourier’s law
t(cpT) x y q xx x y
qx
k
T x
cp T tk x 2T 2 or T t x 2T 2
Boundary Conditions: 1stkind
T(xx')c onstant
2ndkind 3rdkind
kT(xx')c onstant x
Initial condition Boundary condition
FO
2 2
FO0 1
0 0
2 0
Separation of variables ;
matching B.C.; matching I.C.
(,F O ) f(F O )g ()
Temperature in a slab Centerline, = 0.1, Fo = t/L2 = 1
Tooling for a plastic cup
Nozzle
Cavity
Runner Part
For injection molding, order of magnitude ~ 0.1 to 10
Non-Isothermal Flow
Flow rate: 1/t ~V/Lx
v
Heat transfer rate: 1/t ~a/(Lz/2)2
H Fela o rta rw atxe ~ tfe 4 V eL L r2 zx1 4V zL L Lx z
* Source: /trp/inj/inj_time.html
tc
ool
h
alfthicknes2
s
103 cm3 secforpolymers
Time(sec)
Calculate clamp force, & shot size
F=P X A = 420 tons
InjectionMolding1
Outline
Basic operation Cycle time and heat transfer Flow and solidification Part design Tooling New developments Environment
Readings
Small value => Short shot
For injection molding
H Fe l rr o a a a ~ w tt1 4 t1 ee 1 c x 0 / 3 c s m 0 f 2 0 e / .m 1 s cr m 0 1 .1 c c0 m m 2 .5
For Die casting of aluminum
H Fe lrr o a a a ~ w tt1 4 te 1 e c x 0 .0 3 /c m s f 2 0 / m e .s 1 crm 0 1 .1 c c0 m m 1 20
* Very small, therefore it requires thick runners
Injection mold die cast mold
Where would you gate this part?
Weld line, Sink mark
Gate
Mold Filling
Weld line
Solidified part
Sink mark
* Source: /proc/plastic/injection/injection_design_7.htm
F v
h
Fv Ah
F/A
1
v/h
Newtonian Viscosity
v h
Generalization:
:sherarte
()
Injection molding
Typical shear rate for Polymer processes (sec)-1
Extrusion
102~103
Melt Delivery
Cavity
Moulding Core
Basic mould consisting of cavity and core plate
Tooling for a plastic cup
Nozzle
Runner Part
Cavity
Knob
Core
Stripper plate
30 ton, 1.5 oz (45 cm3) Engel
Injection Molding Machine for wheel fabrication
Process & machine schematics
*
*
Schematic of thermoplastic Injection molding machine
Ltotal = Lmold + Lshrinkage
Effects of mold temperature and pressure on shrinkage
Shrinkage
0.030 0.025 0.020 0.015 0.010 0.005 0.000
LDPE
PP with flow
PP across flow
Basic rules in designing ribs to minimize sink marks
Injection Molding
* *
* Source: /proc/plastic/injection/injection_design_2.htm
Where is injection molding?
Acetal
Nylon 6/6
PMMA
6000
8000
10000
12000
14000
16000
18000
Pressure on injection plunger (psi)
Tooling Basics
Sprue
Nozzle
Cavity Plate
Core Plate
Cavity
Gate
Runner
Bi-1 =k/hL
Reynolds Number
Reynolds Number:
V2
Re L
V L2
inertia
VL
viscosu
For typical injection molding
1gcm 3130Nm4 s2; LZ1 03m theiscskn
VPalretng 1t h 01;
sample V=3.5cm/s V=8cm/s
Transverse direction
* Source: G. Menges and W. Wubken, “Influence of processing conditions on Molecular Orientation in Injection Molds”
VolVol Ah h
Rate of Temperature rise cpd dT th v2 ord dT t cph v2
Rate of Conduction out
dT k d2T~ k T
dt cp d2x cp h2
Viscohuesatingv2 Brinkman number
ConductioknT
Temp.
Processing window
Thermal degradation
Flash
Shortshot
Melt
Pressure
Typical pressure/temperature cycle
*
*
Time(sec)
Cooling time generally dominates cycle time
3.8 lbs = 2245 cm3 =75 oz
Actual ; 2 cavity 800 ton
Clamp force and machine cost
Heat transfer Note; Tool > polymer
1-dimensional heat conduction equation :
Center gate: radial flow – severe distortion
Air entrapment Gate
Edge gate: warp free, air entrapment
Diagonal gate: radial flow – twisting
End gates: linear flow – minimum warping
* Source: /proc/plastic/injection/injection_process.htm
Process Operation
Temperature: barrel zones, tool, die zone Pressures: injection max, hold Times: injection, hold, tool opening Shot size: screw travel
Effects of mold temperature and pressure on shrinkage
Shrinkage Shrinkage
0.030 0.025 0.020 0.015 0.010 0.005 0.000
LDPE
PP Acetal
Nylon 6/6
PMMA
100
120 140 160 180 200 220 240
Mold Temperature (F)
0.030 0.025 0.020 0.015 0.010 0.005 0.000
LDPE
PP with flow
PP across flow
Acetal
Nylon 6/6
PMMA
6000
10000
14000
18000
8000
12000
16000
Pressure on injection plunger (psi)
k
T x
(x
x')
h(TT)
The boundary condition of 1st kind applies to injection molding since the tool is often maintained at a constant temperature
Heat transfer