Injection Molding

Question 1

Injection molding advantages (3)

Answer 1

1.Huge Form Freedom
2.High production speed
3.great functional integration

Question 2

Chemistry

Answer 2

Made up of polymers (in plastics usually hydrocarbons)

Question 3

Types of Plastics

Answer 3

Amorphous
Semi-crystalline

Question 4

Amorphous

Answer 4

1.Randomly ordered molecular structure with no set melting point
2.soften slowly w/ increasing temp

Question 5

Semi-crystalline

Answer 5

Highly ordered molecular structure and sharp melting points

Question 6

Heating

Answer 6

Amorphous: dramatic loss of stiffness at glass transition temp (T_g)
At softening temp (T_s) the material is melted

Semi-Crystalline: loses stiffness at glass transition temp(T_g) but not as pronounced as amorphous
Loses strength at melting temp(T_m) - Material is melted(can’t be used)

Question 7

Plastic properties

Answer 7

1.melted plastics have high viscosity

2.Plastic stiffness usually low

3.Base strength around 40 MPA

4.strain-to-failure around 50%

Question 8

Pressure Difference =

Answer 8

[(12mu)/t_in](L/D)^2

mu: dynamic viscosity
L: length
D: diameter of mold
t_in: time to fill length

Question 9

cooling time =

Answer 9

(D^2 / pia) * Ln[(pi/4)TD]

D: diamter
a: lamda/(rho*c)
lamda: thermal conductivity
rho: density
c: specific heat
TD: (T_p - T_d)/(T_e - T_d)
T_p: melt processing temp
T_d: mold wall processing temp
T_e: ejection Temp

Question 10

Injection mold methods

Answer 10

1.Compact
2.Insert/Outsert Molding
3.Gas injection
4.In-Mold decoration (IMD)
5. 2K injection molding