Difference Producing Injection Molds Process in China
Co-injection(sandwich)molding
Fusible(lost, soluble)core injection molding
Gas-assisted injection molding
In-mold decoration and in-mold lamination
Injection-compression molding
Insert and outsert molding
Lamellar (microlayer) injection molding
Low-pressure injection molding
Microinjection molding
Microcellular molding
Multicomponent injection molding(overmolding)
Multiple live-feed injection molding
Powder injection molding
Push-Pull injection molding
Reaction injection molding
Resin transfer molding
Rheomolding
Structural foam injection molding
Structural reaction injection molding
Thin-wall molding
Vibration gas injection molding
Water-assisted injection molding
Rubber injection
Injection molding of liquid silicone rubber
Injection Molding Cycle
The Injection molding is a cyclic operation. The cycle consists of
• Mould close and clamp, (few seconds -depends on machine speeds)
• Injection – Fill (speed) phase, (few seconds) Switchover and Pack (pressure) phase,(few seconds)
• Cooling time, (40 to 60% of cycle time)
We make thousands of plastic molds for our customers. But injection molding is a complex technology with possible production problems. They can either be caused by defects in the molds or more often by injection molded part processing (molding).—following date sheet learns from our American same trade from the internet.
Tolerances and Surfaces
Precision plastic mold processing machine is not selected as the achievable accuracy is not the same, and now the CNC, 0.002MM, EDM, 0.01MM wire walking 0.005MM, hand milling 0.02MM, drilling 0.05MM, grinders 0.005MM, Turning 0.01MM, each is different. You have to question what is it which machining accuracy? Chinese professional mold company can machine precision molds
Cooling for injection molds
The temperature of the mold plastic molding directly affects production efficiency and quality. The temperature is generally in the plastic are required about 200 ○ C by an injection machine nozzle to the mold injecting the melt in the mold about 60 ○ C curing, stripping, the heat radiation except for a few, other than the flowing atmosphere, a large part of the cooling water is introduced into the mold to take.ABS required mold temperature is low ( less than 80 ○ C), and therefore only needs to set the mold cooling system.
1.1 The importance of the mold temperature adjustment
1.1.1 The mold temperature and regulation systems for plastic parts quality. Mold temperature stability, the uniform cooling rate can reduce the volatility of plastic mold shrinkage is the reduction of plastic deformation of the fundamental conditions to ensure dimensional stability.
1.1.2 The mold temperature and regulation systems for production efficiency. The experimental results show that the injection molding of plastic melt in a stable injection temperature of 200 ○ C reduced 60 ○ C. The heat released is in the 5% radiation convection emitted to the atmosphere. And the remaining 95% of the heat is taken away by the cooling medium ( water). The mold cooling time in general throughout the injection cycle of approximately 2 /3. Showing the injection mold production efficiency mainly depends on the cooling time.
1.2 Calculation of the cooling system
Plastic passed to heat the mold
According to the formula [4]: Q = nmq
Wherein Q- unit time to pass the plastic mold heat (kJ / h); n- number of injections per hour; m- injection amount of each plastic, including casting system (kg);
q- unit time of the plastic in the cavity the heat (kJ / kg), q value by the following formula to get: q = Cp (θ1-θ0) where: Cp- plastic heat capacity (kJ / kg · k) its check the value of “practical Mould Technology Handbook” table 12-3; θ1- filling plastic melt temperature (○ C); θ0- plastic mold temperature (○ C).
n = 3600/40 = 90
m = 0.051kg
Cp = 1.47 (kJ / kg · k)
θ1 = 200 ○ C
θ0 = 60 ○ C
Then Q = 90 × 0.051 × 1.47 × (200-60)
= 944.622 (kJ / h)
The heat removed by the cooling water.
According to the formula [4]: Qw = 95% Q, Where: Qw- unit time within the mold cooling water away from the heat (kJ / h);
Q- unit time passed plastic mold heat (kJ / h).Then Qw = 0.95 × 463.05= 897.390 (KJ / h)
Heat transfer area ( cooling water table wall area).
According to the formula [4]: Aw = Qw/3.6hwΔθ
Where: Aw- heat transfer area ( cooling water table wall area ) (m2);
how- cooling water wearing their wall heat transfer coefficient ;
Δθ- the average temperature of the mold cavity surface temperature of the cooling water. The difference between the average (○ C), wherein the cooling water temperature is the average of the cooling water inlet, and outlet temperatures averaged.
hw = 2041 (1 +0.015 Qw-) V0.87/dw0.13
Where: DW- cooling channel diameter ( mm ) ;
V- cooling water flow rate (m / s);
Qw – the average temperature of the cooling water (○ C).
Qw = 439.9 (kJ / h)
hw = 2041 × (1 +0.015 × 40) × 1.660.87/80.13
= 2041 × 1.6 × 1.55 ÷ 1.31
= 3863.9
Δθ = 10 (○ C)
Then Aw = 897.390 ÷ 3.6 ÷ 3863.9 ÷ 10
= 0.006 (m2)
14.2.4 The total length of the cooling water .
Lw = Aw / πdw
Where: Lw- cooling pipe total length.
Lw = 0.006 ÷ 3.14 ÷ 0.008
= 0.24 (m)
Conclusion
The calculated results show mold without the cooling pipe cooling. It is a thin-walled plastic part. So the mold cavity temperature is not very high, molded plastic parts can be cooled after themselves. But in order to shorten the molding cycle, improve production efficiency. The fixed template design mm diameter cooling channels, and put in the waterway diameter of 8 mm brass.
