Fórmulas essenciais de moldagem por injeção que todos os engenheiros devem conhecer

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There are countless injection molding formulas, and every engineer must remember each one.

Injection Molding Formulas Series 1

1. Clamping Force (F in TON):

The clamping force is determined by: F = (Am x Pv) / 1000 Where:

F is the clamping force in TON.
Am denotes the projected area of the mold cavity in cm^2.
Pv stands for the filling pressure, usually between 150-350 kg/cm^2. Materials with good flowability use a lower value, while those with poor flowability require a higher value.

For instance, if the mold cavity projected area is 270cm^2 and the filling pressure is 220kg/cm^2, the clamping force is: F = (270 x 220) / 1000 = 59.4TON

2. Injection Pressure (Pi in kg/cm^2):

The injection pressure is given by: Pi = (P x A) / Ao Where:

Pi is the injection pressure.
P represents the pump pressure.
A is the effective area of the injection cylinder.
Ao is the cross-sectional area of the screw, calculated as A = (π x D^2) / 4, with D being the diameter.

For a pump pressure of 75kg/cm^2, an effective injection cylinder area of 150cm^2, and a screw cross-sectional area of 15.9cm^2 (for a diameter of 45mm), the injection pressure is: Pi = (75 x 150) / 15.9 = 707 kg/cm^2

3. Injection Volume (V in cm^3):

The injection volume is: V = π x (Do/2)^2 x ST Where:

V is the injection volume.
Do denotes the screw diameter.
ST is the injection stroke.

For a screw diameter of 42mm and an injection stroke of 165mm, the injection volume is: V = π x (4.2/2)^2 x 16.5 = 228.6cm^3

4. Injection Weight (Vw in g):

The injection weight is: Vw = V x η x δ Where:

Vw is the injection weight.
V is the injection volume.
η stands for the specific gravity of the material.
δ represents the mechanical efficiency.

Given an injection volume of 228.6cm^3, a mechanical efficiency of 0.85, and a specific gravity of 0.92, the injection weight is: Vw = 228.6 x 0.85 x 0.92 = 178.7g

5. Injection Speed (S in cm/sec):

The injection speed is: S = Q / A Where:

S is the injection speed.
A denotes the effective area of the injection cylinder.
Q is the pump discharge volume per revolution.

For a motor speed of 1000RPM, a pump discharge volume of 85 cc/RPM, and an effective injection cylinder area of 140 cm^2, the injection speed is: S = (85 x 1000) / (60 x 140) = 10.1 cm/sec

6. Injection Rate (Sv in g/sec):

The injection rate is: Sv = S x Ao Where:

Sv is the injection rate.
S represents the injection speed.
Ao is the cross-sectional area of the screw.

For an injection speed of 10cm/sec and a screw diameter of 42mm, the injection rate is: Sv = 13.85 x 10 = 138.5g/sec

These formulas offer a foundational grasp of the pivotal parameters in injection molding, ensuring optimal results in the molding process.

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Injection Molding Formulas Series 2

1. Theoretical Injection Volume:

Using the constant π/4 = 0.785:

Theoretical Injection Volume (cm³) = Screw Diameter² x 0.785 x Injection Stroke.
Injection Stroke (cm) = Theoretical Injection Volume / (0.785 x Screw Diameter).

2. Injection Weight:

Injection Weight (gr) = Theoretical Injection Volume x Plastic Specific Gravity x Injection Constant (0.95).

3. Injection Pressure:

Injection Pressure (kg/cm²) = (Injection Cylinder Area² / Screw Area²) x System Maximum Pressure (140kg/cm²)².
Injection Pressure (kg/cm²) = (Injection Cylinder Diameter² / Screw Diameter²) x System Maximum Pressure (140kg/cm²).
Injection Pressure (kg/cm²) = Maximum Injection Pressure of the Barrel Assembly x Actual Usage Pressure (kg/cm²) / System Maximum Pressure (140kg/cm²).

4. Injection Rate:

Injection Rate (cm³/sec) = Screw Area (cm²) x Injection Speed (cm/sec).
Injection Speed (cm³/sec) = Screw Diameter (cm²) x 0.785 x Injection Speed (cm/sec).

5. Injection Speed:

Injection Speed (cm/sec) = Injection Rate (cm³/sec) / Screw Area (cm²).
Injection Speed (cm/sec) = Pump Single Turn Volume (cc/rev) x Motor Speed (rev/sec) / 60 seconds / Injection Area (cm²).

Motor Speed RPM: 60HZ – 1150, 50HZ – 958.

6. Injection Cylinder Area:

Injection Cylinder Area (cm²) = Injection Pressure (kg/cm²) / System Maximum Pressure (140kg/cm²) x Barrel Area (cm²).
For a single cylinder: Injection Cylinder Area (cm²) = (Injection Cylinder Diameter² – Piston Diameter²) x 0.785.
For a double cylinder: Injection Cylinder Area (cm²) = (Injection Cylinder Diameter² – Piston Diameter²) x 0.785 x 2.

7. Pump Single Turn Volume:

Pump Single Turn Volume (cc/sec) = Injection Cylinder Area (cm²) x Injection Speed (cm/sec) x 60 seconds / Motor Speed.

Motor Speed RPM: 60HZ – 1150, 50HZ – 958.

8. Screw Speed and Hydraulic Motor Single Turn Volume:

Screw Speed = Pump Single Turn Volume (cc/rec) x Motor Speed (RPM) / Hydraulic Motor Single Turn Volume.
Hydraulic Motor Single Turn Volume = Pump Single Turn Volume (cc/rec) x Motor Speed (RPM) / Screw Speed.

9. Total Injection Pressure:

Total Injection Pressure (kg) = System Maximum Pressure (kg/cm²) x Injection Cylinder Area (cm²).
Total Injection Pressure (kg) = Injection Pressure (kg/cm²) x Screw Area (cm²).

1 ounce (oz) = 28.375 grams (gr).
1 pound (lb) = 16 ounces (oz).
1 kilogram (kg) = 2.2 pounds (lb); thus, 1 jin = 1.1 pounds.
1 pound (lb) = 454 grams (gr) = 0.454 kilograms (kg).

11. Clamping Force:

For toggle type: Clamping Force (Ton) = Clamping Cylinder Area (cm²) x System Maximum Pressure (140kg/cm²) / 1000 x Toggle Magnification Rate (20-50).
For single cylinder direct pressure type: Clamping Force (Ton) = Clamping Cylinder Area (cm²) x System Maximum Pressure (140kg/cm²) / 1000.

12. Pillar Diameter and Clamping Force Formula:

Pillar Diameter² (cm²) x 0.785 x Young’s Modulus (scm4 approx. 1000kg/cm²) x 4 = Approximate Clamping Force (Ton).

13. Product Layout Projection Area and Clamping Force Relationship Formula:

Product Layout Projection Area (in²) x Standard Thickness (1.5mm) / Average Product Thickness (mm) x Material Constant / PS Material Constant (1) = Clamping Force (Ton).