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Basic Knowledge of Injection Molding Machine

1. The basic principle of injection molding.

The injection molding machine takes advantage of the nature that the plastic can melt into liquid after being heated to a specific temperature and injects the molten liquid into the closed mold cavity with high pressure. After cooling and shaping, open the mold and eject to get the desired plastic product.


2. The four elements of injection molding.

1) Plastic mold

2)Injection molding machine

3)Plastic material

4)Molding conditions

5)Plastic mold


3. Basic structure.

(1) Male mold (lower mold) male mold fixed plate, male mold auxiliary plate, ejector plate, male mold plate.

(2) Female mold (upper mold) female template, female mold fixed plate, into the rubber ring, positioning ring.

(3)Temperature balance system cooling, stabilize (balance) the mold temperature. Most of them use the two-plate mold, three-plate mold, and some of them have a sliding block of line position mold.


4. Injection molding machine mainly consists of plasticizing and injecting device, mold closing device, and transmission mechanism. Electrical drive motor, motor drive oil pump, oil pump generates oil pressure. Oil pressure drives a piston. The piston drives machinery, and machinery generates action.

1) According to the injection method, it can be divided into:

A. Horizontal injection molding machine

B. Vertical injection molding machine

C. Angle injection molding machine

D. Multi-color injection molding machine.


2) According to the clamping method, it can be divided into:

A. Direct pressure injection molding machine

B. Crankshaft type injection molding machine

C. Direct-pressure, crankshaft compound type.


3) According to the feeding method, it can be divided into:

A. Plunger type injection molding machine

B. Single-pass screw injection molding machine

C. Reciprocating screw injection molding machine.


4) Injection molding machine four systems:

(1) Injection system.

a. Multi-stage, agitation, and corrosion resistance.

b. Injection speed, injection, holding pressure, back pressure, screw speed segmentation control.

c. Stirring, long-life screw device.

d. Interchangeability of material tubes and automatic cleaning.

e. Balance and stability of oil pump.


(2) Mold clamping system.

a. High speed, high steel.

b. Automatic mold adjustment and mold change device.

c. Automatic lubrication system.

d. Balance and stability.


(3) Oil pressure system.

a. Full electronic feedback control.

b. Smooth action, high stability, closed.

c. Fast, energy-saving.

d. Hydraulic oil cooling, self-filtering system.


(4) Electronic control system.

a. Multi-stage, with memory, expansion of the microcomputer control.

b. Closed-loop circuit and loop.

c. SSR (proportional, integral, differential) temperature control.

d. Self-diagnosis. Alarm function.

e. Automatic production quality control and record.


The injection molding machine has three debugging steps:

1. Parameters need to confirm and prepared for setting parameters before setting.

(1) Confirm whether the material drying, mold temperature, and heating temperature are set correctly and reach the processable state.

(2) Check the action and distance settings for opening and closing the mold and ejecting.

(3) Set the injection pressure (P1) at 60% of the maximum value.

(4) Hold pressure (PH) is set at 30% of the maximum value.

(5) Injection speed (V1) is set at 40% of the maximum value.

(6) Screw speed (VS) is set at approximately 60 RPM.

(7) Back pressure (PB) is set at approximately 10 kg/cm2.

(8) Loose retraction is set at about 3 mm.

(9) The position of holding pressure switching is set at 30% of the screw diameter. For example, for a φ100mm screw, set 30 mm.

(10) The total injection time is set slightly shorter, and the cooling time is set slightly longer.


2. Manual operation parameter correction.

(1) Lock the mold (to confirm high-pressure rise) and advance the injection seat.

(2) Shoot out manually until the screw stops completely, and pay attention to the stop position.

(3)Screw rotates back into the material.

(4)Allow to cool down and open the mold to remove the molded products.

(5) Repeat steps (1) – (4), the screw finally stops at 10%-20% of the screw diameter, and the molded product has no short shot, burrs, and whitening, or cracking.


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