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What Do We Need To Pay Attention To In The Design Of Automotive Injection Mold?
Oct 30, 2017

Automotive Injection Mold Metering and plasticizing

In the molding process, the control (metering) of the ejection volume and the uniform melting of the plastic (plasticizing) are performed by the plasticizing mechanism of the ejection machine.

1. Heating Tube Temperature

Although the melting of plastic, about 60--85% is due to the rotation of the heat generated by the screw, but the plastic melting state is still affected by the temperature of the heating cylinder, especially near the nozzle area of the temperature-the front of the temperature is too high when the drop and the removal of the workpiece when the phenomenon of wire.

Attentions of Automotive Injection Mold design

2. Screw speed

(1) The melting of plastics is generally caused by the rotation of the screw, so the screw speed is too fast, there are the following effects:

Thermal decomposition of ① plastics;

② Fiberglass (fiber reinforced plastic) shorter;

③ screw or heating drum wear faster.

(2) The speed of the setting, can be measured by the size of the circumference of the speed:

Circular speed =n (rotational speed) *d (diameter) *π (pi). Usually, low viscosity thermal stability of good plastic, its screw rod rotation of the circumference can be set to 1m/s up and down, but the thermal stability of the poor plastic, it should be as low as 0.1 or so.

(3) In practical application, we can adjust the screw speed as far as possible, so that the rotating feed can be completed before opening the die.

3. Back pressure

(1) when the screw rotating into the material, advancing to the front end of the melt adhesive pressure is called back pressure, in the Automotive Injection Molding, can be adjusted by the injection of oil cylinder pressure to adjust the back pressure can have the following effects:

① melts more uniform melt solution;

② color agents and fillers are more evenly dispersed;

The ③ causes the gas to exit from the blanking port;

Accurate metering of ④ feed;

(2) Back pressure, is based on the viscosity of plastic and its thermal stability to determine, too high back pressure to prolong the feed time, but also due to the increase in rotational shearing force, easy to make plastic overheating. Generally to 5--15kg/cm2 advisable.

Attentions of Automotive Injection Mold design

4, Loose back

(1) Screw rotary feed before starting, so that the appropriate withdrawal of the screw, can make the front end of the melt pressure in the mold, this is called the former loose back, its effect can prevent the nozzle part of the melt gum on the screw pressure, more for hot runner mold molding.

(2) screw rotary feed After the end, so that the appropriate withdrawal of screw rod, you can make the front end of the melt adhesive pressure, this is known as loose back, the effect can prevent the nozzle part of the drop material.

(3) Deficiencies, it is easy to make the mainstream channel (sprue) Visco-mold, and too many loose back, it can be sucked into the air, so that the formation of gas marks.

Second, Automotive Injection Mold design considerations

1, the top should be evenly strong, easy to change.

2, mold core, cavity should be sufficient rigidity and strength.

3, the mold should be hardened, polished, selected wear-resistant steel, easy to wear parts should be easily changed.

4, the mold should be equipped with exhaust overflow trough, and should be located in easy to occur weld trace parts.

5, the pouring system cross-section should be large, the flow is straight and short, in order to facilitate uniform dispersion of fiber.

6, the shape of plastic parts and wall thickness design should be considered in particular to facilitate the flow of filling cavity, as far as possible to avoid sharp corners, gaps.

7, demoulding slope should be large, glass fiber 15% desirable 1°~2°, including glass fiber 30% desirable 2°~3°. When the stripping slope is not allowed, the forced demoulding should be avoided and the transverse parting structure should be adopted.

8, the design feed mouth should be considered to prevent inadequate filling, anisotropic deformation, glass fiber distribution unevenness, easy to produce weld marks and other undesirable consequences. Feed mouth should be thin, wide thin, fan-shaped, annular and multi-point form feed into the mouth to make the flow turbulence, glass fiber evenly dispersed, to reduce the heterogeneity, it is best not to use the needle-like feed mouth, Feed mouth section can be properly enlarged, the length should be short.

Attentions of Automotive Injection Mold design

Third, mold temperature setting of Automotive Injection Mold

1, mold temperature influence the molding cycle and forming quality, in the actual operation is by the use of material minimum appropriate mold temperature to start setting, and then according to the quality of the appropriate adjustment.

2, the correct argument, the mold temperature is in the forming of the mold cavity surface temperature, in the mold design and forming engineering conditions, it is important not only to maintain the appropriate temperature, but also to allow its uniform distribution.

3, uneven mold temperature distribution, will lead to uneven contraction and internal stress, so that the formation of the mouth prone to deformation and warping.

4. The following effects can be obtained by increasing the mold temperature:

(1) Increase the crystallinity and the uniform structure of the forming product;

(2) The shrinkage of the molding is full and the shrinkage decreases;

(3) Improve the strength and heat resistance of molding products;

(4) Reducing internal stress residues, molecular distribution and deformation;

(5) Reduce the flow impedance of filling and reduce the pressure loss;

(6) Make the appearance of the forming products more shiny;

(7) Increase the chance of forming burrs;

(8) increasing the near gate and reducing the concave position of the far gate;

(9) Reducing the apparent degree of the binding line;

(10) Increase cooling time.

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