(1) Shape and wall thickness of plastic parts should be specially considered to facilitate smooth filling of cavity, avoid sharp corners and notches.
(2) Draft angle should be large, 1°to 2° for glass fiber 15%, and 2° to 3° for glass fiber 30%. When draft angle is not allowed, forced demoulding should be avoided, and horizontal split structure should be adopted.
(3) Pouring system should have a large section, process is straight and short to facilitate uniform dispersion of fibers.
(4) Design of feed inlet should be considered to prevent adverse consequences such as insufficient filling, anisotropic deformation, uneven distribution of glass fibers, and easy to produce weld marks. Feed port should be thin, wide, fan-shaped, ring-shaped and multi-point form feed port to make flow flow turbulent, glass fiber is evenly dispersed to reduce anisotropy. It is preferable not to use a needle-shaped feed port, cross section of feed port may be appropriately increased, and length thereof should be short.
(5) Mold core and cavity should have sufficient rigidity and strength.
(6) Mold should be hardened, polished, and wear-resistant steel grades should be selected. Wearable parts should be easy to replace.
(7) Ejection should be even and powerful, and it is easy to change.
(8) Mold shall be provided with an exhaust overflow tank and shall be located at a location where welds are likely to occur.

(1) Mold temperature affects injection molding cycle and forming quality. In actual operation, setting is started by using the lowest appropriate mold temperature of material, and then appropriately adjusted according to quality condition.
(2) Correctly speaking, mold temperature refers to temperature of cavity surface when forming is carried out. In mold design and setting conditions of forming engineering, it is important to maintain not only proper temperature but also uniform distribution.
(3) Uneven mold temperature distribution, which will lead to uneven shrinkage and internal stress, thus making forming port susceptible to deformation and warpage.
(4) Improve mold temperature to achieve following effects
1 Increase crystallinity of molded products and a relatively uniform structure.
2 Mold shrinkage is sufficient, and rear shrinkage is reduced.
3 Improve strength and heat resistance of molded products.
4 Reduce internal stress residual, molecular alignment and deformation.
5 Reduce flow impedance during filling and reduce pressure loss.
6 Make appearance of molded products more lustrous.
7 Increase chance of burrs on molded products.
8 Increase chance of depression near gate and reduce depression of far gate.
9 Reduce obvious degree of bonding line
10 Increase cooling time.

 

(1) In molding processing method, control (metering) of injection amount and uniform melting (plasticization) of plastic are performed by a plasticizing unit of injection machine.

Although melting of plastic, about 60-85% is due to thermal energy generated by rotation of screw, molten state of plastic is still affected by temperature of heating cylinder, especially temperature near front region of nozzle. When temperature in the front region is too high, it is prone to dripping and phenomenon of wire drawing when article is taken out.

A. Melting of plastic is generally due to heat generated by rotation of screw. So if screw speed is too fast, it has following effects:
a. Thermal decomposition of plastics.
b. Glass fiber (fiber plastic) is shortened.
c. Screw or heating cylinder wears up faster.
B. Setting of speed can be measured by speed of peripheral speed:
Peripheral speed = n (speed) * d (diameter) * π (pi)
Generally, for plastics with low viscosity and good thermal stability, circumferential speed of screw rod rotation can be set to about 1 m/s, but plastic with poor thermal stability should be as low as 0.1 or so.
C. In practical applications, we can reduce screw speed as much as possible so that rotary feed can be completed before mold is opened.

A. When screw is rotated and fed, pressure accumulated by melt propelled to front end of screw is called back pressure. During injection molding, it can be adjusted by adjusting oil pressure of injection hydraulic cylinder. Back pressure can have following effect:
a. More uniform melting.
b. Toner and filler are more evenly dispersed.
c. Let gas exit from drop opening.
d. Measurement of feed is accurate.
B. Level of back pressure is determined by viscosity of plastic and its thermal stability. Too high back pressure prolongs feed time and also tends to overheat plastic due to increased rotational shear force. Generally, it is preferably from 5 to 15 kg/cm2.

A. Before screw rotation feed starts, screw can be properly withdrawn, which can reduce pressure of front end of mold. This is called front loosening. Effect is to prevent pressure of melt of nozzle portion on the screw and it is mostly used for molding of hot runner mold.
B. After screw rotary feed is finished, screw can be properly withdrawn, so that melt pressure at the front end of screw can be lowered. This is called post-retraction, and effect is to prevent dripping of nozzle portion.
C. Insufficient, it is easy to make main channel (SPRUE) sticking; and if too much retreat, it can suck air and cause gas marks on molded products.