Clamping Force F = P1 * Projected Area (P1: Injection Pressure)
However, actual clamping force varies due to properties of plastic material itself, mold design and injection operation conditions. Generally, actual clamping force constant needs to be multiplied by ratio of general engineering plastics by about 2-3.
Actual clamping force = P1 * Projected Area * Clamping force constant

Generally about 1/15-1/20 of clamping force

If product height is 150mm and runner (gate) height is 50mm, then mold opening stroke is: 2*150+50=350(mm)
h0>2h1+h2,
h0: mold opening stroke (Wrepin)
H1: product height
H2: runner height

 

Mold opening stroke plus mold thickness is mold capacity

Actual injection volume = theoretical injection volume * stroke efficiency (P)
P≈0.8-0.95 (depending on fluidity of plastic)
Also, check valve cannot achieve 100% function
Generally, weight of molded product is about 30%-70% of maximum injection volume

For same hydraulic system, injection pressure of small screw is higher than that of large screw.

unit: Kg: cm = injection pressure (p*Kg/cm')* stroke volume

cm/sec3

 

Screw should have a sufficient length to ensure uniform plasticization of plastic and maintain a gradual temperature difference for heat-sensitive materials. General L/D ratio is 16-22. A higher L/D ratio brings extra time and energy waste. A smaller L/D ratio has an effective length that is affected, which will affect uniform plasticization effect.
During plasticization process, screw rotates to push plastic forward, so relationship between screw and plastic is like a nut and a bolt. Plastic is nut and screw is the bolt, but plastic cannot rotate with screw. Therefore, in order to make plastic effectively transmitted, there must be sufficient friction between plastic and inner wall of barrel to prevent plastic and screw from rotating at the same time. On the other hand, screw surface must be very smooth to reduce resistance between plastic and screw.

Compression ratio is depth of screw groove in feeding section: depth of screw groove in metering section. General thermoplastic molding compression ratio is 2:1 4:1, which mainly depends on volume coefficient of plastic. The higher compression ratio, the higher temperature of plastic in barrel during plasticization process. In addition, plasticization mixing degree is more uniform, but relative discharge volume is also reduced.

Plastic suppliers generally provide appropriate RPM for reference, and size of screw will also affect selection of RPM.
Small screw: Groove depth is shallow, so plastic absorbs heat source quickly, which is enough to promote softening of reverse material in compression section. In addition, friction heat energy between screw and material tube wall is low. Therefore, a higher RPM can be used to increase plasticization capacity:
Large screw: On the contrary, it is not suitable for high RPM to avoid uneven plasticization and excessive friction heat.

Injection speed 1: Time from injection to gate is set at high speed to shorten molding cycle.

 

Injection speed 2: To prevent bad phenomena near gate, resin speed is generally reduced here.
Injection speed 3: To prevent bad phenomena such as warping and fusion lines, this part will be injected at high speed.
Injection speed 4: To prevent bad phenomena such as burrs and air inclusions, injection speed is reduced slightly before filling. Secondary pressure switching position S4: To prevent bad phenomena such as burrs and over-pressure, switch to secondary pressure before filling.
Holding pressure flow rate:
Increase or decrease according to situation of mold filling when switching secondary pressure. Setting too large will only waste energy; setting too small will not reach set holding pressure and mold will not be filled.

 

Injection pressure: Set high pressure to stabilize injection speed.
Secondary injection pressure: To prevent bending and cracking caused by residual stress or poor separation caused by over-holding pressure, holding pressure value should be kept decreasing
Example 1: When mold thickness changes in mold cavity and thin part has poor exhaust, it will cause gas combustion.

 

Air in mold cavity, air contained in molten plastic are surrounded and cannot escape, and become adiabatically compressed to form high-temperature gas, causing combustion. At this time, reducing injection speed near poor exhaust can solve this problem.
In addition, reducing injection speed in area after filling can make exhaust easier to prevent gas combustion.
Example 2. Thin and deep objects are prone to skew during molding.

 

As shown in figure, you should first inject at a low speed until mold core is fully filled and mold core is relatively stable, then inject at a high speed to avoid undesirable phenomenon of skewness.
Example 3. Flow marks, warping defects

 

To prevent resin in mold cavity from falling, speed setting value (as shown in figure) is gradually increased, and speed of each area in mold cavity is kept constant as much as possible.
Example 4. There are stains, silver bars, burns and other defects near gate.

 

Defects near gate are mainly caused by spraying (ictting) when resin passes through or resin is heated or decomposed due to shear.
In this case, injection speed can be reduced when molten plastic passes through gate, then injection speed can be increased after passing through gate.
Example 5. Thickness of mold cavity is uneven, and dents are generated in thick part

 

Dents are caused by shrinkage during cooling and solidification process. Solution is to reduce injection speed when melt has dents in thick part. At this time, a thicker solidified layer will be formed in thick part, and solidification has a higher density, so undesirable phenomenon of dents can be improved.

Example 1. High holding pressure applied to improve defects such as dents and bubbles will cause excessive residual stress.

 

High holding pressure will cause considerable residual stress inside finished product, cause small cutting marks and cracks on the surface of finished product. In this case, holding pressure can be improved by gradually reducing it before gate solidifies (gate seal).
Example 2. Improper mold or insufficient molding force causes burrs, and there are dents. When there are concerns about weld lines:

 

Improvement of burrs can be improved by controlling injection speed (described separately). If you want to control it by holding pressure, you can lower initial holding pressure, slowly increase holding pressure after cooling and solidification until there is a considerable solidified layer on the surface.

Example 1: During molding, sometimes high-speed injection cannot be used due to undesirable phenomena such as overfilled mold, thus increasing molding cycle time.
Generally, burrs are mainly caused by improper molds, insufficient molding force, etc., and burrs under a certain stroke can be controlled by adjusting injection speed.

 

Gradually reduce injection speed where burrs occur to increase thickness of solidified layer in burr-occurring area.