Size Matching Of Injection Machine And Mold - How To Calculate Size In An Injection Machine & Mold

In order to ensure a good match between the designed mold and the injection machine, please check the relevant data between them, and then design the mold and select the injection machine model. The verification aspects include:

1. Injection amount and injection pressure

2. Clamping force and installation dimension

3. Mold opening stroke

4. Ejection device

Here we provide some tips for matching your needs to the correct clamp and injection mold.


Verification Of Injection Glue Quantity

Whether the mold cavity can be filled with the maximum amount of glue injection allowed by the injection machine is related. If there is a local lack of glue in the finished product, the most likely reason is the insufficient injection amount. Therefore, when designing the mold, the total amount of glue required by the mold should be within the actual maximum injection volume of the injection machine, which is equivalent to 80% of the rated injection volume of the injection machine, because NM1 + M2 ≤ 80% M.

M1 – mass or volume of single finished product

M2 -the mass or volume of raw materials required by the injection system

M – the maximum injection volume allowed by the ejector (g or cm3)

N – number of cavities

Note: N is related to the plasticizing rate of the injection machine, the maximum injection volume and clamping force, as well as the precision of the finished product and the economy of production. Generally speaking, every additional cavity is added. The dimensional accuracy of the finished product is 4% ~ 8% lower, and the higher the mold cost.


Injection Pressure Check

This is to determine whether the maximum injection pressure of the injection machine can meet the needs of the molding of the plastic part. The injection pressure required for the finished product is determined by the type of injection machine, the form of nozzle, the fluidity of raw materials, the flow force of gating system and cavity, etc. If the injection pressure is insufficient, the short shot phenomenon will be formed.

Generally speaking, whether the injection pressure meets the requirements of the intermediate product can be controlled by the machine adjusting personnel, and it can not be adjusted too high to prevent the gate or the mold strength is not enough to be pressed and damaged or the mold parting is difficult.


Check Of Clamping Force

During injection molding, the projection area of the product on the parting surface of the mold is the main factor affecting the clamping force, and the clamping force is proportional to the projection surface. If the clamping force provided by the injection machine is less than that, the parting surface of the mold will not be closed tightly, and the contact and penetration will not be sufficient, so as to directly form the burr or overflow phenomenon. The tonnage type of the injection machine is determined by the clamping force, and the formula for calculating the tonnage required for the clamping force of the injection molding machine is as follows:

F1=(n A1+A2) P

A1 – maximum projected area of finished product, total length * total width, unit: cm2

A2 – projected area of the injection system, unit: cm2

P – pressure coefficient (high pressure: 0.75t/cm2, general pressure: 0.5t/cm2)

F1 – raw material pressure unit: ton

F1 ≤ 80% F F -locking force of injection molding machine


Check Of Installation Dimensions

In order to ensure that the mold can be installed smoothly, it is very important to check the installation size. In this link, designers often neglect the problem due to excessive reliance on computer operations. As a result, the mold cannot be tested on time.


1. Nozzle size:

The following relationships must be satisfied respectively between the diameter dn of the nozzle and the diameter dp of the rubber duct bushing, as well as between the radius rn of the convex spherical surface of the nozzle and the radius rp of the bush surface.

DP = DN + 1.0 mm


The effective injection length of the nozzle should match well with the sinking depth of the injection channel bushing of the mold, so as to prevent the nozzle head from being able to press against the bushing.


2. Spacer size:

The purpose of the application of positioning ring is to ensure that the center line of the mold can coincide with the nozzle and the central ejector rod of the injection machine, so that the injection molding must be carried out smoothly. A certain gap between the positioning ring DH and the center hole DJ of the casting machine fixed supporting plate is: DJ = DH + (0 ~ 0.2mm), and the thickness of the locating ring is 10mm high, which can contact with the center of the supporting plate.


3. Mold thickness:

Mold thickness must meet: Hmin < h=””><>

Hmin: minimum opening distance between moving and fixed supporting plates

Hmax: the maximum mold thickness allowed by the ejector

The clamping thickness of the injection machine is a range, and its value can be adjusted. 


4. Mold installation and fixed size:

The safety relationship between the total width WM of all moulds and the total space width WJ between the columns is Wm≦Wj-50mm. There are two common forms of mold fixation, one is to use the screw to fix (when the screw hole in the fixed position appears on the supporting plate). The other is to fix with screws and pressing plates. When fixing with pressing plates, it is necessary to ensure that the thickness difference between the front and rear plates is less than 5mm, so as to facilitate the use of the same type of pressing plates.


5. Check of mold opening stroke:

Mold opening stroke refers to the moving distance of the movable mold fixed plate during mold opening and closing. Its size directly affects the height of the finished product that the mold can form. If it is too small, the finished product cannot be taken out.


6. Check of ejector device:

● Verify the position of the KO hole opened on the mold according to the specific machine, and whether the hole diameter matches with the zone

● Verify whether the ejection distance of the injection machine meets the needs of the ejection action of the mold, especially in the mold structure of the second ejection, it is easy to produce insufficient ejection, and the ejector length is not as long as the first two pieces of ejection. Support column on the output board

● In the forced-return ejection mechanism, verify whether the mold screw is matched with the screw hole area of the ejector pin head of the injection machine.