Estimation method of "code mold strength" of upper mold of injection mold

Time:2022-11-16 08:46:38 / Popularity: / Source:

In the process of injection molding production, it is very necessary to tighten mold. If mold force is not enough, it is very common for mold to fall off during production, so how to calculate mold force?
How much force does upper molder in injection molding factory apply to code screw during mold? This is a problem. If force is too high, it will damage thread and code screw. If it is small, mold may fall off. So how much strength is good? This article gives the calculation formula.

1. Basis for estimation

(1) Mold is attached to machine board due to pressure of code, and mold screw is tightened under action of external force to generate a tensile force (Qp) that acts on code, static friction force F is generated between code and mold plate, as well as mold plate and positioning machine plate to overcome downward force generated by dead weight of mold ( G);
(2) To prevent mold from sliding down, it is required that F∑≧Ks "G...(1)
Assuming that preload required for each mold screw is Qp, screw is pressed in the middle of mold, and number of screws is 4. Considering safety of sometimes unilateral drop mold:
upper mold of injection mold 
In formula: f- friction coefficient between joint surfaces (0.10~0.16)
i-joint surface (i=2 in figure)
Ks-skid coefficient (Ks=1.1~1.3)
Qp - required preload of screw.
(3) According to calculation, torque T acting on screw and pre-tightening force Qp (tension) of screw have following relationship:
T≈Qp "d …(3) In formula: T-moment acting on screw d-screw diameter
According to formulas (2) and (2), we can get:
upper mold of injection mold 
Then: T≧0.4 "G "d …
(4) And T = F " L F≧0.4 "G "d/L
In formula: effective length of L-pipeline (ie sleeve);
G-die weight;
d-code die screw diameter;
F - force acting vertically on sleeve.

2. Estimation formula

Fmin=0.4 G "d/L, generally d is a fixed value, and there are three specifications: M16, M20, M24; according to different lengths of hoses and different weights of molds, minimum code force to be applied can be roughly estimated. (Appendix) Note: In table, F is minimum force acting vertically on sleeve, L is length of hose, and G is weight of mold.
① When using M16 screws (machines below 220T): (F unit: Kg)
Fmin G(kg)
200 400 600 800 1000
20 6.4 12.8 19.2 25.6 32.0
25 5.1 10.2 15.3 20.4 25.5
30 4.3 8.6 12.9 17.2 21.5
35 3.7 7.4 11.1 14.8 18.5
40 3.2 6.4 9.6 12.8 16.0
45 2.8 5.6 8.4 11.2 14.0
50 2.56 5.22 7.68 10.24 12.8
Remarks: According to statistics, for injection machines with a tonnage of 220T and below, general weight of injection molds is below 800kg.
② When using M20 screw (265 or more tonnage machine): (F unit: Kg)
Fmin (kg)
500 1000 1500 2000
40 10 20 30 40
45 8.9 17.9 26.7 35.6
50 8 16 24 32
55 7.3 14.5 21.8 29.1
60 6.7 13.4 20.1 26.8
③ When using M24 screws (for 850-ton machine only): (F unit: Kg)
Fmin G(kg)
1000 1500 2000 2500
50 19.2 28.8 38.6 48
60 16 24 32 40
70 13.7 20.5 27.6 34.2
80 12 18 24 30

3. Maximum size die strength check

Material used for general screws and machine boards is A3, strength level is 4.6, yield strength of screw is σs=240Mpa, safety factor is S=1.5, and allowable stress of screw hole material is:
It can be obtained: Tmax=[σ] " π/4 "d2 "0.2
When [σ]= 160Mpa, maximum torque acting on screw is as follows:
d(cm) Tmax( L(cm)×Fmax(kg)
16 (M16) 1000 30×33
20 (M20) 1560 40×40
24 (M24) 2250 55×40
Remarks: Maximum arm strength of a normal person is about 35-40kg.

4 Conclusion

(1) In order to prevent screw from being over torqued, we can limit length of sleeve;
M12 screw suitable for L=20~25CM
M16 screw suitable for L=25~30CM
M20 screw suitable for L=40~45CM
M24 screw suitable for L=50~55CM
(2) Screw thread depth H=1.5d, about 12 thread depths are enough, but it must exceed 9 thread depths. If machine plate thread is worn, it needs to be drilled correspondingly;
(3) It is necessary to regularly check whether screw teeth and threaded holes are deformed or damaged, replace and maintain them in time. In threaded holes, iron impurities on inner surface should be cleaned regularly, and screws can be easily put into sufficient depth without large load;
(4) According to difference of each person's arm force (average can be tested), applied force can be controlled; it is not advisable to use weight of the whole body to act on sleeve in order to prevent code from not tightening mold during upper mold.

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