What is Molding Clamping Force

Clamping force refers to the force applied to a mold by the clamping unit of an injection molding machine. In order to keep the mold closed, this force must oppose the separating force, caused by the injection of molten plastic into the mold.

The factors that affect the specific clamping force of the mold are the projected area of the product and the runner on the parting surface, the number and position of the gate, the size of the gate, the viscosity of the plastic, the flow length ratio, the injection speed and other molding conditions.

Here are two methods to calculate the clamping force:

1.Assumed a product is made in PC, 103mm long and 63mm wide, 4 cavities in one mold, the length of the flowing end of the gate is 60mm, and the thickness is 0.8mm

Step 1: Calculate the projected area: 103*63*4=25965mm2=259.65cm2 (projected area)

Step 2: Calculate the flow length ratio: (flow length) 60 / (thickness) 0.8=75

Step 3: Look up the mold pressure table: 75=250

Step 4: 250 (in-mold pressure) *2.0 (check table for material viscosity coefficient) = 500 bar (in-mold pressure of PC)

Step 5: 500bar*1.02=510 kgf/cm2 (1bar=1.02kgf/cm2)

Step 6: The clamping force is 510*259.65=132421kgf=132.4Ton

The above method is more accurate but requires some auxiliary tables to find it. There is another simpler way to quickly calculate the approximate clamping force and combine experience to get it, that is, the projected area is multiplied by the coefficient of the material. The size can be determined empirically according to the thickness and structure of the product.

2. Similarly in the above example, the coefficient of PC material is 0.465-0.775Ton/cm2. Since the flow length value is not large, 0.55 can be taken below the middle, then the clamping force is 0.55*259.65=142Ton, which is actually the simplified version of the above

What we commonly use now is ABS material. The in-mold pressure of ABS material is generally 0.3-0.48Ton/cm2, which is mainly related to flow length, thickness and structure.

If it is not thin-walled molding, the internal pressure of the general product ABS mold can be 0.3Ton/cm2. The theory requires machine = theoretical clamping force * safety factor (the clamping force required for general products is between 30-85% of the machine, so the safety factor is 100/85=1.17)

Hope you have a clear understanding about the clamping force, and as an professional injection mold manufacturer, we will share more information about molding process.

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