How to calculate tonnage & injection pressure

Calculating tonnage in plastic molds can be complicated. It typically requires between 280 and 700 kg/cm squared (projected surface area) to mold a plastic part. A thick walled part with short flow length in an easy flow material (polypropylene, nylon, polyethylene, acetal, etc.) will require much less injection pressure and clamp tonnage than a thin walled part with long flow length in a low flow material (polycarbonate, PPS, highly glass filled materials, etc.). The mold need to have proper venting, runner, gates, and surface temperature control to mold with minimum pressure. This is not too difficult to calculate with simple parts, but can be extremely difficult when working with complex parts with different wall thicknesses and flow lengths from the gates. Mold filling programs like Moldflow are quite good at estimating injection pressure and clamp pressure with complex parts. There are companies that specialize in using mold simulation software that can help identify problems with plastic part designs before they are built into a mold that will not run properly.

my question is i use one mould use in 250 ton machine clamping force is 120 ton when this mould shift to 450 ton machine then how many claming force i use.

Same 120 T

This you can achive by adjusting the pressure valve

you need the same clamping force 120ton

what is Formulae of calculating machine tonnage of plastic mould, during designing a plastic mold.

Hi! I am a die cast process engineer and the formula I use is one called PQ^2. It tells me lock up tonnage needed, injection speeds (ips), shot pressures (psi), and shot positions. I'm sure you plastic guys must have some thing of the same. N.A.D.C.A. (North American Die Cast Asso.) has a good PQ^2 formula. Contact your local S.P.I. chapter.

I'd rather play with metal, though.

I see there have been a few people looking at this one but not responding. I'll chip in two cents worth just to add tot he collective knowledge.

Step 1: Calculate the projected area of the item you are moulding (including runner/sprue and so on) (By this I mean the area that will be covered in a flat plane representing the parting line.)

Step 2: Find the "peak pressure" that will be used in moulding the part. This may be within the injection part of the cycle, but may also be what some technicians call "pack" pressure (after cavity is filled, but before gate/sprue freezes off. This helps reduce sink marks at thick wall section interfaces.).

Step 3: (The easy bit) multiply area by pressure to get the ABSOLUTE minimum force that will hold the die closed during moulding. (Assuming everything is in balance/symetrical across the die face.)

Step 4: Add "safety factor" that will be determined by your moulding specialist to make sure die does not flash at parting lines.

Step 5: Then choose available machine with at least the necessary clamp force.

May I know how do you determine the peak pressure? Usually the peak pressure indicated by the machine when you are running the mold but right now I dont have a injection machine with me.

Perfect Answer !!!!!!!!

If you don't have the mould already built, then you will need to estimate the "peak pressure". This may be an operator set value if it's the pack pressure at the end of injection cycle, or it may be a dynamic value that happens during the injection cycle in which case you need to arrive at an estimate.

When we don't have a tool already built (like when we are quoting new business) we use data from a "similar" mould that we already run using similar material. The next best estimate is then to use the plastic supplier's recommended injection profile for the material and temperature settings that you intend to use.

Hi, Is it possible for you to advise the details of say the follow item as to what machine would be needed. The materal is PP, we encapsulate a DI Steel flange inside the PP. The OD of the finsihed item is 225mm, ID is 135mm, width 22mm. The DI item weight is 2.38kg, the finished item is 3.10kg, so the PP material is 0.36kg in weight. May thanks in advance.

hyeee just an Engineer ,, my area of component is 7341 sq.mm , and its a 6 cav inj mold and material is of pp. mould size is like 650 x 500 x 480 .

we r trying the mold in 318 tonnnage mold.. ders no gap in parting line and its matched dimensionally and with blue also . we confirmed no gap in parting line. still its flashing too much like 0.1 mm (flash thickness).. i doubt its coz of insufficient tonnage where the mould is loaded ...

can u pls exactly say me how to calculate tonnage for the above given parameters.

Thanks in Advance.. it wud be very needful for me..

Bye Gud day

Since this is a comment session, this is just a comment.

This is a six cavity mould. Therefore, projected area calculation might require considerations as to where is the gate point positioned and what is the maximum distance upto which the flow is requried. In simple words, if the cavitiy spacing or gap between each cavity is high for this size of mould, you may require even upto 400+ tonnage machine to fill this part without flash.

So I suggest calculate the projected area not on the component surface area, but on the total component surface area inculsive all cavities- outer dimension.