How to calculate injection moulding clamping force?

Injection pressure x active area in the separation plane of mold x safety coefficient( ≥1.5).

Hi,

I'm also facing the problem of determine the clamping force.

In my situation, i have to calculate the clamping force then choose a suitable type of injection molding machine which close to allowable clamping force of the machine. Injection pressure is one of the variable (in my situation) then i can't use the formula with injection pressure. So is there any formula to calculate the clamping force without using the injection pressure?

Thanks

Regards,

Low

Hello,

I will take a stab at a reply.

You really need to supply more info as each Polymer has a different recommended tonnage per square inch value. This is given by the material manufacturer. Sources below.

We use a huge amount of Polypropylene copolymer. So here is the method of calculation specifically for it. It will flash out with a gap of .0008"-.0012" between the faces of the mold.

Calculation square area" x a tonnage factor given by material mfg

Calculate, closely, the projected surface area of the product to be molded.

That is the projected surface of the part sitting perpendicular to the parting-line of the mold.

Subtract any areas where there are throughholes.

Add in for the runner and gate projected area.

Multiply by 2.25 for any PP or PE and you will have the tonnage needed.

Example: part length x width = 2" x 26"= 52"square - (window areas: 0.2" x 10"= 2" sq + (runner and gate 1/4" x 8"= 2"sq) = 52"sq - 2"sq + 2"sq= 52"sq x 2.25 tons per sq inch= 117 tons.

So now you have the tonnage.

Consideration 1.

Your next consideration is. Can you fit that size of mold between the tie bars of a standard 125 Ton machine. If you can, well and good. Physical Mold size.

Consideration 2.

Then the next consideration is whether the Machine that you must use has a barrel that will plasticize the amount of material that you need to fill the part.

This is tricky. If you are pushed to using a large machine to get the Platen size you need, you may end up with a much larger barrel than necessary. Barrel Size (Vol)

Consideration 3.

Whence you have to consider the residence time in the barrel before the material is used as you may cook the ---- out of the material. Based on the weight of the part.

Lastly:

Here is another sample at the other end of the spectrum. The specific calc for Thermoplastic Elastomer (Rubbery material). You need a minimum of 4 tons per square inch and 5 tons per square inch is recommended. Rubber will flash out of a gap of 0.0005" between the faces of the mold.

Engineering materials typically need less tonnage per square inch eg. Ultem or Glass filled nylons etc. It will flash out with a gap of .0015-.002" between the faces.

LCP or Liquid chrystalline Polymers need hot molds, slightly higher tonnage as the cavity is filled with boost and there is no hold time needed as it sets up so fast. This material likes to travel in straight lines and short flowlengths.

Use www.matweb.com or www.ticona.com for material info and find the recommended molding clamping tonnage recommended.

Great answer 2tinker,

Now, the square area is for each cavity ?? I'm in the process to calculate the machine tonnage for part made of Zytel 70G33L

Thanks for your help

Ed2009

HELLO,

OP WHERE ARE YOU?

Houston we've got a problem!

or is it,

Car 54 where are you?

I give up. Op I hope you get the point.

how do I determine tonnage from tie bar stretch on a toggle machine

Firstly, maybe the OP was after the actual clamp force in a machine rather than the "required" clamp for a particular mould tool. In which case they would need to know their hydraulic pressure and cylinder dimensions if it was an hydraulic machine.

And for the request for tie bar stretch, use the "SEARCH CR4" option using tie bar stretch. There has been a discussion in the last fortnight discussing that including lengthy and knowledgable calculations from many experts.

http://www.custompartnet.com/calculator/clamp-force