Exact mold tonnage requirement?

The formula that I was taught is to take the projected surface area of the part, and multiply it by the recommended tonnage per sq. in. or mm. I believe the HDPE we used required 3-4 tons per sq. inch. This will give you the minimum needed to keep the mold closed. However, if the plastic pressure overcomes the clamp force, you will flash your mold.

It`s a hotrunner mold.
Ejection Hydro-mechanical.
Low pressure mold close distance is 7 to 3mm
Plates are 32mm thick.
Component wall thickness is 1.4mm.

Other things to consider

Runner system -
traditional runner = overall exposed surface area
Hot runner = 0 = no exposed surface area

Plate thickness - even with small parts, if your plates are thin, they'll bend unevenly under clamp because of the preload. This will give you the impression of (1) not enough clamp or (2) warped/non-square plates.

Slides and mechanisms
- Dependent on the of movement of the mold (add in surface area)
- Hydraulic = 0

Shutoff/preload
If you are shutting off on the mold face alone, you'll distribute the tonnage over a large surface area (you'll need more tonnage than you think)

If you are shutting off on a perimeter = 5-10 mm around each cavity and 50-75 mm around each guide pin, you'll have the best use of your clamp tonnage.

NOW THE SILLY BITS
(1) The mold has to be square under full clamp (not only the mold plates but also any nicks in the platen that will cause the mold to 'tilt')
(2) The Platens have to be square (look for scoring on the tie rods)
(3) The tie rods on the machine must stretch evenly (with a square mold and square platen, measure the stretch with a feeler gauge - each rod should stretch within 5% of the over all average)

While you can measure each of these, if everything isn't square or the pressure (tie rod stretch) isn't even, it will fool you into believing you don't have enough clamp.

If you are simply trying to fit a mold into a press, I've given you too much info. When it gets into the press and complaints come that they can't hold it closed, I've given you the reasons. Once you try it out under maximum clamp pressure, lower the clamp pressure until you find the minimum amount required. This will lengthen the life of the mold.

Hope this helps

Bill

(surface area of the molded parts (in) x plasic pressure in the cavity)/2000.

2000 lbs = 1 ton

Other things to take into consideration = wall thickness, draw, etc.