Injection Molding...
Posted by
Joseph A. Delgado
on 2000-02-05 08:31:59 UTC
Mario,
Yes I would need photos. That would be a big help.
To calculate the maximum injection pressure of the machine:
pie times the radius squared= area of cylinder x psi of air, divided by the
diameter of plunger.
Example: 6" air cylinder...3x3=9x3.1417=28.275 square inches, X 120 PSI shop
presssure=3,393 lbs of force. If the plunger is 1/2" in diameter, calculate
the area of the plunger, which is .25 x .25 x 3.1417=.1964 square inches.
Then take the area of the plunger (.1964) and divide into force (3393) and
the total force in PSI at the plunger is 3393/.1964= 17,276 PSI
This will be your maximum cavity presure in PSI, at 120 lbs of shop air
pressure.
Typically, a part thicker than .040" will require only about 1-2 tons of
clamp force for every square inch of part area to keep the mold shut.
Thinner parts will require as much as 5 tons per square inch of part area.
]
Film canisters are usually LDPE. Low Density Polyethylene.
Milk Jugs are usually HDPE Hight Density Polyethylene
Soda bottles are PET
Freezing some plastics will enhance grindability...BUT
Materials such as NYLON, ACETAL, POLYCARBONATE, will not become
any more brittle at freezing temperatures.
I suggest if you want any of these tougher materials, you simply buy a few
pounds.
Also a note..when using recycled plastics, you must be careful. There are
certain combinations, that when heated and put under pressure, will explode.
Stick with known items such as soda, milk jugs, or film canisters
Joseph
Yes I would need photos. That would be a big help.
To calculate the maximum injection pressure of the machine:
pie times the radius squared= area of cylinder x psi of air, divided by the
diameter of plunger.
Example: 6" air cylinder...3x3=9x3.1417=28.275 square inches, X 120 PSI shop
presssure=3,393 lbs of force. If the plunger is 1/2" in diameter, calculate
the area of the plunger, which is .25 x .25 x 3.1417=.1964 square inches.
Then take the area of the plunger (.1964) and divide into force (3393) and
the total force in PSI at the plunger is 3393/.1964= 17,276 PSI
This will be your maximum cavity presure in PSI, at 120 lbs of shop air
pressure.
Typically, a part thicker than .040" will require only about 1-2 tons of
clamp force for every square inch of part area to keep the mold shut.
Thinner parts will require as much as 5 tons per square inch of part area.
]
Film canisters are usually LDPE. Low Density Polyethylene.
Milk Jugs are usually HDPE Hight Density Polyethylene
Soda bottles are PET
Freezing some plastics will enhance grindability...BUT
Materials such as NYLON, ACETAL, POLYCARBONATE, will not become
any more brittle at freezing temperatures.
I suggest if you want any of these tougher materials, you simply buy a few
pounds.
Also a note..when using recycled plastics, you must be careful. There are
certain combinations, that when heated and put under pressure, will explode.
Stick with known items such as soda, milk jugs, or film canisters
Joseph
----- Original Message -----
From: <MIADsgns@...>
To: <CAD_CAM_EDM_DRO@onelist.com>
Sent: Saturday, February 05, 2000 1:47 AM
Subject: Re: [CAD_CAM_EDM_DRO] Injection Molds using CNC
> From: MIADsgns@...
>
> In a message dated 2/4/00 4:59:43 AM SA Eastern Standard Time,
ward@...
> writes:
>
> << > Also Mario, I would be glad to discuss your intended mod's to
facilitate
> auto clamping and ejection. >>
>
> Hi Joseph,
>
> Thanks you for that thought, I would appreciate any suggestions based on
> your expertise to modify my injection press.
>
> What information would you need, I can take pictures of the unit and send
it
> to you for better visualization.
>
> Also, talking about cavity pressures, is there a formula for figuring the
> required pressure based on cavity cubic area? I was told by the seller
that
> the machine I bought is a 1/2 ounce Injection Moulder, how can I reassure
> myself it is so and how can I figure what type of compressor is needed?
>
> Many Thanks,
>
> Mario
>
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