Definition :
Forming constitutes the stage of
treatment during which the sheet is softened in order to
have the shape of the shell of the mould. There exists three
great basic techniques to obtain this result:
evacuation of air so that the sheet adheres to the mould.
· the use of pressurized air to push the sheet against
the mould
· the use of a mechanical force (assisted by a plug
in particular)
These techniques can be employed together in any equipment
of standard forming according to the model of the part to
form.
According to the method of vacuum forming, the softened
sheet is brought back on the mould and is sealed checking
the flow against the mould. A vacuum pump is then used to
evacuate the air between the sheet and the mould; this technique
stretches and maintains the sheet against the mould. Only
agent of forming, the atmospheric pressure limited to I
bar, represents the principal disadvantage of vacuum forming.
It happens that the atmospheric pressure is not enough to
obtain cheese whenever the plasticity of the material is
poor and where it is necessary to obtain a high defnition
of the casting.
Cheese under pressure consists to push and maintain the
sheet against the mould by application of pressurized air.
II is then generally necessary to use a vacuum pump to evacuate
the residual air between the mould and the sheet. The application
of a mechanical force includes the use of matched moulds,
of plugs of reinforcement and gauges of spacing. The plugs
of reinforcement are machine elements used to help the sheet
to penetrate at the bottom of the mould or in the sectors
that are difficult to access. The plugs can be thermoprogrammed
according to the adopted technique of making cheese and
the model. It is generally about aluminium plugs which are
heated to the maximum of tolerance before adhesion or excessive
thinning of the part. If the temperature is too low, the
lower part of the part thickens and is then likely to harden
or adhere to the plug. The volume occupied by the plug compared
to the space of the cavity, the model and the speed of insertion
constitute other important factors with regard to the use
of plugs.
Cheese male/female
One says that thermoforming is male or female according
to whether draping is carried out in convex or concave moulds.
The male castings are sheets which are formed on the mould
and which consequently must be raised to the mould. Conversely
the female castings are formed in the mould and must be
extracted from the mould to the mould. Whatever the adopted
method, the piece is formed either "over" a male
mould, or "in" a female mould
French
Emmental
Selles
on Cher - AOC
Roquefort
Papillon - AOC
Blue
of Auvergne AOC
