Assembly for holding plastic film within a mold
A mold tool includes upper and lower sections defining a cavity within which a plastic film preform is placed before injection of plastic forming a molded article. The plastic film extends between an interface defined between the sections of the mold. The interface secures a position of the plastic film within the mold tool preventing movement during injection of plastic. The interface is specifically configured to secure the plastic film without damage. The specific configuration of the interface is determined according to a relationship between molding process parameters and physical characteristics of the plastic film.
1. A method of securing a plastic film material within a mold comprising the steps of:
a. placing a preform comprising the plastic film material within a cavity defined by first and second mold sections;
b. placing a portion of said preform within an interface between said first and second mold sections;
c. sizing a maximun gap of said interface between said first and second mold sections according to a
m2
(
E
3
)
wherein m2=maximun plastic film thickness; and
E=Elongation as a percentage of plastic film thickness;
d. sizing a minimum gap of said interface between the first and second mold sections according to a relationship:
m1
[
2
(
i
L
)
]
wherein mi=minimum thickness of the plastic film;
L=compressive strenght of said plastic film; and
L=injection pressure of plastic into said cavity; and
e. sizing a width of said interface between said first and second mold sections according to a second relationship between said physical properties of said plastic film and process parameters.
2. A method of securing a plastic film material within a mold comprising the steps of:
a. placing a preform comprising the plastic film material within a cavity defined by first and second mold sections;
b. placing a portion of said preform within an interface between said first and second mold sections;
c. sizing a gap of said interface between said first and second mold sections according to a first relationship between physical properties of said plastic film and process parameters; and
d. sizing a width of said interface between said first and second mold sections according to the relationship:
[
(
H
*
j
)
(
f3
)
]
*
(
E
100
)
wherein: f3=clamping force of said mold tool;
H=length of said perimeter;
j=flexure strength of said plastic film; and
E=Elongation as a percentage of plastic film thickness.
3. The method of claim 1 , wherein said step d is further defined by determining a maximum of said width according to the relationship:
(
H
*
i
f1
)
wherein: f1=maximum clamping force of said mold tool;
H=length of said perimeter; and
i=compressive strength of said plastic film.
4. The method of claim 1 , wherein step d is further defined by determining a minimum of said width according to the relationship:
L
*
(
maximum
gap
)
*
H
n
wherein: m2=maximum plastic film thickness; and
E=Elongation as a percentage of plastic film thickness
H=length of said perimeter;
n=compressive modulus of said plastic film; and
L=injection pressure of plastic into said cavity.
5. A method of method of securing a plastic film material within a mold comprising the steps of:
a. placing a preform comprising the plastic film material within a cavity defined by first and second mold sections;
b. placing a portion of said preform within an interface between said first and second mold sections;
c. sizing a gap of said interface between said first and second mold sections according to a first relationship between physical properties of said plastic film and process parameters, and
d. sizing a width of said interface between said first and second mold sections according to a second relationship between said physical properties of said plastic film and process parameters, wherein one of said physical properties utilized for said step of sizing said gap and sizing said width include an elongation property of said plastic film and one of said process parameters utilized for said step of sizing said gap and sizing said width includes clamping force applied between the first and second mold sections.
6. The method as recited in claim 5 , wherein one of said process parameters utilized for said step c. includes injection pressure of a molten material injected into the mold.