Method for determining an actual volume of an injection moldable compound in an injection molding process
A method for determining an actual volume Vr of an injection-moldable compound during an injection-molding process is disclosed. The injection-moldable compound is introduced into at least one cavity of the mould. The method includes the steps of: a) determining a theoretical volume Vt from process variables at least during a filling phase of the injection-molding process, b) determining and/or measuring at least one value for at least one compound pressure pM, c) selecting a material-specific compression k (p), corresponding to the value of pM, of the injection-moldable compound, and d) calculating an actual volume Vr by taking into account the compression k (p).
1. A method for determining an actual volume V r of an injection-moldable compound during an injection molding process, comprising:
determining a theoretical volume V t from process variables as the injection-moldable compound is introduced into a cavity of a mold during a filling phase of the injection molding process;
determining and/or measuring at least one value for at least one compound pressure p M ;
selecting a material-specific compression k(p) in correspondence to the value of the compound pressure p M of the injection-moldable compound;
calculating an actual volume V r as a function of the material-specific compression k(p), wherein the material-specific compression k(p) of the injection-moldable compound is selected from an adiabatic compression curve k(p);
adapting machine parameters during a pressure-regulated holding pressure phase to realize an ideal actual filling volume ΔV ri by adjusting a holding pressure;
determining a theoretical switch-over volume V tXfrL in a cycle, and switching-over to a holding pressure phase in the cycle when the theoretical switch-over volume V tXfrL is reached;
determining a theoretical reference volume V tRefL at a reference pressure value p Ref in the cycle;
determining in a production cycle downstream from the cycle, a theoretical reference volume V tRefP of the production cycle at the same reference pressure value p Ref ; and
determining an actual switch-over filling volume ΔV rXfrL in the cycle in accordance with the following formula:
Δ
V
rXfrL
=
V
tRefL
1
-
k
(
p
Ref
)
-
V
tXfrL
1
-
k
(
p
XfrL
)
wherein
ΔV rXfrL is the actual switch-over filling volume in the cycle,
V tRefL is the theoretical reference volume at the reference pressure P Ref in the cycle,
V tXfrL is the theoretical switch-over volume at the switch-over pressure P XfrL in the cycle,
p Ref is the reference pressure value,
p XfrL is the switch-over pressure in the cycle,
wherein the reference pressure value is reached at a first point in time t A and a switch-over point is reached at a second point in time t B ,
calculating an actual filling volume ΔV rP at a third point in time t C in a production cycle downstream from the cycle in accordance with the following formula:
Δ
V
rP
=
V
tRefP
1
-
k
(
p
Ref
)
-
V
tPC
1
-
k
(
p
PC
)
wherein
ΔV rP is the actual filling volume in the production cycle,
V tRefP is the theoretical reference volume at the reference pressure value P ref in the production cycle,
V tPC is the theoretical volume at time t c at the pressure value p PC in the production cycle,
p PC is the pressure in the production cycle,
comparing the actual filling volume ΔV rP with the actual switch-over filling volume ΔV rXfrL for the switch-over to the holding pressure phase in the production cycle, and
initiating the switch-over to the holding pressure phase in the production cycle when
Δ V rP ≥ΔV rXfrL .
2. The method of claim 1 , wherein the adiabatic compression curve k(p) is stored in the machine controller.
3. The method of claim 1 , wherein as the compound pressure P M a compound pressure in a cylinder or a compound pressure P F of a molding compound in an internal of the mold or a molding compound pressure P S in a screw antechamber is used, and further comprising determining and/or measuring at least two values A; B of the compound pressure P M .
4. The method of claim 3 , wherein at least one of the two values A; B involves average values relating to a plurality of individual measuring values.
5. The method of claim 3 , wherein the actual filling volume ΔV r corresponds to a volume, which is introduced into the mold without applied pressure, between the two values A; B and is calculated according to the formula:
Δ
V
r
=
V
tFB
1
-
k
(
p
FB
)
-
V
tFA
1
-
k
(
p
FA
)
=
V
tSA
1
-
k
(
p
SA
)
-
V
tSB
1
-
k
(
p
SB
)
wherein:
ΔV r is the actual filling volume,
V tFB is the theoretical volume in the mold at position B,
P FB is the molding compound pressure in the mold at position B,
V tFA is the theoretical volume in the mold at position A, P FA is the molding compound pressure in the mold at position A,
V tSA is the theoretical volume in an injection unit at position A,
p SA is the molding compound pressure in the screw antechamber at position A,
V tSB is the theoretical volume in an injection unit at position B, p SB is the pressure in the screw antechamber at position B.
6. The method of claim 1 , further comprising adding a constant theoretical volume V t * to every measured theoretical volume V t in response to the calculation of the actual filling volume ΔV r .
7. The method of claim 1 , further comprising determining an actual filling volume flow Δ{dot over (V)} r by deriving the actual filling volume ΔV r or the actual volume V r over time, in accordance with the formula
Δ
V
.
r
=
Δ
Vr
t
B
-
t
A
wherein:
Δ{dot over (V)} r is the actual filling volume flow,
ΔV r is the actual filling volume,
t B is one point in time (time of value B)
t A is another point in time (time of value A).
8. The method of claim 7 , further comprising determining the actual volume flow Δ{dot over (V)} r as a function of a screw speed v s not using t A and t B .
9. The method of claim 1 , wherein at least one of the actual filling volume ΔV r or an actual filling volume flow Δ{dot over (V)} r is determined continuously during the filling phase and/or an injection movement for filling the cavity is influenced in such a way that a predetermined actual volume flow profile is employed.
10. The method of claim 1 , wherein at least one of the actual filling volume ΔV r or an actual volume flow Δ{dot over (V)} r is compared during the filling phase to a reference curve of an actual filling volume Δ{dot over (V)} rR and/or of an actual volume flow Δ{dot over (V)} rR .
11. The method of claim 1 , wherein the injection-moldable compound is introduced into the cavity of the mold by a reciprocating screw or a piston.
12. The method of claim 1 , wherein the injection-moldable compound is a melt of thermoplastics or thermosetting molding compounds or silicones or varnishes.
13. The method of claim 1 , further comprising controlling further actions of an injection molding process as a function of the actual filling volume.
14. The method of claim 1 , further comprising transferring learned values for the actual switch-over filling volume ΔV rXfrL in the cycle and the reference pressure p Ref from a first injection molding machine to a second injection molding machine, which is constructionally identical or not constructionally identical to the first injection molding machine.