Definition (modification) of a mold

Definition (modification) of a mold

Ver: 0

DESCRIPTION

In a blow moulding or a thermo-forming process, free surfaces enter into contact with a solid mould. When this occurs, the boundary condition along the free surface suddenly changes from a vanishing force condition to a vanishing velocity condition.

In Polyflow, contact is implemented through a penalty technique. Once a point enters in the solid domain, a normal force, proportional to the penetration length, is applied to this point. In the tangential direction, a slip condition is used.

Contact can also influence the energy equation. In non-isothermal simulations, a thermal contact boundary condition may be imposed. A penalty model is also used to change the flux condition to a temperature condition.

OPTIONS

-1
Upper level menu

The current setup is accepted

1
Definition of the mold domain

Allows for the selection of the subdomains that constitute the solid mould

2
Modification of the contact wall

Select the boundary of the solid domain that must be taken into account for the calculation of the penetration length. The contact detection algorithm considers the whole boundary of the mould, but it is generally more efficient to consider only a part of this boundary for the calculation of the penetration.

3
Definition of a translation velocity

Allows for the definition a translation vector corresponding to the movement of the solid mould

#
Definition of an angular velocity

Not available

5
Modify alpha

When a point of the fluid domain has entered into contact with the mould, a heat exchange may occur between the fluid and the mould. Presently we assume that the heat exchange is controlled by forced convection ; the parameter alpha is the heat transfer coefficient. In particular, alpha vanishes when there is no heat exchange, while alpha receives a large value of the fluid in contact immediately acquires the mould temperature.

6
Modify Talpha

When a point of the fluid domain has entered into contact with the mould, a heat exchange may occur between the fluid and the mould. Presently we assume that the heat exchange is controlled by forced convection, Talpha being the reference temperature of the mould.

7
Modification of the slip coefficient

When a point is entered into contact with the mould, a slip condition is used in the tangential direction. The slip force is calculated as : fs = fslip vs exslip where vs is the velocity component in the tangential direction, fslip is the slip coefficient and exslip the slip exponent.
Default is : 1.0000000E+04

8
Modification of the penalty coefficient

The normal force applied when a point penetrates the solid mould is calculated as :
fn = k d where d is the penetration length and k the penalty coefficient that represents the mould stiffness. Generally, the default value may be used.
Default is : 1.0000000E+07

Modification of the penetration accuracy

If the penetration of a point into the mold is greater than the penetration accuracy, the time step is rejected. Calculation is then restarted from the previous time step with a smaller dt.
Default is set according to the dimensions of the mesh .

10
Modification of the element dilatation

This item allows to 'expand' each finite element of the mold in order to help the contact detection algorithm. Indeed, some numerical errors can lead a point to 'miss' the mold. A small expansion of the finite elements of the mold fixes the problem.
Default is set according to the dimensions of the mesh .

11
Modify amplitude of volume generation

Since the mould is represented by a surface, the mould body needs to be build for proper contact detection. The program will build the mould body by means of volume elements. These volumes elements are obtained by expending (extruding) the surface elements in the direction specified above, and with a selected amplitude. This parameter for volume generation has the units of the finite element mesh. Typically the amplitude can be five times the elements dilatation. If it is too small, contact might be not detectable, while if it is too large, the overall mould geometry may potentially be affected.

12
Specify mold side / cavity side

Since the mould is represented by a surface, the mould body cannot be identified unless the user specifies the appropriate information. Here, arrows will be drawn in a direction selected by the program, and the user has only to specify whether the mould body lies on the side marked be the arrowes or in the other direction.

SEE ALSO

Contact management
Contact domain
Contact wall
Basic concepts / Introduction to boundary conditions (UM)
Free surfaces and interfaces (UM)
Free surfaces and interfaces / Contact lines and contact surfaces (UM)
Generalized Newtonian flow problems / Boundary conditions / Free surface (UM)

-1	Upper level menu
	The current setup is accepted
1	Definition of the mold domain
	Allows for the selection of the subdomains that constitute the solid mould
2	Modification of the contact wall
	Select the boundary of the solid domain that must be taken into account for the calculation of the penetration length. The contact detection algorithm considers the whole boundary of the mould, but it is generally more efficient to consider only a part of this boundary for the calculation of the penetration.
3	Definition of a translation velocity
	Allows for the definition a translation vector corresponding to the movement of the solid mould
#	Definition of an angular velocity
	Not available
5	Modify alpha
	When a point of the fluid domain has entered into contact with the mould, a heat exchange may occur between the fluid and the mould. Presently we assume that the heat exchange is controlled by forced convection ; the parameter alpha is the heat transfer coefficient. In particular, alpha vanishes when there is no heat exchange, while alpha receives a large value of the fluid in contact immediately acquires the mould temperature.
6	Modify Talpha
	When a point of the fluid domain has entered into contact with the mould, a heat exchange may occur between the fluid and the mould. Presently we assume that the heat exchange is controlled by forced convection, Talpha being the reference temperature of the mould.
7	Modification of the slip coefficient
	When a point is entered into contact with the mould, a slip condition is used in the tangential direction. The slip force is calculated as : fs = fslip vs exslip where vs is the velocity component in the tangential direction, fslip is the slip coefficient and exslip the slip exponent. Default is : 1.0000000E+04
8	Modification of the penalty coefficient
	The normal force applied when a point penetrates the solid mould is calculated as : fn = k d where d is the penetration length and k the penalty coefficient that represents the mould stiffness. Generally, the default value may be used. Default is : 1.0000000E+07
	Modification of the penetration accuracy
	If the penetration of a point into the mold is greater than the penetration accuracy, the time step is rejected. Calculation is then restarted from the previous time step with a smaller dt. Default is set according to the dimensions of the mesh .
10	Modification of the element dilatation
	This item allows to 'expand' each finite element of the mold in order to help the contact detection algorithm. Indeed, some numerical errors can lead a point to 'miss' the mold. A small expansion of the finite elements of the mold fixes the problem. Default is set according to the dimensions of the mesh .
11	Modify amplitude of volume generation
	Since the mould is represented by a surface, the mould body needs to be build for proper contact detection. The program will build the mould body by means of volume elements. These volumes elements are obtained by expending (extruding) the surface elements in the direction specified above, and with a selected amplitude. This parameter for volume generation has the units of the finite element mesh. Typically the amplitude can be five times the elements dilatation. If it is too small, contact might be not detectable, while if it is too large, the overall mould geometry may potentially be affected.
12	Specify mold side / cavity side
	Since the mould is represented by a surface, the mould body cannot be identified unless the user specifies the appropriate information. Here, arrows will be drawn in a direction selected by the program, and the user has only to specify whether the mould body lies on the side marked be the arrowes or in the other direction.