In compression-type molding processes, the press reduces the cavity thickness, forcing the resin into unfilled portions of the cavity. The compression direction is set in the + Z direction.
During the molding process, some elements of the model may be compressed, while others may not. The Compression surface property identifies the surface elements on the model that will be compressed.
The following sections describe the terms used in these simulation processes.
Press open distance
The Press open distance is the distance the press has to travel to convert the charge from its uncompressed state to its final, fully molded state.
- Injection-compression molding
- The
Press open distance
is the distance between the initial position of the press at the start of injection and the press position when the gap between the moving and stationary mold halves is equal to the final part thickness. It ranges, typically, from zero to three times the maximum part thickness, and in the ideal case is fully traversed during the press compression stage. Check the analysis log to ensure that the press has fully closed by the end of the compression phase.
- Compression molding
- The Press open distance is dependent on the geometry of the charge and reflects its thickness.
The
Automatic
setting of the
Pure compression press open distance
defines the press open distance (D) as
D = (P2 - P1)
where
- P1 = the upper (moving) side of the part
- P2 = the upper (mold) side of the initial charge after the charge has been moved to the starting position
Note: The movement of charge to the starting position happens automatically.
For a complex geometry, where the compression direction is in the default (-Z) direction,
- P1 = minimum Z value of the press side of the part mesh within the XY lateral extent of the charge mesh,
- P2 = maximum Z value of the charge mesh within the XY lateral extent of the part, measured after the charge has been moved into the starting position.
If the
Specified
press open distance is
- set at a value greater than that determined from the automatic calculation, the flow calculation will not start until the press touches the initial charge. The time it takes to reach this position will not be included in the flow simulation. Only the initial timestep and the press displacement result will change to reflect this additional movement.
- set at a value less than that determined from the automatic calculation, the press open distance will change to reflect the automatic calculation. In this case, a warning will be written.
Press waiting time or Press compression starts
This option applies to injection-compression molding analyses only.
- Midplane models
- The press waiting time term is an option only for Midplane injection-compression molding. With this option, you can delay the start of compression, so that it does not coincide with the start of the injection phase but instead moves once the injection phases is complete.
- 3D models
- In 3D injection-compression analyses, the term Press Compression starts is used instead. By default, this is set to
At the end of packing
, which refers to when the injection pack profile is complete. The injection pack profile starts at the velocity-pressure switchover time, regardless of the option you set for press compression starts. When the pack profile finishes, the injection is closed and the HTC condition is applied to these nodes like the surrounding wall. Since a boundary condition is no longer applied at the injection nodes, the pressure there will simply decay as with the rest of the part.
Press compression time
After a pre-set amount of plastic melt is fed into an open cavity, it is compressed. The compression phase consists of two segments:
- First, the movement of the compression press is under speed control.
- Next, the movement of the compression press is under force control.
The time needed to complete both segments is the
press compression time
. When this time is reached, the press stops and remains stationary, and the cooling time starts, even if the specified press speed and/or force profile are not yet complete, so it is important that sufficient time is provided.
Press compression force
Compression force is the pressure required to move the press to compress the plastic melt. This pressure should be sufficient to compress the plastic melt, without damaging the mold halves. During the analysis, the compression phase is initially under speed control, then switches to force control when the specified press compression force is reached.
Note: The press compression force cannot exceed the maximum clamp force.
Press compression speed
The compression press moves in incremental distances. In each increment, it moves at a constant speed, but the speed can be different from one increment to another. When programming the press compression speed, you should bear in mind that the press will stop moving when the compression time has been reached, even if the press hasn't covered the press open distance. So it is important that the press compression speed is sufficient to cover the press open distance within the press compression time period you enter.