Absolute and relative filling profiles (Concept)

There are two fundamentally different ram speed or filling profiles.

If you have not selected an injection molding machine, you can use a relative ram speed profile. If you know key machine parameters, such as screw diameter and maximum injection rate, you can use an absolute ram speed profile.

A cushion warning limit can be entered, but it does not affect the profile. The cushion is the distance between the forward screw position and the zero screw position, which contains polymer left in the barrel after the cavity is filled. Most of the melt in the cushion is then used for compensation flow during the packing stage. If the screw moves past the cushion warning limit during an analysis, a warning is produced.

Unless you have configured specific molding machine limits, the default settings in the following table are used.

5000 cm³/s	Maximum machine injection rate
180MPa	Maximum machine injection pressure
7000 ton	Maximum machine clamp force

Note:

The pressure profile is begun when the velocity/pressure switchover point has been reached.
If you enter a profile that injects less material than the cavity contains, the end of the filling profile is reached before the specified velocity/pressure switchover point occurs. When this happens, the velocity/pressure switchover occurs early, and the pressure profile is begun.The velocity/pressure switchover may also occur early due to material compression when a high pressure is required to fill a part.

Relative profiles

Relative profiles apply ram speed as a function of the total shot size or stroke, which are determined from the geometry of the part, the runner system and the gate. Relative profiles are usually used when the actual injection molding machine has not yet been selected.

The following relative ram speed profiles are available.

Flow rate vs % Shot volume
% Ram speed vs % Stroke

In a relative ram speed profile, 100 percent stroke indicates the position of the screw after plastication when it is ready to start the shot, and zero percent stroke indicates the position of the screw at the end of injection. A shot volume of 100 percent corresponds to when the part is completely filled, and zero percent shot volume indicates the injection has not yet started.

Note: If you have input a maximum percentage stroke value that is less than 100, or a minimum percentage stroke value that is more than zero, the profile will be extended by using the percentage ram speed values of the closest data entries. For example, the profile in the following Table 1 will be extended to the profile in Table 2.

Original profile
% stroke	% ram speed
80	75
60	100
40	50
20	10

Profile extension
% stroke	% ram speed
100	75
80	75
60	100
40	50
20	10
0	10

Absolute profiles

Absolute profiles are used when key machine parameters are known, such as screw diameter and maximum injection rate. By running an analysis with an absolute ram speed profile, you can compare simulation results with actual results obtained using the molding machine.

Absolute ram speed profiles use the following machine settings in the injection molding machine properties. You can get to this dialog by selecting Home tab > Molding Process Setup panel > Process Settings, select Advanced options, edit the Injection Molding Machine, select the Injection Unit tab, then enter the Screw diameter.

The stroke or ram position is measured as a positive value, offset from the point where the ram cannot move any futher forward because it has hit the barrel end. The starting ram position defines the shot size. If this ram position in the profile does not match the shot size, the profile will be extended to or cut off at the starting ram position value.

Zero or negative velocities in absolute profile steps are ignored.

The following absolute ram speed profiles are available:

Ram speed vs ram position
Flow rate vs ram position
% Maximum ram speed vs ram position
Ram speed vs time
Flow rate vs time
% Maximum ram speed vs time