The Wall slip parameters dialog enables you to enter specific information about your material, to improve the accuracy of your solution.
To access this dialog, make sure you have a 3D model, and that you have selected an analysis sequence that includes Fill.
- Click
(.
- In the Process Settings Wizard dialog, click Next if necessary until you find the Advanced options button.
- Click Advanced options.
- Click Edit associated with the Solver parameters.
- Ensure that Simulate wall slip is set to Yes, then click Edit wall slip parameters.
| Dialog widget | Explanation |
|---|---|
Critical shear stress ( )
|
The critical shear stress, above which slip is likely to occur, defines the part surface area that is under slip conditions. The higher the value of critical shear stress, the smaller the area that is under slip conditions. This parameter is material dependent, but is affected by the mold surface finish and whether a pro-slip agent or slip retardant has been added to the polymer. The value for the critical shear stress varies for different applications, but 0.001- 2 MPa is the typical range. By default 0.1 MPa is used. |
| Slip exponent (m) |
The slip exponent is also material dependent, with a typical range between 0.1-2.5. The default value is 1, which represents a linear relationship between slip velocity and shear stress. Values less than one (1) retard this relationship and values greater than one (1) amplify it. For example, the default set of values for slip parameters produce a slip velocity of 1 mm/sec (1.0e-08 * 100000^1 = 0.001 m/sec = 1 mm/sec). With the same shear stress value and slip coefficient, the slip velocity would increase to 100,000 mm/sec when the slip exponent is set to 2 (1.0e-08 * 100000^2 = 100 m/sec = 100,000 mm/sec). Usually the slip coefficient decreases as the slip exponent increases beyond one (1). |
| Slip coefficient (a) |
There is a strong correlation between slip coefficient and slip exponent, which are usually fitted together after rheological testing. The slip coefficient scales the slip velocity, linearly. The value for the slip coefficient typically ranges between 10-16 and 1 and varies depending on the slip exponent and shear stress values. The default value is 10-08. |
| Temperature dependency (b) |
The use of temperature dependency is not recommended, as no reliable data are available. |
| Pressure dependency (c) |
The use of pressure dependency is not recommended, as no reliable data are available. |