1. Workshop 4A Contact Interface Treatment
Workbench-Mechanical Structural Nonlinearities

2. Workshop 4A: Contact Interface Treatment
Goal
Use interface treatment tools to simulate an interference fit between surfaces.
Model Description
2D Axisymmetric model of injection molding machine nozzle tip assembly
Materials:
Steel for Housing
Copper alloy for Tip
Titanium for Insulator
Tip
Insulator
Housing

3. …Workshop 4A: Contact Interface Treatment
Model Description (cont’d)
Contact Pairs:
Frictionless contact at Housing to Nozzle tip face seal
Bonded contact at Nozzle tip To insulator
Bonded contact at threaded connection between Housing and Nozzle tip (thread details not modeled)

4. …Workshop 4A: Contact Interface Treatment
Model Description (cont’d)
Thermal Boundaries:
Hot 220C
Cold manifold
Nozzle tip band 80 Watts

5. …Workshop 4A: Contact Interface Treatment
Model Description (cont’d)
Structural Boundaries
Frictionless Nozzle Housing Flange
Frictionless Insulator
Structural Loads
1st loadstep reconciles interference fit between housing and tip face seal
2nd loadstep reads in temperatures from steady state thermal run
3rd loadstep applies pressure to melt channel wall.
melt channel
wall

6. …Workshop 4A: Contact Interface Treatment
Steps to Follow:
If you already have Workbench open from a previous run, start a new analysis with Utility Menu>File>New…
Browse for and open “W4a-Offset.wbpj” project file.

7. …Workshop 4A: Contact Interface Treatment
The Project Schematic should look like the picture below.
Note: The engineering data, geometry, loads and boundary conditions for the thermal and structural runs have already been set up. It remains to specify the contact surface offset at the tip-housing face seal, run the solution and post process contact results.

8. …Workshop 4A: Contact Interface Treatment
Highlight the Engineering Data Cell and double click to open
Verify the predefined material properties
Verify that the units are in Metric (Tonne,mm,…) system.
If not, fix this by clicking on…
Utility Menu>Units>Metric(Tonne, mm,..)

9. …Workshop 4A: Contact Interface Treatment
Return to the project schematic page
Double click (or RMB=>Edit…) on the Thermal Model Cell to open Mechanical Session

10. …Workshop 4A: Contact Interface Treatment
Once inside the Mechanical application, verify the working unit system
“Unit > Metric (mm,kg,N,s,mV,mA)”
Expand each folder in the project tree to become familiar with the model set up and to confirm material assignments, boundary conditions, and loads as described on the slides 2 thru 5.
Verify the initial condition of the three predefined contact regions
Highlight the Connections Branch
RMB > Insert >Contact Tool

11. …Workshop 4A: Contact Interface Treatment
Highlight the Initial Information branch of the newly inserted Contact Tool
RMB > Generate Initial Contact Results
This should produce the following table of specifications on the initial condition of the contact regions:

12. …Workshop 4A: Contact Interface Treatment
Note:
The two bonded contact regions are assigned two contact pairs that act equal and opposite to each other to enforce the contact. This reflects “Symmetric” behavior.
The frictionless contact region has only one active pair, reflecting “Asymmetric” behavior. The companion frictionless pair (grayed out) is inactive. It is initially in a “Near Open” status with a small gap.
The initial penetration at the bonded regions is essentially zero and is ignored by default.
Without making any changes to the contact specifications, execute a SOLVE

13. …Workshop 4A: Contact Interface Treatment
Highlight the Solution Information Folder and switch Solution Output to ‘Force Convergence’
The Solution converges quickly and easily in 4 iterations

14. …Workshop 4A: Contact Interface Treatment
Highlight the Solution Branch
RMB > Insert > Contact Tool…
Highlight the newly inserted Contact Tool
RMB > Insert >
Pressure
Penetration
Gap

15. …Workshop 4A: Contact Interface Treatment
Highlight the Contact Tool and filter out the bonded contact pairs by click the checkmark box next to each region
RMB > Evaluate Results

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Using the Time line in the ‘Graph’ window, post process the contact pressure for each load step
As expected, pressure at the frictionless interface is zero at LS1. It ramps up to 50Mpa for LS2 due to thermal differential expansion. It drops back to zero as a result of melt channel pressure load at LS3.
Loadstep 1
Loadstep 2
Loadstep 3

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Post process the contact penetrations and gaps for each load step
Note, in particular, the gap profile (gap = )at the end of LS3. This interface must remain closed in order to prevent leakage in operation.

18. …Workshop 4A: Contact Interface Treatment
Return to the Connections folder, highlight the ‘Frictionless- Housing To Nozzle tip’ contact region
In the Details window, Set Offset to 0.050mm
This will make a mathematical adjustment to the position of all the contact detection points toward the target surface, creating an interference fit

19. …Workshop 4A: Contact Interface Treatment
Use the Contact Tool to verify that the offset has been set in Initial Information in the Contact Tool
RMB > Generate Initial Contact Results
Note: The frictionless contact is now reported closed at the start with an initial penetration of e-2. Is this correct?
Recall, prior to defining the Offset, the initial gap was reported as e-3 (slide 12).
e-3 = e-2
Hence, the offset has been correctly introduced
Execute the another solve

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Highlight the Solution Information Folder and switch Solution Output to ‘Force Convergence’
The Solution takes a few more iterations then the first run, because of the contact offset, but it still converges relatively easily

21. …Workshop 4A: Contact Interface Treatment
Post process the contact pressure
Because of the initial interference, a maximum pressure concentrated at the melt channel wall of about 500Mpa is now established and maintained throughout the load history.

22. …Workshop 4A: Contact Interface Treatment
Note also that when you zoom in on the contact region, there appears to be a small gap where we expect an interference.
This is expected as the Offset is a like a rigid region created by a mathematical adjustment to the contact detection point locations.
This underscores the importance of using this interface treatment tool for very small adjustments only.
Rigid region

23. …Workshop 4A: Contact Interface Treatment
Highlight Solution
RMB>Insert>Probe>Force Reaction
In Details of “Force Reaction” Set..
Location Method = Contact Region
Contact Region = Frictionless- Housing To Nozzle tip
RMB>Evaluate Results

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As expected, the preload is nearly constant across the three loadsteps

25. …Workshop 4A: Contact Interface Treatment
Post process the equivalent stress at LS2.
This peak stress is much higher then the actual yield strength of the material.
Localized yielding is expected and will likely reduce the preload.