Workshop 4A Contact Interface Treatment Workbench-Mechanical Structural Nonlinearities

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

…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)

…Workshop 4A: Contact Interface Treatment Model Description (cont’d) Thermal Boundaries: Hot manifold @ 220C Cold manifold plate @50C Nozzle tip band heater @ 80 Watts

…Workshop 4A: Contact Interface Treatment Model Description (cont’d) Structural Boundaries Frictionless Support @ Nozzle Housing Flange Frictionless Support @ 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

…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.

…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.

…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,..)

…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

…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

…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:

…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

…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

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

…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

…Workshop 4A: Contact Interface Treatment 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

…Workshop 4A: Contact Interface Treatment Post process the contact penetrations and gaps for each load step Note, in particular, the gap profile (gap =0.049176)at the end of LS3. This interface must remain closed in order to prevent leakage in operation.

…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

…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 4.8943e-2. Is this correct? Recall, prior to defining the 0.050 Offset, the initial gap was reported as 1.0567e-3 (slide 12). 0.05 - 1.0567e-3 = 4.8943e-2 Hence, the offset has been correctly introduced Execute the another solve

…Workshop 4A: Contact Interface Treatment 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

…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.

…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

…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

…Workshop 4A: Contact Interface Treatment As expected, the preload is nearly constant across the three loadsteps

…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.