Using the Snap-Fit Design Workspace

Using the Snap-Fit Design Workspace

Introduction

The Snap-Fit Design program is a web-based application that serves as an engineering tool in snap-fit design. The program provides a workspace for the designer to test different scenarios by adjusting various input parameters and selecting different engineering materials for the snap-fit design.

Snap-Type Selection

Different snap-types are selected using the Snap-Type drop-down list. Possible snap-types include: five different uniform beams, two different tapered beams, two different "U" shaped beam cases, and an "L" shaped beam. This will display a graphic of the selected snap-type and populate another drop-down list of possible variables that can be solved for. To preview the graphic images of all snap-types click "View All Snap Types".

Choosing a Variable to Solve For

A single variable can be selected from the Solve For drop-down list. The contents of the list depends on the selected Snap-Type. Upon selection of a variable, the workspace will mark the input fields with a ‘*’ that are required in order to solve for the chosen variable. Initially, the Material section shows "None selected", and Output will default to "Window 1". For subsequent updates of the workspace form, the input fields will retain whatever the contents were prior to the update.

Input Fields

Input fields in the workspace that are required for a particular calculation are marked with “*” (see note below regarding optional fields).

Drop-down lists: Drop-down lists contain predefined values that can be selected for input. Only items in the list can be used for input. An error will be displayed in the output window if nothing has been selected from the list for a required field.

Edit boxes: The edit boxes correspond to a specific measurement in the snap graphic and require numeric input. Numeric values can be entered as integer or decimal. No other characters can be used, including commas. An error will be displayed in the output window if invalid input is used in any of the edit boxes.

Units: Units can be displayed in either English (default) or Metric. Changing the units from the drop-down list will automatically convert the contents of all fields to the selected units and display the selected units next to each edit box.

Optional fields: In cases where optional fields are displayed, all fields marked with "•" are required OR all fields marked with "••" are required. If the "•" optional fields are left blank, then the "••" fields will be used. Otherwise the "•" fields will be used.

Output: The Output Results drop-down list contains "Window 1", "Window 2", and "New Window". The results of the calculation will be displayed in the selected Output window. See Output for more details.

Material fields: See Material Selection.

Material Selection

When not solving for a material, selecting a material from the Grade drop-down list will populate the Coef. of Friction, Filler, Flexural Modulus, and Allowable Strain fields for the chosen material. The Moisture drop-down list is only available for conditioned materials (e.g., Ultramid). These drop-down lists and fields are read-only, allowing for just selection of items that are in the list. The only time the fields can be edited is when the user selects "User Defined" from the Material drop-down list, in which case all fields become editable.

Note: All provided material properties are at 23˚ C (73˚ F). Select the “User Defined” option to enter other material properties. This option can be used to experiment with different material properties, or manually input material properties received from BASF or CAMPUS that are not currently available in the Snap-Fit Design Workspace program.

The material input fields on the workspace form will be populated as follows:

The Material Trade Name drop-down list contains material trade names from the material database.
The Grade drop-down list contains the material grades from the material database for the selected material trade name. In order for grades to show up in this list there must also exist a Coef. of Friction value defined in the database for the selected Moisture type.
The Coef. of Friction drop-down list contains Coef. of Friction fields defined for the chosen material grade. A “User Defined” option is also available. This field will remain “N/A” until a Grade is selected.

Note: the Coefficient of Friction value used in the snap fit calculations is an average value based on tested samples in BASF's test laboratory. It is for plastic on plastic and is for the static condition (vs. dynamic). Many variables influence Coefficient of Friction (part geometry, surface finish, rate on assembly, etc.) and thus, this value may differ slightly for actual part Coefficient of Friction. To use an alternate Coefficient of Friction value in the calculations select the “User Defined” option.

The Moisture drop-down list contains a predetermined list of values: "Dry", "50% RH conditioned", and "None". Selecting a different Moisture repopulates the Grade drop-down list with the matching material grades.
The Filler field is an informational field and is populated according Filler Type defined for the chosen material grade. Some filler types are:

I = Impact Modified
GR = Glass Reinforced
MIN = Mineral
FR = Flame Retardant
C = Crystallization

The Flexural Modulus field is an informational field and is populated according to the chosen material grade.
The Allowable Strain field is an informational field and is populated according to the chosen material grade.

When solving for a material, the General Material drop-down list is populated with general material categories. Selecting a general material and/or trade name from the drop-down lists and specifying a "Filler" will allow for filtering of the results. Likewise, specifying a "Moisture" from the drop-down list allows further filtering. The material input fields used as selection criteria on the workspace form will be populated as follows:

The General Material drop-down list contains a unique list of materials that categorize the specific material grades. The drop-down list also contains the choice of "All" (field ignored in query).
The Material Trade Name drop-down list contains the material trade names from the material database for the selected general material. The drop-down list also contains the choice of "All" (field ignored in query).
The Filler drop-down list contains a unique list of fillers (e.g., Glass, Mineral, Glass & Mineral) defined for the material grades. The drop-down list also contains the choice of "None" (no filler) and "All" (field ignored in query).
The Moisture drop-down list contains a predetermined list of values: "Dry", "50% RH conditioned", "None", and "All".

Performing a Calculation

When the user clicks the Calculation button the program will perform a validation, making sure that all of the necessary input fields have been populated and contain valid data. If any information is missing or invalid, an error message will be displayed in the output window stating the specific problem. Upon successful calculation, the proper Q Factor will be applied, if necessary, and the results will be printed to the output window specified by the user. These results can be printed, saved to a file on the local hard drive, or kept in the output screen where they can be compared with and appended to subsequent calculations.

Note that the calculated forces and deflections are at maximum permissible strain. For your actual forces, check deflection at the forces given and multiply by the ratio of your required deflection to the deflection given at maximum strain.

Capturing Output

The user can choose to output the results of the snap-fit calculations to either Window 1 or Window 2 of the main workspace page. Also, the user to has the option of displaying the results to a New Window, which will open a new browser window. Each time calculations are sent to an output window, the window will be appended to (with the exception of the New Window). Clicking the "Clear" button at the top of Window 1 or Window 2 will clear the contents the respective output window.

Printing
Printing can be performed by choosing to output the results to a new window and choosing "Print" from the web browser's File menu. Alternatively the results of any output window can be saved to a text file and printed from a text editor (see how to save to a text file below).

Depending on the browser, the results of Window 1 or Window 2 may be printed by clicking the left mouse button in the desired output window and choosing Print Frame... from the browser's File menu.

Saving to a Text File
Saving results to a file can be performed by choosing to output the results to a New Window and choosing "Save" from the browser's File menu (save as type *.txt). The results of Window 1 or Window 2 can be saved using the following procedure:

Click the left mouse button in the desired output window to be saved
Choose Select All from the Edit menu (or Ctrl + A)
Choose Copy from the Edit menu (or Ctrl + C)
Open a text editor (e.g., Notepad) and choose Paste from the text editor's Edit menu (or Ctrl + V)
Save the file from the text editor

Depending on the browser, the results of Window 1 or Window 2 may be saved by clicking the left mouse button in the desired output window and choosing Save Frame As... from the browser's File menu (save as type *.txt).