Winding generalised shapes using the NCC Dialog
This topic describes a class of Cadfil functionality based around winding patterns for generalised 3D non-axisymmetric parts. This class of component can have many forms and the feasibility for winding might be very restricted. There is not a single method that can be generally used, it depends on the geometric limitation of the shape, however this section describes some general tools and methods that can be applied within Cadfil. Aspects of this features are experimental in nature and are continuously being developed and added to.
The current features can be accessed under the Generalised 3D Duct/Spar option on the QuickCAD menu via the NCC dialog. The methods are parametric based on input parameters and externally imported geometry. The the time of writing the input parameters are as shown in the dialog below. All number Cadfil data parameters are given a $tag-name as parameters can be accessed in downstream processes such as post-processing should any need arise. In this option all the parameters have the tag $NCC-<descriptive-name>. For those who might want to know what the NCC prefix means, then the answer is quite obscure as much of the functionality is based on code that uses NURBS Composite Curves imported from STEP files ( a standard CAD data format).
Description of NCC Dialog Buttons
The NCC dialog show above has a number of standard option buttons which are briefly described below.
Cancel - exits from the dialog without saving. as does the [x] button in the top right of the dialog.Read Param's - Asks for a name of a parameter (.par) file that have previously been saved and reads the parameters into the dialog edit boxes. All Cadfil .par files are text files and can be opened in any text editor program.
Write Param's - Saves the current parameters into a .par file.
Calculate - Validates the parameter data and attempts to perform the path generation options specified by the parameters
Help - Displays the relevant help topic.
A Brief description of NCC Dialog Parameters
$NCC-CALC-TYPE This is a text field that can currently takes the value PLANE-FIXED-INDEXING, PLANE-VARIABLE-INDEXING or SPINE-FIXED-PITCH. These options are different types of methods to use for calculating sets of winding paths. For each option a selection of the parameters options below will need to be correctly specified. Some options will not be needed whilst other options are optional. These options are not very simple to understand and it is better to follow a specific example that have been made already for a similar type of mandrel geometry. It is our intention the create and expand such examples as an ongoing activity. A list of examples and links can be found near the end of this topic.
$NCC-GMAN This non-optional item should have the name of an existing Cadfil mandrel file (.mnd) Cadfil mandrel files have several different formats, for these options it is expected that the user will have prepared one of the general 3D meshed surface format files. This is descripted in a different section of the the help file
$NCC-STEP-FILE Some of the options required external geometry in the form of guide curves. The guide curves will have been created in an external 3D CAD system and exported as STEP files. This option should have the name of an existing STEP file that has one or more visible composite curves that are relevant ton the 3D geometry in the mandrel file (.mnd) and relevant to the calculation type selected.
$NCC-STEP-CURVE-NO If guide curves are being imported from a step file (see $NCC-STEP-FILE), if this entry is empty then Cadfil will scan the step files and find all VISIBLE composite curves. A composite curve in step is a curve that is constructed by joining one of more curves together, he curves my be and combination or lines, circular arcs or complex NURB (beta spline) curves. The details of the curves found will be listed in the Cadfil text window and a dialog box like the one shown below will be displayed to allow a curve to be picked to use. In STEP all entities are given a unique identity number, in the figure below the curve selected is number 23134 and you can also note that in the CAD system that created the step file this entity was named "Spline.1", you may be able to give names of your choice in you chosen CAD system. If there is more than one curve to choose they will be shown in the Cadfil text window and can be selected in the drop-down box. You can miss out this selection stage by noting (or copying) the curve number and then putting it in the dialog under this entry, that is to set $NCC-STEP-CURVE-NO=23134. Th when you next run the parameter data with "Calculate" you will not be asked to pick a curve.
$NCC-N360 This entry a a parameter that is used to control the number of path points created for every 360 degree rotation around the path spine or mandrel axis. If a small number is used then the path can be very rough looking and may not wind well. Too large a number and it may prove a problem for the capacity of the computer. Note facilities to reduce the number of points for the winding machine exist down stream. It is much better to start with better quality data (more points) and to later reduce that if needed.
$NCC-BANDWIDTH This is the width of the fibre band that will be used in calculations, for visualisations and for calculating mandrel coverage and thickness. The units are the units of the mandrel which are normally in mm (or inch).
$NCC-PLY-T0 This is the thickness of the fibre band, the units are the units of the mandrel which are normally in mm (or inch).
$NCC-FIXED-PITCH If $NCC-CALC-TYPE=SPINE-FIXED-PITCH then this value is the distance along the Guide Curve (the GC is set with $NCC-STEP-CURVE-NO) for which the path will circulate 360 degrees around the spine, and $NCC-N360 data points will be generated. The path will be generated the full length of the GC less some distance at the start and finish set with $NCC-SPN-TRIM-1 and $NCC-SPN-TRIM-2 respectively. One way to imaging this type of path is to consider a plane that is normal to the guide curve that travels along the guide curve. Now consider a laser pointer in the plane that rotates around like a clock hand. As the plane moves along the guide curve the laser rotates (360 degrees per pitch distance) and traces a path on the surface of the mandrel. This path is then checked for friction (slip) stability and is reported in the Cadfil text window. The paths are not in general geodesic they are purely geometric based on the parameters and the geometry of the guide curve and mandrel surface.
$NCC-START-ORIEN For the clock hand analogy used in the previous sections this determines the start position (0 to 360 degrees) of the clock hand. Mathematically the zero position angle is measured relative to the projection of the global Z axis into a plane normal to the guide curve through the initial point of the guide curve. By changing the start orientation e.g 0, 60, 120, 180, 240, 300 you could generate 6 paths that are geometrically spaced around the mandrel by angle.
$NCC-SPN-TRIM-1 This is a distance along the Guide curve measured from the start point that is not used for the path calculation. Use of the two trim values allows path creation using only a portion of the Guide Curve. The default trim values are zero if not set by the user.
$NCC-SPN-TRIM-2 This is a distance along the Guide curve measured from the end point that is not used for the path calculation.
$NCC-MAKE-FEA-FILES If set to YES (Y) the option creates a <job-name&Gt_SPN.binfile what can be used to create FEA models for constant pitch winding on generally curved regular sections. A more general FEA method exits in Cadfil that does not use this option but used the .pay file to add thickness and direction information to the surface of the FEA model based on the position and width of each band segment in the order it is placed on the mandrel.
$NCC-RETURN-PATH This can be set to YES (Y) or NO (N) , if yes is set the $NCC-CALC-TYPE=SPINE-FIXED-PITCH will generate a path by traversing the guide curve and then doing a reverse traverse to generate both the plus and minus wind angles in the path. For other $NCC-CALC-TYPE= values this setting is not used.
$NCC-DIAGNOSTICS This can be set to YES (Y) or NO (N) , if yes is set additional information is written to the Cadfil text window and to data files. This option is mainly for debugging/understanding purposes when the actual path output is confusing or not what is expected. Users would normally not uses this option, the default is No.
$NCC-PL-ROTN AXIS This option applicable to options $NCC-CALC-TYPE=PLANE-XXX and is discussed in more detail in a following section.
$NCC-PLANE-OFFSETS This option applicable to options $NCC-CALC-TYPE=PLANE-XXX and is discussed in more detail in a following section.
$NCC-PLANE-AXIS-ANG This option applicable to options $NCC-CALC-TYPE=PLANE-XXX and is discussed in more detail in a following section. This takes 4 values separated by spaces the first three being the components of a vector normal to the plane (it does not need to be a unit vector) and the fourth value is a clockwise rotation in degrees about the direction specified.
$NCC-WIND-DIRECTION This takes values of +1 or -1 and determines the direction of rotation (helix) of the paths generated around the mandrel.