In the early 1960s the sports car was making more of an appearance on to the roads and into lives of American society. Ford felt unpressured as their bulky Falcon model was nothing to be desired compared to the streamline concepts rival manufactures were producing. Consequently, in August 1964 Ford made an enormous debut by revealing their Ford Mustang model on to the American car market. By the end of the first day of sales, its demand was such that sales surpassed production by 6000 vehicles. It was a guaranteed success. Even to this day, it still manages to turn heads and is referred to as a “classic” in the motorcar world.
In this report I will be discussing the process of modelling and replicating the design of this particular 1964 Ford Mustang model using blueprints and the tools provided in Siemens NX 8 CAD package. NX supports both solid and surfacing modelling, in which I will describe their functionalities in further detail later on in my report.
2. Set up
On opening NX 8 the user is presented with a home screen; from where I selected a new project in the model template. The modelling template allows the user to create parts and components which will later be used in the final assembly. To save time searching for commands it is helpful to load the “Full Menus” option from the menu toolbar to enable more options if needed during to the modelling process.
To create a realistic 3D model it is helpful to use blueprints of the vehicle you wish to model. To do so you need to insert them in to the CAD package. You can do this by inserting a “Raster Image”. A raster image is constrained to a particular plane which can be edited in size, length and direction to the user’s choice. The user can then trace over the image assigned to the plane using the sketch tool in order to create an accurate shape. For my replica I inserted four raster images; a front view, side view, rear view and top view in which I positioned them to appropriate size and orientation.
With the blueprints successfully inserted into NX and on to planes, the user can start creating multiple curves and sketches to create surfaces and solid bodies.
There are a number of different tools within NX that allow you to draw. Like most CAD packages such as SolidWorks, Solid Edge and Catia etc 3D models are created from 2D sketches. These sketches are usually assigned to a plane derived from an X,Y,Z coordinate system or datum. Planes can be created around this in to the user’s choice. I found that there were two methods of creating sketches in NX. A quick way to sketch is to use the sketch tool bar at the bottom of the screen to insert a shape, spline or line to a plane or face. You can then constrain the sketch afterwards. This is for more simple sketches e.g. inserting a circle for extrusion. My more preferred way of sketching would be to enter NX’s sketching tool environment where the user is permitted to assign the sketch to a particular plane and orientation before it is possible to draw. This allows you to draw more entrecote profiles using constraints. By sketching I was able to trance over the raster image.
Curves are similar to sketches; whereas sketches are 2D, curves provide 3D qualities as well as 2D. A good example of this is the Spline tool. The spline tool is a line driven by particular points to manipulate its shape. You can assign a spline to draw in a certain axis such as the Z plane for example. However the spline tool has the potential to draw in the X and Y axis too, therefore creating a 3D profile. If the View option is checked in the spline dialog box then the user will be able to create a quick 3D sketch straight away. This makes the spline tool very affective when creating aerodynamic shapes e.g. the windscreen of my car.
Curves can also reference 2D sketches in order to create their 3D profile. A tool I found useful during the design process was the “Combine Curve” tool. The combine curve tool uses the coordinates from two different sketches on different axis’/planes and combines them into a 3D curve by merging the data of each sketch into one.
NX also allows you to project sketches using the project curve tool. This is useful when sketching on to an uneven face/surface. Curves were important in my design process as they created much of the 3D profile used to create my 1964 Ford Mustang replica.
Once the user has created the appropriate shape using the sketching tools, it will then be possible to create surfaces and solid geometry. NX contains various features that behave differently depending on the sketches and curves that have been created. Closed sections will create Solid geometry whereas open sections will result in surfaces. A section can consist of a single object or multiple objects which can be curves, edges or faces.
The exterior of my model is made from a number of different surfaces in order to meet the requirements of the Ford Mustang’s aerodynamic design. A common method that I used throughout my car was the “Swept” tool. This surface tool involves extruding a sketch or a curve along a guide which can be curve, a solid edge, or a solid face. However, all the objects in each guide string must be smooth and contiguous. You can select one, two, or three guides which can control the orientation and scale of the section string along the sweep using the orientation and scaling options.
When using three guides the user wants to shear the body on an independent axis. When you use three guides, the first and second guide defines the orientation and scaling of the body. The third guide shears the body.
Similar to the Swept tool is the “Studio Surface” tool. This behaves much of the same way. However it does not have a limit to guides or a number of sections that can be used.
You can also edit the output edge by selecting the “points” option from the drop down to create a better transition and smoother surface.
If the section profile is on a flat orientation an efficient method of creating a surface is by using the “Bounded plane” feature. This acts as a fill, however if the orientation of a section is slightly curved or angled then this will not work. On the other hand the “N-Sided Surface” feature will accomplish this task. An N-Sided Surface is used to create a surface with a set of end-connected curves. This is similar to the bounded plane because it also fills in a shape. All sketches and curves must connect for the process to be successful. If there are gaps in the geometry then the feature will fail to create the correct outcome. This feature is perfect to build a surface with an unlimited number of curves or edges that form a simple, open or closed loop, and assign continuity to outside faces. This tool can create a surface from complex drawings. You can also remove holes or gaps in surfaces that are not four-sided. Much of my bodywork for the Ford Mustang was made up from N-sided surfaces such as the rear, side panels and bonnet of my model because this feature displays good continuity.
Another feature that I found affective in my replica model was the “Through Curves”. This command creates a lofted extrusion. Multiple sections parallel to each other change shape to pass through each section creating a loft-like protrusion. The “Through Curves Mesh” acts similarly but is assisted by guide curves; creating a swept effect.
The Through Curve functionality also has the option to create solid surfaces. To create other solid geometry there are tools such as “Extrude” and “Revolve” which I have used to create simple shapes such as the wheels and some of the interior. Surfacing is not needed for these objects because they are created with sketches that are normal to a plane and not in 3D space.
To edit the continuity of a surface for more complex shapes I used a feature called “X-form” which can be found in the Shape Studio environment. This feature allows the user to manipulate the shape and smoothness of the surface’s face by altering the orientation of curves, poles and points on a selected face e.g. creating ripples or deformation. This feature can also be used on extruded solid models too in order to rework the shape.
6. Surface Analysis
As surfaces are created by sketches and 3D curves, it is important to examine the continuity and aesthetic quality of the shape and find any deformation, holes and defects that can be unnoticed by the human eye. The face analysis tool in the shape studio environment completes this task affectively. The face analysis tool applies a colour line finish to the model. The lines will show the level of continuity by stretching or becoming more clustered. The more clustered the line becomes, the less continuity there is between surface faces. I have previously edited surfaces because of this tool.
Another method of finding defects is to use the “Curve Analysis” tool. This feature will perform an analysis of the extent of curvature by displaying a comb. The comb will distort and display a needle peak if the curvature shows any levels of discontinuity. It is useful to the user because it allows them examine where the sketch or curve has problems and consequently can quickly edit and correct the defect.
7. Final Assembly
Once I had completed modelling the Ford Mustang and had checked the level of quality in the surfaces I had created, I needed to assemble all the parts together. When assembling components in NX the user must obligate constraints and specify particular relationships in order to position the parts correctly. Constraints also allow parts to move. In my assembly of the Ford Mustang, I have a total of ten moving parts. The boot, the steering wheel, all four wheels, both the doors and the front seats all move within the constraints that I have assigned to them. The two common constraints I have used are “Tough Align” and “Concentric”.
Touch Align constrains two components so they touch or align with each other. For example, the front seats have sliders underneath them so that they can move backwards and forwards. To prevent them from moving in any other direction I have used the touch align constraint to add a parallel relationship on a face where both parts meet. I have used the touch align to position the bottom of the chair directly on to the floor of the car so that it cannot move up and down.
Concentric on the other hand constrains circular or elliptical edges of two components. This forces the centers to be coincident and the planes of the edges to be coplanar. My wheels have a concentric relationship to the axils allowing them to spin around in circular motion much like a real wheel.
In order to create moving doors and keep their shape and continuity I have created a part copy. The part copy is geometry copied from one part into another. I was able to do this by using the “WAVE Geometry Linker” tool. The doors were created originally in the bodywork of the vehicle. However, the WAVE Geometry Linker command allows the user to select faces of a parent part which is then copied into a new component. This is called a child part and shares a link with the parent part. Once the copy is saved out as a new component then the original (parent) part is simply hidden. The new component can then be constrained and positioned to the desired orientation. This is a great tool to use as it keeps the shape of the car aerodynamically; it is also very efficient.
To surmise, using NX I believe that surfaces are a very good way of creating aerodynamic shapes. Solid modelling has it uses but cannot replicate the level of freedom that surfaces provide. Curves can be edited to alter the shape of very quickly and efficiently. To conclude, by exercising these features I feel I have successfully meet the requirements of replicating the design of Ford’s classic 1964 Mustang and modern vehicle design.