Week 9 - Challenge 2 - Switch Bezel Design
Aim:
Create the Switch Bezel Plastic component through the given Class-A surface. To begin with, the tooling axis for the given Class-A Surface should be created meeting the requirements of the draft angle and at the end perform the Draft analysis on the model.
Take the Thickness of the component to be 2.5 mm.
Objective:
The objective of the project is to design the Switch Bezel and to do a draft analysis for it by creating the required tooling direction with the help of Bisecting method.
- Ensure Proper Tree Structure.
- Geometrical sets should have a proper name based on the sketches present inside them.
- All the sketches should be created under the Geometrical set.
- Use the Close Surface feature to make a solid body from the surface.
- To publish the Tooling Axis, Class A, B, and C surfaces.
Theory:
Surface Continuity:
You might have come across the term, surface continuity quite frequently while working with different concepts in surface modeling of plastic modeling. The term ‘continuity’ is valid only when there is a connection or contact between two surfaces or surface layers. Technically speaking, this is the terminology used in modeling just to define the flow of curves/surfaces. There are different types of surface continuity based on how two surfaces meet.
Surface continuity is crucial in Class-A surface modeling. Surface modeling is the art of building complex geometrical features, one surface at a time. Usually, surface modeling is used to create continuous organic shapes, therefore the junctions between surfaces are quite important.
Generally, we describe the 'smoothness' of a junction, where one surface meets another, using the term 'G' (G stands for 'Geometry'). We can add a suffix to our G to describe how many similar characteristics each surface has. The more alike the surfaces (the more conditions that match across the pair of inputs), the more smoothly the adjoining surfaces flow. If two surfaces are not touching, they have no continuity which can be represented as the surfaces having ‘No-G’.
What are the Types of Continuity Curves?
There are four types of surface continuities based on the variations in which surfaces establish contact with each other. These include:
- G0 – Position (touching)
- G1 – Tangent (angle)
- G2 – Curvature (radius)
- G3 – Acceleration/Torsion (rate of change of curvature)
G0 - Position Continuity :
G0 or Point Continuity is simply when one surface or curve touches another and they share the same boundary. When two curves are having a common endpoint, with no further conditions, and are positionally continuous, a GO surface continuity is created. This is the less smooth type of joint, as the only condition to satisfy is the common endpoint, regardless of the flow of the two curves/surfaces around the joint. In the examples below, you can see what it looks like on both curves and surfaces.
G1 – Tangent Continuity :
G1 or Tangent continuity or Angular continuity implies that two faces/surfaces meet along a common edge and that the tangent plane, at each point along the edge, is equal for both faces/surfaces. They share a common angle; the best example of this is a fillet (Engineering Fillet), a blend with Tangent Continuity, or in some cases a Conic.
You can't have G1 continuity unless you at least have G0 continuity. The further we move ahead in continuities, keep in mind that the preceding number(s) must exist for it to be true. Sometimes, it is also known as the second order of continuity. In the examples below, you can see what it looks like on both curves and surfaces.
G2 – Curvature Continuity
G2 continuity adds another order (condition) that must match across our pair of curves. In this type of surface continuity, the curves must touch, be tangent with each other, and have the same curvature, at the point where they touch. Technically, this means that our input geometry must now be curved as well. Straight lines have no curvature (or infinite curvature, depending on your point of view). Therefore, a pair of inputs containing a straight line can't meet G2 conditions.
This is the minimum math requirement for Class A Surface. Another way to describe this is in a situation where a reflection is cast upon the surfaces and you would not be able to tell where one patch ends and the other begins. In the examples below, you can see what a G2 continuity looks like on both curves and surfaces.
G3 – Acceleration of Curvature / Torsion Continuity
G3 curvature continuity includes the concept of 'Acceleration' of curvature. That is the amount of change in the curvature, over the length of the curve. G3 is looking for balance on the rate of curvature – in other words, the max value of the curvature hits its peak about the middle of the transition area.
Let's take a look at our 2D curvature combs shown above. To achieve G3 continuity, the curvature combs should be heading in the same direction (Tangency), be the same length (Curvature), and, more importantly, be tangent (Acceleration, or rate of change).
What is beyond G3?
Mathematically you can keep on adding more 'orders' across curves to create G4, G5 - Gn continuity, but we are realists, so we are going to stop here. Even if you could create 'smoother' surfaces it would be pretty difficult to measure it.
CAD Software and Continuity
CAD platforms are capable of demonstrating continuity types in the form of mathematical equations to define the continuity in the backend. To boost your imagination on these explanations, you can take a look at the below images with different types of continuity.
Design methodology:
Insert the class A surface of the switch bezel in CATIA software.
Determining the tooling axis for the switch bezel
Creation of class B surface.
Creation of class c surface.
Join the switch bezel's class A, class B, and class c surfaces and ensure all the surfaces are closed.
Use the Close Surface feature to make a solid body from the surface.
finally, Perform the Draft analysis on the switch bezel final plastic component.
Class-A Surface:
Class A Surfaces are primarily used in the automotive environment & refer to those surfaces which are visible in a product. In other words: A-Class surfaces are those aesthetic/free-form surfaces, which are visible to us (interior/ exterior) and have an optimal aesthetic shape & high surface quality.
Here, one should understand the difference between the internal or external and visible or hidden surface. The surfaces or regions which are visible nowadays are considered for Class-A modeling. It is one of the reasons why the importance of Class-A modeling is increasing day by day. The majority of the time is used in Plastic Part Designs.
Class-B Surfaces:
The Class-B finish is a quality finish with only minimal imperfections. A Class B finish is the most common finish for exterior surfaces. It is normally specified on surfaces such as external covers, panels, and parts that are fairly prominent.
Class-C Surfaces:
The Class C finish allows more imperfections than Class A or B. Class C is often specified for interior surfaces not readily visible, surfaces that will be covered by another part when assembled, or surfaces that the customer feels do not need to meet a high cosmetic finish. This Class is generally used for parts or surfaces which are not viewed after installation or viewed only for service.
Creating Tooling Axis:
The ejection from the mold after manufacturing the interior trim must have the nominal 3-degree draft angle.
Hence the tooling directions created by considering the above factor & bisecting method is used.
The base surface of the Class-A was extracted to create a reference point on the surface using the point, create a line in the z-direction & an axis system was inserted to the point then using projection intersection along the yz plane is created & the two inclined lines were drawn inside the positioned sketch. Then bisecting lines with the two inclined lines were created.
Now the same procedure is done along the xz plane, we only have one surface line so the center point is used to extrude a line along the z-direction & gave a measurement of 3-degree, from the surface line.
Bisecting Method:
This method is used for the generation of the tooling axis for that purpose first we need to decide the direction of molding and then we create one dummy tooling axis for the reference to the purpose.
In this method, we select the surfaces which can create problems and take intersections in the x and y-direction. By using these curves we draw two lines and then draw a bisecting line from these two lines in the x-direction and y-direction.
If it is done in x-direction then it is called a tooling axis clearing the x-direction and if in y then the tooling axis clearing y-direction. After completing this we need to draw a final line bisecting these two tooling axis in the X and Y directions to get our final output.
Draft Analysis:
No parts can be ejected from the tool if it is having a straight 90-degree profile from its base surface. A small draft angle is provided to each & every area of the component to get easy removal of the component from the tool. The draft Analysis technique is used to analyze whether our part model created in CAD is manufacturable based on the draft condition applied. Here the part should get easily removed from the panel dies (in case of sheet metal part) or Mold (in case of plastic). Here we are providing a direction in which components should eject to get easy removal of components from the tool. In other words, it also lets us know whether the model is having a draft angle & how much is the draft angle from the tool direction.
What type of components are used to perform Draft Analysis?
Draft Analysis is performed on the components where the ejection of materials happens after the material is made inside the tools. In the case of Automotive Sheet Metal manufacturing, the blank sheet after turning into automotive panels like Hood, Fender, Roof, Side Doors, Back Doors, etc., need to be removed from panel dies. If a considerable amount of draft angle is not provided, the removal of components from the tool will be difficult. The same is the case of mold (plastic components) after getting filled inside the case & cavity. it needs to get ejected easily with the help of ejectors.
What factors should be considered while doing the draft analysis for Plastic/Automotive Sheet Metal?
The major consideration of Draft Analysis is whether a sufficient Draft Angle is provided on the component. Components while designing should be provided with a considerable amount of draft angle depending on the manufacturing consideration. For Plastic components, we provide a draft angle of 3 degrees (A draft Angle of 0.5 degrees is given ideally to the features inside the plastic part). But for Automotive Sheet Metal parts, it will be from 7 degrees to more.
Conclusion:-
Finally, the Class – A, B&C surfaces with the Tooling Direction have been Published and the Switch Bezel is moved on to the designing of the next operation – the creation of B-side features.