Week 8 - Challenge 4 - Bumper
BUMPER REPORT
CLASS-A SURFACE: A surface made by the designer which is given as an input to the plastic modeler to work on. It is an aesthetic surface and the outer most surface.
CLASS B SURFACE:
To create the class B surface, offset the class A surface inside as per our thickness requirement (here the thickness is 3mm, so I offset the class A to 3mm inside). Once the offset is created, we can observe some patches on the offset surface by taking the boundary for the offset surface, those patches are formed due to the fillets on the class A surface. We need to cover those patches with the help of the multi-section surfaces command by extracting the patch boundaries. Once all the patches on the offset are covered properly join all the patches with the offset surface, to get the replicated surface of the class A surface.
CLASS C SURFACE:
To create the class C surface concerning the boundary of the class A surface, I used the sweep command. Initially, I extracted the boundary of the class A surface with tangent continuity, and I sweep the extracted boundary concerning the surface at 93deg (for draft angle) for 4mm to intersect properly with the class B surface. Once we sweep all the surface boundaries of class A, extrapolate the sweep surfaces until both surfaces got intersected properly, and trim them to remove extended extrapolated surfaces to get a proper sweep boundary throughout the entire surface, including the centre hole of the bumper.
Now, join both class A and sweep boundary to get the complete class C surface.
DRAFT ANGLE
A draft angle is a taper applied to the vertical walls of the injection molded component to assist with releasing the part from the mold
IMPORTANCE:
Draft angle is a required feature. A functional part for injection molding has to have drafts facing both cavity and core sides to reduce the risk of damage to the parts and ensure ejection. As the molten plastic flows into the closed die and fills the cavity, the material shrinks inside the mold upon cooling and as a result grips the core.
Without any taper, the part would come out scratched while increasing wear and tear on the mold and shortening the tool life. Even worse - if the part does not eject, it requires a production halt to manually peel it off.
Adding an adequate draft angle ensures that warpage upon ejection is prevented while maintaining a decent cosmetic finish.
ADVANTAGES
- Minimizes the warping to your geometry
- Increases the tool life of the mold
- Improves the surface finish on your plastic parts
- Cuts down cost by reducing the cooling time
TOOLING AXIS:
To create the tooling axis, I extracted a surface from class A and created a point in the middle of the surface by using the point command and created a line at that point through the x-axis. Now, I performed a draft analysis check from that line whether the created tooling axis is in the correct position or not. If, in the draft analysis check the surface highlighted with green colour on both sides of the surface the tooling axis is in the correct position and direction.
DRAFT ANALYSIS:
Draft analysis is a tool in the CAD modelling software using which we can analyse draft angle provided to any component. Draft is indicated through a colour scale variant. There are multiple colours on the scale which we can use to indicate the safe angles and unacceptable angles. Here in the analysis of a Bumper we have used green colour for safe angle and red clour for unacceptable angle. The provided draft angle for the analysis is 3 degrees.
First we analysis the model and then choose dummy axis in x and y direction.
As we intersect, we observed that the side walls are not given any draft. Hence, we assume the axis normal to the base surface and parallel to side walls. This surely will create problems because a minimum draft has to be provided.
