Week 8 - Challenge 4 - Bumper

AIM :

To create the Bumper Plastic component through the given Class-A surface with the creation of the Tooling axis meeting the requirement of the Draft angle, and taking the thickness of the component as 3 mm.

REPORT :

This report demonstrates the design of an Automotive Plastic Component – Front Bumper (Plastic) using industry principles such as Draft angles, Draft Analysis, Determining and implementing of Tooling Axis, Class A, Class B, and Class C surfaces. The component is designed using Surface Design and Solid Design techniques in CATIA V5.

Bumpers of automobiles have been made of a combination of Polycarbonate (PC) and Acrylonitrile Butadiene Styrene (ABS) called PC/ABS. It's also well-suited to heavy-duty applications, so it can be used for automotive body parts, too. The plastic used in cars, like PC/ABS, helps the body absorb and redistribute energy during an impact, keeping passengers safe. And also completely aesthetic.

Fig : BUMPER

OBJECTIVE :

Conduct a Draft Analysis for the Bumper Plastic by determining the appropriate Tooling Axis and checking if all the features are above the Nominal Drafting.

THEORY :

The terms are briefly explained below:

DRAFT :

The draft is an angular tapering given at the design stage to every Plastic Component that has to be manufactured. It is given in the direction of the Mold Movement. The Draft allows the parts to release easily from the mold without creating friction between the surface of the component and the core and cavity plates.

When a Plastic component cools down inside the mold, its natural tendency of it is to shrink and attach to the core or cavity half. The movement of the mold opening causes friction on the walls of the component as well as the core/cavity blocks. This reduces the life of the mold as well as the component itself. The component may also have a rough surface finish as well as a weak structure due to this. This problem can be solved by giving a draft to the component.

Most applications require minimum draft angles of around 0.5º to 1º however, 3º draft angles are widely accepted for cost-saving purposes. 7º Draft angles are given to textured surfaces like Instrument Panels. Minimum possible draft angles are given to screw bosses, ribs, and stiffeners due to their critical nature.

2) DRAFT ANALYSIS :

Draft Analysis is a tool in CATIA that identifies the zones which deviate from the specified values of angles along a defined draft direction using color codes. Draft analysis is the first step performed after receiving the Class A of the component. Draft analysis should be passed in order to make the plastic component manufacturable. Acceptable draft angles are used as a range for draft analysis.

For Analyzing the Draft of the Class A Surface:-

1. Change View Mode Customization to Material mode
2. Go to INSERT ----> ANALYSIS ----> FEATURE DRAFT ANALYSIS.
3. Select the compass from the dialog box, and move the compass to the Tooling Axis.
4. Click on the surface to apply the color region on the component.
5. Change the range to 0º to 2.9º. Apply the settings as shown in Figure.
6. As shown the target area has a 0º draft angle which was the concerned face since it's a flat surface.
7. Thus, it passes the criteria of having a suitable draft and the Class A can be further designed into a solid plastic component and manufactured.

Fig : Draft Analysis for Class A Surface

Fig : Multi-section view

3) TOOLING AXIS :

The tooling Axis is the direction in which the Mold opens and closes. Part Drafts are given along this axis. Identify faces that can potentially create problems while manufacturing. Surfaces at angles along a desired Tooling Axis. Extract a plain surface and create a point on its center for Axis system creation. In this case, X-axis can be a possible Tooling Axis Direction.

4) CLASS A SURFACE :

In automotive design, a class A surface is any of a set of freeform surfaces of high efficiency and quality. It is the visible aesthetic surface of any automotive component. Class A surface refers to those surfaces which are visible and abide by the physical meaning of a product. This classification is primarily used in the automotive and increasingly in the consumer goods industry. It is a requirement where aesthetics has a significant contribution. For this reason, the exterior of automobiles is deemed Class-A.

5) CLASS B SURFACE :

Class B surfaces are Engineering Surfaces that are invisible to the eyes or often on the back side of the Class A surfaces. It is mainly the thickness of the component or Class A. These surfaces need to be designed as per the Class A surface i.e., the continuity, thickness of the component, functionality, etc should be maintained. These surfaces include the main engineering features such as Screw bosses, Ribs, Snaps, Stiffeners, and fixations. B surfaces also do not contain any aesthetic styling content and textures since it is not visible to the eyes.

Below fig shows both Class A & Class B surfaces.

The light blue color is the Class A surface & Dark brown color is the Class B surface.

6) CLASS C SURFACE :

Class C surfaces are connectors between Class A and B surfaces. This surface connects both A and B surfaces along the Tooling Axis. It contains the draft as per the design. It is basically the thickened surface between both A and B surfaces.

The light blue color is the Class A surface, the Dark brown color is the Class B surface & the Grey color is the Class C surface

OPERATIONS :

1) Creation of B surface :

• Offset the relevant surfaces from Class-A surface, the offset length is 3mm since the thickness is 3mm.
• Here are some patches which are not offset as required, these patches must be filled properly with their respective dimensions.
• The patches are on the Grill, Number plate, and Upper lip.
• The offset of these surfaces is shown below.

-------> Starting with the creation of the Grill Section.

The grill patch is visible properly in the fig. shown below

• Extract the required portions i.e. the whole bumper except the grill horizontal surface, and the edge fillet using "Multiple Extract" and keep the complementary mode on. The Complementary mode helps in the selection of the surface which should not be extracted very easily.
• After extraction give a boundary to the surface with limits only to the grill.
• Extrapolate the surface on the boundary with the appropriate length.
• Now extract the horizontal surface, give a boundary on the edge, and extrapolate.
• Where these horizontal and vertical surfaces of the grill intersect with each other use the Trim command to trim.
• Measure the edge fillet radius of any edge of the grill and give the edge fillet.
• Creating fillets.
  • Create Fillets while maintaining the part thickness between the Class A and Class B surfaces.
  • The Value of the Fillet is given by the equation (B surface fillet = A surface fillet +/- Thickness of the Part).
  • The sign + or – must be decided so as to maintain the part thickness which in this case is 3mm.
  • The fillet is 3.5mm
• The Front Grill section is completed.

-------> Now the creation of the Upper Lip Section.

The Upper lip patch is visible properly in the figs. shown below

• Here steps for creating the upper lip will be same as the grill, Multiple extraction with complementary mode on, boundary, and extrapolate.
• The only difference will be smoothing the curve in order to make the edge smooth.
• Creating fillets.
  • Create Fillets while maintaining the part thickness between the Class A and Class B surfaces.
  • The Value of the Fillet is given by the equation (B surface fillet = A surface fillet +/- Thickness of the Part).
  • The sign + or – must be decided so as to maintain the part thickness which in this case is 3mm. The upper lip section measures a radius of 3.668mm so the fillet is given by subtracting the thickness.
  • The fillet is 0.668mm
• The Upper Lip section is completed.

-------> Now the creation of the Number plate Section.

The Number plate patch is visible properly in the fig. shown below

• Extract the required portions i.e. the whole bumper except the number plate, and the edge fillet using "Multiple Extract".
• The complementary mode can be kept on or off. Here I have kept on.
• Since the complementary mode was on I disassembled the extracted surface in order to perform the Untrim operation.
• Now perform the untrim operation to the extracted/disassembled surface.

• After untrim, extrapolate the surface by keeping the point continuity on.

• Trim the extrapolated surface in order to join the whole number plate edges with each other.
• Now spilt the number plate with the XY direction for aligning the intersected cut at the end.

• Creating fillets.
  • Create Fillets while maintaining the part thickness between the Class A and Class B surfaces.
  • The Value of the Fillet is given by the equation (B surface fillet = A surface fillet +/- Thickness of the Part).
  • The sign + or – must be decided so as to maintain the part thickness which in this case is 3mm.
  • The fillet is 3.5mm

The Number Plate section is completed.

Here the Class B surface is created.

2) Creation of C surface :

• Using the Boundary feature, the surface edges of Class A Surface and created boundaries on small surface edges.
• The sweep option is carried on the boundary lines to create a draft length extension (5mm) and draft angle (90°).
• After the Sweep Operation, the surface and the sweep surface are trimmed with each other in order to create the Class C surface.

CONCLUSION:

The Design of the Automotive Plastic Component – Bumper from Class A is completed using concepts of Draft angle, Draft Analysis for Class A and Final enclosed surface, Tooling Axis creation, and implementation, Class B and Class C creation.

Screenshots of the solid model with the proper color code of the draft angle in various orientations (Isometric, Front, Side, and Top View)