Week 8 - Challenge 1 - Base Bracket Design

AIM :

To Create the Base Bracket Plastic component through the given Class-A surface.

OBJECTIVE :

The objective of this challenge is to create a BASE BRACKET DESIGN along with a Solid Part Body from Class-A surface following OEM design standards in CATIA SURFACE WORKBENCH and PART DESIGN.

BASE BRACKET DESIGN :

The Procedure to be followed is given below,

DESCRIPTION :

Four stages of the design life cycle are as follows:

• Concept Sketch :

These are imaginative and innovative sketches. Concept sketches can be defined as a collection of visual cues sufficient to suggest the design to an informed observer. These are the basic sketches that provide a general idea about the design of the product. These sketches are provided to the system either in 2D or isometric form. For Example, a concept sketch of an automobile.

• Class A Creation :

Class A surface refers to those surfaces which are VISIBLE and abide by the physical meaning, of a product. For styling class A surfaces of automobiles ALIAS software is used. These class-A surfaces are used as an input for an Automotive Plastic Designers

• CLAY MODELING :

In clay modeling, class-A surfaces are provided to clay modelers who designs actual models of automobile using industrial clay. Class-A surfaces and clay models are co-related. Using a clay modeling physical representation of the design is possible which helps in further modifications in the design of the vehicle. Clay modeling of an automobile is the most common example of clay modeling.

• NPD CAD :

New Product Development (NPD) Computer Aided Drafting (CAD). This process involves forming a strategy, organizing requirements, generating concepts, and creating products.

CLASS A SURFACE :

Class ‘A’ surfaces are primarily used in the automotive environment and 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, and have an optimal aesthetic shape and 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. Majority of the time this term is used in Plastic Part designs.

CLASS B SURFACE :

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 SURFACE :

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.

INPUT CLASS-A SURFACE :

(Fig 01 : CLASS A SURFACE)

STEP 01 : Creating a Tooling axis

To Create a Tooling axis :

1. The reference point is first created on any hole of Class A surface.
2. A new axis system is deployed on the reference point to plot the clearance lines.
3. Creating an intersection between the part and a plane with the help of new axis system.
4. Two lines are created coinciding with the intersection. (refer fig 02)
5. The bisecting line is created between these two lines.

(Fig 02 : TOOLING AXIS)

STEP 02 : Performing a draft analysis for the given model :

DRAFT ANALYSIS:

Draft Angle:

The draft angle is the amount of taper for molded or cast parts perpendicular to the parting line. It can be measured in degrees or mm/mm (in/in). As the plastic cools, it shrinks and therefore shrinks onto molding surfaces. Because of this and a few other reasons, we draft (angle) the walls of the plastic part, so as the part is removed it breaks free from the molding surfaces easier and without dragging. 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. What’s also important is to overcome the vacuum forces by letting air in between the metal and the plastic for the part to release properly. Adding an adequate draft angle ensures that warpage upon ejection is prevented while maintaining a decent cosmetic finish.

• Draft angles are generally a requirement of injection molding design (though there are a select few soft materials, like nylon, that can get away with draft angles of zero).
• The draft should be a part of the design for manufacture, and the Plastic Product Designer should be aware of its need at the outset of the design process. This allows considerations for design requirements to be taken into account.

Nominal Values for Draft angle:

1. 3 Degree is a nominal Draft.
2. 5 Degrees can also be manufactured. But it will increase the manufacturing cost.
3. 7 Degrees for a textured surface.

Importance of DRAFT in Injection Molding:

• Reduces the chance of damage to the part due to friction during the release
• Reduces wear and tear and chances of damage to the mold
• Ensures a uniform, smooth, unscratched finish when required
• Ensures the integrity and uniformity of other surface finishes and textures
• Reduces overall cooling time by lessening or eliminating the need for unconventional ejection setups
• Most if not all of these benefits, offer either direct or indirect overall production cost reductions.

Steps followed for Draft Analysis:

1. The part created has to be changed to the material mode in the display frame.
2. Compass is enabled. Align compass along with tooling direction.
3. The lock command is then applied to fix the compass along with the tooling axis
4. Color codes are classified and a Draft angle is applied.
5. Running point analysis is used to display permissible draft angles.

(Fig 03 : DRAFT ANALYSIS ON CLASS-A SURFACE)

STEP 03 : Creating Class B Surface from Class A Surface :

1. Extract the relevant surfaces from the Class-A surface which excludes the Fillets and holes. The extraction process is shown in the Figure below

(Fig 04 : Extract of surfaces from Class A)

2. Use Untrim Command to untrim the surfaces and create a natural extend. The Untrimming process is shown in the Figure below

(Fig 05 : Untrim of Extracted Surfaces)

3. Extrapolate the untrimmed surfaces so that each of them intersects clearly and passes way forward than the Class A which will help in its trimming in further operations. The Extrapolating process is shown in the Figure below

(Fig 06 : Extrapolated Surfaces created from Untrimmed Surfaces)

(Fig 07 : Extrapolated Surfaces and Class A Surface )

4. Trim the extra surfaces to obtain similar extended surfaces as in Class A. The operation performed on the Ribs of the Bracket.

(Fig 08 : Trimming of Extrapolated Surfaces )

(Fig 09 : Trimmed Surfaces and Class A Surface )

5. Offset the obtained Trim to the value of required Thickness of the Part. In this case of Bracket, the thickness value is 2.5 mm. The offset faces are the part of B-Surface.

(Fig 10 : Side view of Offset and Class A surface showing the start of B surface creation )

6. Create Fillets while maintaining the part thickness between the Class A and Class b surfaces. The Value of Fillet is given by the equation (B surface fillet = A surface fillet + - Thickness of the Part).

7. The sign + or – must be decided so as to maintain the part thickness which in this case is 2.5mm.

8. The fillet values can also be obtained by maintaining the thickness in the intersection sketch of the two surfaces.

(Fig 11 : Surface Edge Fillets as per the Part Thickness )

(in this case 2.5mm)

(Fig 12 : Class A surface & Class B surface )

(Coloured surface is Class A surface & other one is Class B surface)

STEP 04 : Creating Class C Surface :

1. Use Boundary option to extract the outer boundary of the Class A surface.

(Fig 13 : Giving Boundary to Class A)

2. Use Sweep Operation to extrude the boundary using the Draft direction option and selecting the Tooling Axis as the direction. Sweep the outer boundary and the hole boundaries.

3. Use draft angle as 3º and Sweep it well beyond the B surface.

(Fig 14 : Sweep operation for Class C surfaces )

4. Joining all the Swept surfaces along with the Class A Surface with join command.

(Fig 15 : Join operation for Class C surfaces )

5. Unhidding the Class B surface for further operations.

(Fig 16 : Unhidden Class B surface )

6. Trim the obtained Joined surfaces with the Class B surface to obtain the final enclosed Surface for the Bracket

(Fig 16 : Final Closed Surface )

BASE BRACKET TREE STRUCTURE :

CONCLUSION :

The Design of Plastic Component - Base Bracket from Class A is completed using concepts of Draft angle, Draft Analysis, Tooling Axis, Class B and Class C creation and converting Closed surface to a solid part.

BASE BRACKET (FINAL SOLID BODY) :

(ISOMETRIC VIEW )

(FRONT VIEW )

(BACK VIEW )

(LEFT HAND SIDE VIEW )

(RIGHT HAND SIDE VIEW )

(TOP VIEW )

(BOTTOM VIEW )