Week 9 - Project 1 - Door Applique Design with Engineering Features

AIM:

• Create the Base Bracket 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. 
• Create the Heat Stakes and the locators considering the design rules mentioned in the video for the door applique.  

OBJECTIVE:

        Design of an Automotive Plastic Component – Driver Side RH Door Applique Design with 4-Way, 2-Way Locators and Heat Stakes using industry principles and Design Rules. Concepts such as Rib design rules, Draft angles, Draft Analysis, Determining the Tooling Axis, Class A, Class B and Class C surfaces. The component is designed to maintain a wall thickness of 2.5mm for Applique using Surface Design and Solid Design techniques in CAD package CATIA V5.

INTRODUCTION

Heat Staking:

• Heat staking also known as thermoplastic staking is the process of joining two dissimilar materials together.
• In heat staking we use local heating and cooling to raise the temperature of plastic components and allow plastic reforming to be carried out.
• This reforming can be used in a wide variety of applications.
• The Plastic Stud protrudes through a hole in the component to be locked in place.
• Heated thermal tips are used to melt the top of the studs which fills up the volume of the cavity to produce a head locking the component in place.
• The progressive melting of plastic under continuous pressure forms the head.
• When staking, the right combination of heat and pressure is critical. 
• Applications range from staking plastic boss’s for assembly of car door panels to joining PCB’s to plastic housings.
• Benefits of this technique include; no vibration damage, no particulates, the ability to stake metalized coated applications and the capability to stake in difficult to access or restricted areas.
• In short the Locators locate the component and lock 12 degrees of freedom whereas the Heat Stake is a Fixation which locks the Final DOF.

Advantages of Heat Stakes:

• Similar and dissimilar materials may be joined: metal to metal, plastic to plastic, metal to plastic.
• Accurate control operating within a small process window.
• Local heating resulted in no damage to surrounding materials.
• Processing of glass-filled materials.
• No mechanical vibration.
• Many heat-stake shapes are possible through custom designed tools.

2 and 4 way locators:

• Locators are used to locate a job or a component to arrest its degrees of freedom using the 3-2-1 Principle which is arresting 3 DOF first, then 2 DOF's and last DOF in a sequence.
• A 4 way locator will look like a '+'  and a 2 way locator will look like a '-' .
• Both these locators use the same Rib Design Rules and principles.
• These Locators are placed on the B side of the component and must have the same height  with respect to the B surface.

Rib:

• Rib is a B-Side Engineering feature which provides a means to economical Stiffness and Strength in Plastic Molded parts without increase in overall wall thickness.
• Rib also facilitates locating and arresting components of an assembly.
• It provides alignment in Mating Parts.
• It acts as Stop and Guides for Mechanisms.

Guidelines For Rib Design:

Rib Specification	No-Show Surfaces	Show Surfaces
Draft Angle	Min 0.5º per side, Recommended 1.5º per side	0.5º per side
Rib Thickness at Base (w)	0.5 * t	0.4 * t
Rib Thickness at top	Min 0.75mm	Min 0.75mm
Rib Height (y)	Max 5*t	Max 5*t
Spacing Between 2 Ribs (x)	2*t	2*t
Fillet Radius (r)	0.125*t	Max 0.25mm
Rib Root Dia	± 30 % of t	± 30 % of t
y/x ratio for multiple ribs	3:1 2:1 preferred	3:1 2:1 preferred

DESIGN RULES OF PLASTIC COMPONENTS

• Nominal wall thickness of a plastic component is 3mm. For a strength component such as Instrument Panel, Bumper , door trims the values of thickness are larger than 4mm. For example, Thickness of IP may lie between 5-6mm, for Bumper it may be 6-8mm. For smaller components the thickness may be between 2-3mm as in this case of Coin Holder.
• Deviation of `30% from the wall thickness is allowed with gradual increase or decrease to avoid any plastic defects while manufacturing. For example: A component having wall thickness 3mm should deviate within the range of 2.1 mm minimum and 3.9 mm maximum.
• Ideal draft angle should be 3º for the overall component along for the faces lying in the tooling direction.

Fixture Design Rules:

• For a fixture designer, the major portion of design time is spent deciding how to locate the workpiece in the fixture.
  You know that any free body has a total of twelve degrees of freedom as below:
  6 translational degrees of freedom**: +X, -X, +Y, -Y, +Z, -Z**
  And 6 rotational degrees of freedom:
  - Clockwise around X-axis (CROT-X)
  - Anticlockwise around X-axis (ACROT-X)
  - Clockwise around Y axis (CROT-Y)
  - Anticlockwise around Y axis (ACROT-Y)
  - Clockwise around Z-axis (CROT-Z)
  - Anticlockwise around Z-axis (ACROT-Z)
  You must fix all the 12 degrees of freedom except the three translational degrees of freedom (-X, -Y, and -Z) in order to locate the workpiece in the fixture. So, 9 degrees of freedom of the workpiece need to be fixed By using the 3-2-1 method as shown below:
• Rest the workpiece on three non-collinear points of the bottom surface (XY), and you will be able to fix the +Z, CROT-X, ACROT-X, CROT-Y and ACROT-Y degrees of freedom**.**
  Now, rest the workpiece at two points of the side surface (XZ), and you will be able to fix the +Y and ACROT-Z degrees of freedom.
  Now, rest the workpiece at one point of the adjacent surface (YZ), and you will be able to fix the +X and CROT-Z degrees of freedom.
  So, you can successfully fixate 9 required degrees of freedom by using the 3-2-1 principle of fixture design.
• The jig and fixture are tools used for holding the workpiece in a correct location for mass production. Various types of fixtures are used in the industry. The 3-2-1 method is the fundamental principle for all types of fixture design.

PROCEDURE

Steps to be followed:

Step-1

Class A Input

First input the given Class A into the CATIA software.

Design Check on received Class A:

• After receiving the Class-A for the Applique check for the connectivity of the surfaces on it.
• Use Join operation, boundary operation and disassemble.
• The check is over if any discontinuities do not arise.

Step-2

Determine the Tooling Axis:

• Identify faces which 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 Tooling Axis creation.
• In this case Y axis can be a possible Tooling Axis Direction.
• Also there are no negatively angled problematic walls, so the tooling axis is created along Y axis as shown in Figure5.

 Step-3

Perform Draft Analysis on Class A Surface:

• Change View Mode Customization to Material mode
• Go to INSERT ---> ANALYSIS ----> FEATURE DRAFT ANALYSIS and move the compass to the Tooling Axis.
• Change the range to 2.9º.
• Apply the settings as Shown in Figure

Class B Surface Creation:

• Extract the relevant surfaces from Class-A surface which excludes the Fillets.
• Here the selected faces consist of 2 walls.
• Extract of these surfaces is shown in Figure .

 

Step-4

Class C Surface Creation:

• Extract the edges of the A surface separately as shown in Figure 13
• Use Sweep Operation to extrude the boundary using the ‘With Draft Direction’ option and selecting the boundary for Guide curve and the Tooling Axis as Draft Direction.
• Use angle as 3º draft and select outward direction with appropriate length say 20mm as shown in Figure.

Step-5

Final Closed Surface Creation:

• Join all the Class C surfaces along with the Class A Surface and trim it with Class B Surface.
• The Final trim should be one single Surface Entity without any gaps as shown in Figure.

 

Step-6

Create a Closed Body Part from Final Closed Surface:

• Switch to Part Design Workbench and use Closed Surface option to create a Solid Part from the final obtained surfaces.
• The part created is the required Applique designed from a Class A.
• The obtained solid Part is shown in Figure.

Step-7

Create Locators and Heat Stakes on B Surface 

• Create a Plane on the B side. 
• Create a sketch for a 4 way locator as shown in Figure.
• Create a sketch for a 2 way locator on the same plane as shown in the bottom location in the above figure.
• Extrude the Locators maintaining a thickness of 1.25mm as per rib design rules.
• Translate the 4 way locator to the right side so that all the locators are placed equally far away.
• Make sure the height of the locator is maintained within the rib design rules.
• Create a sketch of concentric circles for the Heat Stakes .
• Maintain Wall thickness as per Rib design rules and extrude the heat stakes at a level which is below the locators by at least 5mm.
• Ensure that each heat stake is at least 50mm apart from each other
• Give Drafts of 0.5 degrees to the walls of all the locators and the heat stakes
• Use Union Trim to keep the required faces with respect to the Applique Body.
• Give Fillets to all the walls and make entry chamfers for the Locators.

Step-8

Draft Analysis on Final Body:

Draft:

• 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, the natural tendency of it is to shrink and attach to the core or cavity half.
• The movement of 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 rough surface finish as well as weak structure due to this.
• This problem can be solved by giving 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 purpose.
• 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.
• Walls having 0º or negative draft are difficult to manufacture thus, are required to redesign from the Class A stage.

Analysis :

• Change View Mode Customization to Material mode
• Go to INSERT ---> ANALYSIS ----> FEATURE DRAFT ANALYSIS and move the compass to the Tooling Axis.
• Change the range to 0.48º.
• Apply the settings as Shown in Figure 37.
• The Final Draft analysis passes on the whole component of Applique along the Main Tooling Axis hence it can be manufactured.

 VIEWS (ISOMETRIC, SIDE, TOP, FRONT)

Tree Structure:

   

CONCLUSION:

The Design of Automotive Plastic Component –Driver Side RH Door Applique Design with 4-Way, 2-Way Locators and Heat Stakes has been completed by using industry principles such as Rib design Rules, Draft Angles, Draft Analysis for Class A and Final enclosed surface, Tooling Axis creation and implementation, Class B and Class C creation and conversion to a solid part.