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

AIM

1. 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.
2. 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 manufacture maintaining 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 resulting in no damage to surrounding materials.
• Processing of glass-filled materials.
• No mechanical vibration.
• Many heat-stake shapes 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 of 3 DOF's 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 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 transitional 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.

[Fig1- Class A Surface]

[Fig2- Door Appliquue]

[Fig3- Door Attachment]

[Fig4- Boundry Check]

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.

[Fig5- Tooling Axis]

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 6.

[Fig6- Draft Analysis Class A SurfaceOf Door Applique]

Step-3

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 the Figure 7.

[Fig7- Door Applique Extract]

• Use Untrim Command to untrim the extracted surfaces and create a natural extend.
• It is shown in Figure 8.

[Fig8- Untrim Extract Surface]

• Extrapolate the untrimmed surfaces so that they intersect clearly and pass way forward than the Class A which will help in its trimming in further operations.
• The operation is shown in Figure 9.

[Fig9- Extrapol Untrim Surface]

• Trim the extra surfaces to obtain similar extended surfaces as in Class A.
• The surface obtained after trim is shown in Figure 10.

[Fig10- TRimmed Surface]

• Offset the trimmed surface to the value of required Thickness of the Part.
• In this case of Applique the thickness is considered as 2.5mm.
• The offset face is the part of B-Surface.
• The operation is shown in Figure 11.

[Fig11- Offseted Trimmed Surface]

• 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).
• The sign + or – must be decided so as to maintain the part thickness which in this case is 2.5mm.
• The operation is shown in Figure 12.
• The obtained surface is the required Class B Surface as shown in Figure 16.

[Fig12- Fillet For The Trimmed Surface]

Step-4

Class C Surface Creation:

• Extract the edges of the A surface seperately as shown in Figure 13

[Fig13- Extract Edge of Class A Surface]

• 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 14.

[Fig15- Creation of Class C Using Sweep]

• The class C surface obtained is shown in Figure 15.

Step-5

Final Closed Surface Creation:

• Join all the Class C surface 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 17.

[Fig16- Final Trim ]

[Fig17- Door Applique Close Surface]

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 18.

[Fig18- Solid Part Of Door Applique]

Step-7

Create Locators and Heat Stakes on B Surface

• Create a Plane on the B side.
• Create a sketch for 4 way locator as shown in Figure 19.

[Fig19- 4 Way Locator]

• Create a sketch for 2 way locator on the same plane as shown in a 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 right side so that all the locators are placed equally far away.
• Make sure the height of the locator is maitained within the rib design rules.

[Fig20- 2 Way Locator]

[Fig21- Chamfer 4 Way Loactor]

[Fig22- Fillet 1]

[Fig23- Fillet 2]

[Fig24- Chamfer & Fillet For 2 Way Locator]

• Create a sketch of concentric circles for the Heat Stakes .
• Maintain Wall thickness as per Rib design rules and exturude the heat stakes at a level which is below the locators by at least 5mm.
• Ensure that each heat stake is at leat 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.

[Fig24- Heat Stake Sketch]

[Fig25-Heat Stakes ]

• Create Counter Clearances for the heat stakes and the Locators on the attachment face.
• Here the attachment face is the Door.
• thicken the Door attachement for reference.
• Create holes to accomodate the Locators and heat stakes through it.
• The hole should have maximum 0.1mm clearance with the locators and the heat stakes.
• The Counter Clearances are shown in Figure 31.

[Fig26- Thicken Door Attachment]

[Fig27- Locator Counter Clearance Sketch]

[Fig28- Counter Clearance For Locators]

[Fig29- Sketch For Heat Stakes Counter Clearance on the Door Attachment]

[Fig30- Counter Clearance For Heat Stakes]

[Fig31- All the Counter Clearance]

[Fig32- Door Applique With Locators, Heat Stakes And Door Attachment With Counter Clearance]

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 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.

[Fig33- Draft Of 4Way Locator] [Fig34- Draft Of 2 Way Locator]

[Fig35- Draft of Heat Stake Counter Clearance] [ Fig36- Draft Of Locator Counter Clearance]

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.

[Fig37- Draft Analysis of Driver Door RH Applique]

[Fig38- Draft Analysis OF B side Features]

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.