Week 10 - Challenge 3 - Door Trim Lower with Engineering Features
Door Trim Lower with Engineering Features
Introduction
Create the Door Trim Lower with Engineering Features and Plastic components 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 also design a Four-way and Two locators, Heat Stakes, a Dog House, and a Rib at the end to perform the Draft analysis on the model.
Tooling axis Creation
In injection molding, the Class A surface is first analyzed to determine the axis or tooling direction that separates the molds. Tooling direction is critical for plastic product design because it determines mold direction
What is Draft Analysis?
Draft Analysis
For molded or cast parts, the draft angle is the amount of taper perpendicular to the parting line. It is measurable in degrees. Because plastic shrinks and sticks on molding surfaces as it cools, we draft the walls of the plastic part so that it ejects or breaks free from the molding surfaces more easily and without dragging. To reduce the risk of damage to the parts and ensure ejection, a functional injection molding part must have drafts on both the cavity and core sides.
Nominal values for Draft angles
- 3 Degrees is a nominal draft angle
- 5 Degrees can also be manufactured. Increasing the manufacturing cost
- 7 Degrees is considered for Textured surface parts
Importance of Draft in injection molding
- Reduces the possibility of part damage due to friction during the release
- Reduces mold wear and tear
- Ensures a uniform, smooth, unscratched finish
- Ensures the integrity and uniformity of other surface finishes and textures
- Reduces overall cooling time by reducing or eliminating the need for unusual ejection setups
Steps followed for Draft Analysis
- The created part must be changed to the material mode in the display frame
- Compass is enabled and placed in the direction of the Tooling Axis
- The lock command is then used to fix the compass along the tooling axis
- Color codes are classified and a Draft angle is applied
- Running point analysis is used to display permissible draft angle
For the given Class A Surface, the draft analysis is performed to determine whether the part is cleared with a draft angle of 3 degree. But with the given Class A Surface is not cleared with the 3 Degree draft angle for the respective tooling direction. It will be cleared when the class A team should rework it.
Input given: class A surface
Creation of Class B Surface
It is the offset surface of the Class A Surface the offset value depends on the thickness of the material, here the offset value is 2.5mm
Class C surface
The surface that Joins both Class A and Class B surfaces is considered to be Class C Surface
Class (A+B+C)
Here we combine all the surfaces into one closed surface using the Trim tool Command
Conversion of Closed surface into Solid Part
Using Solid Command, we convert the closed surface to a solid surface in the Part model
Creating B Surface Engineering Features Like Four-Way and Two-Way Locators, Heat Stakes, Dog Houses, and Ribs
Creating Four-Way Locators on B Surface
Locators are mainly used to Arrest the Degrees of Freedom of the Plastic Component. Usually, there are 2-way and 4-way Locators. It also supports the Position of Plastic Component While Assembly or Joining Components.
A 2-way locating pin restricts motion along 1 axis (or 2 degrees of Freedom), like a round pin in a slot. Likewise, a 4-way pin restricts 4 degrees of freedom along 2 axes. A round locating pin located concentrically in a hole is a common application of a 4-way pin and helps to further secure the piece. 4-way mean you prevent movement at 2 axes (+X, -X, +Y and -Y) on the plane. Generally, you have a cylindrical pin on the fixture and a circular hole at the workpiece part.
Any workpiece has 12 degrees of freedom for movement in space that consists of 6 Axial and 6 Radial Degrees of Freedom. All 12 degrees of freedom must be restricted to ensure proper referencing of a workpiece. These 6 Axial Degrees of Freedom permit Straight-Line Movement in both directions along the 3-principle axis shown as X, Y & Z. The Radial Degrees of Freedom permit Rotational Movement, in both Clockwise & Counterclockwise radial directions around the same three axes.
We have two objectives when assembling the child component with the parent component:
- Accurately position the part at the desired coordinates.
- Restrict all degrees of freedom except the one direction in which it'll fix so that the part cannot move.
Creating Heat Stakes on B Surface
Manufacturing operations currently use many different combinations of attachment methods to keep components together. Common fasteners such as bolts, screws, and rivets can be used to form permanent attachments, but there are attachment methods that don’t require secondary hardware. One of those methods is heat staking, which doesn’t require additional fasteners. Heat staking also known as Thermoplastic staking is the process of joining two Plastic Components together.
Gussets are Support Features that Reinforce Areas such as Walls or Bosses to the floor. Just as bridge beams and columns are supported at their vertex with gussets to add critical strength to the structure, the same concept applies to plastic injection molding.
The difference between Ribs and Gussets is that ribs are usually thin wall supports added internally around walls to achieve better geometry and support. Gussets, on the other hand, are thicker wall supports to add strength and reinforcement to existing plastic features.
Recommended Thickness of a Gusset at the Wall is 50% of the Wall Thickness. Typically, the gusset height is less than four times the wall thickness, preferably two times the wall thickness.
Creating Dog House on B Surface
Dog houses are designed to avoid Sink marks created on the CLASS-A surface by screw bosses and to solve the length issues when giving screw bosses which need to be assembled to other components. It is also useful when perpendicular screw bosses are required on the part of the tooling direction.
The dog house is an engineering feature used in the plastic trim design. Dog houses are used as supporting features. Sometimes other engineering features like snaps, locators, etc. are mounded on them to increase their strength. Dog house and other engineering Features are built on B-surface.
Design Rules For Dog House Creation
"C" is where the doghouse contacts the backside of the surface
Doghouse wall thickness at the intersection of the part wall (C) should be 40% or less than the main wall stock (T).
The height of (B) should be between 3.0 – 6.0 mm
C 40 % of T or ≤ T
B 3 - 6 mm
Width ≥12 mm
Width to Height Ratio 3:1
Draft 1.5
Side Core Axis or Lifter Axis
The side core axis is also a type of Tooling Axis, we can say it is an additional tooling axis for sub-elements on our part body in different axis.
Here we used the axis for inside clearance for the dog house part.
Creating Ribs on B Surface
As per the design rules the ribs are been created, The Solid part for the Door Handle is been created with a thickness of 2.5 mm. For the Door Handle the Calculation are as follows,
- Rib Length = 5×2.5mm = 12.5mm
- Rib Thickness = 0.4×2.5mm = 1.00mm
- Rib Fillet Radius= 25mm
- Rib Draft = 5deg
- Rib Thick at Tip = 75mm
Rib Root Analysis:
Ribs should be designed to be 30-40 percent of the nominal wall thickness. Thinner does not provide much structure and may be hard to fill. Thicker ribs are tempting, but they can begin to introduce sinks on the cosmetic surface.
By using the plane definition, the respective planes are intersected into the middle of the ribs and also the elements are selected to do the intersections on the plane surface. The Rib Root Thickness is being measured using the Tri tangent circle on the faces of the fillets and the bottom surface, the diameter of the root thickness is been measured as 2.686 mm, which is as per the design rules.
Views of the parts
Feature Tree of the parts
Performed draft analysis closed surface.
The green color indicates drafted walls above 3 deg.
The red color indicates drafted walls from 0-3 deg.
The Blue color indicates negative deg.
Analysis shows the drafted walls of Door Trim Lower with Engineering Features are above 3 degrees which is permissible for manufacturing in injection molding
Performed draft analysis for Door Trim Lower with Engineering Features with 0.45deg
Analysis shows the drafted walls of Attachment Feature Creation (Ribs and Screw Boss) are 0.45 degrees which are permissible for manufacturing in injection molding
Conclusion
The Design of the Automotive Plastic Component – Lower Door Trim with engineering features from Class A is completed using concepts of Draft angle, Draft Analysis for Class A & Final enclosed surface, Tooling Axis creation & Implementation, Class B & Class C creation, Heat stakes with supporting ribs, Locators, Dog house, and Ribs.