Week 9 - Project 1 - Door Trim Lower with Engineering Features
DOOR TRIM LOWER
Aim: To Create the Door trim lower component through the given Class-A surface.
Objectives:
• Creation of Tooling axis with appropriate draft angle.
• Creation of other surfaces (eg, B and C surfaces) for creating a solid component.
•Perform Draft analysis on Class A surface and Solid model hence created.
Draft
The draft is the amount of taper for moulded or cast parts perpendicular to the parting.line. Draft angles are a design consideration that makes it much easier for a part to releasecleanly from a mould. A draft angle is calculated as a degree measurement (or, less often,an inch or millimetre measurement) from the vertical axis of a mould, and it helps accountfor thermoplastic shrinkage, a practical reality of the injection moulding process for mostmaterials.
Draft angles are generally a requirement of injection moulding design (though there are aselect few soft materials, like nylon, that can get away with draft angles of zero). The draftshould be a part of the design for manufacture, and all stakeholders and contributorsshould be aware of its need at the outset of the design process. This includes productdesigners, design engineers etc and this allows considerations for design requirements tobe taken into account. Any draft is always better than no draft.
Importance of Draft:
By accounting for thermoplastic shrinkage during the cooling process, draft anglessignificantly reduce friction between the finished, cooled part and the side of the mould,Not only does this create a much easier release process, but it also offers several otherbenefits, depending on the design of the part which is as follows:
• Reduces the chance of damage to the part due to friction during the release.
• Reduces wear and tear and chances of damage to the mould
• Reduces overall cooling time by lessening or eliminating the need for unconventionalejection setups.
• Most, if not all, of these benefits, offer either direct or indirect overall production costreductions.
Procedure for creation of Solid model:
The image below shows the given class A surface for which a solid model is to be created.
Tooling Axis creation:
It is defined as the direction in which the mould/core and cavity open. Selection of thedirection of the tooling axis depends on the ease at which components can be easilyejected.
By analysing the component the most easily ejectable direction is somewhere close to theZ direction,(might be inclined to it) so we have made a sketch on the YZ plane of AxisSystem) to create a bisecting line considering the 2 faces which might be difficult to betooled
As we know minimum draft angle for the faces of the plastic component should be 3degrees. So the value of 2.9 degrees (consideringtolerance) is provided in the Draftanalysis colour mode window Inside the colour scale, the GREEN bar shows the draftangle of 2.9 or above 2.9 degrees. The blue bar shows below 2.9 degrees draft angle theother limit being and the RED bar shows the negative draft angle. As shown in the imagebelow all the top faces and side faces of the component are green, while the bottom facesare red. The line ofdemarcation between the green and red faces is the parting line whichdivides the core and cavity halves. The solid model has cleared the draft analysissuccessfully as shown in the image below
CREATING THE RIB
Ribs are thin wall protrusions that extend perpendicularly from a wall or plane. They areusually found in clusters offering support to a plane that would have otherwise been toothick, but can also be stand-alone support for a single wall. They are commonly used toprovide additional support and strength to a part. Thickness and location are essential torib design.
First, the base surface where the rib has to be created is extracted using the Extractcommand.
Next, the profile is extruded, to find the height,h=Wall thickness * 5
=2.5*5
= 12.5 mm
Therefore, the height is 12.5 mm
The extruded surface is thickened,
Thickness,w=0.4*t
=0.4 2.5
=1mm
Therefore, the thickness of the rib is 1 mm
The draft is applied to the sides of the ribs. As per the design rule, the ideal draft angle is 0 deg
Now, we have to check for the Rib root thickness.
To check for the Rib root thickness, We have to take an Intersection with the XY plane andthe Coin holder component. Once we get to theintersection we have to create a tritangent circle at the rib area and measure it. The value must be within 30% greater of the wall thickness.
The draft is applied to the sides of the ribs. As per the design rule, the ideal draft angle is 0.deg
Hence, the ribs are created for the screw HEAT STAKES
Now we will see how the plastic part is fixed onto the other plastic part. The door applique ifixed on to the door surface with the help oflocators and heat stakes. Every component inspace has 12 degrees of freedom. So these locators and heat stakes restrict all thesedegrees of freedom.Locators are 4-way locators. The locators will follow the rib design guidelines and will be given a minimum draft of 0.5 degrees and a minimum fillet of 0.2mm and an entry chamfe of 3mm. This entry chamfer is given so that the locators can mate with the other part easil
CREATING THE DOGHOUSE
The dog house is an engineering feature used in the plastic trim design. Dog houses areused as a supporting feature. Sometimes otherengineering features like snaps; locators,etc. are mounded on them to increase their strength.
The doghouse is created by following the design rules.
The nominal wall thickness guide range is from 0.75 mm to 3 mm for reinforced materials
and 0.5 mm to 5 mm for unreinforced materials.
Related Courses
WALL THICKNESS (W) = 0.70 (NOMINAL THICKNESS OF PLASTIC MATERIAL)
This process is usually done by Thicken surface command.
An important thing while designing a doghouse is to maintain 40% less thickness than the wall thickness (T) at the area of the intersection to avoid sink marks. So, a C shape is formed at the intersection.
This can be made using the split command to remove the solid at the intersection
Draft Analysis
