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 release cleanly 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 account for thermoplastic shrinkage, a practical reality of the injection moulding process for most materials.
Draft angles are generally a requirement of injection moulding 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 all stakeholders and contributors should be aware of its need at the outset of the design process. This includes product designers, design engineers etc and this allows considerations for design requirements to be taken into account. Any draft is always better than no draft.
Importance of Draft:
By accounting for thermoplastic shrinkage during the cooling process, draft angles significantly 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 other benefits, 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.
• 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
Given sample design
Overview:
Initially, we need to offset the given Door Trim class A surface in the inner direction to the required thickness (here the thickness is 2.5mm). After that, we need to close the patches on the offset surface of the bumper, the patches are formed due to the fillets on the Class A surface. Once all the patches are closed properly join them together to make a proper class B surface and now sweep the boundary of the class A surface to trim with the class B surface to make a closed body. By using the closed body command in the Prat workbench we can get the solid body from the closed surface of the Door Trim. Now, I created the Heat stakes and Locators by considering all the design parameters. After creating all the B-side features on the solid part body of the door trim, I performed a draft analysis for it to check whether all the surfaces are drafted properly or not (The draft angle for the plastic component is 0.5deg to 3deg).
TOOLING AXIS:
To create the tooling axis, I extracted a surface from class A and created a point in the middle of the surface by using the point command and created a line at that point through the x-axis. Now, I performed a draft analysis check from that line whether the created tooling axis is in the correct position or not. If in the draft, analysis check the surface highlighted with green colour on both sides of the surface the tooling axis is in the correct position and direction.
Tooling axis:
DRAFT ANALYSIS FOR CLASS A SURFACE:
We do perform the draft analysis check for class A surface before we make solid and creation of B-side features. Initially I align the compass to the tooling axis and I gave a 3deg draft angle for the green colour in the colour bar. If the surface is highlighted in green colour the draft angle is given properly for class A surface. If the class A surface is not highlighted fully in green colour, that might be the reason for the draft angle of the class A surface.
CLASS B SURFACE:
To create the class B surface, offset the class A surface inside as per our thickness requirement (here the thickness is 2.5mm, so I offset the class A to 2.5mm inside). Once the offset is created, we can observe some patches on the offset surface by taking the boundary for the offset surface, those patches are formed due to the fillets on the class A surface. We need to cover those patches with the help of the multi-section surfaces command by extracting the patch boundaries. Once all the patches on the offset are covered properly join all the patches with the offset surface, to get the replicated surface of the class A surface.
CLASS C SURFACE:
I used the sweep command to create the class C surface concerning the boundary of the class A surface. Initially, I extracted the boundary of the class A surface with tangent continuity, and I sweep the extracted boundary concerning the surface at 93deg (for draft angle) for 4mm to intersect properly with the class B surface. Once we sweep all the surface boundaries of class A, extrapolate the sweeped surfaces until both surfaces got intersect properly, and trim them to remove extended extrapolated surfaces to get a proper sweep boundary throughout the entire surface, including the centre hole of the door trim. Now, join both class A and sweep boundary to get the complete class C surface.
PART BODY:
To create the solid part body from the closed surface, I used the closed surface command in the part workbench.
CREATION OF LOCATORS:
To create the locators, I created a sketch on the body. After creating the sketch, I pad it 20mm in height and thicken it to 1.3mm and I drafted it with 0.5deg in the direction of the tooling axis. I gave 5mm of chamfer with 45deg of inclination and after I gave a fillet of 0.25mm radius.
4-way locator:
CREATION OF HEAT STAKES:
To create the heat stakes, I draw a sketch on the surface. After the creation of the sketch, I pad it to 18mm height and I gave a draft angle of 0.5deg on both sides (inside and outside) and then I gave a fillet with a 0.25mm radius. After creating the heat stake, I created the ribs for supporting purposes. To create the ribs, I draw a sketch and padded it to 12mm in height and 1mm in thickness. After padding the ribs, I drafted 0.5deg in the tooling asix direction and filleted it with a 0.25mm radius. Finally, I union trim the ribs with a heat stake to remove the ribs, which are present inside the heat stakes.
Heat stake with supporting ribs:
Now I Power copy the heat stakes by giving inputs like point and plane copy them in the part body according to the requirement.
Final part body with 4-way locators including all the heat stakes with supporting ribs:
CREATION OF RIBS:
Ribs are a feature in plastic injection molded parts. They are thin extensions that run perpendicular from a wall or plane. They are commonly used to provide additional support and strength to a part. Thickness and location are essential to rib design.
To create the ribs, I draw a sketch and padded it to 12mm in height and 1mm in thickness. After padding the ribs, I drafted 0.5deg in the tooling asix direction and filleted it with a 0.25mm radius.
use power copy to produce rib and another two ribs are produce using tranlate command to have command on both the steps.
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 the direction of the tooling axis depends on the ease at which components can be easily ejected.
By analysing the component the most easily ejectable direction is somewhere close to the Z direction,(might be inclined to it) so we have made a sketch on the YZ plane of Axis System) to create a bisecting line considering the 2 faces which might be difficult to be tooled.
One more sketch is created on the ZX plane of Axis System for considering the lone side face for tooling direction. In the sketch, a line is drawn with a suitable angle to the lone
side face so that with the resultant tooling axis the side face is cleared.
Then resultant tooling axis is created using the bisecting method.
Draft Analysis of Solid Model
Same steps are followed to get the draft analysis of the solid part as in Class A Surface
As we know minimum draft angle for the faces of the plastic component should be 3 degrees. So the value of 2.9 degrees (considering tolerance) is provided in the Draft analysis colour mode window Inside the colour scale, the GREEN bar shows the draft angle of 2.9 or above 2.9 degrees. The blue bar shows below 2.9 degrees draft angle the other limit being and the RED bar shows the negative draft angle. As shown in the image below all the top faces and side faces of the component are green, while the bottom faces are red. The line of demarcation between the green and red faces is the parting line which divides the core and cavity halves. The solid model has cleared the draft analysis successfully as shown in the image below.
CREATING THE RIB
Ribs are thin wall protrusions that extend perpendicularly from a wall or plane. They are usually found in clusters offering support to a plane that would have otherwise been too thick, but can also be stand-alone support for a single wall. They are commonly used to provide additional support and strength to a part. Thickness and location are essential to rib design.
First, the base surface where the rib has to be created is extracted using the Extract command.
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 0.5 deg
Then fillet is applied to the faces of the rib. As per the design rule, the fillet can be 0.25 mm.
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 and the Coin holder component. Once we get to the intersection we have to create a tri-tangent circle at the rib area and measure it. The value must be within 30% greater of the wall thickness.
The locators restrict all the other degrees of freedom except the translation along the direction of tooling axis Le along y-axis. For restricting that degree of freedom we will be using the heat stakes.
In heat staking, we use local heating and cooling to raise the temperature of plastic components and allow plastic reforming to be carried out.
The draft is applied to the sides of the ribs. As per the design rule, the ideal draft angle is 0.5 deg
Then fillet is applied to the faces of the rib. As per the design rule, the fillet can be 0.25 mm.
The Orange colored cylinders are the heat stakes.
These heat stakes will enter the mating component and using a heat staking machine these heat stakes are melted and cooled. When cooled this will get hardened and the two components will stick together. Thus all degrees of freedom are arrested
Then, the ribs are created by following the rib design rules.
The draft is applied to the sides of the ribs. As per the design rule, the ideal draft angle is 0.5 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 is fixed on to the door surface with the help of locators and heat stakes. Every component in space has 12 degrees of freedom. So these locators and heat stakes restrict all these degrees 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 chamfer of 3mm. This entry chamfer is given so that the locators can mate with the other part easily.
The draft is applied to the sides of the ribs. As per the design rule, the ideal draft angle is 0.5 deg
CREATING THE DOGHOUSE
The dog house is an engineering feature used in the plastic trim design. Dog houses are used as a supporting feature. Sometimes other engineering 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.
The fillets and the draft are given as per the design rules.
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
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