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- Aim: Development of a Door Trim panel - Objectives: - To extract all the necessary surfaces like class B and C. - To capture the complex areas properly and make sure the drat is done. - To capture all the attachment features like ribs, snap, heat stakes, 4-way locator, dog house, etc. - To make sure the part is feasible…
Neel sanap
updated on 21 Apr 2021
- Aim: Development of a Door Trim panel
- Objectives:
- To extract all the necessary surfaces like class B and C.
- To capture the complex areas properly and make sure the drat is done.
- To capture all the attachment features like ribs, snap, heat stakes, 4-way locator, dog house, etc.
- To make sure the part is feasible and possible to manufacture at the same time economical and weight is also considered.
- Method:
- Tooling direction is the direction in which mould or cavity opens. This is the place where mould splits into two half and class B and C can be formed. Also, this is the place where class B is taken and whatever necessary corrections are required can be done here.
- Before forming any offset for class B, as all the surfaces are separated, it is necessary to separate them and form as a single surface for each part.
- For this particular project parts to be formed are as follows:
- Door armrest
- Bottle holder
- Map pocket
- Lower substrate
- For extracting the given surface use the join command and clicking the right click on it use all nearby faces which allows the catia to select the faces automatically.
Map pocket |
|
Door armrest |
Bottle holder |
Lower substrate |
- After extracting all the faces separate geometry property can be created and these all have to be assigned there.
- Class A:
- In automotive design, a class A surface is any of a set of freeform surfaces of high efficiency and quality.
- Class A surfacing is done using computer-aided industrial design applications. Class A surface modellers are also called "digital sculptors" in the industry. Industrial designers develop their design styling through the A-Surface, the physical surface the end-user can feel, touch, see etc.
- A common method of working is to start with a prototype model and produce smooth mathematical Class A surfaces to describe the product's outer body. From this, the production of tools and inspection of finished parts can be carried out. Class A surfacing complements the prototype modelling stage by reducing time and increasing control over design iterations.
- Class A surfaces can be defined as any surface, that has styling intent, that is either seen, touched,
- Class B:
- Class B is the one surface that is mostly used to capture the 2nd half of the part, it is the part that splits into the mould.
- Class B surfaces are the secondary surfaces that you can see sometimes, but are less important, such as the inside of your glove box, ashtray, etc. These must be smooth and "error-free" as well but are not held to the standards that class A surfaces are.
- Class C surfaces:
- These are the backside surfaces that can have tool marks, flash and other imperfections without hurting appearance, function, etc.
Following are some steps that show how class B&C can be taken and some errors encountered:
Class B can be taken as an offset from class A to a distance of the thickness of the part. |
Class C can be taken by using the sweep command and this sweep can be taken as a reference to the surface or to the tooling direction. Step by step sweep can be done in order to capture the surfaces more properly, |
In order to form class C, sweep has to be done and in order to form the surface, sweep has to be done either with reference to the surface or with tooling axis. |
|
Some errors are there which are need to be taken care and those are shown above. |
|
Some errors due to which solid cannot be formed as the surface is not a closed one. |
- Solid surface:
- Once the closed surface is formed a solid can be captured using part workbench and this solid can be further used to capture all the features and perform draft analysis.
Bottom holder |
Map pocket |
Lower substrate |
Arm rest 1 |
Arm rest 2 |
- Draft analysis:
- This type of analysis is performed based on colour ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.
- The draft analysis button within CATIA V5 will help you quickly gather the draft angle on multiple surfaces without the need for tedious manual measurements.
- You need to take into account the behaviour of the plastic as it is injected and as it cools. You also need to think about how your part will be removed from the mould. CATIA V5 has special features for making this process easier.
From the image, it can be seen that the draft analysis is done for the given component and as the entire surface shows the green that means the draft angle is above 3 degrees and it is feasible to manufacture the component. For the given component the tooling axis is needed to be given as shown in the image and for all the components separate tooling axis is needed to be done. |
As the entire surface is not getting drafted from a single tooling axis it needs to be draft using a second tooling axis which will come as shown in the image. This results in providing a side core that can be used to produce the component and to make sure that it passes the draft criterias. |
Draft for map pocket is done and as shown in the image it can be seen the entire surface shows green which means the tooling axis angle is correct and it is feasible to manufacture the component. |
For the area which shows red, as it does not satisfy the draft criteria, a separate tooling axis is needed to be done and a separate analysis has to be done. |
- Entire solid has been done and all the surfaces are properly captured.
- Features for door trim:
- Heat stakes:
- Heat staking technology is quite simple in concept. Whenever two or more components need to be attached to one another, and at least one is made of a thermoplastic, a combination of heat and pressure can be used to reform the plastic to the many shapes or profiles to retain or join the parts together.
- This creates a solid, hardware-free bond that uses the plastic’s inherent strength to keep the finished assembly together.
- The main advantage to heat staking, when compared to fastener-based technologies, is that manufacturers can perform all heat staking in one machine cycle and motion versus individual motions required for each fastener. A secondary benefit is that the manufacturers do not need to change the base material – it can remain “AS-IS” while the plastic is heat staked to conform to its final dimensions.
- Heat staking technology, on the other hand, creates almost no mechanical stress because it operates through precise control and application of the temperature and pressure to cause the reforming of the plastic that it makes contact with.
- From the image, the basic design guidelines can be taken. Though this may vary as per the requirement.
As the heat stake is getting attached to the lower substrate it is necessary to pad the heat stake in the same direction as that of the tooling direction for the lower substrate. |
|
- Ribs:
- Ribs are a feature in plastic injection moulded parts. They are thin extensions that run perpendicular to 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. Here are some helpful design guidelines:
- They should be designed with a thickness that is ½ the wall thickness to avoid a thick section at the wall base
- To minimize sink marks, design ribs that are approximately 60% of the joining wall thickness for minimum risk
- Best practices include spacing at a distance of at least twice the wall thickness
- Glossy materials require a thinner rib (40% of wall thickness)
- An advantage of using ribs is that they increase the strength of the part without increasing wall thickness. Walls that are too thick can sink, warp or result in other defects. Their integration into a part results in less material usage; therefore a more cost-effective solution.
- Working with an experienced injection moulding manufacturer can not only lessen your risk with production issues but also save costs and time in the long run.
Offset the surface with which the ribs need to be split with. In this case, it is class b which is offset to a distance of 2mm. Also draft is need to be provided for all the ribs. |
Once all the ribs are created perform the union trim and remove all the unnecessary solid. |
Same ribs need to be provided on the map pocket and the lower substrate. |
|
- Flanges:
- In order to position the heat stakes and 4-way locators flanges are need to be provided. The pad direction for the flanges should be as per the tooling direction of the solid where it is going to be attached.
- Snap-fit:
- A snap-fit is an assembly method used to attach flexible parts, usually plastic, to form the final product by pushing the parts' interlocking components together. There are a number of variations in snap-fits, including cantilever, torsional and annular. Snap-fits, as integral attachment features, are an alternative to assembly using nails or screws and have the advantages of speed and no loose parts. Snap-fit connectors can be found in everyday products such as battery compartment lids, snap fasteners and pens.
- A large proportion of snap joints are basically simple cantilever snaps, which may be rectangular or of a geometrically more complex cross-section. It is suggested to design the finger so that either its thickness (h) or width (b) tapers from the root to the hook in this way, the load-bearing cross-section at any point bears a more appropriate relation to the local load. The maximum strain on the material can therefore be reduced, and less material is needed.
- Dog house:
- Dog house is an engineering feature used in the plastic trim design. Dog houses are used as supporting feature. Sometimes other engineering features like snaps; locators etc. are mounded on them to increase their strength. Dog houses are subjected to draft analysis to prevent breakage of the component during ejection from the mould cavity. Dog house and other engineering components are built on B-surface.
DESIGN CONSIDERATION FOR CREATING DOG HOUSE:
Wall thickness = 0.70 x Thickness of the plastic material
Fillet on the inner side = 0.25 x Thickness of the plastic material
Fillet on the outer side = 1.25 x Thickness of the plastic material
Fillet on the coring edges = 0.25 x Thickness of the plastic material
Coring thickness = 0.40 x Thickness of the plastic material
Draft angle 2deg to 3deg
Sketch for the dog house. Once the sketch is prepared, shaft operation can be used for 180 degrees and the body can be formed. |
In order to represent the ribs for the dog house, either a surface can be created which then thicked or a sketch with open lines can be created which then pad in order to represent the ribs. Later union trim need to be created and this dog house needs to be added to the lower substrate and using union trim unnecessary surfaces are need to be removed. |
- Finished part:
- Reference:
https://www.thermalpress.com/why-use-heat-staking-for-plastic-assembly/
http://fab.cba.mit.edu/classes/S62.12/people/vernelle.noel/Plastic_Snap_fit_design.pdf
https://mechanicalvinoth17.files.wordpress.com/2014/11/dog-house2.pdf
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