Saturday, 11 September 2021

Plastic part design Rules

Overview:- The following is a summary of the design rules covered in both Designing Injection Molded Parts and this course. Keep in mind that these rules are more or less guidelines intending to help you design parts that can be successfully molded. In extreme cases, it is possible to bend or even break some of these rules. You should consult a tool designer to determine the mold capabilities available for your design.

Wall Thickness:-

 Maintain uniform wall thickness as much as possible.

If you have not yet determined a material, a thickness of approximately 2.25 to 3 millimeters (.09 to .12 inches) is a good starting point.

Typical wall thickness' based on material are outlined in this table. 

When changing wall thickness, do so gradually over a distance of at least three times the change in thickness. Use a radius for a smooth transition.

When changing the wall thickness, do not exceed 25%.

Draft:-

 Always add draft to the walls of a part. Draft can be as small as 1/4 degree, but many materials require more.

Add more draft to walls greater than 25 millimeters (1 inch) in depth.

Add a minimum of 5 degrees for textured surfaces. Some texture may require more.

Undercuts:-
 Add draft to undercut surfaces to easy operation of slides or lifters. 

Plan for cosmetic blemishes formed by slides and lifters. 

Openings:- Ensure there is a minimum of at .125mm, or .005in, for the contacting steel to pass for a shutoff opening. An angle of 3 degrees is preferable. 

Bosses:- 
Add Draft to the inside and outside walls of a hollow boss whenever possible.

Blend the outside corners using a radius of 25% of the nominal thickness.

The thickness should be 50% - 75% of the nominal thickness.

For use with self-tapping screws, the outer diameter should be 2-1/2 times the major diameter of the screw.


Holes:-
 Limit the depth of a hole to twice its diameter.

Ribs:- The thickness should be 50% - 75% of the nominal thickness. 

The height should be limited to 3 times the nominal thickness.

Ensure the top of a rib is at least 1mm (.04in) in thickness.

Blend the base of a rib 25% of the thickness.

Blend the top of a rib at least .25 mm (.010in)

Space multiple ribs apart by at least twice the nominal thickness.

Friday, 10 September 2021

Why Dassault Systems invent solidworks when its have best 3d CAD software like catia?

 CATIA and Solidworks both are powerful software but both have different expertise to deal with complex design that's why dassault systems have both software to stand at top in global  market. 

-> CATIA was released in 1977 and is now owned by dassault systems. It is a product lifecycle management (PLM) software which means that it manages data during product development. It improves productivity and workflow, as usually many people work on same project.

CATIA is Powerful 3D modeling software and dominating in Automotive, Aerospace and Aeronautics.


->SolidWorks is also owned by dessault systems, launched in 1995. it is basically Parametric 3D modeling software, means by changing dimension value whole design got changed. 

Solidworks have also powerful tools which increase ability to draw using either parts or assemblies, rendering and simulation and others.

Solidworks have friendly user interface and commands to use easily. SolidWorks is very popular in industrial and products design, machinery, education, railways and medical industries.


As per above given details we can conclude, CATIA is mainly using for complex design where we need to use surfacing work. Example- Automotive, aerospace etc.

on the other hand, Solidworks have ability to work with part level design, assembly and development.

So, by the both software dessault system can cover maximum market of design and development that's why it invented and getting  continuously up-gradation in both softwares to make more friendly and easy to operate with accuracy and efficiency .


Thursday, 9 September 2021

Designing plastic parts for strength

 Overview:  Interior trim parts must withstand substantial pressure and stress specifically parts such as door panels and handles. This document explains various design options to help strengthen the part.


Plastic Filler Materials: Some plastics have fillers added for additional strength. These plastic types tend to be strong however, they can wear out the mold. These fillers have a tendency to wear out mold components like gates, runners, and manifold systems. They can also have effects inside the mold when having to flow around sharp corners or into small features. Some mold vendors prefer to place inserts into high wear areas making the area in question easy to replace. This tends to add more cost to the mold, but can save in the end by reducing the need to completely rebuild an entire mold.

Using Ribs for Strength: Using ribs is probably the most common way to strengthen a part. Ribs give strength to a part and prevent a part from warping. Ribs can be a challenge if they are too tall. You have to be aware of how thick a rib is at the base of the part. Ribs that get too wide at the base can produce a sink mark in the opposite side of the part. This is not good for cosmetic parts because these flaws can be apparent. One consideration is to reduce your rib versus wall thickness percentage. The general rule is to make the rib thickness 60% the thickness of the part. You can reduce this to 50% of the part thickness to help keep the thickness at the base to a smaller size.


Coring versus Ribs:Sometimes ribs are not the appropriate tool to use. In the following example, a door handle is created and shown with its outer shape. 



In this scenario, the part needs to look and feel as if it is a solid part. The part has a thickness that is too large to mold with a multitude of flaws including sink marks and warping. If you try to shell the part and add ribs for strength, you might create a sharper edge on the backside making it uncomfortable to grasp.

In this situation, coring can be a viable solution. By removing a series of pockets on the backside, you can simulate the feel of a complete part, but have the necessary walls in it to avoid the problems.


Wednesday, 8 September 2021

Plastic part Design CAD process

Plastic Part design CAD process
Overview:  Design requires careful planning during the entire process. Knowing how to use the available tools is the key to creating successful designs.

Conceptualization: Before creating your part, it's a good idea to conceptualize your design. Some designers begin with a 2-D layout or even a rough CAD model, which will be redone. Hand-drawn sketches can even be a tremendous advantage in getting started. Many good designs started as a rough sketch on a napkin. 

Conceptualization


For styled consumer products, many designers sculpt their parts out of clay or Styrofoam before ever attempting to create a CAD model. This can be useful in that you can create a mockup of your part. You can study this crude prototype to determine both how functional and moldable it is. Quite often, the most obvious molding issues are revealed at this stage. Reshaping your part to make it moldable before starting your CAD model saves valuable time.

Orienting the Part: The idea behind conceptualizing is to determine how to approach your CAD model. Think about your part in a mold tool. What features does it have and how are they oriented? Can the part be oriented in the mold tool so that there are no undercuts?

By answering these questions, you can determine the draw direction and parting line for your part. Then you have a starting point for your CAD model. 

Orienting the part


Modeling the Basic Shape: Many models begin by creating a Pad with a Sketch. 


With plastic parts, you should first concentrate on modeling the main portion of your part. That is, the overall shape of the part without the individual features. This portion of your model has a nominal, uniform thickness.

Shape your part by adding additional features. Creating sketches to define split profiles is a good approach. You can Pad or Shaft these sketches to Split the solid body. 


You should already be thinking about draft. Adding Draft features while creating the model in these early stages saves you time when you must prepare your model for tool design.

Padding sketches may not always define the desired shape. You may find it necessary to create surfaces or additional solid bodies. Doing this allows more flexibility in the way you can define the necessary shape. These bodies are commonly referred to as tools. Use these tools to Split or Remove material away from your solid body.




You also need to be thinking about Fillets. Use this feature to eliminate the sharp corners of your model. Fillets are normally added after Draft features.


By concentrating on only the basic shape of the part, you can now use the Shell feature to easily give the part a nominal, uniform thickness. 



Adding Features: Now you can begin adding features such as snaps, ribs, and bosses. The reason for holding off on these features until now is that they typically have a thickness smaller than the nominal thickness. The Shell feature is used to define the nominal thickness, so these features should be added after the Shell feature.


Evaluating the Design: Once you have completed your model, you need to check it. You can use operations such as Measure Between to verify the thickness in different areas. Doing this gives you a chance to catch anything you might have missed. Correcting thickness problems allows you to avoid having to deal with sink marks after the part has started a test production run.


Draft Analysis is another key tool for analyzing your part. This allows you to graphically note the draft angles. It can be quite easy to forget to draft some faces of your model.


Identifying problem areas on your model is an important step in the design process. Once a mold tool is cut, it can be quite expensive to modify. Carefully scrutinizing your design can easily save thousands of dollars.