Category: Design

Boolean operation is an important feature in CATIA V5. Types of Boolean operations include Assemble, Add, Remove, Intersect, Union Trim, and Remove Lump.

Assemble

The Assemble command basically works considering the polarity of the solid bodies. One may be interested to know what actually is the polarity of a body. In simple words, it can be said that whenever a new body is created using material formation like pad, shaft and rib or multi-section solid, then that body can be considered as positive polar body. Pocket, groove, slot and remove multi-section solid is considered as negative polar body.

A part body is created as a rectangular block and Body-1 as a solid cylinder as shown below. Consider this Body-1 as positive polar body as it is created using pad command and intersects with part body. Now if we use Assemble Boolean operation, then this cylinder will join the rectangular part body and will act as a single body.

Now again Body-2 is being created as a rectangular block  and is considered as negative polar body because pocket command is used. Whenever Body-2 is assembled with rectangular part body, it will go for material removal in intersected area due to the selection of negative polar body.

Add

Add operation removes only the intersected portion between two bodies so that both parts act as a single body irrespective of the polarity of the bodies. Here, the bodies may be with positive polarity or negative polarity or a combination of both.

Remove

Remove operation removes the selected body first and then is merged with the second body irrespective of the polarity of the bodies. Below is an example on how to create Housing using Add and Remove Boolean operation.

Intersect

 To derive a single body from two different bodies, Intersect Boolean operation is used. Basically, the intersected portion is the output which is displayed as a single body. There is no effect of polar bodies here.

In the above example, there are two sketches intersecting each other in the first picture. In the second picture, pad is created on both sides with a certain limit. After using Intersect Boolean operation, the result shows only the common portion which can be seen in third picture.

Union Trim

Unwanted material can be removed from any two bodies by using Union Trim operation which results in a single desired body.

Consider the example below:

In Model Tree, it can be seen that one rectangular body is intersecting with another circular body and the unwanted intersected area needs to be trimmed. After clicking on Union Trim, it gives an option to the user to keep/remove any face. After selecting the shape to be removed, the result can be seen as below:

Remove Lump

Remove Lump Boolean operation removes the lump inside the body.

During the operation, a tab will give the option to the user to keep/remove any face as required. Using this Boolean operation, a user can remove N number of lump face areas.

Below is an example of creating a lump first by using Remove Boolean operation and then using Remove Lump Boolean operation, it is shown how a lump can be removed.

The image below shows Remove Lump definition tab which allows to choose the particular faces. After selecting the face, result is generated.

For a stable design where design features are interlinked, Boolean operation may be a good operation to go with. After all, design aspect is important as it shows how a designer wants to edit a design in later stages through Boolean operations and allow to modify the particular part where designer wants to modify the part and not the complete body. For product benchmarking where few parameters are changing, changing the particular body can be a timesaver.

 

Plastic part design consideration plays a significant role in designing and manufacturing a plastic component. Whenever a Product Designer designs a plastic part, it is important to take care of factors such as the moulding process, selection of material, mass manufacturing process and overall area of the part around the functional need by keeping the design intent intact or the end use in consideration.

1. Overall Area of the Part

While engineering plastics are used in many diverse and demanding applications, the most common design elements or features influencing the overall area includes wall thickness and radius, ribs, bosses, draft etc.

• Wall thickness and radius: Wall thickness strongly influences many key part characteristics including mechanical performance, appearance, moldability and durability. So, to work with wall thickness, instead of increasing the entire wall thickness, the designer can check whether any kind of ribs, corrugations or curves can be added to get the same strength in the part as with increased wall thickness, as it leads to more weight and less moldability. By providing radius for each element instead of sharp edges, part ejection becomes easier during moulding process. Sharp edges create wear and tear which may result in malfunctioning of the final component after repeated use. The designer can then do a stiffness analysis from Analysis section before finalizing the product design.



 

• Ribs and Core Out: In case of rib design, the designer needs to take care of rib thickness. Typically, for a plastic part, rib thickness should be approx. 70% of wall thickness. Along with this, draft and edge radius should also be included. Meanwhile, if there is a complete solid area, the designer can check whether any core out is possible or not as core out gives better manufacturability maintaining right thickness, order and material flow to avoid multiple defects like sink mark, bubbles, fins etc.



 

• Bosses and Gussets: For boss design, the most important factor is to plan for the right diameter. As a thumb rule, the outside diameter should be 2 times the inside diameter. Meanwhile, if some bosses need to be placed in flange wall or at an increased height, coring out is the better design practice as it helps to reduce flow hesitation of material during moulding process. Gussets are similar to features boss with an additional stiffener. During design of Gussets, designer needs to take care of the design and ensure that no air traps and material filling arises. Refer below image for the same.





 

• Draft: Draft is the most important feature in plastic design. The purpose of providing angles or tapered face by draft is to remove the part from the mould with ease so that it is parallel to the direction of mould release. As a standard, one degree of draft is applied with additional one degree of draft for every 0.0254 mm of texture depth.



 

The above characteristics are pretty basic consideration for all kinds of plastic design components. In addition to the above characteristics, the designer should always take into consideration the undercuts, sharp corners, core creations etc.

2. Moulding Process

Plastic moulding is the process of pouring liquid plastic into a mould so that after a specific time, it solidifies in accordance with the provided design shape or customized shape. There are multiple types of moulding processes like extrusion moulding, blow moulding, injection moulding, rotational moulding and compression moulding.

• Extrusion moulding: In extrusion moulding, hot melted plastic is extruded and pressed through compressed air to get the desired shape. When using this process, the product will continuously have the same shape along the length.



• Injection moulding: This type of moulding is widely used in the industry. In this process, melted plastic is injected into a designed mould by applying high pressure. Injection moulding is often used for mass production with high levels of accuracy.



• Blow moulding: With blow moulding, the accuracy level of the finished component is less and thin walled. In this process, air pressure is applied inside the mould to achieve the desired shape.

3. Selection of Material

In plastic design, material selection is a very important factor. For material selection, one needs to consider application of the part. For example, if in the application area, there is some thermal stress to withstand or some kind of impact to be tolerated, then for those areas material needs to be selected as per that particular requirement.

4. Mass Manufacturing Process

Defining the right manufacturing method can help in mass manufacturing right quality products which is the final goal for any manufacturer. Here, these two aspects design for manufacturability and design for assembly comes in. This helps to identify the right assembly process – whether the assembly will be done by fitment process or by pressed process.

5. Parting Line

Defining parting line while designing a part is crucial as this parting line defines the area where the mould in halves during moulding process. Multiple aspects need to be taken care like draft angle, material roughness, any surface finish etc. CATIA has Draft Analysis feature which helps the designer to ensure sufficient draft angle is provided.

6. CATIA Integration – Analysis

Product iteration is very expensive and time consuming for an injection manufacturing process. In case structural, stiffness or curvature analysis need to be checked, they can be easily done using engineering simulation applications. CATIA Analysis for Designers is one such application which the designer can readily use to check for validating these aspects.

7. Industry Pain Areas

Most of the plastic product manufacturing organizations face multiple problems during manufacturing. Some common challenges faced by plastic manufacturing organizations are:

• When a part is to be ejected against the draft direction – in such cases, the designer must be aware of manufacturing constraints and the quantum of force ejection that can be done.
• When there are multiple no. of lifter or slider arrangements – in such cases, tool designer must analyse the slider movement with respect to time taking into consideration the cooling time. So, in those cases, CATIA Mould Tooling workbench can really be helpful.
• When designer reverse engineers a product – in such cases, achieving the desired parameter in terms of performance is a challenging task. This can be mitigated by simulating the results through virtual analysis.
• Assembly of rubber part and plastic part – for a leak proof product, the designer should not prefer the parting line as it creates material flushes in those particular junctions and it results in leakage as well as breakage or tear of rubber parts from inner surface. All these challenges can be addressed beforehand by analysing the parting line position and by doing a mock up.