3D Modelling Techniques

What is ‘parametric’ 3D modeling?

Parametric modeling uses parameters – dimensions for example – to define a model. The term parametric can be applied to either feature-based or direct-modeling software and it simply means that a design can be modified and driven with parameters.


What is ‘feature-based’ modeling?

Feature-based modeling tools work on a set of instructions (also described as a recipe) to build the model, each of which have a level of interdependency, which in a way is quite similar to programming software code. Feature-based modeling deconstructs the design into a list of steps or features that act as instructions to create the shape of the overall part. This has enabled the ability to create and work with highly complex models. Unfortunately, as there are many ways to implement feature-based 3D CAD technology, over the past 30 years or so, the market-leading modeling tool vendors have developed 3D CAD tools that are not compatible or interoperable with each other.

What is ‘direct’ 3D modeling?

Direct modeling is all about creating geometry without having to manage any feature ‘history’ or associated complexity. Designs created in a direct modeling tool do need not be held together by constraints, which basically are the relationships between entities or parts that make up a particular shape – otherwise the model would fall apart.

In the case of a direct modeling tool, users can change the size of a block for example (via a pull tool). The software can create annotations in which there are dimensions that provide the size of the block and the position of a hole for example. Engineers can then use those dimensions to edit the model. In simulation, users will often import models from a CAD system and then add the desired parameters.

When would I use feature-based modeling?

Feature-based modeling has an exceptionally strong case to be used in the creation of large and highly complex designs, which could the design of an aircraft for example. However, this approach can be inefficient for significantly smaller designs.


Why would I use direct modeling in electronic and mechanical design?

Direct modeling can eliminate many of the problems associated with traditional feature-based tools, as engineers who may not use CAD on a regular basis easily can make changes to models without having to fully understand all the instructions or constraints of a feature-based model.

The direct modeling approach allows quick iteration on concepts, whereas traditional CAD can often be a cumbersome approach when conceptualizing new ideas in response to RFQs (Request-for-Quotation). Combining a potential customer’s data and process requirements allows the cost potential and risks to be easily explored. Then once contracts are secured and work is underway, the same tools can enhance all aspects of the project – from preparation for manufacturing, adding machining stock, removing features and even into viewing and adjusting tooling arrangements.

In addition, a direct-modeling tool allows non-expert CAD users to employ a 3D-engineering tool, and often right in front of prospective customers. It can also streamline workflows as it lets users build confidence in concepts early in the design cycle. Direct modeling can also support other tasks for smaller designs including reverse engineering, machining and rapid prototyping.


Can I run CAD and 3D modeling tools on my PC?

Before the mid-1980s, CAD systems were computers that were designed specifically to perform CAD. Since then, CAD software from a wide number of vendors is available for purchase to run on general-purpose PCs and workstations. The current level of performance now offered by PCs and workstations means that, in general, they should be able to cope easily with some quite sophisticated 3D CAD software packages, which was not the case around 30 years ago. This means that the power of 3D CAD tools is now considerably more accessible to engineers and others involved in product and system design. However, it is estimated that approximately 70% of electronics design in Europe, for example, is being done in 3D, but unfortunately only about 5% of the engineering universe have access to  highly expensive 3D CAD software.