As we have seen in the article on Product Lifecycle Management (PLM), there is a lot of thought process that goes behind the development of every product. One of the important tools that designers and engineers use at the early stages of product development includes 3D modelling. 3D modelling is nothing but a mathematical representation of the object by the use of CAD software. The object can be as simple as a water bottle or as complex as a railway engine; a 3D representation always helps in better visualization. Coupled with simulation software, a 3D model gives the design team insights about how the object will fare when subject to different conditions like heat, stress, pressure, and so on. The past two decades has seen a tremendous rise in computer hardware power, and consequently, a great advance in CAD / CAE software that is used for 3D modelling and product development. 3D models can convey an object’s size, shape and texture, and are used in diverse industries like heavy engineering, automobile & aerospace engineering, film and animation and architecture. There are quite a few 3D modelling software available ranging from free to paid; the better class of software like PTC Creo offers a vast range of features required for even complex product development. Today’s CAD software renders model in two prominent ways – direct modelling and parametric modelling. Both have their pros and cons.
Direct Modelling
3D modelling tries to capture the essence of an object's shape in a 3D space using mathematical entities like lines, polygons and curves. While capturing of straight lines and polygons is pretty straightforward, capturing curves is tricky as many curves do not fit into any known mathematical equation. Direct modelling allows designers to interact with the geometry of the object to be modelled in a simple, straightforward manner. With today’s WYSIWYG (What You See Is What You Get) CAD software, this can be as simple as pushing or pulling the shape of the object. One of the key features of direct modelling is that unlike parametric modelling, the geometry can be modified regardless of its history. Since it allows designers a lot of creative freedom and flexibility, direct modelling makes it possible to render the model faster. Just as an analogy, you can consider the work of a sculptor as kind of direct modelling. The design intent (“what is the purpose of the way in which the object is designed?”) of the sculptor’s work becomes clear only when he / she has chipped away a lot of unwanted material. Direct modelling allows design engineers to manipulate the design more quickly, so it can be convenient at the beginning of the conception of a project. For more accuracy, technical specificities and better visualization of the project, parametric modelling software is deemed to be a better solution.
Parametric Modelling
The Oxford dictionary defines parameter as 'a numerical or other measurable factor forming one of a set that defines a system or sets the conditions of its operation.' Parametric modelling is thus the process of rendering a 3D digital model based on a series of computer generated rules or algorithms, called as parameters. Parametric models often deal with discrete values, whereas non-parametric models will frequently incorporate continuous values. Parametric models are built from a set of mathematical equations. These equations may be standard mathematical equations (like those for circle, rectangle, parabola, etc.) that are found in mathematical textbooks, or can be proprietary equations developed by software vendors, or a combination of both. Since parametric models are feature based (mix of tool / operation and geometrical object), it is necessary to maintain the model history. Each modelling step depends upon one or multiple previous steps. This is the reason why parametric modelling is also called as ‘history based modelling’. The history structure of a parametric CAD model contains all the information related to features, dimensions, constraints and their relationships. However, parametric modelling eliminates the need for a design engineer to constantly redraw a design every time one of the design dimensions change. Since parametric modelling defines a dimension’s ability to change a model’s geometry with minimal changes, it is very useful for industrial projects that need to be skillful and very accurate. Parametric models keep a history of how objects are built. When you change parameters in the element, the element is updated automatically. The most important advantages of parametric modelling are that it allows engineers and designers to explore various design alternatives simply by varying the parameters, managing complexity and saving edit time as the part need not be recreated each time some parameter is tweaked.
Just as an interesting bit of CAD modelling software history, Pro/ENGINEER was launched by PTC, a leading provider of CAD, IIoT and other software solutions, in 1988. It was the first software with parametric, associative feature-based solid modelling capabilities. The software quickly became industry standard for parametric modelling. When PTC acquired direct modelling software Co-Create in 2007 (https://support.ptc.com/company/cocreate/), it set out to integrate both direct and parametric modelling solutions in a single software. This software was PTC Creo, and it was launched in 2010. Today, PTC Creo provides a formidable array of CAD features that has made it one of the leading CAD software in U.S.A, Europe and India.
The main difference between direct modelling and parametric modelling is that direct modelling is geometry based and parametric modelling is feature based. Both direct and parametric modelling have their pros and cons. Direct modelling is best at the conceptual level, when designers need the freedom to explore different creative ideas without being constrained. Direct model is flexible and fast. Parametric modelling makes it easier to modify dimensions later on. Thus, a good parametric model is very scalable. Whether to use direct modelling or parametric modelling depends entirely on the design requirements. In general, since direct modelling allows you to tweak the object design more quickly, it is best suited at the initial stages, where form is more important than function. However, for better accuracy, precise technical specifications and better visualization, parametric modelling is a better choice.
Industry leading software like PTC Creo offers both direct and parametric modelling as an integrated solution.