CAD and the art of complex machine design

3D CAD software offers critical time, cost, and quality benefits for machine designers, says Ved Narayan*, vice president, Asia Pacific, SolidWorks Corporation.

Visualising product designs developed on a 3D computer aided design (CAD) system is clearly easier than interpreting and extrapolating 3D physical objects from flat 2D line drawings, and while the direct, intuitive nature of 3D design is useful for designers of all types of products, 3D CAD software is particularly beneficial to designers of complex machinery and mechanisms.

Regardless of a specific machine''s size or purpose, machine design typically involves the development of moving assemblies consisting of numerous components that interact and operate in unison to achieve distinct functions. Whether a machine is physically large, such as an 18-meter-long transport vehicle, or comparatively small, such as the assemblies required to operate an automated bio-assay high throughput screening system for processing laboratory samples, 3D CAD offers important benefits that save manufacturers time and money, while at the same time providing the necessary tools for improving design performance and solving difficult engineering problems.

The benefits of using 3D CAD software for machine design stem from the improved capacity to visualise, evaluate, and ''interrogate'' assembly designs and leverage design data for downstream functions, offering greater flexibility, better insight, and higher

levels of automation than the tedious, time-consuming, trial-and-error approach that is characteristic of 2D design.

Improved interrogation of machine designs
Using 3D CAD, machine designers can more effectively assess fit and function, confirm clearances within assemblies, leverage the use of standardised components, apply modular design techniques, evaluate various assembly configurations, validate design performance, make design changes, communicate design information, create design documentation, and utilise complementary engineering and manufacturing applications.

Instead of employing the repetitive prototype development approach that is common to 2D design, engineers can use the improved visualisation and validation capabilities of 3D CAD, such as interference / collision detection and the ability to view inside hidden assemblies, to ''interrogate'' machine designs fully before ever creating a physical prototype, enabling them to optimise designs more quickly and cost effectively.

After achieving an optimal design in 3D CAD software, machine designers can also realise the productivity benefits related to the versatility of 3D design data by applying it for downstream functions in a more automated fashion. Integrated design analysis, automatic generation of engineering drawings, instant output of bills of materials (BOMS), direct links to computer-aided manufacturing (CAM) applications, development of exploded views for product documentation, creation of assembly instructions, and machine animations are just some of the additional capabilities associated with using 3D CAD for machine design.

Working in conjunction with the UK''s Lancaster and Northumbria Universities with partial funding from the Department of Trade and Industry (DTI), Silvertip Design (Skeeby, Richmond, North Yorkshire) streamlined its design process on the development of the revolutionary Blade Runner transport vehicle — an 18-meter-long, dual-mode road-to-rail vehicle — by using the SolidWorks 3D mechanical design system, according to lead engineer Carl Henderson. The Blade Runner looks like a highly styled, articulated lorry but converts to a train at the flick of a switch by deploying retractable steel wheels located between its rubber tyres, allowing for a smooth transition from road to rail.

Utilising standard truck chassis designs, Silvertip used 3D software to develop the assemblies and mechanisms that support road-to-rail transport. "It would have been virtually impossible to design the Blade Runner in 2D," Henderson explains. "We would have been forced to take our best stab at it, build a prototype, and chop off corners and refine the design through a costly, time-consuming process of trial and error. Using software, we could fully interrogate the design and have confidence the model would work before building it."

Silvertip designed the mechanisms for the Blade Runner directly on a standard truck unit and used the software''s collision / detection and measuring capabilities to optimise components for performance and maintenance. "We were not just interested in avoiding interference, but wanted to make the gaps large enough so someone could fit their fingers around it for replacing parts. We could look through the chassis model in the softwarwe and easily align our assemblies in the right position, picking up bolt patterns and features and avoiding much of the guesswork associated with 2D," Henderson adds.

Silvertip was able to design a 1/8th scale radio-controlled model of the Blade Runner in just three months. Silvertip used integrated design analysis software to strengthen areas of high stress and manufacturing software to machine components directly from the model he had created using the 3d software. Silvertip was also able to use design and manufacturing software to overcome an engineering problem that prevents articulated lorries from cornering safely at high speeds by developing a unique coupling system.

Automating medical equipment design
Team Consulting, Ltd. (Ickleton, Cambridge), a product development consulting firm that specialises in medical devices, uses 3d design software for all of its product designs but especially benefits from using 3D for machine design, such as an automated bio-assay high throughput screening system for processing laboratory samples, according to Colin Mathews, director of operations. "Using 3D shifts the focus away from the manual editing of drawings onto the process of developing an effective mechanism," Mathews points out. "Any changes we make to a component ripple throughout the entire assembly in a controlled fashion. With a 3D model, it''s so much easier to visualise and interrogate a design from different aspects and angles."

The company also benefits from using 3D models with integrated software, such as design analysis software for validating machine designs, communications applications for reviewing design concepts with customers.

Mathews notes that developing sophisticated laboratory equipment like the automated bio-assay high throughput screening system in 2D would extend design cycles and increase costs. "Working in 2D would be extremely cumbersome for us," he says. "We could not be in the business we are in without 3D CAD. It''s not just nice to have. It''s a necessity. If you are in the business of machine design, 3D CAD is a must-have capability."

*The author is vice president, Asia-Pacific, SolidWorks Corporation, tye 3-D mechanical design software subsidiary of France''s Dassault Systèmes.