Fastening and assembly are too often overlooked or shortchanged in the design process. Cumbersome or expensive assembly systems can ruin the cost effectiveness of a project, or worse, raise questions about its fitness for use.
The best designs include considerations for manufacturing and assembly. Design for assembly starts with the concept of reducing the design to the least number of parts possible. Assembly methods can vary from simple mechanical or chemical fastening techniques to automated systems, such as “outsert” molding in which plastic pieces are attached to two- or three-dimensional metal bases in an injection molding machine.
If the whole process of fastening seems simple to you, you probably aren’t trying hard enough.
One example is work done by engineers at Southco to develop constant-torque position-control hinges for precise positioning of panels in a variety of applications, such as flat-panel displays for small notebook computers, auto navigation or home TV screens. Properly engineered position-control hinges can make flat screens easier for users to position and view conveniently and comfortably. Increasing screen sizes, unique mounting styles and varying forces are requiring design engineers to evaluate more complex questions about their requirements, such as the weight of the screen in the application and whether the strength of the hinge holding the screen might hinder easy positioning.
Southco says designers also need to consider how well-balanced the screen is in the application. The farther the center of gravity is from the axis of rotation, the more force the screen will exert on the hinges.
Another consideration is the range of motion required by the application. Does the display have a single pivot point requiring just a few degrees of rotation to adjust the viewing angle? Or is it a multi-axis (tilt-and-swivel) application that also needs to rotate 180 degrees or more to be shared among multiple viewers? If the display will be used in a touch-screen application, will it be able to withstand the pressures exerted by different users? The designer must also understand how frequently the screen will be moved or repositioned. Will it be fully deployed with each use or simply be adjusted infrequently by the end user? How many cycles are anticipated over the life of the application — a few thousand or tens of thousands? Will the equipment be portable or subject to shock or vibration? How will the hinge be mounted — base mounted or cantilevered?
Depending on other mechanical requirements, design engineers might also combine frictional torque with counterbalancing springs for weight-bearing and weight-compensating designs that can make heavy display screens — some weighing 100 pounds and more — feel so light that they can be positioned with just the touch of a finger, says Southco. Or the designer may incorporate a two-axis operation to create "tilt-and-swivel" operation that maintains perfect viewing angles for all user preferences even in bumpy, moving automotive applications. Other design options include variable torque for easier opening without fear of accidental closing, detents at one or both extremes to provide positive retention points for "open" and "shut" positioning or "soft" detents for quiet, yet secure operation.
Another highly engineered solution to assembly is outsert molding, a process in which bending, punching and spouting take place in a single automated process. All parts (including rotating) and functions are placed at the same time in an injection molding machine, creating a permanent and precise assembly. Meeting one of the primary goals of a good assembly, up to two-thirds of parts can be eliminated using outsert molding.
Applications for outsert molding include CD/DVD and tape chassis, front visors DVD-modules, sun-roof systems, windshields for sun-roofs, mechatronic assembly tools for doors, electromechanical components for medical equipment with micro transmissions, mechatronic components for automatic teller machines, assembly frames for electric controls and mechatronic components for microchip assembly machines. One technology leader in the field is the TB&C Outsert Center.