How new additive manufacturing technology may give you more electronic design freedom

We’ve all heard about design for manufacturing (DFM), which in essence restricts design freedom and puts the focus the manufacturability. The concept’s goals are primarily productivity, repeatability, quality and, ultimately, enhancing profitability. But now and then, a manufacturing concept comes along that has the opposite effect on design. Instead of restricting a product designer’s options, it creates greater design freedom, sometimes making new product concepts physically or economically viable for the first time.

The first printed circuit boards (PCBs) appeared in the early 20th century and rapidly gained popularity as a way of replacing a lot of point-to-point wiring, which was getting out of hand as electronic products became more complex. Multilayer boards represented another major step, but one that required more sophisticated schematic capture, layout, and simulation tools. These, together with flexible PCB technology, which first found favour in the 1960s and 1970s, were enabling technologies, without which many of the products we take for granted today could not have been created.

Surface mount components and their associated automated placement technology were enthusiastically embraced from around the mid-1980s. They heralded new opportunities for creative electronic product design.

?So, over the last century, manufacturing automation has advanced in leaps and bounds with PCBs as the universal foundation of many electronic products. But the wire (or cable) harnesses needed to connect one part of a product to another have continued to be a significant barrier to full manufacturing automation. They’re still mostly made by hand and wire harnesses have become a significant barrier to achieving the size, weight, cost, and reliability design goals for many electronic and electrical products.

?But there’s good news on the horizon. A recent development in additive manufacturing technology promises to eliminate, or at least mitigate, the design and manufacturing limitations created by the need for wire harness interconnect. Here’s how.

What is additive manufacturing (AM)?

Additive manufacturing, the most common form of which is 3D printing, is a process of creating objects by adding layers of material based on a digital model. It allows for complex and intricate designs that are difficult to achieve otherwise and enables rapid prototyping, reducing time and costs for iterative design and development. AM can also improve supply chain efficiency by enabling on-demand and localised production and it facilitates rapid customisation. The aerospace and automotive sectors have adopted the technology widely.

Most 3D products produced using AM are made using 3-axis printers but more recently, 5-axis machines have become popular because they permit more complex shapes to be produced. Sometimes, they enable multiple components to be consolidated into one piece and they can improve both the structural integrity and surface finishes of products. 5-axis machines also minimise materials wastage by eliminating the support structures needed for some 3D-printed products.

What’s the problem with wire harnesses?

?Whether products are made using AM or other techniques, connecting them using wire harnesses poses several challenges. Harnesses are made by hand, making them expensive and prone to errors during manufacture. Because most are made in countries with low-cost labour, they have to be transported, sometimes thousands of miles, making the supply chain complex and costly.

Wire harnesses are flexible and rarely anchored along their whole length. As a result, in many transportation and industrial applications, they’re prone to chaffing and insulation damage whenever they are moved, intentionally or otherwise. This means that system designers may need to over-specify wiring to ensure reliability, considering mechanical as well as electrical factors. Conductors may have to be of a heavier gauge than strictly required for their current-carrying capabilities, and insulation may need to be thicker. Both factors add cost and weight, a particular problem in automotive and aerospace manufacturing but an important consideration in most industrial and consumer products. ?

How ‘electrical function integration’ may eliminate these and other design constraints

The most recent 5-axis robots have moved beyond simply building composite structures. They can now lay down electrical conductors within the structure of composite products using dedicated robotic heads called end effectors. The conductors may be bare wires up to 3mm in diameter or insulated wires, and terminations can be printed into the structure too. The conductors will carry power at currents of 10 amps or more, data, or signals and the process can be applied directly to flat or curved surfaces. This technique is known as ‘electrical function integration’.

As with all advances in automation technology, the commercial benefits are improved product quality and consistency, and increased manufacturing throughput. But electrical function integration also has profound implications for system design anywhere that a wire harness may previously have been used.

Because the path of integrated conductors can be accurately defined with the composite structures to which they’re applied, the shortest viable routes within a product can be used. Careful design can therefore minimise both series inductance and capacitive coupling between conductors, and resistive losses.

The conductors can be accurately set within printed channels created in the body of the product and, where needed, they may be further secured by printing tiny composite fixings over the top of the wires.

Because the wires are so well fixed, bare wires may be used where insulated types are needed in conventional harnesses. The wires are not going to touch, so there is no possibility of short circuits. Also, there is no need to over-specify the conductor diameter because functionally integrated wiring is not subject to the same mechanical stresses as a conventional wire harness. Both of these factors can save considerable weight. In an evaluation of the technology for replacing the wiring in a business-class airline seat, weight savings of at least 5kg per seat were deemed possible. Such weight advantages benefit aircraft and other forms of transportation by delivering increased range for a given amount of fuel or each battery charge. Lower CO2 emissions are an important and attractive consequence of this.?

Weight reduction also creates new design opportunities. For example, hand-held power tools, aircraft simulator grips, or game controllers, many of which use a clamshell design, may be more attractive to customers if they are lighter and less tiring to use. Alternatively, the designer of such products may be able to add greater electronic functionality to differentiate these devices from those of competitors, without making them excessively heavy.

The same benefits apply to the size of a product. With no need to make mechanical design compromises to accommodate traditional excessively bulky wiring and connectors, products can be made more compact. Or the space savings created by electrical function integration may permit the addition of more functions, perhaps enabling more user controls or interfaces to be introduced, without exceeding the physical size or form factor goals for a product.

Also, the mechanical constraints that are eliminated by electrical function integration will enable new physical form factors to be explored for many products, without adding unacceptable cost, weight, or size.

These opportunities will be amplified by today’s trend for electronics design engineers to become multi-disciplined. They are increasingly taking a holistic approach to product design, spanning electronic hardware, software, and mechanical engineering.

The next design revolution?

Printed circuit boards and flexible circuits transformed electronic design in the first three-quarters of the last century. Surface mount technologies, including components and new levels of automation in manufacturing, had a similarly revolutionary impact on design during the final quarter of the last millennium. It will be fascinating to see what the creativity of the electronic design community will make of the new opportunities presented by electrical function integration.

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