Improving the design process for wire harnesses and cable assemblies can dramatically affect overall time-to-market, cost and quality of an electromechanical product.

Many manual design and manufacturing processes have benefited from auto-mation. Drafting tables have been replaced by 2D drafting software packages. Printed circuit boards are now laid out and analyzed on a computer. Data for sophisticated milling machines are automatically generated from 3D CAD models.

However, the time-consuming job of wire harness design is often overlooked when assemblers of electromechanical products decide to automate their design processes. Surprisingly, wire harness design has remained largely a manual process. This is because, until recently, harness design software has been unavailable or has been too limited in scope for general use.

The manual method for designing wire harnesses typically involves waiting for a hardware prototype, manually measuring wire paths and processing numerous engineering change orders. The process consumes a lot of time and materials, and often is costly to expedite.

Although a functioning wiring system is necessary to power-up an electromechanical device, it usually is the last component of a product to be designed. This can create problems. For example, the weight of the wiring and the space requirements are significant factors that are better accounted for before final assembly. Without automation, these details must be extracted from a manual design process that, in the worst case, is based on trial and error.

Indeed, the variety and quantity of data needed to assemble even simple wire harnesses can be overwhelming. For instance, a simple wire connecting two pins is defined by the type of wire, the wire length, the wire bend radius, the terminating hardware on either end, and any shields or coverings. Multiply this by the thousands of wires contained in many of today's electromechanical products, and the task of accurately tracking that data becomes an enormous challenge. The late timing of the wiring design compounds the problems created by dealing with such a large amount of data, especially when the production schedule slips. Trying to accelerate such a detail-oriented process is difficult and frustrating.

In light of the manual design process, the resources needed to assemble wire harnesses, and the critical position of wiring in the overall machine design, wire harness design is a worthy candidate for automation. The gains of automation should outweigh the costs of any new hardware and software, including the time to learn the new process. But, the most compelling case for automation is that it can enable quality products to get to market faster.

Automating Harness Design

A software solution to wiring design should understand all the multidisciplinary data involved in the current man-ual design process. Mechanical, electrical and manufacturing inputs must be considered. Accurate, detailed manufacturing outputs must then be generated automatically to prevent human error. This merger of data can be thought of as a hub, or database, that understands all wiring elements and their relation to each other, as well as the design and manufacturing processes. Besides the hub, the software should provide a complete automated design environment for wire harnesses and cables.

The primary reasons to automate are to save time and money, and improve quality. The data hub accomplishes this in several ways. On the most basic level, the merger of the electrical connectivity with the mechanical model enables a 3D model, or virtual prototype, of the harness to be created far in advance of any hardware prototype of the machine. This virtual prototype can be used to determine wire bundles, paths and lengths, and to eliminate the process of manual measurements. Errors are caught on the software model and easily corrected before a single wire is cut or terminated. For example, the software can provide various design rule checks (DRCs) that verify wire lengths, bundle diameters and terminal sizes. The software also can ensure that wires for data and power are separated.

Design changes are an inevitable part of the process. The electrical system in a machine will evolve as the design progresses, and modifications to the original harness design will be required. With a central data hub, a change only needs to be made in one place. The revised data are automatically distributed to all affected parts of the design.

Streamlining manufacturing inputs is also a key benefit of automation. The 3D model of the harness contains all of the physical harness information and can be checked for accuracy using the DRCs. In the past, transferring this information to manufacturing required manual data entry. Wiring design software will automatically output the documents needed to manufacture the harness. For example, the software can create 2D nailboards and inspection drawings, as well as files that provide data input to wire strippers, labelers, cutters and testers. Because manufacturing is receiving accurate computer-generated data, many of the iterations required to reconcile parts and other discrepancies are eliminated.

Design reuse is another benefit of the hub approach. Because many new designs are just modifications to older products, the ability to leverage related design data saves enormous amounts of time in the project schedule.

Beyond Automation

Once basic automation is embraced, more advanced, value-added functions can be implemented. Harness quality can be further improved by optimizing the design according to various criteria, such as weight, cost, signal integrity, ease of manufacture, and component lead time. Automation saves much of the time required for manual measurements and non-linked documents, enabling harness designers to spend more time designing the harnesses and performing trade-off analyses.

Automation also promotes standardization. As more data is stored in a common format on a computer, it becomes easier for OEMs and suppliers to share intelligent, electronic data and develop standards that strengthen their relationships. The combination of a central hub and standardization also makes it possible for other groups, such as field service personnel, component suppliers and final assembly workers, to have access to the data appropriate to their role in the process.

Feb 2000