Wire Harness Manufacturing Process Management
There are no shortcuts to manufacturing a quality wire harness. But there are ways to plan a
more secure and more cost-effective design process.

By Nick Smith, Mentor Graphics

Wire harnesses are vital components in modern transportation platforms such as aircraft and automobiles. They distribute power and signals between the various devices that deliver electrical and electronic functionality. The wire harness set of a modern automobile is typically also the most expensive component, after the powertrain. For this reason, harness manufacturers are under relentless pressure to reduce costs.

However, harness manufacturing is logistically complex. Each harness comprises hundreds or even thousands of components that are assembled via a sequence of operations. Also, each harness is typically manufactured in a range of configurations that reflects the optional content specified for each vehicle. And in this industry, design change is a daily occurrence, making it hard to optimize by experience.

These factors create a real challenge for harness manufacturing engineers and production planners, who must decide what, where, and how to build their products. They must identify an efficient assembly pattern for each harness design, and create the data needed to drive Enterprise Resource Planning (ERP) systems that manage inventory, govern component purchasing, schedule work-in-process (WIP), and so forth. This activity is generically termed Manufacturing Process Management (MPM).

Unfortunately, few harness MPM software applications exist to help the manufacturing engineers and production planners. Although some in-house applications have been created, manual ad hoc methods are mostly used, at best supported by spreadsheet macros.

Hierarchical Assembly

With the exception of low volume items such as prototypes, harnesses are always built in a sequence of steps rather than as a single operation from a collection of basic components.

For example, spools of wire must be cut into pieces of the correct length, stripped, and terminated. These three tasks can usually be automated into a single operation and will typically result in WIP inventory that may even be assigned an internal part number. Maybe a group of processed wires are then spliced together, creating a small subassembly that is a distinct WIP item with its own part number. Note that the subassembly may in fact be identical to one used to build another apparently unrelated harness. Various subassemblies and other components may then be brought together on a formboard. Terminated wires are loaded into connector cavities, bundles taped, fixings added. Finally, the harness is tested and boxed ready for shipment.

There is industrial logic behind this sequence. For example, wires cannot be loaded into connector cavities before they have been terminated. So every harness design can be decomposed into a hierarchical set of manufacturing steps, each of which consumes components or subassemblies and results in new subassemblies until the finished harness has been built. A key output of this decomposition analysis is a structured bill of materials (SBOM) that reflects the sequential process, as distinct from a flat bill of materials that can be calculated simply from the harness design. Figure 1 illustrates this hierarchical principle for a simple harness.

Figure 1: Hierarchical assembly steps create the finished harness

This said, all but the simplest harness can be decomposed in different ways. So the task is not merely to find a feasible manufacturing pattern, but to find a good one. This in turn depends on both the harness design (example: are butt or centerstrip splices used?) and also on the factory capabilities (example: can we automatically handle large battery cables?). Good decisions even depend on optimization objectives (example: minimize cost or cycle time?).

Considering the challenges of design complexity, configuration complexity, frequent change, and varying factory capabilities we can easily appreciate the difficulty of the task. Harness MPM software to the rescue!

Flow Overview

Figure 2: Design – manufacturing process management – enterprise resource planning flow overview

Figure 2 depicts the flow at a high level. Although straightforward in principle, effective execution requires substantial domain expertise and sophistication. The key elements are:

1. Capture of the harness to be built as a computer model (digital description). Powerful design software can create rich, validated digital descriptions of wire harnesses, and also robustly manage configuration complexity and design change. Harness design software creates a bill of materials (BOM) correct to the tiniest detail and also a description of the harness structure, such as the branch configuration. Examples of modern harness design software include Mentor Graphics Capital HarnessXC, Capital ModularXC, and VeSys Harness products.

2. Capture of the factory(s) process capabilities, again as a computer model. Example process capabilities include maximum and minimum wire gauges for cut/strip/terminate equipment, maximum wire count for splicing machines, and preferences for connector subassembly creation. These digital descriptions should be captured within harness MPM software, and must be easy to maintain but rich enough to allow automation of production process modelling: see element 4.

3. Access to the harness design data by the MPM application. This is straightforward when the harness design software vendor also provides MPM software, because the meaning, richness, and integrity of the design data are guaranteed. In the case of data centric environments like Mentor’s Capital suite, additional data, such as library components that may not be part of the harness design per se, could be automatically and even conditionally added to aid process management automation.

4. Calculation of an appropriate structured bill of materials aligned to the parameters and conditions for each operation in the manufacturing process. This step is the heart of MPM. Crucially, configurable rules that guide this analysis should be captured within the MPM software. In addition to the factory capabilities, these rules represent the manufacturing intellectual property (IP) of the harness manufacturer. They must be robustly and securely trapped: see below.
   
   The technology that automates the decompositional analysis can be thought of as domain specific reasoning engine. This reasoning engine understands the industrial logic of harness assembly and hence calculates only appropriate subassemblies.
   
   Calculation against the manufacturing pattern results in a hierarchical (multi level) description of the harness assembly process, specifically an SBOM. At this point, it is also important to identify subassemblies that are common to more than one harness design. This capability alone can dramatically impact manufacturing costs via economies of scale, machine utilization, etc.
   
   Having created the hierarchical bill of materials, manufacturing engineers will typically then want to review the results, maybe visualize the outputs by cross-highlighting subassemblies in the context of the harness design diagram, and make any changes or additions necessary to complete the task before subassembly part number generation/commonization. Any such manual work should be preserved so it can be re-applied to subsequent design revisions.

5. The hierarchical SBOM is now used to drive ERP, another core application for harness makers. Fortunately, the data required to drive ERP is relatively common across various ERP system vendors: it is straightforward to create outputs from MPM that can be read by ERP systems. In addition, one could imagine using MPM data as inputs for other domains, such as ergonomic modelling of production activities.
   
   Note that the term Material Requirements Planning (MRP) and its extension Manufacturing Resource Planning (MRP II) are sometimes still used to describe a subset of ERP activities.

6. The ERP system calculates the works orders and component purchase orders needed to drive operations. As an aside, the rich harness design data created at element 1 can be repurposed to drive production equipment such as wire processing machines and automatic test benches, further streamlining the overall flow.

This description explains how automated decompositional analysis of harness designs in order to create SBOMs can be accomplished. But while very substantial automation is indeed available, it’s also vital to permit flexibility. For example, a piece of manufacturing equipment may be unavailable due to maintenance, repair, or upgrade; or a process safety problem may be identified; or the capacity of the optimum manufacturing pattern may be reached. Such eventualities mandate flexibility in process definition, so it should be possible for authorized staff to override automatically generated manufacturing patterns. Again, it should be possible to preserve and re-apply such overrides so that no value-add work is lost.

Intellectual Property: In-House Versus Cots

This in turn leads to the question of IP capture and protection. This is a critical subject because factory capabilities (custom built equipment, for example) and process logic lie at the heart of harness manufacturers’ competitive position. Modern harness MPM software provides an infrastructure to capture IP fully and securely. In particular, rules that drive the decompositional logic are constructed from a set of templates that are configured to capture manufacturers’ IP: see figure 3. These templates pertain specifically to wire harness manufacturing. Rules thus created can be combined to build rich rule decks against which harness designs are analyzed. Importantly, the rules are private and specific to each harness manufacturer. Rules would normally be set up by an authorized “rules librarian.” Once established, they merely require maintenance; for example, as new factories are built or process capabilities are improved.

Note that this paradigm changes the job function of at least some manufacturing engineering/production planning staff. Some, typically the most skilled, transition from working on individual harnesses to creating rule decks that capture their expertise. In effect this expertise is leveraged many times over via its capture as reusable IP.

Figure 3: Flexible capture of intellectual property

The architecture described above can be thought of as an extensible, customizable, rules-based framework. Because the factory descriptions and rules are flexible and private, they extend or customize the core MPM software. The core software provides the user interface, reasoning engine, data access and export, configurable part number assignment, etc. This is relevant to the discussion of in-house application development versus commercial off the shelf (COTS) software.

Certainly there is a temptation to undertake in-house development of applications that impact commercially sensitive business areas, either directly or using a paid subcontractor. The argument is that in-house software secures IP more tightly.

However, the extensibility architecture described above allows IP to be secured while still enjoying the advantages of COTS software. Briefly, these advantages are:

• Lower costs, because the commercial software vendor is able to defray development and maintenance expenses over a much wider user base while still making a profit.

• Reduced likelihood of being trapped in outdated paradigms, because the commercial software vendor can draw on a wide range of inputs.

• Focus of resources on core activities, which for the wire harness industry is not software development.

These arguments have been played out in multiple industries, from printed circuit board design to graphic arts. The result is always the same: COTS software (with or without an extensibility infrastructure) comes to dominate and the industry as a whole becomes more efficient.

Benefits of Effective Wire Harness MPM Software

At first sight the key advantage of effective wire harness MPM software seems to be time- and therefore cost- savings for the manufacturing engineering and production planning communities. Substantial automation assistance is given to this difficult task, which includes not only manufacturing pattern decisions but also peripheral tasks such as assignment of WIP part numbers.

Certainly this is an important benefit, but there are many other benefits, including:

1. Manufacturing cost reductions by systematically modelling harness designs against production capabilities based on captured IP, rather than relying on multiple individuals who may have differing levels of expertise. The what, where, and how to build questions can be robustly answered.

2. Manufacturing cost reductions by readily enabling the creation of multi-level BOMs that accurately reflect manufacturing patterns that have been optimized.

3. Manufacturing, inventory, and obsolescence cost reductions via the identification of common subassemblies. This allows economies of scale to be realized and duplication to be avoided.

4. Error correction and validation time reductions by avoiding data re-keying. Digital continuity is created from the harness design environment through to manufacturing. This is particularly valuable in situations characterized by frequent design change.

5. Avoidance of crises by early identification of resource needs, such as new tooling.

6. Reduced staff training costs via systematic capture and application of IP. This is valuable following factory relocations, when the experience of key staff members can easily be lost.

7. Systematic capture of data to support investment decisions based on desirable manufacturing operations.

8. Improved corporate visibility, for example at the quotation stage, by systematically modelling manufacturing capabilities.

These advantages provide harness manufacturers with a substantial return on the investment of purchasing and deploying modern MPM technology. Those that don’t make this investment will risk erosion of their position in this intensely competitive industry.

Conclusion

Wire harness manufacturing process management is an intellectually demanding subject that is central to suppliers’ profitability. Pressure for cost reductions will never diminish, and indeed the challenges will grow as the industry becomes ever more global and the era of mass customization fully takes root. Until now harness manufacturing engineers and production planners have been poorly served by commercial software vendors. Data needed to drive ERP systems is created manually or by in-house applications that are expensive to maintain, perpetuate paradigms, and cause organizational defocus.

But now a new generation of harness manufacturing process management tools is emerging that substantially automate key tasks while also providing full protection of intellectual property. Multiple benefits are delivered by such software, which can be deployed by wire harness manufacturers supplying the automotive, offroad, aerospace, defense, or other industries that require all but the simplest harnesses.

Mentor Graphics Capital Harness MPM is a COTS software product specifically developed for the wire harness manufacturing industry (see figure 4). It has all of the characteristics described above.

Figure 4: Capital Harness MPM used in conjunction with Capital HarnessXC