How to Successfully Contract Out Cable Harness Assembly
A lot of OEMs (particularly smaller ones) use cable assemblies in their products built in-house and usually do the assembly by hand with the help of tools like crimpers, strippers, and heat guns. Building these harnesses by hand is very labor intensive, so eventually OEMs hire a contract manufacturer with the aim of lowering costs and increasing volume.
Unfortunately, there are a lot of ways for this outsourcing to backfire. It can result in late deliveries and increased costs due to scrapped cable assemblies, reworking harnesses, and/or time spent fixing documentation.
One of the key reasons for this is that cable assemblies can become complex, as the system they’re used in matures and changes over time. For high-technology products such as scientific instruments and medical devices, the addition of new features very often requires new wires and connectors to send the signals and power to the components that makes those new features work. This is especially true for products whose designs are modified well past the prototype stage in order to meet safety requirements (such as those from CSA or UL).
Another common reason stems from how the documentation and testing of wiring harnesses are sometimes maintained within an OEM. The wiring can get neglected because some companies mistakenly believe there’s not much focus necessary there. On the contrary, there can be a lot of labor costs built into wire harness assemblies that have layer upon layer of modifications: needing to use jump wire; sending some of a cable’s wires to one connector while terminating the other wires somewhere else; use of multiple cables with the same wire colors in a harness, etc. These are all symptoms of cable assemblies that have accumulated a series of quick and easy “band aid” fixes instead of a more thorough redesign.
But there are a myriad of other ways OEMs sabotage their own success when it comes to outsourcing cable assemblies.
Mistakes OEMs Make
Specifying too many particulars of the assembly instead of the final product: Your focus should be on things like: overall length (with reasonable tolerances), jacket strip length, etc. Your contract manufacturer should know enough about things like cable stretch, to be able to factor those in and meet your overall requirements. If not, then you shouldn’t be working with them.
Using the wrong cabling: Do you really need a foil shield or a ground wire? Can you use discrete wires instead of jacketed cable? Does the cable you’re using have 8 conductors but you’re now only using 6? Working around these things adds time and ultimately cost.
Ambiguity in connector orientation and pinout: Make abundantly clear the pinout of all connectors; especially connectors whose front and back look almost identical. In the drawing, use views which clearly show the correct orientation by relying on asymmetric features (locking ramps, locking tabs on panel mount connectors, etc.).
Speaking of connectors, whenever possible, stick with the numbering scheme on the connector itself (like the pin #1 indicator). We all know that assemblers should follow the drawing and nothing else, but in real life this causes real headaches.
Inconsistencies between the BOM and drawing: Like all other drawings, put the BOM directly on the cable harness drawing. In SolidWorks, you can automatically generate the BOM from the drawing. When the cable drawing and BOM are separate documents, there is a tendency for the BOM to fall out of sync with the drawing, which in turn causes problems for your cable assembly vendor who is more likely to gather the required terminals and cable lengths according to the BOM.
Your own assemblers however, often start with the drawing (and inside knowledge), then work backward to determine the quantity of raw materials needed. This is why, of course, inconsistencies between the BOM and drawing are seldom caught before the documentation is handed off to an outside vendor: no one was working off the BOM when you were building the cables in-house.
Ambigious or Conflicting Crimping Specs: Give detailed specifications and examples of crimp terminal quality, especially if your needs deviate from the terminal manufacturer’s specs or industry standards for crimp quality. A bad crimp can easily cause intermittent contact opens which are hard to catch, even via electrical continuity tests.
Tips for Smoothly Outsourcing Cable Assemblies
There are things you can do as an OEM to ensure a smooth and successful transition from in-house cable assembly to buying finished harnesses (for less cost) from your contract manufacturer.
Make it easy for your CM to get it right the first time: Share and document any custom jigs/fixtures that you are currently using in making the harnesses in-house. Also, give your contract manufacturer good example cables. Yes, as we said above with pin out we all know that the drawing should be enough, but the end goal is an acceptable finished product, not to test your vendor’s ability to correctly interpret ambiguities in your documentation.
Include simple tests in the drawing itself: Include a simple point-to-point resistance test as a note or step on the drawing. Not only will this allow the assembler to verify the pinout, but they may also be able to spot a bad terminal crimp. Also, a visual check using the wire run list (pin out table) and wire colors will help too. You won’t need to create and maintain a separate testing document, and your contract manufacturer will be able to catch problems before products hit your incoming inspection.
Pick a contract manufacturer who can automate most of the assembly: Automation, not necessarily lower labor costs, will be what ultimately saves you money on wire harnesses. Look for a contract manufacturer that has wire processors and automated crimping machines suitable for the terminals you are using in your wiring harnesses. Otherwise, you’re not going to save much (if at all) by farming it out.
DFM applies to cable harnesses too: Use pre-molded cable assemblies or terminated wires that you can buy off the shelf and simply drop ship to your vendor. Whenever possible in a cable assembly, use wires with different colors, as this will make visual inspection and continuity tests much easier.
Whether your cable assemblies are simple or complicated, ready for production or need some design refinement, Providence has the expertise and assembly capabilities to take your production to the next level.