A wire harness is used to organize a group of wires transmitting power and information to devices to perform specific functions. Commonly used in aerospace and automotive industries, wire harness assembly comes in various shapes and dimensions. They are designed to fit in particular spaces in an organized and protected manner.
This application note examines the common challenges facing wire harness manufacturers to produce fault free wire harnesses.
Design/Research and Development
Hidden behind the steering wheel or within an aircraft’s airframe, wire harnesses are designed to manage wires and fit within a specified space. Engineers will select the correct type of wire. Designers must consider how space limitations will affect the wire harness’s size and shape and the workflow without disturbing transmission or preventing electrical issues. Using 3D modeling packages and 3D imaging systems prevents many workflow-related faults at this stage of the process.
A wire harness prototype brings the design to life. A test user can now test the working prototype for its intended use before production. Inspection and measurement tools may be used during this stage to ensure the prototype matches the design by comparing it to the CAD drawing. If a wire harness fails to meet the specification at this point, it would be reworked or scrapped. Getting the wire harness prototype correct at this stage saves production time and costs down the road.
Wire and components used from suppliers should be inspected before the assembly process to prevent defects before production. The wire should be measured to make sure it matches the gauge required. Designers check connectors for damage; terminal spacing should be measured to prevent the pins from being placed too close to each other. A digital system is ideal for inspection since fixing may require documentation if incoming products are not correct or defective.
Once the prototype passes inspection, the production of the wire harness can begin. Following quality processes and utilizing inspection systems in each step of the assembly process will improve the finished wire harness quality. Accuracy during this stage is crucial to meet production deadlines, prevent lost profits, and uphold its quality reputation. The wires in the wire harness are cut to the length indicated in the design. A wire cutting machine will measure, mark, and cut each wire individually. The cables are then labeled and laid out to match the design. Insulation at the ends of the wire are then stripped, contacts crimped onto the end of the wire, wire inserted into the connector.
Inspection of Wire Harnesses
Once the wires have been stripped, contacts are then crimped onto the cables’ end by automatic or manual crimpers. Failure to crumple to the correct height causes defective continuity or displacement of the wire. Extreme crimping can lead to wire damage. Poor crimping will result in the cables becoming loose and disconnected when pulled, whether the crimping process is performed by a machine or manually. Examining the finished crimped wires through an inspection system will identify any defects and prevent faults that can occur once the wire harness is finally connected.
After the wires pass the crimping process, they are manually fitted with terminals or pins. The cables are then sealed by soldering or inserted directly into the terminal. Since wire harnesses and their components are continually getting smaller, using a microscope during the soldering and terminal placement process is essential. It will help the assembler see the parts clearly to avoid damage and defects at this stage.
Once the wire harness is produced, it will undergo electrical safety testing. This critical step ensures the final function will perform correctly. The final inspection will include pull tests, continuity, a megohm test, and visual inspection under magnification. Minimal final adjustments are made at this stage to the wire harness to pass testing.
Here are a few defects to look out for during a visual inspection:
• Wires should be free or any deformities
The crimp secures
• Wires and the crimp is placed at the correct height.
• Wires are together, no birdcage
• Insulation is free from cracks, fraying, discoloration, and pinching
• The insulation covers the wire and extends past the insulation crimp tab
• The contact is free from any defects
Achieving Quality with Wire Harness Assembly
The wire harnesses manufacturing process contains several steps with a large amount of manual production. Most manufacturers will follow the “IPC/WHMA-A-620A Requirements and Acceptance for Cable and Wire Harness Assemblies” and AS9100C, a widely adopted quality management system in the aerospace industry. In obtaining the highest level of quality, HELTRONICS have strict quality processes in place.
Manufacturing fault free harnesses is challenging. However, we have a clearly defined quality control process, which includes using tailored inspection. Equipment from design to testing will limit faults, improve production output, and reduce costs.