Connector insertion and extraction forces in electrical wire harness design

Jun 26, 2024

The design of Electrical Wire Harnesses (EWH) is a critical process in various industries, including automotive, aerospace, and medical equipment manufacturing. A key aspect of the design and functionality of EWHs involves the connectors that provide an electrical path between components, assemblies, and subsystems. The proper evaluation of these connectors is essential, as both mechanical and electrical aspects must be considered to ensure performance and reliability (IEEE)

Importance of connector force validation

Connectors are an essential component of wire harnesses, providing the necessary electrical connections between different subsystems. The forces required to insert and extract these connectors from their mating parts must be carefully measured and controlled.

If the insertion force is too high, it could lead to assembly difficulties, potential damage to the connectors or the equipment, and increased manufacturing time and cost. Conversely, if the extraction force is too low, it could result in loose connections that may lead to intermittent signals or power losses, which are unacceptable in critical systems such as those found in the aerospace or automotive industries.

What is connector insertion force?

Connector insertion force refers to the amount of force required to join two connector halves or a connector to a mating component. This force is a crucial parameter in the design of connectors, as it can affect user experience and the longevity of the connector itself. The insertion force is composed of two main stages: the spreading stage, which is associated with higher force and responsible for the peak force, and the sliding stage (Samtec).

During the spreading stage, components within the connector are forced apart to accommodate the joining piece, leading to the peak force experienced. This force is a result of both frictional and normal forces acting on the connector components. The sliding stage involves less force as the components slide into place to complete the connection.

If the insertion force is too high, it can lead to several issues. For instance, excessive force may damage the connector pins or the housing, leading to poor contact and potential failure in the electrical circuit (IEEE). Moreover, a high insertion force can increase the risk of repetitive strain injuries for workers who frequently engage in the manual assembly of connectors, particularly in large-scale production environments.

Conversely, an insertion force that is too low may result in a loose connection, which can cause intermittent signal loss or complete disconnection under vibrational stress, particularly in automotive systems where connectors are subjected to continuous movement. Therefore, it is imperative to design and produce connectors with a controlled insertion force, ensuring stability and reliability throughout their use.

Why is Understanding Connector Extraction Force Important?

Equally important is the extraction force. The connector extraction force, the force required to disengage the connector halves. If the extraction force is too great, it poses a risk of damaging the connector during disassembly, which can lead to increased maintenance costs and downtime. Additionally, a high extraction force can make it difficult to perform repairs or upgrades, as technicians may struggle to disconnect components without causing harm to the surrounding circuitry.

On the flip side, an extraction force that is too weak may lead to connectors becoming dislodged unintentionally. This is particularly hazardous in applications where connectors are exposed to external forces or vibrations, such as in aerospace or automotive industries. Unintended disconnections can lead to catastrophic system failures, posing serious safety risks.

How Are These Forces Measured?

To measure insertion and extraction forces, a force test is conducted. This involves placing two pluggable electronic connectors in an initial position and setting force and torque gauge readings to zero. The connector is then inserted or extracted at a rate specified by the product's specifications, and the peak forces are recorded.

When Should These Forces Be Considered?

The design and production processes for EWHs must consider insertion and extraction forces early on. Contact resistance, which directly affects these forces, should be strictly controlled to ensure stability and reliability during the use of the connector.

Where Do Environmental Factors Come Into Play?

Environmental protection is another key consideration. Connectors should be shielded from environmental factors such as moisture, dust, and extreme temperatures, which can affect both mechanical and electrical performance.

Standards and guidelines

To ensure reliability and safety, the industry adheres to various standards such as AS50881 for the aerospace industry, ISO 26262 for automotive safety, and IEEE 315-1975 for graphical symbols for diagrams, among others. These standards provide guidelines on the acceptable range of insertion and extraction forces, among other parameters, to ensure that connectors perform reliably under the expected range of operating conditions.

How Are These Forces Optimized?

Optimization of these forces is driven by a combination of technology and market factors. Miniaturization and increasing pin counts in technology require precise control over insertion and extraction forces, while market factors demand low-cost and durable solutions. Deflection, or the amount of deformation under load, also impacts these forces and must be taken into account.

Example of Insertion and Extraction Force Optimization

An example of this optimization process can be seen in a study where the insertion and extraction forces for a snap-fit were found to be 140 N and 170 N, respectively. Through convergence and animation, a smooth insertion and extraction process was depicted, demonstrating the successful optimization of these forces.

The Process of Measuring Connector Forces

The process of measuring connector forces typically involves the following steps:

  1. Selection of Appropriate Equipment: Specialized force gauges and test fixtures are required to measure the insertion and extraction forces of connectors accurately. The equipment must be calibrated and maintained to provide reliable measurements.

  2. Preparation of Test Samples: Connectors and their mating parts must be prepared according to the specifications of the wire harness design. This includes ensuring that they are clean and free from defects.

  3. Conducting the Test: The force gauge is used to apply a steady force to insert or extract the connector, with the value being recorded by the equipment. The test should be repeated several times to ensure consistency and reliability of results.

  4. Data Analysis: The recorded forces are analyzed to determine if they fall within the acceptable range as defined by the relevant industry standards. Statistical methods can be used to assess the variability and predict the performance of the connectors in actual use.

  5. Documentation and Feedback: Detailed records of the testing process and results are kept. If any connectors do not meet the required standards, the design or manufacturing process must be reviewed to identify and correct the cause of the issue.

Case Examples

In the automotive industry, for example, the ISO 26262 standard mandates safety requirements throughout the lifecycle of automotive electronic systems. A manufacturer of vehicle wiring harnesses would use force measurement tests to ensure that the connectors meet the standard's requirements, which could include specific insertion and extraction forces to prevent accidental disconnection due to vibrations or impacts.

In aerospace, the AS50881 standard provides guidance on the design of aircraft wiring systems, including connector force requirements. A failure to meet these requirements could result in catastrophic failures due to loss of signal or power in critical flight systems.

In conclusion, understanding and validating connector insertion and extraction forces is a vital part of the EWH design and manufacturing process. Adherence to industry standards and rigorous testing ensure that connectors perform reliably, which is critical to the safety and functionality of the end products. By implementing a structured approach to measure these forces, manufacturers can minimize the risk of errors, reduce costs, and ensure the timely delivery of high-quality wire harnesses to their customers.