Issue link: https://iconnect007.uberflip.com/i/1518339
74 SMT007 MAGAZINE I APRIL 2024 For electrical cables and harnesses, each con- nector is populated with electrical contacts. A reliable crimping process should consider sev- eral factors, such as the tool used, the materi- als being crimped, and the settings of the tool. Each of these factors need to be controlled to ensure that each crimp connection is made consistently throughout the manufacturing process from beginning to end. is process is validated through a test called pull force test- ing. An example of a pull force tester machine is shown in Figure 3. Permanent crimped terminations can be affected by spring-back, which is the tendency of metallic materials to elastically rebound. is effect is more frequently observed on the outer crimped contact (i.e. terminal) than in the wire. NASA defines the minimum pull force requirements in NASA-STD-8739.4A 1 Work- manship Standard for Crimping, Intercon- necting Cables, Harnesses, and Wiring. Pull force testing, commonly referred to as a "pull test" or "tensile test," is typically conducted before and aer the preparation of a crimp ter- mination for flight hardware. is is always performed as a destructive test for flight hard- ware, such that the test samples are rendered unusable aer the test rig separates the contact from the wire. For harness designs with elec- trical contacts which are not mass-produced, full adherence to the existing pull force test- ing requirements can add costs to the project. e pull test results are recorded in a log sheet for traceability, with pass/fail criteria defined by the applicable standard. For high-volume production environments, the results of the pull tests can be statistically analyzed to iden- tify anomalies in the crimping process, such as crimp die wear, tool setting adjustments, and improper tool usage. An advantage of some pull test machines is that they offer network-connected computer interfaces to assist in operating the machine, as well as data collection tools for statistical anal- ysis 4 . However, NASA missions tend to have a smaller production volume such that both the crimp process and pull force test are oen conducted with hand tools and test machines without data collection mechanisms beyond a physical log sheet. Figure 3: Example of a pull force tensile tester.