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78 SMT007 MAGAZINE I APRIL 2024 Requirements for Crimping Process Control To minimize variation in manufacturing, process controls should be applied to all tools, equipment, and contact/conductor pairs (i.e. contact/wires or C/W). e crimp process is validated for each new crimp configura- tion where tool settings must be determined for a contact/conductor pair. Both the NASA- STD-8739.4 and the IPC/WHMA-A-620C standards require a three-sample pull test. For example, the NASA-STD-8739.4 § 12.3.5.a states: (1) For each new crimp process where a crimp tool setting must be determined for a contact- conductor pair (or a crimp ferrule-conductor combination), a three-sample pull test at each of the different crimp tool settings considered for use are required using the force and pull strength cri- teria in Table 12-1. Fur thermore, the IPC/W HMA-A-620C Space Applications Requirements §19.7.2, states the following: "ree test samples shall be prepared for each contact/conductor combination test. A crimp- contact-conductor combination is defined as a specific contact used with a specific wire con- struction, e.g., if a drawing calls out a combina- tion of single wires and twisted pairs of the same construction, e.g., gauge, strand count, alloy (base metal), and plating , the test samples of the single wire qualifies the tool to be used on the twisted pairs." The NA SA-STD -8739.4A w/Change 2, §12.3.5 c, Integrity of Crimped Connections, describes the pull force and pull strength crite- ria as follows 1 : (1) e crimp contacts or ferrules shall be placed in a tensile-testing device with appropri- ate fixtures, and sufficient force shall be applied to pull the wire out of the assembly or to break the wire or crimped item. (2) e head travel speed of the tensile device shall be 25.4 ± 6.3 mm (1.0 ± .25 in) per minute. e holding surfaces of the tensile device clamp may be serrated to provide sufficient gripping and holding ability. (3) Crimp pull strengths shall meet the values in Table 12-1. Wire pull out, wire breaks at the crimp, and contact rupture which occur below the minimum pull strength value are considered test failures. (4) For those contact-conductor crimp con- nections not contained in Table 12-1, the tensile strength of the crimp connection shall be no less than 60 percent of the tensile strength of the wire. Reference the manufacturer's datasheet for wire tensile strength. (5) For crimp ferrule-conductor combinations the wire pulled shall meet the tensile requirement for a single wire of the same gauge being tested in its "properly sized" contact. (6) Examination of Test Samples. Each indi- vidual test sample shall be inspected to the requirements of 12.3.5.c(3) and the observations should be recorded and maintained for passing units and shall be recorded for failing units. (7) e pull strength and break or release con- dition for test failures shall be recorded. In addition to these controls, further accep- tance and rejection criteria are described in NASA-STD-8739.4A w/ Change 2, § 20.5, Inspection Cr iter ia 1 . Rejectable cr iter ia for cr imped connections include improp - erly located crimp indents, plating problems, discoloration, and out of roundness of the con- tact barrel. In many cases, these product qual- ity issues can be identified by inspecting con- tacts before insertion of wire and crimping, which is also a requirement from NASA-STD- 8739.4A w/Change 2, § 12.2.1. Conductors Wire sizes are specified in units of Ameri- can Wire Gauge (AWG) or Circular Mil Area (CMA). e wire selection depends on the current needs for the application and the oper- ating environment [6] . A crimped termination is recommended on the following types of wires as shown in Table 1 7 :