InDent CRIMP tools anD aCCessoRIes Indent CrImp tools and aCCessorIesCrimping Pin and socket Contacts CRIMPING CRIMP DEPTH DETERMINATION Crimping may be defined as the art of joining a conductor to a pin or Having resolved an indenter design, the determination of crimp depth socket contact by controlled compression and displacement of metal. range must be established for each application. There are many factors It has been used for many years. which contribute to the selection of the proper indenter setting. These are primarily related to contact material and dimensions as well as wire type In a good crimp joint, there is a mutual metal flow causing symmetrical and size. distortion of wire strands and contact material. The mil cross-sectional The proper crimp depth for a given contact is the one that yields the best area is but slightly reduced and all voids are practically eliminated. Such a joint is similar to a cold weld. Mechanical strength and good mechanical and electrical joint. To determine this setting, many contacts of the same type are crimped though a range of indenter settings from electrical continuity are established. Because of the new environments to which electrical connectors are subjected, there has been a drastic too loose to too tight. The crimped contacts are then subjected to tensile and voltage drop tests. change in thinking relative to the use of precision crimp joints in preference to solder. WIRE PREPARATION CRIMPING CONFIGURATIONS Proper wire preparation also plays an important part in making a There are many different types of crimps employed good crimp joint. There are two popular methods of wire stripping fIG 1 today. These range from the terminal fold-over mechanical and thermal. During the mechanical stripping process, tab type of crimp to the single indent crimp, the extreme care must be taken to avoid nicking or removing wire strands, dual indenter crimp, the three indenter crimp, hex otherwise a loss of tensile strength will result. Conversely, if the crimps, and, finally, the MIL standard four indenter insulation is not completely removed, erratic values may be obtained. crimp. The four indenter crimp (Fig. 1) provides Heat stripping eliminates the danger of nicking strands. However, the most uniform displacement of wire and depending on the type of insulation being stripped, too much heat can contact material. The wire strands and the contact cause actual charring of the insulation or decompose the insulation with 4-Indenter Crimp material are formed together in a solid mass with the evolution of corrosive gases which react with the conductor platings. Cross-section little or no reduction of the mil area of the wire There is also a possibility of local annealing of the conductor. Too little across axis strands. A minimum of voids exists and very little heat can deposit an insulation film which can act as a lubricant. Any of extrusion of the wire strands takes place. these conditions can affect tensile results. Wire preparation is, therefore, another area that requires control if proper tensiles are to be achieved The four indenter crimp principle with a wire-contact combination. fIG 2 has been used to produce a variety of impressions, the most Before making a tensile test it is also important that the stripped length common being the bathtub of the wire be checked to ensure that the wire extends all the way into and octadent (also called the contact wire barrel. During the tensile test it is necessary for the double indent) (Fig. 2) The uncrimped end of the wire to be held in such a way that the pull force is octadent Crimp octadent configuration has evenly distributed to all the strands. Horizontal Cross-section been chosen by the Military for TENSILE TESTING use in the M22520/1 and /2 tools. Tensile testing is a controlled pull test on the crimp joint to determine CRIMPING CHARACTERISTICS its mechanical strength. It is a destructive test which usually results in Connectors utilizing crimping contacts usually permit the removal of wire breakage in the crimped barrel, the wire pulling out of the crimped these contacts several times so that modification, circuit changes, or barrel, or wire breakage outside of the crimped area. The method and replacement of contacts may be made with little difficulty and with the device used to conduct this test have a direct bearing on the results same quality assurance as in production line assembly. Crimping may obtained. Per specification, the testing device pulls at the rate of one be accomplished either with hand tools, power tools, or automated power inch per minute. During the tensile test, the wire is elongating. The tools. Repeatability of the crimp operation is characteristic provided breakage or separation point, therefore, is associated with not only the precision crimping tools are employed. These tools must be capable pull force but also the rate of increase of this force. of being gaged to insure that proper crimp depths are maintained. Tensile curves are plotted for each contact and wire combination. They Inspection holes in each contact permit quality control personnel to view will usually differ, depending on the type of wire, plating, size of wire, the wire strand ends thereby assuring that the conductor is properly and variations in contact design and material. A desirable tensile range positioned in the crimp barrel. must be determined for each of these combinations. MIL-DTL-22520 MILLIVOLT DROP This specification covers all the requirements for crimping tools used on Millivolt drop tests are performed across the crimp joint to determine the removable type contacts in electrical connectors. electrical characteristics. The test current is passed through the contacts and voltage drop is measured from a point on the shoulder of the contact to a point on the wire. Voltage drop values under the maximum allowable indicate a good electrical joint. 4 Copyright 2008 Astro Tool Corp. , 21615 SW Tualatin Valley Highway, Beaverton, OR 97006 Tel: (503) 642-9853 www.astrotool.com