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Chapter 4
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  1. Chapter 4 Electrical Connections and Wire Harness Assembly Dr. Mohammad Abuhaiba

  2. 4.1 INTRODUCTION • A descramblerfor satellite TV reception. • 10 PCBs • 51 connecting wires or cables • 31 circuit board jumper wires • total of 164 connections. • Table 4.1: Original Design • Assembly time = 7236s • 68% of total assembly time of 10,613 s • Table 4.2: Redesign • 10 PCBs could be combined into one • eliminate interconnections and jumper wires • Reduce assembly costs by 61% Dr. Mohammad Abuhaiba

  3. 4.1 INTRODUCTION Dr. Mohammad Abuhaiba

  4. 4.1 INTRODUCTION Dr. Mohammad Abuhaiba

  5. 4.2 WIRE OR CABLE HARNESS ASSEMBLY • Figure 4.3: Harness assembly • Figure 4.4: principal operations involved: • wire preparation • harness assembly • installation in product • Harnesses are usually constructed by manually laying out individual wires or cables on a board that has a full-size schematic drawing of harness mounted on its surface to guide the assembly worker. Dr. Mohammad Abuhaiba

  6. 4.2 WIRE OR CABLE HARNESS ASSEMBLY Dr. Mohammad Abuhaiba

  7. 4.2 WIRE OR CABLE HARNESS ASSEMBLY Dr. Mohammad Abuhaiba

  8. 4.2 WIRE OR CABLE HARNESS ASSEMBLY Dr. Mohammad Abuhaiba

  9. 4.2 WIRE OR CABLE HARNESS ASSEMBLY • During construction, ends of wires must be held in position. • If wires are to be terminated in a connector, then connector may previously have been inserted into a receptacle mounted on board in correct position. • Ends of terminated wires are then inserted into back of connector. Dr. Mohammad Abuhaiba

  10. 4.2 WIRE OR CABLE HARNESS ASSEMBLY • Wire ends that are to be connected during installation in product are retained temporarily on board. • Use of a helical spring mounted on board with its axis horizontal & perpendicular to direction of wire. • Once all wires or cables have been laid, they are bundled together using: • tie wraps • Lacing • split conduit tubing • bound with electrical tape. Dr. Mohammad Abuhaiba

  11. 4.2 WIRE OR CABLE HARNESS ASSEMBLY • When complex harnesses are assembled, connector receptacles are wired to a computer that continually tests whether wires have been inserted properly. • Figure 4.5: sequence of operations for low, normal, and high complexities • Degree of automation used in wire harness assembly depends on: • complexity of harness • quantity to be produced Dr. Mohammad Abuhaiba

  12. 4.2 WIRE OR CABLE HARNESS ASSEMBLY Dr. Mohammad Abuhaiba

  13. 4.2 WIRE OR CABLE HARNESS ASSEMBLY Dr. Mohammad Abuhaiba

  14. 4.3 TYPES OF ELECTRICAL CONNECTIONS Dr. Mohammad Abuhaiba

  15. 4.3 TYPES OF ELECTRICAL CONNECTIONS - Low-Pressure Connections • can be separated without aid of a tool • frequent disconnection and reconnection • tend to minimize errors during servicing because wires remain in correct sequence when disconnected. Dr. Mohammad Abuhaiba

  16. 4.3 TYPES OF ELECTRICAL CONNECTIONS - Low-Pressure Connections • General expectations from low-pressure connections: • Sufficient contact force for good conduction • Good cleaning action during assembly • Low resistance to mating of parts • Low wear on parts • Long life • Ease in connecting and disconnecting Dr. Mohammad Abuhaiba

  17. 4.3 TYPES OF ELECTRICAL CONNECTIONS - Low-Pressure Connections Points to consider when choosing a connector: • types of conductors to be terminated • assemblies to be connected • No. of contacts required • final product function • cost Dr. Mohammad Abuhaiba

  18. 4.3 TYPES OF ELECTRICAL CONNECTIONS - Low-Pressure Connections Dr. Mohammad Abuhaiba

  19. 4.3 TYPES OF ELECTRICAL CONNECTIONS - 4.3.3 High-Pressure Connections • Most commonly used methods: • wire-wrap • Crimp • screw connections • ultrasonic welding • riveting Dr. Mohammad Abuhaiba

  20. 4.3 TYPES OF ELECTRICAL CONNECTIONS - High-Pressure Connections Dr. Mohammad Abuhaiba

  21. 4.3 TYPES OF ELECTRICAL CONNECTIONS - High-Pressure Connections Dr. Mohammad Abuhaiba

  22. 4.4 TYPES OF WIRES AND CABLES • Wire conductors are selected for their: • current-carrying capacity • mechanical strength • type of insulation • Cost • Cables consist of two or more conductors within a common covering and are terminated by one or more connectors. • Electrical conductors include: • single solid or stranded wire • twisted pair and trio • multi-conductor cables • coaxial cable • ribbon cable • flexible flat cable Dr. Mohammad Abuhaiba

  23. 4.4 TYPES OF WIRES AND CABLES • Solid and stranded wire is designated by: • American Wire Gauge (AWG) number, • diameter of the wire in mils (thousandths of an inch), or • X-section in circular mils (square of diam expressed in mils). • A twisted pair consists of two stranded conductor insulated wires twisted together. • A twisted trio is the same as a twisted pair except that it consists of three conductors. Dr. Mohammad Abuhaiba

  24. 4.4 TYPES OF WIRES AND CABLES • Multi-conductor cable consists of two or more color-coded rubber- or PVC insulated conductors. • Coaxial cable consists of an insulated length of conductor enclosed in a conductive envelope of braided wire shield and an outer insulating jacket isolating the shield from ground. • Ribbon cable consists of numerous conductors of same gauge held side by side in flexible strips of insulation. • During termination, the U-contact displaces the insulation and each conductor is then forced and wedged within a U-contact. Dr. Mohammad Abuhaiba

  25. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation Manual operation: (Figure 4.11) • Insert wire to correct length into proper station of a stripping tool. • close tool to severe the insulation, which is removed by the tool. • Average experimental time = 7.0s Machine stripping: • Grasp wire and insert end into a stripping machine. • This triggers machine to strip off insulation to correct length. • Average Stripping time = 3s Dr. Mohammad Abuhaiba

  26. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation Dr. Mohammad Abuhaiba

  27. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Soldering iron Tinning time = 9 s • Solder pot tinning time = 7.2s Dr. Mohammad Abuhaiba

  28. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Figure 4.13: times for crimping one terminal to bare end of a wire. • Manual crimping: • insert terminal into a color-coded notch of a crimping tool • place bare end of wire into barrel of terminal. • close tool to compress barrel so that it clamps tightly onto the wire. • Experimental time = 13.9s Dr. Mohammad Abuhaiba

  29. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation Dr. Mohammad Abuhaiba

  30. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Semiautomatic crimping: • place bare end of wire into die set, triggering crimping machine. • After crimping, a new terminal advances automatically into die set for next crimping operation. • time = 3 s • Some Semiautomatic machines can strip wire and crimp a terminal after insertion of unstripped wire into the machine. • Insertion of wire is carried out manually • total time = 3.6s • Machines capable of automatically cutting, stripping, and crimping terminals to wires in one operation. • Time = 1.8 s per wire end for a length of 3 m. Dr. Mohammad Abuhaiba

  31. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • 30 s is required for stripping a multi-conductor having two wires • For each additional wire, a time of 6 s should be added. • Manual stripping of outer insulation = 18s Dr. Mohammad Abuhaiba

  32. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Figure 4.15: manual assembly times for soldering contacts of circular or rectangular connectors. • place connector into a fixture and fill all solder cups. • A handful of wires is then grasped using one hand, with other hand holding soldering iron. • A solder cup is reheated and simultaneously a bare wire is inserted. • Wire is held in position until solder solidifies. Dr. Mohammad Abuhaiba

  33. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • time for filling solder cups = (6.8 + 3.1 Nc) • Time for soldering wires = (0.2 + 8.3Nc) • Total time tsfor assembling a rectangular or circular connector : ts = 7+11.4 Nc(4.1) • This eqdoes not include cutting & stripping wires or assembling connector Dr. Mohammad Abuhaiba

  34. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Figure 4.16: manual assembly times for crimping contacts of circular or rectangular connectors. • Insert a contact into a crimping tool • place bare end of wire into the contact • squeeze tool so that barrel of contact grips bare end of wire as well as insulation on wire • Operation is repeated for each contact • With connector clamped in a fixture, wire contacts are then inserted one by one, using an insertion tool. • Times for crimping contacts to wires = (1.5 + 12.4 Nc) • inserting wire contacts =(1.1 +4.9 Nc) • Total time tpfor assembling wires to a circular or rectangular connector: • tp = 2.6+ 17.3Nc (4.2) • Nc =number of contacts Dr. Mohammad Abuhaiba

  35. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Time given by this eq does not include cutting & stripping of wires and assembly of connector • Semiautomatic crimping of contacts to wires: • 3 s per contact • manually inserting the crimped contacts into the connector =(1.1 + 4.9 Nc) • total time of 9 s for one contact • add 7.9 s to basic time per contact for installing more than one contact Dr. Mohammad Abuhaiba

  36. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Figure 4.17: manual assembly times for one coaxial connector termination. • Coaxial cable is cut to length • outer insulation is stripped • polyethylene dielectric and shield braid are cut to correct dimensions. • shield braid is then folded back smoothly and a plastic grommet assembled onto the cable. • The contact is crimped to the conductor after it is assembled, flush against the dielectric. • connector body is then assembled, braid clamp crimped, and grommet pushed flush against the body. • time for assembling coaxial connector =152 s. Dr. Mohammad Abuhaiba

  37. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation Dr. Mohammad Abuhaiba

  38. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation • Figure 4.18: manual assembly time for mass termination of a flat cable. • place body of connector into the locator plate of a press. • position flat cable into body of connector and the mating connector cover is placed over the assembly. • The UFIG contacts of the connector are forced into the flat cable conductors by operating the press. • cable connector is removed from locator plate. • Time for flat cable connector termination = 30 s • For flat cable connector termination using a press machine, a time of 2 s is suggested. Dr. Mohammad Abuhaiba

  39. 4.5 PREPARATION AND ASSEMBLY TIMES - Preparation Dr. Mohammad Abuhaiba

  40. 4.5 PREPARATION AND ASSEMBLY TIMES - Assembly and Installation • After one end of wire is attached, it is dressed to equipment chassis before other end of wire is attached. • Dressing time does not include cutting & stripping ends of wire, adding terminations, or attaching terminated wire • Experimental time for dressing: td= 3.4 + 1.2 Lw (Lw in ft) td= 3.4 + 3.94 Lw (Lw in m) Dr. Mohammad Abuhaiba

  41. 4.5 PREPARATION AND ASSEMBLY TIMES - Assembly and Installation Dressing wire into U-channel • After wire is attached at one end, it is inserted into U-channel before other end of wire is attached. • Dressing time does not include cutting and stripping ends of wire, adding terminations, or attaching terminated wire Dr. Mohammad Abuhaiba

  42. 4.5 PREPARATION AND ASSEMBLY TIMES - Assembly and Installation • Dressing flat cable after flat cable connector is attached onto its mating part. • Time for laying a flat cable does not include time for bending and pressing of cable so that it stays bent during laying. • A time of 15.1s per bend should be added to time for laying a flat cable. Dr. Mohammad Abuhaiba

  43. 4.5 PREPARATION AND ASSEMBLY TIMES - Assembly and Installation • A wire is grasped and one end is attached to a holding device. • Wire is then laid on board according to wiring layout and finished, with the other end of wire being attached to another holding device. Dr. Mohammad Abuhaiba

  44. 4.5 PREPARATION AND ASSEMBLY TIMES - Assembly and Installation • Time tnto assemble Nwwires simultaneously is Dr. Mohammad Abuhaiba

  45. 4.5 PREPARATION AND ASSEMBLY TIMES - Assembly and Installation • selection of wire(s) after cable connector is installed on harness jig • laying wire(s) according to wiring layout, and attaching ends to a holding device. • Times do not include attaching cable connector to its mating part on harness jig. Dr. Mohammad Abuhaiba

  46. 4.5 PREPARATION AND ASSEMBLY TIMES - Assembly and Installation • time tmto assembly Nw wires simultaneously from a connector is: Dr. Mohammad Abuhaiba

  47. 4.5 PREPARATION AND ASSEMBLY TIMES - Securing • Times for: • acquiring a tie cord • spot tying a bundle of wires • cutting excess cord with a pair of scissors. • Experimental time = 16.6 s is Dr. Mohammad Abuhaiba

  48. 4.5 PREPARATION AND ASSEMBLY TIMES - Securing • Times for tying a cable tie or strap onto a bundle of wires. • acquiring a cable tie, looping tapered end of strap around harness • inserting it through strap eyelet. • strap is pulled tightly and excess is cut off with a tool. • Experimental time = 14.4 s Dr. Mohammad Abuhaiba

  49. 4.5 PREPARATION AND ASSEMBLY TIMES - Securing • Times for lacing a wire harness. • Completion of lacing terminates when end of cord is secured and trimmed. • Experimental time tst: • Nst= No of stitches Dr. Mohammad Abuhaiba

  50. 4.5 PREPARATION AND ASSEMBLY TIMES - Securing • Times for taping a bundle of wires. • Time for taping 1 in. =13.8 s for first wrap. • a time of 7 s per additional inch Dr. Mohammad Abuhaiba