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Automotive Wiring HarnessAutomotive Wiring Harness

Manufacturing Process

Prepared by: Carlos Ayala

Date: February 5 1999

ECE 539


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IntroductionThis report describes the manufacture and assembly process for an

automotive wiring harness. The main function of a harness is to transmitpower to the different components and modules in the automotive. Therange of complexity for a wiring harness depends by the quantity of wiresand components required for complete its assembly. I will use a mediumsize harness for illustrations and examples.

This report will follow the sequence that the operations occur in the actualmanufacturing process. This sequence is not strictly followed in all thecases, in fact there are many operations that can be perform at the sametime and the particular sequence will depend in the specific wiringharness design. Storage, incoming inspection and packaging will not be

included in this report.

Contents

1)

Cutting and crimping

Preparation of circuits and subassemblies

Assembly Process (manufacturing strategies)

Testing (Electrical Continuity and visual inspection)

2)

3)

4)

5)

6)

7)


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Cut t ing and Cr imp Term inat ion

The first part of the wiring harness manufacturing process is the preparation of thecircuits. Circuit is a wire cut at the required length and with terminals in one or both

ends, in other words is the raw material converted useful component for the wiringharness assembly. The parameters that define a circuit are the color, insulationmaterial, gage, strands and terminals. Other characteristics often used are wire sealand shrinking tubes. About 100 circuits compound a typical medium size harness.The document that encloses all characteristics for particular circuit is the Cut sheet.The information required to develop the cutsheet comes from the wiring harnessblue print and translated in manufacturing terms.

Samples of different circuits

The typical equipment that is required during this phase is an automatic cuttingmachine. This machine is a high tech piece of equipment drive by the use of acomputer. The operator will introduce the circuit parameters in its memory and setup the tooling and material required.


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The wire is pull from the wire-packaging barrel by the feeding system in anautomatic wire processing machine and cut the raw wire to the required length. Ashort length of insulation is remove from both ends of the circuit. A mechanical armwill hold the end of the circuit and lead it to the die applicator station, passing thougha sensor, which will verify that the circuit end has been strip correctly. Once the

circuit end arrives to the die applicator station and it is in correct position, themachine will activate a 5-ton press to apply the terminal. The terminal is present in aroll loaded over a carrier strip and is pull from the die applicator. Finally, the circuit isdeliver to a container, which is release in batches. The cycle of this complete circuitprocessing takes only a few seconds and will be repeating as the quantity desire.

Almost all parameters in the cutter are easy to adjust according to the circuitcharacteristics with the exception of the terminal applicator. The terminal die is acustomized tool for each type of terminal, and is adjust for particular wire size-insulation and terminal combination. The optimization of the cutter machine in largewill depends of the capacity for performing a quick tooling change in the machine.

Some smed techniques are use in order to minimize the set-up time. For low volumeof circuits is necessary to create a buffer of circuits in order to optimize the machineset-up.

During this phase, crimping is the most critical operation because is going todeterminate the electrical continuity between the terminal and wire. There are twoparameters considered in direct relationship with conductivity. Those parametersmust be monitoring in order to assure the quality of the crimping. First the pull forcerequired to remove a crimped terminal from the wire and the second is the shape ofthe crimping area (high and width dimensions).

Figure 2 shows the cross section photo of a good crimping conditions.

Figure 2


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Each terminal type will require different high and width parameters and actuallydifferent gages of the same terminal type will also require different parameters.Figure 3 illustrate a table of values required for the same terminal type in severalgage applications.

Figure 3

Because the importance of having a good crimping condition the process requiresvery, close monitoring. Since the cutting rate is about 3,000 circuits per hour is verydifficult the implementation of SPC. A very good aid for monitoring 100% of theproduction is a device called crimp force monitor (CFM). The CFM is an electronic

device connected to the CPU of the cuter. The CFM will compare a curve of forcerequired by the system to apply good crimping Vs every single application that

follows the same pattern. When there is a terminal change a new curve, have to begenerating with the first ten samples. The material variation (terminal and wire),defective wire processing, wrong material and mechanical failures are the reasonsof deviation from the sample curve.


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Once the cutting and crimping process are complete the some circuits will go directlyto the assembly line and others will go to the Preparation of circuits andsubassemblies area.

Preparat ion of c i rc ui ts and

subassembl ies

The most common processes involve in a circuit preparation are:

a) Circ uit s Splic ing :

Circuits splicing are use in places where, as a result of the design of the wiringharness, there is not other possibility of a fixing wiring connection. In addition, it isuse to avoid complicated looping of the individual circuits from one consumingdevice to another.

The circuit splicing are used as wiring distributors and serve to distribute the currentfrom the supply line to the individual consumer supply lines.

From thee approved methods for splicing, ultrasonic welding is the one that willprovide best quality of conductivity. Also ultrasonic welding process is clean, fastand uses no consumables.


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The ultrasonic welds are produced by the introduction of high frequency mechanicalvibration between two components. One component is held stationary while theother is "scrubbed" against it at 20,000 or 40,000 cycles per second. When pressureis applied between the two components, the surface films and oxides are dispersedand precisely controlled friction weld is achieved. As the molecules are mixed

between similar or dissimilar metals at the weld interface, the true metallurgic bondis produced.

The wires to be joined are placed between the tip and the anvil in the ultrasonicwelder by the operator and depressing the foot switch starts the weld cycle. An aircylinder advances the ultrasonic stack to compact the wire within the cavity formedby the tip and anvil (see figure) 4. The ultrasonic vibration of the tip scrubs the wiresagainst each other causing the bonding between wire strands. At completion of thetime cycle, the tip retracts permitting the weld nugget to be removed.


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Once the join is complete, the nugget is insulated using dielectric tape or heatshrinking tube.

As more wires are present on each side of a splice, the difficulty in positioning thewires within the welder cavity increases. This depends on the size of the wires that

the operator must pick and arrange in the cavity. This can result in poor qualitywelds and in some cases frayed strands.

As well as crimping, the conductivity of the splice is very important, and theparameters in direct relationship with conductivity are, the nugget dimension and thepull force required for take apart a circuit from the welding. The nugget dimensions(high and width) are automatically controlled by the ultrasonic welding machine andin fact SPC can be monitored automatically as well. The pull force is also monitoredby SPC sampling the process and plotting results.

b) Molding

The mold process has several applications in the manufacture of wiring assemblies.Mold insulation is used over terminals, connectors, splices, and on harnessbranches. The most common use is on grommets molded over the harness branch

and used in those places where the wiring harness has to pass through theautomotive frame. Grommets are used as a sealing component to prevent waterintrusion and noise reduction.

There are several types of molding machines and its application will depend on,mold size and mold material. One of the molding machines with wider applications isthe Newbury injection-molding machine. This is a 30-ton reciprocating screwmachine and has capacity for manufacture in 1 and 3 ounces and mold a widevariety of plastic materials. The machine is equipped with a lower mold shuttle whichallows parts to be located into 1 mold half while the part in the other mold half isbeing process. The cycle time is a function of how large the shot is the materialbeing used, and the design of the part. Large parts with thick wall sections requiremore curing time to stabilize dimensions.

The sequence of operation is as follow: At the conclusion of the cycle, the clampopens and the machine stops. The operator that was installing the harness in theother half of mold depress the two close-mold pushbuttons simultaneously causingthe shuttle table to shift, and place the mold half with the wiring in it under the clamp.


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After a hesitation, the mold closes and the cycle start over, providing thepushbuttons remain depressed. If the pushbuttons are released during the hesitationperiod, the machine will not continue the cycle until the buttons are againdepressed.

Although molded parts are very useful in wiring harnesses, its use has decreasedsignificantly due the high quality risk and extreme safety actions required to operatethe equipment.

New connectors design has replaced molds in terminals and connectors, and e--molded rubber Applied grommets are now available for replace the moldedgrommets. Applied grommets are now more common that mold grommets an itsassembly is much simpler than a molded grommet. The grommet stretcher is thedevices used for attach the grommet to the harness and can vary from manual to apneumatic device.

Assembly Proc essThe assembly process is the major step in the wiring harness manufacturingprocess. Harness assembly is an operator dependent process and the goal is toreduce this and increase automation. Here all the components of a wiring harnessare assembly to complete the part.

Unlikely the other process production lines in assembly have to be separated byfamily harness. A family harness is compounded by a group of harnesses that aresimilar and can be produced in the same tool.

Several manufacturing techniques can be used to complete the harness assembly.A rotary assembly line consists of Jigboards, conveyor rotary and off-line equipment.Jigboards are mounted on top of the conveyor rotary chain, which moves theJigboards in a horizontal flow rotating around the conveyor.

The Jigboards is the harness assembly tool and is made of wood or perforate steelto hold the wiring harness during its assembly. It serves as an aid in getting the


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correct dimensions, orientations and provides ease in taping, blocking and wirestringing operations.

The jigs are individually mounted on a jig car, which are hooked to the rotaryconveyor chain. The jig is a board with an overlay sheet pasted on the surface and

covered with a plastic protection. The overlay is the drawing representation of thepart and indicates position for the jig components such as holding fixtures forconnectors and clips, brackets, forks and indicators. The jig components assist inholding connectors and circuits, routing bundles, taping and clip presentation.


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Overlay for 98AG-14401 wiring harness family

Rotary conveyors consist of 10-foot sections and 2 end sections together with avariable high-speed torque motor. It provides the circular transfer motion of theboards during assembly operations. The rotary is designed for continuos motion at a

set speed necessary for the line to catch up with the production schedule. The rotaryline is designed to produce a specific number of harnesses per rotation.

Wiring assembly production line using the Rotary concept.

The production output is controlled by the speed of the conveyor. The assemblystarts at one point of the rotary (first end), is partially assembly in the differentworkstations, and is completed as the rotary conveyor is transferring it from onestation to another. The harness is taken off in the other end of the rotary when it iscomplete.

Assembly set-upIN

OUT


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Elect r ic a l Test ing.

After the last operation affecting continuity, all wiring assemblies shall be electricallytested 100%. The electrical test must check for crossed circuits, opens and shorts.Connectors that are mounted to a bracket before shipment, clips and othercomponents must be checked to verify that they are in the correct position. The testis conducted sequentially, testing each circuit and each branch of each circuit. Thistest includes the functionality of electronic components as diodes or relays.Connectors assemblies that uses a secondary terminal lock component such awedge or bar are also tested to verify the presence and correct position of thissecondary lock component.

All wire assembly harness is subject to the continuity test. It is required re-testing allpositions if any connector fails to have every position successful tested.


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Once the test is successful complete, the test board provides the operator with asuccess signal and releases the locking mechanism on the fixtures that hold the

connectors.

Modular electrical test boar


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