Wiring Harness Manufacturing Quality Issues

Many business owners, engineers, production managers, and any other personnel, who are responsible for the quality and knowledge of their electrical or electronic wire processing, lack the information and training necessary to make sound decisions about quality issues concerning custom wire harness and cable assemblies.  When it comes This information lack is partly due to the fact that the knowledge, and information necessary to expose the issues involved in wire harness or cable assembly has typically been kept amongst a relatively few individuals. People who own, and or at one time or another worked for a cable assembly facility, that was exposed to a proper quality system, don’t let this information out freely.  There is a great deal of competition in the cable assembly and wire harness manufacturing industry, but at C-T we believe an informed customer is a good customer.

There is a large amount of information to go through to understand how to set up and control quality in a wire or cable facility.  Whether your cable wire fabrication shop is internal , and only part of a larger operation, or it is your main business focus, the need to set up a proper quality system is vital.  The cost of making a mistake is too large not to heed the recommendations of this article. 

At C-T Wire Prep Inc. the most valuable assets we have is our reputation and strong relationships with our customer base, and our well trained employees.   Training employees is vital to quality and following the methods that are described below are all part of a proper wiring harness quality system.

As you read through this article your will soon realize that the heart of quality in making wiring harness, cable assemblies, or even a simple lead assembly, relies heavily on good pull testing and a verification of repeatability program.  You will realize there is a good deal of testing involved in this field to maintain excellent quality.  As I go through the process of explaining the issues, I realize that not everyone will be familiar with the wire processing or cable assembly terminology, so I have added a glossary of terms page.  Keep in mind that there are always new processes and equipment coming along every year in the cable industry and this article is in no way considered finished.  Quality is always a work in process at C-T Wire Prep Inc. and therefore so is this document. I always encourage anyone who reads this article and wants to use it for teaching purposes, please feel free to do so.  All I ask is you return a link from your website with a remark as to where you got your information. 

Starting with the simplest operation in wire processing and build up to the most complicated manufacturing issues.  Lead assemblies are considered the simplest form of wire processing.  These will consist of wire cut to length, stripped, crimped or terminated on one or both ends with terminals or some other process.  Lead assemblies are considered the building blocks for wire harnesses.  Wire harnesses are lead assemblies added together in some fashion, and tied together becoming a wire harness.  Think of lead assemblies as having just two ends.  Wire harnesses have 3 or more ends running to various places (branches) making 3 or more connections.  Cable assemblies are a form of wire harness, but because of their nature have only two relatively distinct ends that run through the same jacket.  Most of the time the cable is brought in and processed in a different manner than wire harnesses. Cable assemblies can be made by creating lead assemblies of similar length, and fishing them through a loom or jacket, to produce the cable. Cable assemblies can also be made of extruded cable.  The ends are processed in a poke and strip manner, terminated and housed.  So to understand how to create an excellent quality model for wire harnesses, we need to understand the simplest item, which is the lead assembly.  In the making of a lead assembly there are several processes that can create a problem.  Wire type, wire length, wire colour, the length of the stripping of one or both ends, and what will be terminated on each end correctly, all must be considered.    Deeper than that are the real issues to obtaining excellent quality.  First do we have repeatability of the processes mentioned above and a true understanding of how to test a terminated wire properly is necessary.  So lets look at the repeatability process first.  This means understanding the options of how to build a wire lead assembly and which method is best suited. 
Crimping or terminating a wire with some kind of electrical or electronic contact can be done by hand (last resort), done on a semi-automatic foot pedal controlled press, or a fully automatic wire processing machine. 

First lets consider the hand tool.  Sometimes it is necessary to use a hand tool.  It is the least likely to give repeatability because it relies on operator skill, competence, and a quality attitude.  The operator is responsible to load the correct terminal, place the correct stripped end of wire into the proper place, all while holding the hand tool steady enough.  Once the operator feels sure they have the placement of terminal and wire correct they must squeeze the pliers handles together and create the crimp pressure to bottom out the hand tool so it will form terminal onto the wire.   
Benefits of hand tools: They are the cheapest method of tooling up.  They allow you to buy loose piece terminals and only what you need to do the job. 
Drawbacks of hand tools:  Repeatability is low for all critical criteria from terminal and wire placement to follow through on complete crimping action.  The operator will eventually become fatigued and run the risk of carpal tunnel, which could lead to a workman compensation claim.  Speed of operation is 100 – 200 crimps per hour.

Nest let’s consider the semi automatic press.  These machines were the next levels of developement in wire processing to eliminate the hand tool drawbacks.  The operator places the wire into a die, and when they feel it is properly situated, the activate the foot pedal to set the press in motion for one complete cycle of crimp.  These machines allow more control of the process because the die usually has a wire stop to aid in placement.  The terminals are also placed automatically by the die.  The press is set to the correct repeatable shut height, creating what is called terminal crimp height.  One extra item that can be added to these presses is some form of electronic crimp quality monitoring device.  (CQM) to catch mistakes as they happen in real time. 
Benefits of Presses:  Repeatability increases over that of hand tools substantially because the operator is responsible for less placement as well as not required to create the force necessary to crimp.   Speed of operator increases approx. 4 – 5 times that of hand tool rate.  Terminals are cheaper to buy per piece because of the minimum requirement of buying a spool at a time. 
Drawbacks of Presses:  Cost of press and associated tooling is substantially higher than a hand tool. Compared to a hand tool this method can range from 10 to 50 times more expensive.  You must buy terminals in larger quantities, usually on spools of 5000 pieces or more.  This may or may not be a problem depending on order quantity.  Training cycle to correctly set up a press of this type is a fairly long process. 

Now let’s look at the fully automatic wire processing machine.  This machine was developed to cut costs associated with processing wire, by combining the cut and strip  operation with the terminating operation for both sides of the wire all in a controlled cycle.  These machines usually are fed with wire from a barrel pack.  They have two presses similar to the semi automatic press above, that terminate both ends of cut to lenght and stripped wires.  Robotic feed arms control all placement and processing through the machine in a very repeatable fashion.
Benefits of automatic wire processing machines:  Repeatability when set up properly is extremely high.  Speed of operation is highest of all, approaching 3 – 4 thousand pieces per hour depending on length of wire cuts. Once the overhead of purchasing such a machine is out of the picture the cost associated with production is the lowest making for a competitive advantage.
Drawbacks of automatic wire processing machines:  Cost of the machine and associated tooling.  If the operator is not well trained a large volume of wire and terminals can be lost very quickly.  The training cycle for set up of this machine is a long process.

Obviously the more money you spend on the processing capability the higher level of quality you should achieve.  This only holds true if you have the rest of the necessary quality requirements in place that we will identify. 

Companies that have a low volume of wire to process are most likely to go the hand tool route, until they have a need for more wire processing.  Once that plateau is reached a decision has to be made as to whether or not to invest in semi automatic presses and dies, or farm out the work to a company like C-T Wire Prep Inc. If they have a mindset for quality it is really an easy decision to make.  As explained you aren’t likely to achieve the highest level of quality unless you purchase the most expensive equipment and train an operator properly.  Once the realization sets in that there is little to be gained unless you have a huge volume of wire to be processed, they may as well save their money and cut their overhead by finding a dedicated wire processor.  We have only touched on the 3 types of methods to process wire crimping, let alone involve the many other aspects of proper crimping methods and machinery to measure crimps.  The money a company could spend on setting up a good wire processing area would be more wisely spent of the promotion of their main business focus to gain market share.

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