Introduction:
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 information to make sound decisions about quality issues concerning custom wire and cables . When it comes down to the actual looking after and planning for excellent quality results when producing a simple lead assembly, more complicated wire harness, or cable assembly, you must know what you’re dealing with. Quite often wire needs and the quality processing involved are pushed to the low man on the totem pole because it is deemed to be easy or looks easy. This is a common misconception.
This article was written to educate and eliminate the lack of information.
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 two most valuable assets we have is our reputation and strong relationships with our customer base and our well trained employees. As you read through this article you will soon realise the heart of quality in making a wire harness, cable assembly, or even a simply lead assembly relies heavily on a good pull testing and a verification of repeatability program.
You will realise 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 realise that not everyone will be familiar with the wire processing or cable assembly terminology, so I have added a glossary of terms in appendix B.
Keep in mind also 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 will be posting this document on the Internet in the near future. I would always encourage anyone who reads it on the internet, and feels they have relevant information to add, to email me and I will read and digest their information and add it here if it is valid.
I will start with the simplest operations in wire processing and build up to the most complicated.
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 wires 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 stripping of one or both ends, and what will be terminated on each end correctly, all must be controlled. 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 we’ll jump into that next.
Crimping or terminating a wire with some kind of electrical contact can be done by hand (last resort) or done on a semi-automatic foot pedal controlled press, or a fully automatic wire processing machine.
First let’s 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 terminal, place the correct stripped end of wire into the proper place all while holding the hand tool steady enough to do this. Once they feel that is correct they must squeeze the Pliers handles together and create the crimp pressure to bottom out the hand tool so it will form the terminal onto the wire.
Benefits of Hand tools:
Drawbacks of Hand Tools:
Next let’s consider the semi automatic press. These machines were the next levels of development in wire processing to eliminate the hand tool drawbacks. The operator places the wire into a die and when they feel it is proper they 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 wire usually has a stop to aid in placement. The terminals are also placed automatically by the die, and the press is set to the correct shut height to create what is called the 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:
Drawbacks of Presses:
1) Cost of press and associated tooling. Compared to a hand tool this method can range from 10 to 50 times more expensive to set up. Hand tools range in price from really cheap ones 50 dollars upward to 500 dollars.
Presses range in price from 2-7 thousand dollars and the associated die can range in price from a few thousand dollars to 7 thousand dollars.
The fully automatic wire processing machine.
This machine was developed to cut costs associated with processing by combining the cut and strip operation with the terminating operation. These machines are fed wire from a barrel pack and usually have two presses similar to the semi automatic presses on them, to terminate both ends of the wire as feed arms or roller wheels guide the wire through the machine. The operator needs to be well trained to operate this machine because if something goes wrong you can have a lot of scrap wire on your hands very quickly. Once it is set up and running well, it has the highest repeatability of all. This machine can also incorporate crimp quality monitoring into its process.
Benefits of automatic wire processor:
Drawbacks of automatic wire processors:
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 items in place, which we will consider next.
Small 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 send out the work to a wire processor like C-T Wire Prep Inc.
If they have a mindset for quality it is really an easy decision. You most likely will not achieve the highest quality unless you purchase the most expensive equipment. You gain nothing in trying to do it yourself when all is considered. The automatic processing machine is very expensive and not the only thing needed to produce the excellent quality results. There are a number of other expensive items needed and expertise in using them properly. We have only just considered the basic machinery necessary for wire processing at this stage. Why spend all that time, money and effort on an expertise that is not your main business focus. The money you would spend on setting up a proper wire harness processing area would more wisely be spent on marketing and promotion of your main business focus to gain market share. The information in this article will allow you to make an informed decision as to which company; you may like to do business with for your wire harness needs.
Next we will consider the quality of crimp action and repeatability of performing this process.
Whether you use a hand tool, semi automatic press, or a fully automatic wire processor you will need to know if the method you use is repeating and set up correctly from the beginning to the end of the run.
A combination of understanding crimp height, what is required for each terminal, crimp pressure, pull test or tensile strength of the crimped area and how to make the necessary measurements and adjustments are necessary to achieve excellent quality results.
Crimp height is in layman’s terms is just how much pressure the hand tool or press exerts while forming the terminal onto the wire. You measure it by using a vernier calliper or crimp height dial gauge. (See diagram) A long time ago it was determined by engineers and the regulatory agencies like UL or CSA and others as to what pressure was necessary to form and close a crimp terminal onto a wire to form a gas tight area at the crimp zone. For a given compression and forming of the terminal on the wire, a corresponding pull test measurement was achieved and documented. (See appendix A of this article UL pulls test requirements for various gages of wire.) Remember your customer may also specify even higher pull test requirements.
So adjustment of crimp height (shut height of the press) is important to achieve a proper pull test also known as tensile strength.
Crimp pressure can be monitored by CQM devices (crimp quality monitors) which are mounted in the press and monitor the pressure. But these devices should only be considered an indicator and not relied on instead of pull testing.
The measurement of pull test requires another important piece of machinery, namely the pull tester.
Pull test devices need to be in calibration and operated properly to know the true value of the pull test. The crimp area must be held straight with the pull force exerted directly out from the back of the terminal. (see diagram). Care must be taken to insure the crimp area has no pressure put on it from any other direction, or the pull test will be invalid.
Choosing a pull test machine is an important decision. It needs to be addressed by considering what size of wire and terminals you will be processing. There are many brand name manufacturers with different offerings. This in itself is a whole area to delve into and check out.
I will someday write an article about this topic but for now all that is necessary for excellent quality is to know that the pull test must be accurate and done in a desired frequency to show that your crimping process has repeatability.
There are a few different methods of pull testing you will hear about. Some are non-destructive such as the UL486 specification, which states that the minimum pull out force be applied and maintained for a period of one minute. This can be done with a pull tester that incorporates a pull and hold option. There are other standards for other industries. It would be wise to check with each customer as to what they require.
You could of course set up a pull tester with certified weights and exert the force necessary to achieve the desired test for this type of test but there are some issues to consider with this method.
The real true definitive test is the destructive pull test ( most recommended) that applies a pressure test to the point of separation of the wire from the terminal. Ideally the wire strands should rip behind the crimp area somewhere between the terminal being held and the wire clamp area where the pull test device grabs the wire.
Frequency of testing is another consideration. Your customer may specify this. If it is left up to your decision the best thing to start out with is to check the set up of your process in the beginning with at least 5 or 6 pull test samples, creating an upper and lower limit. This will confirm repeatability, and it would be wise to check again approx. 1 of every 1000 pieces produced for a new first run and again verify the repeatability. You should see that the pull test falls with in the same upper limit and lower limit of your original 5 or 6 tests. Once a history is developed over a period of time you may want to back off the amount of testing especially if it is a small run. It is wise to apply SPC testing parameters with this type of pull test to monitor the process.
Monitor both crimp height and pull test data and keep records by run number so to have traceability for an optimum quality program.
You now know what’s involved with testing a crimp terminal. There are still other issues that need to be addressed to create an excellent quality program in a wire processing facility.
The workers need training from day one before they begin any processing. At C-T Wire Prep we have ongoing training sessions. Before any new employee is allowed to start working on the shop floor, they must take the initial training course. This training encompasses all issues related to quality and safety. Creating quality workmanship must be instilled in a worker and the proper tools given to keep them on track. This involves training them to know what good crimping, wire cutting and stripping looks like.
This is a whole area of understanding that can only be gained from someone with experience. Proper quality plans which address checking operator set ups for all machinery, along with proven production procedures will create a data history that confirms proper workmanship, and eliminates costly mistakes. First off evaluations and approved samples should also be a part of the quality system. Wire harnesses and Cable assemblies should also be continuity-tested whenever possible to eliminate wiring mistakes. It is part of our quality system at C-T Wire Prep that all closed end wire harnesses or cables must be continuity tested. This is another expense that can get costly to perform. It requires another piece of equipment called the wire harness tester. There are a number of companies that specialise in these machines with many options. Some machines will just give you basic continuity testing, while others can also hi-pot test (running up to 3000V through the conductors to check for insulation breach). Depending on the machine you choose, you can even eliminate mistakes in real time. These machines run from basic 500-dollar end to end testers upwards of 10,000 dollars for one with all the bells and whistles.
Conclusion:
For an excellent quality program the following elements are necessary
I believe an ISO program addresses many issues of the overall running of a company properly. This is not to say you must be a certified ISO company, but make every effort to be as though you were.
Quality must be managed from the top down.
The heart of quality in a wire processing facility is the recognition and implementation of proper wire processing, crimp inspection and a testing program, along with proper operator training. This will create repeatability.
Compiling data on the processing of wire and testing of crimps will confirm quality, and be a reliable source of information for the future.
Always strive to eliminate problems before they happen. Keep abreast of new machinery aids and methods. I hope this has given you insight into how an excellent quality program for wire processing works.
At C-T Wire Prep Inc. we have an excellent quality program incorporating what you have read in this article and more. This article being limited in size cannot address the customisation of quality plans.
C-T Wire Prep is a member of the