Wire and Cable Technology International — July/August 2012
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Wire Processing Essentials - Part 1: Wire Prefeeding
J. Ruben Lozano

Premier of new Wire Cable Connector article series that reviews the basics of wire processing.

In our Industry, wire diversity is the norm. From automotive wire harnesses to appliance harnesses and electrical or electronic consumer goods, a tremendous variety of wire designs and types is being used. And for these processes, a notable variety of wire processing machines and systems is required.

Thus, given this permutation of wire types with diverse processing equipment choices available in the marketplace, the wire processing manufacturer has to figuratively step back and consider a number of essential notions that will furnish him or her with some practical knowledge basis, which can assist in making the best out of the process and the equipment at hand, or perhaps when considering the purchase of new equipment. The first thing you have to do is to take into consideration your particular wire’s characteristics—nothing fancy or technically profound at this point, just the basics.

Is it flexible or is it rigid? What about the insulation? Is it soft or is it hard? Does it have the consistency of a rubber band or a golf ball or something in between? Is the insulation material smooth and slippery or is it coarse and dry? Is the conductor core stranded or solid? Any combination of these descriptive elements can offer you clues on how this wire will react when it traverses across your equipment’s processing stages. And if you raise your own awareness on this, it will in turn allow you to also understand the limits and capabilities of those processing stage mechanisms.

The next thing is to think about what exactly these processing stage mechanisms within your wire processing system are, and what are they designed to do.

Basically, they are contained within three major divisions: preprocess, process and post-process. Preprocess includes all of those operations performed on the wire prior to processing it such as de-reeling, prefeeding, marking, straightening, slitting, etc. Process is the group of functions that transform the bulk wire into a processed wire segment, (measuring, cutting, stripping, crimping a terminal or any other additional process such as weather seal insertion or applying solder to the exposed ends, etc.). Post-process includes any additional operations immediately performed on the processed wire segment such as inspection, stacking, tying, bundling, etc. Let’s now take a look at the beginning stage in the wire process chain—the prefeeder.

Wire Prefeeding

As an example, let’s assume that your wire is a solid 14 AWG with a semi-rigid PVC insulation, which is hard and slippery. Since the core is solid and the insulation is hard, it will tend to coil-up on you as you pull it out of its reel, (preprocess). Say that your prefeeder has a take-up pulley system of 4" diameter pulleys—most likely these small pulleys aren’t large enough to contain the wire’s natural curl, and you experience continuous “jumping-off” and jamming inside the prefeeder unit, especially as the wire reel gets smaller.

Out of frustration, you bypass the prefeeding operation altogether and feed directly into the machine using the machine’s own pulling/measuring stage. Seems okay at first. However you later receive reports of inconsistent strip dimensions and/or overall length variations. You also notice that the wire is getting jammed inside the wire straightener rollers, so you relieve the pressure on them. This solves the length variation issue, but not the inconsistent strip dimension, and now the wire is sporadically curling out of the cutter-head blade area and sometimes it hacks-off the stripped end. By this time, it seems that your machine has been possessed and has a mind of its own. But in reality, the origin of the problem remains squarely on the physical characteristics of the wire itself: the wire-insulation combo is stiff enough that it curls and the curl gets worse as the reel is depleted because the wire is wound tighter on a gradually smaller and smaller diameter.

What could you do to solve this? Obviously, the ideal solution would have to do with eliminating or limiting the curl, perhaps by asking the wire manufacturer to provide the wire in loose-coil barrel container presentation rather than in reel form. If this is not possible, perhaps you have one of your Process Engineers take samples of wire curls as the reel is depleted and measure the corresponding curl radius and by observation, determine at what stage of the reel depletion you begin to experience prefeeder failure. This is known as the critical curl radius. You now compare this critical curl radius with your Take-up pulley radius and most likely you will see that the prefeeder’s pulley take-up radius is smaller than the critical curl.

One applied solution would be to replace the smaller takeup pulleys with larger pulleys that are at least 10% bigger than the critical curl radius. Another practical applied solution would be to install jump-off prevention shields around the outer perimeter of the take-up pulleys, or perhaps to add a pre-prefeed wire straightener between the reel and the prefeeder in order to neutralize the curl.

Need to Focus on Wire Characteristic

The above described theoretical situation describes but one of myriads of possible scenarios faced by manufacturers in our Industry. In my experience on both sides of the fence (as a Manufacturing Engineer inside a wire processing facility and on the capital equipment and perishable tool supply side) I have seen equipment users focusing almost exclusively on the machine’s process mechanisms when they attempt to troubleshoot a particular process issue. And they very rarely look forensically at the wire characteristic and how it interacts with the equipment at hand. I’ve had many instances where a client would scoff at me when I point out that the wire condition is contributing to the process issue. The immediate response is, “Wire is wire”, and perhaps understandably so because it is easier to gravitate towards familiar things rather than hidden or unknown factors.

But at the end of the day, in any and all processes, there is always interaction between the material being processed and the processing equipment itself. The key is to better understand what is available to you, the user, within the process mechanisms in the form of setups or adjustments that could assist in managing your wire’s condition or characteristic. Please note here that the operating phrase is “managing your wire’s condition”, and that there is a vast difference between managing and adapting. Managing implies using available on-hand resources while adapting implies some degree of modification. Nobody wants to invest in a piece of equipment that you have to modify later. Nor do you want to redesign the material’s characteristics in order to satisfy the equipment’s limitations. Thus, the key here is, “Know thy wire”, first, and the rest falls in place.

In Part 2, we will look at wire construction basics and the differences between aluminum and copper materials.

About Lakes Precision, Inc.

From hand strippers to fully automated wire processing equipment, Lakes Precision Inc. has the tooling to meet your requirements. Lakes Precision offers the widest range of blade sizes providing the perfect blade to wire application. The company’s extensive inventory allows same-day shipment on the most commonly used perishable tooling and accessories., Lakes Precision is your global source for wire processing and perishable tooling. Www.lakesprecision.com