Critical Attributes of Wire Prefeeders
By Bil DeGrace
A wire prefeeder is essential to maximizing the productivity of any automatic wire processing machine. The prefeeder accomplishes this by performing several important operations that ensure the wire entering the automatic wire processing machine is in the optimal state for cutting, stripping, or terminating.
This article discusses the critical pre-processing operations of a prefeeder. It then pivots to additional features you should consider when specifying this equipment for your operation. WHN sought the help of Bil DeGrace, Vice President of Mechtrix Corporation, for this article. Mechtrix manufacturers ancillary equipment and products for the harness industry, including prefeeders. However, the information put forward is a useful analysis without regard to the brand of prefeeder. Following are the critical operations of a prefeeder:
- Removes the wire from the storage reel or barrel at a constant rate to minimize the stress on the insulation. Basically, a prefeeder smooths out the process of pulling the wire from the source (typically a reel). Imagine pulling wire from a large reel. Initially, it takes a higher amount of force to overcome inertia, and get the reel turning. A much lower force is needed to keep it turning. A prefeeder reduces the starting and stopping of the reel by pulling wire continuously as opposed to it being pulled directly by the wire processing machine. Otherwise, the resulting jerking motion can damage or stretch the insulation resulting in wire strip lengths outside acceptable tolerance parameters as the insulation creeps back after being cut.
- Loads the wire into a controlled draw source to make more of the wire instantly available to the automatic wire processing machine during the wire feeding operation. The draw source is a series of accumulation pulleys around which the operator wraps a sufficient length of wire before feeding it into the wire processor. This creates a buffer of wire between the reel and the wire processing machine.
- Provides more consistent and controlled tension on the wire presented to the automatic wire processing machine. Because we deal mostly with stranded conductors in our industry, there can be a significant amount of stretch under extreme pulling loads. Variability in the pulling load from a reel can cause unacceptable variation in the overall wire length. The controlled back pressure provided by a prefeeder all but eliminates this inconsistency.
- Reduces the coiled “memory” in the wire by routing it back and forth thru a series of pulleys to help straighten it for more efficient feeding by the automatic wire processing machine. When wire sits on a reel or in a barrel for a length of time, it develops memory. It tends to retain a coiled shape. This can cause issues when cutting, stripping, and especially terminating the wire. By running the wire through a series of pulleys, the memory is reduced. Although most wire processing machines also have a series of straightening rollers, these alone are not always enough to overcome wire memory.
- Prevents tangles or snags in the wire from damaging the automatic wire processing machine’s expensive feeding system by providing a signal to warn the machine that wire is not ready or available. Many variables can cause tangles or snags in wire. A common situation results when a reel is partially used. After a production run, wire is often rewound back onto the reel, resulting in overlaps or tangles. Damage to the feeding mechanism on wire processing machines due to snags can be quite expensive. Smaller bench top units can actually pull themselves off the bench with catastrophic results. Ideally, the prefeeder sends a signal to the wire processing machine to stop if the wire is not available due to a snag or tangle.
Additional Features and Options for Consideration
Following are some equipment features that you should look into when shopping prefeeders:
- A mechanical system for safely lifting the heavy reels of wire into the prefeeder so only one person is needed to load or unload new reels of wire. Many large reels can weigh up to 200 pounds and beyond. Even smaller reels can weigh 50 pounds and are generally awkward to maneuver. A reel stand with a lifting device makes loading heavy reels quick and safe.
- A prefeeder properly sized for the speed and range of wires to be processed by the automatic wire processing machine. Most shops in the low volume/high mix realm use many different wire gage sizes and cable configurations. This makes it prudent to choose a prefeeder that can handle this wide variety.
- A communication interface to your automatic wire processing machine to prevent wire feeding errors. An interface cable connected to the wire processing machines’ e-stop circuit will send a signal to stop both machines in case of a wire jam or other prefeeding error to prevent the likelihood of damage to either machine.
- The ability or optional items required to run wire supplied in various configurations or formats such as small hanks of wire, various size barrels of wire and both small and large reels of wire. Although most wire comes on reels, barrel or hanks (flat coiled bundles) are also used. It’s wise to choose a prefeeder that can handle any type of wire packaging.
- The cost of replacement parts such as feed wheels, feed belts and replacement pulleys. As with any equipment, it’s always good to have an idea of price and availability of consumable products like belts and pulleys. (The only significant consumable on the Mechtrix equipment, for example, is the feed belt. They are readily available for about $10)
- The amount of routine and preventative maintenance required for the everyday operation of the prefeeder.Routine Maintenance procedures and schedules of prospective machines should be reviewed and compared before investing in a prefeeder.
- The amount of operator interaction or training required to properly use the prefeeder. The goal should be to minimize the amount of operator adjustments necessary during equipment run time and at setups.
Since 1982, the Mechtrix Corporation has specialized in the design and manufacture of tooling, technology, and equipment for the electrical wire processing industry. Mechtrix provides proven, innovative technical expertise in solving difficult wire processing problems through their dedicated engineering support staff. They are driven by a commitment to find the right solution to unique wire applications.
Mechtrix has incorporated over 30 years of proven experience in developing wire prefeeders for the harness industry. Read about their newest generation, the MPF-40 Wire Prefeeding System in the News Plugs section.