Blade Types for Wire Cut-and-strip Machines
Machine programmability has enabled the evolution of blade types and designs for wire processing machines.
Many blade types are available for use in today`s automatic measure cut-and-strip machines for wire and cable processing. Why are there so many? With the introduction of the microprocessor and improved motor technology in the early 1980s, machine programmability has increased dramatically in lieu of mechanical tooling changeover. This programmability has enabled the evolution of different blade types and designs and has become an important factor in many wire processing solutions.
V-Blades
The most widely used blades in wire cut-and-strip machines are V-blades. These blades cut the insulation on four sides (see Figure 1). The biggest advantage of using V-blades is that often no blade changeover is required between jobs that process two different-sized wires. Tooling changeover is minimized or eliminated altogether because of the programmability of the machines. A library of data (e.g., cut depth) is available for standard wire sizes that can be selected when using a typical wire program in memory.
Figure 1. V-blade cut geometry.
The drawback of using V-blades is that much of the insulation is "ripped" because of the rectangular cut geometry around a circular inner conductor. Therefore, for hard-to-strip materials or very thin insulations, V-blades may not work and another blade type is required. In addition, V-blades lack any means for centering the wire during the cutting. Sometimes, this causes damage to the inner conductor because of one blade going too deep and the other blade going too shallow. Generally, V-blades work best with polyvinyl chloride (PVC) and other soft insulation materials.
Radius Blades
Radius blades are also commonly used in wire cut-and-strip machines, especially when trying to improve the strip quality over that of V-blades. Radius blades are designed so that the blade makes a circular cut with a diameter slightly larger than the wire inner conductor (see Figure 2). The advantage of using radius blades is improved strip quality and increased processing capability. Radius blades are commonly used for PVC, cross-linked PVC, thin, and hard-to-strip insulations.
Figure 2. Radius blade cut geometry.
There are two disadvantages of using radius blades. First, blade changeover is required for processing different wire sizes. This can be time-consuming and not efficient in a world where changeover time is critical. Second, as with V-blades, radius blades do not have the means for centering the wire during cutting.
Radius V-Blades
There is radius blade offshoot referred to as a radius V-blade. These blades are similar to V-blades except they incorporate a radius at the apex of the V. This allows processing where the cut geometry must be oval- or "football"-shaped. This is often a requirement for multiconductor cable that changes shape under the pressure of standard radius blades, although multiple-size wires or cable could work using one radius V-blade, minimizing blade changeover. The same two disadvantages apply: blade changeovers are required for different wire sizes and there is a lack of wire centering capability.
Shouldered Radius Blades
A second offshoot of the radius blade is a shouldered radius blade. The cut geometry is the same as for radius blades, except the blades have a shoulder that centers the wire during the cutting (see Figure 3).
Figure 3. Shouldered radius blade cut geometry.
This centering feature is extremely useful when processing loose-jacketed cable where there is not much pressure (anvil) to work against the blades, such as Category 5 cable. Although ideal centering is done using die blades, shouldered radius blades allow for cut-depth adjustment, whereas die blades butt together.
Die Blades
For the highest precision and stripping quality, other than rotary blades, die blades offer the most features. The cut geometry is circular, they have a means for wire centering, and they butt together ("die") for repeatable and precise cutting (see Figure 4).
Figure 4. Die blade cut geometry.
There are two important dimensions that must be known when sizing die blades. The first is the drill size, which is the actual cutting portion of the blade. This dimension should be slightly larger than the core diameter of the wire. The second dimension is the counterbore. The counterbore acts as the shoulder of the blades that centers the wire as the blades close. The counterbore dimension should be equal to the outer diameter of the wire insulation.
Die blades are commonly used with thin insulations such as Tefzel or PTFE, and are often used by industries that demand the best in cut quality, such as aerospace, military and medical. The only real disadvantage of using die blades is that changeover is required for different wire sizes.
Other Blade Types
The blade types discussed so far are the most commonly used blades in today`s wire cut-and-strip machines. In addition to these blades, there is a variety of other blade types (see Figure 5).
- Flat/U-contour blades are used for processing flat material such as ribbon cable or jacketed phone cable.
- Slitting blades are used in conjunction with stripping blades on a multiple-blade cutterhead to add slitting capability. A number of slitters can be incorporated in one blade for processing multiconductor round or flat cable. Slitting blades can also be used for wires that cannot be stripped because of tightly extruded jackets.
- Forming blades are used to form wires. Although not commonly used, they can be a unique option for use in multiple-blade cutterheads.
- Multiple radius blades have the same concept as radius blades, except there is more than one cutting radius in a single blade. These are often used for processing flat multiconductor cable or zip cord, and often times are used in conjunction with a slitting blade.
- Rotary blades are used in wire cut-and-strip machines that have this unique capability. Most machines that incorporate rotary blades use a complex wire centering system. This concept provides the best cut quality on the market. The other huge advantage of a rotary cutting system in the fact that its universal. No blade changeover is required. For the user looking for the highest quality with minimal or no changeover, rotary technology is the perfect solution.
Figure 5. Other blade types.
Conclusion
There are many blade types being used in today`s wire processing machines, especially in automatic measure cut-and-strip machines. As machine designers continue to use programmability in place of tooling changeover, and mechanical advancements such as indexing cutterheads and rotary cutting continue to progress, the role of blades will expand even further and new types will be developed.
Main Point
Many blade types are being used in today`s wire processing machines, especially in automatic measure cut-and-strip machines. As machine designers continue to use programmability in place of tooling changeover, and mechanical advancements such as indexing cutterheads and rotary cutting continue to progress, the role of the blades will expand even further and new types will be developed.
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