Wire Cut & Strip Machines

Blade Types and Their Applications
 
 

By John Benson,
Product Manager,
Schleuniger, Inc.
 
 

Introduction:

There are many blade types that are available for use in today's automatic Measure,Cut & 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 1980's, 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.

The purpose of this article is to explain the different blade types available on today's Cut & Strip machines, including an explanation of the blade geometry, some advantages and disadvantages, and their real-world practical applications.
 
 

V Blades

The most widely used blade in cut & strip machines is the V blade. The V blade cuts the insulation on four sides as shown in figure (1).

Figure 1. V blade cut geometry

The biggest advantage in using the V blade is that no blade change is required between jobs that process two different size wires. Tooling changeover is minimized or eliminated altogether, due to the programmability of the machine; a library of data (e.g. cut depth) can be selected for standard wire sizes that can be selected when using a typical wire program in memory.

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, the V blade may not work and another blade type is required. In addition, the V blade lacks any means for centering the wire during the cut, sometimes causing damage to the inner conductor due to one blade going too deep and the other blade too shallow. Generally, V blades work best with PVC and other soft insulation materials.
 
 

Radius Blades

The radius blade is also commonly used, especially when trying to improve the strip quality seen with V blades. The radius blade is designed so that the blade makes a circular cut with a diameter slightly larger than the wire inner conductor as shown in figure 2.

Figure 2. Radius blade cut geometry

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.

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, the radius blades do not have a means of centering (as described above with V blades).
 
 

Radius V Blades

There is radius blade offshoot that is referred to as the radiused V blade. This blade is similar to a V blade except it incorporates 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 the standard radius blade, although multiple size wires or cable could work using one radiused V blade, minimizing blade changeover. The same two disadvantages apply; changeovers are required between wires and there is a lack of centering.
 
 

Shouldered Radius Blades

A second offshoot of the Radius blade is the Shouldered Radius blade. The cut geometry is the exact same as a radius blade, except the blade has a shoulder that centers the wire during the cut (as shown in Figure 3).

Figure 3. Shouldered radius blade cut geometry

This centering feature is extremely useful when processing loose jacketed material, such as Category 5 cable. Although the ideal centering is done using a die blade (explained later), shouldered radius blades allow for cut depth adjustment (where die blades butt together). This feature is especially useful for loose jacketed cable, where there isn't much pressure (anvil) to work against the blades.
 
 

Die Blades

For the highest precision and stripping quality (other than rotary blades), the die blade offers the most features. The cut geometery is circular, they have a means for cable centering, and they butt together ("die") for repeatable and precise cutting.

There are two important dimensions which 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. This is the shoulder of the blade that centers the wire or cable as the blades close. The counterbore dimension should be equal to the outer diameter of the wire insulation.

Figure 4. Die blade cut geometry

Die blades are commonly used with thin insulations such as Tefzel or Teflon, and often used by industries that demand the best in cut quality such as aerospace, military, medical, etc. The only real disadvantage of using die blade is changeover between different wire sizes.
 
 

Other Blade Types

The blade types discussed so far are the most commonly used blades in today's cut & strip machines. In addition to these blades, there are a variety of other blade types. These include:

Figure 5. Other blade types

Flat/U-contour blades: used for processing flat material such as ribbon cable or jacketed phone cable.

Slitting: used in conjunction with a stripping blade on a multiple blade head 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 can not be stripped due to tightly extruded jackets.

Forming: used to form wires, not commonly used, but can be a unique option for use in multiple blade cutter heads.

Multiple radius: used the same concept as radius blades, except there is more than one cutting radius in a single blade. This is often used for processing flat multiconductor or zip cord, and often times used in conjunction with a slitting blade.

Rotary blade: used in cut & strip machines that have this unique capability. Most machines that incorporate rotary blades use a complex 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 it's universal. No blade changeover is required. For a user who is looking for the highest quality with minimal or no changeover, the rotary technology is the perfect solution.
 
 

Example of programmability - multiple blade cutterheads
 
 

New machines are appearing on the market that take programmability to a whole new level. One of these developments is a wire processing machine with a cutterhead that can hold multiple blade sets or different types of tooling. The cutterhead can be programmed to automatically select the desired tooling during the particular program that is being run. A typical example might include

1.) cutting with V blades

2.) indexing to radius V blade position

3.) stripping the cable jacket

4.) indexing to slitting blade position

5.) slitting the cable jacket lengthwise with custom slitting blades, all in one wire program.

This is just one example that shows why and how the evolution of different blade types is a result of increased machine programmability.
 
 

Conclusion

There are many blade types being used in today's wire processing machines, especially in automatic measure,cut &strip machines. As machine designers continue to use programmability in place of tooling changeover, and mechanical advancements such as indexing cutter heads and rotary cutting continue to progress, the role of blades will expand even further and new types will be developed.

For further information contact Schleuniger, Incorporated, 87 Colin Drive, Manchester, NH 03103. Phone (603) 668-8117 or Fax (603) 668-8119. E-mail: sales@schleuniger.com or visit Internet: http://www.schleuniger.com