Page 134 - Industrial Cutting of Textile Materials

Automated cutting of textile materials 121

Fig. 9.7 Round knife with decagonal blade.

The segmented blades reduce drag force; they chop the material more than they cut.
They are good to cut hard materials.
The knife can act in a nonmotorized or motorized way. Low-cost nonmotorized
freely moving knives – ‘pizza wheels’/wheel knives – are used for easy applications,
while robust powered knives cut harder and challenging materials. They can be driven
at different rotation frequencies (rpm) depending on material properties. The depth
of the cut is dependent either on the cutting pressure or on shoulders of the cutting
31
blade . Round blade knives are used to cut very wide range of textiles such as apparel,
technical, and composite materials and to process plastics, rubbers, paper, and foams.
Advantages of the tool: Because of the movement way (rolling over the material), a dis-
placement of the cut material on the work surface is small. In certain applications, single-ply
cutting by a round knife can be performed even without vacuum holddown of the material
ply. As with drag knives, round tools must be used on a hard and durable cutting surface.
However, as the pressure from the blade is not concentrated in one point only (as it is cutting
by the drag knife), the working surface is sacrificing less.
32
Disadvantages of the tool: Because of large overcut , round blades cannot be used to pro-
cess detailed shapes and sharp corners.
9.3.1.3 Oscillating knife

A straight knife that during the cutting process performs vertical movement up and
down (the Z-axis) in regular rhythm is called oscillating or reciprocating knife (see
Fig. 9.8). Oscillation is a motion that repeats with a constant period. Reciprocating
motion includes the restriction that the motion is linear. This way, knives performing
up and down motion in a single-ply cutter should be called oscillating, but knives
in a high-ply cutter where the vertical motion of a knife has to be more precise/re-
stricted should be called reciprocating. Although there is a difference in meanings of
these two terms (unfortunately not very clearly stated) knives moving up and down in
regular rhythm performing both single and multi-ply cutting process are most often
called oscillating knives. These kinds of knives are used to cut tough materials (which
are difficult to cut with a drag knife) and also thick materials and multi-ply spreads.
Oscillating knives can process both simple and complex shapes.

31 The tapered step in the side of a blade where the bevel meets the flat tang.
32 The distance between the point of entry of the cutting edge into the material in the direction of travel and
the last point of contact between the edge of the blade and the material.