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maximum tool life performance with
minimized life-cycle costs.
universities and users to create an extensive product
portfolio ranging from PM-HSS gear hobs and SpeedCore
gear hobs to single-part carbide gear hobs (CarbideLine-S and
CarbideLine-H) and indexable insert systems (CarbideLine-I).
The quality requirements for gear systems are
increasing
In addition to the increased requirements for a longer life
of gearboxes and lower noise levels this now also applies
to the surface quality and dimensional accuracy of gears.
With regard to tools, single-part gear hobs made from PM-
HSS, SpeedCore and carbide are at the top of the quality
scale. However, if you are looking at the overall productivity
of these tools, a differentiation must be made. In this case,
single-part carbide tools are the best choice.
For the manufacture of large series in the lower module
range solid carbide gear hobs are the most powerful solution.
Due to their high manufacturing precision they enable a
high gear quality up to 6. They even machine high-strength
materials of 1,400 N/mm2 at high cutting speeds without any
problems while offering a long tool life. For the manufacture
of medium-sized series in the higher module range hybrid
tools are recommended.
Solid carbide hobs have the general benefits of single-
part tools, such as a high number of gashes and a larger
effective number of teeth. This results in tools with a higher
performance, even if the nominal cutting speed is lower.
Ultimately this will result in reduced gear costs (costs per
part). In addition, single-part tools are reconditioned in one
of the many LMT service stations to the manufacturer’s
original specifications after the end of the tool life, ensuring
35 | january-february 2019 |
However, solid carbide gear hobs
also have limitations with regard to
their applications, mainly due to the
higher cost of the material and the
associated manufacturing costs. This
means that they currently reach the
limit of their cost-effectiveness in the
dimensional range at module 5. For
carbide tools in the larger range up to
module 12, LMT Fette has developed
the new gear hob CarbideLine-H
(image 1). The tool is a hybrid
design. Its carbide cutting edges are
permanently attached to the carrier
tool (Hybrid Carbide Tools). These
innovative gear hobs enable a high
gear cutting quality up to grade AAA.
Their preferred applications are the
manufacture of commercial vehicles,
machine construction and power
engineering.
A combination of efficiency and precision
An innovative example for the efficient design of gear hobs
is the all new gear hob with indexable inserts - UNIFY -
which will be presented at the EMO trade fair for the first
time (image 2). It strengthens the area of application of the
proven gear hob family CarbideLine-I (I= Indexable) in the
module range from 5 -12 and is the preferred choice when
high performance and high quality are a requirement for the
machining of gears.
The new design of the UNIFY has created a single-part,
compact, very robust tool body which works with extreme
precision due to the minimum number of interfaces. The
compact design enables the use of indexable inserts for gear
hobbing, starting from a diameter of 160 mm which brings
many benefits: It can be used on smaller machines, fewer
limitations due to collisions and advantages with regards to
processing time.
The new gear hob with indexable insert has already passed
a crucial test in a practical application. It was used for the
machining of module 9 helical-tooth spur gears from the 18
CrNiMo 7-6 material with 88 teeth and a gear width of 220
mm. The tool had a diameter of 210 mm and 12 effective
cutting edges.
The UNIFY which was designed especially for this application,
used a protuberance plate with 4 cutting edges to achieve a
gear quality of 9 with its first attempt. The customer was very
happy with the smooth running and the very even surface of
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