Mitsubishi Heavy Industries Technical Review Vol. 49 No. 3 (September 2012)
49Precision Cutting Tools for Turbine Blade Groovesof Power Systems and Aircraft Engines

S a l e s D e pa r t m e n t
M a c h i n e To o l

The MHI Machine Tool Division is one of the few machine tool manufacturers that deal withboth tools and machines. We have offered our products to a wide range of areas including theautomotive and construction machine industries, and have received high evaluations. MHI is one of
the best power system and aircraft engine manufacturers in the world. The Machine Tool Division
has been supporting the in-house manufacturing of power systems and aircraft engines for morethan twenty years, and has accumulated abundant experience, technologies, and expertise regarding
machine work. In addition, in March 2012 we acquired Federal Broach and Machine Company
based in United States, one of the global broach and broaching machine manufacturers. We intend
to attain a higher level of technology through cooperation with this acquired company.
This document describes a broach and a side entry cutter that are accurate cutting tools formachining blade grooves of a turbine rotor and a turbine disk, which are key components of powersystems and aircraft engines.

|1. Broach
A broach is a rod shaped precision cutting tool consisting of many cutting teeth – thedimensions of which increase gradually – that is intended to be set on a broaching machine to forma workpiece. The features of the broach are high productivity and stable cutting accuracy. In
particular, turbine blade grooves of power systems and aircraft engines have complicated shapes
and require high levels of cutting accuracy and surface finish quality due to their harsh use
environment.

1.1

Specifications of workpiece

We have experience in various forms of broaching, using both teeth profiles of fir tree shapes
and dovetail shapes, a wide range of groove depth, groove width and skew angles and a broad arrayof workpiece materials from hot-resisting steel to difficult to machine materials such as Inconel.

1.2
(1)

Features

Optimum design generated by unique cutting technologies and expertise
Based on the abundant results as described above, we have developed our unique cutting
technologies and expertise and established the optimum design. For example, we have attained
efficient and accurate machining through determination of the cuts per tooth and the broaching
method, as well as the rake, relief, back angles, etc., suitable for the accuracy required for thepart to be cut, in addition to the chip pocket suitable for handling chips.
(2) Use of unique high performance, high speed steels and coating technologies
We have established longer tool life and machining accuracy by taking advantage ofunique materials and coating technologies obtained through our division's high speed gear
cutting technology at a speed of 300 m/min or faster and past cutting experiences of difficult tomachine materials. Figure 1 shows one example of improvement of tool life.
(3) Outstanding tooth profile accuracy and creation of sharp edges
We have attained high quality cutting with a thinner damaged layer through the use of
our technologies: a tooth profile grinding technology that realizes precision dimensions andMitsubishi Heavy Industries Technical Review Vol. 49 No. 3 (September 2012)50

shapes with an accuracy of a few micrometers and enables high quality finish of tooth surface,and a unique sharpening technology that reduces burrs and chipping and enables a sharp edge
finish. (Figure 2)

Figure 1 Example of tool life improvement due
to unique design and optimization of toolmaterial

1.3

Figure 2 Superb surface finish quality
achieved by high quality cutting

Overall support of broaching including broaching machine, broach sharpening
machine, etc.

Our chain type broaching machine (Figure 3), which has block shaped rotating tool holders
and enables single-pass machining of turbine blade grooves from rough cutting to finish cutting, iswell received by customers for its ability to contribute significantly to productivity. In addition, weprovide our unique NC control wet broach sharpening machine for re-sharpening operation, whichgrinds and removes the worn portion of used cutting edges for reuse. We offer overall support ofcustomer broaching operations including the usage of a cutter.

Figure 3

Chain type broaching machine|2. Side entry cutter
A side entry cutter is a formed milling cutter that is used for cutting blade grooves thatcannot be broached. Typically a side entry cutter includes fir tree shapes and dovetail shapes asshown in Figure 4 and is sometimes named a fir tree cutter after the shape of its cutting teeth.

2.1
(1)

Features
Achievement of accurate tooth profile
Typically, the tooth profile accuracy of a side entry cutter is maintained by superposing
the cutter's tooth profile projected by a projector on the form drawing. In this procedure, animage magnified several tens of times is projected for measurement. In our division, tooth
profile is magnified up to two hundred fold from a three-dimensional view and is measuredentirely and automatically using three fixed CCD cameras. This correctly evaluates the cutting
teeth accuracy of a cutter and enables accuracy compensation in increments of micrometers,
resulting in the establishment of accurate tooth profile maintenance.

Mitsubishi Heavy Industries Technical Review Vol. 49 No. 3 (September 2012)
51

Figure 4 Shape of side entry
cutter

The left cutter is fir tree shaped and theright cutter is dovetail shaped

(2)

2.2

Figure 5 Example of cutting with MHI high speed
steelComparison of tool wear through a cutting test in which simulated
turbine rotor blade grooves were cut

Use of tool material with superb wear resistance and toughness
In our division, high speed steel with both superb wear resistance and toughness is usedas the cutter material. This material includes a lot of finely and evenly dispersed vanadium
carbide, which is a hard granular substance, to significantly improve wear resistance andtoughness in comparison with conventional high speed steel. As a result, longer tool life andmore efficient cutting can be expected.
Figure 5 compares after-groove-cutting wear of a cutter made of high speed steel used inour division with that made of conventional powder metal high speed steel. The wear of thecutter made of high speed steel used in our division is 40% smaller than that made of
conventional powder metal high speed steel.

Side entry blade groove machine

We also manufacture a side entry blade groove machine that can simultaneously cut up tofour grooves, and have established a framework for supporting tools and a machine integrally.

|3. Future prospects
Currently we are developing broaches for the manufacture of new type gas turbines in thePower Systems Division. Together with the Engineering Headquarters and Manufacturing
Technology Center of our division, we provide overall support including responding to the need forfurther improvement of productivity, etc.
In order to accelerate global development in the power system and aircraft engine industries,
we are going to establish, for both technology and marketing, a trilateral system consisting ofJapanese, American and Indian bases through cooperation with Federal Broach and MachineCompany, which we acquired in March 2012, and MHI-IPT in India, which was founded as anoverseas production base for tools.