Tech Talk
What are "Multifacet Drill Points or MFDs"?
Performances:
Multifacet Drill (MFD) is an advanced drill point. It has been proved both in laboratory and on workshop floor that the point produces high quality holes with extended tool life. It has 3 to 6 times longer life thatn that of a conventional point with same drill amterial and flute design in drilling cast iron, titanium alloys, aluminum alloys, steels, and other metals as well as fiber reinforced plastics.
In recent years, researchers in the University of Michigan have been working with industries to implement MFD. Some of examples are given as follows:
1. In Tecumseh Products Inc. (Tecumseh, MI), a modified MFD achieved over 55,000 hole/per drill which means 60 times of more tool life than that of the previous drill point (800 holes/per drill, parabolic style from Cleveland Twist Drill).
2. In GM Saginaw Division, four pairs of MFD were designed to drill and to chamfer on ring gears made of SAE 4118 steel. The hole location accuracy was substantially improved. The scrap rate was cut down from 15% to 7% and the tool life was extended 5 times.
3. In GM BOC Group, two MFD points were applied in drilling cast iron engine blocks. They outperformed original drills (Racon) by three times tool life. 15,000 holes/per drill was achieved.
4. In Versa Tech Inc. (Detroit, MI), an assymetrical MFD enabled the engineers to increase feedrate from 0.010 inch/rev to 0.020 inc.rev and to increase speed from 250 rpm to 500 rpm in drilling aluminum alloy.
History:
MFD was invented in early 50s China. From 50s to 70s, researchers in China had worked on further development of MFD. A group of more than one dozen drills were designed for different applications. Their research was mainly focused on experiment. In early 80s the later professor S.M. Wu introduced MFD to the world. From then, Dr. Wu, his students and his researchers have focused on analytic study. Mathematical models were developed for MFDs. Grinding methodology was also developed. One of the significant achievement is the software which enables CNC grinders to precisely produce the designed shape of the drill points.
Characteristics:
A typical MFD has six facets in a symmetric form. Flank one is similar to the conventional point. Flank 2 forms an arc cutting edge in the middle of the cutting lip. Flank 3 forms a cylindrical surface to reduce the chisel edge.
The special design of MFD results in
a) an excellent self-centering capability which reduces lateral motion in drilling and better hole quality in terms of hole location, straightness and surface finishing;
b) low cutting forces (torque and thrust) due to
i) the arc shape cutting edge increasing rake angle of inner edge,
ii) a shortened chisel edge reducing thrust, and
iii) a large point angle increasing the rake angle of the outer edge;
c) an improved chip ejeciton due to
i) dividing the chips and forming relatively straight and long chips,
ii) using large point angle for outer edge;
d) a low temperature of cutting edges due to
i) producing less heat,
ii) more space for coolant;
e) an enhanced hole quality due to
i) less scratch on the formed surface,
ii) less drill wondering;
f) less drill wear due to reasons mentioned above.
Conclusions:
Although Chinese invented the drill point 40 years ago, it has not been widely used due to the difficult in grinding. The original points were manually made by highly skilled workers and only large size points can be produced. Using CNC grinder for MFD is a significant and historical breakthrough. A well designed software based on the drill mathematical models and grinding mathematical models is the key. It has been done on Walter grinder. It can be confidently concluded that the future of MFD is very bright.
