Technical Articles:
High
Speed Machining: Die/Mold The Leadtime Challenge
Cutter
Strategies
Most
of the tool types that are familiar to mold and die makers using
conventional machining techniques are also applied in high speed
machining: ball nose, bull nose and toroid, for example. However,
high speed processing capabilities may encourage shops to consider
departing from conventional cutter wisdom in some cases such as
applying face mills to cut molds and dies.
Face
Mills
 Face
mills can bring a major metal removal rate for roughing along with
high accuracy for finishing flats. It depends on sufficient torque
capability from the machine tool, but depending on the number of cutters,
surface speed and chip load can be maintained at lower rpm.
- In materials up to 42 HrC, use positive rake
- For harder materials, use neutral or negative rake
- PVD and CVD insert coatings
- Rough Milling (round inserts)
- Finishing Flats (square, triangle or rectangle inserts)
Ball
Nose End Mills
 Ball
nose cutters are the workhorse of the mold and die industry. Whether
solid body or indexable insert designs, they are applied in roughing,
semi-finishing and finishing operations on cores and cavities. In
general, application differences between an insert cutter and a
solid carbide tool are marginal. Inserts cost less but solid tends
to be stiffer. Inserts have effective size limits ranging from 0.25
inch diameter to 1.25 inches in diameter.
- Use in materials up to 62 HrC
- PVD coatings available
- 6 to 10 percent cobalt content with micro grain carbide
- Specify ground inserts over pressed <
- Use for cores and cavities
- Helical hole boring
- Roughing slots or channels
When
cutting slots or channels in hard metals, conventional milling techniques
suggest a bull nose end mill. "At high speed," says Millstar
manager Ron Field, "we've found that roughing the slot or channel
with a ball nose mill–then coming in to finish size and shape
with a bull nose or square corner end mill–is actually a faster
process than using the bull nose or end mill alone at conventional
speeds."
Bull
Nose End Mills
 Bull
nose cutters are applied in milling flats and sides. Their distinguishing
feature is a radius on the edges that allows the cutter better heat
distribution when end milling.
Even
a radius of 0.5 mm provides significant strength over a square shoulder
end mill.
- Use in materials up to 54 HrC
- PVD coating available
- Larger diameters can be used with small corner radii
- Use in cores and cavities
- Semi-finishing and finishing
- Straight sides and corner radii
Toroid
Bull Nose End Mills
 Toroid
bull nose end mills blend ball nose and bull nose cutter design
into a versatile core and cavity cutting tool. No area in the toroid
cutter's active zone has zero cut speed. Step-over can be larger
without creating a cusp. Finish surfaces tend to be smooth because
there is no rubbing from a dead center area.
- Use in materials up 62 HrC
- PVD coatings available
- Larger radius edge gives better heat displacement
- Use for roughing, semi-finishing and finishing
- Can be used for helical hole boring
High
speed machining gives shops an opportunity to look closely at their
cutting tool strategies.–GCK
Source:
Millstar (Warren, Michigan)
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