of M8 x 1.25 holes with 16-mm thread depth has a hole-to-hole cycle time of 5
seconds in aluminum and 8 seconds in cast iron, according to the testing done
by major auto manufacturers. This represents a 6:1 advantage over conventional
methods on CNC machining centers, Fig. 3-4-6.
A time comparison of
conventional machining and thrilling a M12 threaded hole in aluminium. (Turchan
a special Thriller Spindle, it is believed that threaded holes in aluminum can
be made at the rate of 120/min with a single spindle. Cradled in an eccentric
quill, this special 60,000 r/min. spindle has built-in three-axis CNC motion
Drilling and Threading Cross-Holes
Inc. (Lexington, Michigan), an automotive component supplier to the Big Three,
is using the Thriller tool to drill and thread a cross-hole in 6005-T5 aluminum
parts. The combined operation, performed on a Sugino V8 machining center,
eliminates a separate tapping tool and one tool change.
speed throughout the combined operation is 6,000 r/min. Drilling is performed
at a feed rate of 60 in/min; threading (by helical interpolation) at 6 in/min.
The 3/8-24 thread form produced is machined to a depth of approximately 1 ½
times the thread diameter. Total machining cycle time is 6.1 seconds. Tool life
is approximately 15,000 parts.
the product engineers involved, a plus is that it produces a good thread form
without the tearing or load-up associated with tapping aluminum. The
combination tool saves space for one or more additional tools in the automatic
toolchanger. The machining center used for the cross-hole threading operation
has only eight tool positions. Saving even one of those positions for another
tool can be a big help in changing over to a new job.
a spotfacing operation also required in the cross-hole processing is performed
by a separate tool. Huron is looking at a tool that will combine the drilling,
spotfacing, and threading cuts in a single operation.
British pump manufacturer put to the test the concept that a combination tool
like the Thriller tool could drill/ countersink and thread mill a cast-iron
pump casing in a single operation. The test part selected was a casing
processed on a machining center in the pump company’s end suction unit. Several
M10 and M12 internal threads are required on this part.
the threads were produced by first drilling a hole with a conventional tap
drill (HSS-TiN-coated), then using a conventional tap to generate the thread
form. Use of the new combination tool eliminated one tool and one tool change
and it reduced cycle time per hole from 40 seconds to 12.
both the tap drill and tap requiring replacement every 1,000 holes (in contrast
to 20,000 holes with the Thriller solid-carbide replacement), and based on a
machine-time cost of $45.00 per hour, the total cost per thread was cut from
$0.56 to $0.18.
these results, using a single tool for drilling and threading was quickly
adopted as the permanent process for threading the casing. In two years, this
type of cutting tool averaged 20,000 parts per tool. In contrast to previous
costs of $11,240 to drill and tap 20,000 parts, the cost is now $3,600.