MACHINING CENTRES LATEST CASE STUDIES & PRODUCT NEWS
316 stainless steel casting, it involves
roughing the same face on an HMC and
then roughing the front face, bores and
ports on the same machine. The part is
transferred to a lathe to turn the port
details using single-tip boring bars. It then
returns to an HMC to re-skim either the
front or back face to provide a location for
mounting the part on a window xture to
nish-machine both faces. Production of a
batch of 50 to 60 bodies takes four weeks
by this method.
In contrast, set-up on the Spinner takes
just one hour and the new process route is
completed in two clampings, which means
that batches of 10- to 15-off can now be
produced economically. In the rst
operation, roughing and nishing of the
back face and the interpolated bores are
carried out by respective 16 mm diameter,
solid carbide end-mills from MA Ford Europe
(www.is.gd/olavig).
A Schunk (www.is.gd/odeyew) pneumatic
zero-point xturing system presents the part
to the spindle for the second operation in a
time that rivals the speed of an automatic
pallet changer. A probe doublechecks
the datum and also that the
bores machined in the rst
operation are the correct size.
Face-mills complete the rough and
nish machining on the front of the
pump body. The savings offered by
this method of production sees all
50 to 60 bodies completed in one
week rather than four.
Metaltech’s managing director,
Doug Murphy, comments: “We sent
drawings to Whitehouse and they
came back with set-up and cycle
times on the Spinner that looked
really good, which was largely down
to producing the bores by circular
interpolation milling, instead of
single-point turning on a separate
lathe.
“We were worried that it would
be dif cult to hold the required
20-microns diameter tolerance
using this method. However, our
fears were allayed by a set of three
cutting trials the supplier carried
out in its Kenilworth showroom. We
checked the bores on our CMM for
size, ovality and taper and they
were within microns.”
Adds technical director Mick Bignell:
“Another concern we had was that the new
method of roughing and nishing the back
face completely before turning the part over
to machine the front face and outside
would put stress into the casting, causing
distortion and movement of the datums.
This also proved to be unfounded.
“We had to look carefully at the surface
nish of the internals and bores, as these
rotary lobe pumps are used in the food
industry and any roughness could cause
hygiene problems. External nish is also
important to our customer, as the polished
appearance is a sales advantage. The
interpolation milling cycles established by
Whitehouse have proved to be equal to
these requirements and produce a nish
equivalent to single-point turning.”
FULL MAGAZINE BENEFIT
Savings in tooling costs result from the new
production method. The rst thing to note is
that on the HMCs, which use large
indexable-insert cutters for roughing, the
60-station tool magazines are not big
enough to accommodate all cutters needed
for every pump variant. On the Spinner, with
the new process allowing commonality of
tooling, the 32 pockets are suf cient to
machine the complete range.
Using a waveform rough milling strategy
with the 16 mm diameter cutter at high
speeds and feeds, typically 2,700 rpm and
2,400 mm/min, rapid metal removal rates
are achieved without unduly heating and
stressing the part, helping to maintain
accuracy. It is largely this lighter machining
that allows the BT40 vertical-spindle
machine to attain the same level of
precision as a 50-taper HMC when cutting
tough stainless steel.
On tooling costs, BIgnell says that one
16 mm end-mill can rough 22 pump bodies,
while a nishing end-mill had completed 50
parts and was half way through the next
batch at the time of interview. A further
bene t of these £120 solid carbide cutters
is that two or three regrinds are possible at
a cost of £25 per time. Overall, the lower
cost of tooling represents a monetary
XYZ Machine Tools provided
the technology to allow Howdon
Power Transmissions to rapidly
develop new products, p24
www.machinery.co.uk | MachineryMagazine | @MachineryTweets | July/August 2020 23
/olavig)
/odeyew)
/www.machinery.co.uk