FIVE-AXIS MACHINING SUPPLEMENT
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September 2020 | www.machinery.co.uk | MachineryMagazine | @MachineryTweets
MACHINING CASE STUDIES
36
Sometimes orders were impossible to ful l and
discussions with customers regarding alterations to the
schedule had to be undertaken.
That was because the traditional machining process
takes 10 to 15 hours to set up. After skimming the back
face of a 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 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 ( 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 double-checks the
datum and 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-micron 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.”
Technical director Mick Bignell adds: “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.”
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.
Tool life is very good, according to Bignell, who says
that one 16 mm end-mill can rough 22 pump bodies,
while a nishing end-mill had completed 50 parts and
was halfway 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 saving that Bignell describes as
“immense”.
A further economy derives from reduced power
consumption. The Spinner draws between 10 and 20 A,
whereas an HMC pulls 30 to 40 A. Murphy estimates
that overall electricity usage will fall by two-thirds using
the new pump body manufacturing process.
(Continued on page 41)
SUPPLEMENTFIVE-Metaltech Precision Engineers has
scored multiple benefi ts through the
installation of this Spinner U-620 5-axis
machining centre
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