In its 25th anniversary year, the Plymouth plant of hydraulic motor, pump and valve manufacturer Kawasaki Precision Machinery has seen a far-reaching re-organisation of its K3VL axial-piston pump machine shop.

This follows the purchase in October last year of a pair of twin-pallet horizontal-spindle machining centres (HMCs) to replace two ageing double-pallet models on which it was becoming difficult to hold tolerance.

One of the new Heller H2000 HMCs — manufactured at the Redditch factory of Heller Machine Tools Ltd (www.heller.biz) — is devoted to machining pump cases, while the other mills and drills valve covers.

The components are produced from grey-iron castings that have had their bores pre-turned on a lathe in preparation for two-operation prismatic machining.

Around 20,000 of each component are produced per year.

Production engineer Mark Pellow said: “In the case of the valve cover, the machining time of 50min — plus 10min load/unload on the former production centre — has been replaced by a 32min cycle on an H2000.

“For the pump case, the former machining time was 48min — plus 10min for handling; the current cycle takes just 30min.

“As set-up is carried out on the other pallet during machining, the next component is presented to the spindle within seconds by automatic pallet change, so productivity has been nearly doubled for both components.”

The two process routes have been changed to enable this increase in output.

Parts are still loaded two at a time on a tombstone for Op 1 and Op 2 machining.

One difference now is that fixtures have been built into a suite of tombstones to accept the castings directly, rather than first having to mount them on work-holding plates (the double-handling procedure used to eat into much of the spindle up-time on the previous machines).

Improved access

There is a second — and particularly important — difference.

When nearby Morris Engineering produced the work-holding solutions for Kawasaki, it arranged the two fixtures so that one is on a tombstone face and the other is mounted across the top, improving tool access.

The result is that any given tool can machine more features throughout the whole cycle; because the program is no longer split in two, fewer tool changes are needed — leading to less idle time.

Tool exchange itself is also faster at 2.8sec chip-to-chip, as are rapid traverses — up to 90m/min around the 630mm working cube.

In-cut times on the Hellers are also shorter, due to the higher cutting feed rates and spindle speeds.

These are coupled with the use of modern inserted and solid-carbide tooling from Seco; these tools offer a longer service life, reducing the need for worn-tool replacement.

An example of the ability to take advantage of modern tooling is a 6.2mm-diameter solid-carbide drill which now produces holes to depth in one pass at a high feed rate; this compares with the previous need for a high-speed-steel drill to peck (in 5mm increments) up to 20 times — and at a lower feed rate.

The use of carbide form drills also speeds up hole production.

Further savings in the machining cycles derive from the better probing of more features for establishing workpiece position, which allows most fixed datums to be live, minimising operator adjustments relative to them.

Not only is productivity almost doubled by the new processes, but accuracy of machining is also improved, allowing tolerances to be held easily.

For instance, 50µm valve cover concentricity, 20µm servo piston concentricity and 0.2mm dimensional accuracy on bolt holes are achieved to support a process capability of at least Cpk 1.33.

Previously, some tolerances were close to their limits when checked on the Mitutoyo shopfloor CMM, and intervention was frequently needed.

Currently, production for one pump frame size is carried out on the H2000s, but two more sizes will be phased in over the coming months.

Heller in top spot

Regarding Kawasaki’s choice of Heller HMCs for this latest project, bearing in mind that there are already two other brands of horizontal-spindle machine on the shopfloor and a fourth was also considered, Mr Pellow said: “As is often the case with machine tool purchases, we drew up a checklist of machine attributes, from speeds and feeds through health-and-safety features to price.

“In this appraisal, 19 items were listed on a spreadsheet, and Heller’s overall score came out on top.

“The fact that we use four other Heller HMCs, which are about a dozen years old yet are still reliably producing a valve block and two cases for our KV3 pump, also helped the decision-making process.”