A fundamental change to the way stainless-steel pump bodies are machined by East Sussex-based sub-contractor Metaltech Precision Engineers is resulting in far-reaching benefits.

These include a drastic reduction in set-up time that cuts the economical batch size by a factor of four, shorter lead times, faster cycles, savings in the cost of tooling, and less wear on the machine tool.

Additional advantages of the new production route are reductions in power and the space taken up on the shopfloor; both are in short supply at the company’s Hailsham factory and were the main drivers of the company wanting to find an alternative manufacturing process.

High-value 500 and 630mm twin-pallet 50-taper horizontal machining centres (HMCs) with box ways and high-torque spindles (of which there are nine on site) — plus CNC lathes — have underpinned pump body production since the company was established in 1976.

The components were typically produced in five operations on three machines.

A 40-taper five-axis vertical-spindle machining centre now machines the components in two operations.

The German-built Spinner U-620 (without a pallet changer) was supplied as a turn-key package by Kenilworth-based sole UK agent Whitehouse Machine Tools Ltd (www.wmtcnc.com).

Installed and operational within one week during November 2019, the cell ‘heralds a progression’ at Metaltech from the use of raw power to ‘smart machining methodology’.

The pump bodies in question — there are eight types, ranging in diameter from 160 to 280mm and featuring numerous different port details — are produced for a customer in batches of 50-60 to a monthly schedule that might include as many as 15 component variants.

Orders were sometimes impossible to fulfil, and discussions had to take place regarding alterations to the schedule, because the traditional machining process took 10-15hr to set up.

After skimming the back face of a 316 stainless-steel casting, the process involved roughing the same face on an HMC and then roughing the front face, bores and ports on the same machine.

The part was transferred to a lathe to turn the port details, using single-tip boring bars. It then returned to an HMC to re-skim either the front or back face, to provide a location for mounting the part on a ‘window ’fixture to finish-machine both faces.

Production of a batch of 50-60 bodies took four weeks by this method.

Dramatic savings

In contrast, set-up on the Spinner takes just 1hr, and the new process route is completed in two clampings, which means that 10-15 parts can now be produced economically.

In the first operation, roughing and finishing of the back face and interpolation of the bores are carried out by 16mm-diameter solid-carbide end mills from Derby-based MA Ford Europe Ltd.

Next, a Schunk pneumatic zero-point fixturing 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 first operation are the correct size.

Face mills complete the rough and finish machining on the front of the pump body.

The savings offered by this method of production mean that all 50-60 bodies can be completed in one week, rather than four.

Metaltech’s managing director, Doug Murphy, said: “We sent drawings to Whitehouse, which came back with set-up and cycle times on the Spinner that looked really good and were largely down to producing the bores by circular-interpolation milling, instead of single-point turning on a separate lathe.

“We were concerned that it would be difficult to hold the required 20µm tolerance on the diameter with interpolation, but our fears were allayed by a set of three cutting trials that the supplier carried out in its Kenilworth showroom.

“We checked the bores on our CMM for size, ovality and taper; they were within microns.”

Technical director Mick Bignell said: “Another concern we had was that the new method of roughing and finishing 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 proved to be unfounded.

“We also had to look carefully at the surface finish achieved on the internal features and bores, as these rotary lobe pumps are used in the food industry, and any roughness could cause hygiene problems.

“External finish 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 finish equivalent to single-point turning.”

Tooling benefits

Savings in tooling costs also result from the new production method.

The HMCs use large indexable-insert cutters for roughing, but the 60-station tool magazines are not big enough to accommodate all the cutters needed for every pump variant.

However, the Spinner and the new process allow a commonality of tooling, and its 32-tool capacity is sufficient to machine the complete range of pump bodies.

Using a waveform rough-milling strategy with a 16mm-diameter cutter at high speeds and feeds (typically 2,700rev/min and 2,400mm/min respectively), 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.

Mr Bignell said that tool life is very good, and that one 16mm-diameter end mill can rough 22 pump bodies, while a finishing end mill had completed 50 parts and was half-way through the next batch at the time of interview.

A further benefit 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 Mr Bignell describes as “immense”.

A further economy derives from reduced power consumption.

The Spinner draws between 10 and 20A, whereas an HMC draws 30-40A.

Indeed, Mr Murphy estimates that overall electricity consumption will fall by two thirds, using the new manufacturing process for pump bodies.

“As demand for these pumps is continually rising, finding more-efficient ways of manufacturing them is imperative.

“The reduction in set-up time from as much as 15hr to 1hr is a big game-changer with the Spinner, as is the elimination of work-in-progress.

“The new process has lowered the economical batch size and is helping not only to increase flexibility of production but also to reduce the cost; and handling the parts fewer times means there is less risk of scrap.

“The customer also benefits, as they can reduce stock levels.

“The ability of Whitehouse to provide this turn-key installation has given us a path to expansion that was difficult to see before.

“We were out of space and out of power here in Hailsham, and the high cost of relocation was not an option.

“The Spinner U-620 requires half the floor space of an HMC and consumes one third of the power, while delivering the same quality of parts four-times faster. It has been a sea change for us.”