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Sub-contractor started out with one sliding-head lathe — there are now 10

Posted on 24 Feb 2021 and read 1193 times
Sub-contractor started out with one sliding-head lathe — there are now 10Paul Cobb, owner of Ilkeston-based HPC Services

When physics graduate Paul Cobb asked his father Reg in 1997 to help him invest in a sub-contract machining business specialising in CNC sliding-head turning, Mr Cobb senior groaned; he knew it would mean a sizeable investment.

At the time, both father and son were partners in the family's sub-contracting firm Stapleford-based Hemlock Engineering, which specialised in producing mainly prismatic parts and continues to do so.

However, Paul was keen to embark on a project of his own. He chose not to become a computer programmer or geological analyst but instead started HPC Services.

A small factory unit was rented in nearby Ilkeston and a Japanese-built Citizen Cincom L25 sliding-head, bar-fed, turn-mill centre was duly installed supplied by Bushey-based Citizen Machinery. At the time it was the first of a new, updated design to arrive in the UK.

From that moment onwards, HPC’s approach has been to acquire the very latest, most highly productive CNC equipment available on the market, designed to slash production times, reduce costs and improve component quality. Under Paul’s influence, it has become Hemlock’s maxim as well.

Over the intervening 24 years, HPC has invested in around 20 CNC sliding-head, twin-spindle lathes of nominally 12, 20 or 32mm bar capacity, all exclusively from the same supplier. Ten Cincoms are in operation, the others having been systematically replaced with newer models. There are also seven fixed-head, twin-spindle CNC lathes on the shopfloor of the current premises, where around 30 staff are employed.

When Paul launched HPC, he took with him from Hemlock one production job to get him started, a shaft for a sell-by date label printing machine. The food industry still accounts for around one-third of HPC’s turnover.

The job previously involved turning the component in two operations, after which it was ground and then milled on a machining centre, all in a total time of 7min. On the Citizen L25, the same job was completed in one hit in a 1min cycle. The parts are machined today on a different slider at a rate of 1,000 per month.

HPC 1Due to complete machining in one set-up, the components produced by HPC were of better quality, 5µm concentricity and 10µm dimensional tolerance being held reliably. Moreover, the price charged to the customer has consistently fallen in real terms due to the progressively higher level of automation on the newer lathes, which have the capability to run unattended around the clock.

Paul said: “Over the years, turned parts sub-contractors from around the world have quoted for this work. However, by harnessing the efficiency and accuracy of machines like the Cincom sliders we are globally competitive on price as well as quality, even for large production volumes.

“In the past that was not the case, but it is possible now with modern, ultra-high speed plant. Of course, our delivery times are much better than Far Eastern competition can offer, added to which control over projects is easier. As a result, we are seeing a strong trend towards reshoring of work.”

Today, HPC has some 5,000 different part numbers on its books. Components are produced from 38mm diameter bar or smaller on the Cincoms. Quantities range from 100- to 40,000-off in a vast range of materials, from exotic alloys through stainless steels, brass and aluminium to plastics.

Two million parts machined annually

The two million parts machined annually account for two-thirds of the company's £3 million annual turnover, the remainder being fixed-head turning. Around 10% of revenue is reinvested every year in new plant and equipment, a proportion that also applies to Hemlock’s £7 million turnover.

One of the latest components produced at HPC in one hit on a sliding-head lathe requires only milling, there being no turning content at all. The parts are being machined on one of a pair of recently delivered Cincom M32-VIIIs of a radically different design compared with the earlier M32s on site. The first of the new machines was delivered in November 2020 and Paul was so impressed with its performance that a second arrived a month later.

The prismatic component looks as though it has being machined from flat bar but is in fact milled from 303 stainless steel round bar, as it is difficult to source flat bar in that material in the UK. Part of a date-coding machine, it is produced in one operation in a cycle time of 4min 53sec on the lathe, whereas it would require four operations totalling 7min on a vertical machining centre.

A year or so before the arrival of the two new M32s, which have been supplied with kits to allow bar up to 38 mm diameter to be accommodated, the chief designer from Citizen's Japanese factory visited HPC to ask Paul what he would like to see in the fifth generation of this sliding-head lathe.

His response was “more rigidity”. The Japanese manufacturer obliged, endowing the latest model with box guideways rather than linear slides, a tang instead of a worm drive on the turret and higher power motors throughout.

HPC 2Paul explained: “The difference is amazing. It is possible to machine exotic alloys at double the speed compared with on a fourth generation M32 and you get four times the tool life, especially as coolant is now delivered through the tool platen as well as the turret.

"It is a massive step up in performance. A 10mm cutter purrs into the bar, even using a mill with carbide inserts rather than a solid carbide tool, which we need to use on the earlier M32s. Any production engineer would know that the new model is a very rigid machine.”

Other aspects of the latest design that he appreciates are the increased number of driven tools and a platen tool post with a programmable B-axis. It is useful for producing angled features on components and additionally is able to carry out front working so that the turret can be freed up earlier to perform operations on the reverse end.

Cycles for many jobs are significantly quicker. For example, when producing a particular 303 stainless steel flange from 38mm bar, it was previously necessary to wait for the turret to become available to deburr the component. At 57sec the cycle time is now 25sec quicker, representing a saving of 30%.

Just as important for reducing production costs is the ability to swap the machine over in half an hour to guide bush-less mode to save remnant wastage when producing relatively short components like the flanges.

In this case, 262 parts can be produced from a 3m bar compared with 225 if the guide bush is in place, delivering 37 extra parts, an increase of 16.4%. With 5,000 of the flanges produced annually, the saving is significant.

Citizen’s advanced technology came to the rescue a few years earlier, when HPC received a contract to produce plastic internal components for a manufacturer of high quality taps. Moulding these top-end parts is not feasible, as flash on the sealing surfaces could cause leakage and removing it would be too time-consuming.

Turn-milling the components from acetyl bar was the preferred method of manufacture, but plastics are notoriously difficult to machine, as copious quantities of long, stringy swarf is produced, especially when grooving.

Citizen had recently invented its patented, low frequency vibration (LFV) software that breaks such swarf into short, manageable lengths. Running in the Cincom's Mitsubishi control, where it is integrated into the operating system rather than being a macro, the facility can be switched in and out of a programmed cycle by G-code command.

Paul concluded: “LFV on the Cincom L20 we bought in 2017 is absolutely brilliant for turning plastic. Normally on a lathe we regularly have to remove swarf by hand that has tangled around the component and tooling, which takes ages and risks damaging the part, but that is eliminated by the software.

“It not only saves a lot of production time but also allows us to run the lathe unattended for long periods, which normally would be impossible when machining this type of material. The software will also be a big advantage if we receive contracts for producing components from ductile, long-chipping metals such as copper.”