Live and let die

to casting production, machining, finishing, assembly and on time supply of finished products. As Solutions discovers, the use of die castings coupled with high specification machine tools can minimise waste and take productivity to new levels.

Kemlows began machining aluminium and zinc castings in 2000, mainly using a Brother twin pallet machining centre. More recently, the die caster installed three further 4-axis Brother machines – supplied through UK sales and service agent, Whitehouse Machine Tools.

Founded in 1946 and now located in Hoddesdon, Hertfordshire, Kemlows was acquired by its present managing director, Carm Teoli, through a management buyout in 2001. Since that time, continuous improvement and capital investment have moved the focus of manufacture into larger casting projects covering a wide range of industries and castings users. Customers are principally in the UK, but are also to be found in Germany, the Czech Republic, Mexico and the USA.

These days, excellent quality, on time delivery and exemplary customer service are expected from suppliers who implement Lean and Six Sigma methodologies to help achieve those goals. Kemlows has gone beyond that to embrace Value Analysis/Value Engineering to focus on taking cost out of production and so improve value to the customer. Designs are carefully considered before recommendations are put forward that will reduce the cost and/or improve the performance of the finished product.

Waste not, want not

A good example of this was the production of a complex telecommunications component, which was migrating from small batch production up to medium volumes. Manufacturing cost has been substantially reduced by modifying the design and machining it from a high pressure aluminium die casting, rather than from solid billet.

As a result of using the near net shape technique, 70% of the material is saved from being turned into large volumes of swarf, avoiding the inconvenience of managing it on the shopfloor and the expense of recycling. The machining cycle is much faster, as only 0.75mm has to be skimmed from the surface of the castings.

When the cube shaped component was produced from solid by another subcontract machinist, over 60% of the volume was removed. Almost all of this aluminium is saved by using a casting. A further 10% of material has been taken out following consultation with the customer and re-engineering its IGES solid model in Kemlows' SolidWorks CAD system.

The additional saving was achieved by reducing the size of internal bosses and other unnecessarily thick sections. Material was also taken away from the exterior by introducing pockets all around the part, including on the base.

The resulting casting combines minimum material volume with a geometry capable of being cast without cooling problems or difficulty in making the tool. The timeline for this particular project was just 12 weeks.

Over the top

A considerable amount of engineering input was provided by Whitehouse to develop the application which included fitting Nikken trunnions to add a fourth axis to each of the three latest Brother machines, sourcing the tooling and proving out the process at the supplier's Kenilworth technical centre.

Once the machines were installed at Hoddesdon, Whitehouse teamed up with Renishaw to provide a system for probing the castings to verify their quality before machining starts. This combined with additional advice in other areas such as roll tapping, PCD face milling and harmonic flute deburring, has taken a further 12% out of the cutting cycle time.

Kemlows' manufacturing manager, Geoff Eustace explains: “As about a fifth of our contracts are for finish machined components, we carefully researched the market to find the most efficient equipment for light-duty milling and drilling of our castings.

“Most machines are over-specified for this work, however, the Brother TC-S2C/D-O CNC machining centre is ideal, with its 500mm x 400mm x 300mm working envelope and 16,000rpm delivered to 21 BT30 tools around a circular turret, which minimises non-cutting time.

“Rigid tapping at 6,000rpm was twice as fast as on the other shortlisted machine, which is a major advantage for us as many of our castings have drilled and tapped holes,” he adds. “Vacuum casting results in an absence of porosity, maximising the life of the cutters and avoiding breakage.

“Furthermore, we have been pleased with Whitehouse Machine Tools' service of the Brother TC-31A twin pallet machining centre since it was installed in 2000.”

On the up

The first TC-S2C-O machine arrived on Kemlows' shopfloor in mid 2009, at which time anticipated volumes of the new telecoms component were expected to increase from 200 to 330 per week by the August. Actual demand was nearly twice this, so a second Brother TC-S2C-O was added. Production has now peaked at 900 per week, necessitating a third Brother machining centre, a TC-S2D-O. This machine is even quicker than its predecessors, as it has a servo motor driven turret to speed automatic tool change (ATC) to 1.6 seconds chip to chip.
Mr Eustace confirmed that uptime of the Brother machines is consistently above 90%, which is commendable for machines that are manually loaded. The in cut proportion of the cycle time is high, as rapid traverse rates of 50m/minute and quick ATC lead to minimum idle times. Castings are routinely checked on coordinate measuring machines as part of the die caster's accent on quality control.

Kemlows' machining facility runs 24 hours a day, producing a wide range of castings spanning many industries including telecommunications, automotive, defence, brewing, electronics, medical, white goods and leisure items such as model locomotives and jack stars. The strong performance of the company during the downturn and its strength now that manufacturing is coming out of recession are attributed in part to this policy of pursuing an extensive variety of work.

Mr Teoli concludes: "We have eight aluminium casting machines with locking forces up to 840 tonnes enabling us to produce parts from a few grammes to 8kg shot weight.

"Our long experience in supplying the highly demanding automotive sector in particular has helped us to develop a strong team and a wealth of experience in die casting, which is becoming more and more difficult to find these days.

"Manufacturing is still important to the UK economy and likely to become more so. That is why Kemlows is always ready to invest in the best new plant and equipment in order to give our customers the best possible service."

Whitehouse Machine Tools
www.wmtcnc.com