Distinguishing factors

1024 682 Paul Cobb

A third 5-axis, vertical-spindle machining centre has been installed by subcontractor Hemlock Engineering, Nottingham, in response to a steady increase in work from a variety of sources.

Aircraft seat parts, medical prostheses, components for laser equipment used in dentistry and printing, fire suppression nozzles and parts for camera tripods and beer pumps are typical of the diverse range of contracts regularly received from more than 200 customers.

A long-time user of over twenty 3-axis and 4-axis VMCs, the company later invested in two 5-axis machines with 36,000rpm spindles and 90m/minute rapids for high-speed finishing. In contrast, the latest Hermle C 22 U, supplied through UK agent Geo Kingsbury, is a more robust 5-axis model capable of highly productive metal removal.

Even though 95% of jobs undertaken by Hemlock are in aluminium, high power and torque are still needed when taking deep cuts to prevent the cutter stalling. The Hermle’s 25kW/80Nm/20,000rpm spindle, 45m/minute rapids and 450 x 600 x 330mm working envelope are ideal for the subcontractor’s needs.

Two factors distinguish the C 22 U in the view of Hemlock’s managing director, Paul Cobb. First is the machine’s reliability, as it has operated faultlessly since it was installed in March 2013. Second is its ability to hold extremely high tolerances, down to a few microns on some optical parts used in dental laser equipment.

Mr Cobb comments: “There were less expensive machines on the market than the Hermle, but it was by no means the costliest. We also prefer the Heidenhain control option rather than the Fanuc CNC system which comes as standard on many other machines.

“The price of a machine tool is of secondary importance, particularly at the moment with interest rates as low as they are. It is uptime that is crucial in order to maintain output and profitability and also the cost of repairs, which tends to be high when a 5-axis machine goes down.

Hemlock’s managing director, Paul Cobb

“Repair bills have been a problem with some of the machines we have installed over the years, but the C 22 U has performed well. It has not missed a beat working 20 hours a day for the time that we have owned it.

“I thought it was going to be a good machine when I saw them being made at the German factory and it has not disappointed. The build quality is awesome and the clever design ensures that vibration is minimised, resulting in lower tooling costs, higher accuracy and less wear and tear on the machine.

“I know it will still be good in 10 years and more, so now I could not imagine buying any other make of 5-axis machine.”

Hemlock’s managing director, Paul Cobb

It is rare for the Hermle C 22 U at Hemlock to be used in full 5-axis mode. Most jobs require one or two operations involving 3-axis machining with the two rotary axes fixed. Cycles are created offline using seats of hyperMILL and Mastercam.

Typical of components produced are aluminium blocks that direct a laser beam through a multi-axis articulating arm used for hardening dental fillings. A couple of microns has to be held to achieve the required angular tolerance either side of 45°, which is only possible in a shopfloor environment by machining it on three sides in one set-up on the C 22 U. Brackets for military night vision goggles are another example of tightly toleranced parts produced on the machine, requiring ±10µm to be held.

Production of large aluminium heat sinks for electronic equipment is a regular job to be found on the machine. Their dimensions preclude extrusion and castings do not have the correct thermal diffusion characteristics, so they have to be machined from solid. Deep, closely spaced fins complicate their manufacture, but again the combination of high metal removal rate on the Hermle using small cutters at 20,000rpm together with rotary axis positioning allows the parts to be produced in two hits in much faster cycle times than previously.

Hemlock Engineering has a sister company, HPC services, specialising in sliding head turn/milling from up to 32mm bar and fixed head turning to 65mm diameter. The group was established in 1986, employs 70 people, has a turnover of £7 million and in addition to production runs, regularly undertakes prototyping and sub assembly.

Read the original story at Kingsbury UK


Paul Cobb

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