In November 2014, Huddersfield-based Reliance Precision strengthened its five-axis machining capability by purchasing a Hermle C 22 U flexible manufacturing cell (FMC). This was fitted with the manufacturer’s IH60 integrated handling system and a 24-position magazine for housing workpiece pallets from System 3R.
The FMC — installed by Hermle’s UK agent Geo Kingsbury Ltd, Gosport (
www.geokingsbury.com) — is the first automated machining centre with a vertical spindle in the Huddersfield factory and complements a four-axis Hermle C 20 U installed in 2013. All other machines on the shopfloor served by pallet pools or twin pallet changers are horizontal-spindle models.
Describing itself as a specialist engineering company providing custom-built high-precision components and sub-systems for diverse applications, Reliance Precision has extensive in-house design, development, prototyping, manufacturing, assembly and test facilities. Half of the company’s turnover is derived from the scientific and medical sectors, while aerospace and defence accounts for another 30%.
The company has operated three five-axis vertical machining centres from a different manufacturer for several years but wanted to upgrade this area of production to meet customers’ demands for ever higher precision.
Estimating manager Alex Greenhalgh said: “The flexibility and high level of spindle utilisation possible on the Hermle C 22 U FMC were prime reasons for selecting it. We wanted to increase efficiency while reducing manufacturing costs, which the automation equipment enables by allowing extended periods of minimally manned machining.
Furthermore, the work-piece magazine is not fixed in front of the machine, but moves to the left at the touch of a button. This arrangement provides free access to the working area for setting the machine — and for running off small batches or items requiring a high level of operator intervention.”
On-machine probing
Kenny Marsden, Reliance Precision’s milling-department team leader, said: “Even though the C 22 U has been producing for only a few months, its accuracy is already evident. This has been proved by the on-machine probing, which verifies that tolerances have been achieved. Indeed, the system is so precise that it prompted us to question the results we were getting from our existing shopfloor co-ordinate measuring machines.
"It led to the purchase of two new Zeiss Duramax CMMs — one for milled components and another for turned parts. Moreover, manufacturing processes on the Hermle are ‘right first time’ and remain within tolerance from first- to last-off, allowing the machine to be run largely unsupervised.”
Most of the five-axis machining on the FMC at the Huddersfield factory relates to prismatic components, where access to multiple sides of the part with a high degree of accuracy is the primary requirement. It ensures that the tool can machine the component more efficiently in fewer operations, without the need for costly fixturing. Dimensional accuracies and positional relationships on components are often demanding, and minimising reclamping helps to achieve them.
For example, Complex aerospace parts in titanium and stainless steel, frequently require bores to be accurate to within 5µm and true dimensional positions to be within 10µm; there is a 5µm tolerance for squareness and parallelism. These levels of precision are achieved routinely on the FMC, whereas a significant amount of manual intervention was previously needed on other types of machine at Huddersfield to achieve a similar level of quality.
Much production work has already been transferred to the five-axis machine, especially the more complex and exacting aerospace jobs.
Time savings with the FMC are considerable. In one instance, an aluminium housing that used to take up to an hour to clock into position on another machining centre takes just 5min to set up on the C 22 U; this is largely due to in-cycle probing using a Blum TC52 in the spindle.
Consistency and repeatability are just as good, if not better, and cost savings on work-holding are another benefit.The success of the Hermle installations has already prompted Reliance Precision to order a third machine — another five-axis C 22 U, but this time without the pallet-handling system. It will be used for development, freeing the FMC for production. However, the table of the new machine will be automation-ready and could be interfaced with a System 3R pallet magazine at any time. Installation of a fourth Hermle — another automated five-axis cell — is already envisaged.
High accuracy
To assist in achieving the high levels of precision required, Reliance Precision maintains the temperature of its shopfloor to within ±1°C.
Furthermore, the C 22 U was supplied with an enhanced specification, which includes control of the cutting-fluid temperature and enhanced accuracy for all machine axes throughout the entire 450 x 600 x 330mm working volume.
Heidenhain linear scales are fitted as standard to ensure high-resolution feedback, and the thermally stable polymer-concrete bed is vibration-resistant, contributing further to high accuracy as well as extending tool life.
Moreover, because the table does not move, the machine is thermally symmetrical around the X axis and compensation needs only to be applied in the Y axis. The three linear guideways are above the working zone, keeping them free from swarf. Probing compensates for any thermal movement in the Y and Z axes.
Reliance Precision has standardised on the HSK-A63 spindle interface for its Hermle machines, providing stable face-and-taper contact with the tool-holder. The HSK tool system also provides better accuracy in the Z axis, especially at higher spindle speeds. The tool-holder is also smaller, lighter and stiffer than conventional BT-type spindle tooling. Blum laser tool length measuring and breakage detection is included; this further supports unattended machining.
To help maintain high levels of precision, Hermle condition monitoring was performed after the machine was commissioned at Hudders-field to benchmark its performance over a standard range of tests. These are repeated periodically to determine accuracy drift and predict when the next routine maintenance will be required.
Mr Marsden added: “There are some particularly useful features on the Hermle machines. For example, the high-pressure coolant is fully programmable anywhere from zero to 80 bar, enabling us to match coolant delivery to the type of machining operation for best results and minimum energy consumption.
“Another good feature is the protection afforded to the spindle by six collapsible sleeves. Geo Kingsbury can replace the crushed sleeves and get the machine running again quickly, saving a lot of time and potentially the cost of a new spindle. Also, the System 3R GPS 240 chuck has been integrated into — rather than bolted onto — the rotary table to ensure high precision without loss of Z-axis travel.”
So that the manufacturing engineer can view the machining area when the pallet magazine has been pulled in front of the machine for an automated production run, Reliance Precision has installed a camera pointing at the table and an external monitor positioned above the Heidenhain iTNC 530 control system. The images could be monitored remotely, but this is not done at present.