What does an orbiting telescope currently mapping the Milky Way have in common with the first all-English wristwatch to be produced in half a century?

The Basildon-based sub-contractor Microtec EDM supplied prototypes and components for both ventures, as well as for a host of other innovative and high profile-projects.

Moreover, the company recently raised the capability of its metrology department by installing a powerful CNC video measuring system — an iNEXIV VMA-4540 from Nikon Metrology (www.nikonmetrology.com).

Until this machine was installed (at the end of 2014), Microtec relied on manual video measuring using another make of instrument.

Owner and managing director Graham Cranfield says: “We are currently seven years into an 18-year contract involving electro discharge machining and centreless grinding of nickel-copper alloy tube to produce a decoy missile component.

“A complete inspection of the part using our manual video measuring system used to take 20min; now that the job has been programmed on our new Nikon machine, the same inspection cycle is completed automatically in just 20sec. We find that time savings of this magnitude are typical; they have revolutionised the productivity of our metrology department.”

He says that it took them only a few hours to create the inspection cycle for this fairly complex job, based on a CAD model of the part, adding that the process will become even shorter as inspection staff become more familiar with programming.

For contracts that frequently repeat, the automated measuring approach saves a lot of time in the long term. After measuring just a dozen of the missile tubes, the programming time had been justified.

The component is required in quantities of a few thousand every year; and even though only one in 12 needs to be inspected, the saving in measuring time during 2015 alone will be more than double the programming time.

By the same reasoning, prototypes and components needed in small batches are more productively inspected manually on the pre-existing video measuring machine, or indeed on the iNEXIV VMA-4540 operated in manual mode.

Component sizes

Work carried out by Microtec for space missions includes making parts for the joint ESA/JAXA (Japan Aerospace Exploration Agency) BepiColombo mission to Mercury, which will set off in July 2016 on a 7.5-year journey.

Another project involves the manufacture of prototypes and components for an orbiting telescope.

In both cases, the telescope parts are relatively large, but many other components that the Basildon sub-contractor produces have features as small as 20µm, placing the firm in a very select group of specialist providers of wire-cut and solid-sink EDM services in the UK.

A current project in the micro-machining area entails sparking slots that are 30µm wide x 3mm deep into copper components for Oxford-based Reaction Engines, which is designing a multi-use Mach 5 engine for launching satellites.

Another project involves the wire erosion of 70µm-wide vanes in copper and molybdenum grids, required in quantities of 50 per year for an electron beam gun.

Somewhere between these extremes in size lie the components that Microtec machines for Charles Frodsham & Co — clockmaker to the British Royal family.

Later this year, managing director Philip Whyte plans to launch the first all-English-made wristwatch to be produced on a production basis in half a century. It will be manufactured from start to finish at the company’s workshop near Heathfield, East Sussex.

Charles Frodsham has a long-standing business relationship with Microtec; it regularly wire-erodes gold watch cases and produces springs for the clockmaker, which in turn carries out micro-scale turning, milling and drilling that is beyond the capabilities of Microtec’s production equipment.

AS9100 accreditation

Aerospace and defence contracts are the mainstay of Microtec’s business, with Rolls-Royce, BAE Systems, Selex Galileo and Astrium being regular clients and the principal reason for Microtec seeking AS9100 accreditation — a process that will be assisted by the purchase of the Nikon Metrology iNEXIV machine.

It will be especially important for shortening the time required to produce first-article inspection reports; the Nikon Metrology VMA AutoMeasure software automatically compares measured results against CAD models and allows reports to be produced quickly and in a standardised format.

Motor-sport, which is closely related technologically with aerospace, is becoming an increasingly important market for Microtec; work for the medical and dental industries is another specialism. A current contract involves producing very small tweezers with serrations that are eroded with 20µm wire, five-times thinner than an average human hair. Another medical job requires a plastic filter mould to be produced with 0.25mm-wide ribs.

Mould and tool manufacture accounted for 80% of Microtec’s turn-over in the 1990s, dropping to 20% in subsequent years as China absorbed much of that business. The percentage has recently been increasing, with mould-making being re-shored due to an increase in the cost of production overseas, as well as problems relating to quality and logistics.

Most wire-cut EDM work requires 2-D inspection, for which video measuring is ideal. However, some spark-eroded components need to be measured in 3-D, and one of the advantages of iNEXIV video inspection is the ability to measure heights, using the instrument’s 73.5mm operating range.

Mould refurbishment

Early in January this year, Microtec was tasked with refurbishing a plastic injection mould used by the British manufacturer MK to produce electrical plug sockets. No drawings or CAD model were available, so the mould’s broken upstands were remanufactured in tool steel after the height and width of the relevant sections were measured on the iNEXIV.

A similar procedure allows reverse engineering of legacy components for which no data exists, such as parts for classic cars. In this case, after the data has been collected, the DXF file that is output can be used directly in a machine tool’s CNC or in a CAD/CAM system to generate the cutter paths.

Furthermore, Nikon Metrology’s part-to-CAD software can compare the machined component with the DXF file to ensure that it is within tolerance.

Some features, such as sloping faces and under-cuts, do not lend themselves to optical measurement. In such cases, the iNEXIV VMA-4540 uses a Renishaw TP20 or TP200 touch probe to capture the point data. The probe is offset from the optical axis but works in the same 450 x 400 x 200mm working volume, with only slightly reduced measuring
capacity. A stylus changer is also provided.

Mr Cranfield says: “We always use vision if we can, because it is generally quicker and more accurate. However, if parts are not the right shape or not scrupulously clean, touch probing is the better option.

“On the other hand, some features — such as the curved surface of a dome — would be difficult to inspect with a touch probe, as calculations to compensate for the stylus tip diameter at each measurement point across the surface would be impractical.

“Furthermore, with the auto focus — AF — feature of the iNEXIV, we can accurately capture heights very quickly. There is also a laser AF option that we are thinking of retrofitting; this provides highly repeatable Z-axis measurements on flat surfaces.”

It is even possible to mix optical and tactile measurements in the same cycle. For example, the BepiColombo telescope parts mainly require the 2-D optical inspection of apertures, but there are arrays of 2mm-diameter tapped holes that will need to be probed during the same program.

This job will also use the image-stitching feature within the Nikon Metrology software, as the aluminium components are 550mm in diameter and will need to be scanned in four quadrants.

The instrument’s versatility is further enhanced by a variety of illumination options; it has episcopic, diascopic and eight-segment ring LEDs.

Used in combination, these allow the accurate detection of low-contrast edges; and even when a workpiece is misaligned, an intelligent search feature automatically locks on to it (based on a target image recorded in a teaching file).