Her Majesty’s face was created using a 7-axis Starrag Bumotec S-191 mill-turn centre. Parkin and Thickett’s understanding of the machine’s behaviour allowed them to produce four detailed Queen’s heads – with diameters of 11.2, 7, 2.8 and 1.4 mm – on a single piece of circular brass.
The pair used micro end mills supplied by Sandvik Coromant to achieve the basic shape of the design before switching to tiny but precise ball-nose cutters - the smallest of which measures just 0.2 mm - to carry out detailed contouring of the Queen’s face.
“We wanted to show our partners and wider industry what is achievable; that we can work to an accuracy of 0.001 mm on workpieces as small as 1.5 mm,” says Parkin. “To get Her Majesty’s face, we scanned a real coin using a 3D microscope that’s normally reserved for detecting surface roughness. It works by taking a series of pictures, which are then layered to create a 3D image. After, we gave the digital 3D image to an engineer in the Design and Prototyping Group - Valdis Krumins - who was able to turn it into an STL file.
“The STL file was uploaded into Siemens NX 12 CAD,” she continues. “In this environment we were able to make a program for the tool paths. The software is important, because the difficulty with micro-machining is that you can’t hear the cutter’s health, so you have to get the feeds and speeds right first time. We started with a 4 mm diameter cutter to remove the bulk material and then went down in size. When we got to the finishing operations with the 0.2 mm ball-nose cutter, we were doing micron step-overs, which is literally moving a micron every time, back and forth.”
It is this ability to achieve accuracies to 1 micron that is increasingly important for modern micro, ultra-precision and high-value manufacturing across a broad range of applications, from automotive, aerospace and medical, to watchmaking, electronics, cryogenics and space.
Says Parkin: “We have a few places in the UK that specialise in high precision, but the numbers are few. It’s more machine-tool companies and cutting-tool companies who tend to sell you their machines and pass on some knowledge, but to me that is not the best way. Instead, we have tech that we can give out to bridge that gap. The gain is that by adopting this best practice, companies could potentially increase productivity and manufacture components in-house that would normally be deemed too difficult.”
Parkin is hoping the ‘coin’ demonstrator will lead to further micro-machining R&D and commercial projects for the AMRC, which is part of the High Value Manufacturing (HVM) Catapult network.
“I just want people to come and have a look at what we’re doing,” she says. “At the moment, when people come to the AMRC, and here to Factory of the Future, what they see is aerospace, with massive aerospace components on display and huge machines. However, I want people to think ‘wow’ the AMRC can also make some really small parts, let’s work with them.”
