It's a small world

Over the course of the past decade, there has been significant growth in worldwide demand for micro-machining services. And yet this doesn't only encompass the manufacture of tiny components, but also much larger parts exhibiting micro-features, typically in the 1-100 micron range. For example, such parts might include medical equipment (micro surgery tools, implants, pacemaker features, fluidic mixing chambers, capillary units), automotive components (fuel injectors, gears, pumps) and aerospace parts (cooling holes in engine components, pressure transducer parts, gyroscope parts). The complex and intricate nature of such components means that, often, the key to their successful machining lies not just with the machine or cutting tool, but with the workholding. Providing an excellent example of how best to approach the problem of workholding in micro applications is Charles Frodsham & Co, the UK's oldest established chronometer, watch and clock makers, which plans to introduce an innovative new men's wristwatch this year, developed with the help of System 3R (01844 274455) machining and workholding technology. And it is no ordinary wristwatch, as it incorporates the hitherto unexploited oil-free double impulse chronometer escapement invented by arguably the world's greatest living watchmaker, George Daniels. "We recognised that if we could miniaturise this escapement, we would have a timekeeper of the finest quality and performance," says Philip Whyte, director at Charles Frodsham. This is where System 3R was able to provide the machining accuracy and stability required to help the company manufacture parts on its Kern HSPC precision mill, with tolerances down to 2-5 micron. System 3R's VDP system introduced 'vibration damped palletisation' to the milling process. VDP not only reduces vibration, but also reduces noise when high speed cutting, as well as improving surface finish. It also helps to reduce tool wear and is less stressful on the machine spindle. "The finish is far better, especially on the cases, where the contours are sharper and the angles nice and crisp," says watchmaker Martin Dorsch. "Also, there is no need for a sub-plate with the Macro system, whose reference elements save us time in toolmaking and deliver the repeatable accuracy we need, even when cutting at critical angles." Kern, which is represented in the UK by Rainford Precision (01744 889726), has an established pedigree in producing machine tools for micro machining. In fact, the company has recently launched its 'co-ordinate or jig grinding' package for customers specifying the Kern Pyramid Nano. This new development makes it possible for end users to conduct high speed milling and jig grinding in a single set-up. The result is that movements as tiny as 0.1 micron are now possible without jerking, using milling or grinding strategies. Image: Micro-machining will support the introduction of a new, novel watch by Charles Frodsham; left, Kern's 'jig grinding package' offers more capability for its Nano machine Another machine tool builder looking to target similar markets is Tornos (01530 513100), which, through the recent acquisition of Almac, can now offer machining centres for micro applications such as the new Almac CU1005 5-axis model. Both Tornos and Almac have a long history of success in the watchmaking and electronics sectors, and it is hoped the CU1005 will fulfil a genuine requirement for a well specified, flexible yet sturdy machine. Its stability is created by a mechanically welded base that sits on a load-bearing cast iron frame that has significant mass to help guarantee the surface finishes and accuracy required of many micro features. Increasing numbers of turning machine builders are also concentrating their development efforts on models suited to micro components, particularly sliding-head types. A case in point is the new Citizen (01923 691500) R04-VI, a 4 mm capacity, 6-axis CNC sliding head turn-mill centre that can be specified with programmable high speed drilling/milling spindles capable of up to 100,000 rpm to perform operations such as thread whirling on diameters smaller than 1 mm. A recent example of the productivity gains available was demonstrated by milling a TORX female drive socket on a bone screw made from 316 stainless steel. The R04 saved some 70 per cent over a standard milling spindle application. A 0.8 mm diameter, four-flute end mill was run at 35,800 rpm and a feed rate of 0.005 mm/rev to produce a clean, burr-free milled finish on the component. Image: Click here for image Another supplier of sliding-head turning technology that is enjoying success in the micro machining arena is Star Micronics (01332 864455). Supporting this statement is Star customer Rotamatic Precision Engineering of Crediton, Devon, which is successfully producing a number of micro components for the aerospace sector on its recently installed Star SR-20RIII sliding-head lathe. Reductions in cycle time have, in fact, helped Rotamatic achieve its cost reduction target from the customer. One example of the parts produced by Rotamatic is a 1.6 mm diameter dowel for an aircraft motor housing, which is turned to ±6.25 micron tolerance. Moving on to drilling, the requirement to produce small, deep holes was arguably one of the first drivers of new technology for micro-machining applications. Today, the capability of Mollart Engineering (020 8391 2282) to develop a precision, micro deep-hole drilling solution for oxyacetylene gas cutting torch nozzles has enabled its US customer to reduce a 35-machine installation to just five Mollart 4-spindle Microdrill VDMs. As a result, components are now produced at a rate of almost 1,000 per hour from the new installations, regenerating output capacity of some 25 per cent. The machine build contract, worth in excess of £1.5 million to Mollart, combines, in a single cycle, the deep hole drilling of a 2.3 mm diameter central stepped bore for gas feed by an impressive 75 mm deep in Terillium copper. This bore is then counterbored to 3 mm diameter by 50 mm deep, with a further six, 2 mm diameter through-holes created for air feed. These 2 mm diameter holes are set on a 12.4 mm PCD, but which are inclined in a converging fan pattern towards the central bore at an angle of 6° 20'. No one can doubt that the machining of micro features is challenging enough, so spare a thought for those tasked with producing the associated cutting tools. Thankfully, here, too, new innovation is both simplifying and accelerating the task. Take the new Walter 6-axis Helitronic Micro tool grinder from Körber Schleifring (01926 485047), for example, which has been designed for the production of micro tools as small as 0.1 mm diameter and the regrinding of tools down to 2 mm diameter. As an example of cycle times, a drill of 0.4 mm diameter and 2 mm long can be produced in 3.33 minutes, while a 0.4 mm diameter square end mill 1.5 mm long can be ground in just 4.5 minutes. Box Item Micro EDM Away from conventional 'cutting' technologies, GF AgieCharmilles (024 7653 8666) says that its new CUT 1000 wire EDM opens up new possibilities in micro machining. Using the machine's F module (for very fine wires), new opportunities in micro-machining can be exploited with wires of 0.02 mm diameter being used to achieve internal radii of 0.015 mm. GF AgieCharmilles is quoting positional accuracy of ±1 micron and achievable surface finishes of 0.05Ra. Box Item Micro-manufacturing seminar The Micro Manufacturing Technology Seminar (www.micro-show.com) will be a full two-day conference this year. Held at the Ricoh Arena, Coventry, 20-21 October, the finalised conference programme features influential and knowledgeable experts, and is a free-to-attend event. The conference has been devised to address the key issues of micro manufacturing, offering a state-of-the-industry overview on micro-moulding, micro-machining, micro- EDM, electrochemical machinery, metrology and assembly. First published in Machinery August 2009