Little by little

Micro-machining covers a broad spectrum of manufacturing processes, each capable of creating discrete components or functional features on larger components, mostly in the range of 0.5 to 250 micron. The majority of these processes, typically micro-milling, micro- EDM or laser micro-machining, depend on single point ablation. In such processes, increasing complexity invariably takes longer and incurs higher costs. As a result, they are limited to small/medium volume production requirements. However, Birmingham-based subcontractor Precision Micro (0121 380 0100) has developed new process routes that, it says, are capable of creating precise micro components and features in prototype to high volume quantities, and where increased complexity does not incur a cost penalty. The essence of its laser evolved micromachining (LEM) is the ability to combine advanced laser direct imaging with precision electroforming and etch processing. There are two processes, Laser evolved etching process (LEEP) and Laser evolved electroforming (LEEF). LEEP incorporates laser technology in the precision etching process. Using laser direct imaging (LDI), it supports the manufacture of micro components, with both fine features and high complexity, to tolerances measured in microns. Front-to-back feature alignment is precise, and the higher resolution exposure guarantees that edges are sharper and more precisely defined. It is now possible to create micro-channels in the 25 micron range and achieve a four-fold improvement in pitch accuracy across an 800 by 600 mm sheet. Image: Precision Micro is a specialist in producing small details such as these LEEF is the second process. Once the plated material (typically nickel) has accumulated to the desired thickness, the electroformed part is stripped from the master substrate. Parts created this way have superior edge definition and a near optical finish, with accuracy and fine feature limits being defined by the photographically produced pattern on the substrate: features less than 15 micron can be achieved with high repeatability. A long-time competitor process to laser profiling is water jet and this is set to continue in the realms of micro-machining. At least this is what's indicated by Water Jet Sweden's (01937 845499) decision to enter the micro-machining market, with fellow Swedish company Finecut AB. With the launch of the companies' range of 'fine abrasive water jet' (FAW) models, WJS and Finecut predict that the fine and micro-abrasive waterjet cutting market itself may soon become as large as today's conventional water jet market, as a better understanding of the capabilities and availability of these new techniques takes hold. These capabilities include, by way of example, a reduction in kerf width from the industry normal minimum of 0.5 mm to 0.3 mm on currently released models, and a potential 0.2 mm, pending successful ongoing trials. FAW models feature cutting jet diameters between 50 and 300 micron. EDM technology is also finding its niche in micro-machining. With this in mind, many of the leading EDM suppliers are launching new machines aimed at this category of component. A case in point is Sodick, represented in the UK by Sodi-Tech (02476 511677), which has extended its range of small hole (0.25-3.00 mm diameter) EDM drill machines with the K3HN machine – a model that comes equipped as standard with Sodick's KSMC Motion Controller, providing servo control, so doubling the hole drill speed – as well as the possibility of micro-step feed with the micro-step servo control. Image: Sodi-Tech EDM's K3HN is an addition to the range of small hole EDM drilling units DOWN TO THE WIRE This new CNC-controlled high-end addition to Sodick's K-series hole drill range is particularly suited to cutting multiple start holes for wire EDM machining in die plates, where there is also a need for an auxiliary axis to index or rotate the workpiece – for example in aerospace and medical applications. The medical market is, in fact, driving many recent investments in micro-machining technologies, particularly in Ireland, where a sizeable cluster of medical OEMs is based. Schaublin Machine Tools (01264 811602), for instance, has announced that Clada Medical of Calsa, County Galway, and Dublin-based Alta Science have both recently selected the 102TM CNC turning centre for micro machining applications. Schaublin says it was the ±3 micron accuracy level and the optional grinding attachment that caught the attention of the two medical customers. With Clada Medical being a medical research and development company, the tight tolerance capabilities were an important factor in the acquisition. At Alta Science, all the parts produced on the 102TM CNC are less than 2 mm in diameter. Another turning machine pitched at the micro-machining sector is the recently introduced R04-VI, a 4 mm capacity, 6-axis sliding-head turn-mill centre from Citizen (01923 691500) that can now be specified with programmable high speed drilling/milling spindles capable of 100,000 rpm. Citizen says this allows it to take maximum advantage of the latest ultra-fine coated cutting tools and perform operations such as high-speed thread whirling on diameters smaller than 1 mm. Image: Citizen's R04 has a high speed, 100,000 rpm milling/drilling spindle A recent example of the level of productivity gain was demonstrated in the milling of a TORX female drive socket on a bone screw made from 316 stainless steel. 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. It saved 70 per cent over a standard milling-spindle application. MILLING CUTTERS SIZE UP Moving from turning to milling, many of the leading cutting tool vendors are unveiling new cutter ranges to meet the needs of manufacturers machining micro components. LMT (01676 523440), for example, has recently launched micro-size, 4-flute, centre-cutting, solid carbide end mills, available in diameters as small as 1 mm from the DHC (Different Helix Cutter) series. The tools are ground with two different helix angles of 35° and 38° on consecutive flutes. Image:LMT's 4-flute solid carbide end mills offer diameters as small as 1 mm The successive differences in the helix angle from tip to tip creates a continuously changing pitch to the cutting edge, reduces cutting forces and creates chips with different cross-sectional areas. As a result, any tendency for vibration is reduced. In a recent cutting trial performing a slotting operation in heat treated steel, a 2 mm diameter DHC 1521C long series cutter with four flutes was run at 18,000 rpm (113 m/min), with 2 mm depth of cut and 0.01 mm/min feed per tooth. Elsewhere, Rainford Precision (01744 889726) has announced it is offering, initially, the Kyocera Micro Tools range of micro boring bars and thread mills. The 38 mm long micro precision boring bars are available from 0.4 to 1.7 mm diameter, in 0.1 mm increments, with further bars from 2 to 8 mm diameter available, in 0.5 mm increments. Image: Kyocera tooling, suitable for micro-machining The thread mills are available from M0.5 to M1.1, in 0.1 mm increments, with M1.2 to M2 available in 0.2 mm increments. There is little doubt that micro-machining is now considered a key enabling technology across a broad range of industries. Small parts are fast becoming big business. First published in Machinery, May 2010