Mollart extends subcontract service to include micro deep hole drilling capability

The highly specialised development of precision small deep hole machining techniques for the medical, defence, electronic and fuel injection industry involving machine tool, tooling, process application and measurement of results has led Mollart Engineering to expand its subcontractor machining operations at Chessington in Surrey and Resolven in South Wales. The expansion of its highly successful deep hole and added value service encompasses a precision micro-drilling and ultra-thin wall hole component production service for holes as fine as 0.5 mm diameter by up to 50 mm deep.

The service, which stretches the current boundaries of hole machining technology, can be applied to materials as diverse as plastics to challenging materials such as titanium and high alloy steels. Said managing director Guy Mollart: "To achieve this level of expertise we drew together our machine tool building, deep hole tooling development, materials knowledge and application skills so we are able to provide a fast turn around for customers." Micro deep hole drilling is fraught with problems. There are several processes now available for producing small precision holes such as laser drilling and electro-discharge machining (EDM) but each has a distinct disadvantage to drilling. Drilling, creates a higher level of geometry for roundness, straightness and concentricity and problems such as molten materials at the break out position are eliminated. Drilling is also a far quicker process but needs precise tool and machine setting and monitoring that Mollart equipment can provide to avoid breakage and hole wander. An important addition to the micro-drilling service, is that Mollart also has the in-house capability to add value through other processes such as turning, milling, grinding and honing, as well as providing ancillary processes such as heat treatment, plating and crack detection that create a true 'one stop' service to customers. Indeed, hand in glove with the development of the precision micro-drilling expertise is the quality and inspection capability of the £6 million turnover subcontract operation which has manufacturing facilities of 20,000 ft2 in Chessington and Resolven. At Chessington for instance, in addition to two 3-dimensional measuring machines are a shadowgraph with digital readout, a Mahr Perthen unit able to check surface finish on holes as small as 1 mm diameter, a Surtronic unit with extensions able to check holes from 4 mm diameter and up to 3 m in depth and a Borescope to check for burrs and hole intersections from 4 mm diameter. In addition, a wealth of knowledge and tooling is available to perform precise straightness and concentricity checks. Said Mr Mollart: "Having a global experience in selling deep hole drilling technology and continuously pushing out the boundaries of the process with blue chip automotive, medical, fluid power, oil and defence industries means we have a thorough understanding not only of the process, but also the usage of the components we have to machine and the particular demands of each sector." Typical of the components produced at Chessington are very challenging thin walled plugs in stainless steel for an oil industry customer. The hole is 3.3 mm diameter by 100 mm long. However, concentricity between the OD and bore has to be within 0.2 mm TIR and the wall thickness is only 0.75 mm! Adding to the machining problems is a bore surface finish requirement that must not exceed 3.2 micro metre CLA. High length to diameter ratios are the mainstay but can be very daunting when applying the deep hole drilling process and currently holes of 0.5 mm diameter are restricted by Mollart to a length of 50 mm. It has also to be borne in mind that the tool has coolant feed and a flute to enable swarf and coolant to be ejected during the process. As sizes increase to 1 mm diameter, the depth capability also increases to 100 mm while 2 mm hole sizes can be produced to 300 mm depths. At Chessington, the maximum bore size machined is 80 mm and most drilling operations make full use of the 160 bar coolant pressure to maintain swarf control, temperature and tool life. For an American medical customer, Mollart has recently produced batches of a special screw for brain surgery out of titanium that will support and guide an inspection probe into the skull of a patient. The diameter of the bore is just 0.81 mm and the hole is 35 mm deep. Equine dental drills for use by vets on horses are made from 316 stainless steel with a central cooling hole of 1 mm diameter drilled to a depth of 24 mm. This hole breaks into three straight flutes behind the tool point that are ground by Mollart to precisely create geometry of the cutting edge. An almost continuous contract for special tubes machined out of Inconel, some 1,300 mm long with a wall thickness of just 4 mm, is a perfect illustration of Mollart's capability to apply its applications' expertise to subcontract production. The outside diameter is machined to 30.48 mm diameter with a concentricity tolerance of just 0.04 mm TIR over the entire length to the 22.25 mm bore. Produced in batches of 20, each part is rough turned, gundrilled and finish turned to size with the addition of certain cross holes, counterbores and internal threads at each end prior to finish honing to a + 0.025 mm tolerance in the bore. The component is completed on a recently installed horizontal honing machine with a minimum capacity of 6 mm diameter and will accommodate parts up to 2 metres in length. Each component is checked using ultrasonics as well as traditional inspection methods. Said Mr Mollart: "Both our facilities in Surrey and South Wales have been equipped to provide a short turnaround service for customers which means process development cannot be drawn-out. Our subcontract manager is able to call upon any resource within the company and because we have a high level of operational experience with difficult materials, we are able to quickly develop and tailor each operation to achieve the quality and delivery requirements of the customer."