Mollart extends subcontract service

The specialised development of precision small deep-hole machining techniques has led Mollart Engineering to expand its subcontractor machining operations.

The expansion of Mollart's deep-hole and added-value service encompasses a precision micro drilling and ultra-thin wall hole component production service for holes as fine as 0.5mm diameter by up to 50mm deep.

The service, which stretches the current boundaries of hole machining technology, can be applied to materials from plastics to titanium and high alloy steels.

Managing director, Guy Mollart, said: '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.' 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 breakout 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.

Mollart also provides ancillary processes such as heat treatment, plating and crack detection to create a one-stop service to customers.

With the development of the precision micro-drilling expertise come the quality and inspection capability of the subcontract operation, which has manufacturing facilities of 26,000ft2 in Chessington and 14,000ft2 at Resolven.

At Chessington, for instance, in addition to two 3D measuring machines are: a shadowgraph with digital readout; a Mahr Perthen unit able to check surface finish on holes as small as 1mm diameter; a Surtronic unit with extensions able to check holes from 4mm diameter and up to 3m in depth; and a Borescope to check for burrs and hole intersections from 4mm diameter.

In addition, a wealth of knowledge and tooling is available to perform precise straightness and concentricity checks.

Typical components produced at Chessington include thin walled plugs in stainless steel for an oil industry customer.

The hole is 3.3mm diameter by 100mm long.

However, concentricity between the OD and bore has to be within 0.2mm TIR and the wall thickness is only 0.75mm.

Adding to the machining problems is a bore surface finish requirement that must not exceed 3.2um CLA.

High length-to-diameter ratios are the mainstay, but it can be very daunting when applying the deep-hole drilling process.

Currently, holes of 0.5mm diameter are restricted by Mollart to a length of 50mm.

It also has to be taken into consideration that the tool has coolant feed and a flute to enable swarf and coolant to be ejected during the process.

As sizes increase to 1mm diameter, the depth capability also increases to 100mm, while 2mm hole sizes can be produced to 300mm depths.

At Chessington, the maximum bore size machined is 80mm 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 0.81mm and the hole is 35mm deep.

Equine dental drills for use by vets on horses are made from 316 stainless steel with a central cooling hole of 1mm diameter drilled to a depth of 24mm.

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 1300mm long with a wall thickness of just 4mm, is another illustration of Mollart's capability.

The outside diameter is machined to 30.48mm with a concentricity tolerance of just 0.04mm TIR over the entire length to the 22.25mm 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 + 0.025mm tolerance in the bore.

The component is completed on a recently installed horizontal honing machine with a minimum capacity of 6mm diameter and will accommodate parts up to 2m in length.

Each component is checked using ultrasonics as well as traditional inspection methods.

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