Swarfless process speeds hole operations

A novel swarfless hole drilling process has cut hole production time by 80% for Rehabilitation Manufacturing Services.

Servicing the UK and Ireland with customised wheelchairs and disablement accessories to meet the special needs of users has become a niche market operation for Rehabilitation Manufacturing Services (RMS) based in Gillingham, Kent.

And as managing director Roger Thompson outlines: "To maintain a competitive service to the National Health Service we have a target to reduce our manufacturing lead time from the current order to delivery of three weeks to just seven working days and reduce production costs in order to meet continuous cost-cutting demands of the NHS".

However, due to the bespoke nature of the business, in which just 1% of its main product, the Gillingham Tilt wheelchair, is standard, the company also produces a wide range of modular designed accessories.

This means production of the 700 or so wheelchair units a year has to be jobshop based and hence very flexible.

As an example of reducing costs in the workshop environment, the simple process of drilling holes in the tubular frame of the wheelchair has been taken to task by RMS with the adoption of the Flowdrill swarfless process and as such, has cut hole production time by 80%.

In addition, the thermal drilling process has eliminated the need for deburring and the stocking and fitting of captive nut systems for securing chair backs, seat cushions and head rests to the tubular frames.

RMS has serviced the NHS with wheelchairs for some 25 years and over the last decade focused on special needs as overseas suppliers have moved-in and captured the volume production market.

The company's Gillingham Tilt wheelchair, launched in 1998, is available in motorised or manual versions, in 16 and 18in widths, has three chassis types with either a long or short wheel base variant and is built to a dedicated user specification.

As part of the customer service, the company employs its own physiotherapist and has five design/application engineers based nationwide who carry out assessments of the user and specify the chair features such as thoracic supports, special arm, headrests and foot control.

They are also able to adapt the chair to suit any specific function required by the user to suit the part of the body, for instance, when the user has been subjected to traumatic injuries or debilitating illness.

Roger Thompson first picked-up the idea of the Flowdrill process from an office furniture manufacturer and called in Flowdrill (UK) of nearby Chatham in Kent, to advise on the application.

The Flowdrill process is very quick and simple to use and is ideal for creating holes up to 50mm diameter in hollow tubes, box sections or fabrications.

As RMS Production Manager Wayne Cotter describes: "It is a swarfless process, does not require any pilot hole, can be applied to any ductile material and is accurate enough for screw threading without any further processing or deburring".

The process is similar in concept to friction welding and uses the heat created by a tungsten carbide toolbit to plasticise the material to be drilled.

At RMS, the toolbit, which is 4.5mm diameter for subsequent fluteless tapping of an M5 thread, is held in the spindle of a knee-mill.

The 18 gauge tubular steel component is then positioned against an end stop and the machine's digital readout system used to position the hole to the drawing requirements.

It is then a simple matter for the operator to start the spindle at 2500rev/min and, using the hand feed, touch the toolbit against the outer surface of the tube.

Pressure similar to that required when using a conventional twist drill is then applied.

The friction created by the combination of rotary tool motion and pressure immediately plasticises the material and as the following angle behind the point of the tool penetrates the softened area, it then creates an internal bush of the displaced material.

Due to the nature of the operation the hole is produced to high orders of accuracy.

At RMS, in order to ensure the frame of the wheelchair is rigid and as lightweight as possible, the company fits a smaller tube inside the centre bore of the outer tube.

This is easily accommodated by the Flowdrill process as the toolbit penetrates the outer tube which then acts as a guide or drill bush as it carries on to penetrate the wall of the inner tube.

The plasticised material from both tubes is then formed into a single homogeneous bush in the centre bore which is later tapped for the M5 screw thread using Flowdrill's fluteless threading tools.

Says Roger Thompson: "Flowdrill has revolutionised our drilling process.

It is so quick and clean, provides a strong thread for attaching the canvas and seats and we don't have to worry about fiddling around fitting thread inserts.

When you consider a 200 batch of headrests, which have eight holes in the tubular frame, that is a considerable saving in time and cost.

Most important we know the quality of thread will be high and the form very strong".

As a further bonus adds Wayne Cotter: "We do not have to worry about drill breakage, sharpening or guide bushes to start the drills and we have produced thousands of holes with the same tungsten carbide toolbit".

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