Time to introduce automatic, in-cycle deburring

Component finishing, specifically burr-free production, is one of the most important factors in production machining techniques, and according to Boris Sciaroni, 'remove sharp edges' is not enough.

A designer's traditional opt out of defining exactly what is not required in terms of burrs on components is to add the 'remove sharp edges' statement to a drawing.

Those three words loosely covered a multitude of problems associated with ragged and sharp corners and they protected management when colleagues (particularly those involved in assembly) suffered cuts and splinters.

They did little to inform production or quality control what was really required, leading to misinterpretation and possible on-cost.

Component finishing, specifically burr-free production, is one of the most important factors in modern production machining techniques.

Mikron - a world-leader in special-purpose machine tool technology used particularly in the fuel injection, hydraulic, pneumatic, electronic component, lock and writing instruments sectors - recently carried out a survey of production processes and customer requirements for burr-free production.

This very critical area of machining can add between 12 and 18% to the price of a production component.

* Modern trend demanded by customers of combining operations - a Mikron forte in production machining providing single cycle or 'one-hit' production sequences - means - deburring in-process is now a 'no argument/must have' with customers and the requirements are very strictly controlled.

Due to its constant involvement with such demanding sectors of industry the company has developed a wealth of knowledge on the subject of controlling and eliminating burrs and sharp edges.

This is especially so for machining cycles such as for ball pen tip production.

Here Mikron is the clear market leader and parts are made and assembled in one cycle complete with ball at a rate up to 480/minute on its machines which rank as the fastest rotary transfer machines in the world.

From this experience, Mikron's first question to customers on new projects is always: how do you define a burr or sharp edge? The second is, how is it measured? These two requirements have a strong influence on the layout of the machine, its tool design, production rate and, most important, final cost.

In Mikron's view, burr removal is easier to control when it is removed by cutting, and the method is determined by the material, the speed of the machining cycle, the design, condition and control of tooling as well as desired tool life efficiency.

In the initial engineering response to a machine enquiry, debate and discussion follow about controlling the burr, the shape, position and direction of the sharp edge, and where and when it can be removed.

Quite often, it is imperative the burr must never be deformed or bent, and the part must not be damaged during the removal process.

Critically, in high volume production, this process can seriously influence final cycle time.

Mikron has even been faced with a corner specified as having, for instance, maximum burr 0.01mm in this direction, or 'must have a sharp edge' and here precise control of the tool has to be a machine tool led solution.

Traditionally, burrs were removed at the bench, with some companies adopting the philosophy: 'you put the burr on - it's your responsibility to take it off'.

But this is always down to personal interpretation of what's needed by the operator and the quality department.

In short, it was never a pleasant task and rarely consistent in result.

Processes such as thermal deburring, electro-chemical machining, high pressure oil, abrasive, mechanical, vibratory and shotblasting processes all provide solutions but can be difficult to control especially when fuel injection or hydraulic systems are involved with their unseen internal hole breakthroughs.

They are also additional processes that require labour, extended lead time and work queues.

While certain of the Mikron range of machines such as the 'Multistar' is mechanically driven via cams, the 'Multifactor' and 'Multistep' machining systems incorporate CNC to perform a particular process or provide additional flexibility through programming of multi-axis operations.

This capability is put to good use in the deburring process enabling tools to be sequenced to approach from different directions, perform repeat cycles on a component feature or the addition of a variable feed rate or dwell in the cycle.

In the case of the very latest, up to 140-axis Mikron NRG-50, a 12-station machine with up to 30 NC machining heads, it can incorporate the additional flexibility of 5-axis positioning.

This capability has proven to be an important element in component production especially in the fuel injection business to provide whatever level of burr-free or controlled edge definition the customer requires.

It also creates very high orders of flexibility by enabling, through interpolation, the different axes to follow elliptical profiles, for instance, such as when one hole breaks into another and compound angle holes break into grooves or recesses.

When drilling, Mikron's production expertise and understanding of application requirements enables it to position the burr where it can be effectively removed under a controlled cutting cycle.

In conjunction with its sister company Mikron Tool, special tool geometries are often developed.

These can include special or very complicated profiles, tools similar to a punch that can be used to shear the burr without distorting the component.

Rotary burrs are often utilised to break corners or to create a known size of secondary burr that can then be removed using diamond or carbide brushes.

But the company maintains, depending on the application this can be slow and wear of the tool unpredictable.

We prefer to cut burrs - this gives us total control, we know how the material will react and with the accuracy and repeatability built into the machine, cutting the offending material can be performed with the same level of precision we can deliver for general component machining.

Indeed, such is the level of precision in the Mikron machines that intersecting areas of holes as small as 0.35mm diameter can be successfully processed.

For internal threads, Mikron mostly uses synchronised tapping cycles, this has the advantage that when a cross-hole, recess or slot breaks into the thread, redrilling and retapping cycles can be accurately performed at production rates, and the thread brushed to remove any sharp edges.

Quite often, due to the type of part produced and especially on seal faces and sealing recesses, common on fuel injection equipment, Mikron's application team at Agno uses recessing heads with the tooling specially developed and ground with a blending radius tangential to the surface that eliminates at source any potential for burrs.

Removing or preventing burrs is one technical area, another is identifying what has happened - often deep in the heart of a very complex component.

Following the installation of the OGP 'SmartScope 650 Vantage' 3D measuring centre which has a full, 5-axis capability, the Quality Laboratory at Agno is now able to program the machine to position components at the right attitude from which it can show exactly what has happened during machining.

The machine combines touch-trigger probing, laser scanning and non-contact internal or external video measurement at up to 400 times magnification.

This investment was seen as a key element in the inspection, measurement and display of edge definition of corners and burrs, especially on breakthrough positions of one component feature to another such as oil feed passages.

This machine also reduces the need for components to be cut up and measured manually and it provides and records a clear display of the measured result.

Included in the machine specification is a specialist 0.1mm diameter Apollo probe to check and trace for chamfers, forms and radii now very common in the ultra-small holes and internal features.

Once burrs are removed during the machining cycle up to 1,000 bar, high pressure directional jets of air or coolant can be included in the Mikron rotary transfer machine operation to ensure that swarf is cleared from internal cavities and recesses.

In addition and depending on the application inspection probes or gauging units can be fitted to ensure parts conform to specification and are burr free.

This confirms that once a component leaves the machine it is processed according to operational requirements, is fully deburred and is clean and ready for the customer's next process.

* About the author - Boris Sciaroni is marketing manager of Mikron Machining Technology based in Agno, Switzerland.

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