The need to build a competitive edge by reducing lead times and production times sees manufacturers integrating as many processes as possible into their machining cycles.

However, a particular problem is that of drilling and the removal of any burrs that this operation produces — especially when drill break-out is part of the cycle.

Here, Chessington-based Mollart Engineering Ltd — a pioneer in all aspects of deep-hole production — is continuing to build on the considerable success achieved with its E-Z Burr, BCU back-chamfering and Burr-Zit deburring tool ranges.

These tools offer an engineered solution to the often used designer’s note of ‘Remove all Burrs and Sharp Edges’, which leaves its interpretation to the reader of the drawing.

At the other extreme, a designer who is concerned with the possibility of leaving burrs and ragged edges might well specify tightly toleranced radii or special chamfers that are costly to achieve in many cases and often difficult to measure — and have no bearing on the part’s function.

Burrs need removing because they not only make parts dangerous to handle but also influence the accuracy of relocation on following processes. They can also break off, causing blockages in lubrication systems (and subsequent component seizure), and they can create problems with mating parts in an assembly. They are also unsightly and detract from the quality of a product.

Many companies have relied on manual deburring, using an operator at a workbench ‘armed’ with racks of files, scrapers, special tools, airlines, rags, cotton waste and cleaning materials. However, the diversity of deburring applications makes the operation difficult to cost — and control.

Mark Dore, Mollart Engineering’s sales manager, says: “The first priority is to plan for the right machine and emphasise that its set-up should ideally achieve a burr-free cycle.

“However, this can often prove to be difficult, due to the most appropriate machine not being available. Production variables can also have a big influence on burr creation.

“For instance, material can vary in specification and size, production tools wear, vibration and chatter can occur; and if the wrong cutting data is applied, any resulting burrs can be inconsistent in size and nature.”

On-going tool development

Mr Dore says that in today’s competitive production environment, this scenario does not need to be tolerated, as burr removal can become a cost-effective and controlled process applied to both small- and larger-volume operations.

“For Mollart Engineering, with its long-term association with deep-hole drilling, machine design, process development and production technology, burr prevention and removal has always been high on its agenda.”

For example, the company’s E-Z Burr series of tools for hole diameters between 1 and 50.80mm now includes a Stubby-series version for holes from 3.18 to 6mm in diameter.

This has been designed for in-cycle use on the types of cross hole that are now commonly produced on turn-mill centres — and especially CNC sliding-head machines.

E-Z Burr tools can be programmed to machine away burrs or create chamfers around the edges of holes at both the front end and the breakthrough in a single pass of the tool. BCU is a micro-adjustable precision back-chamfering and back-countersinking tool designed for use in restricted spaces; it can be used on manual, CNC or special-purpose machinery for processing holes between 4.76 and 20mm in diameter, and it features the use of a pilot guide to maximise concentricity.

There are two standard pilot lengths for bores up to 25 or 45mm deep; and while a 45deg blade is standard, others can be supplied — as can a wide range of materials and coatings. It typically takes 5-6sec to make a cut.

Meanwhile, Burr-Zit is a deburring tool that can be used to deburr both sides of a drilled, punched or reamed hole between 2 and 25.4mm in diameter in a single operation.

The tool also overcomes the difficulty of restricted access to a workpiece (such as when access is only possible from one side). Burr-Zit is available in two styles: System I covers both front and back deburring, while System II is purely for back deburring.

For bores over 8mm in diameter, an internal pin allows tension to be adjusted without removing the tool from the machine. Standard tools are made from M2, with a selection of coating options to suit the application. Tools can be easily reground, and tool materials for special applications are also available.

Deburring application

A recent application of Mollart’s E-Z Burr to replace skilled manual deburring of an aero-engine turbine stator made from Inconel 718 not only created a consistent and high level of control over quality but also saved 30min per part in the overall production time.

The component had 24 holes, each 2.38mm in diameter and passing through a 6.5mm-thick flange, then across a gap into a second flange, where the hole became ‘blind’.

Every hole in the face of each flange required a chamfer to be maintained to a tolerance of 0.15-0.40mm, which put high demands on the operator.

By including the E-Z Burr tool into a programmed single cycle on a machining centre and running at 650rev/min with a feed rate of 0.1mm/rev, the three corners of each pair of holes were automatically and consistently chamfered to the required tolerance.

E-Z Burr tools, which are designed for general-purpose applications across a wide range of component types, can be used on CNC lathes and machining centres, as well as special-purpose machine tools; in certain circumstances, they can also be used in conjunction with powered hand tools.

Graphic simulations of E-Z Burr Tools can be viewed on the Mollart Web site (www.mollart.com), where the advantage and operation of the patented two-piece tool and solid arbour-style holder can be appreciated.

The tools comprise an extended blade, having either one or two cutting edges, which are located via a dovetail in the holder.

The dovetail, which also acts as a fulcrum, allows the cutting blade to act as a flexible arm that pivots in the holder.

There is a choice of solid-carbide or high-speed steel (HSS) blades, and both can be changed within a few seconds on a machine tool without changing the tool setting.

The solid-carbide tool can also be used on heavy burrs at cutting speeds that are at least three-times greater than those used by the HSS version.

Tough and exotic materials, as well as non-ferrous types, can be machined; and due to the durability of the carbide and the TiN coating, tool life should be some five-times greater than the HSS version.

In use, the tool is fed into the workpiece, and as the extended blade contacts and cuts the burr at the front, its spring-like action around a lock screw allows it to slide back into the holder.

The blade fully contracts as it continues through the bore, the polished crown on the top of the blade ensuring that there is no marking or scoring of the hole.

Once the tool clears the back of the bore, the blade and cutting edge flex back out of the holder; and when the direction of feed is reversed, any rear burr is removed by the withdrawing tool cutting a chamfer.

With the cutting cycle complete and the blade fully retracted into the holder, the tool can be withdrawn at a rapid rate.

While the E-Z Burr HSS series of tools ranges from 1 to 50.8mm in diameter, the carbide version is designed for holes from 3.17 to 25mm in diameter.

Customised and combination tools are also available, the latter being able to both drill and deburr.