Drilling – why use up too much time?

According to a leading cutting tool supplier, some 36% of machining hours in Europe are spent in making holes, maybe not all shops are aware of the benefits of carbide tooling, writes Mike Page

Any machinist from the 1960s would be ‘scared stiff’ at the rate at which a solid carbide drill enters a workpiece in 2007. Nor would he take you seriously if you suggested he could cary out deep-hole drilling using his expensive, USA-built, punched paper NC tape operated ‘Milwaukeematic’ machining centre.

In 2007, there are still machine shops relying mostly on high-speed steel drills for production work.

It is not so much that these machine shops are unaware of the benefits of carbide drills.

More likely, either a shortsighted purchasing department sees carbide tooling as more expensive or, the old machine tool simply would not have the ‘guts’ to use a solid carbide drill.

According to one solid carbide drill supplier, solid carbide drills run at cutting speeds of up to 200m/min in steels compared with, say, below 80m/min 20 years ago.

Not every machine shop has the drilling machine or machining centre rigid or powerful enough to drill at such cutting speeds, nor provide the through coolant delivery.

But if you machine shop or production line is producing a lot of holes and not yet using carbide tooling, then some recent developments may provide something to consider.

* Solid carbide drills – drill suppliers are regularly introducing new tool geometries that improve swarf removal as drill penetration rates increase.

New coatings appear, with the intention of increasing the tool’s surface hardness and reducing friction between it and the work surface.

Perhaps one of the most recent developments is Stellram’s dual carbide drills with ‘Hardcore Technology’.

These drills are claimed to offer twice the cutting speed, while halving the cost/hole and quadrupling tool life.

What Stellram has done is to construct a drill consisting of a ‘hard core’ of micrograin carbide, which copes with high downward forces and resists chipping or breakage at the drill point.

A carbide grade formulated to withstand the higher speeds and wear at the cutting edge surrounds this ‘hard core’.

Stellram reckoned that its Hardcore drills could reduce holemaking costs by up to a half.

To check out Stellram’s claim, the company is offering production engineers calculators so they can predict their actual cost savings when they change to Hardcore Technology drills.

* Swarf removal – swarf can be a big problem when drilling aluminium, but Perschmann believes it has ‘cracked’ the problem with its novel Garant solid carbide drill.

Novel, because each drill has four coolant channels that exit axially on the end face of the drill.

This arrangement has the effect of generating hydrostatic support at a working pressure not less than 25 bar during drilling.

In this way, the drill is continually producing a lubricating film that reduces friction at the drilling interface and ensures centralised guidance for the drill.

To give you an idea, when drilling AlMg3 aluminium alloy, a Garant drill operated at cutting speeds of 350-400m/min, a feed rate of 0.55mm/rev and a rotational speed of 15,000 rev/min.

It efficiently cleared the generated short chips.

For more universal applications Perschmann also make its ‘Holex’ solid carbide drill range, which features a 140 deg point angle, self-centring accuracy and TiN coating.

For steels and cast irons, the tooling geometry of Kennametal’s B222HP solid carbide drill allows high penetration rates and increased productivity in wet or dry drilling.

Kennametal said that the B222HP solid carbide drill could bring productivity gains of up to 30%.

A smooth multi layer TiAIN coating reduces the risk of a built up edge and also promotes free flow of the chips away from the component.

For unmanned machining systems an important feature, is that the drill ensures long predictable tool life.

Note that this product is not a through coolant drill.

The B222HP is in cutting diameters from 3.0-19.05mm with a form A cylindrical shank.

There is also a short version, the B221HP.

* Small holes – Looking at small holes first – even solid carbide drills down to 1mm diameter are now available with through coolant to speed up drilling or make it more consistent.

The WTX Mini series of solid carbide drills from WNT is available in a range of diameters between 1.0 and 2.9mm and even the smallest diameter drill can have through tool coolant.

These self-centring drills have a flute geometry that ensures optimum swarf control and evacuation.

Suitable for machining a wide range of materials the drills are made from micro-grain carbide and are coated with WNT’s Ti 700 multi-layer coating.

Rainford Precision supplies the Union Tool range of Super Micro Grain Carbide drills that start at 0.1mm diameter and increment in 0.01mm steps up to 2.0mm diameter and then 0.05mm steps up to 3.0mm diameter.

Rainford said that one user was surprised to find that using the Union Tool drills to drill 54HRC tool steel was easier than he had ever imagined.

The user was drilling 0.25mm holes to a depth of 3mm; the target of 20 holes was achieved using only one drill.

The strength and rigidity of the Union Tool 0.25mm diameter drill has eliminated the need for drilling with an EDM fast hole-drilling machine, thereby saving the customer considerable processing time and money.

A second user continually produces large volumes of holes (400 per component) in stainless steel and has improved product quality by using the Union Tool Drills.

Before, the user said that the drills used were erratic in hole size and proved inconsistent, resulting in poor product quality and a higher scrap rate.

However, by using the new drills from Union Tool, the user is now capable of consistently drilling 400+ holes with less than a 5 micron hole size deviation.

The user said that it had reduced its tooling costs by over 40% and enhanced product quality considerably.

The TaeguTec T-Drill line of small diameter solid carbide drills has been extended to diameters from 12.5 to 15mm.

They are available in 2xD, 3xD and 4xD (D = diameter) drilling depths, increasing in 0.5mm increments.

Taegutec said that the T-Drill has extremely high rigidity and produces an exceptional surface finish and maintains a high level of concentricity to produce holes to tight tolerances.

* Deep holes – for many deep hole-drilling operations, one often associates the process with special deep-hole drilling equipment.

To produce a deep hole conventionally, a machinist would have to resort to ‘pecking’ cycles – to clear swarf and keep the drill cool.

Drill-makers Titex and WNT have sought to remedy the situation and enable a degree of deep hole drilling to be performed on machining centres.

WNT, for example, said that to drill holes to depths of between 20x and 30x diameter normally would require gun drills and specialist deep hole drilling equipment.

But in some cases, not any more.

WNT has introduced its WTX range of solid carbide drills for producing holes up too 30x diameter in sizes ranging from 3mm to 12mm.

WNT said the drills could be used on any conventional cnc machine tool equipped with through tool coolant that can run at standard carbide drill feeds and speeds.

For example, to drill a 6mm diameter hole to a depth of 180mm in a 42CrMo4 steel workpiece, the cutting data used is 70m/min at a feedrate of 0.1mm/rev.

To start off the process a pilot hole of 3mm diameter and 3xD has to be drilled first.

These drills operate without a ‘pecking’ cycle.

Titex has also developed a solid carbide twist drill with internal coolant supply for deep hole drilling.

Titex said that its Titex XD technology (patent pending), eX tremely Deep drills can be used for most materials and are very tolerant in terms of the cooling lubricant type and feed applied.

During rotation, the drill helix forces the chips out of the hole and allows the safe transport of large, jamming chips such as produced by long-chip materials.

Dry machining or processing using minimum quantity lubrication are also possible, said Titex.

Titex XD technology makes extreme increases in productivity by up to 600% possible for a large range of applications and XD deep hole drills can be used on all ‘standard machines’ and machining centres – depending upon the application and metals/alloys to be deep-hole drilled

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