PCB machining technology: drilling application knowledge

In fact, when users select the right bit, they can substantially increase productivity and reduce overall cost per hole. For end users with hard alloy cutting bit four basic forms: select the whole hard alloy, cemented carbide indexable inserts, welding drill and removable hard alloy drill. Each has its advantages in a particular application.


The first monolithic carbide drill was used in modern machining centers. It is made of hard alloy and fine particles, and improve TiAlN coating tool life, the self centering drill bit cutting edge due to its special design and in most of the workpiece material get excellent control chip and chip. The integral carbide drill has a self centering geometric angle and a good accuracy to ensure high quality holes without any further processing.


Indexable bit drills cover a wide range of diameters when drilling depth ranges from 2XD to 5XD. They can be used in rotating applications as well as in lathes. For most workpiece materials, these drills use a self centering geometric angle to reduce cutting forces and chip control well.

The bore of the welding bit has a high surface finish, a high dimensional accuracy and a good position accuracy, without further finishing. Because of the cooling hole, the drill bit can be used for welding processing center, CNC lathe or other sufficient stability and speed of the machine.


Finally, a bit form steel knife body and a removable solid carbide drill is called the crown together. The drill provides higher productivity at lower processing costs under the condition of providing the same accuracy as the drill bits. The new generation drill with a carbide crown provides precise dimensional increments and has a self centering geometric angle that guarantees high machining accuracy.


Consider tolerances and machine tools carefully


The factory shall select the drill according to the specified tolerances. Usually, small bore tolerances are tighter. As a result, the bit manufacturer sorts the drill bit by specifying nominal bore size and upper tolerance. In all bit forms, the overall hard alloy drill is the most tight. This makes them the best choice for drilling holes with extremely tight tolerances. The plant can be used with an integral solid carbide drill with a diameter of 10mm, and the drilling tolerance is from 0 to +0.03mm.


On the other hand, welding drills or high mountains with convertible hard alloy crown drills machined out of holes with tolerances ranging from 0 to +0.07mm. These drills are often a good choice for drilling, processing, and processing. Indexable insert drill bit is the industry doing heavy work. Although their initial cost is usually lower than other drills, the drill has the greatest tolerances, and the tolerances vary from 0 to +0.3mm depending on the diameter / hole depth ratio. This means that the end user needs in the hole with greater tolerances can be used when the indexable insert drill, otherwise they must prepare the finishing hole with boring cutter.


Together with the tolerance of the hole, the factory needs to consider the stability of the machine during the selection process. Because of stability, the tool life and drilling accuracy are guaranteed. The factory shall verify the status of the spindle, jig and attachment of the machine. They should also consider the inherent stability of the drill bit. For example, the monolithic carbide drill provides the best rigidity, which allows it to achieve very high accuracy. Indexable inserts, on the other hand, are prone to deviation.


The welded bit and convertible crown bit are designed to form two symmetrical cutting edges that form a self centering geometric angle. This high stability cutting design allows the drill to enter the workpiece at full speed of feed. The only exception is that when the bit and the machined surface are not vertical, it is recommended to reduce the feed from 30% to 50% while cutting in and out. The steel drill bit permits slight deviation so that it can be successfully applied to the lathe. The hard, solid cemented carbide bit may easily break, especially if the workpiece is not properly centring.


Check life cycle cost


Productivity or per hole cost is the biggest trend in drilling today. This means that drill manufacturers must find ways to combine certain operations and to develop drills that can accommodate high throughput and high speed machining. The latest bits with interchangeable carbide tips provide superior economics. Instead of replacing the entire bit cutter, the end user only buys the carbide cutter head at the price equivalent to the regrinding of a welded bit or an integral carbide bit.


The factory should also take into account the overall life of the tool when examining the cost of each hole. Typically, a solid carbide drill can be regrinding 7 to 10 times for a mill, whereas a welded drill can only be regrinding 3 to 4 times. On the other hand, the steel body of the crown drill bit can be used for at least 20 to 30 crowns for the processing of steel parts. There is also a productivity problem here.


Welding bit or whole carbide drill must be regrinding; therefore, the factory tends to reduce speed to avoid sticking. But the tool bit can not be regrinding, so the factory can use sufficient feed speed and speed without worrying about cemented carbide. This new crown type drill has a more consistent tool life than a welded drill or an integral carbide drill.


 

(Source: internal information)

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