Knowledge of machining and drilling of PCB

- Sep 22, 2018-

Many factories mistakenly believe that drilling must be done at low feed and low speed.This used to be true in the past, but it is different in today's cemented carbide bits.

In fact, by choosing the right bit, the user can dramatically increase productivity and reduce costs per hole across the board.For end users, there are four basic types of bits with carbide cutting edges available: solid carbide, indexable blades, welded carbide tips and removable carbide tips.Each has its advantages in a particular application.

The first solid carbide drill is used in modern machining centers.Manufactured from fine granular cemented carbides and with a TiAlN coating that increases tool life, these self-centering bits get excellent chip control and chip removal in most workpiece materials due to their specially designed cutting edges.The self-centering geometry and good precision of the solid carbide drill ensure that the quality holes are obtained without any further processing.

The indexable blade bit covers a wide range of diameters at drilling depth from 2XD to 5XD.They can be used for both rotary applications and lathes.For most workpiece materials, these bits use a self-centering geometric Angle that reduces cutting force and is well controlled.

The hole processed by welding bit has high surface finish, high dimension accuracy and good position accuracy, without further finishing.With cooling through holes, welded drill bit can be used in machining centers, CNC lathes or other machine tools with sufficient stability and speed.

The final bit form combines the steel cutter body with the replaceable solid carbide drill tip called the crown.This bit provides the same precision as the welding bit to achieve higher productivity at lower processing costs.This new generation drill with a carbide crown provides precise dimension increment and a self-centering geometry that ensures high machining dimension accuracy.

Carefully consider tolerance and machine tool stability

The factory should choose the drill bit according to the specific tolerance on the processing.Generally smaller bore tolerances are tighter.The bit maker then classifies the bit by specifying nominal bore sizes and upper tolerances.Of all the bit types, the tolerances of the solid carbide set bit are the tightest.This makes them the best choice for drilling holes with very tight tolerances.The factory is able to drill a solid carbide drill with a diameter of 10mm from 0 to +0.03mm.

On the other hand, the machining hole tolerance of a welding bit or a drill with a removable cemented carbide crown is 0 to +0.07mm.These drills are often a good choice for drilling production.The rotary bit is a heavy - duty bit in industry.Although their upfront cost is usually lower than other bits, this bit also has the maximum tolerance, which can range from 0 to +0.3mm according to diameter/hole depth ratio tolerance.This means that the end user can use the indexable bit when the hole tolerance is large, or they must be prepared to finish the hole with a boring cutter.

Together with the hole tolerances, the plant needs to consider the stability of the machine tool in the selection process.Because stability ensures tool life and drilling accuracy.The factory shall verify the status of the spindle, clamp and accessories of the machine tool.They should also consider the inherent stability of the drill bit.For example, solid carbide bits provide optimum rigidity, which allows for high precision.On the other hand, the indexable bit is prone to deflection.These drills are equipped with two blades - an inner blade in the center and a blade extending outward from the inner blade to the edge - with only one blade initially participating in the cutting.This creates an unstable situation that causes the bit body to deflect.And the bit's length skews more.Therefore, the factory should consider reducing the feed during processing of the first millimeter and then increasing it to normal feed when using 4XD or above indexable bit bit.

The welding bit and the replaceable crown bit are designed to be symmetrical to form a self-centering geometric Angle of the cutting edge.This high stability cutting design allows the drill to feed into the workpiece at full speed.The only exception is when the bit and machined surface are not perpendicular, it is recommended to reduce the feed to 30% to 50% when cutting and cutting.The steel bit body allows slight deflection to occur, enabling it to be successfully applied to the lathe.A rigid solid solid carbide drill may break easily, especially if the workpiece is not centering well.Don't ignore the problem of chip removal in many factories.In fact, chip difference is the most common problem in drilling, especially for low carbon steel.And no matter what kind of drill bit you use.

Factories often use external cooling to solve this problem, but only if the hole depth is less than 1XD and cutting parameters are reduced.Otherwise, they must use a suitable coolant that matches the flow and pressure of the bore.For machine tools that do not have spindle central cooling, the plant should use a coolant external to internal device.Remember, the deeper the hole, the more difficult it is to chip out, and the greater the cooling pressure is required.

Always check manufacturer's recommended minimum flow level of coolant.At lower flow rates, a reduction in feed may be necessary.

Check lifecycle costs

Productivity or cost per hole is the biggest trend affecting today's drilling.This means that bit makers must find a way to combine certain types of machining and develop drills that can be adapted to high feed and high speed machining.The latest bit with replaceable solid carbide tip provides superior economy.Instead of replacing the entire drill bit body, the end user only buys carbide tip equivalent to regrinding a welding bit or a solid carbide bit.These crowns are easily and accurately replaced, and the factory can use multiple crowns on one drill bit body to drill several different sizes of hollows.

This modular drilling system reduces the inventory cost of bits with diameters from 12mm to 20mm.In addition, it eliminates the cost of backing up bits when welding bits or integral carbide bits are reground.

When reviewing the cost per hole, the factory should also take the total tool life into account.Generally, a solid carbide drill bit can be reground 7 to 10 times for a factory, while a welding bit can only be reground 3 to 4 times.On the other hand, at least 20 to 30 crowns can be exchanged for the steel cutter body of the crown drill during the processing of the steel pieces.There is also a productivity problem.

Welding bit or solid carbide bit must be re - ground;As a result, factories tend to slow down to avoid sticky debris.But the replaceable bit doesn't need to be reground, so the factory can process with enough feed and speed without worrying about the cement.This new crown type bit has a more consistent tool life than the welded bit or solid carbide bit.

In many cases, the reground bit does not perform as well as the new bit.This is because it is difficult to regrind a cutting edge in the same shape as a new drill.Improper blade grinding will make the drill easier to chip, require more torque or power to process, or generate more heat, resulting in shorter tool life.