What are the four types of carbide bits?

The four common types of carbide drill bits are solid carbide drill bits, carbide indexable insert drill bits, welded carbide drill bits and replaceable tip carbide drill bits. Each type of carbide drill bit has its own advantages in specific situations.

In mechanical processing, hole processing is one of the common processing methods, and drilling stones account for 30% of the entire hole processing. Compared with traditional drill bits, carbide drill bits are more wear-resistant, have high hardness, and long life, and have the characteristics of high speed and high precision. There are more and more customers using carbide drill bits.

In the past, people have always believed that drilling must be performed at lower feed rates and cutting speeds. This view used to be correct under the processing conditions of using ordinary drills.

Today, with the emergence of carbide drills, the concept of drilling has also changed. In fact, through the correct selection of suitable carbide drill bits, drilling productivity can be greatly improved and the cost per hole can be reduced.


carbide drill bits

Classification and application of cemented carbide drill bits


1. Solid carbide drill bit


Solid carbide drill bits are suitable for use in advanced machining centres. This drill bit is made of fine-grained carbide material. In order to extend its service life, it is also treated with TiAlN coating. The specially designed geometric edge shape makes the drill bit self-centred and has good performance when drilling most workpiece materials. Chip control and chip evacuation performance. The drill’s self-centring feature and tightly controlled manufacturing accuracy ensure high-quality holes without the need for subsequent finishing operations after drilling.


2. Carbide indexable inserts


Drill bits equipped with carbide indexable inserts can process a wide range of hole diameters, and the processing depth range is 2D ~ 5D (D is the hole diameter) and can be applied to lathes and other rotary processing machine tools. These drills use a self-centring geometry that reduces cutting forces and provides good chip control for most workpiece materials.


3. Welded carbide drill bit


Welded carbide drill bits are made of a carbide crown firmly welded to a steel drill body. This kind of drill adopts a self-centring geometric edge shape, which has low cutting force and can achieve good chip control on most workpiece materials. The machined holes have a good surface finish, high dimensional accuracy and positioning accuracy, and there is no need for subsequent precision. processing. This drill adopts an internal cooling method and can be used in machining centres, CNC lathes or other high-rigidity, high-speed machine tools.


4. Replaceable carbide crown drill bit


Replaceable carbide crown drill bits are a new generation of drilling tools developed in recent years. It is composed of a steel drill body and a replaceable solid carbide tooth crown. Compared with welded carbide drill bits, its processing accuracy is comparable, but because the tooth crown is replaceable, the processing cost can be reduced. Improve drilling productivity. This drill achieves precise hole size increments and is self-centering, resulting in high-precision hole drilling.

The drill body and the carbide crown are locked with each other using a precision-ground interlocking V-groove connection mechanism, which ensures that the drill bit assembly has the same dimensional accuracy and overall rigidity as a welded carbide drill bit. At the same time, this locking mechanism has only one correct matching position, making it easy to install the tooth crown on the matching pull rod, thereby ensuring repeatable positioning accuracy when replacing the tooth crown. When the tie rod is tightened by the locking screw, the crown drill body assembly is firmly locked with each other, and its connection stiffness is sufficient to meet the high productivity hole processing requirements of large feed and high speed.


How should the factory choose carbide drill bits? What precautions should be taken when using carbide drill bits?


Careful consideration of tolerances and machine tool stability


The factory should select drill bits based on the specific tolerances of the machining. Small diameter holes typically have tighter tolerances. Drill bit manufacturers then classify drill bits by specifying nominal bore diameters and upper tolerances.

Solid carbide drills have the tightest tolerances of all drill bit styles. This makes them the best choice for drilling holes with extremely tight tolerances. The factory can drill holes with a tolerance of 0 to +0.03mm using a 10mm diameter solid carbide drill bit.
On the other hand, weld drills or Seco drills with replaceable carbide crowns produce holes with tolerances from 0 to +0.07mm. These drill bits are often a good choice for production drilling operations.

Indexable insert drills are the ones that do the heavy lifting in the industry. Although their upfront cost is generally lower than other drill bits, these drill bits also have the largest tolerances, ranging from 0 to +0.3mm depending on the diameter/hole depth ratio. This means that end users can use indexable insert drills when they need a hole with larger tolerances that they would otherwise have to prepare with a boring tool to finish the hole.

Along with hole tolerances, shops need to consider machine tool stability during the selection process. Because stability is crucial to ensuring tool life and drilling accuracy. Factories should verify the condition of machine tool spindles, fixtures and accessories.

They should also consider the inherent stability of the drill bit. For example, solid carbide drill bits provide optimal rigidity, which allows it to achieve high accuracy.

Indexable insert drills, on the other hand, tend to deflect. These drills are equipped with two blades – an inner blade in the centre and a blade extending outward from the inner blade to the edge – and initially, only one blade is involved in the cut. This creates an unstable situation that causes the drill body to deflect. And the longer the drill bit is, the greater the deflection will be. Therefore, shops using indexable insert drills of 4XD and above should consider reducing the feed rate during the first millimetre of machining and then increasing it to the normal feed rate.

Weld drills and replaceable crown drills are designed with two symmetrical cutting edges forming a self-centring geometry. This stable cutting design allows the drill to enter the workpiece at full feed speed. The only exception is when the drill bit is not perpendicular to the surface being machined and it is recommended to reduce the feed by 30% to 50% when cutting in and out. The steel drill body allows for slight deflection, allowing it to be used successfully on lathes. However, solid carbide drill bits with good rigidity may break easily, especially if the workpiece is not properly centred.


Don’t ignore the chips


Many factories encounter chip removal problems. In fact, poor chip evacuation is the most common problem in drilling, especially when machining mild steel. And it doesn’t matter what kind of drill bit is used.

Factories often use external cooling to solve this problem, but this only works when the hole depth is less than 1XD and the cutting parameters are reduced. Otherwise, they must use an appropriate coolant with a flow rate and pressure that matches the bore size. For machine tools that do not have central spindle cooling, the shop should use a coolant-inside-out device.

Remember, the deeper the hole, the more difficult it is to remove chips and require greater cooling pressure. Always check the manufacturer’s recommended minimum coolant flow level. At lower flow rates, lower feed rates may be necessary.


Check life cycle costs


Productivity or cost per hole is the biggest trend affecting drilling today. This means that drill manufacturers must find ways to combine certain operations and develop drills that can handle high feed rates and high-speed operations.

The latest drill bits with replaceable solid carbide tips offer superior economy. Instead of replacing the entire drill body, the end user only purchases a carbide tip that costs the equivalent of resharpening a welded or solid carbide drill. These crowns are easy to replace and accurate, and the factory can use multiple crowns on one drill body to drill several holes of different specifications.

This modular drilling system reduces inventory costs for drill bits from 12mm to 20mm in diameter. Additionally, it eliminates the cost of backing up drill bits when welded drill bits or solid carbide drill bits are re-sharpened.

Shops should also take total tool life into consideration when reviewing cost per hole. Typically, a solid carbide drill can be regrinded 7 to 10 times by a factory, while a welded drill can only be regrinded 3 to 4 times. On the other hand, the steel body of a crown-type drill can replace at least 20 to 30 crowns when processing steel parts.

There is also a productivity issue here. Welded or solid carbide drill bits must be reground; therefore, shops tend to reduce speed to avoid chip sticking. However, drill bits with replaceable bits do not need to be reground, so the factory can use sufficient feed and speed during processing without worrying about chips sticking to the carbide material.

The new crown-style drills also have more consistent tool life than welded or solid carbide drills. In many cases, a resharpened drill bit will not perform as well as a new drill bit. This is because it is difficult to make the cutting-edge shape and edge grinding exactly the same as the new drill when regrinding. Improper edge grinding can cause the drill to become more susceptible to chip sticking, require more torque or power to process, or generate more heat, thereby shortening tool life.

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