Solid carbide drills for steel drilling

John Dotday, Sandvik Coromant's drilling product and industry expert, points out that while it's important to increase productivity, the company found that manufacturers of high-volume parts are often more concerned about how to improve and achieve predictable tool life in steel drilling. This is especially true because small changes in the material in different batches can cause tool damage.

The solid carbide drill, CoroDrill 860-PM, which was launched in March 2012, was developed to increase the safety and machining efficiency of steel (including hardened steel and mild steel) drilling. Dotday pointed out that the drilling of low-hardness, high-viscosity, low-alloy steels such as 1018 steel and 1020 steel is challenging because of the built-up edge and chip control problems. Although these pieces of work material are difficult to break, CoroDrill 860-PM drills can form very fine chips with very short tails.

Dotday explained that in addition to optimizing the drill bit geometry for steel machining, passivation of the cutting edge of the drill bit and drill tip reinforcement prevent chipping of the drill tip, increasing the strength and safety of the drilling process. The cutting edge passivation is achieved on the grinder using an abrasive brush. This new method of cutting edge preparation and a tough 4234 carbide substrate prevent excessive wear of the drill bit and increase the dimensional accuracy and surface finish of the drill hole. Dotday said, "We want a controlled wear pattern."

The drill not only provides predictable tool life, but also extends tool life. Compared to other drills, the life span of CoroDrill 860-PM is increased by 20% to 40%. The drill's internal cooling function also contributes to chip control, and Dotday recommends using a coolant pressure of no less than 220 psi. For end users who do not have internal cooling functions on the machine tools used, the company also offers a limited number of external cooling drills, but these drills can only be used to drill shallow holes that do not exceed 3 times the hole diameter, and the cutting speed should be The feed rate is reduced by 25%. For internally cooled drills, the recommended feed rate is approximately 0.25 mm/r. When machining mild steel and hard steel, the recommended surface cutting speeds are 120 to 240 m/min and 60 to 100 m/min, respectively.

After the drill bit cuts the easy-to-handle chips, the multilayered TiAlN coating applied after brush blunting helps to improve lubricity and chip removal performance. The coating looks as smooth as a polished surface. The standard CoroDrill 860-PM drill has a diameter range of 3 to 20 mm and a maximum drilling depth of 8 times the hole diameter. The drill angle is 139° to 144° (depending on the drill diameter). Predrill centering holes are not recommended even when drilling holes in rough surfaces. Dotday explained, "Unless you use a centering drill of the right geometry, centering holes will cause problems and make the drill bit faster."

When the drill bit needs to be reground, Sandvik Coromant requires specialized sharpening and cutting edge preparation equipment to ensure that the repaired bit has the same service life as the new bit. Drill bit repair shortens the tool length by approximately 1mm and causes a slight increase in bit diameter due to recoating. A drill bit can be repaired 3 times, but after more than 3 times, the recoating coating will have delamination problems. Since the repair of the drill bit will shorten its length, the user needs to determine whether the length of the drill bit can still meet the processing requirements after several repairs.

When using CoroDrill 860-PM to machine through holes with different hole diameters, always drill the hole with the largest hole diameter to minimize burr formation and prevent bit deviation.