Common tool materials in tool grinding

Tool material

Common tool materials in tool grinding are: high speed steel, powder metallurgy high speed steel, hard alloy and PCD, CBN, cermet and other superhard materials. High-speed steel cutters are sharp and tough, and carbide tools have high hardness but poor toughness. The density of cemented carbide tools is significantly greater than that of high speed steel tools. These two materials are the main materials for drills, reamers, milling cutters and taps. The performance of powder metallurgy high speed steel is between the above two materials, mainly used to manufacture rough milling cutters and taps.

High-speed steel tools are less sensitive to collisions due to their good material toughness. However, carbide tools are hard and brittle, sensitive to collisions, and easy to cut. Therefore, during the grinding process, the operation and placement of the carbide tool must be very careful to prevent collisions between the tools or tools falling.

Because the precision of high-speed steel tools is relatively low, the grinding requirements are not high, and the price is not high, so many manufacturers set their own tool workshop to repair them. However, carbide tools often need to be sent to a professional grinding center for grinding. According to the statistics of some tool grinding centers in China, more than 80% of the tools sent for repair are carbide tools.

Tool grinder

Since the tool material is very hard, it is generally only possible to use grinding to change its shape. There are several types of tool grinding machines commonly used in the manufacture and grinding of tools:

1. Grinding machine: grinding the groove or back of the tool such as drill bit and end mill.

2. Grinding angle machine: the taper apex angle (or eccentric back angle) of the grinding bit.

3. Repair the edge cutter: Correct the chisel edge of the drill.

4. Manual universal tool grinding machine: grinding outer circle, groove, back, top angle, chisel edge, plane, rake face, etc. Commonly used in small quantities and complex shapes.

5.CNC grinding machine: generally five-axis linkage, the function is determined by software. Generally used for grinding large quantities, high precision, but not complicated tools, such as drills, end mills, reamers, etc.

Grinding wheel

Abrasive grain

Abrasive wheels of different materials are suitable for grinding tools of different materials. The size of the abrasive particles required for different parts of the tool is also different to ensure the best combination of cutting edge protection and processing efficiency.

Alumina: For grinding HSS tools. The grinding wheel is cheap and easy to modify into different shapes for grinding complex tools (corundum).

Silicon Carbide: Used to modify CBN grinding wheels and diamond grinding wheels.

CBN (cubic boron carbide): used to grind HSS tools.

Diamond: Used to grind HM tools.

2. Shape

In order to facilitate the grinding of different parts of the tool, the grinding wheel should have a different shape. The most common ones are:

Parallel grinding wheel (1A1): grinding angle, outer diameter, back, etc.

Disc-shaped grinding wheel (12V9, 11V9): grinding spiral groove, main and auxiliary cutting edges of milling cutter, trimming edge and so on.

After a period of use, the wheel needs to be corrected for its shape (including plane, angle and fillet R). Grinding wheels must often be cleaned with clean stones to remove the chips filled between the abrasive grains to improve the grinding ability of the grinding wheel.

Grinding standard

Whether or not you have a good tool grinding standard is a measure of whether a grinding center is professional. In the grinding standard, the technical parameters of the cutting edge of different tools when cutting different materials are generally specified, including blade inclination angle, apex angle, rake angle, back angle, reverse edge, chamfering and the like (in the cemented carbide drill bit) The process of passivating the blade is called “reverse edge”. The width of the reverse edge is related to the material to be cut, generally between 0.03-0.25 Mm. The process of chamfering on the edge (the tip point) is called “chamfering”. .

The difference between HM drill bit and HSS drill bit

HSS drill bit: The apex angle is generally 118 degrees, sometimes greater than 130 degrees; the blade edge is sharp; the accuracy (edge height difference, symmetry, circumferential runout) is relatively low. There are many ways to modify the chisel.

HM drill bit: The apex angle is generally 140 degrees; the straight groove drill is usually 130 degrees, and the three-edged drill is generally 150 degrees. The blade and the tip (on the edge) are not sharp and are often passivated, or inverted and chamfered; they require high precision. The chisel edge is often trimmed into an S-shape to facilitate chip breaking.

Back angle

The back angle of the blade is very important for the tool. The back angle is too large, the blade is easy to smash and easy to "saw the knife"; when the back angle is too small, the friction is too large and the cutting is unfavorable.

The back angle of the tool varies with the material being cut, the type of tool, and the diameter of the tool. In general, the relief angle decreases as the diameter of the tool increases. In addition, if the material to be cut is hard, the back angle is smaller, otherwise, the back angle is larger.

Tool inspection equipment

Tool inspection equipment is generally divided into three categories: tool setting, projector and universal tool measuring instrument. The tool setting instrument is mainly used for tool setting (such as length) of CNC equipment such as machining center. It is also used to detect parameters such as angle, radius and step length. The function of the projector is also used to detect parameters such as angle, radius and step length. . However, the above two generally cannot measure the back angle of the tool. The universal tool gauge can measure most of the geometry of the tool, including the back angle.

Therefore, the tool professional grinding center must be equipped with a universal tool measuring instrument. However, there are not many suppliers of such equipment, and there are German and French products on the market.

Grinding mechanic

The best equipment also requires personnel to operate, and the training of the grinding technician is naturally one of the most critical aspects.