6 Key Points of Tool Grinding

       Common tool materials in tool grinding are: high-speed steel, powder metallurgy high-speed steel, cemented carbide, PCD, CBN, cermet and other super-hard materials. High-speed steel tools are sharp and have good toughness, while cemented 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, and it is mainly used to manufacture rough milling cutters and taps.

　　High-speed steel tools are not very sensitive to collisions due to their good toughness. However, cemented carbide tools have high hardness and brittleness, are very sensitive to collision, and the cutting edge is easy to jump. Therefore, in the grinding process, the operation and placement of the carbide tools must be very careful to prevent collisions between the tools or the tools from falling.

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

Tool grinder

      Because the tool material is very hard, generally only grinding can be used to change its shape. Common tool grinders in tool manufacturing and grinding are as follows:

1. Groove grinding machine: Grind the groove or back of tools such as drills and end mills.

2. Top angle grinding machine: To grind the cone apex angle (or eccentric back angle) of the drill bit.

3. Chisel edge trimming machine: Correct the chisel edge of the drill.

4. Manual universal tool grinder: grinding external circle, groove, back, top angle, chisel edge, plane, rake face, etc. It is often used for tools with a small number of complex shapes.

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

Grinding wheel

1. Abrasive particles

　　Grinding wheels of different materials are suitable for grinding tools of different materials. Different parts of the tool need to use different sizes of abrasive grains to ensure the best combination of edge protection and processing efficiency.

　　Alumina: used to grind 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 for grinding 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 different shapes. The most commonly used are:

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

　　Disc-shaped grinding wheel (12V9, 11V9): Grinding the main and minor cutting edges of spiral grooves, milling cutters, and trimming chisel edges, etc.

　　After a period of use, the shape of the grinding wheel (including plane, angle and rounded corner R) needs to be corrected. The grinding wheel must often use cleaning stones to clean up the chips filled between the abrasive grains to improve the grinding ability of the grinding wheel.

Grinding standard

       Whether you have a good set of tool grinding standards 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 the edge angle, apex angle, rake angle, relief angle, chamfering, chamfering, etc. The process of dulling the blade is called "back edge". The width of the back edge is related to the material to be cut, generally between 0.03-0.25 Mm. The process of chamfering on the edge (tip point) is called "chamfering" .

The difference between HM bit and HSS bit

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

　　HM drill bit: the top angle is generally 140 degrees; the straight flute drill is often 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 dulled, or called chamfering and chamfering; high precision is required. Chisel blades are often repaired into an S-shape to facilitate chip breaking.

　　Back angle

       The clearance angle of the cutting edge is very important for the tool. If the relief angle is too large, the blade is easy to jump and "stick"; if the relief angle is too small, the friction is too large and the cutting is unfavorable.

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

Tool inspection equipment

       Tool testing equipment is generally divided into three categories: tool setting instruments, projectors and universal tool measuring instruments. The tool setting instrument is mainly used for the preparation of tool setting (such as length, etc.) of CNC equipment such as machining centers. It is also used to detect angle, radius, step length and other parameters; the function of the projector is also used to detect angle, radius, step length and other parameters . However, the above two generally cannot measure the clearance angle of the tool. The universal tool measuring instrument can measure most of the geometric parameters of the tool, including the relief angle.

　　Therefore, the professional tool grinding center must be equipped with a universal tool measuring instrument. However, there are not many suppliers of this 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 grinding technicians is naturally one of the most critical links.