1.Cutting tools material
Common tool materials in tool grinding include: high-speed steel, powder metallurgy high-speed steel, cemented carbide, PCD, CBN, cermet and other superhard materials. High speed steel tools are sharp and have good toughness, while carbide tools have high hardness but poor toughness. The density of cemented carbide tools is significantly higher than that of high-speed steel tools. These two materials are the main materials for drill bits, reamers, milling cutters and taps. The performance of powder metallurgy high speed steel is between the above two materials, and it is mainly used for manufacturing rough milling cutter and tap.
High speed steel tools are not sensitive to collision due to their good toughness. However, cemented carbide tools have high hardness and brittleness, are very sensitive to collision, and the edge is easy to jump. Therefore, in the process of grinding, it is necessary to be very careful about the operation and placement of cemented carbide tools to prevent collision between tools or falling of tools.
Because the precision of high-speed steel tools is relatively low, their grinding requirements are not high, and their prices are not high, many manufacturers set up their own tool workshops to grind them. However, cemented carbide tools often need to be sent to a professional grinding center for grinding. According to the statistics of many tool grinding centers, more than 80% of the tools sent for repair are cemented carbide tools.
2. Cutting Tool grinder
Because the tool material is very hard, it can only be changed by grinding. Common tool grinders used in tool manufacturing and grinding include the following:
(1). Grooving machine: grinding the groove or back of drill bits, end mills and other tools.
(2). Angle grinder: grinding the conical top angle (or eccentric back angle) of the drill bit.
(3).Trimming machine：Correct the lateral edge of the drill bit.
(4). Manual universal tool grinder: grinding the outer circle, groove, back, top angle, transverse edge, plane, front face, etc. It is often used for tools with small quantity and complex shape.
(5). CNC grinding machine: generally five-axis linkage, with functions determined by software. It is generally used for grinding tools with large quantity and high precision requirements, but not complicated, such as drill bits, end mills, reamers, etc. The main suppliers of such grinders are from Germany, Switzerland, the United States, Australia and Japan.
3.Grinding wheel
(1). Abrasive particles
Grinding wheel abrasive particles of different materials are suitable for grinding tools of different materials. Different parts of the tool require different abrasive sizes to ensure the best combination of edge protection and processing efficiency.
Alumina: used for grinding HSS tools. The grinding wheel is cheap and easy to be modified into different shapes for grinding complex tools (corundum).
Silicon carbide: used to correct CBN grinding wheel and diamond grinding wheel.
CBN (cubic boron carbide): used for grinding HSS tools. High price, but durable.
Internationally, grinding wheel is represented by B, such as B107, where 107 represents the size of abrasive particle diameter
Diamond: It is used for grinding HM tools. It is expensive but durable.
(2). Shape
In order to facilitate grinding different parts of the tool, the grinding wheel should have different shapes. The most commonly used ones are:
Parallel grinding wheel (1A1): grinding top angle, outer diameter, back, etc.
Dished grinding wheel (12V9, 11V9): grinding spiral groove, main and auxiliary cutting edges of milling cutter, trimming horizontal edge, etc
After the grinding wheel has been used for a period of time, its shape (including plane, angle and fillet R) needs to be corrected. The grinding wheel must often use a cleaning stone to remove the chips filled between the abrasive grains to improve the grinding ability of the grinding wheel.
4.Grinding standard
Whether there is a good set of tool grinding standards is the standard to measure 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 angle of inclination, top angle, front angle, back angle, chamfer, chamfer and other parameters (in the cemented carbide bit, the process of passivating the cutting edge is called "chamfer", and the width of the chamfer is related to the material to be cut, generally between 0.03-0.5Mm and 0.25Mm. The process of chamfering on the edge (tool point) is called "chamfer". Each professional company has its own grinding standards summarized over the years.
Difference between HM bit and HSS bit:
HSS bit: the top angle is generally 118 degrees, sometimes greater than 130 degrees; The blade is sharp; The requirements for accuracy (blade height difference, symmetry, circumferential runout) are relatively low. There are many ways to repair the horizontal blade.
HM bit: the top angle is generally 140 degrees; Straight slot drills are usually 130 degrees, and three-edge drills are generally 150 degrees. The blade and tip (on the edge) are not sharp and are often passivated, or called chamfer and chamfer; It requires high accuracy. The horizontal blade is often trimmed into S-shape to facilitate chip breaking。
Back angle: The back angle of the blade is very important for the tool. The back corner is too large, and the blade is easy to jump and "stab"; If the back angle is too small, the friction will be too large and the cutting will be unfavorable.
The back angle of the tool varies with the material to be cut and the type and diameter of the tool. Generally speaking, the back angle decreases with the increase of tool diameter. In addition, if the material to be cut is hard, the back angle will be smaller, otherwise, the back angle will be larger.
5.Cutting Tools detection equipment
Cutting Tools detection equipment is generally divided into three categories: tool setting instrument, projector and universal tool measuring instrument. The tool setting instrument is mainly used for tool setting preparation (such as length) of CNC equipment such as machining centers, and also for detecting parameters such as angle, radius, step length, etc; The function of the projector is also used to detect parameters such as angle, radius, step length, etc. However, the above two cannot measure the back angle of the tool. The universal tool measuring instrument can measure most of the geometric parameters of the tool, including the back angle.
Therefore, the professional tool grinding center must be equipped with a universal tool measuring instrument. However, there are few suppliers of such equipment, and there are German and French products on the market.
6. Grinding technician
The best equipment also needs personnel to operate, and the training of grinding technicians is naturally one of the most critical links. Due to the relatively backward tool manufacturing industry in China and the serious shortage of vocational and technical training, the training of tool grinding technicians can only be solved by the enterprise itself.
7. Conclusion
With the grinding equipment, testing equipment and other hardware as well as the grinding standards, grinding technicians and other software, the grinding of precision tools can begin. Due to the complexity of tool application, the professional grinding center must timely modify the grinding plan according to the failure form of the tool to be grinded, and track the use effect of the tool. A professional tool grinding center must constantly sum up experience to make the tool grinding better and more professional!
Post time: Feb-24-2023