Should the tool be worn to repair the old knife or buy a new one? It is a problem that many machining users often consider. The sluggishness brought about by the winter of manufacturing has stimulated the diligence of manufacturers. When considering tool grinding, there are many variables such as tool geometry, use, substrate and coating that all have an impact on the decision to fix a tool. Other factors include the value of the workpiece, tool life, process complexity, processing location and processing technology. The most important thing for grinding tools is to ensure the consistency of the quality geometry parameters.
First, the tool material
Common tool materials in tool grinding are: HSS, PM-HSS, HM and PCD, CBN 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 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.
Second, the 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 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. Five-axis linkage CNC grinding machine: The function is determined by software. Generally used for grinding large quantities, high precision, but not complicated tools, such as drills, end mills, etc.
Third, the 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.
Silicon Carbide: Used to modify CBN grinding wheels and diamond grinding wheels.
CBN (cubic boron carbide): For grinding HSS tools. The price is high but durable. Internationally, the grinding wheel is represented by B, such as B107, where 107 represents the size of the abrasive grain.
Diamond: Used to grind HM tools, high price, but durable. The grinding wheel is indicated by D, such as D64, where 64 represents the size of the abrasive grain.
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, chisel 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.
Fourth, the tool parameters
1. Name definition
It is hereby stipulated that in the cemented carbide drill bit, the process of passivating the cutting edge is called "reverse edge", and the width of the inverted blade 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".
In the end mill, the blade on the circumferential surface is the main cutting edge. The edge on the end face is the minor cutting edge.
2. 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.
Fifth, the need to repair
1. Correctly select the grinding wheel (type, model).
2. For newly arrived tools, first measure the main geometric parameters and record them, especially the reverse edge, chamfer and chisel correction of the drill bit.
3. Enter the wheel data first, then enter the tool data.
4. After grinding, measure the main parameters of the tool and compare it with the grinding standard before correcting.
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