Due to the complexity of tool applications, professional grinding centers need to quickly change the grinding plan according to the failure mode of the tool being grinded and track the use effect of the tool. A professional tool sharpening center must also constantly capitalize on its experience in order to sharpen tools better and more professionally!
The following will introduce six problems that need to be paid attention to when grinding tools from the perspectives of tool material itself, grinding equipment, testing equipment and other equipment, standards grinders and grinding technicians.
1. Tool material
Common tool materials used in tool grinding include: high speed steel, powder metallurgy high speed steel, cemented carbide, and ultrahard materials such as PCD, CBN, and cermets. High speed steel tools are sharp and have good toughness, while carbide tools have high hardness but poor toughness. The density of carbide cutting tools is significantly higher than that of high speed steel cutting tools. These two materials are the main materials for drills, reamers, countersinks and taps. The performance of powder metallurgy high speed steel is between the above two materials and is mainly used to make rough milling cutters and taps.
High speed steel cutting tools are less susceptible to collisions due to the good toughness of their materials. However, carbide tools have high hardness and are fragile, are very sensitive to collisions, and the cutting edges tend to jump. Therefore, during the grinding process, you must be very careful when operating and placing carbide tools to avoid collisions between tools or tools falling.
Since the precision of most high speed steel cutting tools is relatively low, their grinding requirements are not high and their prices are not high. Therefore, many manufacturers set up their own tool shops to grind them. However, carbide cutting tools often need to be sent to professional grinding centers for grinding. According to statistics from some national tool sharpening centers, more than 80% of tools sent for repair are carbide tools.
2. Tool grinder
Because the tool material is very hard, grinding is usually the only way to change its shape. Common tool grinders used in tool manufacturing and grinding include the following types:
1. Groove grinding machine: Grinds grooves or backs of drill bits, end mills and other tools.
2. Top angle grinder: Grinds the tapered top angle (or eccentric back angle) of the drill bit.
3. Chisel edge repair machine: fixes the chisel edge of the drill bit.
4. Manual universal tool grinder: grinding outer circle, groove, back, top angle, chisel edge, plane, rake surface, etc. Often used for tools with small numbers and complex shapes.
5. CNC grinder: usually five-axis linkage, the function is determined by software. It is typically used for grinding large quantities of tools that require high precision but are not complex, such as drill bits, end mills, reamers, etc. The main suppliers of this type of grinding machines come from Germany, Switzerland, USA, Australia and Japan.
3. Grindstone
3.1 Abrasive grains
Grinding wheel abrasive grains of different materials are suitable for grinding tools of different materials. Different parts of the tool require different abrasive grain sizes to ensure the best combination of edge protection and processing efficiency.
Aluminum Oxide: Used to grind HSS cutting tools. The grinding wheel is cheap and easy to modify into different shapes to grind complex tools (corundum type).
Silicon carbide: used to modify CBN grinding wheels and diamond grinding wheels.
CBN (Cubic Boron Carbide): Used to grind HSS cutting tools. Expensive, but durable.
Internationally, grinding wheels are represented by B, such as B107, where 107 represents the diameter of the abrasive grains.
Diamond: used to sharpen HM tools, expensive but durable. The grinding wheel is represented by D, such as D64, where 64 represents the diameter of the abrasive grain.
3.2.Shape
In order to facilitate grinding different parts of the tool, the grinding wheels should have different shapes. The most commonly used are:
Parallel grinding wheel (1A1): grinding top angle, outer diameter, back, etc.
Disc-shaped grinding wheel (12V9, 11V9): grinding spiral grooves, main and secondary cutting edges of milling cutters, cutting chisel edges, etc.
After a period of use, the shape of the grinding wheel should be changed (including plane, angle and fillet R). The grinding wheel often needs to use cleaning stones to remove the chips filled between the abrasive grains to improve the grinding ability of the grinding wheel.
4. Grinding standards
Having a good set of tool sharpening standards helps determine whether a sharpening center is professional. Grinding standards generally stipulate the technical parameters of the cutting edges of different tools when cutting different materials, including edge inclination angle, apex angle, rake angle, angle clearance, chamfer, chamfer and other parameters (in carbide drills, the process of blunting the blade is called “Chamfer”, the width of the chamfer is related to the material to be cut, generally between 0.03 and 0.25 mm The process of chamfering on the edge (point tip) is called “chamfering”. Each professional company has its own method. Grinding standards summarized.
The difference between HM drills and HSS drills:
HSS drill bit: The top angle is usually 118 degrees, sometimes more than 130 degrees; the blade is sharp; the precision requirements (difference in blade height, symmetry, circumferential runout) are relatively low. There are many ways to practice scissoring.
HM drill: The top angle is generally 140 degrees; straight flute bits are typically 130 degrees and three-edged bits are typically 150 degrees. The blade and tip (on the edge) are not sharp and are often dull, or called chamfers and chamfers, high precision requirements are required; The edge of the chisel is often S-shaped to make chip breaking easier.
Back corner:
The clearance angle of the blade is very important for a knife. If the clearance angle is too large, the edge will be weak and easy to jump and “stick”; if the clearance angle is too small, the friction will be too great and the cut will be unfavorable.
The tool clearance angle varies depending on the material being cut, the type of tool and the diameter of the tool. Generally speaking, the clearance angle decreases as the tool diameter increases. Also, if the material to be cut is hard, the draft angle will be smaller, otherwise the draft angle will be larger.
5. Tool testing equipment
Tool inspection equipment is generally divided into three categories: tool setters, projectors, and universal tool measuring instruments. The tool setter is mainly used for the preparation of tool setting (such as length, etc.) of CNC equipment such as machining centers, and is also used to detect parameters such as angle, radius, step length, etc. is also used to detect parameters such as angle, radius, step length, etc. However, the above two methods generally cannot measure the tool clearance angle. The universal tool measuring instrument can measure most tool geometric parameters, including clearance angle.
That is why professional tool sharpening centers must be equipped with universal tool measuring instruments. However, there are not many suppliers of this material and there are German and French products on the market.
6. Grinding Technician
The best equipment also requires people to operate it, and the training of grinding technicians is naturally one of the most critical links.
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