Due to the complexity of tool application, the professional grinding center must timely repair and repair the grinding plan according to the failure form of the sharpened tool, and track the use effect of the tool. A professional tool grinding center must also continue to summarize experience, in order to grind the tool better, more specialized!
First, cutting tool materials
The common tool materials in the tool grinding are: high speed steel, powder metallurgy high speed steel, hard alloy and PCD, CBN, metal ceramics and other superhard materials. High - speed steel cutting tool is sharp, good toughness, carbide cutting tool hardness is high but poor toughness. The density of carbide tool is obviously higher than that of high speed steel tool. These two materials are the main materials for drill bits, reamer, milling cutters and taps. The properties of powder metallurgy high speed steels are between the above two materials and they are mainly used in the manufacture of rough milling cutters and taps.
The high speed steel tool is not sensitive to collision because of its good toughness. But the hardness of cemented carbide tool is high and brittle, sensitive to collision, and the edge is easy to jump. Therefore, in the process of grinding, it is necessary to be very careful of the operation and placement of carbide tools, to prevent the collision between the tools or tool fall.
Due to the high speed steel tool precision is relatively low, its grinding requirements are not high, coupled with its price is not high, so, many manufacturers set their own tool workshop for grinding. But carbide cutting tools often need to be sent to a professional grinding center for grinding. According to the statistics of some domestic tool grinding center, more than 80% of the repair tools are carbide tools.
Two, tool grinding machine
Because the tool material is very hard, so, generally can only be used to change its shape by grinding. There are several common tool grinders in the manufacturing and grinding of the tool:
1. Groove grinding machine: grinding the grooves or backs of drill bits, end mills and other cutting tools.
2. Top Angle Grinding Machine: Grinding the cone top Angle (or eccentric back Angle) of the drill bit.
3. Cutting machine: to correct the cutting edge of the drill bit.
4. Manual universal cutter grinder: grinding the outer circle, groove, back, top Angle, transverse edge, plane, front cutter face, etc. Often used in a small number of complex shapes cutting tools.
5 CNC grinder: generally five-axis linkage, function determined by software. It is generally used for grinding large quantity, high precision requirements, but not complex cutting tools, such as drill, end milling cutter, reamer, etc. The main suppliers of this type of grinder are from Germany, Switzerland, the United States, Australia and Japan.
Three, grinding wheel
1. The abrasive grain
Grinding wheel grains of different materials are suitable for grinding tools of different materials. Different parts of the tool need to use different sizes of abrasive particles to ensure the best combination of edge protection and processing efficiency.
Alumina: used for grinding HSS tools. Grinding wheels are cheap and easy to modify into different shapes for grinding complex tools (corundum type).
Silicon carbide: used to modify CBN grinding wheels and diamond grinding wheels.
CBN(cubic boron carbide) : used for grinding HSS tools. Expensive but durable.
In the world, the grinding wheel is represented by B, such as B107, where 107 represents the size of the abrasive particle diameter
Diamond: used for sharpening HM tools, expensive, but durable. D is used to represent the grinding wheel, such as D64, where 64 represents the size of the abrasive particle diameter.
Shape of 2.
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, outside diameter, back, etc.
Disc grinding wheel (12V9,11V9) : grinding the main and secondary cutting edges of spiral grooves and milling cutters, trimming the transverse edges, etc
After a period of use, the grinding wheel needs to modify its shape (including plane, Angle and fillet R). In order to improve the grinding ability of the grinding wheel, the chip filling between the abrasive grains must be removed by cleaning stone frequently.
Four, grinding standards
Whether to have a set of good tool grinding standards is to measure whether a grinding center is professional standards. Standard of grinding, the general rules for different cutting tool in cutting different materials when the cutting edge of technology parameters, including the blade Angle, apex Angle, rake Angle, Angle, blade, after chamfering etc parameters (in the carbide drill, make the blade passivation process is called "blade", pour the width of the blade and the cutting material, generally between 0.03 0.25 Mm. The process of chamfering on the edge (tip) is called "chamfering". Each professional company has its own grinding standards summarized over the years.
Difference between HM bit and HSS bit:
HSS bit: top Angle is generally 118 degrees, sometimes more than 130 degrees; A sharp blade; The accuracy (blade height difference, symmetry, circumferential runout) is relatively low. There are many ways of trimming the blade.
HM bit: top Angle is generally 140 degrees; Straight slot drills are usually 130 degrees, and three-edge drills are usually 150 degrees. Blade and tip (edge) are not sharp, often passivated, or chamfered edge and chamfered; High requirement for precision. The transverse blade is often trimmed into an S- shape to facilitate chip breaking.
After the Angle:
The back Angle of the blade is very important to the cutting tool. The back horn is too large, the blade is easy to jump and "prick"; The back Angle is too small, the friction is too large, unfavorable cutting.
The back Angle of the tool varies with the material being cut and the type of tool and the diameter of the tool. In general, the back Angle decreases as the tool diameter increases. In addition, the cutting material is hard, the back Angle is smaller, otherwise, the back Angle is larger.
Five, tool detection equipment
Tool testing equipment is generally divided into three categories: tool alignment instrument, projector and universal tool measuring instrument. Tool setting instrument is mainly used for tool setting preparation (such as length, etc.) of CNC equipment such as machining center, and is also used to detect parameters such as Angle, radius, ladder length, etc. The function of the projector is also used to detect the Angle, radius, ladder length and other parameters. However, the above two can not generally 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 tool professional grinding center must be equipped with universal tool measuring instrument. But there are not many suppliers of such equipment. There are German and French products on the market.
6. Grinding technician
The best equipment also needs personnel to operate, and the training of the repairman is naturally one of the most critical links. As the tool manufacturing industry in China is relatively backward, coupled with the serious lack of vocational technical training, the training of tool repair and grinding technicians can only be solved by the enterprises themselves.
VII. Conclusion
With the grinding equipment, testing equipment and other hardware and grinding standards, grinding technicians and other software, precision tool grinding work can begin. Due to the complexity of tool application, the professional grinding center must timely repair and repair the grinding plan according to the failure form of the sharpened tool, and track the use effect of the tool. A professional tool grinding center must also continue to summarize experience, in order to grind the tool better, more specialized!
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