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CNC cutting tools resharpening tips

 CNC cutting tools resharpening tips 


First, the tool material

In tool regrinding common tool materials are: high-speed steel (HSS), powder metallurgy high-speed steel (PM-HSS), cemented carbide (HM) and PCD, CBN, metal ceramics and other super-hard materials. HSS tools are sharp and tough, while cemented carbide tools have high hardness but poor toughness. The density of cemented carbide tools is significantly greater than that of HSS tools. These two materials are the main materials for drills, reamers, milling cutters and taps. Powder metallurgy high-speed steel performance between the above two materials, mainly used in the manufacture of rough milling cutters and taps.

High-speed steel cutting tools are less sensitive to collision because of the good toughness of the material. However, the hard alloy tool hardness is high and brittle, very sensitive to collision, the edge is easy to pop. Therefore, in the regrinding process, the carbide tool must be operated and placed very carefully to prevent collision between the tool or tool fall.

As most of the precision of high-speed steel tools are relatively low, its repair and grinding requirements are not high, coupled with its price is not high, so many manufacturers set up their own tool shop for its repair and grinding. However, carbide tools often need to be sent to professional regrinding centers for regrinding. According to the statistics of Arnold tool sharpening center, more than 80% of the tools are carbide tools.

Second, tool grinding machine

Because the tool material is very hard, so, generally can only be used to change the shape of the grinding. In the tool manufacturing, repair and grinding in the common tool grinder has the following types:

1, grinding slot machine: grinding drills, end mills and other tools of the slot or back.

2, grinding top angle machine: grinding drill bit taper top angle (or eccentric back angle).

3、Fixing cross cutting edge machine: correct the cross cutting edge of the drill bit.

4、Manual universal tool grinder: grinding cylindrical, groove, back, top angle, transverse edge, flat surface, front cutter surface, etc.. Commonly used in a small number of complex shape of the tool.

5, CNC grinding machine: generally five-axis linkage, the function is determined by the software. Generally used to regrind a large number of tools with high precision requirements, but not complex, such as drills, end mills, reamers, etc.. The main suppliers of these grinding machines come from Germany, Switzerland, the United States, Australia and Japan.

Grinding Wheel

1、Grinding Grain

Grinding wheel grits made of different materials are suitable for grinding tools made of different materials. Different parts of the tool need to use a different size of abrasive grain to ensure the best combination of edge protection and processing efficiency.

Aluminum oxide: for grinding HSS tools. The wheels are inexpensive and can be easily modified to different profiles for resharpening complex tools (corundum type).

Silicon Carbide: Used to dress CBN and diamond grinding wheels.

CBN (Cubic Boron Carbide): Used for grinding HSS tools. Highly priced, but durable.

Internationally, grinding wheels are denoted by B, e.g. B107, where 107 indicates the size of the diameter of the abrasive grain.

Diamond: Used for grinding HM tools, expensive but durable. Grinding wheel with D to indicate, such as D64, of which 64 indicates the size of the diameter of the abrasive grain.

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 corner, outside diameter, back, etc..

Disc-shaped grinding wheel (12V9, 11V9): grinding spiral groove, the main and secondary cutting edge of the milling cutter, repairing the horizontal edge, and so on.

Grinding wheels need to be corrected after a period of time after the use of its shape (including plane, angle and rounding R). Grinding wheels must often be cleaned up with a cleaning stone to fill in the chips between the abrasive grains to clean up to improve the grinding capacity of the wheel.

Fourth, grinding standards

Whether a good set of tool grinding standards is a measure of a grinding center is a professional standard. Regrinding standards, generally provides for different tools in cutting different materials when the cutting edge of the technical parameters, including edge inclination, top angle, front angle, back angle, chamfering, chamfering and other parameters (in the carbide drill, so that the blade of the blunt process called “reverse edge”, the width of the reverse edge of the cutting material is related to the cutting edge, generally in the range of 0.03- 0.25Mm. 0.25Mm. The process of chamfering on the edge (tip point) is called “chamfering”. Each professional company has its own standard for chamfering, which has been summarized over the years.

Difference between HM and HSS drills:

HSS drill: the top angle is generally 118 degrees, sometimes more than 130 degrees; the cutting edge is sharp; the requirements for precision (edge height difference, symmetry, circumferential runout) are relatively low. There are various ways to repair the cross edge.

HM drills: top angle is usually 140 degrees; straight flute drills are often 130 degrees, and triple edge drills are usually 150 degrees. The cutting edge and tip (on the prongs) are not sharp and are often blunted, or chamfered and chamfered; high accuracy is required. The cross edge is often trimmed to an S- shape to facilitate chip breaking.

Back Angle: The back angle of the blade is very important to the tool. After the angle is too large, the edge of the virtual easy to pop, easy to “tie the knife”; after the angle is too small, the friction is too large, cutting is unfavorable.

The back angle of the tool with the cutting material and tool type, tool diameter is different. Generally speaking, the rear angle decreases with the diameter of the tool. In addition, the cutting material is hard, the rear angle is smaller, otherwise, the rear angle is larger.

Fifth, tool testing equipment

Tool testing equipment is generally divided into three categories: tool setting instrument, projector and universal tool measuring instrument. Tool setting instrument is mainly used for machining centers and other CNC equipment for tool preparation (e.g., length, etc.), but also used to detect the angle, radius, step length and other parameters; projector function is also used to detect the angle, radius, step length and other parameters. However, the above two generally can not measure the back angle of the tool. While the universal tool measuring instrument can measure most of the geometric parameters of the tool, including the rear angle.

Therefore, the tool professional resharpening center must be equipped with universal tool measuring instrument. But this equipment is not many suppliers, the market has the German and French products.

Six, grinding mechanic

The best equipment also needs to be operated by personnel, grinding mechanic training is naturally one of the most critical aspects. As China's tool manufacturing industry is relatively backward, coupled with a serious lack of vocational and technical training, tool grinding technician training can only be resolved by the enterprise itself.

Due to the specificity of tool resharpening industry, Arnold & Son draws on the training method of German technicians and formulates a set of evaluation standards for the technical grade of tool resharpening technicians according to its own experience for many years. The technical level of the resharpening technician is divided into eight levels, and the eighth level is the highest. A technical school graduates in Arnold after half a year of training and practice can generally reach the level of third-level technician.

VII. Conclusion

With regrinding equipment, testing equipment and other hardware and regrinding standards, regrinding technicians and other software, precision tool regrinding work can begin. Due to the complexity of the application of tools, professional regrinding center must be repaired according to the failure of the grinding tool in a timely manner to repair the grinding program, and track the effectiveness of the use of tools. A professional tool resharpening center must also continue to sum up experience in order to resharpen the tool better and more professional!


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