Six main points about tool grinding
Jan 09, 2020

Because of the complexity of tool application, the professional grinding center must modify the grinding scheme in time according to the failure form of the polished tool, and track the use effect of the tool. Aprofessional tool grinding centermust continue to sum up experience, in order to tool grinding better, more specialized! From the point of view of tool material, grinding equipment, testing equipment and other hardware and grinding standards, grinding technicians and so on, this paper introduces six problems that tool grinding must not be ignored!

1.The Common Tool Materials

the common tool materials in tool grinding are: high speed steel, powder metallurgy high speed steel, cemented carbide and PCD,CBN, cermet and other superhard materials. High speed steel knife with sharp, good toughness, cemented carbide tool hardness is high but toughness is poor. The density ofcemented carbide toolsis obviously higher than that of high speed steel tools. These two materials are the main materials of drill bits, winches, milling cutters and taps. The properties of powder metallurgy high speed steel are between the above two materials, which are mainly used in the manufacture of rough milling cutters and taps. High speed steel knife tools are not very sensitive to collision because of their good toughness. However, cemented carbide tools have high hardness and brittleness, sensitive to collision, and easy to jump at the edge. Therefore, in the process of grinding, we must be very careful in the operation and placement of cemented carbide tools to prevent the collision between cutting tools or tool fall. Because the accuracy of high speed steel cutting tools is relatively low, its grinding requirements are not high, and its price is not high, so many manufacturers set up their own tool workshops to repair and grind them. However, cemented carbide tools often need to be sent to the professional grinding center for grinding. According to the statistics of some tool grinding centers in China, more than 80% of the cutting tools are cemented carbide tools.

 tools and cutter grinding

2.Tool Machine

Because the tool material is very hard, the tool grinder can only change its shape by grinding. In the manufacture of cutting tools, there are the following common tool grinders in the manufacture and grinding of cutting tools:

  • 1. Slot grinder: the groove or back of a drill bit, end milling cutter, etc.
  • 2.Grinding top angle machine: the conical top angle (or eccentric rear angle) of the grinding bit.
  • 3. Repair machine: correct the cross edge of the bit.
  • 4. Manual universal tool grinder: grinding outer circle, slot, back, top angle, transverse edge, plane, front knife surface, etc. It is often used in a small number of tools with complex shapes. 5.CNC grinder: generally five-axis linkage, the function is determined by the software. It is generally used for cutting tools with large grinding quantity and high precision, but not complicated, such as drill bit, end milling cutter, reamer and so on. The main suppliers of such grinders come from Germany, Switzerland, the United States, Australia and Japan.

3.Grinding Wheel

3.1. Grinding wheels of different materials are suitable for grinding tools of different materials. The size of abrasive particles used in different parts of the tool is also different in order to ensure the best combination of edge protection and machining efficiency. Alumina: used to grind HSS tools. The grinding wheel is cheap and easy to modify into different shapes for grinding complex cutting tools (corundum). Silicon carbide: used to correct CBN grinding wheel and diamond grinding wheel. CBN (cubic boron carbide): used to grind HSS tools. The price is high, but it is durable. Internationally, grinding wheels are represented by B, such as B 107, where 107 represents the size of the abrasive diameter. Diamond: used for grinding HM tools, high price, but durable. The grinding wheel is represented by D, such as D 64, where 64 represents the size of the abrasive diameter.

3.2. 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 top angle, outer diameter, back and so on. Disc grinding wheel (12V9, 11V9): grinding screw groove, main and auxiliary cutting edge of milling cutter, trimming edge, etc. After a period of use, the grinding wheel needs to be modified (including plane, angle and fillet R). The grinding wheel must often use clear stone to clean up the chips filled between the abrasive particles in order to improve the grinding ability of the grinding wheel.

Parallel grinding wheel

4.Tool Grinding Standards

Whether the grinding standard has a good set of tool grinding standards is a standard to measure whether a grinding center is professional. In the grinding standard, the technical parameters of the cutting edge of different cutting tools in cutting different materials are generally specified, including the inclination angle of the edge, the top angle, the front angle, the rear angle, the inverted edge, the chamfering edge and so on (in cemented carbide bit, the process of passivating the blade is called "inverted edge". The width of the inverted edge is related to the cutting material, generally between the cutting materials. The process of chamfering on the edge (tip of the knife) is called chamfering. Each professional company has its own grinding standards summarized for many years. The difference between HM bit and HSS bit: the top angle is usually 118 degrees, sometimes more than 130 degrees; the blade is sharp; the precision (blade height difference, symmetry, circumferential runout) is relatively low. There are many ways to practice the transverse blade. HM bit: the top angle is 140 degrees, the straight groove drill is often 130 degrees, and the three-edge drill is usually 150 degrees. Blade and tip (edge) are not sharp, often passivated, or inverted edge and chamfer; high precision requirements. The transverse blade is often modified into S-shape to facilitate chip breaking. Rear angle: the rear angle of the blade is very important to the tool. The rear corner is too large, the blade is empty and easy to jump, and the rear corner is too small, the friction is too large, and the cutting is unfavorable. The rear angle of the tool varies with the cutting material, tool type and tool diameter. Generally speaking, the rear angle decreases with the increase of tool diameter. In addition, when the cutting material is hard, the rear corner is smaller, otherwise, the rear corner is larger.

5.Tool Detection Equipment Tool

Testing equipment is generally divided into three categories: tool counter, projector and universal tool measuring instrument. The tool alignment instrument is mainly used for tool preparation (such as length, etc.) of NC equipment such as machining center, and is also used to detect the parameters such as angle, radius, step length and so on, and the function of projector is also used to detect the parameters such as angle, radius, step length and so on. However, the above two can not measure the rear angle of the tool. The universal tool measuring instrument can measure most of the geometric parameters of the tool, including the rear angle. Therefore, the tool professional grinding center must be equipped with a universal tool measuring instrument. But there are not many suppliers of this equipment, and there are German and French products on the market.

Diamond Grinding Wheel For CNC Mahching

6. Regrinding Mechanic

The best equipment also requires the operation of the personnel, and the training of the grinding mechanic is one of the most critical links. Because of the relative backwardness of the tool manufacturing industry in our country, and the serious shortage of vocational training, the training of the tool grinding technology can only be solved by the enterprise itself.

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