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Due to the complexity of the tool application, the professional tool and cutter grinding center should adjust the dressing plan in time according to the failure mode of the tool being repaired, and track the use effect of the tool. A professional tool grinding center should also continuously study the experience in order to make the tool better and more professional.
Here are 6 problems that cannot be ignored from the perspective of the tool itself, grinding equipment, testing equipment, grinding standards, and grinding mechanics.
Tool and cutter material
Tool materials in tool regrinding are high-speed steel, powder metallurgy high-speed steel, tungsten carbide, PCD, CBN, cermet and other superhard materials. High-speed steel cutter feature sharp and tough. Tungsten carbide tools have high hardness but poor toughness. The density of the tungsten carbide tool is larger than that of a high-speed cutter. They are the main materials of drill bits, reamers, milling cutters, and taps. The performance of powder metallurgy high-speed steel is between the above two materials, mainly used for manufacturing rough milling cutters and taps.
Because the precision of high-speed steel tools is relatively low, and the regrinding requirements are not high, and the price is not high, so many manufacturers have their own tool workshop to repair them. However, tungsten carbide often needs to be sent to the professional grinding center. According to the statistics of some tool grinding centers in China, more than 80% of the tools sent for repair are tungsten carbide tools.
Tool and cutter grinding machine
Since the tool materials are very hard, it is usually possible to change the shapes by grinding. There are several types of tool grinding machines in the manufacture and regrinding of the tool.
- Notch grinder: for grinding the groove or back of the tool such as drill bits and end mills.
- Grinding machine for angle: for grinding the conical top angle( or eccentric rear angle) of drill bits.
- Grinding machine for chisel edge: correct the chisel edge of the drill bits.
- Manual universal tool grinding machine: for a cylindrical, groove, back, top angle, chisel edge, plane, rake face, and etc. used for small quantities and complex shapes tool.
- CNC grinding machine: It is usually five-axis, and the function is determined by software. It is usually used for regrinding large quantities, high precision, but not complicated tools such as drill bits, end mills, reamers, and etc. The main suppliers are from Germany, Switzerland, the USA, Australia, and Japan.
Tool and cutter grinding wheel
- Abrasive grain
Grinding wheels with different materials are suitable for grinding tools made by different materials. The grain size of abrasive required for different parts of the tool is also different to ensure the best combination of cutting edge protection and processing efficiency.
Alumina: for HSS tools. The grinding wheel is cheap and easy to true to different shapes and for grinding complex tools( fused alumina).
Silicon carbide: used for truing CBN and diamond grinding wheels.
CBN grinding wheel(cubic boron carbide): for HSS tools. high price but durable.
Internationally, the grinding wheel is represented by B, such as B107, which represents the grain diameter of abrasive.
Diamond grinding wheel: used for grinding HM tools, high price but durable
The grinding wheel is represented by D, such as D64, which represents the grain diameter of abrasive.
In order to grind the different parts of the tool, the grinding wheel should have different shapes.
Plane grinding wheel(1A1): for grinding top angle, outer diameter, back, and etc.
Disc grinding wheel(12V9, 11V9): for grinding spiral groove, main and auxiliary cutting edges of milling cutter, trimming chisel edge and etc.
After a period of usage, the grinding wheels need to be trued( including plane, angle and fillet R).
Tool and cutter grinding standard
Whether or not you have a grinding standard of the tool is a measure of whether the grinding center is professional. In the grinding standard, it regulars the technical parameters of cutting edge of the different tools when cutting different materials, including cutting edge inclination angle, apex angle, rake angle, rear angel, reverse edge, chamfering and etc.
The difference between HM drill bit and HSS drill bit:
HSS drill bit: The apex angle is usually 118, sometimes more than 130. The cutting edge is sharp. The precision( edge height difference, symmetry, circumferential runout) is relatively low. There are many ways to true the chisel edge.
HM drill bit: The apex angle is usually 140, the drill for the straight groove is usually 130, and the three-edged drill is usually 150. The edge and the tip( on the edge) are not sharp and are often passivated, or called inverted and chamfered. They require high precision. The chisel edge is often trued into an S-shape for chip breaking.
The rear angle of the edge is very important for the tool. The rear angle is too large, the edge is easy to smash. When the rear angle is too small, the friction is too large and the cutting is unfavorable.
The rear angle of the tool varies with the material being cut, type of tool, and the diameter of the tool. In general, the rear angle decreases as the diameter of the tool increases. In addition, if the material to be cut is hard, the rear angle is smaller, otherwise, the rear angle is larger.
Tool and cutter testing equipment
Tool inspection equipment has 3 types, toolset, projector and universal tool measuring instrument. The tool setting instrument is mainly used for tool setting( such as length) of CNC equipment such as the machining center. It is also used for inspecting parameters such as angle, radius, and step length. The projector is also used for inspecting parameters such as angle, radius, and step length. However, the above two usually cannot measure the rear angle of the tool. The universal tool measuring instrument can measure most of the geometry of the tool, including the rear angle.
Therefore, the tool professional grinding center should be equipped with a universal tool measuring instrument.
The best equipment also requires personnel to operate, and the training of the grinding technician is one of the most critical aspects. Strengthen the skills training for mechanics and improve the grinding skills of mechanics.
In the actual tool and cutting grinding process, these 6 factors complement each other, and anyone of the links may indeed lead to poor tool grinding quality, we should pay attention to it.