Important points of how to grinding tools

Important points of how to grinding tools

1.Tool materials

Common tool materials: high-speed steel, powder metallurgy high-speed steel, carbide and PCD, the CBN, metal ceramics and other super-hard materials in tool regrinding. High-speed steel tool have good sharp, good toughness, carbide tool have better 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  tools are less sensitive to collision because of the good toughness of the material. However, carbide tools are hard and brittle, very sensitive to collision, and 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 fall.

Most of high-speed steel tools are relatively low precision, 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 a professional regrinding centre for regrinding. According to the statistics of some domestic tool regrinding centres, more than 80% of the tools sent for regrinding are carbide tools.

2.Tool Grinding Machines

Since the tool material is very hard, so, generally only grinding can be used to change its shape. There are several kinds of tool grinding machines commonly used in the manufacture and regrinding of tools:

2.1. Groove grinding machine: grinding the groove or back of drills, end mills and other tools.

2.2. Grinding top angle machine: grinding the tapered top angle (or eccentric back angle) of drills.

2.3. Cross-Cutting machine: correct the cross-cutting edge of the drill.

2.4. Manual universal tool grinder: grinding cylindrical, groove, back, top angle, transverse edge, flat surface, front face and so on. Commonly used in a small number of complex shape of the tool.

2.5.CNC grinding machine: generally five-axis linkage, the function is determined by the software. Generally used for regrinding tools with large quantity and high precision requirements, but not complicated, such as drills, end mills, reamers and so on.

3.Grinding Wheel

3.1. Grinding Grain

Grinding wheel grits of different materials are suitable for grinding tools made of different materials. Different parts of the tool require different grit sizes to ensure the best combination of edge protection and machining efficiency.

Aluminium oxide: for grinding HSS tools. The wheels are inexpensive and easy to modify to different profiles for resharpening complex tools (corundum type).

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

CBN (Cubic Boron Carbide): for grinding HSS tools.

Diamond: Used for grinding HM tools.

3.2.Shape

In order to facilitate the grinding of different parts of the tool, the grinding wheel should have different shapes. The most commonly used ones are:

Parallel grinding wheel (1A1): to grind top angle, outer diameter, back, etc.

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

The grinding wheel needs to correct its shape (including plane, angle and fillet R) after a period of use. The grinding wheel must often use a cleaning stone to clean out the chips that fill in between the abrasive grains in order to improve the grinding capacity of the grinding wheel.

4.Sharpening standard

Whether there is a good set of tool resharpening standards is judging a resharpening centre is professional or not. Sharpening standards generally stipulate the technical parameters of cutting edges of different tools when cutting different materials, including camber, top angle, front angle, back angle, chamfering, chamfering and other parameters (in carbide drills, the process of dulling the cutting edge is called "chamfering", and the width of the chamfering edge is related to the material to be cut, which is generally in the range of 0.03- 0.25 Mm). 0.25 Mm. The process of chamfering on the edge (tip point) is called "chamfering".

Difference between HM drill and HSS drill

HSS drill: top angle is generally 118 degrees, sometimes more than 130 degrees; sharp cutting edge; relatively low requirements for precision (edge height difference, symmetry, circumferential runout). 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.

Rear Angle

The back angle of the cutting edge 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 unfavourable.

The rear angle of the tool with the material to be cut and the type of tool, tool diameter is different. Generally speaking, the rear angle decreases as the diameter of the tool becomes larger. In addition, if the material to be cut is hard, the rear angle is smaller, otherwise, the rear angle is larger.

5.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 CNC equipment such as machining centres to prepare for tool setting (e.g. length, etc.), but also used to detect the angle, radius, step length and other parameters; the function of the projector 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 the vast majority of geometric parameters of the tool, including the rear angle.

6.Regrinding technicians

The best equipment requires personnel to operate it, and the training of regrinders is naturally one of the most critical aspects.