Application of carbide bit grinding and coating technology

At present, the products processed in the workshop are HOWO passive bevel gears, with 16 φ 17, the material of which is sae8822h. The hardness of the raw material of the product is hb165-190, and the viscosity is large due to the presence of certain Ni elements. According to the characteristics of the workpiece, it is urgent to select the appropriate drill bit, optimize the cutting parameters and improve the machining efficiency.

Selection of bit materials

According to the processing characteristics of the material, the drill bit is required to have the following characteristics: the hardness of the drill bit must be greater than that of the workpiece to be processed; Since the drill bit bears great torsional and axial forces when machining the workpiece, it must have sufficient strength and toughness; Due to the good toughness of the material to be machined, the cutting edge is required to be sharp enough during cutting, so the tool material must have sufficient wear resistance, so as to reduce work hardening; Due to the high chemical properties of the workpiece, the affinity between the tool material and titanium alloy is required to be poor to avoid tool sticking and drill breaking caused by stroke diffusion.

At present, there are many kinds of materials suitable for cutting tools, including tool steel, cemented carbide, superhard materials, etc.

At first, we tried to use ordinary high-speed steel bit for coating test. The ordinary high-speed steel bit is cheap. When the coating technology is adopted, the friction coefficient between the tool and the workpiece can be significantly reduced and the tool life can be improved. However, due to the high rotating speed of the machine tool and the insufficient strength of the drill bit used, the drill bit was broken during the processing, and the effect was not ideal.

Cemented carbide is a cutting tool material developed by * and is suitable for rough and finish machining of most materials, including steel, cast iron, special materials and plastics. For this reason, it is decided to use integral cemented carbide bit.

Determination of parameters for bit grinding

1. main auxiliary plane of fried dough twist drill

The main auxiliary planes of fried dough twist drill are base plane, cutting plane, middle section and column section.

If the auxiliary motion is not considered, the base surface of any point on the main cutting edge of the fried dough twist drill is variable due to the structural characteristics of the fried dough twist drill.

The cutting plane of any point on the main cutting edge is the plane containing the cutting speed direction of the point and tangent to the machining surface of the point. The cutting plane is perpendicular to the base plane, and the cutting planes of each point on the main cutting edge are different. The cylinder section at any point on the main cutting edge is a cylindrical surface which passes through the point and takes the center line of the drill bit as the center line. Different cylinder sections on the main cutting edge are cylindrical surfaces with different radii.

2. selection of main geometric parameters of fried dough twist drill bit

The main geometric parameters of the fried dough twist drill bit include the selection of the top angle of the bit, the selection of the rake angle and rake angle of the cutting edge of the bit, the analysis of the influence of the helix angle of the bit on the service life of the bit and the related treatment of the cutting edge.

The tip angle of the bit determines the chip width and the rake angle of the bit. When the drill bit diameter and feed rate are fixed, increasing the top angle will narrow the iron filings and reduce the load on the unit cutting edge. The vertex angle has a great influence on the rake angle, and increasing the vertex angle correspondingly will improve the cutting conditions at the drill center. The vertex angle affects the direction of chip flow. According to the relevant tool design data, combined with the characteristics of low hardness but high viscosity of the processed products, the top angle of the drill bit is selected as 140 °.

The rake angle of a fried dough twist drill is determined by other geometric parameters of the drill. When the machine tool is used for high-speed cutting, the rake angle has little effect on the cutting deformation and cutting force, and the tool tip strength can be enhanced when the rake angle is small. After the current angle is determined, the larger the rear angle is, the sharper the cutting edge will be, but the wedge angle will be reduced accordingly, which will affect the tool strength and heat dissipation area. For this reason, the bit back angle is chosen to be smaller and is taken as 8 °.

3. analysis of influence of bit helix angle on bit life

According to the shape characteristics of the fried dough twist drill, the helix angle of each point on the cutting edge changes, and the helix angle directly affects the rake angle of the main cutting edge. The larger the helix angle is, the sharper the cutting edge will be and the faster the cutting will be. Otherwise, severe work hardening will be caused and the cutting edge will be worn quickly. According to the relevant tool design data, the helix angle of 30 ° can meet the use requirements and facilitate mass production.

4. relevant treatment of cutting edge

The treatment of cutting edge includes horizontal edge correction, chamfering and chamfering. According to the material to be machined, the machining performance of the machine tool, the machining parameters and the working conditions of the fixture, the cutting edge of the drill bit is properly passivated to improve the drilling performance of the drill bit and reduce the tool wear.

Application of coating technology

In the case of constant cutting parameters, in order to improve production efficiency and reduce production costs, it is becoming a trend to use coating technology to reduce tool wear and improve tool durability.

The tool coating is a thin layer of refractory metal or nonmetallic compound with good wear resistance on the surface of cemented carbide or high speed steel (HSS) with good strength and toughness by vapor deposition. As a chemical and thermal barrier, the coating reduces the diffusion and chemical reaction between the tool and the workpiece, thus reducing tool wear. Coated tools have the characteristics of high surface hardness, good wear resistance, stable chemical properties, heat and oxidation resistance, low friction coefficient and low thermal conductivity.

The number of drill bits processed after coating has been significantly increased, and the single piece cost has been greatly reduced.