The so-called hard alloy is tungsten carbide powder as the matrix, cobalt powder as binder by pressure, sintering. It usually contains 94% tungsten carbide and 6% cobalt. Because of its high hardness, very wear-resistant, has a certain strength, suitable for high speed cutting. But the toughness is poor, very brittle, in order to improve the performance of cemented carbide, some use a layer of 5 ~ 7 micron hard titanium carbide (TIC) or titanium nitride (TIN) on the carbide matrix chemical vapor deposition, so that it has a higher hardness. Some use ion implantation techniques to inject titanium, nitrogen, and carbon into the matrix to a certain depth, which not only improves hardness and strength, but also allows the injected components to move in when the bit is reground. Others use physical methods to generate a layer of diamond film on the top of the bit, which greatly improves the hardness and wear resistance of the bit.
Selection of drill material
According to the processing characteristics of the material, the drilling bit is required to have the following characteristics: the hardness of the drill bit must be greater than the hardness of the processed workpiece; Because drill bit is subjected to great torsional force and axial force when machining workpiece, it must have sufficient strength and toughness. Because the toughness of the processed material is good, the cutting blade is required to be sharp enough, so the tool material must have enough wear resistance, so as to reduce work hardening; Due to the high chemical characteristics of the workpiece, the affinity of the tool material and titanium alloy is required to be poor, so as not to cause the phenomenon of sticking knife and drilling caused by stroke diffusion.
At present, there are many kinds of materials suitable for cutting tools, including tool steel, hard alloy, super hard materials and so on.
At first, ordinary HSS drill bits were tried to be coated. Ordinary HSS drill bits were cheap, and when coated, the friction coefficient between the tool and the workpiece was significantly reduced and the tool life was improved. However, due to the high speed of the machine tool, the strength of the drill bit used is not enough, and the drill bit is broken in the process of processing, the effect is not ideal.
Cemented carbide is a newly developed tool material suitable for the rough finishing of most materials, including steel, cast iron, special materials and plastics. For this reason, it was decided to use a solid carbide bit.
Confirm the parameters of drilling bit repair and grinding
1. The main auxiliary plane of twist drill
The main auxiliary planes of twist drill are base plane, cutting plane, middle section and column section.
If the auxiliary motion is not considered, the base plane of any point on the main cutting edge of the twist bit is changed due to the structural characteristics of the twist bit.
The cutting plane of any point on the main cutting edge is the plane that contains the direction of the cutting speed of that point and cuts to the machined surface of that point. The cutting plane is perpendicular to the base plane, and the cutting plane at each point on the main cutting edge is different. The column profile of any point on the main cutting edge is a cylindrical surface made through the point and with the center line of the drill bit as the center line. The different column profiles on the main cutting edge are cylindrical surfaces of different radii.
2. Selection of main geometric parameters of twist drill bit
The selection of the main geometric parameters of twist drill bit includes the selection of tip Angle, the selection of forward and backward Angle of the bit cutting edge, the analysis of the influence of the screw Angle on the bit life and the related processing of the cutting edge.
The tip Angle of the bit determines the chip width and rake Angle. When the bit diameter and feed rate are constant, increasing the tip Angle will narrow the iron chip and reduce the load on the unit cutting edge. Tip Angle has a great influence on rake Angle. Correspondingly increasing tip Angle is beneficial to improve cutting conditions at drill center. Tip Angle affects the direction of chip outflow. According to the relevant tool design data, combined with the machining product hardness is not high, but the characteristics of large viscosity, the selection of the drill tip Angle of 140°.
The rake Angle of the twist drill is determined by other geometric parameters of the bit. In high speed cutting, rake Angle has little influence on cutting deformation and cutting force, and a smaller rake Angle can enhance tool tip strength. After the current Angle is determined, the larger the back Angle is, the sharper the edge will be, but the wedge Angle will reduce the influence of the tool strength and heat dissipation area. Therefore, the rear Angle of the bit was selected as a smaller 8°.
3. Analysis of the influence of bit screw Angle on bit life
It can be known from the shape characteristics of twist drill that the helix Angle of each point on the cutting edge is changed, and the helix Angle directly affects the front Angle of the main cutting edge. The larger the helix Angle, the sharper the edge, the more light cutting, otherwise it will cause serious work hardening phenomenon makes the blade quickly wear. According to the relevant tool design data, the screw Angle of 30° can meet the use requirements, and facilitate mass production.
4. Related processing of cutting edge
The cutting edge treatment includes cutting edge correction chamfering and cutting edge. According to the material to be processed, machine tool processing performance, processing parameters and fixture conditions, the cutting edge of the drill is passivated appropriately, improve the drilling performance of the drill, reduce tool wear.