The choice of drill bits for metal

let’s Start with the fact that metal drills are made of HSS high-speed steel (R6M5, for example the best Soviet or Р6М5Ф8) and hard alloy (in common WIN), when using carbide drills necessary cooling and the desired minimum axial vibration. In my memory, drill ø 5 mm can withstand a deflection of the axis at 0.3 mm then destroyed. Brought from HSS for metal less critical of the coolant and the machine. Therefore, in the case of use of metal drills for CNC machine better to use a drill of a hard alloy-they are much heavier and darker if uncoated. For the machine without the CNC to use a drill bit of high speed alloy.

 

the Geometric parameters of metal drills

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the Influence of the geometry of drill bits for metal cutting process

Geometry of drill bits for metal

 

Angle of elevation of the screw groove of the drill

When you increase the angle of the helix

effective power decreases

decreases the rigidity of the drill.

Improved chip removal

 

Length of the working part of drill

the working part of the auger facilitates the removal of chips and coolant. Too long working part reduces the stiffness of the structure, and too short degrades the chip and could cause damage to the instrument.

 

the apex Angle of drill

Optimum choice of the angle depends on the properties of the processed material and affects the value of axial forces.

decrease

reduced axial cutting force

processing of the material with low hardness, aluminum

increase

the Increase in the resistance of axial cutting force

the Increase in the probability of the formation of agnail

Machining of workpieces with high hardness

the Increase in torque

 

the Width of the ribbon drill

Ribbons drills serve as guides. A smooth blend of the back of the tooth and the ribbon reduces the stress concentration caused by the drilling process.

decrease

the reduced friction between the drill and the workpiece

the Increase in drill withdrawal

increase

the reduced friction between the drill and the workpiece

Reduction of drill withdrawal

 

Width drill

the hardness of the drill depends on the width of the jumper. For effective centering when drilling a sufcient width of the jumper. At the same time, a broad jumper increases the cutting forces. The width of the cutting edge more than 50% defines the axial component cutting forces.

decreasing

Reduction of cutting force

the Decrease in the rigidity of the drill

chip

increase

the Increase of cutting force

increase the rigidity of the drill

a Bad chip

Machining of workpieces with high hardness

 

the Use of coolant when working metal drill bit

Application of cutting fluid to drill bits for metal

•monitor sufficient coolant to the cutting zone

•Normal pressure : 3~5 kg/cm2, the coolant flow : 2-5 l/min

Steps to increase the life of drill bits for metal

 

To increase the lifetime need reface of the drill even at small chips or wear and tear.

the Total size of the shear layer at regrinding the rear surface must not exceed 1.5 mm.

the cracks eliminates the possibility of sharpening.

When you drill sharpening it is recommended to use grinding machines with CNC.

 

the Process of sharpening drills on metal

Sharpening drill bits for metal

Training
to Determine the need for regrinding.
to Check for chipping and wear.
If the chip is large enough to remove the rough sharpening.

Operation sharpening
to Install and secure workpiece in Chuck.
Chuck Runout should not exceed 0.02 mm.

Remove the bumps with grinding wheel
Please note the deviation of the axis of the jumper and the drill axis must not exceed 0,03 — 0,08 mm
the drill Axis must be tilted at 343 — 40= relative to a tangent of the grinding wheel

Sharpening drill bits for metal

Final sharpening is done with diamond needle files. Initially you have to handle the plane throughout the length of the cutting edge. Then finally finish using diamond paste.

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