The five key issues in drilling and machining are recommended to be bookmarked!

As the most common tool in hole processing, drills are widely used in machinery manufacturing. As the most common tool, it is widely used in mechanical manufacturing, especially for the cooling device, power generation equipment, tube plate and steam generator parts such as hole processing, etc., the application surface is particularly wide and important.

First, the characteristics of drilling

Drill usually has two main cutting edges, processing, the drill in the rotation at the same time for cutting. The front angle of the drill is getting bigger and bigger from the center axis to the outer edge, the closer to the outer circle part of the drill, the higher the cutting speed is, the cutting speed decreases to the center, and the cutting speed of the rotating center of the drill is zero. The transverse edge of the drill is located near the axis of the rotary center, the vice front angle of the transverse edge is larger, there is no space for chips, and the cutting speed is low, thus generating a larger axial resistance. If the cross cutting edge is sharpened to DIN1414 type A or C, and the cutting edge near the center axis is positively angled, the cutting resistance can be reduced and the cutting performance can be significantly improved.

According to the shape of the workpiece, material, structure, function, etc., the drill can be divided into many types, such as high-speed steel drills (twist drills, group drills, flat drills), integral carbide drills, indexable shallow hole drills, deep hole drills, nesting drills and interchangeable drills and so on.

Second, chip breaking and chip removal

The cutting of the drill is carried out in the hole with narrow space, and the chips must be discharged through the cutting edge groove of the drill, so the shape of the chips has a great influence on the cutting performance of the drill. Common chip shapes are flake chip, tubular chip, needle chip, conical spiral chip, strip chip, fan chip, powder chip and so on.

The key to drilling processing - chip control

When the chip shape is inappropriate, the following problems will occur:

① Fine chips block the edge groove, affecting the drilling accuracy, reducing the life of the drill bit, or even break the drill bit (such as powder chips, fan-shaped chips, etc.).

② Long chips wrap around the drill bit, hindering the operation, causing the drill bit to break or preventing the cutting fluid from entering the hole (such as spiral chips, banded chips, etc.).

How to solve the problem of inappropriate chip shape:

①Chip breakage and chip removal effect can be improved by increasing the feed volume, intermittent feeding, trimming the cross edge, and installing a chip breaker, etc., respectively or jointly, to eliminate the problems caused by chips.

② Professional chip breaker drills can be used to make holes. For example, adding a designed chipbreaker to the groove of the drill bit breaks the chips into more easily removable shavings. The chips are smoothly removed along the grooves without clogging in the grooves. As a result, the new chipbreaker drill achieves much smoother cutting results than conventional drills.

At the same time, the short chips make it easier for coolant to flow to the drill tip, further improving heat dissipation and cutting performance during machining. And because the new chipbreaker penetrates the entire groove of the drill, it retains its shape and function after many sharpenings. In addition to these functional improvements, it is worth mentioning that the design strengthens the rigidity of the drill body, significantly increasing the number of holes drilled before a single resharpening.

Drilling Accuracy

Hole accuracy is mainly composed of hole size, positional accuracy, coaxiality, roundness, surface roughness and hole burrs.

Factors affecting the accuracy of the hole being processed when drilling:

① Clamping accuracy of the drill and cutting conditions, such as tool clamp, cutting speed, feed, cutting fluid, etc..

② drill size and shape, such as the length of the drill, the shape of the edge, the shape of the drill core.

③ Workpiece shape, such as hole side shape, hole shape, thickness, mounting status, etc.

1

Reaming

Hole reaming is caused by the oscillation of the drill bit during machining. The oscillation of the toolholder has a great influence on the hole diameter and the positioning accuracy of the hole, so when the toolholder is worn out seriously, it should be replaced with a new toolholder in time. When drilling small holes, it is difficult to measure and adjust the oscillation, so it is best to use the cutting edge and shank. It is better to use a thick shank and shank coaxial coefficient is good small edge diameter drill. When using resharpened drills, the cause of hole accuracy degradation is mostly due to the asymmetry of the back shape. Controlling the height difference of the cutting edge can effectively inhibit the hole expansion.

2

Hole roundness

Due to the vibration of the drill bit, the drilled holes are easily polygonal, and the hole wall appears like a rifling pattern. Common polygonal holes are mostly triangular or pentagonal. The reason for triangular holes is that the drill has two rotary centers when drilling, they vibrate at a frequency of 600 per interval exchange, the vibration is mainly due to cutting resistance imbalance, when the drill rotates a turn, due to the processing of the hole roundness is not good, resulting in the second turn of the cutting resistance imbalance, repeat the last vibration, but the vibration phase has a certain offset, resulting in the appearance of rifling patterns on the hole wall. When the drilling depth reaches a certain degree, the friction between the edge band prism of the drill bit and the hole wall increases, the vibration attenuates, the rifling line disappears, and the roundness becomes good. This hole type is funnel-shaped from the longitudinal section of the hole. For the same reason, cutting may also appear pentagonal, heptagonal holes and so on. In order to eliminate this phenomenon, in addition to the control of collet vibration, cutting edge height difference, back and edge flap shape asymmetry and other factors, should be taken to improve the drill bit