1. How is deep hole generally defined in the industry?

In the mechanical manufacturing industry, the cylindrical hole with the hole depth more than 10 times of the hole diameter is generally called a deep hole. Deep holes can generally be divided into general deep holes, medium deep holes and special deep holes according to the ratio of hole depth to hole diameter (L/D).

(1) L/D=10-20, belonging to general deep hole. It is often processed with an extended fried dough twist drill on a drilling machine or lathe.

(2) L/D=20 ～ 30, belonging to medium deep hole. It is often machined on a lathe.

(3) L/D=30~100, belonging to special deep hole. The deep hole drill must be used for processing on the deep hole drilling machine or special equipment.

2. Difficulties in deep hole processing

(1) Limited by the hole diameter, the cutter bar has small diameter and large length, resulting in poor rigidity and low strength. It is easy to generate vibration, ripple and taper during cutting, which will affect the straightness and surface roughness of deep holes;

(2) When drilling and reaming, it is difficult to input the cooling lubricant into the cutting area without using special devices, which reduces the tool durability and makes it difficult to remove chips;

(3) In the process of deep hole processing, it is not allowed to directly observe the cutting condition of the tool, but only to judge whether the cutting process is normal by working experience to listen to the sound of cutting, look at the chips, touch the vibration and workpiece temperature, and watch the instrument (oil pressure gauge and electric meter);

(4) It is difficult to remove chips. Reliable means must be used to break chips and control the length and shape of chips to facilitate smooth removal and prevent chip blockage;

(5) In order to ensure the smooth processing of deep holes and meet the required processing quality, the internal (or external) chip removal device of the tool, the tool guide and support device and the high-pressure cooling and lubricating device should be added;

(6) The poor heat dissipation condition of the tool and the increase of cutting temperature reduce the durability of the tool;

3. Type, scope of use and working principle of deep hole drill

The deep hole drill can be divided into two types according to the chip removal mode: external chip removal and internal chip removal. The external chip removal includes gun drill and integral alloy deep hole drill (with cooling hole and without cooling hole);

The internal chip removal is divided into BTA deep hole drill, jet suction drill and DF system deep hole drill.

4. Precautions for deep hole processing

(1) Key points for deep hole processing: the coaxiality of the centerline of the spindle and tool guide sleeve, tool bar support sleeve, workpiece support sleeve, etc. shall meet the requirements; The cutting fluid system shall be smooth and normal; There shall be no center hole on the processing end face of the workpiece, and drilling on the inclined plane shall be avoided; The chip shape shall be kept normal to avoid the generation of straight strip chips; The through-hole shall be processed at a high speed. When the drill bit is about to drill through, the speed shall be reduced or the machine shall be stopped to prevent damage to the drill bit.

(2) Cutting fluid for deep hole machining: a large amount of cutting heat will be generated in the process of deep hole machining, which is not easy to spread, and sufficient cutting fluid needs to be supplied to lubricate and cool the tool. Generally, 1:100 emulsion or extreme pressure emulsion is selected. When high machining accuracy and surface quality or processing toughness materials are required, extreme pressure emulsion or high concentration extreme pressure emulsion is selected. The kinematic viscosity of cutting oil is generally 10~20cm2/s (40 ℃), and the flow rate of cutting fluid is 15~18m/s; Select cutting oil with low viscosity when the machining diameter is small; For deep hole machining with high precision, the cutting oil ratio can be 40% extreme pressure vulcanized oil+40% kerosene+20% chlorinated paraffin. The pressure and flow rate of cutting fluid are closely related to the hole diameter and processing method

(3) In order to ensure the service life of the tool, it is better to adopt automatic tool feeding.

(4) If the guide elements in the liquid feeder and movable center support are worn, they should be replaced in time to avoid affecting the drilling accuracy.