The characteristics of deep hole drilling processing analysis

Use the dry machining scheme is mainly the use of compressed air for chip removal and cooling, using atomized cutting fluid lubrication, its processing system is mainly composed of chip in deep hole drilling machine, air compressor, atomizer, gas-liquid mixing nozzle and so on, its working process is: air compressor to provide certain pressure (about 0.5 ~ 0.6 MPa) air, divided into two road at the exit, including all the way through the atomizer with a certain amount of cutting fluid vapor liquid mixture formation, in the nozzle and the compressed air to meet all the way, vapor liquid mixture into the intake device through the nozzle is accelerated and the cavity of jet, forming high pressure, high-speed atomized cutting fluid, finally through the passage between the drill pipe outer wall and wall of hole were sent to the cutting position of the drill bit, cooling, lubrication cutting tool and the chip back blow out from inside the drill pipe.

Due to the dry deep hole processing system adopts the atomized cutting fluid lubrication and cooling cutting tool and chip removal using compressed air cooling, both to overcome the traditional deep hole processing a large number of circulation use of cutting fluid in the many ills, greatly reduces the cutting fluid usage, and ensure that the guide block and the inner hole surface, cutting tool between before and after the knife and cutting fluid lubrication layer between the chip, at the same time cutting fluid in uniform endothermic atomization condition fully, lubrication, can play a better role. Using compressed air continuous chip can not only increase chip space (as opposed to the use of high pressure oil), and can quickly blow out the scraps from the cutting zone, shortens the time of chip heat transfer and can directly out of the part quantity of heat, reducing the temperature of cutting zone.

The design of the dry deep hole drill

Deep hole drilling tool is the design and development to achieve one of the key technology of the dry deep hole processing, directly affects the stability and reliability of the machining system, is the important guarantee of the deep hole processing smoothly. Tool geometric parameters on the stress of the cutting tool, chip breaker, durability, processing surface quality plays an important role; The cutting tool material the cutting efficiency and service life for the cutting tool, cutting tool and the affinity of workpiece plays a decisive influence. The dry deep hole processing of cutting characteristics with the traditional deep hole processing, so the requirements for the design of deep hole drill also has its particularity.

(1) the dry deep hole processing requirement for cutting tools

(1) due to the deep hole machining was conducted in closed condition, there is no loop cutting oil cooling and lubrication cutter, heat exchange, so the cutting zone temperature is higher, which requires the blade material must have high strength, hardness, and good heat resistance, red hardness and impact resistance, coefficient of friction between tool and chip at the same time should be as small as possible.

(2) in deep hole machining, the tool chip channel is longer, chip is not easy to expel, to adopt the air clearance and dry processing, this problem is more outstanding. Chip in order to ensure the smooth and rapid cooling, must increase export clearance, reduce the air resistance, speed up the chip, chip stay time.

(3) the deep hole processing using dry cutting liquid cooling chip removal and compressed air atomization, so chip shape is not too wide too long. In order to prevent the chip congestion, it is best to form small "C" type chip; To make the chip surface faster from the knife, cutting tool and chip interface shoulds not be too big, can be used for scrap blade or compulsory measures of chip breaker.

In view of the above requirements, our tool for the structural analysis and optimal design, make it meet the processing requirements of the system.

(2) the selection of cutting tool structure and optimization design

Deep hole machining tool chip type is mainly divided into outside and inside the chip removal. Outside chip way for gun drill system, suitable for processing small diameter (generally phi < 20 mm) deep hole. Internal chip removal way used to BTA system, the ejector drilling system and DF system. Ejector drilling system and the effect of DF system are the same, but because the ejector drilling system structure is complex, chip space is limited by a double pipe, so it has less use. DF system mainly using double feed device for chip to push, dual function, prompting them to expel. In chip removal effect at the same time, can reduce the pressure of seal, and improve the machining accuracy. BTA deep hole drill is divided into two single tooth and tooth, the applicability of the single tooth cutting tool aperture is from 6 ~ 25 mm, gear cutting tools are more suitable for machining large diameter deep hole (phi more than 25 mm).

In this experiment, we chose the single tooth bit BTA. On the bit structure design, considering the characteristic of the dry deep hole processing, on the basis of the traditional single tooth bit BTA section optimization design was carried out, mainly reflected in the following:

(1) the appropriate increase the space of blade with the hole wall between h (that is, the inlet gap) to reduce the air resistance, can quickly reach the compressed air and spray liquid lubrication and cooling cutting zone.

(2) the appropriate increase tool chip, chip form inverted conical mouth, make the chip can quickly and smoothly into the chip removal channel, not easy to block crumbs; At the same time at the entrance of chip formation "ejector effect", increase the speed of chip removal.

(3) increasing points crumbs blade, widen the chip breaker, implement mandatory points crumbs and chip breaker, and narrow the chip and is easy to break, help chip removal and cooling.

Some improvements were made in the tool geometric angles are also, main show is:

(1) the appropriate increase before the blade Angle between o, to reduce the tool rake face and chip of contact area, security and compressed air atomization cutting fluid can be fully into the cutting zone cooling and lubrication of cutting tool. Due to the blade mainly bear axial extrusion in cutting, to increase the blade strength, cutting edge Angle can be appropriately increased.

(2) after appropriate increase the blade Angle alpha o, to reduce the cutting tool knife after surface, the friction between machined surface and has also make it easier for cutting tool to cut into the workpiece, can reduce the tool wear, increase the tool life.

(3) increase the width of chip breaker sets and radius, lengthen the period of chip curling deformation, friction reducing chip and the rake face and chip on the impact of the chip breaker convex platform, make the chip smoothly through the chip breaker, at the transition fillet part increase additional deformation, lose some of the plastic materials, and then bend the top to the end, under the action of bending deformation, again the last chip breaker, which can reduce the chip deformation, the cutting heat, cutting force and friction force are changed, such as control chip formation small "C" type.

(3) the blade material selection

Many currently used in dry machining of cutting tool materials, such as ultra-fine grain cemented carbide, CBN, PCD, ceramic and metal ceramic, all kinds of coating hard cutting tool and so on, but most of these tool material applies only to ordinary dry milling and dry turning. At present domestic use more in deep hole processing is mainly welded deep hole drill, the blade material mainly adopts domestic blades such as YD15 and YG8, YW1, YT726, YT798 etc, these material chemical composition and physical properties of each are not identical, the applicable scope also have difference. We try to choose through cutting test is suitable for the dry deep hole processing of the blade material.

The cutting test scheme is: use the above five kinds of bit of blade material, the cutter structure and geometric parameters are the same respectively under the condition of the processing of 45 steel (tempering hardness HRC28), detection under the condition of the dry cutting all the stress of the cutting tool and chip, after measuring tool knife surface abrasion, inner hole surface quality, etc., choose the most suitable for processing of 45 steel and dry cutting tool materials.

Using the cutting test conditions as follows: processing diameter: 20.2 mm, workpiece length: 1000 mm, the spindle speed v = 800 r/min, tool axial feeding f/r = 0.01 mm, cutting fluid, Germany Aaron emulsion number 5.

Deep hole drill bits of various blade material after cutting performance and outer profile cutters wear as you can see, in the deep hole drill of 5 kinds of blade material, minimum value YD15 knife after surface abrasion, the axial force, torque and inner hole surface roughness value is minimum; The second is YG8. Reflect YD15 blade has higher heat resistance and good wear resistance, good processing stability and processing quality. Therefore, YD15 fit in with the class of 45 steel workpiece materials and dry deep hole processing; The processing effect of YG8 relative somewhat difference; Due to severe wear, and several other materials are not suitable for the dry deep hole processing. Test result in accordance with the cutting tool material performance is: YD15 good red hardness, good wear resistance, high bending strength, high temperature alloy material is especially suitable for processing. In addition, as can be seen from the machining process, the dry deep hole processing system of chip removal effect is good, almost no chip blocking phenomenon occurs, and scraps discharge temperature is low (no burning thermal), is silvery white, atomization and cooling effect is good, can satisfy the requirement of the dry deep hole processing.

The dry deep hole processing and performance comparison with traditional deep hole processing

YD15 blade can be determined through the analysis of the test material is suitable for medium carbon steel and the dry deep hole processing. But its processing performance and tool life compared with wet deep hole machining if there is a difference, will be the dry deep hole processing technology can obtain the key to popularization and application. To this end, we conducted a comparative cutting test, namely under the condition of the traditional deep hole processing, using YD15 and YG8 deep hole drill drilling (cutting tool geometry parameter) same same length of 45 steel workpiece (v = 800 r/min, f/r = 0.01 mm, 10 # machine oil cooling lubrication). Measured by the test data can be seen, processed by the traditional methods, the knife knife surface after wear and cutting force are smaller than in the dry machining conditions, suggesting that the dry processing when the friction between cutter and workpiece, tool and chip is larger than the traditional processing, the cutting fluid lubrication performance is poorer, it is associated with the use of cutting fluid. The dry process is adopted in the water-based emulsion (its atomization properties than cutting oil), and is used in the traditional processing cutting oil (its lubricity is better). It also determines the direction for our future research, namely the need to find a both good atomization, cutting fluid and has good lubricity. In addition, two kinds of processing way is not the amount of tool wear gap is very big, in the dry deep hole processing conditions can guarantee a certain number of tool life.

Will use two ways of processing the specimen cut open after the test, found the inner hole surface hardness is almost no difference, and the dry machining inner hole surface roughness value is smaller, the surface quality is better. It also suggests that in the dry deep hole processing, good cooling effect on the surface of the inner hole, the cutting temperature is not high. In addition, the adoption of special formula of emulsion, has a certain resistance to squeeze effect, therefore the drill guide block does not appear the tear and wear, also ensure the quality of the inner hole surface treatment.

conclusion

Based on the cutting test and comparative analysis of the results, the following conclusions:

(1) the design of the dry deep hole processing system can better complete deep hole machining process, and can obtain satisfactory processing effect, has certain actual application value.

(2) based on several common deep hole machining cutting tool material cutting test, determine the way in the dry deep hole processing, YD15 material is suitable for processing class of 45 steel workpiece materials, and has a good processing effect. For other workpiece material, also can be found through the test method for cutting tool materials.

(3) through the dry, wet two kinds of processing mode tool cutting performance test and analysis, it can be seen that the dry deep hole processing can achieve high tool life and good processing effect.

(4) for the dry question of tool wear in deep hole processing, can also adopt the method of low temperature air cooling or increase the coolant oil, to improve the effect of cooling and lubrication, reduce tool wear. Double spindle machining center