Drill bushings can play an important supporting role in the machining of holes in parts. An in-depth understanding of the use of drill bushings allows technicians to better use them for machining operations, and at the same time to properly handle the drill bushes in case of failure, avoiding some improper use and treatment methods, and effectively improving production efficiency.

About 70% of machining contents of automobile engine and gearbox need to select drilling, reaming, reaming and boring and other different processing forms, and use separate or combined processing to complete. The hole processing of parts due to the difference in equipment (CNC machining center and special machine processing production line) determines that some of the tools cannot be separated from the auxiliary support of the drill sleeve when machining special holes. In practical production, the rational use of drill bushings is a key point that operators and technical support personnel of machining production lines must pay attention to. Familiarization with the correct use of drill bushings can ensure that the holes in the machined parts meet the requirements of the technology. Conversely, drill bit breaks, tool diameters accelerate wear, drill deflections, post-machining, and replacement drill bushing times can occur. Ultimately, it directly affects the starting rate of the production line. Therefore, the technician must understand and be familiar with the relevant knowledge and control methods of the drill sleeve.

The role of drill sleeve

The main role of the drill sleeve is to control the position and size of the tool and the feed direction of the guide tool, so as to meet the technical requirements of the higher hole tolerance of the machining hole and drilling on the inclined surface and the curved surface (see Figure 1). When the positioning accuracy of the fixtures on the equipment processing parts is not ideal, sometimes the drilling shaft can be deliberately changed the offset of the spindle to achieve the technical requirements of the machining hole position, which is a premise of the time-consuming adjustment equipment. Emergency methods. In addition, drill sleeves on individual stations of special planes can also perform error proof verification of diameter tools. That is, the line operator inserts a new tool into the drill collar hole before replacing the drill bit or reamer tool to verify whether it can Through this, the risk of overshooting the tool diameter is controlled.

Fig.1 Drill bushing device for machining inclined oil holes on tappet holes

Drill sleeve material

According to the difference of the processing objects and the material of the tool, generally the drill sleeve will use hard alloy or alloy steel materials; the drill sleeve of high-speed steel drill bits or reamer tools will generally select the alloy steel material or hard alloy material; and the hard alloy Drill bushings for drill bits or reamer knives will choose carbide materials. From the point of view of the material of the drill sleeve, although the final hardness has been reached (usual hardness of the alloy steel drill sleeve after heat treatment is about HRC58-65, and the hardness of the cemented carbide drill sleeve is higher, it can reach 89-93HRA). However, the drill sleeve will still fail if it is used for a long time or if it is used improperly.

The relative position of the drill sleeve and the machining object

The gap distance between the drill sleeve and the machining surface is determined according to the machining hole, the machining method, and the form of the machining tool. Some drilling bushes have a certain clearance with the machining surface after positioning, and some drill bushings are positioned after contact with the machining surface without gaps.

1. Non-contact longitudinal positioning

The positioning method is when the position of the processing hole is relatively low, the longitudinal dimension of the processing object is relatively large, the rigidity of the drill bit is high, and the longitudinal position of the drill sleeve is a fixed positioning device. Faces often choose to have a certain gap distance. This is the positioning method for most drill bushings.

2. Contact-based longitudinal positioning

In this type of mechanism, the positioning of the drill sleeve often uses spring devices or hydraulic/pneumatic devices to ensure the actual contact between the drill sleeve and the processing object. This device can not only ensure that the internal cooling pressure is in a more ideal state, but the positioning on the inclined plane or the curved surface can further reduce the tool offset during the initial machining and ensure the final position of the machining hole. The following form needs to choose the vertical contact positioning method:

(1) Particularity of the surface of the processing object

Machining holes with high requirements of positional position, machining objects are inclined or curved holes (such as inclined oil holes in cylinder head tappet holes), and some are two-way offset machining object holes (such as the inclined oil hole on the crankshaft journal). ) At this time, it is often the case that the positioning of the drilling sleeve and the surface of the machining contact or the positioning of the drilling sleeve with a small clearance is often selected. This can ensure that the position of the hole in the tool processing is controlled within the scope of the process requirements.

(2) Internal cold processing

According to the use of the tool, it determines the longitudinal positioning of the drill sleeve and the machining object. There is no internal cooling tool processing, generally choose a certain gap between the drill sleeve and the processing surface; while the high-pressure internal cooling drill tool, often choose the drill sleeve and the processing surface longitudinal contact or seal state. When the contact and sealing state is selected, although the longitudinal positioning of the drill sleeve needs a fixed frame and a complicated expansion device is added, the pressure of the high pressure cooling in the tool can be ensured, so that the chip can be smoothly discharged out of the drill sleeve and the drill sleeve can be avoided. When there is clearance in the processing surface, because the high-pressure internal coolant directly releases pressure in the gap, the cooling fluid reduces the force that pushes the chips in the drill sleeve to discharge backwards, causing the chips to clog in the chip chip flutes, and in severe cases, causing the drill bit to resist rising. And break the tool.

Drill sleeve failure

The failure of the drill sleeve means that the drill sleeve cannot meet the supporting support it should assume after a certain period of time. Therefore, the production line operator should pay attention to the failure phenomenon of the drill sleeve in actual production. Its common failure has the following three aspects:

Drill hole wear

The hole wall wear of the drill sleeve is due to the long-term relative friction of the secondary cutting edge of the drill or the reamer and the borehole wall of the drill sleeve, or the short-term unilateral sharp wear, forming the wear of the entire hole wall (see Figure 2) or a certain range of hole wall wear. The long use time of the drill sleeve directly leads to the increase of the inner diameter size of the drill sleeve. Once the bore diameter becomes larger, it will directly cause the hole size and the machining aperture of the drill processing object hole to be out of tolerance. One reason for the unilateral wear of the drill bushing is that the position of the machining hole in the front process of the part is greater than the concentricity of the machining tool position in the following process; the other reason is that the coaxiality of the spindle and the drill bushing is not Well caused. In actual production, due to the slight displacement of the spindle on the special engine power head and the drill sleeve above the clamp, this difference is often due to the difficulty in adjusting the equipment, and only by replacing the drill sleeve to ensure the position of the machined parts, and finally Causes the drill sleeve to wear unilaterally.

Figure 2 drill hole wall wear

2. Partial wear of drill collar wall

(1) Partial unilateral wear of drill sleeve

Auxiliary drill sleeves used when machining the inclined oil holes of camshafts and crankshafts have a certain angle of inclination during machining because the drill bit tools and the machined surface do not feed perpendicular to the tangential direction. Although some drill bushes have also achieved the longitudinal positioning with the surface of the machining hole, due to the uneven force in the drilling process, one side of the drill bushing wall is subjected to a large force, which directly leads to the wall of the drilling bush. While accelerating wear, there is a potential risk of breakage of the drill bit as wear becomes worse. When the gap value set between the outlet surface of the drill sleeve and the machining surface is unreasonable, the unilateral wear of the drill sleeve is more serious, and the small diameter drill bit tool is more easily broken. For example, some drill heads for tapping hole drilling holes of single-cylinder cover production line have relatively large gaps between the exit end face of the drill sleeve and the tap hole hole wall, reaching as much as 6mm, so that the 4mm drill bit is used to process the inclined oil hole. The phenomenon of broken drilling occurred frequently and also accelerated the unilateral wear of the local hole wall of the drill sleeve (see Figure 3).

Fig. 3 Unilateral wear of local hole wall of drilling sleeve

(2) Drill sleeve wear at the intersection

When the concentricity of the position of the drilling sleeve and the position of the main shaft is poor, the bit tool processing will cause local wear of the relative position of the drill sleeve inlet and outlet after machining for a period of time. As shown in FIG. 4 , since the drill bit cutter is different from the drill collar, the drill bit touches the left hole wall when entering the drill sleeve, which causes the straightness of the drill bit to change. When the drill bit continues to feed, due to the clearance between the drill bit and the drill sleeve, it also causes the drill bit to hit the right side of the drill sleeve at the exit of the drill sleeve. In this way, the verticality of the processing hole is not only poor, but also the use time. The length also results in the wear of the opposite hole wall locations in the inlet and outlet bore walls of the drill sleeve. At the beginning of this phenomenon, the processing hole is still within the allowable range of the process. However, over time, the position of the processing hole will have an overshoot phenomenon. Therefore, the method of replacing the drill sleeve can only be used to satisfy the position of the processing hole. Claim.

Figure 4 Cross-position wear of drill sleeve

3. Drill sleeve seal wear

Some drill sleeves are also assembled on the top with a seal ring. The wear of the seal ring of this combination drill sleeve directly affects the pressure drop of the system coolant supply during tool processing, and affects the discharge of chips during the cutting process. Therefore, the inspection and timely replacement of the drill collar seal ring is a work point that needs attention. The seal ring in the drill sleeve assembly shown in FIG. 5 is also a failure concern in the use of the drill collar.

Figure 5 Drill collar seals

Drill bushing replacement principle

During the actual use of the drill sleeve, the hole wall of the drill sleeve and the diameter tool rub against each other. When the machining technology requirements cannot be met, the new drill sleeve needs to be replaced. The principle of replacement of drill bushings depends on the failure situation of the drill bushings. The common types are as follows:

1. Drilling hole diameter excess scrap

The drilling hole diameter of the drilling sleeve must follow certain standard manufacturing requirements during the manufacturing process, that is, when drilling, reaming, reaming, and reaming. When some drill bushes are used for a long time and the inner diameter becomes larger, which causes the hole size of the machining object to be excessive or the diameter of the machining hole becomes larger, such drill bushes shall be scrapped and replaced.

2. Drill bushing bore wall has serious local wear

Although some special drill sleeves do not have all the wear of the boreholes, the drill bit breakage has been caused by the wear of the partial boreholes. Therefore, the new drill sleeves should also be replaced in time.

3. Drill sleeve service life expires

Some drill bushes are based on the service life in actual production. Although the positions of the machined parts holes have not yet exceeded the position, but they have reached the set service life, such drill bushes should also be replaced normally.

4. Breakage of drill sleeve and stuck die

The breakage of the drill bit directly affects the damage of the drill sleeve, chipping, and the broken drill stuck in the drill sleeve, so that the drill sleeve has to be replaced again.

Drill sleeve service life setting

The service life of the drill sleeve is set to better control the common failure phenomena during use. Generally, the setting of the service life of the drill sleeve is the same as that of other tool-assisted tools and the consumable tool. Certain methods can also be used.

First, it can be controlled by the equipment supplier's recommendation value; secondly, it is set according to the empirical value in actual production. However, there are also differences between the set service life and the service life of the tool. The tool can directly determine whether the life setting is reasonable from the status of the processing object and the degree of wear of the tool. The failure of the drill sleeve is due to the longer use time. , it is often not noticed. In addition, it is difficult to observe the influence of the drill sleeve on the tool and the satisfaction degree of the processed part requirements in actual production. Therefore, people often need to determine whether it can be based on the measurement result of the shape and position size of the processing object and the periodic inspection and judgment of the drill sleeve. Continue to use, through multiple cycles of data acquisition, can be obtained under normal conditions of service life.

The normal hole wall wear of the drill sleeve can be ensured by the normal service life setting, which is set by the shape and position accuracy of the machining hole and the processing concentricity required to meet the next procedure. The wear of some holes in the drill collars is a potential risk that is not easily detected. Therefore, the actual production must implement the relevant processing results to determine the wear of the drill sleeve and reduce the phenomenon of emergency replacement of the drill sleeve. If the degree of wear of the drill sleeve is predicted by the positional degrees of the processed holes before and after processing the parts; visually measure the coaxiality of the processing of the drilled holes and the reamer processing to judge the wear of the drill sleeve and periodically check the actual wear of the drill sleeve. Wait. At present, in actual production, drill bushes are often replaced based on the degree of hole machining and frequent occurrence of broken drills. Therefore, people should choose the preventive PM time, use the planned PM time to replace the non-planned replacement drilling time, and use this reasonably set PM verification frequency to achieve the purpose of controlling the normal service life of the drill sleeve.

Conclusion

Drill bushing is the main auxiliary tool for the hole-making tool processing hole of the machining plane production line. The reasonable use of the drill bushing can be summarized by certain rules. The drill sleeve does not need to be replaced when the drill or reamer breaks, nor is it always available for long periods of time. Only in the premise of a certain standard use process can we ensure that the used drill bit or reamer cutter tends to be in a reasonable state, so as to ensure the shape and position accuracy requirements of the hole of the processed part, and at the same time make the drill sleeve use normally and reasonably.

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Luoyang Golden Egret Geotools Co., Ltd , https://www.xtcthermalspray.com