Boring and reaming of the hottest deep hole

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Boring and reaming of deep holes

deep hole precision machining has always been a difficult problem in hole machining. It is an effective method to improve the effect of deep hole precision machining by designing new structure cutting tools and process system

we have developed a complete set of self-directed boring reamers and their process systems for the precision machining of the inner hole of the cylinder block made of 40Cr (quenched and tempered) steel, with a length of 2800mm, an aperture of 65+0.08mm, a surface roughness of Ra0.8 m and a straightness of 0.12mm. The production verification shows that the machining effect is good

1 self Guided Boring Reamer

the structure of self guided boring reamer is shown in Figure 1. The blade material used is yw1, which is pressed on the blade body with a wedge; The material of the guide body is T15 (hardened), and its outer circle is slightly smaller than that of the blade by 0.04 ~ 0.06mm. The cylindrical surface of the blade and the guide sleeve shall be ground to make its surface roughness at least one level higher than that of the hole wall after the workpiece is processed. There are bushings made of zqsn at both ends of the guide inner hole, and the inner hole of the bushing is clearance fit with the cutter body. After the knife body, guide sleeve, one-way thrust ball bearing and lock nut are assembled, but iron is the most common, the guide body and one-way thrust ball bearing are required to rotate flexibly without axial movement; Top the Boring Reamer on the deflector and check it with a dial indicator. The blade position and radial total runout should not be greater than 0.01mm, and the radial total runout when the guide body rotates around the cutter body should not be greater than 0.02mm

Figure 1 self Guided Boring Reamer

the main parameters of the boring reamer blade are: blade inclination λ= 3 °, front angle γ= 0 ° record the downtime, damage position, fracture condition ~ 3 °, rear angle α= 5 ° ~ 8 °, cutting edge width f1=0.05 ~ 0.08mm, guide edge width f2=0.2 ~ 0.25mm

when boring and reaming the inner hole, the chip breaking performance of the tool is very important. If the chips are often wrapped on the boring bar or tool, it may damage the blade, damage the machined surface, and easily block the oil outlet pipe. Therefore, when machining deep hole boring and reaming, we must ensure that the chip breaking is stable and reliable, that is, during machining, the chip should flow out directionally, curl first and then break. For this reason, it is necessary to grind a crescent shaped chip breaking groove at the front corner of the blade to make the chips roll into small rolls, and the more the rolls become larger, until they are bent and broken by the extrusion of the front of the tool and the chip surface. The crescent depression can be ground on a tool grinder, and then 20% white mud and 80% silicon carbide powder are mixed into a paste with water as the abrasive, and the requirements can be met by grinding with a cast iron grinding wheel with an arc radius of 1 ~ 1.5mm for 15 ~ 30 seconds. The main parameters of crescent depression are: chamfer width f=0.55 ~ 0.85mm, groove width b=1.3 ~ 1.5mm

when the Boring Reamer starts machining, the guide body can rotate relative to the cutter body, the axial force generated by broach cutting is borne by the one-way thrust ball bearing, and the guide body and the machined hole wall maintain a rolling friction state. The Boring Reamer we designed in the past has no rotatable guide body, but three guide blocks are arranged on the outer circular surface of the cutter. Because the guide block is too short, it is in a sliding friction state with the machined hole wall during cutting, resulting in black stripes on the hole wall due to irregular periodic hard extrusion, and gray white stripes on the non extruded part. Thus, the full-length surface of the processed hole wall forms bright and dark annular stripes with a certain width. By improving the design, after using the rotatable guide, the annular stripes on the hole wall disappear after machining, showing a uniform and smooth black surface

when machining with this Boring Reamer, the cutting parameters are: speed n=100 ~ 120r/min, cutting depth t=1.5 ~ 2 Thus, the shaft is less extended to the luggage compartment area by 5mm (one side), and the tool travel is s=0.3 ~ 0.5mm/min

2 deep hole boring and reaming process system

deep hole boring and reaming process system is shown in Figure 2. The system can be installed on an extended ordinary lathe or a horizontal boring machine for machining. First, rough drill the hole on the workpiece to 77mm; Then clamp the workpiece with two V-shaped blocks, fasten the fixing rings at both ends with the outer circle of the workpiece with bolts, and then fasten the end cover and O-ring with the fixing ring with hexagon socket screws; Finally, the boring bar and the boring reamer are sent together from the right end. After the boring bar passes through the bushing, the end of the boring bar is inserted into the universal joint sleeve, locked with a taper pin, and then the positioning sleeve and the guide sleeve are sleeved with the Boring Reamer, and the positioning sleeve is connected with the fixing ring at the right end. After installation, start the oil pump motor, put the cooling oil pump into the inner hole of the workpiece, then start the machine tool, the boring bar rotates, and start cutting. The parameters of oil pump are: pressure 8Mpa, flow 12L/min. The coolant is sulfurized oil (add an appropriate amount of Chlorinated Paraffin). In addition to cooling the tool, the cooling oil can also play a lubricating role between the blade, guide body and the machined hole wall, reduce friction, and forcibly discharge the cuttings from the left oil outlet pipe

Figure 2 deep hole boring and reaming process system

the workpiece feeding direction of the process system is to move to the right, which belongs to the tensile cutting mode. Compared with thrust cutting, its boring bar and Boring Reamer do not bear axial thrust, so the vibration is significantly reduced, and the blade is not easy to collapse. When the tool enters the machined hole, the guide edge of the blade can play a guiding role. The guide edge of the blade and the rotating body are always supported on the hole wall of the machined hole, which can balance the radial cutting force generated by cutting, guide the tool into the hole smoothly, and enhance the dynamic stiffness of the boring bar to ensure that the axis of the machined hole is not biased, so as to improve the straightness of the deep hole. Another function of the blade guide blade is to squeeze the hole wall. In machining, the guide edge squeezes the hole wall of the machined hole under the action of cutting force, causing it to produce severe elastic-plastic deformation, so as to iron the surface knife marks formed by cutting and reduce the surface roughness value of the hole. In addition, in the strong extrusion contact area between the guide edge and the hole wall, the extrusion temperature is very high, which can make the metal phase change. Due to the action of the guide edge, the metallographic fibers in the metal layer near the hole wall are elongated and the lattice is distorted. Under the condition of sufficient cooling and lubrication, the surface metal cools rapidly to form a cold work hardening layer, and generates residual stress in the surface metal matrix of the hole, thereby improving the metal strength of the surface layer of the hole wall. It can be seen that the quality of deep hole machining does not only depend on the machining condition of the cutting edge of the tool, but also has a great relationship with the cutting of the cutting edge, the surface extrusion of the guide edge and the support of the guide body

in deep hole machining, due to the slender boring bar, its torsional vibration will directly affect the machining accuracy, tool durability and cutting efficiency. If the project can be effectively supported by the "hundred talents plan" project of the Chinese Academy of Sciences and the financial support of cooperative enterprises, controlling the boring bar vibration can improve the deep hole machining accuracy. The self-directed Boring Reamer we developed has a cutting edge, a guiding edge and a rolling guiding body, and the left end of the workpiece has a bushing to support the boring bar, and the tensile cutting method is adopted, which effectively solves the vibration problem of the boring bar and improves the machining accuracy of deep holes and the surface quality of the hole wall

3 machining effect

after machining the cylinder block hole with self-directed Boring Reamer and its process system, the surface of the workpiece hole wall presents a uniform black bright surface, the surface roughness can reach Ra0.8 m, the size deviation range of the hole is 0.02 ~ 0.05mm, and the straightness of the hole is qualified by check and flux gauge. Further use the micrometer method to measure the straightness of the hole: first level the workpiece hole, zero the indicator at the port of the hole, and then measure along the prime line of its vertical section. Because the hole is deep, the indicator can only probe into the hole from the port for about 300mm. After measuring several sections, take the maximum error value as the straightness error, and the measurement result is less than 0.02mm, and the straightness error value of the whole length is less than 0.08mm. The tool durability can process 3 workpieces. After each workpiece is processed, the blade edge must be carefully grinded with diamond. If the blade is found to be broken and ineffective after grinding, the blade should be replaced in time. In the process of machining, if there is bad chip breaking or the machining is interrupted due to chip blockage, the tool should be exited in time for cleaning. In addition, the grinding quality of the chip breaking groove also directly affects the chip breaking effect, so the chip breaking groove should be ground in strict accordance with the design requirements. (end)

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