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1 The problem was proposed in the project of “Technical Transformation of Lathes for Both Ends of the Front and Rear Axle Housing Machining†in our factory. It is required that the holes at both ends be dimensioned to Ø60, the chamfer of the orifice 4×30°, and the surface roughness Ra12.5. Workpiece hole is cast bottom hole, workpiece material ZG270-500, hardness>HB143. The original unilateral machining allowance is 5mm, but in actuality, due to the poor quality of the blank, the eccentricity of the casting hole is serious and the machining allowance is extremely uneven. The maximum unilateral allowance is 9mm and the minimum is 1mm), which brings great processing to the positioning hole. Difficulties, high processing scrap rate. We tackled this problem through the “Technical Renovation of Front and Rear Axle Shell Machining Holes, Lathes, and Lathes†project. Through the comparison of different machining solutions, we selected the hole drilling technology and designed a special reaming drill to solve this large margin. Hole processing problems.
2 Boring process According to the processing requirements of the workpiece, three boring programs can be selected. Arrange coarse and fine boring burrs on one mast to share the remainder of the excision, then chamfer after boring. In order not to affect the beat of the production, two rough and fine guillotine cutters must work simultaneously. Since the hole diameter is only Ø60mm and the hole depth is 65mm, the maximum diameter of the boring bar does not exceed Ø46mm, the maximum section size of the boring bar is 14×14mm, and the maximum diameter of the compression screw is M8. Due to the drilling and tapping on the mast, the rigidity and strength of the mast are further weakened. The uneven distribution of the boring allowance makes the cutting force very large. The two boring tools work at the same time to make the power of the machine tool insufficient. Therefore, the cutting vibration is inevitably caused and the machining accuracy and surface roughness requirements of the workpiece cannot be satisfied. Arrange coarse and fine boring boring cutters on the same mast to share the removal of the remaining amount: use the first boring tool to remove the remaining 5 to 6 mm, and then use the second hoe to remove the remaining balance. A chamfering tool is used to machine 4 x 30° chamfers, but any two of them must not work at the same time. Although this program can reduce the cutting force, the length of the mast has increased twice, resulting in insufficient rigidity of the mast; at the same time, the processing time per unit has also doubled, and the production cycle time has not been guaranteed. Arrange two machines, that is, add a semi-finishing bed to share the remaining finishing. Although this solution can solve the problem, the processing cost of the workpiece is too high. In addition, since the workpiece is a steel casting, the chips are continuous, so chip removal during processing is also a very important issue. With the boring process, the space between the boring bar and the hole wall of the workpiece is very small. In the horizontal boring machine, the chips are easily clogged near the guillotine cutting edge, so the knife shooting phenomenon often occurs. 3 Reaming process: Since the reamer drill drills with four teeth at the same time to participate in cutting, the cutting force can be balanced during the cutting process. At the same cutting feed amount, the allowance for each tooth of the reamer is 镗One quarter of the knife, the cutting load per tooth is greatly reduced; the overall rigidity of the reamer is much larger than that of the boring knife, and the tool's durability is also greatly improved; in addition, the reamer drill has a spiral groove, and has enough chip space. During the machining process, the chips can be smoothly discharged along the spiral groove, which can meet the workpiece machining accuracy and surface roughness requirements. Therefore, under the same machining allowance, as long as the rigidity of the machine tool is guaranteed, the efficiency of the hole expanding process is much higher than that of the boring hole. Reaming Drill Designing Features of Reaming Drill Reaming drills are available in a variety of forms, including integral, inserts, and sets, and should be selected based on different usage conditions. For the processing conditions of the workpiece, we use the set of reamer, the tool with a M16 screw compaction. The tool has the following advantages: The tool can withstand large cutting loads. The set reamer drill adopts the mandrel centering, and the end face bears the cutting load and the key transmits the torque, so the tool slip phenomenon will not occur under the larger cutting load. The tool is small in length, light in weight and easy to manufacture. The tool is easy to adjust and easy to load and unload. The selection of cutting parameters of the reamer takes into account the serious eccentricity of the casting hole, and the unilateral machining allowance is greater than the machining allowance required by the technology. Therefore, the insert blade with a large blade width is used, and the face reamer face has an edge face and cutting. Chamfering edge. The chamfering edge plays the main cutting action, cutting away most of the headroom; the facet edge assists the cutting action and shares the margin caused by hole eccentricity (up to 9mm). Because the geometric parameters of the main cutting edge, the chip flutes, etc. will affect the precision and surface quality of the hole being machined, it should be carefully chosen. Main angle. The main cutting edge declination should be based on the cutting performance of the workpiece. The size of the main cutting edge declination not only affects the thickness of the cutting layer, but also affects the cutting stability and the straightness of the hole during the hole expansion. Increase the main cutting edge declination angle, make the straightness of the hole become better, and correct the straightness of the prefabricated hole, but as the declination of the main cutting edge increases, the cutting thickness increases, and the cutting edge enters the hole. The orientation and stability will deteriorate. Therefore, a larger main cutting edge angle is generally used for hole expansion. In the front corner, the workpiece material is gray cast iron, and the tool takes a 0° rake angle, which not only facilitates the manufacture of the tool, but also enhances the rigidity of the cutting edge and the thermal capacity of the cutting edge, which can significantly improve the tool life. The relief angle of the relief angle tool should mainly meet the requirement of reducing the friction between the relief surface and the machined surface. Taking a 12° angle of relief not only ensures the sharpness of the cutting edge but also satisfies the strength requirements of the cutting edge. Helix angle and chip flutes In order to correct the inaccuracy of prefabricated holes to obtain an accurate hole diameter, the helix angle of the reamer cannot be too large, taking 10°. Considering the need for chip and chip removal, in addition to the spiral groove on the drill bit, there are chamfered edge chip flutes and face edge chip flutes on the tool end face to ensure enough chip space and avoid chips. Clogged and knifed. The choice of cutting amount The cutting amount has an effect on the cutting efficiency, the tool durability, and the machining quality. After on-site debugging, determine the rotation speed n=200r/min; the cutting depth ap is determined according to the machining allowance, requiring that all allowances be removed by one pass, and ap=9mm is selected according to the maximum one-sided allowance; since the bottom hole of the workpiece is a casting hole, there are Crust, sand and other defects, while the workpiece machining allowance is large and the balance is uneven, in order to reduce the impact and thermal stress, select the lower cutting speed, take v = 37.5m/min; comprehensive workpiece material, workpiece diameter, tool Rigidity and other factors, based on experience selected feed f = 0.4mm/r. Processing effect In the test of selecting the hole expanding process to process the above-mentioned workpieces, due to the correct selection of the process scheme, during the debugging of the workpiece, the machine tool runs smoothly and completely avoids the vibration of the spindle, so that the existing rigidity and strength of the machine tool fully satisfy the workpiece. Processing process requirements. Although the casting hole deviation is serious, but the reamer cutting light, cuttings discharged smoothly, the hole surface roughness and precision meet the requirements, and the quality of the product in use has been very stable, machine tool commissioning and acceptance of a successful, fully achieve the desired effect .
2 Boring process According to the processing requirements of the workpiece, three boring programs can be selected. Arrange coarse and fine boring burrs on one mast to share the remainder of the excision, then chamfer after boring. In order not to affect the beat of the production, two rough and fine guillotine cutters must work simultaneously. Since the hole diameter is only Ø60mm and the hole depth is 65mm, the maximum diameter of the boring bar does not exceed Ø46mm, the maximum section size of the boring bar is 14×14mm, and the maximum diameter of the compression screw is M8. Due to the drilling and tapping on the mast, the rigidity and strength of the mast are further weakened. The uneven distribution of the boring allowance makes the cutting force very large. The two boring tools work at the same time to make the power of the machine tool insufficient. Therefore, the cutting vibration is inevitably caused and the machining accuracy and surface roughness requirements of the workpiece cannot be satisfied. Arrange coarse and fine boring boring cutters on the same mast to share the removal of the remaining amount: use the first boring tool to remove the remaining 5 to 6 mm, and then use the second hoe to remove the remaining balance. A chamfering tool is used to machine 4 x 30° chamfers, but any two of them must not work at the same time. Although this program can reduce the cutting force, the length of the mast has increased twice, resulting in insufficient rigidity of the mast; at the same time, the processing time per unit has also doubled, and the production cycle time has not been guaranteed. Arrange two machines, that is, add a semi-finishing bed to share the remaining finishing. Although this solution can solve the problem, the processing cost of the workpiece is too high. In addition, since the workpiece is a steel casting, the chips are continuous, so chip removal during processing is also a very important issue. With the boring process, the space between the boring bar and the hole wall of the workpiece is very small. In the horizontal boring machine, the chips are easily clogged near the guillotine cutting edge, so the knife shooting phenomenon often occurs. 3 Reaming process: Since the reamer drill drills with four teeth at the same time to participate in cutting, the cutting force can be balanced during the cutting process. At the same cutting feed amount, the allowance for each tooth of the reamer is 镗One quarter of the knife, the cutting load per tooth is greatly reduced; the overall rigidity of the reamer is much larger than that of the boring knife, and the tool's durability is also greatly improved; in addition, the reamer drill has a spiral groove, and has enough chip space. During the machining process, the chips can be smoothly discharged along the spiral groove, which can meet the workpiece machining accuracy and surface roughness requirements. Therefore, under the same machining allowance, as long as the rigidity of the machine tool is guaranteed, the efficiency of the hole expanding process is much higher than that of the boring hole. Reaming Drill Designing Features of Reaming Drill Reaming drills are available in a variety of forms, including integral, inserts, and sets, and should be selected based on different usage conditions. For the processing conditions of the workpiece, we use the set of reamer, the tool with a M16 screw compaction. The tool has the following advantages: The tool can withstand large cutting loads. The set reamer drill adopts the mandrel centering, and the end face bears the cutting load and the key transmits the torque, so the tool slip phenomenon will not occur under the larger cutting load. The tool is small in length, light in weight and easy to manufacture. The tool is easy to adjust and easy to load and unload. The selection of cutting parameters of the reamer takes into account the serious eccentricity of the casting hole, and the unilateral machining allowance is greater than the machining allowance required by the technology. Therefore, the insert blade with a large blade width is used, and the face reamer face has an edge face and cutting. Chamfering edge. The chamfering edge plays the main cutting action, cutting away most of the headroom; the facet edge assists the cutting action and shares the margin caused by hole eccentricity (up to 9mm). Because the geometric parameters of the main cutting edge, the chip flutes, etc. will affect the precision and surface quality of the hole being machined, it should be carefully chosen. Main angle. The main cutting edge declination should be based on the cutting performance of the workpiece. The size of the main cutting edge declination not only affects the thickness of the cutting layer, but also affects the cutting stability and the straightness of the hole during the hole expansion. Increase the main cutting edge declination angle, make the straightness of the hole become better, and correct the straightness of the prefabricated hole, but as the declination of the main cutting edge increases, the cutting thickness increases, and the cutting edge enters the hole. The orientation and stability will deteriorate. Therefore, a larger main cutting edge angle is generally used for hole expansion. In the front corner, the workpiece material is gray cast iron, and the tool takes a 0° rake angle, which not only facilitates the manufacture of the tool, but also enhances the rigidity of the cutting edge and the thermal capacity of the cutting edge, which can significantly improve the tool life. The relief angle of the relief angle tool should mainly meet the requirement of reducing the friction between the relief surface and the machined surface. Taking a 12° angle of relief not only ensures the sharpness of the cutting edge but also satisfies the strength requirements of the cutting edge. Helix angle and chip flutes In order to correct the inaccuracy of prefabricated holes to obtain an accurate hole diameter, the helix angle of the reamer cannot be too large, taking 10°. Considering the need for chip and chip removal, in addition to the spiral groove on the drill bit, there are chamfered edge chip flutes and face edge chip flutes on the tool end face to ensure enough chip space and avoid chips. Clogged and knifed. The choice of cutting amount The cutting amount has an effect on the cutting efficiency, the tool durability, and the machining quality. After on-site debugging, determine the rotation speed n=200r/min; the cutting depth ap is determined according to the machining allowance, requiring that all allowances be removed by one pass, and ap=9mm is selected according to the maximum one-sided allowance; since the bottom hole of the workpiece is a casting hole, there are Crust, sand and other defects, while the workpiece machining allowance is large and the balance is uneven, in order to reduce the impact and thermal stress, select the lower cutting speed, take v = 37.5m/min; comprehensive workpiece material, workpiece diameter, tool Rigidity and other factors, based on experience selected feed f = 0.4mm/r. Processing effect In the test of selecting the hole expanding process to process the above-mentioned workpieces, due to the correct selection of the process scheme, during the debugging of the workpiece, the machine tool runs smoothly and completely avoids the vibration of the spindle, so that the existing rigidity and strength of the machine tool fully satisfy the workpiece. Processing process requirements. Although the casting hole deviation is serious, but the reamer cutting light, cuttings discharged smoothly, the hole surface roughness and precision meet the requirements, and the quality of the product in use has been very stable, machine tool commissioning and acceptance of a successful, fully achieve the desired effect .
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