The machining of the gearbox hole system is a typical process problem often encountered in the production of automobiles and tractors. Due to the limitation of the blank production process, the remaining amount of the prefabricated hole is not easy to control and often causes difficulties for the subsequent machining process. Due to the high performance requirements of the product, the dimensional accuracy, shape accuracy, and surface quality of the gearbox hole system are high. At the same time, in order to reduce the production cost, the process design needs to simplify the process and reduce the number of processes. Therefore, the development of high-precision, High-efficiency, low-cost gearbox hole machining tools are very important. When we developed the two-face machining combination machine tool for the transmission housing of the walking tractor, we designed a nesting tool for rough machining, which better solved the problem that the non-uniformity of the prefabricated hole (excessive local allowance) affected the machining accuracy. Through the two processes of rough and fine machining, the complete processing of the two faces of the transmission housing can be completed, and the machining accuracy meets or exceeds the product requirements.
Fig. 1 Hole machining requirements
Figure 2 set of tool structure
1 The machining requirements for the gearbox hole system are based on the user's requirements. Two operations are required to complete the roughing and finishing of all hole systems on both sides of the manual tractor gearbox housing. Hole machining requirements are shown in Figure 1. After processing, the dimensional accuracy of each hole is H7. Concentricity requirements for both sides of holes 1, 3, 4, and 5 are 0.04mm. Concentricity of two holes is required to be 0.015mm. Each hole is required to have a roundness of 0.013mm. . In order to reduce the influence of uneven machining allowance (precision machining allowance can reach 12mm) on machining accuracy, roughing and semi-finishing machining are performed using nesting tools in the process arrangement, and finishing is performed using the boring process. At the same time, the structure of the nesting tool has been improved. 2 Structure improvement of the set of cutting tools The basic structure of the nesting cutting tool shown in Fig. 2 is similar to that of ordinary nesting tools, but the arrangement of the cutting teeth and the structure of the cutting teeth have been improved. If the number of teeth of the nesting cutter is too much, it will limit the effective chip space and affect the single tooth strength and rigidity of the cutter; if the number of cutter teeth is too small, the number of working teeth will decrease, which will affect the cutting amount and production efficiency. For this purpose, we have chosen the appropriate number of teeth for the diameter of the hole to be machined (Ø35 to 90 mm). In order to reduce the axial resistance when the tool is processed, the single tooth width of the tool should be reduced as much as possible under the premise of ensuring the strength of the cutter teeth. For this reason, the single tooth width of the cutter is selected to be 5mm. In order to reduce the working load of the main cutting edge and increase the stability of the cutter teeth during work, each cutter tooth has a secondary cutting edge on the inner and outer sides of the blade, except for the end cutting edge. In order to ensure that there is a proper clearance between the work tooth side and the machined surface of the tool tooth to reduce the friction between the side surface of the tool tooth and the workpiece surface, the inverted cone is ground axially on both sides of the tool tooth. In order to increase the wear resistance of the tooth, the material of the tooth is carbide. The body material uses 45 steel. 3 Processing features Using nesting material → fine boring process route and through-structured improved nesting tools for through hole processing of brittle material shell parts, has the following advantages: 1 with the original process route (rough 镗 → semi-finished 镗 → expansion Compared with holes, fine boring, etc., it can simplify the processing process, reduce the production cost, and increase the production efficiency by more than 2 times. 2 Compared with the original processing method, the axial resistance of the nesting processing is smaller and the cutting is more stable and can be avoided. Damage to the machine due to overloading machining, this is particularly important for the combined machine tools; 3 sets of tools is a multi-bored machining tool, integrating the characteristics of drills, grooving tools, reamers, boring tools and other tools, processing efficiency High (especially for workpieces with rough residual reserves), good processing technology, simple tool structure, high durability (the tool can still work normally after individual cutter teeth are damaged), and on the premise of good system rigidity, High hole machining accuracy (straightness 0.01mm, roundness 0.01mm, coaxiality 0.01mm, surface roughness up to 6 levels); cutting fluids are not required during the use of 4 sets of material knives; controlled by the amount of metal removed System, dust significantly reduced, is conducive to environmental protection and improve working conditions; 5 If the process requires, the nesting tool can also be combined with reamer or chamfering knife; through its further improvement in structure, can also be applied to No prefabricated hole processing. The adoption of nesting, fine boring, and improved nesting tools provides a new way of realizing the machining of the box hole system. It is especially suitable for the holes of the shell parts where the prefabricated hole of the blank has a large machining allowance and the part machining precision is high. Processing, with a wide range of promotion and application value.
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