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1, determine the workpiece processing parts and specific content
Determine the content of the work to be processed on the machine and the connection with the previous and following processes.
Workpieces before processing in this process. For example, castings, forgings or bars, shapes, sizes, allowances, etc.
The shape, size of the processed part of the previous process, or the reference surface and reference hole processed in the previous process are required for this process.
The part and specific content to be processed in this process.
In order to facilitate the preparation of processes and procedures, a rough drawing of the process and a process drawing of the process should be drawn.
2, determine the workpiece clamping method and design fixture
The fixture is selected or designed according to the determined workpiece processing location, positioning reference and clamping requirements. CNC lathes often use three-jaw self-centering chucks to hold workpieces; shaft-type workpieces can also use tailstock tips to support workpieces. Due to the extremely high spindle speed of CNC lathes, hydraulic high-speed power chucks are used to facilitate the clamping of workpieces. Because it has passed strict balance in the production plant, it has high rotation speed (limit rotation speed up to 4000~6000r/min) and high. Clamping force (maximum push-pull force is 2000~8000N), high precision, convenient claw adjustment, through hole, long service life, etc. It is also possible to use soft jaws to hold the workpiece. The soft jaw arc surface is randomly formulated by the operator to achieve the desired clamping accuracy. By adjusting the cylinder pressure, the clamping force of the chuck can be changed to meet the special needs of clamping various thin-walled and easily deformable parts. In order to reduce the stress deformation of the slender shaft machining, improve the machining accuracy, and when machining the hole of the shaft with a hole, the hydraulic centering center frame can be used, and the centering accuracy can reach 0.03mm.
3, determine the processing plan
The principle of determining the processing plan
The processing plan is also called the process plan. The processing plan of the CNC machine tool includes the preparation of processes, work steps, and the route of the knife.
In the processing of CNC machine tools, due to the complex and diverse processing objects, in particular the shape and position of the profile curve, and the influence of various factors such as different materials, different batches, etc., a specific analysis should be performed when formulating a specific part. Treated differently and differently. Only in this way can the rationalized processing plan be established, so as to achieve the objectives of high quality, high efficiency, and low cost.
The general principles for formulating a processing plan are: first coarse after finishing, first near and far, first inside and outside, least program segment, shortest cutting path, and special treatment under special circumstances.
First coarse finish
In order to increase production efficiency and guarantee the finishing quality of the parts, the roughing process should be arranged in the cutting process, and a large amount of machining allowance before finishing in a short period of time (as shown in the dashed line in Figure 3-4). The part shown) is removed while satisfying the requirement for the uniformity of the remaining allowance for finishing.
After the rough machining process is completed, the semi-finishing and finishing operations performed after the tool change should be arranged. Among them, the purpose of arranging the semi-finishing is to arrange semi-finishing as a transitional process so that the balance of the finishing allowance is small and uniform when the uniformity of the remaining amount after roughing cannot meet the finishing requirements.
When arranging a finishing operation that can be performed with one or more knives, the final contour of the part should be continuously machined from the last knife. At this time, the position of the cutting tool should be properly considered. Try not to arrange cutting and cutting or tool changing and pauses in the continuous contour to avoid elastic deformation caused by abrupt changes in cutting force, resulting in a smooth connecting surface. Scratches, shape mutations, or stabbed knife marks.
First and last
The far and near distances mentioned here are based on the distance of the machining part relative to the knife point. In general circumstances, especially when roughing, it is usually arranged that the part near the tool cutting point is first machined, and the part far away from the tool point is post-processed so as to shorten the tool movement distance and reduce the idle travel time. For turning processing, the first and the second are far to help maintain the rigidity of the blank or semi-finished part and improve the cutting conditions.
First inside and outside
For parts that require processing of the inner surface (inner shape, cavity) and outer surface, the inner and inner cavities should normally be arranged before the outer surface is processed. This is because it is difficult to control the size and shape of the inner surface, the rigidity of the tool is correspondingly poor, the durability of the cutting edge (blade) is easily affected by the heat of cutting, and it is difficult to remove the cutting chips during processing.
The shortest route
The work focus of determining the cutting path is mainly used to determine the cutting path for roughing and idle stroke. The cutting path of the finishing cutting process is basically carried out along the outline of its parts.
The tool path generally refers to the path from the start of tool movement (or the fixed origin of the machine) until the tool returns to this point and ends the machining program, including the cutting path and the non-cutting idle path such as tool introduction and cutting.
Under the premise of guaranteeing the processing quality, making the processing program have the shortest cutting path, not only can save the execution time of the whole processing process, but also can reduce some unnecessary tool consumption and the wear of sliding parts of the machine feed mechanism.
In addition to relying on a great deal of practical experience, the optimized process plan should also be good at analysis, and can be supplemented with some simple calculations if necessary.
The above principles are not static, and in some special cases, flexible and variable solutions are needed. If any of the workpieces must be rough machined after finishing, in order to ensure the accuracy and quality of its processing. These all depend on the constant accumulation and learning of the programmer's actual processing experience.
Relationship between processing route and machining allowance
Under the condition that the numerical control lathe has not reached universal use, generally, excessive allowances on the blanks, especially forged and cast hard skins, should be arranged on ordinary lathes for processing. If you must use CNC lathe processing, you must pay attention to the flexible arrangement of the program. Arrange some subroutines to do a certain amount of machining on the excess parts.
Machining route for step cutting of large margin blanks
The end position of the tool during the layer cutting
Spindle speed when threading
When CNC lathes process threads, due to the change of the transmission chain, in principle, the speed is only required to ensure that the tool displaces one pitch in the direction of the main feed axis (mostly in the Z axis) every rotation of the spindle, and should not be limited. However, when CNC lathes machine threads, they will be affected by the following aspects:
The pitch (lead) value of the command in the thread cutting block corresponds to the feedrate F in terms of feedrate (mm/r). If the spindle speed of the machine is selected too high, the converted feedrate ( Mm/min) must be significantly greater than the normal value;
At the beginning and end of the displacement of the tool, the tool will be constrained by the up/down frequency of the servo drive system and the interpolation speed of the numerical control device. Because the up/down frequency characteristics cannot meet the machining needs, it may be generated due to the main feed motion. Out of "lead" and "lagging" lead to partial thread pitch does not meet the requirements;
The turning thread must be realized by the synchronous running function of the spindle, ie a spindle pulse generator (encoder) is required for the turning thread.
Determine the content of the work to be processed on the machine and the connection with the previous and following processes.
Workpieces before processing in this process. For example, castings, forgings or bars, shapes, sizes, allowances, etc.
The shape, size of the processed part of the previous process, or the reference surface and reference hole processed in the previous process are required for this process.
The part and specific content to be processed in this process.
In order to facilitate the preparation of processes and procedures, a rough drawing of the process and a process drawing of the process should be drawn.
2, determine the workpiece clamping method and design fixture
The fixture is selected or designed according to the determined workpiece processing location, positioning reference and clamping requirements. CNC lathes often use three-jaw self-centering chucks to hold workpieces; shaft-type workpieces can also use tailstock tips to support workpieces. Due to the extremely high spindle speed of CNC lathes, hydraulic high-speed power chucks are used to facilitate the clamping of workpieces. Because it has passed strict balance in the production plant, it has high rotation speed (limit rotation speed up to 4000~6000r/min) and high. Clamping force (maximum push-pull force is 2000~8000N), high precision, convenient claw adjustment, through hole, long service life, etc. It is also possible to use soft jaws to hold the workpiece. The soft jaw arc surface is randomly formulated by the operator to achieve the desired clamping accuracy. By adjusting the cylinder pressure, the clamping force of the chuck can be changed to meet the special needs of clamping various thin-walled and easily deformable parts. In order to reduce the stress deformation of the slender shaft machining, improve the machining accuracy, and when machining the hole of the shaft with a hole, the hydraulic centering center frame can be used, and the centering accuracy can reach 0.03mm.
3, determine the processing plan
The principle of determining the processing plan
The processing plan is also called the process plan. The processing plan of the CNC machine tool includes the preparation of processes, work steps, and the route of the knife.
In the processing of CNC machine tools, due to the complex and diverse processing objects, in particular the shape and position of the profile curve, and the influence of various factors such as different materials, different batches, etc., a specific analysis should be performed when formulating a specific part. Treated differently and differently. Only in this way can the rationalized processing plan be established, so as to achieve the objectives of high quality, high efficiency, and low cost.
The general principles for formulating a processing plan are: first coarse after finishing, first near and far, first inside and outside, least program segment, shortest cutting path, and special treatment under special circumstances.
First coarse finish
In order to increase production efficiency and guarantee the finishing quality of the parts, the roughing process should be arranged in the cutting process, and a large amount of machining allowance before finishing in a short period of time (as shown in the dashed line in Figure 3-4). The part shown) is removed while satisfying the requirement for the uniformity of the remaining allowance for finishing.
After the rough machining process is completed, the semi-finishing and finishing operations performed after the tool change should be arranged. Among them, the purpose of arranging the semi-finishing is to arrange semi-finishing as a transitional process so that the balance of the finishing allowance is small and uniform when the uniformity of the remaining amount after roughing cannot meet the finishing requirements.
When arranging a finishing operation that can be performed with one or more knives, the final contour of the part should be continuously machined from the last knife. At this time, the position of the cutting tool should be properly considered. Try not to arrange cutting and cutting or tool changing and pauses in the continuous contour to avoid elastic deformation caused by abrupt changes in cutting force, resulting in a smooth connecting surface. Scratches, shape mutations, or stabbed knife marks.
First and last
The far and near distances mentioned here are based on the distance of the machining part relative to the knife point. In general circumstances, especially when roughing, it is usually arranged that the part near the tool cutting point is first machined, and the part far away from the tool point is post-processed so as to shorten the tool movement distance and reduce the idle travel time. For turning processing, the first and the second are far to help maintain the rigidity of the blank or semi-finished part and improve the cutting conditions.
First inside and outside
For parts that require processing of the inner surface (inner shape, cavity) and outer surface, the inner and inner cavities should normally be arranged before the outer surface is processed. This is because it is difficult to control the size and shape of the inner surface, the rigidity of the tool is correspondingly poor, the durability of the cutting edge (blade) is easily affected by the heat of cutting, and it is difficult to remove the cutting chips during processing.
The shortest route
The work focus of determining the cutting path is mainly used to determine the cutting path for roughing and idle stroke. The cutting path of the finishing cutting process is basically carried out along the outline of its parts.
The tool path generally refers to the path from the start of tool movement (or the fixed origin of the machine) until the tool returns to this point and ends the machining program, including the cutting path and the non-cutting idle path such as tool introduction and cutting.
Under the premise of guaranteeing the processing quality, making the processing program have the shortest cutting path, not only can save the execution time of the whole processing process, but also can reduce some unnecessary tool consumption and the wear of sliding parts of the machine feed mechanism.
In addition to relying on a great deal of practical experience, the optimized process plan should also be good at analysis, and can be supplemented with some simple calculations if necessary.
The above principles are not static, and in some special cases, flexible and variable solutions are needed. If any of the workpieces must be rough machined after finishing, in order to ensure the accuracy and quality of its processing. These all depend on the constant accumulation and learning of the programmer's actual processing experience.
Relationship between processing route and machining allowance
Under the condition that the numerical control lathe has not reached universal use, generally, excessive allowances on the blanks, especially forged and cast hard skins, should be arranged on ordinary lathes for processing. If you must use CNC lathe processing, you must pay attention to the flexible arrangement of the program. Arrange some subroutines to do a certain amount of machining on the excess parts.
Machining route for step cutting of large margin blanks
The end position of the tool during the layer cutting
Spindle speed when threading
When CNC lathes process threads, due to the change of the transmission chain, in principle, the speed is only required to ensure that the tool displaces one pitch in the direction of the main feed axis (mostly in the Z axis) every rotation of the spindle, and should not be limited. However, when CNC lathes machine threads, they will be affected by the following aspects:
The pitch (lead) value of the command in the thread cutting block corresponds to the feedrate F in terms of feedrate (mm/r). If the spindle speed of the machine is selected too high, the converted feedrate ( Mm/min) must be significantly greater than the normal value;
At the beginning and end of the displacement of the tool, the tool will be constrained by the up/down frequency of the servo drive system and the interpolation speed of the numerical control device. Because the up/down frequency characteristics cannot meet the machining needs, it may be generated due to the main feed motion. Out of "lead" and "lagging" lead to partial thread pitch does not meet the requirements;
The turning thread must be realized by the synchronous running function of the spindle, ie a spindle pulse generator (encoder) is required for the turning thread.
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