Because of the different uses and performances of various machines, the materials, structures and technical requirements of their parts are also different. Therefore, the processing technology of various parts is different, even for the same type of parts, because of the different production conditions and batch sizes, the process is also different, so it is necessary to formulate reasonable process regulations. In NC machining, the machining process route represents the trajectory of the tool position relative to the workpiece, also known as the feed route. It not only includes the processing content, but also reflects the processing sequence, which is the main basis of programming work.
abstract
The important position and great benefits of CNC technology and CNC machine tools in today's machinery manufacturing industry show their strategic role in the modernization of national basic industries, and become an important means and symbol for the upgrading and transformation of traditional machinery manufacturing industry and the realization of automation, flexibility and integrated production. The wide application of numerical control technology and numerical control machine tools has brought revolutionary changes to the industrial structure, product types and grades and production methods of machinery manufacturing industry. CNC machine tool is the most important equipment in modern machining workshop. Its development is the result of the combination of information technology (1T) and manufacturing technology (MT). Modern CAD/CAM and manufacturing technology are based on numerical control technology. It is very important for students majoring in modern numerical control technology to master the knowledge of modern numerical control technology.
This graduation project introduces the characteristics of NC machining, processing technology analysis and general steps of NC programming. The analysis method of NC machining process is introduced in detail through examples.
Keywords: NC technology processing technology programming
The important position and great benefits of CNC and CNC machine tool technology in today's machinery manufacturing industry show its strategic role in the national infrastructure of industrial modernization, and have become an important means and symbol for the transformation of traditional machinery manufacturing industry and the improvement of automation, flexibility and integrated production. The wide application of numerical control technology and numerical control machine tools has brought revolutionary changes to the industrial structure, product variety and quality and production mode of machinery manufacturing industry. CNC machine tool is the most important modern equipment in the processing workshop. It is the result of the development of information technology (1 T) and manufacturing technology (MT). Modern CAD/CAM, FMS, CIMS, agile manufacturing and intelligent manufacturing technologies are all based on numerical control technology. It is essential for students majoring in numerical control to master modern mechanical and electronic knowledge.
The content of this design expounds the characteristics of NC, the general steps of machining and NC programming. Moreover, the process of NC machining is analyzed through a detailed example.
Keywords: CNC programming technology, processing technology
Select 1 blank.
I. Blanks and materials of shaft parts
(A) the blank of shaft parts
Shaft parts can be in the form of bars, forgings and other blanks according to the use requirements, production types, equipment conditions and structure. For shafts with similar cylindrical diameters, bars are generally the main ones; Forgings are often used for stepped shafts or important shafts with large cylinder diameters, which not only saves materials, reduces processing workload, but also improves mechanical properties.
According to the different production scale, there are two forging methods for blanks: free forging and die forging. Free forging is mostly used in small and medium batch production, while die forging is used in large batch production.
(2) Materials of shaft parts
Different materials and heat treatment specifications (such as quenching and tempering, normalizing, quenching, etc. ) Shaft parts should be selected according to different working conditions and use requirements to obtain certain strength, toughness and wear resistance.
45 steel is a common material for shaft parts. The price is low. After quenching and tempering (or normalizing), better cutting performance, higher strength and toughness and other comprehensive mechanical properties can be obtained, and the surface hardness after quenching can reach 45~52HRC.
Alloy structural steels such as 40Cr are suitable for shaft parts with medium precision and high speed. After quenching and tempering, these steels have good comprehensive mechanical properties.
Bearing steel GCr 15 and spring steel 65Mn, after quenching and tempering and surface high-frequency quenching, the surface hardness can reach 50~58HRC, which has high fatigue resistance and good wear resistance, so high-precision shafts can be manufactured.
The spindle of precision machine tools (such as grinding wheel spindle of grinder and spindle of coordinate boring machine) can be made of 38CrMoAIA nitride steel. After quenching and tempering and surface nitriding, this steel can not only obtain higher surface hardness, but also maintain a soft core, so it has good impact toughness. Compared with carburized and quenched steel, it has the characteristics of small heat treatment deformation and high hardness.
2 process analysis of part drawing
When designing the machining program of parts, the machining object should be deeply analyzed first. NC turning should consider the following aspects:
1. Geometric conditions that constitute the outline of a part.
When turning by manual programming, the coordinates of each node should be calculated; In automatic programming, all geometric elements that make up the outline of a part should be defined. Therefore, when analyzing part drawings, we should pay attention to:
(1) Whether a certain dimension is omitted from the part drawing, which makes its geometric conditions insufficient and affects the composition of the outline of the part;
(2) Whether the position of the line on the part drawing is vague or the size is unclear, which makes it impossible to program;
(3) Whether the geometric conditions given on the part drawing are unreasonable or not leads to difficulties in mathematical processing.
(4) The dimensioning method on the part drawing should adapt to the characteristics of NC lathe processing, and the dimensioning should adopt the same benchmark or directly give the coordinate size.
2. Requirements for dimensional accuracy
Analyze the dimensional accuracy requirements of part drawings, judge whether it can be realized by turning process, and determine the process method to control dimensional accuracy.
In this analysis process, some dimensions can also be converted at the same time, such as incremental dimensions and absolute dimensions and dimension chain calculation. When turning parts with CNC lathe, the average of the maximum and minimum limit dimensions is often taken as the dimension basis of programming.
3. Shape and position accuracy requirements
The form and position tolerance given on the part drawing is an important basis to ensure the accuracy of the part. During machining, the positioning datum and measuring datum of parts should be determined according to the requirements of parts, and some technical treatments can be carried out according to the special needs of CNC lathes to effectively control the shape and position accuracy of parts.
4. Surface roughness requirements
Surface roughness is an important requirement to ensure the surface micro-precision of parts, and it is also the basis for selecting CNC lathes and tools reasonably and determining cutting parameters.
5. Material and heat treatment requirements
The material and heat treatment requirements given in the part drawing are the basis for selecting the model of cutter and CNC lathe and determining the cutting parameters.
2. 1 parts processing technology analysis
1 determination principle of processing route
Whether the processing route is reasonable or not is related to the processing quality of parts.
And the production efficiency is improved. When determining the processing route, comprehensive consideration should be given to guarantee.
Under the premise of ensuring the machining accuracy, the machining process is shortened to the maximum extent.
Line. So the NC machining process route should follow the following principles:
(1) In order to ensure the product quality, the machining accuracy and tables of parts should be guaranteed.
Priority should be given to surface roughness requirements.
(2) Improve labor productivity and reduce production costs. Warranty parts
On the premise of ensuring the processing quality, try to shorten the processing route and reduce it as much as possible.
Idle travel time, improve processing efficiency.
(3) Under the condition of meeting the processing quality and production efficiency of parts, do everything possible.
Simplify the numerical calculation workload of mathematical processing, thus simplifying the programming work.
In addition, the shape of the parts should be considered comprehensively when determining the processing route.
And rigidity of machine tools and cutters. , to determine the feed.
Given or fed many times, design the tangent point and tangent point of the tool.
Inward and outward When milling, do you use forward milling or reverse milling?
Milling and so on.
2 Selection points of processing technology
In NC programming, it is necessary to strengthen the process program and choose a reasonable process program.
Processing route, optimization programming. It should be closed when making the processing route.
Please note the following points:
(1) When determining the processing route, in order to shorten the distance, we should consider it as much as possible.
Shorten the idle stroke of the tool. Usually, it is reasonable and safe to choose the cutting point reasonably.
Idle stroke can shorten idle stroke and improve production efficiency.
(2) When arranging the processing route, we should also consider the process set.
The principle is. Parts in a clamping, try to use the same knife.
The more surfaces are machined, the fewer tool changes and the simpler machining.
Route, shorten the auxiliary time. Conditional people can use compound cutter, when a.
After all parts of the tool are processed, do it for the next working procedure as much as possible.
Some pre-treatments, such as pre-drilling positioning holes or marking positions with a small drill. or
Rough machining, and then change tools for finishing.
(3) Select the processing route with small deformation of the workpiece after processing. such as
Fractions are applied to slender parts or thin plate parts with small cross-sectional area.
Transfer the tool to the final size or arrange the machining by symmetrically removing the allowance.