CNC machinists must understand the 42 essential knowledge points
1. What are the three methods of workpiece clamping?
{1. clamping in the fixture; 2. direct positive clamping; 3. scribing to find the positive clamping}
2、What does the processing system include?
{Machine tool, workpiece, fixture, tool}
3, the composition of the machining process?
{Rough machining, semi-finishing, finishing, super-finishing}
4、How to classify the benchmark?
{1. design benchmark 2. process benchmark: process, measurement, assembly, positioning: (original, additional): (rough benchmark, fine benchmark)}
What does machining accuracy include?
{1. Dimensional accuracy 2. Shape accuracy 3. Position accuracy }
5. What is included in the original error that occurs during processing?
{ Principle error – positioning error – adjustment error – tool error – fixture error – machine tool spindle rotation error – machine tool guide error – machine tool transmission error – process system deformation by force – process system deformation by heat – tool wear – measurement error – error caused by residual stress of the workpiece – }
6, Does the processing system stiffness impact machining accuracy (machine tool deformation, workpiece deformation)?
{1. workpiece shape error caused by changes in the location of the point of action of the cutting force 2. machining error caused by changes in the size of the cutting force 3. machining error caused by clamping force and gravity 4. the impact of the transmission force and inertia force on machining accuracy}
7, the machine guide error and spindle rotation error include which content?
{1. guide rail mainly includes the relative displacement error of the tool and workpiece in the error-sensitive direction caused by the guide rail 2. spindle radial circular runout – axial circular runout – tilt swing}
8、What is the “error reflection” phenomenon? What is the error reflection coefficient? What are the measures to reduce the error reflection?
{Deformation of the process system error due to changes in the blank error is partially reflected in the workpiece Measures: increase the number of tooling, increase the stiffness of the processing system, reduce the amount of feed, improve the accuracy of the blank}
9, the machine tool drive chain drive error analysis? Measures to reduce the transmission chain drive error?
{ error analysis: that is, the use of the end of the drive chain components to measure the angular error Δφ
Measures: 1. The fewer the number of pieces of the drive chain, the shorter the drive chain; Δφ is smaller, the higher the accuracy 2. The smaller the transmission ratio I, especially the first and last ends of the transmission ratio, is small, 3. As a lot of the transmission pieces of the error have the most significant impact, it should be made as accurate as possible 4.}
10、How to classify the machining error? Which errors belong to the constant value error? Which errors belong to the variable value of the system error? Which errors belong to the random error
{ system error: (constant value system error variable value system error) unexpected error
Constant-value system error: the processing principle error, machine tools, tools, fixtures manufacturing errors, process systems such as force deformation caused by the processing error
Variable system error: prop wear; tool, fixture, machine tool, etc., in thermal equilibrium before the thermal deformation error
Random error: copy of the blank error, positioning error, tightening error, the error of multiple adjustments, residual stress caused by the deformation error }
11. What are the ways to ensure and improve machining accuracy?
{Error prevention technology: the reasonable use of advanced technology and equipment directly reduces the original error transfer the original error uniform inferior actual error homogenization of the initial error
2. Error compensation technology: online inspection, automatic grinding of coupling parts, active control of decisive error factors}
12、What does the surface geometry of processing include?
{Geometric roughness, surface ripple degree, texture direction, surface defects}
13、What are the physical and chemical properties of the surface layer materials?
{Cold hardening of surface layer metal 2. Metallographic Deformation of surface layer metal 3. Residual stress of surface layer metal}
14、Try to analyze the factors affecting the surface roughness of the cutting process.
{Roughness value by: the height of the cutting residual area Main factors: the radius of the tooltip arc Main deflection angle Sub-deflection angle Feed secondary factors: increase in cutting speed Proper selection of cutting fluid Proper increase in the front angle of the tool Improve the quality of tool sharpening }
15. Try to analyze the factors affecting the surface roughness of the grinding process?
{1. Geometric factors: influence of grinding amount on surface roughness 2. influence of crushing wheel size and grinding wheel dressing on surface roughness 2. influence of physical factors: plastic deformation of the metal in the surface layer: grinding amount Selection of grinding wheel}
16. Try to analyze the factors affecting the cold work hardening of the cutting surface?
{The influence of cutting amount, The effect of tool geometry, The power of machining material properties}
17、What is tempering burn on grinding? What is grinding quenching burn? What is grinding annealing burn?
{Tempering: If the temperature of the grinding zone does not exceed the phase transformation temperature of the quenched steel but exceeds the transformation temperature of the martensite, the martensite of the surface metal of the workpiece will be transformed into a tempered tissue with lower hardness Quenching: If the temperature of the grinding zone exceeds the phase transformation temperature, coupled with the cooling effect of the coolant, the surface metal will have a secondary quenched martensite tissue with higher hardness than the original martensite; in its lower layer, due to the slower cooling If the temperature of the grinding zone exceeds the phase change temperature and there is no coolant in the grinding process, the surface metal will be annealed and the hardness of the surface metal will drop sharply}
18. Prevention and control of machining vibration
{eliminate or weaken the conditions that produce machining vibration; improve the dynamic characteristics of the processing system. Improve the stability of the processing system using various vibration elimination and damping devices}
19、Briefly describe the main differences between machining process cards, process cards, and application occasions.
{Process card: small batch production of a single piece using standard processing methods Machining process card: medium batch production Process card: large batch production type requires close, detailed organization of work}
20、Rough datum selection principle? Acceptable benchmark selection principles?
{ coarse benchmark: 1. to ensure that the principle of mutual position requirements; 2. to ensure that the processing surface machining allowance reasonable distribution of the principle; 3. to facilitate the workpiece clamping principle; 4. coarse benchmark shall not generally reuse the principle of acceptable benchmark: 1. benchmark overlap principle; 2. unified benchmark principle; 3. mutual benchmark principle; 4. since the principle of the benchmark; 5. to facilitate the principle of clamping }
21, the process sequence according to what principles?
{ 1. Machining the reference surface first, then other surfaces; 2. In half of the cases, machining the surface first, then the hole; 3. Machining the main surface first, then the second surface; 4. Rough machining process foremost, then finishing process }
22、How to divide the machining stages? What are the benefits of separating the machining stages?
{Division of machining stages: 1. Roughing stage – Semi-finishing stage – Finishing stage – Precision finishing stage It can ensure sufficient time to eliminate thermal Deformation and eliminate residual stresses generated by rough machining so that the subsequent machining accuracy can be improved. In addition, when defects are found in the roughing stage, carrying out the next processing stage is unnecessary to avoid waste. In addition, you can also rational use of equipment, low precision machine tools for roughing precision machine tools dedicated to finishing to maintain the precision level of precision machine tools; reasonable arrangement of human resources, highly skilled workers specializing in precision ultra-precision machining, which is very important to ensure product quality, improve the level of technology.}
23、What are the factors affecting the process margin?
{1. the dimensional tolerance Ta of the previous process; 2. the surface roughness Ry and surface defects deep Ha produced by the previous process; 3. the space error left by the previous process}
24、What does the composition of the work time quota include?
{T quota = T single-piece time + t quasi-final time / n number of pieces}
25、What are the process ways to improve productivity
{1. shorten the basic time; 2. reduce the auxiliary time and the basic time overlap; 3. reduce the layout of the workplace time; 4. reduce the preparation and ending time}
26、What are the main contents of the assembly process procedures?
{Analysis of product drawings, Division of the assembly unit, determine the assembly method; 2.}
27、What should be considered in the assembly process of the machine structure?
{The machine structure should be divided into independent assembly units; 2. reduce the assembly of the repair and machining; 3. the machine structure should be easy to assemble and disassemble}
28、What does the assembly accuracy generally include?
{1. mutual position accuracy; 2. mutual motion accuracy; 3. mutual fit accuracy}
29、Find the dimensional assembly chain should pay attention to what issues?
{The assembly size chain should be simplified as necessary; 2. The assembly size chain consists of “one piece of a ring”; 3. Assembly dimensional chain}
30、What are the methods to ensure assembly accuracy? What is the application of various methods?
{1. interchange method; 2. selection method; 3. repair method; 4. adjustment method}
31、The composition and function of machine tool jig?
{The machine tool jig is a device to clamp the workpiece on the machine tool. Its role is to make the workpiece has a correct position relative to the machine and tool. And in the process of processing to maintain this position remains unchanged. Components are 1. positioning elements or devices. 2. tool guiding elements or devices. 3. clamping elements or devices. 4. coupling elements 5. clamping body 6. other components or devices.
Main functions 1. to ensure processing quality 2. to improve production efficiency. 3. to expand the scope of the machine tool process 4. to reduce the labor intensity of workers to ensure production safety.}
32、According to the scope of use of fixtures, how to classify machine tool fixtures?
{1. general-purpose fixture 2. special fixture 3. adjustable fixture and group fixture 4. combination fixture and random fixture}
33、What are the commonly used positioning elements for workpiece positioning on a flat surface? And analyze the elimination of degrees of freedom.
{The workpiece is positioned on a flat surface. The common positioning elements are 1. fixed support 2. adjustable support 3. self-locating support 4. auxiliary support}
34、What are the common positioning elements when the workpiece is positioned by a cylindrical hole? And analyze the elimination of degrees of freedom.
{The workpiece is positioned with a cylindrical hole. . Commonly used positioning elements are 1. mandrel 2. positioning pin}
35、What are the common positioning elements to position the workpiece on the outer surface? And analyze the elimination of degrees of freedom.
{The workpiece is positioned on an external circular surface. . The common positioning elements are V-block}
36、The workpiece is positioned with “two pins on one side” how do you design the two pins?
{Determine the size and tolerance of the center distance of the two pins, determine the diameter of the cylindrical pin and its tolerance, and determine the diameter of the width of the diamond pin and its tolerance.}
37、Which two aspects are included in the positioning error? What are the methods to calculate the positioning error?
{1. The inaccuracy of the workpiece positioning surface or fixture on the production of positioning elements caused by the positioning error is called the reference position error. 2.}
38, the basic requirements for the design of the workpiece clamping device.
{1. The clamping process should maintain the correct position of the workpiece positioning obtained. 2. Clamping force size appropriate, the clamping mechanism should ensure that the workpiece does not loosen or vibrate during processing, but also to avoid improper Deformation and surface damage to the workpiece, the clamping mechanism should generally be a self-locking role
3. clamping devices should be easy to operate, labor-saving, and safe. 4. the complexity of the clamping device and the degree of automation should be adapted to the production batch and production methods. Structural design should strive to be simple, compact, and as far as possible to use standardized components}
39, the clamping force to determine the three elements? Clamping force direction and the role of the point of choice, respectively, what are the principles?
{ size direction action point The choice of clamping force direction should generally follow the following principles: 1, the focus of action of the clamping force should be conducive to the accurate positioning of the workpiece without destroying the positioning, for which the main clamping power is generally required to point vertically to the positioning surface 2, the clamping force direction of action should be consistent with the law of the workpiece stiffness as much as possible to reduce the workpiece clamping deformation 3, the clamping force direction of movement should be as much as possible with the cutting force, the law of gravity of the workpiece Consistent with the required clamping force to reduce the clamping force point of action selection of general principles.
1, the clamping force point of action should be the support element formed by the support surface to ensure that the workpiece has been positioned unchanged
2, the clamping force point of action should be in a rigid part to reduce the workpiece clamping deformation 3, the clamping force point of action should be as close as possible to the processing surface to reduce the cutting force on the workpiece caused by the turning torque}
40, what are the commonly used clamping mechanisms? Focus on the Analysis of the master tilt wedge clamping mechanism.
{1, wedge clamping structure 2, spiral clamping structure 3, eccentric clamping structure 4, hinge clamping structure 5, centering clamping structure 6, linkage clamping structure}
41, according to the structural characteristics of the Drilling die, how to classify it? How to classify according to the structural elements of the drill sleeve? Which categories are classified according to the specific coupling between the drilling die and the clamping?
{Drilling die according to the total structural characteristics:
1. Fixed Drilling die 2. Rotary Drilling dies 3. Flip-up Drilling dies 4. Covered Drilling dies 5. Sliding pillar drilling dies Classification of Drilling die structural features.
2、1、Fixed Drilling die 2、Interchangeable Drilling die 3、Quick change drilling die 4Special Drilling die The connection method between drilling die and clamping die:
3, fixed type hinged type separated type hanging type}
42、What are the features of machining center machine clamps?
{1、Simplified function 2、Full positioning 3、Open structure 4、Quick re-adjustment}
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