CNC Machining · 2021年5月8日 0

How much do you know about CNC machining process?

How much do you know about CNC machining process?
1. What are the three methods for workpiece clamping?

1. Clamping in the fixture; 2. Directly aligning the clamping; 3. Crossing the line to align the clamping

2. What is included in the process system?

Machine tools, workpieces, fixtures, tools

3. What is the composition of the machining process?

Rough machining, semi-finishing, finishing, super finishing

4. How are benchmarks classified?

1. Design benchmark 2. Process benchmark: process, measurement, assembly, positioning: (original, additional): (coarse benchmark, fine benchmark)

What does machining accuracy include?

1. Dimension accuracy 2. Shape accuracy 3. Position accuracy

5. What are the original errors in the processing process?

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 stress deformation, process system thermal deformation, tool wear, measurement error, and residual stress on the workpiece Error of

6. How does the rigidity of the process system affect the machining accuracy (machine deformation, workpiece deformation)?

1. The shape error of the workpiece caused by the change of the position of the cutting force application point 2. The machining error caused by the change of the cutting force 3. The machining error caused by the clamping force and gravity 4. The influence of the transmission force and the inertial force on the machining accuracy

7. What is included in the guide error of the machine tool guide rail and the spindle rotation error?

1. The guide rail mainly includes the relative displacement error of the tool and the workpiece in the error-sensitive direction caused by the guide rail 2. The spindle radial circular runout, axial circular runout, and tilt swing

8. What is the “error replay” phenomenon? What is the error remapping coefficient? What are the measures to reduce errors in re-screening?

Due to the change of process system error and deformation, the part of the blank error is reflected on the workpiece. Measures: increase the number of passes, increase the rigidity of the process system, reduce the feed rate, and improve the accuracy of the blank

9. Analysis of transmission error of machine tool transmission chain? Measures to reduce the transmission error of the transmission chain?

Error analysis: it is measured by the angle error Δφ of the end element of the transmission chain

Measures: 1. The fewer the number of transmission chains, the shorter the transmission chain, the smaller the Δφ, the higher the accuracy 2. The smaller the transmission ratio i, especially the small transmission ratio at the first and the end, 3. Because of the end pieces in the transmission parts The error affects the most, so it should be as accurate as possible 4. Use a correction device

10. How to classify processing errors? Which errors are constant errors? Which errors are variable system errors? Which errors are random errors

System error: (constant value system error, variable value system error) random error

Constant system error: machining error caused by machining principle error, manufacturing error of machine tool, tool, fixture, force deformation of process system, etc.

Variable value system error: the wear of props; tools, fixtures, machine tools, etc. get thermal deformation errors before thermal equilibrium

Random error: copy of blank error, positioning error, tightening error, error of multiple adjustments, deformation error caused by residual stress

11. What are the ways to ensure and improve machining accuracy?

1. Error prevention technology: reasonable use of advanced technology and equipment to directly reduce the original error, transfer the original error, both inferior to the original error, and equalize the original error

2. Error compensation technology: on-line detection, automatic matching and grinding of mating parts, and active control of the decisive error factors

12. What are the contents of the processed surface geometry?

Geometric roughness, surface waviness, grain direction, surface defects

13. What are the physical and chemical properties of surface layer materials?

1. Cold work hardening of surface layer metal 2. Metallographic structure deformation of surface layer metal 3. Residual stress of surface layer metal

14. Try to analyze the factors that affect the surface roughness of cutting?

The roughness value is determined by: the height of the cutting residual area. The main factor: the radius of the tool nose, the main deflection angle and the secondary deflection feed. The secondary factor: the increase in cutting speed, the appropriate choice of cutting fluid, the appropriate increase of the rake angle of the tool, and the improvement of the sharpening of the tool. quality

15. Try to analyze the factors that affect the surface roughness of the grinding process?

1. Geometric factors: the influence of grinding amount on surface roughness 2. The influence of grinding wheel particle size and grinding wheel dressing on surface roughness 2. The influence of physical factors: plastic deformation of surface layer metal: grinding amount Selection of grinding wheel

16. Try to analyze the factors that affect the cold work hardening of the cutting surface?

The influence of cutting amount The influence of tool geometry The influence of machining material properties

17. What is grinding and tempering burn? 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 has exceeded the transformation temperature of martensite, the martensite of the surface metal of the workpiece will be transformed into a tempered structure with lower hardness. Quenching: If grinding The temperature of the zone exceeds the phase transition temperature, coupled with the cooling effect of the coolant, the surface metal will have a secondary quenched martensite structure, and the hardness is higher than the original martensite; in the lower layer, the hardness appears due to slow cooling Annealing of tempered structure lower than the original tempered martensite: If the temperature of the grinding zone exceeds the phase transition temperature and there is no coolant during the grinding process, the surface metal will appear annealed structure, and the hardness of the surface metal will drop sharply

18. Prevention of vibration in machining

Eliminate or weaken the conditions that produce mechanical processing vibration; improve the dynamic characteristics of the process system, improve the stability of the process system, and adopt various vibration damping devices

19. Briefly describe the main differences and applications of mechanical processing process cards, process cards, and process cards.

Process card: single-piece small batch production using common processing methods. Machining process card: medium batch production. Process card: mass production type requires strict and meticulous organization.

20. The principle of rough benchmark selection? Fine benchmark selection principle?

Coarse datum: 1. The principle of ensuring mutual position requirements; 2. The principle of ensuring the reasonable distribution of machining allowances on the machined surface; 3. The principle of facilitating workpiece clamping; 4. The principle of rough datum generally not allowed to be reused. Fine datum: 1. Datum The principle of coincidence; 2. The principle of unified benchmark; 3. The principle of mutual benchmark; 4. The principle of self-standard; 5. The principle of easy clamping

21. What are the principles of the process sequence according to the arrangement?

1. Process the datum surface first, and then process other surfaces; 2. In half of the cases, process the surface first, then process the hole; 3. Process the main surface first, then process the secondary surface; 4. Arrange the rough machining process first, and then arrange the fine Processing procedure

22. How to divide the processing stage? What are the benefits of dividing the processing stages?

Processing stages are divided: 1. Roughing stage, semi-finishing stage, finishing stage, precision finishing stage. It can ensure that there is sufficient time to eliminate thermal deformation and eliminate residual stress caused by roughing, so that the subsequent processing accuracy is improved. In addition, when the blank is found to be defective in the roughing stage, it is not necessary to perform the next processing stage to avoid waste. In addition, you can also use equipment reasonably. Low-precision machine tools are used for rough machining. Precision machine tools are used for precision machining to maintain the precision level of precision machine tools. Human resources are reasonably arranged. High-skilled workers specialize in precision and ultra-precision machining. This guarantees Product quality is very important in terms of improving the level of craftsmanship.

23. What are the factors that affect the process margin?

1. The dimensional tolerance Ta of the upper process; 2. The surface roughness Ry and the surface defect depth Ha produced by the upper process; 3. The spatial error left by the upper process

24. What is included in the composition of the working hour quota?

T quota = T single piece time + t quasi-final time / n pieces

25. What are the technological ways to improve productivity

1. Shorten the basic time; 2. Reduce the overlap between the auxiliary time and the basic time; 3. Reduce the time for arranging the work place; 4. Reduce the preparation and termination time

26. What are the main contents of the assembly process specification?

1. Analyze the product drawings, divide the assembly unit, and determine the assembly method; 2. Formulate the assembly sequence and divide the assembly process; 3. Calculate the assembly time quota; 4. Determine the assembly technical requirements, quality inspection methods and inspection tools of each process; 5. Confirm The conveying method of the assembly parts and the required equipment and tools; 6. Selection and design of the tools, fixtures and special equipment required in the assembly process

27. What should be considered in the assembly process of the machine structure?

1. The machine structure should be able to be divided into independent assembly units; 2. The repair and machining during assembly should be reduced; 3. The machine structure should be easy to assemble and disassemble

28. What content does assembly accuracy generally include?

1. Mutual position accuracy; 2. Mutual movement accuracy; 3. Mutual coordination accuracy

29. What problems should be paid attention to when searching for the assembly dimension chain?

1. The assembly dimension chain should be simplified as necessary; 2. The “one piece and one link” composed of the assembly dimension chain; 3. The “directivity” of the assembly dimension chain in the same assembly structure has assembly accuracy in different positions and directions When required, the assembly dimension chain should be supervised in different directions

30. What are the methods to ensure assembly accuracy? How are the various methods applied?

1. Interchange method; 2. Selection method; 3. Fitting method; 4. Adjustment method

31. The composition and function of machine tool fixtures?

The machine tool fixture is a device for clamping the workpiece on the machine tool. Its function is to make the workpiece have a correct position relative to the machine tool and the knife. And keep this position unchanged during the machining process. The components are: 1. Positioning element or device. 2. Tool guide element or device. 3. Clamping element or device. 4. Connection element. 5. Clamping device. 6. Other elements or devices.

Main functions 1. Guarantee processing quality 2. Improve production efficiency 3. Expand machine tool process range 4. Reduce labor intensity of workers and ensure production safety.

32. According to the scope of use of fixtures, how to classify machine tool fixtures?

1. General fixture 2. Special fixture 3. Adjustable fixture and group fixture 4. Modular fixture and random fixture

33. The workpiece is positioned on a plane. What are the commonly used positioning components? And analyze the elimination of degrees of freedom.

The workpiece is positioned on a plane. Commonly used positioning elements are 1. Fixed support 2. Adjustable support 3. Self-position support 4. Auxiliary support

34. The workpiece is positioned with a cylindrical hole. What are the commonly used positioning components? And analyze the elimination of degrees of freedom.

The workpiece is positioned with a cylindrical hole. The commonly used positioning components are 1 spindle 2. locating pin

35. What are the common positioning components for positioning on the outer surface of the workpiece? And analyze the elimination of degrees of freedom.

Positioning on the outer surface of the workpiece… Commonly used positioning elements are V-shaped blocks

36. The workpiece is positioned with “two pins on one side”, how to design two pins?

1. Determine the size and tolerance of the center distance between the two pins. 2. Determine the diameter and tolerance of the cylindrical pin. 3. Determine the width, diameter and tolerance of the diamond pin.

37. What are the two aspects of positioning error? What are the methods to calculate the positioning error?

There are two aspects of positioning error. 1. The positioning error caused by the inaccurate production of the positioning element on the workpiece positioning surface or the fixture is called the reference position error. 2. The positioning error caused by the misalignment of the process reference of the workpiece and the positioning reference is called the reference misalignment error

38. The basic requirements for the design of the workpiece clamping device.

1. During the clamping process, it should be able to maintain the correct position obtained when the workpiece is positioned. 2. The clamping force should be appropriate, and the clamping mechanism should be able to ensure that the workpiece does not loosen or vibrate during the processing process, and at the same time avoid the workpiece Inappropriate deformation and surface damage, the clamping mechanism should generally have a self-locking effect

3. The clamping device should be easy to operate, labor-saving and safe. 4. The complexity and degree of automation of the clamping device should be compatible with the production batch and production methods. The structural design should be simple, compact and try to use standardized components

39. Three elements to determine the clamping force? What are the principles for the direction of clamping force and the selection of points of application?

The selection of the direction of the clamping force at the point of action of the large and small directions should generally follow the following principles: 1. The acting direction of the clamping force should be conducive to the accurate positioning of the workpiece without destroying the positioning. For this reason, the main clamping force is generally required to be directed to the positioning surface 2 、The direction of clamping force should be consistent with the direction of the workpiece stiffness as far as possible to reduce the clamping deformation of the workpiece. General principles for the selection of clamping force application points:

1. The point of application of the clamping force should be directly on the supporting surface formed by the supporting element to ensure that the positioning of the workpiece remains unchanged.

2. The point of application of the clamping force should be at a position with better rigidity to reduce the clamping deformation of the workpiece. 3. The point of application of the clamping force should be as close as possible to the machining surface to reduce the turning moment caused by the cutting force on the workpiece

40. What are the commonly used clamping mechanisms? Focus on analyzing and mastering the oblique 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. How to classify according to the structure characteristics of drilling jigs? How to classify drill sleeves according to their structural characteristics? According to the specific connection mode of the drill template and the clamp, which types are divided into?

According to the characteristics of the common structure:

1. Fixed drilling jig 2. Rotating drilling jig 3. Flip drilling jig 4. Cover plate drilling jig 5. Sliding column drilling jig and drilling jig structure characteristics classification:

2. 1. Fixed drilling mold 2. Replaceable drilling mold 3. Quick-change drilling mold 4. Specific connection method of special drilling mold drilling template to the clamp:

3. Fixed, hinged, separated, suspended

42. What are the characteristics of the machine tool clamp of the machining center?

1. Simplified function 2. Complete positioning 3. Open structure 4. Quick readjustment