42 Machining Process Knowledge and Skills
1. What are the three methods of workpiece clamping?
{1. Clamping in fixtures; 2. Direct alignment clamping; 3. Marking alignment clamping}
2. What does the process system include?
{Machine tools, workpieces, fixtures, cutting tools}
3. What are the components of the machining process?
{Rough machining, semi-finishing, finishing, ultra-finishing}
4. How are benchmarks classified?
{1. Design benchmark; 2. Process benchmark: operation, measurement, assembly, positioning: (original, additional): (rough benchmark, fine benchmark)}
5. What does machining accuracy include?
{1. Dimensional accuracy; 2. Shape accuracy; 3. Position accuracy}
6. What are the original errors that occur during the machining process?
{Principle error, positioning error, adjustment error, tool error, fixture error, machine tool spindle rotation error, machine tool guideway alignment error, machine tool transmission error, process system deformation due to force, process system deformation due to heat, tool wear, measurement error, error caused by residual stress in the workpiece}
7. How does the stiffness of the process system affect machining accuracy (machine tool deformation, workpiece deformation)?
{1. Workpiece shape error caused by changes in the cutting force application point; 2. Machining error caused by changes in cutting force magnitude; 3. Machining error caused by clamping force and gravity; 4. Influence of transmission force and inertial force on machining accuracy}
8. What are the guiding errors of machine tool guideways and the rotation errors of the spindle?
{1. Guideways: mainly include relative displacement errors between the tool and workpiece in the error-sensitive direction caused by guideways; 2. Spindle: radial runout, axial runout, angular wobble}
9. What is the "error replication" phenomenon? What is the error replication coefficient? What measures can reduce error replication?
{Due to changes in process system error deformation, part of the blank error is reflected on the workpiece. Measures: increase the number of passes, increase process system stiffness, reduce feed rate, improve blank accuracy}
10. How is machining error classified? Which errors are constant errors? Which are variable systematic errors? Which are random errors?
{Systematic errors: (constant systematic errors, variable systematic errors); Random errors.
Constant systematic errors: machining principle errors, machine tool, tool, fixture manufacturing errors, process system deformation due to force, etc.
Variable systematic errors: tool wear; tool, fixture, machine tool thermal deformation errors before reaching thermal equilibrium.
Random errors: blank error replication, positioning error, clamping error, multiple adjustment errors, deformation error caused by residual stress}
11. What are the approaches to ensure and improve machining accuracy?
{1. Error prevention technology: rational adoption of advanced processes and equipment, direct reduction of original errors, transfer of original errors, averaging of original errors.
2. Error compensation technology: online detection, automatic matching of mating parts, proactive control of decisive error factors}
12. What does the geometric morphology of the machined surface include?
{Geometric roughness, surface waviness, texture direction, surface defects}
13. What are the physical and chemical properties of the surface layer material?
{1. Cold working hardening of the surface layer metal; 2. Metallographic structure deformation of the surface layer metal; 3. Residual stress in the surface layer metal}
14. What factors affect the surface roughness in cutting?
{Roughness value is determined by: height of the cutting residual area. Main factors: tool nose radius, main cutting edge angle, secondary cutting edge angle, feed rate. Secondary factors: increase in cutting speed, appropriate selection of cutting fluid, appropriate increase in tool rake angle, improvement in tool grinding quality}
15. What factors affect the surface roughness in grinding?
{1. Geometric factors: influence of grinding parameters on surface roughness; 2. Influence of grinding wheel grain size and dressing on surface roughness; 3. Physical factors: plastic deformation of the surface layer metal: grinding parameters, grinding wheel selection}
16. What factors affect the cold working hardening of the machined surface?
{Influence of cutting parameters, influence of tool geometry, influence of material properties}
17. What is grinding tempering burn? What is grinding quenching burn? What is grinding annealing burn?
{Tempering: if the temperature in the grinding zone does not exceed the phase transformation temperature of quenched steel but exceeds the transformation temperature of martensite, the martensite in the workpiece surface will transform into a lower hardness tempered structure. Quenching: if the temperature in the grinding zone exceeds the phase transformation temperature, and with the cooling effect of the coolant, the surface metal will exhibit secondary quenched martensite structure, with higher hardness than the original martensite; in the lower layer, due to slower cooling, a tempered structure with lower hardness than the original tempered martensite appears. Annealing: if the temperature in the grinding zone exceeds the phase transformation temperature and there is no coolant during grinding, the surface metal will exhibit an annealed structure, and the surface hardness will decrease sharply}
18. How to prevent and control mechanical machining vibrations?
{Eliminate or weaken the conditions that generate mechanical machining vibrations; improve the dynamic characteristics of the process system, enhance the stability of the process system, adopt various vibration damping and reduction devices}
19. Briefly describe the main differences and applications of machining process cards, process cards, and operation cards.
{Process cards: used for single-piece or small-batch production with conventional machining methods. Machining process cards: used for medium-batch production. Operation cards: used for large-batch or mass production types requiring strict and detailed organization}
20. What are the principles for selecting rough and fine benchmarks?
{Rough benchmark: 1. Principle of ensuring mutual position requirements; 2. Principle of ensuring reasonable distribution of machining allowance; 3. Principle of facilitating workpiece clamping; 4. Principle of generally not reusing rough benchmarks. Fine benchmark: 1. Principle of benchmark coincidence; 2. Principle of unified benchmark; 3. Principle of mutual benchmark; 4. Principle of self-benchmark; 5. Principle of facilitating clamping}
21. What are the principles for arranging process sequences?
{1. First machine the reference surface, then other surfaces; 2. Generally, machine surfaces first, then holes; 3. Machine main surfaces first, then secondary surfaces; 4. Arrange rough machining first, then finishing}
22. How to divide machining stages? What are the benefits of dividing machining stages?
{Machining stage division: 1. Rough machining stage, semi-finishing stage, finishing stage, precision finishing stage. It ensures sufficient time to eliminate thermal deformation and residual stress from rough machining, improving subsequent machining accuracy. Additionally, if defects are found in the blank during the rough machining stage, the next machining stage can be avoided, preventing waste. It also allows for rational use of equipment, with low-precision machine tools for rough machining and precision machine tools exclusively for finishing, maintaining the precision level of precision machine tools; rational arrangement of human resources, with highly skilled workers specializing in precision and ultra-precision machining, which is crucial for ensuring product quality and improving process level}
23. What factors affect the process allowance?
{1. Dimensional tolerance of the previous process; 2. Surface roughness and defect depth of the previous process; 3. Spatial error left by the previous process}
24. What does the composition of time quota include?
{T quota = T unit time + t setup time / n number of pieces}
25. What are the process approaches to improve productivity?
{1. Shorten basic time; 2. Reduce auxiliary time overlapping with basic time; 3. Reduce workplace arrangement time; 4. Reduce setup and finishing time}
26. What are the main contents of assembly process planning?
{1. Analyze product drawings, divide assembly units, determine assembly methods; 2. Draft assembly sequence, divide assembly operations; 3. Calculate assembly time quota; 4. Determine technical requirements for each operation, quality inspection methods and tools; 5. Determine the transportation method of assembly parts and required equipment and tools; 6. Select and design tools, fixtures, and special equipment required in the assembly process}
27. What should be considered in the assembly processability of machine structures?
{1. Machine structure should be divisible into independent assembly units; 2. Reduce assembly fitting and machining; 3. Machine structure should be easy to assemble and disassemble}
28. What does assembly accuracy generally include?
{1. Mutual position accuracy; 2. Mutual motion accuracy; 3. Mutual fit accuracy}
29. What should be noted when searching for assembly dimension chains?
{1. Assembly dimension chains should be appropriately simplified; 2. Assembly dimension chains should follow the "one part, one link" principle; 3. The "directionality" of assembly dimension chains: in the same assembly structure, if there are assembly accuracy requirements in different positions and directions, assembly dimension chains should be established according to different directions}
30. What are the methods to ensure assembly accuracy? How are these methods applied?
{1. Interchangeability method; 2. Selection method; 3. Fitting method; 4. Adjustment method}
31. What are the components and functions of machine tool fixtures?
{Machine tool fixtures are devices used to clamp workpieces on machine tools. Their function is to position the workpiece relative to the machine tool and cutting tool correctly and maintain this position during machining. Components include: 1. Positioning elements or devices; 2. Tool guiding elements or devices; 3. Clamping elements or devices; 4. Connecting elements; 5. Fixture body; 6. Other elements or devices. Main functions: 1. Ensure machining quality; 2. Improve production efficiency; 3. Expand machine tool process range; 4. Reduce worker labor intensity and ensure production safety}
32. How are machine tool fixtures classified according to their application range?
{1. General fixtures; 2. Special fixtures; 3. Adjustable fixtures and group fixtures; 4. Modular fixtures and random fixtures}
33. What are the commonly used positioning elements for planar workpiece positioning? Analyze the degree of freedom elimination.
{Commonly used positioning elements for planar workpiece positioning: 1. Fixed supports; 2. Adjustable supports; 3. Self-aligning supports; 4. Auxiliary supports}
34. What are the commonly used positioning elements for cylindrical hole workpiece positioning? Analyze the degree of freedom elimination.
{Commonly used positioning elements for cylindrical hole workpiece positioning: 1. Mandrels; 2. Positioning pins}
35. What are the commonly used positioning elements for external cylindrical surface workpiece positioning? Analyze the degree of freedom elimination.
{Commonly used positioning elements for external cylindrical surface workpiece positioning: V-blocks}
36. How to design two pins for "one surface, two pins" positioning?
{1. Determine the center distance dimension and tolerance of 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 for calculating positioning error?
{Two aspects of positioning error: 1. Positioning error caused by inaccuracies in the workpiece positioning surface or fixture positioning elements is called datum position error; 2. Positioning error caused by the non-coincidence of the workpiece process datum and positioning datum is called datum non-coincidence error}
38. What are the basic requirements for designing workpiece clamping devices?
{1. Maintain the correct position obtained during workpiece positioning during clamping; 2. Clamping force should be appropriate, the clamping mechanism should ensure no loosening or vibration during machining, while avoiding improper deformation and surface damage, the clamping mechanism should generally have a self-locking function; 3. Clamping devices should be easy to operate, labor-saving, and safe; 4. The complexity and automation level of clamping devices should match the production batch and mode. Structural design should strive for simplicity, compactness, and the use of standardized components}
39. What are the three elements of clamping force determination? What are the principles for selecting clamping force direction and application points?
{Magnitude, direction, application point. Principles for selecting clamping force direction: 1. Clamping force direction should facilitate accurate workpiece positioning without disrupting it, generally requiring the main clamping force to be perpendicular to the positioning surface; 2. Clamping force direction should align with the direction of maximum workpiece stiffness to reduce clamping deformation; 3. Clamping force direction should align with cutting force and workpiece gravity direction to reduce required clamping force. Principles for selecting clamping force application points: 1. Clamping force application points should be within the support surface formed by support elements to maintain workpiece positioning; 2. Clamping force application points should be on rigid parts to reduce clamping deformation; 3. Clamping force application points should be as close as possible to the machining surface to reduce the overturning moment caused by cutting force}
40. What are the commonly used clamping mechanisms? Focus on analyzing the wedge clamping mechanism.
{1. Wedge clamping mechanism; 2. Screw clamping mechanism; 3. Eccentric clamping mechanism; 4. Hinge clamping mechanism; 5. Centering clamping mechanism; 6. Linkage clamping mechanism}
41. How are drilling jigs classified according to structural features? How are drill bushings classified according to structural features? How are drill templates classified according to their connection with the fixture body?
{Drilling jigs classified by structural features: 1. Fixed drilling jigs; 2. Rotary drilling jigs; 3. Flip-type drilling jigs; 4. Cover plate drilling jigs; 5. Sliding column drilling jigs. Drill bushings classified by structural features: 1. Fixed drill bushings; 2. Replaceable drill bushings; 3. Quick-change drill bushings; 4. Special drill bushings. Drill templates classified by connection with the fixture body: 1. Fixed; 2. Hinged; 3. Separated; 4. Suspended}
42. What are the characteristics of machining center fixtures?
{1. Simplified functions; 2. Complete positioning; 3. Open structure; 4. Quick readjustment}