1. What are the three methods of workpiece clamping?
1). Clamping in fixtures 2. Direct alignment clamping 3. Layout alignment clamping
2. What does the process system include?
Machine tools, workpieces, fixtures, cutting tools
3. What are the stages of the mechanical machining process?
Rough machining, semi-finishing, finishing, superfinishing
4. How are benchmarks classified?
1). Design reference points
2). Process reference points: Operation, measurement, assembly, positioning: (Original, additional): (Rough reference, precision reference)
5. What constitutes primary errors during machining?
Fundamental errors · Positioning errors · Adjustment errors · Tooling errors · Fixture errors · Spindle rotation errors · Guideway errors · Transmission errors · Deformation due to forces in the process system · Thermal deformation in the process system · Tool wear · Measurement errors · Errors caused by residual stresses in the workpiece
6. How does the rigidity of the process system affect machining accuracy (machine tool deformation, workpiece deformation)?
1). Workpiece shape errors caused by variations in cutting force application points
2). Machining errors caused by variations in cutting force magnitude
3). Machining errors caused by clamping force and gravity
4). Effects of transmission forces and inertial forces on machining accuracy
7. What do machine tool guideway positioning errors and spindle rotational errors encompass?
1). Guideways: Primarily include relative displacement errors between tool and workpiece in error-sensitive directions caused by guideways.
2). Spindle: Radial runout, axial runout, angular runout.
8. What is the “error reflection” phenomenon? What is the error reflection coefficient? What measures reduce error reflection?
Error reflection occurs when variations in process system errors cause blank errors to partially transfer to the workpiece.
Measures: Increase cutting passes, enhance process system rigidity, reduce feed rate, improve blank accuracy
9. Analysis of transmission errors in machine tool drive chains? Measures to reduce transmission chain errors?
Error analysis: Evaluated using the angular error Δφ at the drive chain’s terminal component
Countermeasures:
1). Fewer transmission chain components and shorter chain length minimize Δφ, enhancing precision.
2). Lower transmission ratio i, especially at the first and last links.
3). Prioritize precision of terminal components due to their dominant influence.
4). Employ correction devices.
10. How are machining errors classified? Which errors belong to constant errors? Which errors belong to variable systematic errors? Which errors belong to random errors?
Systematic Errors: (Constant Systematic Errors Variable Systematic Errors) Random Errors
Constant Systematic Errors: Errors caused by machining principles, manufacturing errors of machine tools, cutting tools, and fixtures, as well as deformation under stress in the process system.
Variable System Errors: Tool wear, thermal deformation errors in tools, fixtures, and machine tools before thermal equilibrium
Random Errors: Replication of blank errors, positioning errors, clamping errors, errors from multiple adjustments, deformation errors caused by residual stresses
11. What are the methods to ensure and improve machining accuracy?
1). Error prevention techniques: Rational adoption of advanced processes and equipment, direct reduction of primary errors, transfer of primary errors, equalization of primary errors, homogenization of primary errors
2). Error compensation techniques: In-process inspection, automatic grinding of mating parts, proactive control of decisive error factors
12. What does the geometric morphology of machined surfaces encompass?
Geometric roughness, surface waviness, texture orientation, surface defects
13. What physical and chemical properties does the surface layer material encompass?
1). Cold work hardening of the surface layer metal
2). Microstructural deformation of the surface layer metal
3). Residual stresses in the surface layer metal
14. Analyze factors affecting surface roughness in cutting processes.
Roughness value is determined by: height of residual cutting area
Primary factors: tool tip radius, main rake angle, secondary rake angle, feed rate
Secondary factors: increasing cutting speed, selecting appropriate coolant, appropriately increasing tool front angle, improving tool grinding quality
15. Analyze the factors affecting surface roughness in grinding operations.
1). Geometric factors: Influence of grinding parameters on surface roughness
2). Influence of abrasive grit size and wheel dressing on surface roughness
3). Physical factors: Plastic deformation of surface layer metal: Grinding parameters, wheel selection
16. Analyze the factors affecting work hardening of machined surfaces.
Influence of cutting parameters
Influence of tool geometry
Influence of material properties
17. What is grinding temper 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 surpasses the martensite transformation temperature, the martensite in the workpiece surface metal transforms into a tempered structure with lower hardness.
Quenching: If the temperature in the grinding zone exceeds the phase transformation temperature, combined with the cooling effect of the coolant, the surface metal develops a secondary quenched martensite structure with higher hardness than the original martensite. Beneath this layer, slower cooling produces a tempered structure with lower hardness than the original tempered martensite.
Annealing: If the grinding zone temperature exceeds the transformation temperature and no coolant is used during grinding, the surface metal develops an annealed structure, causing a sharp decrease in surface hardness.
18. Prevention and Control of Machining Vibrations
Eliminate or reduce conditions causing machining vibrations, improve the dynamic characteristics of the process system; enhance the stability of the process system, adopt various vibration-damping and vibration-reduction devices.
19. Briefly describe the main differences and application scenarios of the machining process card, process card, and operation card.
Process Cards: Single-piece or small-batch production using conventional machining methods.
Machining Process Cards: Medium-batch production.
Process Cards: Mass production requiring rigorous and detailed organizational planning.
20. Principles for selecting rough benchmarks? Principles for selecting precision benchmarks?
Rough Benchmarks: 1. Principle of ensuring mutual positional requirements. 2. Principle of ensuring reasonable distribution of machining allowances on surfaces. 3. Principle of facilitating workpiece clamping. 4. Principle that rough benchmarks should generally not be reused.
Precision Benchmarks: 1. Principle of benchmark coincidence. 2. Principle of unified benchmarks. 3. Principle of mutual benchmarks. 4. Principle of self-benchmarking. 5. Principle of facilitating clamping.
21. What are the principles for arranging the machining sequence?
1). Machine reference surfaces first, then other surfaces.
2). In most cases, machine surfaces before holes.
3). Machine primary surfaces before secondary surfaces.
4). Schedule roughing operations before finishing operations.
22. How are machining stages divided? What are the benefits of dividing machining stages?
Machining stage division:
1. Roughing stage · Semi-finishing stage · Finishing stage · Precision finishing stage
This ensures sufficient time to eliminate thermal deformation and residual stresses from roughing, enhancing subsequent machining accuracy. Additionally, identifying issues during roughing allows for timely adjustments. Roughing stage · Semi-finishing stage · Finishing stage · Precision finishing stage This ensures sufficient time to eliminate thermal deformation and residual stresses from roughing, enhancing subsequent machining accuracy. Additionally, defects discovered during roughing can halt further processing, preventing waste. It also enables rational equipment utilization: low-precision machines for roughing, precision machines exclusively for finishing to maintain their accuracy levels; Rational allocation of human resources, with highly skilled workers dedicated to precision and ultra-precision machining, is crucial for ensuring product quality and advancing process capabilities.
23. What factors influence machining allowances?
1). Dimensional tolerance Ta from preceding operations.
2). Surface roughness Ry and surface defect depth Ha generated by preceding operations.
3). Spatial errors left by preceding operations.
24. What components constitute the labor time quota?
Tquota = Tsingle-piece time + tquasi-final time / npiece count
25. What process approaches enhance productivity?
1). Reduce basic processing time
2). Minimize overlap between auxiliary and basic processing times
3). Reduce workstation setup time; 4. Decrease preparation and completion time
26. What are the main contents of assembly process specifications?
1). Analyze product drawings, divide into assembly units, and determine assembly methods.
2). Establish assembly sequence and divide into assembly operations.
3). Calculate assembly time quotas.
4). Determine technical requirements, quality inspection methods, and inspection tools for each operation; 5. Determine the transportation method for assembly components and the required equipment and tools.
6). Select and design the tools, fixtures, and specialized equipment needed during assembly.
27. What aspects should be considered regarding the assembly workability of machine structures?
1). Machine structures should be divisible into independent assembly units.
2). Minimize fitting and machining during assembly.
3). Machine structures should facilitate both assembly and disassembly.
28. What aspects are generally included in assembly accuracy?
1). Mutual positional accuracy.
2). Mutual motion accuracy.
3). Mutual fit accuracy.
29. What issues should be noted when determining assembly dimension chains?
1). Assembly dimension chains should be simplified as necessary.
2). The “one-part-one-link” principle for dimension chain composition; 3. Directionality of assembly dimension chains: When assembly accuracy requirements exist in different positions and directions within the same assembly structure, dimension chains should be monitored according to their respective directions.
30. What methods ensure assembly accuracy? How are these methods applied?
1). Interchangeability method 2). Selection method 3). Fitting method 4). Adjustment method
31. Composition and function of machine tool fixtures?
Machine tool fixtures are devices for clamping workpieces on machine tools. Their function is to establish the correct position of the workpiece relative to the machine tool and cutting tool, and maintain this position unchanged during machining. Components include:
1). Locating 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.
Primary Functions: 1. Ensure machining quality 2. Improve production efficiency 3. Expand the range of machine tool processes 4. Reduce labor intensity and ensure production safety.
32. How are machine tool fixtures classified based on their scope of application?
1). General-purpose fixtures
2). Special-purpose fixtures
3). Adjustable fixtures and group fixtures
4). Modular fixtures and random fixtures
33. What are the common locating elements when workpieces are positioned by flat surfaces? Analyze the elimination of degrees of freedom.
For workpiece positioning on a plane surface, common locating elements include:
1). Fixed supports
2). Adjustable supports
3). Self-locating supports
4). Auxiliary supports
34. For workpiece positioning using cylindrical bores, what are the common locating elements? Analyze the elimination of degrees of freedom.
For workpiece positioning using cylindrical bores, common locating elements include:
1. Mandrels
2. Locating pins
35. When a workpiece is positioned using an outer cylindrical surface, what are the commonly used locating elements? Analyze the elimination of degrees of freedom.
When a workpiece is positioned using an outer cylindrical surface, commonly used locating elements include: V-blocks.
36. When a workpiece is positioned using “one face and two pins,” how should the two pins be designed?
1. Determine the center distance and tolerance between the two pins.
2. Determine the diameter and tolerance of the cylindrical pins.
3. Determine the width, diameter, and tolerance of the diamond-shaped pins.
37. What are the two aspects of locating errors? What methods are used to calculate locating errors?
Locating errors comprise two aspects:
1. Errors caused by inaccuracies in the workpiece locating surfaces or fixture locating elements are termed reference position errors.
2. Errors resulting from non-coincidence between the workpiece’s process reference and locating reference are called reference non-coincidence errors.
38. Fundamental requirements for workpiece clamping device design.
1. Maintain the correct position achieved during workpiece locating throughout the clamping process. 2. Apply appropriate clamping force. The clamping mechanism must prevent workpiece loosening or vibration during machining while avoiding undue deformation and surface damage. Clamping mechanisms should generally incorporate self-locking functionality.
3. The clamping device should be easy to operate, require minimal effort, and be safe. 4. The complexity and automation level of the clamping device should align with production batch size and manufacturing methods. Structural design should strive for simplicity and compactness, utilizing standardized components whenever possible.
39. What are the three key factors in determining clamping force? What principles guide the selection of clamping force direction and point of application?
Magnitude Direction Point of Application
The selection of clamping force direction generally follows these principles:
1. The clamping force direction should facilitate accurate workpiece positioning without compromising it. Therefore, the primary clamping force is typically directed perpendicular to the locating surface.
2. The clamping force direction should align as closely as possible with the direction of the workpiece’s highest rigidity to minimize clamping deformation.
3. The clamping force direction should align as closely as possible with the cutting force and workpiece gravity direction to reduce the required clamping force. General principles for selecting the clamping force point of application:
1). The clamping force application point should be directly within the support plane formed by the support elements to ensure the achieved positioning remains unchanged.
2). The clamping force application point should be located on a rigid section to minimize clamping deformation of the workpiece.
3). The clamping force application point should be as close as possible to the machined surface to reduce the overturning moment caused by cutting forces on the workpiece.
40. What are the common clamping mechanisms? Focus on analyzing and mastering the inclined wedge clamping mechanism.
1. Inclined wedge clamping mechanism
2. Screw clamping mechanism
3. Eccentric clamping mechanism
4. Hinge clamping mechanism
5. Centering clamping mechanism
6. Interlocking clamping mechanism
41. How are drill jigs classified based on structural characteristics? How are they classified based on drill sleeve structure? What are the categories based on the connection method between the drill template and the clamping body?
Drill jigs classified by structural characteristics:
1. Fixed drill jig 2. Rotary drill jig 3. Flip-type drill jig 4. Cover plate drill jig 5. Slide column drill jig
Drill jig classification by structural features:
2. 1. Fixed Drill Jig 2. Interchangeable Drill Jig 3. Quick-Change Drill Jig 4. Special Drill Jig Connection Methods Between Drill Plate and Clamping Body:
3. Fixed Type, Hinged Type, Detachable Type, Suspended Type
42. What are the characteristics of machining center machine tool clamping devices?
1. Simplified Functionality 2. Complete Positioning 3. Open Structure 4. Rapid Readjustment
