1.What are the three methods of workpiece clamping?
1. Fixture clamping; 2. Direct alignment clamping; 3. Line alignment clamping
2.What does the process system include?
Machine tool, workpiece, fixture, cutting tool
3.What are the components of the mechanical machining process?
Rough machining, semi-finishing, finishing, ultra-finishing
4.How are benchmarks classified?
1. Design benchmark;
2. Process benchmark: operation, measurement, assembly, positioning: (primary, additional): (rough benchmark, fine benchmark)
What does machining accuracy include?
1. Dimensional accuracy; 2. Shape accuracy; 3. Position accuracy
5.What are the types of primary errors that occur during the machining process?
Principle error, positioning error, adjustment error, tool error, fixture error, spindle rotation error of machine tool, guide rail deviation error of machine tool, transmission error of machine tool, deformation of process system due to force, deformation of process system due to heat, tool wear, measurement error, error caused by residual stress of workpiece.
6.How does the rigidity of the process system affect machining accuracy (machine tool deformation, workpiece deformation)?
1. Workpiece shape errors caused by changes in the location of cutting force application;
2. Machining errors caused by changes in cutting force magnitude;
3. Machining errors caused by clamping force and gravity;
4. Impact of transmission force and inertia force on machining accuracy.
7.What does the guide rail deviation and spindle rotation error of the machine tool include?
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 runout, axial runout, tilt oscillation.
8.What is the “error reflection” phenomenon? What is the error reflection coefficient? What measures are taken to reduce error reflection?
Error reflection refers to the reflection of the error portion of the blank onto the workpiece due to changes in the deformation of the process system. Measures: Increase the number of tool passes, increase the rigidity of the process system, reduce the feed rate, improve the blank precision.
9.Analysis of transmission chain transmission errors of machine tools? Measures to reduce transmission chain transmission errors?
Error analysis: It uses the angle error Δφ of the end element of the transmission chain to measure.
Measures: 1. The fewer the number of transmission chain components, the shorter the transmission chain, the smaller the Δφ, and the higher the accuracy.
2. The smaller the transmission ratio i, especially the smaller the transmission ratio at the two ends.
3. Since the error of the end element of the transmission components has the greatest impact, it should be made as accurate as possible.
4. Use correction devices.
10.How are machining errors classified? Which errors belong to constant value errors? Which errors belong to variable value system errors? Which errors belong to random errors?
Systematic errors: (constant value system errors, variable value system errors) Random errors
Constant value system errors: Machining principle errors, manufacturing errors of machine tools, cutting tools, fixtures, and machining errors caused by deformation of the process system due to force.
Variable value system errors: Tool wear; errors in thermal deformation of cutting tools, fixtures, and machine tools before thermal equilibrium.
Random errors: Copying errors of the blank, positioning errors, clamping errors, errors from multiple adjustments, deformation errors caused by residual stress.
11.What are the ways to ensure and improve machining accuracy?
1.Error prevention technology: Reasonably adopt advanced processes and equipment to directly reduce original errors, transfer original errors, equalize original errors, and homogenize original errors.
2.Error compensation technology: Online detection, automatic grinding of mating parts, and actively control the determining error factors.
12.What does the surface geometric morphology of machined parts include?
Geometric roughness, surface waviness, texture direction, surface defects.
13.What are the physical and chemical properties of surface layer materials?
1.Cold work hardening of surface layer metal
2.Deformation of metallographic structure of surface layer metal
3.Residual stress of surface layer metal
14.What factors affect the surface roughness of cutting processes?
The roughness value is determined by the height of the cutting residual area. Major factors include: tool tip radius, main rake angle, secondary rake angle, feed rate. Minor factors include: increasing cutting speed, appropriately selecting cutting fluid, appropriately increasing tool front angle, and improving tool grinding quality.
15.Analyze the factors affecting surface roughness in grinding processes:
Geometric factors: Influence of grinding allowance on surface roughness.
1.Influence of grit size and wheel dressing on surface roughness.
2.Influence of physical factors: Plastic deformation of surface layer 3.metal: Grinding allowance, selection of grinding wheel.
16.Analyze the factors affecting surface work hardening in cutting processes:
Effects of cutting allowance, tool geometry, and material properties.
17.What are grinding burn, quenching burn, and annealing burn?
Burn: If the temperature in the grinding area does not exceed the phase transition temperature of quenched steel but exceeds the transformation temperature of martensite, martensite on the surface of the workpiece will transform into lower hardness tempered structure.
Quenching: If the temperature in the grinding area exceeds the phase transition temperature, coupled with the cooling effect of the coolant, secondary quenched martensitic structure with higher hardness appears on the surface metal; in its lower layer, lower hardness tempered structure appears due to slower cooling.
Annealing: If the temperature in the grinding area exceeds the phase transition temperature and there is no coolant during the grinding process, the surface metal will exhibit annealed structure, and the hardness of the surface metal will decrease sharply.
18.Prevention and control of mechanical machining vibration:
Eliminate or reduce the conditions that cause mechanical machining vibration; improve the dynamic characteristics of the process system; enhance the stability of the process system; utilize various vibration damping devices.
19.Briefly describe the main differences and applications of process cards, machining process cards, and operation cards in mechanical machining processes.
Process card: Used for single-piece or small-batch production with conventional machining methods.
Machining process card: Used for medium-batch production.
Operation card: Used for large-batch mass production with strict and detailed organizational requirements.
20.Principles of selecting rough and precision datum:
Rough datum: 1. Ensure the requirements of mutual positions. 2. Ensure reasonable distribution of machining allowances on surfaces. 3. Facilitate workpiece clamping. 4. Rough datum should generally not be reused.
Precision datum: 1. Principle of datum coincidence. 2. Principle of unified datum. 3. Principle of mutual reference. 4. Principle of self-reference. 5. Facilitate clamping.
21.What are the principles for arranging process sequences?
Machine the reference surfaces first, then machine other surfaces.
In most cases, machine surfaces first, then drill holes.
Machine primary surfaces first, then secondary surfaces.
Arrange rough machining operations first, followed by finishing operations.
22.How to divide the machining stages? What are the benefits of dividing the machining stages?
Dividing the machining stages into rough machining, semi-finishing, finishing, and precision polishing stages ensures sufficient time for eliminating thermal deformation and residual stresses generated during rough machining, thus improving the accuracy of subsequent machining. Additionally, defects discovered during rough machining can prevent further processing stages, avoiding waste. Furthermore, it allows for the rational use of equipment, with low-precision machine tools used for rough machining and precision machine tools dedicated to finishing, maintaining the accuracy level of precision machine tools. Rational allocation of manpower resources is also facilitated, with highly skilled workers specializing in precision and ultra-precision machining, which is crucial for ensuring product quality and improving technological proficiency.
23.Factors affecting process margin include:
Dimensional tolerance of the preceding process (Ta).
Surface roughness (Ry) and deep surface defects (Ha) generated by the preceding process.
Spatial errors left by the preceding process.
25.Approaches to improve productivity include:
1.Shortening basic time.
2.Reducing overlap between auxiliary time and basic time.
3.Reducing time for setting up workspaces.
4.Reducing preparation and finishing time.
26.What are the main contents of the assembly process specification?
1.Analyzing product drawings, dividing assembly units, and determining assembly methods.
2.Drafting assembly sequences and dividing assembly processes.
3.Calculating assembly time quotas.
4.Determining the technical requirements for each assembly process, quality inspection methods, and inspection tools.
5.Determining the transportation methods for assembly components and the required equipment and tools.
6.Selecting and designing the tools, fixtures, and specialized equipment required during the assembly process.
27.What aspects of assembly process feasibility should be considered for machine structures?
1.Machine structures should be divisible into independent assembly units.
2.Minimizing rework and mechanical machining during assembly.
3.Machine structures should be easy to assemble and disassemble.
28.What does assembly accuracy generally include?
1.Mutual positional accuracy.
2.Mutual motion accuracy.
3.Mutual fit accuracy.
29.What should be considered when searching for assembly dimension chains?
1.Assembly dimension chains should be simplified as necessary.
2.The “one link, one part” composition of assembly dimension chains.
3.The “directionality” of assembly dimension chains: When assembly accuracy is required in different directions within the same assembly structure, assembly dimension chains should be monitored accordingly in 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.Machine Tool Fixture Composition and Functions:
A machine tool fixture is a device used to clamp workpieces on a machine tool. Its function is to position the workpiece correctly relative to the machine tool and cutting tool and to maintain this position during the machining process. The 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 the range of machine tool processes.
4.Reduce labor intensity and ensure production safety.
32.Classification of Machine Tool Fixtures by Usage Scope:
1.General fixtures
2.Special fixtures
3.Adjustable fixtures and modular fixtures
4.Combination fixtures and dedicated fixtures
33.The workpiece is positioned on a flat surface. What are the commonly used positioning components?Analyze the situation of eliminating degrees of freedom.
For workpieces positioned on a flat surface, commonly used locating elements include:
1.Fixed supports2.Adjustable supports3.Self-locating supports4.Auxiliary supports
34.The workpiece is positioned with a cylindrical hole. What are the commonly used positioning components? And analyze the situation of eliminating degrees of freedom.
The workpiece is positioned with a cylindrical hole. Commonly used positioning components include 1. Spindle 2. Positioning pin
35. When positioning a workpiece on an outer circular surface, what are the commonly used positioning components? And analyze the situation of eliminating degrees of freedom.
The workpiece is positioned on the outer circular surface. Commonly used positioning components include V-shaped blocks
36.For workpieces positioned with “one side, two pins,” the design of the two pins involves:
- Determining the center-to-center distance and tolerance.
- Establishing the diameter and tolerance of the cylindrical pin.
- Specifying the width diameter and tolerance of the diamond-shaped pin.
37.Locating errors encompass two aspects:
- Positional errors due to inaccuracies in the locating elements on the workpiece or fixture are termed as datum location errors.
- Errors arising from misalignment between the workpiece’s process datum and the locating datum are referred to as datum misalignment errors.
38.Basic requirements for the design of workpiece clamping devices include:
- The clamping mechanism should maintain the correct position obtained during workpiece positioning.
- Appropriate clamping force should prevent workpiece loosening or vibration during processing, avoiding improper deformation and surface damage while ensuring self-locking.
- Clamping devices should be easy, labor-saving, and safe to operate.
- The complexity and automation level of clamping devices should match production batch and method, with structural design aiming for simplicity, compactness, and the use of standardized components as much as possible.
39.The three determining factors for clamping force are:
Magnitude: The amount of force required to securely hold the workpiece.
Direction: The orientation of the clamping force relative to the workpiece.
Point of application: The location on the workpiece or fixture where the clamping force is applied.
The selection of clamping force direction and point of application should follow these principles:
Direction of Clamping Force:
The direction of clamping force should facilitate accurate positioning of the workpiece without compromising its alignment. Therefore, the primary clamping force is typically directed perpendicular to the locating surface.
The direction of clamping force should align with the direction of maximum rigidity of the workpiece to minimize workpiece deformation.
The direction of clamping force should align with the direction of cutting forces and workpiece gravity to minimize the required clamping force.
Point of Application of Clamping Force:
The point of application of clamping force should be aligned with the supporting elements forming the supporting surface to maintain the established workpiece positioning.
The point of application of clamping force should be located in areas of higher rigidity to minimize workpiece deformation.
The point of application of clamping force should be as close as possible to the machining surface to reduce the overturning moment caused by cutting forces on the workpiece.
40. What are the commonly used clamping mechanisms? Focus on analyzing and mastering the wedge clamping mechanism.
1. Inclined 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 drilling molds according to their structural characteristics? How to classify drill sleeves according to their structural characteristics? What are the categories according to the specific connection methods between the drill template and the clamp?
The drilling mold is based on the total structural characteristics:
1. Fixed drilling die 2. Rotary drilling die 3. Flip-type drilling die 4. Cover type drilling die 5. Sliding column drilling die Drilling die structural features classification:
2. 1. Fixed drilling mold 2. Replaceable drilling mold 3. Quick-change drilling mold 4. Special drilling mold and the specific connection method of the drilling template to the clamp:
3. Fixed, hinged, separated and suspended
