Examination content and answers for junior fitter

Elementary test questions for machine repair and fitter

Elementary

1. Fill in the blanks

1. The hydraulic oil pump is the (power) mechanism in the hydraulic transmission system .

2. Gray cast iron is represented by the symbol (HT), ductile iron is represented by the symbol (QT), and malleable cast iron is represented by the symbol (KT).

3. The commonly used tooth profile angle of standard cylindrical gears is (20°).

4. When the belt is driven, if the tension is (insufficient), the belt will easily slip when under load; if the tension (is too large), the life of the belt will be greatly shortened.

5. Hot fitting is suitable for (interference) fit.

6. If the coaxiality of the spindle journal exceeds the allowable tolerance, it will cause the spindle to rotate (circular runout).

7. For the national standard first-class flat plate, the grinding points within 25mmX25mm should be (20 o'clock - 25 o'clock).

8. Manual correction includes (twisting), (bending), (extension), (stretching) and other methods.

9. The choice of file thickness depends on the workpiece (machining allowance), (machining accuracy), (surface roughness) and (material properties).

10. To correct the convex sheet in the middle, you must first hammer (edge) from (outside) to (inside) and gradually from heavy to light, from dense to sparse, so that The raised parts will gradually become flat.

11. Screw transmission can convert the (rotary) motion of the driving part into the (linear reciprocating) motion of the driven part.

12. The types of chain drives are (transmission) chain drive, (lifting) chain drive, and (traction) chain drive.

13. Cutting fluid has the functions of (cooling), (lubrication) and (cleaning).

14. When assembling an ordinary wedge key, make sure that the (upper and lower working surfaces) of the key are in close contact with the bottom of the shaft groove and hub groove, and there should be a gap (on both sides).

15. Cutting motion is the relative motion of (cutting tool) and (workpiece) contacting each other to cut off excess metal.

16. The cutting edge of the drill bit is distributed symmetrically to the (axis), and the radial cutting forces cancel each other out, so the drill bit is not easy to bend.

17. In planing processing, (linear reciprocating) motion is the main motion.

18. In order to ensure that the rolling bearing has a certain room for thermal expansion during operation, among the two coaxial bearings, there must be an inner or outer ring of one bearing that can expand during thermal expansion (axial direction) move.

19. The accuracy of the shaft mainly includes (dimensional accuracy), (geometric shape accuracy), (mutual position accuracy) and (surface roughness).

20. When assembling the worm drive mechanism, the axial position of the worm gear can be adjusted by changing (the thickness of the washer).

21. The fit between the pulley hole and the shaft usually adopts (HT/K6) excessive fit.

22. For a rigid rotor whose rotation speed is not very high, its unbalanced state can be divided into two types, namely (static) unbalance and (dynamic) unbalance.

23. When starting the saw, apply appropriate pressure, the reciprocating stroke should be short, and the sawing angle should be slightly less than (15°).

24. The fixed sleeve of the micrometer is engraved with engraved lines at intervals of 0.5mm, and the circumference of the micrometer cylinder is evenly engraved with 50 grids. Therefore, every time the micrometer cylinder rotates one division, the micrometer screw moves forward (0.01mm).

25. Tempering can be divided into (low temperature) tempering, (medium temperature) tempering and (high temperature) tempering.

26. To ensure the correct meshing of each pair of teeth of a pair of involute gears, it is necessary to ensure that their (module) and (tooth profile angle) are equal.

27. The assembly methods of rolling bearings include: knock-in method, (press-in) method, and (temperature difference) method.

28. GCr15 is ball bearing steel, G means (ball bearing steel), 15 means (chromium content 1.5).

29. Three views include (main) view, (top) view and (sitting) view.

30. Damage to mechanical parts can be divided into two ways: (natural wear) and (accidental wear).

2. Multiple choice

1. Use a universal angle ruler to measure. If the measured angle is greater than 90° and less than 180°, an (A) should be added to the reading.

A.90° B. 180° C.360° D.270°

2. On the vernier of the 0.02mm vernier caliper, the 50th grid is marked on the ruler body (A) mm line alignment.

A.19 B.39 C.29 D.49

3. There is a hole with a size of Φ20 0 0.33mm and a shaft with a size of Φ20 0 0.33mm. The maximum The gap should be (B) mm.

A. 0.066 B.0.033 C.0 0.044

4. When installing the V pulley, the radial circular runout is required to be (A) times the diameter of the pulley.

A.0.0025-0.0005 B.0.025-0.005 C.0.25-0.5 D.2.5-5

5. In hydraulic transmission, (B) is used to change the movement of the piston speed.

A. Directional valve B. Throttle valve C. Relief valve D. Safety valve

6. The sum of the rake angle, relief angle and wedge angle of the tool (C) .

A. Greater than 90° B. Less than 90° C. Equal to 90° D. 0°

7. (C) Applicable to transmission between two parallel shafts.

A. Bevel gear B. Worm, worm gear C. Cylindrical gear D. Spiral gear

8. The method of using a press to correct the screw belongs to method (C).

A. Stretch B. Twist C. Bending D. Extension

9. When the holes to be processed need to be drilled, expanded and reamed in sequence, you need to use Use (C).

A. Fixed drill bushing B. Replaceable drill bushing C. Quick-change drill bushing D. Special drill bushing

10. The long transmission screw and light screw removed from the machine tool The bar should be (D) so that it will not deform.

A. Use V-shaped frame to support both ends and lay flat B. Free and constant position C. Inclined D. Hang vertically

11. When chiseling, the back angle of the chisel is generally (B).

A. 3°—5° B.5°—8° C.8°—10° D.10°—12°

12. Vertex angle of standard twist drill 2Φ is (B).

A. 110°Φ±2° B.118°±2° C.125°±2° D.130°±2°

13. Sawing hard materials, When cutting parts such as pipes or thin plates, (C) saw blades should be used.

A. Coarse teeth B. Medium teeth C. Fine teeth D. Fine teeth

14. Good heat resistance and cutting temperature up to 540°C-620°C The tool material is (B).

A. Carbide B. High-speed steel C. Alloy tool steel D. Carbon tool steel

15. Among the following four types of steel (A) has the highest hardness.

A.T10 steel B.20 steel C.65Mn steel D.A3 steel

16. Quenching and tempering treatment is the heat treatment of (C).

A. Quenching at low temperature and tempering B. Quenching at medium temperature and tempering C. Quenching at high temperature and tempering D. Quenching

17. Typical heat treatment process after forging to make ruler teeth from 40Cr steel Should be (B).

A. Normalizing treatment B. Complete annealing C. Quenching and tempering treatment D. Tempering treatment

18. In order to improve the surface hardness and wear resistance of gray cast iron, (B ) heat treatment method is better.

A. Quenching and heating and tempering after carburizing B. Electric contact heating surface quenching

C. Isothermal quenching D. High temperature tempering

19.P10 Carbide tools are often used for cutting (A).

A. General steel B. Heat-resistant steel C. Cast iron D. Alloy steel

20. During the tensile test, the sample The maximum stress that can be endured before breaking is called the material's (B).

A. Yield point B. Tensile strength C. Elastic limit D. Impact toughness

21. The better the material (B), the better its breakability .

A. Strength B. Plasticity C. Hardness D. Toughness

22. When scribing, the line used to determine the size, geometric shape and relative position of each part of the workpiece is called ( C) line.

A. Original B. Zero position C. Reference D. Center

23. When marking lines on the surface of castings and forging blanks, (C) paint can be used.

A. Purple B. Copper sulfate solution C. Lime water D. Red powder

24. During chisel cutting, the gap between the rake surface and the base surface of the chisel The angle is (B).

A. Wedge angle B. Front angle C. Back angle D. Edge angle

25. The main working surface of a file refers to the file teeth (A).

A. Upper and lower sides B. Two sides C. One upper and lower side D. All surfaces

26. The nominal diameter of the thread refers to the basic size of the major diameter of the thread, that is (A ).

A. External thread crest diameter or internal thread crest diameter

B. External thread crest diameter or internal thread crest diameter

C. Internal , External thread crest diameter

D. Internal and external thread bottom diameter

27. The abrasives mainly used in carbon tool steel, alloy tool steel, high-speed steel and cast iron work are (B).

A. Carbide abrasives B. Oxide abrasives C. Diamond abrasives D. Others

28. The characteristic of static unbalance is that the weight always stays in the direction of the plumb bob (B ).

A. The same position B. The lowest position C. The highest position D. Different positions

29. The relative motion of the lathe spindle driving the tool and the workpiece to complete the cutting work is (A).

A. Main movement B. Feed movement C. Auxiliary movement D. Motorized feed

30. The straightness tolerance of the bed guide rail for the horizontal lathe slide is in the vertical direction Each meter of length in the plane is 0.02mm, over the entire stroke (B)

A. Only concave is allowed B. Only convex is allowed C. Concave or convex can be allowed

D. It can be concave or convex

31. Radial circular runout and axial movement of the CA6140 horizontal lathe spindle (C).

A. None shall be larger than 0.01mm B. None shall be smaller than 0.03mm

C. All within 0.02mm～0.03mm D. All within 0.01mm～0.02mm

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32. The Z525 power drilling gearbox can obtain nine different speeds.

Speed ??conversion is achieved by changing the meshing of (B) slip gears mounted on two spline shafts.

A. Two groups of two joints B. Two groups of triple joints C. Three groups of triple joints D. Three groups of four joints

33. Among the assembly methods, the repair method is applicable to (A).

A. Single piece production B. Batch production C. Quantitative production D. Mass production

34. Among the mechanical method anti-loosening devices are (A) anti-loosening devices.

A. Stop washer B. Spring washer C. Locking nut D. Overhead nut

35. Bearing type that bears both radial force and axial force (C) .

A. Centripetal bearing B. Thrust bearing C. Centripetal thrust bearing D. Needle roller bearing

36. The small diameter of the rolling bearing model 2000 is (A) mm.

A.10 B.15 C.20 D.25

37. Cylindrical bore bearings can be disassembled using (A).

A. Press or tensioner B. Hammer C. Knocking in D. Temperature difference method

38. The operation process of connecting and combining components, components, and parts into a whole machine is called for (C).

A. Component assembly B. Component assembly C. General assembly D. Single-piece assembly

39. After the worm shaft assembly of the reduction gearbox is installed into the box, the shaft end and the bearing cover shaft The clearance should be (A).

A.0.01mm~0.02mm B.0.1mm~0.2mm C.1mm~2mm D.0.2mm~0.3m

40. In chain transmission, the teeth of the sprocket Gradually wear and tear, the tooth pitch increases, causing the chain to wear faster. It should be (C) when the wear is serious.

A. Adjust the center distance of the sprocket B. Replace individual chain links C. Replace the chain and sprocket D. Replace the sprocket

41. After (B), the metal parts can Increase part hardness.

A. Annealing B. Quenching C. Tempering D. Normalizing

42. After reaming is completed, the reamer should be withdrawn (B).

A. Reverse rotation B. Forward rotation C. No rotation D. Hammering

43. Clean the equipment, partially disassemble and inspect parts or partially replace worn parts, and adjust the tightening mechanism , ensuring that the equipment can meet the production process requirements and other tasks belong to (C).

A. Overhaul B. Medium repair C. Minor repair D. Custom repair

44. The profile angle of metric standard triangular thread is (A).

A .60° B.55° C.40° D.30°

45. When repairing a horizontal lathe, if the center line of the spindle taper hole and the center line of the tail seat top vertebral hole do not meet the requirements, (C) can be used to meet the requirements.

A. Selection method B. Adjustment method C. Repair method D. Assembly method

46. To make the structure of the mechanical transmission mechanism compact, the transmission accurate and the transmission close, you can Select (A) transmission.

A. Gear B. Belt C. Chain D. Spiral

47. When filing, if the torque generated by the force used is unbalanced, the surface of the workpiece will be frustrated. into one (B).

A. Flat surface B. Arc convex surface C. Arc concave surface D. Curved surface

48. When connecting threads in the box, (A) is usually used to lock and prevent loosening.

A. Locking nut B. Spring washer C. Series wire D. Stop washer

49. When machinery is under heavy pressure, slow movement speed and low precision requirements, Lubricating oil (A) should be used.

A. High viscosity B. Low viscosity C. High evaporation point D. Low evaporation point

50. When assembling double-headed studs, their axis must be in line with the surface of the machine body ( C).

A. Coaxial line B. Parallel C. Perpendicular D. Staggered

3. Judgment

1. On the planer, the reciprocating linear motion of the planer Become the main movement. (√)

2. The thickness of the file is divided into No. 5, with No. 1 being the thickest and No. 5 being the thinnest. (√)

3. When reaming cast iron holes, adding kerosene for lubrication will reduce the hole diameter after reaming. (√)

4. When installing the strip, you must not only pay attention to the direction of the tooth tip, but also the tightness. (√)

5. When scraping the original flat plate, the method of scraping four flat plates against each other should be adopted. (X)

6. When bending, the neutral layer is generally not in the center of the material, but towards the side of the inner material. (√)

7. National standards stipulate the basic hole system and the basic shaft system. Under normal circumstances, the basic shaft system should be used first. (X)

8. The universal angle ruler can measure any angle from 0° to 360°. (×)

9. When the circumference is divided into equal parts according to the same chord length, the more equal parts there are, the smaller the product error will be. (X)

10. When drilling, the purpose of cooling and lubrication is mainly lubrication. (×)

11. When testing shape errors, the variation of the measured actual elements relative to their ideal elements is the shape tolerance. (X)

12. A public step often includes one or several processes. (×)

13. During assembly, cleaning of parts is a very important task. Rubber products (such as sealing ring parts) must be cleaned with gasoline. (×)

14. Rolling bearings must be cleaned with a brush and cotton yarn before assembly. Only in this way can they be cleaned. (×)

15. The function of static balance is to remove the partial weight of the part at any position so that the center of gravity of the rotating part coincides with the center of rotation. (√)

16. The double-nut locking anti-loosening device is a mechanical anti-loosening device. (×)

17. The neutrality of a loose key connection is better than that of a tight key connection. (√)

18. When installing the V-belt, you should first put the V-belt in the groove of the large pulley, and then put it on the small pulley. (×)

19. The chain transmission mechanism is suitable for transmission between two axes that are close to each other. (×)

20. In gear transmission, gear backlash is not an accuracy index, but different tooth side clearances must be determined according to different gear working conditions. (√)

21. In component assembly work, supplementary processing mainly refers to the mechanical processing of parts during the assembly process. (√)

22. Selecting the assembly method is a commonly used method to achieve assembly accuracy when the assembly accuracy requirements are very high and the number of components is small in mass production. (√)

23. When disassembling mechanical equipment, it should be carried out in the same order as during assembly. (×)

24. Conduct daily inspections of equipment with the purpose of detecting and eliminating abnormal phenomena in a timely manner. (√)

25. The grade of lubricating oil is represented by a number. The larger the number, the higher the viscosity. (√)

26. It is generally not advisable to disassemble and reassemble parts with interference fit after assembly. (√)

27. The smaller the pitch of the thread, the higher the accuracy of the thread.

(×)

28. All materials can be straightened and bent. (×)

29. When the integral sliding bearing is damaged, repair methods are generally used. (×)

30. The purpose of thread locking is to prevent the friction torque from reducing and the nut from rotating. (√)

31. When connecting with ordinary wedge keys, the upper and lower sides of the key are the working surfaces, and there is a certain gap between the key side and the keyway. (√)

32. When assembling the tight key, use the coloring method to check the contact between the two sides of the key and the shaft groove and hub groove. (×)

33. When using a bench vise to perform powerful operations, try to direct the force toward the movable vise body. (×)

34. When marking large batches of the same workpiece, copy marking can be used. (×)

35. When reaming holes in cast iron, in order to improve the surface roughness, kerosene can be used as the cutting fluid. (√)

36. The correction part of the tap has a complete tooth shape, and the cutting part is ground with a taper angle. (√)

37. The dimensional tolerance of parts can be positive, negative and zero. (×)

38. In the assembly dimension chain, the last ring formed is the composition ring. (×)

39. The original clearance of rolling bearings is greater than the matching clearance, and under normal circumstances the matching clearance is greater than the working clearance. (×)

40. When the workpiece is positioned with two holes on one side, one hole is positioned with a cylindrical pin and the other hole is positioned with a tapered pin. (×)

4. Short answers

1. What basic operations must a fitter master?

Answer: The fitter must master scribing, carving, sawing, filing, drilling, reaming, countersinking, reaming, tapping and threading, straightening and bending, riveting, scraping, Basic operations such as grinding, assembly and commissioning, measurement and simple heat treatment.

2. When sawing, why does the saw blade need to have a saw path?

Answer: After the saw blade has a saw path, the width of the saw kerf on the workpiece is greater than the thickness of the back of the saw blade, which can prevent "saw clamping" or saw blade overheating and reduce saw blade wear.

3. Why can’t the reamer be reversed when reaming?

Answer: Reversal will cause the chips to roll between the hole wall and the flank surface of the reamer teeth, roughening the hole wall. In addition, reversing can easily cause the reamer to wear and even chip. Therefore, the reamer cannot be reversed when reaming.

4. Why must the diameter of the bottom hole before tapping be larger than the basic size of the small diameter of the thread?

Answer: If the diameter of the bottom hole is equal to the diameter of the threaded hole, then the squeezing effect during tapping will cause there to be insufficient clearance between the thread crest and the tap bottom, and the tap will be easily clamped, causing problems. Continuing to tap the thread causes difficulty and may even break the tap. Therefore, the diameter of the bottom hole before tapping must be larger than the basic size of the small diameter of the thread.

5. What are the characteristics of the repair method assembly?

Answer: (1) Reduce the processing accuracy requirements of parts.

(2) No high-precision processing equipment is required, saving machining time.

(3) The assembly work is complicated and the assembly time is increased. It is suitable for single-piece, small-batch production or batch production of high-precision products.

6. What are the assembly methods for interference connections?

Answer: Press fit method, thermal expansion fit method, shrink fit method, hydraulic sleeve method, explosion pressing method.

7. What are the similarities and differences between couplings and clutches?

Answer: Similarities: Couplings and clutches are often used to connect two shafts so that they rotate together and transmit torque. The difference: the coupling can only be separated by disassembly when the machine is stopped; the clutch can be engaged and separated at any time through the operating system while the machine is running.

8. What are the characteristics of sliding bearings?

Answer: It has reliable operation, smooth transmission, no noise, the lubricating oil film has vibration absorption ability, and can withstand large impact loads, etc.

9. What is the clearance of rolling bearings?

Answer: When one ring of the rolling bearing is fixed, the maximum amount of movement of the other ring in the radial and axial directions is called the clearance of the rolling shaft.

10. What are the causes of errors when the gear is installed on the shaft?

Answer: The gear is eccentric, skewed, the cross section is not close to the shaft shoulder, etc.

11. What auxiliary measures can be taken when the threads are corroded and difficult to disassemble?

Answer: Spray special thread loosening agent or soak with kerosene; tap; heat the nut with flame.

12. What are the four parts of the product assembly process?

Answer: Pre-installation preparation; assembly; adjustment, accuracy inspection, trial operation; painting, oiling, and packaging.

13. What are the methods to control the preload force during thread assembly?

Answer: Use special assembly tools to control; measure the elongation of the bolt; use the torsion angle method to control.

14. What are the causes of machine noise?

Answer: Fluid impact; friction between objects; mechanical vibration.

15. What are the functions of grinding?

Answer: Reduce surface roughness; achieve precise dimensional requirements; improve the geometry of the workpiece.

16. What are the types of scraping?

Answer: Scraping can be divided into flat scraping and curved surface scraping.

17. What are the common forms of damage to belt drive mechanisms?

Answer: Common forms of damage to the belt transmission mechanism include bending of the journal, loose fit between the pulley hole and the shaft, wear of the pulley groove, elongation or breakage of the belt, and wear.

18. What are the main causes of tool wear?

Answer: There are three main causes of tool wear: mechanical wear, phase change wear, and chemical wear.

19. What is the purpose of performing balancing tests on rotating parts?

Answer: Mainly to prevent unbalanced centrifugal force when the machine is working; to eliminate vibrations caused by unbalanced movement of the machine parts to ensure the accuracy of the machine and extend its service life.

20. What are the technical requirements for assembling a spiral mechanism?

Answer: There are the following technical requirements for assembling a screw mechanism: 1. The fit clearance must be reasonable 2. The screw and the nut should be flexible in rotating with each other 3. The coaxiality error between the screw and the nut should not be too large.

21. What is the main function of the assembly unit system diagram?

Answer: 1. Clearly reflect the assembly process, part names, numbers and quantities of the product. 2. The assembly process can be divided according to the assembly unit system diagram.

22. What basic requirements should the materials for the cutting part of the tool have? What are the commonly used tool materials?

Answer: The cutting tool materials have the following requirements: high hardness; sufficient strength and toughness; high wear resistance; high heat resistance; good thermal conductivity; good process performance, etc. Commonly used tool materials for fitters include carbon tool steel, alloy tool steel, high-speed steel, carbide, etc.

23.What is dynamic imbalance?

Answer: The rotating parts have biased weights (or offset each other) in the radial position and the two biased weights are separated by a certain distance in the axial position, causing rotational imbalance, which is called dynamic imbalance.

24. How is the accuracy of screw rotation expressed?

Answer: The rotation accuracy of the screw is mainly represented by the radial circular runout and axial movement of the screw.

25.What is the assembly dimension chain? What are its characteristics?

Answer: The so-called assembly dimension chain refers to the general term for interrelated dimensions. The assembly dimension chain has two characteristics: 1. All relevant dimensions are connected into a closed shape. 2. Each independent dimensional error that constitutes this closed shape affects the assembly accuracy.

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