Car Maintenance Basics

Chapter 6 Project 3 Basic Knowledge of Automobile Maintenance Fitter ([-])
Tapping is to use a tap to cut an internal thread on the wall of the hole.The sleeve thread is to use the die to cut the external thread on the cylinder.Tapping and threading often occur in automobile maintenance operations. Many parts or components are connected by threads. When the external thread or internal thread is damaged (chaotic buckle), it must be repaired by tapping or threading.For example, screw threads on the cylinder block, slippage or thread breakage, half-shaft bolt breakage, etc., all require tapping or threading.

1. Tapping thread

(1) Taps and hinge bars

① tap.The tap is a forming tool specially used to process small-diameter internal threads (Fig. 2-42). The tap is made of alloy tool steel or high-speed steel and hardened by quenching.It is mainly composed of cutting part, smoothing part, chip groove and shank.

The cutting part of the tap is often ground into a conical shape with a sharp cutting edge. The rake angle of the blade is 8°-10°, and the rear angle is 4°-6°, which is used to complete the work of cutting threads.The function of the smoothing part is to smooth the thread and guide the tap.There are 3-4 chip flutes on the tap for chip containment and chip removal.The shank of the tap is a square head, and its function is to cooperate with the hinge rod and transmit torque.

There are two types of taps: hand taps and machine taps.Taps are generally composed of two or three sets, divided into cones, two cones or three cones. Their taper bevel angles are not equal, and the outer diameters of the finishing parts are also different. The distribution of cutting workload is as follows: The head cone is 60%, the second cone is 30%, and the triple cone is 10%.Now due to the improvement of the quality of the manufacturing tap materials, generally, most of the taps below M10 are one set, and those above M10 are two sets.

② Hinge bar.The hinge bar is a tool used to hold the tap (Figure 2-43).The commonly used adjustable hinge lever can adjust the size of the square hole by turning the right handle.

To hold taps of different sizes.The length of the hinge rod should be selected according to the size of the tap in order to control the screw force (torque) during tapping and prevent the tap from breaking due to improper force application.

(2) Determination of the diameter of the bottom hole

Taps are mainly used to cut metal, but they also have the effect of extruding metal, especially when processing materials with good plasticity.Before tapping the thread, the bottom hole diameter of the workpiece must be greater than the small diameter of the thread specified in the thread standard. The method of determining the diameter of the bottom hole drill can be determined by the look-up method (see the relevant manual) or by the following experience Formula calculation:
(3) Tapping method and precautions

①Before tapping the thread, first chamfer the end face of the threaded drilling hole to facilitate the cutting of the tap.

② When tapping the thread, use the head cone to tap the thread first.First, rotate the person 1-2 times to check whether the tap is perpendicular to the end face of the hole (visual inspection or a square can be used to check in two directions perpendicular to each other).Then continue to rotate the hinge bar with light pressure. When the cutting part of the tap has cut into the workpiece, it can only be rotated without pressure. After each revolution, it should be reversed by 1/4 circle so that the chips will fall off (Figure 2-44 ).

③ After tapping the head cone, continue to tap the second and third cones. Every time a cone is replaced, it must be rotated 1-2 times to center it and position it, and then use the hinge bar to prevent random buckling.

④ When changing steel workpieces, lubricate with machine oil to make the thread smooth and prolong the service life of the tap. For cast iron parts, add kerosene to lubricate.

2. Set thread (1) die and die holder
①Die.The die is a tool for processing external threads. It is made of carbon tool steel or high-speed steel and has been quenched and hardened. Its shape is like a round nut, but there are several chip removal holes drilled on it to form a blade (Figure 2-45 ).

The types of dies include round dies, adjustable round dies, square dies, flexible pipe dies and conical pipe thread dies.

The die is composed of cutting part, sizing part and chip removal hole.There are 60 at both ends of the chip hole.The taper plays the main role of cutting, and the sizing part plays the role of smoothing.The outer circle of the die has a deep groove and four cone pits, which are used for positioning and fastening the die.

②Die rack.The die is used on the die holder, and the die holder is a tool for clamping the die and transmitting torque.The tool factory manufactures a variety of supporting die holders according to the outer diameter of the die for users to choose.

If the outer diameter of the round rod is too large, the die is difficult to fit; if it is too small, the shape of the screw thread is incomplete.Therefore, the diameter of the round rod should be slightly smaller than the nominal size of the thread.The diameter of the round rod can be calculated by empirical formula:

In the formula, d-thread outer diameter, mm;

D-Rod diameter, mm;

p-pitch, mm.

How to set thread
① The end of the round rod with threaded thread should be reversed by 30°.Angle (Figure 2-46), the small head of the chamfered cone should be smaller than the inner diameter of the thread, so that it is easy to cut people.

②Under the premise of not affecting the required length of the thread, the length of the workpiece protruding from the jaw should be as short as possible.

③The threading process is similar to that of tapping. The end face of the die should be perpendicular to the round rod, and the force should be uniform during operation.

④ When starting to turn the die, apply a little pressure.

⑤套人3-4扣后，可只转动不加压，并每转1/2-1周反转1/4周，以便断屑。

⑥ In order to maintain the cutting performance of the die and ensure the surface roughness of the thread, it is necessary to properly select the cutting fluid according to the different properties of the material when threading.

Eight, Chisel

Chiseling is the operation of cutting metal by striking a chisel with a hand hammer.The function of chiseling is to chisel off or break metal to achieve the desired shape and size.Chiseling is often used in automobile maintenance operations. Due to its greater flexibility, chiseling is not limited by equipment and venues, and it is often used when it cannot be processed on a machine tool.For example, dismantling rusted bolts and nuts in the automobile maintenance industry, making thin plate washers, etc.

Chiseling is one of the basic skills that auto mechanics need to master. The training of chiseling can improve the accuracy of the operator's knocking and lay the foundation for disassembly, assembly and repair.

1. Chisel tool
Chisel cutting tools are mainly chisels and hand hammers.

(1) chisel
The hardness of the chisel blade must be greater than the hardness of the workpiece material, and it must be made into a wedge shape, so that the metal can be smoothly divided and the purpose of chisel processing can be achieved.

錾子由切削刃、斜面、柄部和头部4个部分组成，其柄部一般制成菱形，全长170mm左右，直径18-20mm(图2-47)。

Bevelled head
① flat chisel.The flat chisel has a wider cutting edge, the blade width is generally about 15-20mm, and can be used for chiseling large planes, thinner sheets, bars with smaller diameters, cleaning burrs on castings and forgings on the edges of weldments, Fly and wait.

② pointed chisel.The sharp chisel has a narrow blade, generally about 2-10mm, and is used for chiseling keyways and rivets.

③ Oil tank chisel.The blade of the oil groove chisel is very short and arc-shaped, and its slope is made into a curved shape, which can be used for chiseling the crankshaft bearing bush and the oil groove on the lubricating surface of the machine tool.

(2) Hand Hammer
Hand hammer (Figure 2-49) is a tool for chiseling, cutting, straightening, riveting and assembling.When chiseling a workpiece with a chisel, the chiseling can only be completed by the hammer force of the hand hammer.

The hand hammer consists of two parts: the hammer head and the wooden handle.Hand hammers are divided into two types: hard hand hammers and soft hand hammers. The hammer heads of soft hand hammers are made of duralumin, copper, hard rubber or hard wood; the hammer heads of hard hand hammers are made of carbon tool steel. Quenched hardened, polished, etc., the top surface is slightly raised.The shape of the other end of the hammer head can be made into round head, flat head, duckbill and other shapes as required.The specifications of the hand hammer are represented by the weight of the hammer head, and its specifications are 0.25kg (about 0.5lb), 0.5kg (about 1lb), 0.75kg (about 1.3Ib), 1kg (about 21b) and so on.The wooden handle needs to be made of tough wood material (sandalwood, birch, elm), and its cross-sectional shape is generally oval.The length of the wooden handle should be appropriate. If it is too long, it will be inconvenient to operate, and if it is too short, the hammering force cannot be exerted.The length of the wooden handle is generally 300-350mm. When the wooden handle is installed in the hammer hole, a wedge must be punched (Figure 2-50) to prevent the hammer head from falling off and hurting people.

2. Chiseling method
①Forehand grip.Hold the body of the chisel with the palm of the hand down, the thumb and index finger naturally stretch out, and the middle finger, ring finger, and little finger naturally bend and close to hold the chisel body.This grip is suitable for chiseling flat surfaces.

② Anti-grip method.With the palm up, the fingers naturally pinch the chisel handle, and the palm is suspended in the air.This grip is good for small flat or side chisels.

(a) il grip
(b) Underhand grip

(c) standing grip

③ Standing grip.This kind of grip is that the tiger's mouth is facing upwards, the thumb is placed on one side of the chisel, and the index finger, middle finger, ring finger, and little finger are placed on the other side to pinch the chisel.This grip is suitable for vertical chisel work, such as chiseling off material on an anvil.

(2) The grip of the hammer

①Close grip method (Figure 2-52).The five fingers of the right hand hold the hammer handle tightly, the thumb is closed on the index finger, the tiger's mouth is aligned with the direction of the hammer head, and the end of the wooden handle is exposed by 15-30mm, and the five fingers are always held tightly during the hammering process.Beginners often use this method.

② Loose grip method (Figure 2-53).During the hammering process, the thumb and index finger still hold the hammer handle tightly, and the middle finger, ring finger, and little finger are slightly loose and press the hammer handle naturally.When hammering, the middle finger, ring finger, and little finger gradually clenched with the impact. When swinging the hammer, relax the fingers in the opposite order.The advantage of this grip is that it is light and comfortable, the hammer is powerful, and it is not easy to fatigue, so it is often used in operation.

(3) Hammer swing method
There are three ways to swing the hammer: wrist swing, elbow swing and arm swing (Figure 2-54).

① Wrist swing.Wrist swing refers to relying on the movement of the wrist, swinging a hammer to strike.This method has a small hammering force, and is suitable for the beginning and end of chiseling, or places where the force is not large, such as chiseling oil grooves, punching holes, etc.

②Elbow wave.The elbow swing is a hammering motion with the wrist and elbow together.When swinging the hammer, the wrist and elbow are swung back, the upper arm does not move much, and then quickly hit the top of the chisel.The elbow swing has a greater hammering force and is the most widely used.

③ Arm swing.The arm swing relies on the joint action of the wrist, elbow and arm.High hammering force, suitable for occasions with high hammering force.

(4) Step and posture when chiseling

When chiseling, the center of gravity of the operator's body is biased towards the right leg, the hammer should be swung naturally, and the eyes should face the chisel knife squarely.The step position and posture during chiseling are shown in Figure 2-55.

(5) The influence of the main angle of chiseling on chiseling
During the chiseling process, the chisel must form a certain angle with the chiseling plane (Figure 2-56).

The main functions of each angle are as follows:
① Rear angle a.The role of the relief angle a is to reduce the friction between the flank and the machined surface, and make it easy for the chisel to cut into the workpiece.

②Rake angle L The role of rake angle Y is to reduce chip deformation and make chiseling light and fast. The larger the rake angle, the more labor-saving the cutting.

③ cutting angle S.The size of the cutting angle 5 has a great relationship with the chisel quality and chisel work efficiency.By 5 = rape " can know, the size of 5 is determined by P and "

It is determined, and the wedge angle is selected according to the softness and hardness of the material to be processed, and it is constant in the work, so the size of the cutting angle depends on the clearance angle ".If the back angle is too large, the chisel will cut into the workpiece too deeply, making it difficult to chisel, and even damage the cutting edge of the chisel and the workpiece (Fig. 2-57, Fig. 2-58).If the back angle is too small, the chisel is easy to slip out of the material surface, or the cutting is very shallow, and the efficiency is not high.Therefore, when chiseling, the relief angle is the relative angle, generally 5°-8° is appropriate.During the chiseling process, the chisel should be mastered so that the back angle remains stable, otherwise the surface of the workpiece will be uneven.

(a) The relief angle is too large (b>The relief angle is too small
(a) How to start (b) How to finish chiseling

(6) Chiseling method
When starting the chisel, the chisel should be tilted as far as possible to the right about 45° (Fig. 2-58), and tilted downward by 30° from the sharp corner of the workpiece, and hit the chisel lightly, so that the chisel can easily cut into the material.Then according to the normal chisel angle, gradually chisel to the middle.

When the chisel is about 10mm away from the workpiece head, the chisel should be turned to chisel off the remaining part, so as to avoid the corner cracking at the end of the one-way chisel.During the chiseling process, the number of hammer blows per minute is about 40.The cutting edge should not always stand against the workpiece. After every two or three chisels, the chisel can be retracted a little, so that the flatness of the chiseled plane can be observed to ensure the chiseled quality.

task implementation
In the process of task implementation, they will learn the operating procedures and maintenance methods of safety equipment commonly used in automobile maintenance companies, and implement them in groups to complete the work within the specified time.

[-]. Tool preparation

[-]. Technical standards and requirements
① All operations meet the requirements for safe operation.

②All operations conform to the technical standards of automobile maintenance fitters.

③ Safety accidents are not allowed during the operation.

[-]. The work to be done

1. Manufacture of hex nut

(1) Hex nut pattern 30.

learning assessment
[-]. Self-evaluation

1. Summarize the main methods of auto repair fitters.

2. Please write down your experience of this learning task.

3. Self-evaluation of the learning environment (including dress, learning attitude, mastery of knowledge and skills, completion of work pages, etc.).

[-]. Group evaluation

Evaluation status of serial number evaluation items
Good to bad

1 team spirit
2 Whether learning is proactive
3 The situation of obeying the work arrangement

4 Use of tools and instruments
5. Tool finishing and site cleaning
[-]. Teacher Evaluation

Evaluation status of serial number evaluation items
Good to bad

1 Attendance
2 dressing situation

3 classroom order
4 Whether learning is proactive
5. Fill out the learning task book

6 Use of tools and instruments
7. Tool finishing and site cleaning
thinking and practice
1. What is the function of underline?
2. How many types of marking tools are there?How to use it correctly?

3. What is lithium cutting?

4. What are the types of lithium knives?How are fitter lithium knives classified?

5. According to what principle to choose the thickness of the lithium knife?
6. What is the operation essentials of Liping workpiece?
7. How to correctly use forward lithium method, cross lithium method and push lithium method?
8. What is sawing?How to install the saw blade?How to start the saw when sawing?

9. How to distinguish coarse, medium and fine tooth saw blades?How to choose correctly?

10. How to saw the round pipe?

11. What is scraping?What are the scraping tools?

12. How to scrape and match the connecting rod bearing?
13. How to scrape and match the crankshaft bearing?
14. What is riveting?What are the types of riveting?What are the characteristics of each?
15. What are the riveting tools?How many riveting methods are there?

16. How to remove the rivets?
17. What is drilling?How to carry out drilling operation?
18. What are the names and functions of the components of the drill bit?
19. What are the main angles of the drill bit?What is the standard top angle?
20. How to sharpen the drill bit?
21. What is the difference between drilling, reaming and reaming?
22. What is tapping thread?What is a sleeve thread?
23. Briefly describe the structure of taps and dies?
24. How to determine the diameter of the bottom hole before tapping?
25. How to determine the diameter of the round rod before threading?
26 How to perform tapping and threading operations?

27. What is chiseling?

28. How many types of chisels are there?What is the use of each?
29. How many hammer swing methods are there when chiseling?

30 How to carry out the chisel operation?

(End of this chapter)