Car Maintenance Basics

Chapter 5 Project 2 Basic Knowledge of Automobile Maintenance Fitter ([-])
Riveting is the operation of joining two or more workpieces with rivets.The riveting of automobile maintenance fitter mainly refers to the riveting of frame longitudinal beams and beams, riveting of clutch friction plates and steel plates, riveting of brake shoes and friction plates, riveting of steel plates and steel plates, etc.

1. Types of riveting

Riveting can be divided into two types: active riveting and fixed riveting.

(1) Active riveting
Active riveting is also called hinge riveting.Its combined parts can rotate with each other.For example, riveting of common scissors, long pliers, compasses and various hand pliers.

(2) Fixed riveting
The joint part of the fixed riveting cannot be moved, and it is suitable for structures that require sufficient strength.Fixed riveting is widely used in automobile repair projects such as frame, body, brake shoe, friction plate, friction plate of clutch driven disc, etc.

2. Form of riveting

The form of riveting is determined by the position where the parts are combined with each other. There are mainly three forms:
(1) Overlap
Lap joint is a relatively simple connection form in riveting [Fig. 2-29(a)]. When two plates are required to be on the same plane after riveting, one of the plates should be folded first and then lapped.

(c) angle 抜
Docking
There are two types of butt joints: single-cover butt and double-cover butt [Figure 2-29(b)].

(3) Corner joint
According to different requirements, angle joints are divided into single angle steel angle joints and double angle steel angle joints [Figure 2-29(c)].

3. Types of riveting and riveting tools
(1) Types of rivets

①According to different shapes, it can be divided into semi-round head, flat head, countersunk head and hollow rivets (Figure 2-30).

② According to different materials, it can be divided into steel, copper and aluminum rivets.

③ According to the purpose, it can be divided into steel structure, belt and boiler rivets.

(2) Riveting tools
①Hand hammer.Generally, a hand hammer with a round head is used. The size of the hammer is selected according to the diameter of the rivet. A small hand hammer with a weight of 0.2-0.5kg is commonly used.

② Press the punch [Figure 2-31(a)].The compression punch is used to impact the riveted sheets to press them against each other.

③Cover mold and top mold [Figure 2-31(b), (c)].Their tops are all semicircular concave balls, but there are two parallel planes on the stem of the top mold, which is convenient for clamping and firmness.

(3) Determination of rivet diameter and length
① Determination of rivet diameter.The determination of the rivet diameter is related to the minimum thickness of the plate to be connected, which is generally equal to 1.8 times the minimum thickness of the plate, and the drilling diameter can be determined according to the standard rivet diameter.Standard rivet diameter units are shown in Table 2-1.

② Determination of the length of the rivet.The determination of the length of the rivet is related to the length of the protruding part.The selected length of the half-round head rivet should be 1.25-1.5 times the total thickness of the riveted object plus the rivet diameter, and the selected length of the countersunk rivet should be 0.8-1.2 times the total thickness of the riveted object plus the rivet diameter.

(4) Riveting method
There are three methods of riveting: cold riveting, hot riveting and mixed riveting.

①Cold riveting.When cold riveting, the rivet does not need to be heated, and the riveting point is directly upset, so the rivet material must have high ductility, and the rivet with a diameter below 8mm can be riveted by cold riveting.

②Hot riveting.When hot riveting, the rivet is heated to a certain degree, and then riveted. After the rivet is heated, the ductility is good, the material is also softened by heating, and it is easy to form, and the rivet rod shrinks after cold shrinkage, which increases the bonding strength.When hot riveting, considering the expansion of the heated rivet rod, the hole diameter should be enlarged by 0.5-1mm (or larger), so that the rivet is easy to insert when it is in a hot state.Steel rivets with a diameter greater than 8mm are mostly hot riveted.For example, when the rivets of the car frame are loose, they can be repaired by hot riveting.

③ mixed riveting.When mixing riveting, the rivet is not fully heated, but only the riveting end of the rivet is heated. For rivets with relatively long rivet stems, this method will not bend the rivet stem.The riveting commonly used in automobile maintenance is mostly cold riveting, and the riveting head is directly upset by hand or machine at room temperature.Figure 2-32 shows the riveting process of a round head rivet.In rare cases, such as riveting a limited number of steel rivets with large diameters, the mixed riveting method is used.

(5) How to remove the rivets

① For rivets with smaller diameters, use tools such as files, chisels or hand-held grinders to remove the rivet head, and then punch out the rivets with a punch.

② For rivets with large diameter or too tight riveting, the method of drilling is generally used for disassembly. Select a drill bit slightly smaller than the diameter of the rivet rod, and remove the rivet after drilling a hole in the center of the rivet.

[-]. Drilling, reaming and reaming
Drilling, reaming and reaming are frequent fitter jobs in automotive repair operations.Drilling, reaming and reaming are mostly carried out on a special drilling machine, but when repairing a car, because the parts are inconvenient to disassemble (or when repairing the car), sometimes a hand electric drill is also used for operation.

1. Drilling
The operation of machining a hole in a solid workpiece with a drill is called drilling.The machining accuracy of drilling is generally below IT10 level, and the surface roughness of drilling is about R = 12.5.

(1) Drilling machine
Commonly used drill presses include bench drill presses, vertical drill presses, and radial drill presses. Hand drills are also commonly used drilling tools. Bench drill presses and hand drills are mainly used in automobile maintenance operations.

① Bench drilling machine (Figure 2-33).The bench drill is referred to as a bench drill, which is a small drill used on a workbench.The bench drill is light in weight, easy to move, and high in speed (the minimum speed is above 400r/min). It is suitable for processing small holes with a diameter of no more than 13mm on small parts. The spindle feed is manual.

②Hand electric drill (Figure 2-34).The electric hand drill is mainly used to drill holes with a diameter of less than 12mm, and it is often used in occasions where it is inconvenient to use a drill press to drill holes.The power supply of the electric hand drill is 220V and 380V. Because the electric hand drill is easy to carry, easy to operate and flexible to use, it is widely used in automobile repair operations.

(2) drill bit
The drill bit is the main tool for drilling, which is made of high-speed steel, and its working part is hardened to 62-65HRC after heat treatment.The drill bit consists of a shank, a neck and a working part (Fig. 2-35).

① handle.The shank is the clamping part of the drill bit, which plays the role of transmitting power. There are two kinds of straight shank and tapered shank.Straight shank transmits small torque and is generally used for drills with a diameter less than 12mm; tapered shank can transmit large torque and is used for drills with a diameter greater than 12mm.The top of the tapered shank is a flat tail, which plays a role in transmitting torque.

②Neck.The neck is used for the grinding and retracting of the grinding wheel when the drill bit is manufactured.The drill diameter, material and factory standard are generally engraved on the neck.

③ Working part.The working part includes a guiding part and a cutting part.The guide part has two long and narrow, spiral edges that are 0.5-1mm higher than the back of the tooth. The spiral groove can be used to remove chips and transport cutting fluid, and the entire guide part is also a backup part of the cutting part.The cutting part (see Figure 2-36 for its parameters) has three cutting edges; the intersection of the rake face and the flank face forms two main cutting edges, which are responsible for the main cutting function; the two edge edges formed by the intersection of the two flank faces (secondary cutting Edge) plays the role of smoothing the hole wall; grinding the chisel edge is to reduce the drilling axial force and scraping phenomenon and improve the centering ability and cutting stability of the drill.

The geometric angles of the cutting part are as follows:

a. Top angle.The apex angle is the angle between the two main cutting edges.The larger the vertex angle, the greater the axial force during drilling; the smaller the vertex angle, the smaller the axial force during drilling.The commonly used top angle is 116°118.

b. Spiral angle ".The angle between the tangent of the edge and the centerline of the drill bit is called the helix angle.Generally = 30°.

c. Front angle 7.The angle between the rake face and the normal plane of the cutting plane is called the rake angle, which has a great relationship with the helix angle, and the rake angle is the largest at the edge of the outer diameter of the drill, about 30.Left and right, gradually decreasing from the outside to the center, such as -30 near the chisel edge.On the chisel edge, it is -54°--60.The larger the rake angle, the more labor-saving the cutting.

d. Rear angle ".The angle between the flank and the cutting plane is called the relief angle.The relief angle of the drill is not equal at all points on the cutting edge, contrary to the rake angle, it is smaller at the outer diameter edge by 8°-14°.The closer to the center, the larger, usually 20°-26 at the core.

e. Chisel edge bevel 9.The acute angle between the cutting edge and the main cutting edge in a plane perpendicular to the axis of the drill bit.Usually 50. -55°
(3) Sharpening of the drill bit

The cutting part of the drill bit has a direct impact on drilling quality and efficiency.The purpose of drill sharpening is to sharpen the blunt or damaged cutting part into the correct geometry and maintain the good cutting performance of the drill.

① Grinding the main cutting edge.Its purpose is to sharpen the blunt or damaged main cutting edge, and at the same time grind the relief angle and top angle to the correct angle required.The method is to pinch the drill bit by hand, level the main cutting edge, and the angle between the center of the drill bit and the surface of the grinding wheel is equal to 1/2 the top angle.When sharpening, the right hand makes the cutting edge touch the grinding wheel, and the left hand makes the drill bit handle swing down, and the swing angle is the back angle of the drill bit.When swinging downwards, twist the drill bit with the left hand to rotate around its own center line, so that the back angle at the core of the drill bit will be larger, which is conducive to cutting.After grinding one main cutting edge, grind the other main cutting edge.

② Grinding chisel edge.The purpose is to shorten the chisel edge and increase the rake angle at the drill core, so that the drill bit is easy to locate, reduce the axial resistance, and facilitate cutting.The cutting performance of the ground drill often depends on the chisel edge.If the material is soft, grind away more.Generally, the chisel blade is shortened to 1/3-1/5 of the original.Generally, drills with small diameters (within 5mm) do not need to sharpen the chisel edge.The method of grinding the chisel edge is that the grinding point is roughly on the horizontal center plane of the grinding wheel.The relative positions of the drill bit and the grinding wheel are shown in Figure 2-37.
成视
The drill bit forms an angle of 15° with the side of the grinding wheel (to the left), and forms an angle of about 55° with the center surface of the grinding wheel.When sharpening, the back of the drill bit is in contact with the rounded corner of the grinding wheel, and the grinding is to gradually move to the center of the drill until the rake angle of the inner blade is ground.When grinding, the drill bit rotates slightly, and the amount of grinding increases from small to large. When grinding to the center of the drill, the rake angle and bevel angle of the inner blade should be ensured, and the transverse length should be accurate.When grinding, the action should be light to prevent the annealing of the cutting edge or the core being too thin.

③ Grinding drill bit for thin plate.Drilling holes in thin steel plates is often encountered during car maintenance.Drilling with an ordinary drill bit will cause the hole to be out of round, the hole will be flashed, the hole will be torn, the burr will be large, and even the sheet will be deformed and accidents will occur. Therefore, the drill bit must be ground into the shape shown in Figure 2-38 (usually Also called a flat drill bit).When drilling, the drill core first cuts into the workpiece, fixes the center, and plays the role of clamping the workpiece, and then quickly cuts into the workpiece with two sharp outer points to make it cut away.If the sharp edge is ground flat and lower than the core, it can also be used for drilling general counterbore or scribing planes.

④ Requirements for drill sharpening.When sharpening, the angle of the cutting part of the drill bit should meet the requirements, the two main cutting edges are equal in length, and the top angle should be bisected by the center line of the drill bit. It can be used as a top angle model and inspected while grinding.In actual work, it is generally checked by visual inspection.The drill can be rotated 180° for visual inspection, and after several repetitions, it can be identified whether the two edges are consistent.When sharpening the drill bit, the drill shank must not swing away from the horizontal plane to prevent a negative back angle from being ground.In order to prevent the annealing of the cutting edge, it must be immersed in water frequently for cooling.

(4) Drilling method

Workpiece clamping (Figure 2-39).When drilling holes below [-] mm, if the workpiece can be held firmly by hand, the workpiece can be held by hand; for small workpieces that cannot be held by hand or the diameter of the drilled hole exceeds [-] mm, it must be clamped by hand vise; when drilling holes on round workpieces, Use a V-shaped frame with screws and clamps to keep the workpiece from rotating when drilling.

Workholding method
Generally, the center of the hole to be drilled should be punched out with a center punch before drilling.If the hole is drilled on an inclined surface, a flat surface can be milled out with an end mill, or a small plane can be chiseled with a chisel on the inclined surface, and punched with a sample.When drilling a hole with a larger diameter, it must be drilled twice, and the diameter of each drill is generally 0.5-0.7 times the required diameter.When drilling, the drill bit will heat up and lose its original hardness, so it needs to be cooled by liquid flow when drilling.When the hole is about to be drilled, the feed rate should also be reduced to ensure the quality of the hole and the drill bit is not easily damaged.

2. Reaming
Reaming is the operation of enlarging the existing hole on the workpiece with a reaming drill.It can correct the axis deviation of the hole and make it get more correct geometry and smaller surface roughness.Reaming can be used as the final processing of holes with low requirements, or as semi-finishing before finishing (such as reaming), and the reaming allowance is 0.5-4mm.Twist drills are generally used as reaming drills in automobile maintenance.When the reaming accuracy is required to be high, special reaming drills are also used for reaming.The reaming drill is similar to the twist drill, the difference is that it has 3-4 cutting edges, but no chisel edge, its top is flat, and the spiral groove is shallow, so the drill core is thick, rigid, not easy to deform, and guide Good performance.Figure 2-40 shows the reaming drill and the situation when drilling with reaming.

3. Reaming
Reaming is a processing method that uses a reamer to remove trace metal layers from the workpiece wall to improve its dimensional accuracy and surface quality. The machining accuracy of reaming can be as high as IT7-FT6, and the surface roughness of reaming is 0.8-0.4 m.The tool for reaming is a reamer. The reamer has 4-12 cutting edges, and its guiding performance is good when reaming.Due to the shallow alveolus of the cutter teeth, the cross-sectional area of ​​the reamer is large, so the rigidity of the reamer is good.According to the method of use, the reamer is divided into two types: hand and machine, and according to the shape of the reamed hole, it is divided into two types: cylindrical and conical (Figure 2-41).

Reaming is actually a scraping process because of the small allowance and the rake angle of the cutting edge.Especially when reaming by hand, because the cutting speed is very low, it will not be affected by cutting heat and vibration, so reaming is a method for finishing the hole.When reaming, the reamer cannot be reversed, otherwise, chips will be stuck between the hole wall and the cutting edge, thereby scratching the hole wall or chipping the cutting edge.When reaming, if cutting fluid is used, the surface roughness of the hole wall will be smaller.Reaming is often encountered in auto repair, such as reaming connecting rod sleeves, piston holes, steering knuckle kingpin bushing holes, etc. This is also the basic skill of auto mechanics. Only by practicing the basic skills can the basic maintenance be guaranteed. quality.

[-]. Tapping thread and sleeve thread
(End of this chapter)