Car Maintenance Basics

Chapter 4 Project 1 Basic Knowledge of Automobile Maintenance Fitter ([-])
Auto repair fitter work is the foundation of the auto repair craft.The grade standard of automobile technicians stipulates that all automobile maintenance workers above the third grade should have the basic operation of fitter.The maintenance and repair of automobiles, the new production of auto parts and the restoration of old parts, and the assembly of automobiles all require a certain foundation of fitter.This chapter introduces the basic knowledge of automobile maintenance fitters from a practical point of view. Its main content includes marking, filing, sawing, scraping, riveting, tapping, the use of common tools and special tools for automobile maintenance fitters, etc.

learning purpose

Knowledge goal:

Understand the basic technical requirements of fitters.

Master the basic operation skills of fitter.

Master the steps and methods of auto repair fitter work.

Skill Goal:
Can make simple parts using fitter tools.

Able to skillfully use fitter measuring tools.

Master the operation of an automobile repair fitter.

task description
Under the guidance of relevant knowledge, understand the basic knowledge and technical requirements of automobile maintenance fitters.Under the guidance of work order tasks, use the fitter's measuring tools to complete the production of nuts and small hammers, and master the fitter's operation skills by making small parts and hammers.Record and archive the completed work, consciously maintain safe operation and 5S work requirements.

related information
Underline
According to the requirements of drawings and objects, the operation of accurately drawing the processing boundary line on the surface of the part (blank surface or processed surface) is called scribing.Scribing is a basic operation of an automobile maintenance fitter and an important process in the process of parts processing or maintenance.

Steel ruler,

1. The role of the line

①Determine the machining allowance and the position of the holes on each surface, so that the machining has a clear mark.

②Through scribing, you can check whether there is an error in the workpiece, and whether there is a corrective remedy to avoid wasting machining hours.

2. The basic tool for drawing lines

(1) Stitching
The scribing needle is a tool used to scribe along the steel ruler, ruler or template on the surface of the workpiece to be scribed.Commonly used scribing needles are made of ≤ 3-sealed mm spring steel wires. There are generally two kinds of elbow scribing needles and straight scribing needles. The elbow scribing needles are used in places where straight scribing needles cannot.

(2) Scribing plate

There are common marking discs and micro-adjustable marking discs.As shown in Figure 2-1, it is a kind of finely adjustable scribing plate.The scribing plate is a common tool for scribing on the workpiece and correcting the position of the workpiece. One end of the scribing needle is welded with carbide, and the elbow at the other end is used for correcting the workpiece.When scribing, take out the size on the measuring ruler [Figure 2-2(a)] for operation, and the scribing accuracy is 0.2mm; when the scribing plate is not in use, place the scribing needle head down.

(a) measuring height ruler (b> height vernier caliper
(3) Altitude vernier caliper
The height vernier caliper [Figure 2-2(b)] is a marking tool made according to the principle of a vernier caliper, with a general accuracy of 0.02mm, and is used for marking semi-finished products (processed surfaces).The height vernier caliper is a precision tool, and it is not allowed to use it to scratch the blank.

(4) Planning
Zero line
The measured size is moved to the workpiece with a planer to draw a line segment, make an angle, draw a fillet or curve, measure the distance between two points, etc.

(5) sample punch
Sample punching (Fig. 2-4) is a tool used when punching the marked line.The punching is to strengthen the display of the processing boundary drawn by the stylus, and also to make the drawn line have a permanent position mark. In addition, it can also be used as a centering foot point when drawing an arc.

In order to prevent damage to the mating surface of the relative parts due to disassembly, the sample punch is often used as a mark.For example, to disassemble connecting rods, pistons, valves, etc., it is necessary to punch the X cylinder or the X cylinder with a sample punch.

3. Plane marking
(1) draw parallel lines
There are several ways to draw parallel lines:

① As shown in Figure 2-5, use a steel tape to measure two identical dimensions at both ends of the workpiece, draw a short line on each, and then use a steel ruler to connect the two lines to obtain the desired parallel line.

②Use the planning plan to take the distance between parallel lines as the radius, randomly select two points on the known straight line of the workpiece as the center of the circle (the two centers should be kept at an appropriate distance), and draw two arcs to the same side.Then draw their tangents with a steel ruler to obtain the desired parallel lines.

③As shown in Figure 2-6, if the workpiece can stand vertically on the platform or lean on the vertical plane of the angle iron or square box, you can use the height vernier or height measuring ruler to draw parallel lines with the needle plate.

(2) Draw a circular arc to find the center of the circle
Use the method of drawing arcs on the plane line to find the center of the circle, which is a problem often encountered by fitters in the cooperation of car maintenance and repair work.For example, if the original bolts of the cylinder block are broken, the parallel lines are drawn to cooperate with the water pump bolts, and the bolts are damaged, and the half-axis screws are fastened randomly, etc., the holes need to be reamed.The operation process is shown in Figure 2-7. Insert the cork into the hole, draw a circular arc according to the required radius with a planer, and finally make a sample punch at the center point.

Two, filing

The surface of the workpiece is cut with a file to make it reach the shape, size and surface roughness required by the part drawing. This processing method is called filing.Filing can process the workpiece surface, inner hole, groove and various complex outer surfaces, the precision can reach O.Olmm, and the surface roughness R can reach 0.8pm.During car maintenance, uneven wear and deformation of individual parts require filing and finishing.Filing is a manual operation, and it is one of the main methods for assessing the practical skills of a car repair fitter.

1. Lithium knife
(1) Materials for making files

Files are generally made of carbon tool steel D12 and D13, and are hardened to 62-67HRC after heat treatment.

(2) Composition of the file

A file is composed of a file face, a file edge, a file tongue, a file tail, and a wooden handle, as shown in Figure 2-8.

(3) Types and selection principles of files
① Types of files.According to the purpose, it can be divided into three categories: fitter files, special files and plastic files.

a. Fitter file (Figure 2-9).According to its cross-sectional shape, it can be divided into five types: flat file, round file, semi-round file, square file and triangular file; according to its tooth pattern, it can be divided into single-tooth pattern file and double-tooth pattern file; There are five kinds of tooth files, medium tooth files, fine tooth files, rough oil (double fine tooth) files, and fine oil light files.

b. Shaping file (Figure 2-10).It is mainly used for fine processing and trimming of small parts that are difficult to machine on the workpiece. It consists of a set of files with various cross-sectional shapes.

c. Special files (Figure 2-11).It can be used to process special surfaces on parts. It has two types: straight and curved, and its cross-sectional shapes are many.

The shape of the file should be selected according to the shape of the workpiece to be processed; the thickness of the file should be selected according to the size of the machining allowance, the level of machining accuracy and the hardness of the workpiece material.Generally, rough files are suitable for soft metals with large processing allowance, low processing accuracy and surface roughness, and vice versa for fine files.

2. Filing operation diagram

(1) How to hold the file

① How to hold a large file: put the palm of your right hand against the end of the handle of the file, place your thumb on top of the wooden handle of the file, and bend the other four fingers below, and hold the wooden handle of the file with your thumb; use your left hand according to the size of the file Depending on the weight, you can choose a variety of postures (Figure 2-12).

②Holding method of the middle file: the right hand holding method is the same as the large file holding method, while the left hand needs to pinch the front end of the file with the thumb and index finger [Figure 2-13(a)].

③How to hold the small file: straighten the index finger of the right hand, put the thumb on the wooden handle of the file, lean the index finger against the edge of the file, and press the fingers of the left hand on the middle of the file [Figure 2-13(b)].

④ Grip of a smaller file (orthopedic file): hold the file in the right hand, place the index finger on top of the file, and place the thumb on the left side of the file [Figure 2-13(c)].

(2) Filing posture

The correct filing posture can reduce fatigue and improve the quality and efficiency of filing.The standing position of a person is shown in Figure 2-14, that is, the left leg is bent, the right leg is straightened, the body is leaning forward, and the center of gravity falls on the left leg.

(3) Application of filing force
① Balance of moments.When filing, the balance of filing force must be correctly grasped.When starting to push the file, the pressure of the left hand should be greater, and the pressure of the right hand should be less and the thrust should be greater.With the advancement of the file, the pressure applied by the left hand should gradually decrease from large to small, and the pressure applied by the right hand should gradually increase from small to small. No pressure should be applied when the file returns to reduce the wear of the file teeth.Only by mastering the technical essentials of filing the plane, can the pressure at both ends of the file be balanced against the moment of the center of the workpiece when the file is at any position on the workpiece. Otherwise, the file will not be balanced, and a convex or drum-shaped surface will be produced in the middle of the workpiece. .

② Filing speed.Generally 30-60 times per minute.If it is too fast, the operator will be easily fatigued and the teeth will be blunted; if it is too slow, the cutting efficiency will be low.

3. File method for workpieces of various shapes

(1) Flat file method

①Forward file method [Figure 2-15(a)].The forward filing method is the most basic filing method, which is used for the final filing and leveling of small planes.

②Cross file method [Figure 2-15(b)].This method is the main file method, the file surface is longer, the file is held firmly, and the chip removal is faster, and the level of the file surface can be judged according to the intersection of the file marks.

(b) Cross method
③ Push file method [Figure 2-15(c)].Push files are generally used to file narrow surfaces or to polish the surface with abrasive cloth.

(2) File method of curved surface

①The filing method of the outer arc surface (Figure 2-16).There are two commonly used outer arc surface filing methods: rolling filing method and horizontal filing method.The rolling file method is to make the file file along the arc surface, and the horizontal file method is to make the file file along the arc surface.The former is used for finishing the outer arc surface, and the latter is used for rough filing the outer arc surface.For example, in the first aid of a mechanical accident vehicle (the crankshaft is rough due to lack of oil), the shaping of the crankshaft connecting rod journal; the repair of the deformed axle head, etc.

(b) Horizontal blunt filing

②The filing method of the inner arc surface (Figure 2-17).The file must complete three movements at the same time: forward movement, left and right movement and self-rotation.

③ File method of through hole (Figure 2-18).According to the shape of the through hole, workpiece material, machining allowance, machining accuracy and surface roughness, etc., select the required file to file the through hole.

[-]. Sawing

Sawing is a sawing process in which a raw material or workpiece is divided into several parts with a saw blade.Large workpieces or raw materials are usually cut by mechanical saws, shears, gas cutting, electric cutting, etc.Auto mechanics generally use hand saws to cut smaller materials or workpieces.For example, at the maintenance site, sawing rusted or deformed bolts, slotting, trimming parts, etc.Therefore, proficiency in using a hand saw is one of the basic skills that a car maintenance worker needs to master.

1. hand silver
The hand saw consists of two parts: the bow and the blade.

⑴ saw bow

There are two types of saw bows: fixed and adjustable.The bow frame of the fixed saw bow is integral and can only be equipped with saw blades of one length specification [Fig. 2-19(a)]; the bow frame of the adjustable saw bow is divided into front and rear sections. The interior can be stretched, so saw blades of several length specifications can be installed [Fig. 2-19(b)].

(a) fixed (b) adjustable

(2) saw blade
The saw blade used on the saw bow is generally made of carbon tool steel or alloy steel and hardened by heat treatment.The saw blade is generally 300mm long, 12mm wide and 0.8mm thick.The thickness of the sawtooth is represented by the number of teeth on the saw blade per 25mm length, 14-18 teeth are coarse teeth, 24 teeth are medium teeth, and 32 teeth are fine teeth.

The thickness of the sawtooth should be selected according to the hardness and thickness of the processed material.When sawing soft or thick materials, due to the large amount of sawdust, a larger space for chip accommodation is required, and coarse-toothed saw blades should be used; when sawing hard or thin materials, because the material is hard, the sawtooth is not easy to cut, and the sawdust The amount is small, and there is no need for a large chip space, and the saw teeth of thin materials are easily caught by the workpiece and cracked during sawing. Multiple teeth need to work at the same time, so that the force on the saw teeth is reduced, so these two cases should choose fine tooth saw blades , Generally, medium-toothed saw blades are used for medium-hard materials.

2. Silver cutting method

(1) Installation of the saw blade

The hand saw only cuts when it is pushed forward, the direction of the tip of the tooth is forward, and it cannot be reversed.

The tension of the saw blade should be appropriate. If it is too tight, the saw blade will lose its proper elasticity during the sawing process and is easy to break; if it is too loose, it will be twisted and broken during the sawing process, and the saw kerf of the workpiece will be easily skewed.

Workpiece clamping

The workpiece should be clamped on the left side of the bench vise as much as possible to facilitate operation; the sawing line should be perpendicular to the jaws to prevent sawing; the sawing line should not be too far away from the jaws to prevent trembling during sawing; The clamping should be stable, firm, and free of vibration, so as to prevent the saw blade from breaking due to the movement of the workpiece during sawing; at the same time, it is also necessary to prevent the clamping of the processed surface and deformation of the workpiece due to excessive clamping force.

(3) The method of sawing

As shown in Figure 2-20, the standing posture for sawing is similar to the filing posture, and the sawing is generally carried out in two ways: remote sawing or close sawing.The angle of sawing is appropriate, equal to 15.as well.If it is too large, the saw teeth will be easily caught by the edge of the workpiece; if it is too small, it will not be easy to cut the material and will slip.

fit too big too small

(c) The sawing angle is too large or too small. In order to make the sawing position accurate and stable, the left thumb can be used to block the saw blade for positioning, or a triangular file can be used to file a groove at the sawing position.

(4) Pressure, speed and reciprocating length of sawing

①The pressure of sawing.When holding the saw bow, you should stretch it naturally, hold the handle firmly with your right hand, and lightly support the front end of the bow frame with your left hand.When exercising, apply force with your right hand, and don't use too much pressure with your left hand. When starting the saw, the pressure should be small and the reciprocating stroke short; Reduce sawtooth wear; when the workpiece is sawed off quickly, the pressure should be reduced.

②Sawing speed.The sawing speed should be reciprocating 20-40 times per minute. It can be faster when sawing soft materials, and slower when sawing hard materials.

③The reciprocating length of sawing.When sawing, as long as the ends of the bow frame do not touch the workpiece, the effective length of the saw blade should be used as much as possible.Generally, the reciprocating length should not be less than 2/3 of the total length of the saw blade. Only in this way can the wear of the saw blade during sawing be reduced and the service life extended.

(5) Sawing method of typical workpieces

① round tube.When sawing thin tubes, the tube should be sandwiched between two wooden V-groove pads to prevent flattening the tube (Figure 2-21).When sawing, it cannot be sawed from one direction to the bottom [Figure 2-22(b)]. The reason is that after the sawtooth saws through the inner wall of the pipe, the sawtooth cuts on the thin wall, and the force is concentrated, so it is easy to be caught by the pipe wall and break off.The correct method of sawing circular pipes is: change the direction several times for sawing, each direction can only saw the inner wall of the pipe, then turn the pipe at an angle, change it one by one, and cut it one by one until it is cut off until.

② Thin plate.When sawing a thin board, it should be sawed from the wide side as much as possible. If it can only be sawed on the narrow side of the board, the thin board can be sandwiched between two boards and sawed together [Figure 2-23 (a)], which can Prevents the teeth from snagging and also increases the rigidity of the board.When the sheet is too wide to be clamped in a bench vise, it should be sawed horizontally [Fig. 2-23(b)].

(b) Horizontal miter sawing
③ deep seam.When the depth of the saw kerf exceeds the height of the saw bow [Figure 2-24(a)], the saw blade should be turned 90° to reinstall, and the saw bow should be turned to the side of the workpiece [Figure 2-24(b)].After the saw bow is down, if the height is still not enough, you can also turn the saw bow 2° as shown in Figure 24-180(c), and install the saw blade teeth in the saw bow for sawing.

Four, scraping

Scraping is the operation of scraping off a thin layer of metal on the machined surface of a workpiece with a scraper.The scraping of the automobile maintenance fitter mainly refers to scraping the crankshaft main shaft bearing (main bearing), crankshaft connecting rod bearing (connecting rod bearing) and camshaft bearing, etc.

1. A scraping tool

(1) scraper
The scraper is generally forged with carbon tool steel 10A-T12A or bearing steel, and some scraper heads are welded with hard alloy to scrape hard metal.There are two types of scrapers: flat scrapers and curved scrapers.In the process of car repair, only the triangular scraper scraping the inner curved surface is used to scrape the bearing bush, etc.

① Plane scraper.The plane scraper is used to scrape the plane, and there are two kinds of common scraper [Figure 2-25(a)] and movable head scraper [Figure 2-25(b)].

(a) Ordinary scraper
Plane scrapers can be divided into three types: rough scrapers, fine scrapers and fine scrapers according to the accuracy of the scraped surface (Figure 2-26).

(b) Fine scraper
②Curved surface scraper.The curved surface scraper is used to scrape the inner arc surface (mainly the bearing bush of the sliding bearing), and there are many types (Fig. 2-27), among which the triangular scraper is the most common.

(2) Calibration tool
The calibration tool has two functions: one is used to cooperate with the scraping surface to display the flatness of the scraping surface by the number of contact points and the density of the distribution, and provide a basis for scraping; the other is to test the accuracy of the scraping surface.When scraping the inner arc surface, the shaft used to match it is often used as a calibration tool.Crankshafts, for example, are used as calibration tools.

(a) Spoon scraper 7]
(b) Triangular scraper
(3) Display agent

The display agent is an auxiliary material applied to show the degree of adhesion between the scraped surface and the standard surface. Commonly used are red lead oil and blue oil.Red lead oil is made of iron oxide or aluminum oxide plus machine oil, the former is purple-red, and the latter is orange-yellow. They are mostly used for scraping cast iron and steel; blue oil is made of Prussian blue plus castor oil, and it is mostly used for copper and aluminum. scraping.

2. The method of scraping

(1) Surface scraping
For the bearing pads of some sliding bearings with higher requirements, a good fit can be obtained by scraping.Use a triangular scraper when scraping the bearing bush, and the method of grinding the idea is to spread the display agent evenly on the shaft, and then grind it with the shaft (Figure 2-28).

(2) Scraping and alignment of connecting rod bearings
First apply some very thin red ink on the surface of the connecting rod journal, then install the connecting rod bearing and pad on the crankshaft according to the correct position, tighten the bolts (tighten gradually, scrape in stages), and after turning the connecting rod for several turns, Remove the connecting rod, observe the fit of the imprint on the surface of the inner hole of the bearing, and scrape off the surface of the alloy layer with the imprint with a scraper.Grasp the principle of scraping heavy and keeping light, scraping big and keeping small, and repeating this, so that the contact area of ​​the bearing will continue to increase.Finally, tighten the bolts according to the specified torque until each mark is uniform and the contact surface is <85%.

(3) Crankshaft bearing scraping and alignment

Assemble the bearings and crankshaft.Tighten the bolts a little according to 2, 3, 1, 4 for the four steps, and 4, 2, 6, 3, 5, 1, 7 for the seven steps, turn the crankshaft several times when tightening each step, loosen the bolts slightly, and carry out another step. One step, after all the steps are completed, remove all crankshaft bearing caps, check the marks, and repair and scrape.

Repairing and scraping the bearing must be repeated several times, and the bolts of each bearing cover should be tightened gradually with the same torque.The contact surface of the bearing after scraping should be >75%; the last step should be >85% to prevent oil leakage.

Five, riveting

(End of this chapter)