1 Skills and skills in marking papers
By marking, the machining position and machining allowance of each machining surface on the workpiece can be determined, and whether the shape and size of the blank conform to the drawing and meet the machining requirements can be checked. When there are some defects in the blank, the so-called "borrowing" method can be used to remedy them. Common marking tools include steel ruler, marking platform, marking needle, marking gauge, height ruler, 90 square, universal square and so on. In order to make the drawn lines clear, a thin and uniform coating is usually applied to the scribing part of the workpiece before scribing. Lime water is used to draw lines on rough cast iron and forging blanks, and an appropriate amount of Niu Pijiao can be added to increase adhesion. The treated surface adopts alcohol coloring solution and copper sulfate solution. Using marker pen is a simple and practical method, especially when there is a crossed line error, you can erase the wrong line with marker pen and draw it again. Before scribing, the scribing platform and workpiece should be cleaned, especially when the workpiece has burrs, which will affect the scribing accuracy. The burr of the workpiece can be scraped off with a small file or a broken saw blade. Then analyze the pattern, understand the processing parts and requirements of the workpiece, and choose the marking benchmark. When selecting the marking datum, pay attention to make the marking datum as consistent as possible with the design datum. There are usually three forms of marking datum: two mutually perpendicular planes, two mutually perpendicular centerlines, one plane and one centerline. When marking, the marking datum should be selected in each direction of the workpiece. Therefore, plane marking generally selects two marking benchmarks, and three marking benchmarks are generally selected for three-dimensional marking. In order to improve the marking accuracy, the following points should be achieved: (1) The marking needle with height ruler should be kept sharp and repaired and polished in time after wear; (2) There should be no excessive gap between the cursor and the main ruler; (3) When adjusting the scale, the fine-tuning nut can be used for precise adjustment, and the eyes and the target scale should be kept at the same level; (4) When moving the base of the height ruler, keep the marking needle at an angle of 45 ~ 75 with the surface of the workpiece, and press down the base hard; (5) The contact force between the marking needle and the workpiece should not be too great, and the marking should be done once as far as possible to make the drawn lines clear and accurate.
2 sawing operation skills and skills
Saws can be used to cut or slot workpieces. Sawing is a kind of rough machining, which affects the next filing process. Only by mastering the correct operating posture and skills can we achieve higher sawing accuracy. Sawing posture includes hand saw holding method, standing posture, operation method and sawing method. The hand saw grip method adopts the method that the right hand fully grasps the saw handle and the left hand gently supports the front end of the saw bow. When standing, the left foot is in front, the right foot is behind, and the body forms a 45-degree angle with the axis of the vice. The operation method generally adopts swing type, and the body swings up and down slightly with the saw bow. There are two kinds of sawing methods: far saw and near saw. When sawing, the pressure should be low and the speed should be slow. The saw blade can rest on the thumb of the left hand to prevent the saw blade from sliding on the surface of the workpiece. It is the key to improve the sawing operation level to analyze the causes of various problems in the sawing process and correct them in time. The reasons for the fracture of the saw blade are: the workpiece is not clamped, and the workpiece is loose during sawing; The saw blade is installed too loosely or too tightly; The sawing pressure is too high or the sawing direction suddenly deviates from the sawing direction; Forcibly correct the skewed kerf, or replace it with a new saw blade, but still cut hard in the original kerf; When sawing, the middle part of the saw blade is worn, and it will be broken after sawing for a long time; When stopped using, the hand saw was not taken out of the workpiece and broke. The causes of sawtooth cracking are: improper selection of saw blade, such as using coarse teeth when sawing thin plates and pipes; When sawing, the sawing angle is too large; The sawing motion suddenly swings too much, and the sawtooth collides too hard. The reasons for the skew of saw seam are as follows: when the workpiece is installed, the saw seam is inconsistent with the vertical line; The saw blade is too loose or twisted relative to the plane of the saw bow; Use a saw blade with uneven wear on both sides of the sawtooth; Excessive sawing pressure makes the saw blade swing left and right; The saw bow is not righted or forced to skew, so that the saw blade deviates from the central plane of the saw seam and leans against one side of the saw cutting surface.
In addition, when sawing, eyes should always pay attention to the straightness of sawing seam and correct it in time. If the skew is too severe, it will increase the difficulty of correction, or even be impossible to correct. When the workpiece is about to be sawed off, it is necessary to reduce the force, so as to prevent the workpiece from breaking suddenly due to excessive force, and the hand will be scratched when it rushes forward. Hold the broken part of the workpiece with your left hand to prevent the workpiece from falling and hurting your feet. When sawing steel parts, some engine oil can be added to reduce the friction between the saw blade and the sawing section and cool the saw blade, thus improving the service life of the saw blade.
3 filing skills and techniques
Filing is an important basic operation for locksmith. By filing, the size, shape, position and surface roughness of the workpiece meet the specified requirements. It can process all kinds of complicated inner and outer planes, inner and outer curved surfaces, inner and outer angles, grooves and curved surfaces. In the assembly process, the trimming and repair of individual parts and the processing of some complex parts under the condition of small batch production also need to be completed by manual filing. Correct posture is the basis of mastering filing skills, and the improvement of filing accuracy can only be achieved through repeated practice and corresponding skills. Filing posture includes filing grip and posture action. For the grip method of board file larger than 250mm, the right hand holds the file handle, the handle end is pressed against the palm, the thumb is placed on the upper part of the handle, the other four fingers hold the handle, the root of the thumb of the left hand is pressed on the file head, the middle finger and the ring finger hold the front end, and the index finger and the little finger naturally close. The standing posture, posture and filing action during filing are as follows: standing naturally, the center of gravity of the body falls on the left foot, the right knee is straight, the left knee is bent, and it flexes and stretches with the reciprocating motion of the file. The text is in front of the file and moves forward with the file. When the file reaches about three-quarters of the stroke, the body stops moving forward and the arms continue to file forward to the head. At the same time, the left foot is naturally straightened, and the center of gravity is moved backward by the reaction force during filing, so that the body can be restored to its original position and the file can be conveniently retracted. At the end of filing, the body began to lean forward to file for the second time. When filing, the pressure of the right hand will gradually increase with the advancement of the file, and the pressure of the left hand will gradually decrease with the advancement of the file. Whether the speed and accuracy of reporting can be improved at the same time is the key to passing the corresponding skill level appraisal. Once the scale of filing exceeds the lower limit, there is no room for remedy. Therefore, the closer you get to the size, the more careful you are to slow down the filing speed. However, if the speed is too slow, it is difficult to complete all the processing. Therefore, in addition to the corresponding basic skills, you must also master the rhythm, fast where you can, and slow where you need to be slow. For the machining of a certain size, we must first make an analysis to see its tolerance range and its size, that is, there are three situations: the tolerance range is above zero, the tolerance range is below zero, and the tolerance range is above and below zero. If the tolerance range is larger, it will be easier to control and the corresponding processing speed can be faster; If the tolerance range is small, it will be difficult to control and the corresponding processing speed will be slow. Next, do a good job of marking and try to improve the accuracy of marking. After marking, check the compound with vernier caliper to avoid mistakes and be aware of it. When sawing to remove redundant materials, slow down the speed appropriately and get close to the line as far as possible, and control the allowance at about 0.5~ 1.0mm to reduce the filing process in the back. Then rough file. At this stage, we should speed up the filing, and then slow down when the filing is close to the marking. Based on the principle of non-contact marking, vernier caliper should be used for the first measurement. When the allowance reaches 0. 1~0.2mm, measure the related verticality and flatness with a knife edge ruler, trim with a plate file of 150mm, and increase the number of measurements with a vernier caliper to avoid exceeding the tolerance range as much as possible and gradually approach the target size. When the allowance is about 0.04mm, a plastic file is used to improve the flatness and reduce the roughness of the workpiece surface by pushing the file. Measure the size with vernier caliper to make it within the tolerance range, and finally measure and verify it with micrometer.
4 Drilling skills and technology
When drilling, the drill bit is cutting in a semi-closed state, which has the advantages of high rotation speed, large cutting amount, difficult cutting, serious friction, easy jitter of the drill bit and low machining accuracy. In order to obtain higher dimensional accuracy and smaller surface roughness, reaming is needed after drilling. Reaming can only improve the dimensional accuracy of the hole itself and reduce its surface roughness. In skill appraisal and examination, there are often high requirements for hole spacing and other dimensions, and the tolerance range is between 0.10 ~ 0.25mm. Only when the equipment conditions are limited, can we improve the technical level of drilling operations and master the corresponding skills. Generally, standard twist drills are used to drill holes. The standard twist drill mainly has the following shortcomings: the cross blade is long, the rake angle at the cross blade is negative, the cross blade is in the state of squeezing and scraping during cutting, the axial force is large, and the turning head is easy to shake and difficult to center; The rake angle of each point on the main cutting edge is different, which leads to different cutting performance of each point. Because the rake angle near the center of the bit is negative, the cutting is in the state of squeezing and scraping, the cutting performance is poor, the bit is heated, and the bit is seriously worn. The secondary rake angle of the blade is zero, and the blade near the cutting part has serious friction with the hole wall, which is easy to heat and wear; The outer edge of the main cutting edge has small tip angle, large rake angle and weak cutter teeth, where the cutting speed is the highest and the cutting heat is the most serious. The main cutting edges are long and all participate in cutting, which increases the chip deformation and makes it difficult to remove chips. In order to improve the cutting performance of standard twist drill, improve drilling efficiency and prolong tool life, it is usually necessary to grind the cutting part. According to the specific requirements of drilling, the twist drill is selectively ground. The most basic grinding method is to shorten the chisel edge near the center of the drill bit and increase the rake angle. There are also grinding main cutting edge, grinding edge, grinding rake face and grinding chip groove.
Second, welder's skills:
1. After the workpieces are assembled, spot-weld firmly before welding. The width-height ratio of the weld is 2 ~ 3, and the width of the weld is generally 1.5 ~ 2 times. Initial welding refers to the part that has just started welding. After arc initiation, the arc should be slightly lengthened, the welding end should be preheated, and then the arc length should be appropriately shortened for normal welding.
2. End of weld means that when the weld ends, the arc pit at the end should be filled. If the arc is broken immediately at the end, an arc pit below the surface of the weldment will be formed, which will weaken the strength of the weld end and lead to cracks. So there is no arc pit at the end, and the arc pit should be filled up.
3. Due to the limitation of the length of covered electrode, sometimes covered electrode can't finish welding. The starting point of the weld required to be welded first is slightly lower. When connecting, start the arc ignition slightly before the starting point of the weld, slightly lengthen the arc to lead the arc to the starting point, cover the end of a weld, and then move along the welding direction after the starting point weld is leveled.
4. Generally speaking, zigzag or crescent-shaped strip conveying method is used for the width of weld. This method has the advantages of high weld strengthening, good metal melting, long heat preservation time, gas evolution and slag floating to the surface easily, which is beneficial to improve weld quality.