1. Fitter: Fitter is a cutting method based on manual operation.
2. There are three major advantages: flexible processing, the ability to process parts with complex shapes and high precision, and low investment.
Two major disadvantages (low production efficiency and high labor intensity, and poor processing quality) Stablize).
(1) Flexible processing In situations that are not suitable for mechanical processing, especially in the maintenance of mechanical equipment, fitter processing can achieve satisfactory results.
(2) Can process parts with complex shapes and high precision. Skilled fitters can process parts that are more precise and smooth than those processed by modern machine tools, and can process parts that even modern machine tools cannot process. Parts with very complex shapes, such as high-precision measuring tools, prototypes, molds with complex beginnings, etc.
(3) Invest in small benchwork tools and equipment that are cheap and easy to carry.
(4) Low production efficiency and high labor intensity
(5) Unstable processing quality. The processing quality is affected by the technical proficiency of workers.
Fitter skills require strengthening the practice of basic skills, strict requirements, standardized operations, more practice, more thinking, diligence and innovation.
Basic operating skills are the basis for product production and the basis for fitter professional skills. Therefore, they must be mastered first before they can gradually become more comfortable and easy to use in future work.
There are many basic operation items for fitters, and the learning and mastering of various skills have a certain interdependence. Therefore, we are required to proceed step by step, from easy to difficult, from simple to complex, and learn each item step by step. All operations must be learned and mastered as required. Basic operations are a combination of technical knowledge, skills and strength, and no one aspect can be neglected. We must consciously abide by disciplines, have a hard-working spirit, and operate in strict accordance with the operating requirements of each type of work. Only in this way can basic training be completed well.
Fitter is a method of cutting workpieces clamped on the bench vise with hand-held tools. It is one of the important types of work in mechanical manufacturing. The basic operations of a fitter can be divided into:
1. Auxiliary operations, namely scribing, which is an operation to draw the processing boundary on the blank or semi-finished workpiece according to the drawing.
2. Cutting operations include carving, sawing, filing, tapping, and threading. Various operations including drilling (reaming, reaming), scraping and grinding.
3. Assembly operation is assembly, the process of assembling parts or components into machines according to the technical requirements of the drawings.
4. Maintenance operations refer to maintenance, which is the operation of maintaining, inspecting and repairing machinery and equipment in service.
2. Scope of work of fitter and role in machinery manufacturing and maintenance
1. Scope of work of ordinary fitter (1) Preparation work before processing, such as cleaning blanks, blanks or Marking on semi-finished workpieces, etc.; (2) Repair processing of single parts; (3) Drilling, reaming, tapping and threading during parts assembly; (4) Processing of precision parts, such as scraping or grinding Fitting surfaces of machines, measuring tools and tools, finishing of fixtures and molds, etc. (5) Matching and trimming during parts assembly; (6) Machine assembly, commissioning, adjustment and maintenance, etc.
2. The role of fitter in machinery manufacturing and maintenance
Fitter is a relatively complex, delicate job with high process requirements. Although there are various advanced processing methods at present, the tools used by fitters are simple, the processing is diverse and flexible, the operation is convenient, and the adaptability is wide. Therefore, many jobs still need to be completed by fitters. As mentioned earlier, the scope of application of fitters is work. Therefore, fitters play a special and irreplaceable role in machinery manufacturing and machinery maintenance. However, fitter operations are highly labor-intensive, have low production efficiency, and require high technical level of workers.
3. Fitter’s workbench and vise
1. Fitter’s workbench
Referred to as the bench, it is usually made of hard wood or steel and must be solid and It is stable, the table height is about 800~900mm, and a vise and protective net are installed on the table.
2. Vise
The vise is used to clamp workpieces. Its specifications are expressed by the width of the jaws. There are three commonly used ones: 100, 125 and 150mm. Use a vise. When clamping, you should pay attention to:
(1) The workpiece should be clamped in the middle of the jaws as much as possible so that the force on the jaws is even; (2) The clamped workpiece should be stable and reliable, easy to process, and not deformed. ;
(3) When clamping the workpiece, it is generally only allowed to rely on the strength of the hand to pull the handle. Do not hit the handle with a hammer or randomly put a long pipe on the handle to avoid the screw and nut. Or the clamp body is damaged. (4) Do not tap on the smooth surface of the movable vise body to avoid reducing the matching performance; (5) It is best to apply force toward the fixed vise body during processing.
Tapping and threading and their precautions
In addition to mechanical processing of commonly used angular threaded workpieces, the threads can also be tapped and threaded in the pliers processing method. Thread to get. Threading (also known as tapping) uses a tap to process internal threads on the inner cylindrical surface of the workpiece; threading (also known as threading or toggle) uses a die to process external threads on a cylindrical rod.
1. Tapping
1. Taps and reamers
(1) Taps
Taps are used to process smaller diameters Internal thread forming tools are generally made of alloy tool steel 9SiGr and are made by heat treatment. Usually, a set of taps from M6 to M24 has two taps, which are called head tapers and two tapers; a set of taps below M6 and above M24 has three taps, namely, head tapers, two tapers and three tapers.
Each tap consists of a working part and a handle. The working part is composed of cutting part and calibration part. There are several (usually three or four) chip flutes in the axial direction, correspondingly forming several blades (cutting edges) and rake angles. The cutting part (that is, the incomplete tooth part) is an important part of cutting threads and is often ground into a conical shape in order to distribute the cutting load over several teeth. The cone angle of the head cone is smaller, with 5 to 7 teeth; the cone angle of the dicone is larger, with 3 to 4 teeth. The calibration part has complete teeth for smoothing threads and guiding the tap in axial movement. The handle has a square head, and its function is to cooperate with the hinge and transmit torque.
(2) Hinge
The hinge is a tool used to hold taps. The most commonly used one is the adjustable hinge. The size of the square hole can be adjusted by turning the handle to accommodate taps of different sizes. The length of the hinge should be selected according to the size of the tap to control the torque when tapping and prevent the tap from being twisted due to improper force application.
2. Determination of the diameter and depth of the drilled hole and chamfering of the hole before tapping
(1) Determination of the diameter of the bottom hole
The tap is During the thread tapping process, the cutting edge mainly cuts metal, but it also has the function of extruding metal, causing the metal to bulge and flow toward the tooth tips. Therefore, before tapping, the diameter of the drilled hole (i.e., the bottom hole) should be Larger than the inner diameter of the thread. The diameter of the bottom hole can be found in the manual or calculated according to the following empirical formula:
Brittle materials (cast iron, bronze, etc.): drilling diameter d0=d (thread outer diameter)-1.1p (pitch)
p>
Plastic materials (steel, copper, etc.): drilling diameter d0=d (thread outer diameter)-p (pitch)
(2) Determination of drilling depth
When tapping the thread of a blind hole (no through hole), because the tap cannot tap to the bottom, the depth of the hole must be greater than the length of the thread. The depth of the blind hole can be calculated according to the following formula:
Depth of the hole =Depth of the required thread-.7d
(3) Hole chamfering
Before tapping, the hole of the drilled hole should be chamfered to facilitate the positioning and placement of the tap. Cut in. The depth of the chamfer is greater than the pitch of the thread.
3. Key points and precautions for thread tapping operations (1) Select the tap correctly according to the specifications of the threaded hole on the workpiece, with the first taper first and the second taper second. Do not use it upside down. (2) When clamping the workpiece, make sure the center of the hole is perpendicular to the jaws to prevent the thread from being twisted. (3) When tapping a thread with a taper, after screwing in 1 to 2 turns, check whether the tap is perpendicular to the end face of the hole (it can be checked visually or with a right-angle ruler in two mutually perpendicular directions). After the cutting part has cut into the workpiece, it should be reversed 1/4 turn every 1 to 2 turns to facilitate chip breakage; at the same time, no more pressure can be applied (that is, only turning without applying pressure) to avoid chipping of the tap or thread tapping. The teeth are thin. (4) When tapping internal threads on steel parts, add engine oil to lubricate them, which can make the threads smooth, save labor and extend the service life of the tap; tap internal threads on cast iron without adding lubricant, or add kerosene; when tapping aluminum, aluminum alloys, and copper Emulsion can be added to the internal thread on the machine. (5) Do not blow the chips directly with your mouth to prevent the chips from flying into your eyes.
2. Threading
1. Die and die frame
(1) Die is a tool for processing external threads, made of alloy tool steel 9SiGr , and hardened by heat treatment. It looks like a round nut, but has 3 to 4 chip removal holes drilled on it and forms a blade.
The die consists of a chip part, a positioning part and a chip discharge hole. There are 40° taper parts at both ends of the circular die screw hole, which are the cutting parts of the die. The positioning part plays the role of trimming light. The outer circle of the die has a deep groove and four cone pits, which are used to position and fasten the die.
(2) Die holder The die holder is a tool used to hold the die and transmit torque. Dies with different outer diameters should use different die frames.
2. Determination and chamfering of the diameter of the round rod before threading
(1) Determination of the diameter of the round rod is the same as tapping. There is cutting and extrusion when threading. The role of metal. Therefore, the diameter of the round pile must be checked before threading. 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 looking up a table or using an empirical formula. Empirical formula: diameter of round rod = outer diameter of thread d-(0.13~0.2) pitch p
(2) Chamfering of the end of the round rod The end of the round rod should be chamfered before inserting the thread to make it easier to die Aimed at the center of the workpiece, it is also easy to cut into. The chamfer length should be greater than one pitch, and the bevel angle should be 15° to 30°.
3. Operational points and precautions for threading (1) Before each threading, the chips in the die flutes and threads should be cleared; (2) The round rod should be inspected before threading. Diameter size and end chamfer; (3) The cutting torque is very large when threading, and the processed surface of the round rod is easily damaged, so a hardwood V-groove liner or a thick copper plate should be used as a protective sheet for clamping artifact. The length of the workpiece extending out of the jaws should be as short as possible without affecting the required thread length. (4) When threading, the end face of the die should be perpendicular to the round rod, and the force should be even during operation. When starting to rotate the die, apply a little pressure. After inserting 3 to 4 teeth, you can just rotate without applying pressure, and reverse it frequently to facilitate chip breaking. (5) When threading the steel round rod, add engine oil for lubrication.
3. Grinding
The finishing method of using grinding tools and abrasives to remove an extremely thin surface layer from the workpiece is called grinding. The surface roughness after grinding is Ra=0.8~0.05μm. Grinding has manual and mechanical operations.
1. Lapping tools and abrasives
(1) Lapping tools The shape of the grinding tools is the same as the surface to be ground. For surface grinding, the grinding tool is a flat block. The hardness of the grinding tool material is generally lower than that of the workpiece material to be ground. But it can't be too low. Otherwise, the abrasive will be completely embedded in the grinding tool and lose its grinding effect. Gray cast iron is a common grinding tool material (mild steel and copper are also available).
(2) Abrasive Abrasive is a mixture of abrasives and grinding fluid.
Abrasives play a cutting role in grinding.
Commonly used abrasives are: corundum abrasives - used for grinding carbon tool steel, alloy tool steel, high-speed steel and cast iron and other workpieces; silicon carbide abrasives - used for grinding high-hardness workpieces such as carbide and ceramics, and can also be used Used for grinding steel parts; diamond abrasive - it has high hardness and good practical effect but is expensive.
Grinding fluid It plays a role in grinding by mixing abrasives, cooling and lubricating. Commonly used grinding fluids include kerosene, gasoline, industrial glycerin and cooked lard.
2. Surface grinding
Surface grinding is generally performed on a flat plate (lapping tool) with a very flat surface. Coarse grinding commonly uses the method of making grooves on a flat surface, which can scrape off excess abrasive to ensure uniform contact between the grinding surface of the workpiece and the flat plate; at the same time, the heat during grinding can be dissipated from the grooves. When fine grinding, in order to obtain smaller surface roughness, it should be carried out on a smooth flat plate.
When grinding, all parts of the workpiece surface must be cut evenly. Reasonable movement during manual grinding has a direct impact on improving grinding efficiency, workpiece surface quality and the durability of the grinding tool. When manually grinding, straight lines, spiral shapes, figure 8 shapes, etc. are generally used. The figure-8 shape is often used for grinding small flat workpieces.
Before grinding, the surface of the flat plate should be cleaned first, add appropriate abrasives, put the surface to be ground on the flat plate surface, and use an appropriate motion trajectory for grinding. The pressure and speed during grinding should be appropriate. Generally, when grinding rough grinding or grinding workpieces with smaller hardness, larger pressure and slower speed can be used; while when grinding fine grinding or grinding large workpieces, small pressure and fast speed should be used. grinding speed.
The concept of assembly
Any piece of machinery and equipment is composed of many parts. Several qualified parts are combined into components according to the specified technical requirements, or several parts are combined with each other. The process in which components are combined into machines and equipment and become qualified products through adjustments, tests, etc. is called assembly. For example, a bicycle is composed of dozens of parts, and the front wheel and the rear wheel are components.
Assembly is the last process in machine manufacturing, so it is the key to ensuring that the machine meets various technical requirements. The quality of assembly work plays an important role in the quality of the product.