In the machining industry, the surface roughness of mechanical parts is also a part of the quality. How to control the surface roughness in machining, what effect does the surface roughness have on the quality of parts, let’s take a look at it next
In the mechanical parts processing drawings, will indicate the surface roughness processing requirements. If the machining process fails to meet the requirements, the surface roughness of parts has a great impact on the mechanical assembly performance and service life
If the surface roughness of the parts can not meet the requirements, the contact area will be reduced, the pressure per unit area will be increased, the contact deformation will be increased, the friction resistance will be increased, and the wear of the parts will be accelerated;
The surface roughness affects the fit properties. For clearance fit, the surface roughness is easy to wear, resulting in the rapid increase of clearance. For interference fit, during assembly, it can flatten the small convex peaks, reduce the effective interference, and reduce the strength of fit parts;
The surface of the parts is rough and low, and corrosive substances are easy to accumulate at the bottom of the surface, which is difficult to remove, causing surface corrosion;
When the part bears the load, the stress concentration is easy to occur at the concave bottom, resulting in cracks and fracture of the part.
In the machining process of mechanical parts, the machining allowance should be reserved for the parts with high surface roughness.
In the field of mechanical processing industry, with the continuous development of science and technology, ordinary processing equipment has been unable to meet the market demand. Most mechanical processing manufacturers have added or replaced precision CNC processing equipment (CNC machine tools). Precision CNC processing has replaced ordinary machine tools, which improves the production and processing efficiency and stabilizes the production and processing quality. This is the main advantage of CNC precision machining equipment, but there are also disadvantages, let’s see
Advantages: high precision CNC machining, high efficiency; Pearl River Delta region, Dongguan processing industry, precision CNC processing also known as computer gong processing, also belongs to CNC machine tool processing equipment. In the process of processing, the automatic operation is completely controlled by the code command, which reduces the labor operation. Because it belongs to numerical control processing equipment, the production efficiency is many times that of ordinary machine tools, and the processing quality is relatively stable. When multiple or batch parts are processed, the production efficiency is more obvious.
Disadvantages: CNC processing failure, maintenance costs are high; In case of failure in precision CNC processing, after-sales service can replace the parts, or the parts have passed the shelf life, the cost of maintenance is quite expensive, because in CNC processing precision, sometimes there may be small problems, and the equipment can not operate normally, so it needs professional technicians to maintain. But the general professional technician salary is high, causes the maintenance cost to increase.
In the field of mechanical processing industry, the reasonable processing technology should be selected for the machining process of mechanical parts in order to produce and process more efficiently and accurately. Before the machining of mechanical parts, how to better reflect the efficient and accurate machining quality? Let’s take a look at the formulation of the machining process route of mechanical parts
Now we have a simple understanding of the formulation of the processing route of mechanical parts, which is mainly divided into three steps:
Draw up the processing route: analyze and study the contents and technical requirements of parts production drawings, draw up the processing method, processing scheme and process route of parts processing.
Arrange the processing procedure
(1) Select blank（ 2) Arrange machining procedure 1, select machining scheme 2 and determine datum plane reasonably（ 3) Arrange the heat treatment process 1. The heat treatment process to improve the cutting performance of metal materials, such as annealing and normalizing, is generally arranged before rough machining. 2. The heat treatment process to eliminate internal stress, such as intermediate annealing, tempering and aging, is generally arranged before rough machining and rough machining. 3. The heat treatment process to improve the performance of mechanical parts, such as quenching, tempering and aging Quenching and tempering, carburizing and other surface treatment are generally arranged before the final processing. All the heat treatment processes are carried out before the final processing of the parts, because the parts must change after the heat treatment process, and the errors caused by deformation can be corrected during the final processing（ 4) Arrange the inspection process well. During the production and processing of small batch parts, self inspection, mutual inspection and special inspection shall be carried out. The products can only be delivered after passing the inspection.
Draw up the processing technology process: the purpose of making the processing technology route is to ensure the product quality and improve the economic benefits. At the same time, it is to determine the number of production personnel and select the processing equipment. The principle of processing sequence arrangement: base surface first, rough and fine separation, rough and fine first, surface first and hole second.
Mechanical parts processing technology requirements are different, according to the requirements to choose a reasonable processing route. For precision parts with special requirements, select the precise processing route.
In the field of machining, dimensional error has a direct impact on the working performance and service life of products, and the error is closely related to the processing quality of parts and the assembly accuracy of products. Precision machinery parts, automation equipment and other industries spare parts processing technology is generally finished by finishing and rough processing, the selection of processing technology is unreasonable or processing technology problems, will cause dimensional error of parts.
Dimensional error refers to the requirement that the actual geometric parameters (drawing process size, geometric shape and mutual position) of parts after processing are consistent with the geometric parameters of processing technology. The deviation between them is machining error, and the size of machining error reflects the machining precision. The accuracy of parts processing is expressed by the size of processing error, that is, by the relevant national tolerance standards. The actual parameters obtained by any processing method will not be absolutely accurate. In machining practice, under the premise of ensuring the working performance of the machine tool, the machining error does not exceed the deviation required by the customer’s drawing process is qualified.
In order to ensure and improve the machining accuracy of mechanical parts, it is the main responsibility to master the basic law of the change of machining dimension error. As the saying goes, to produce good equipment, we must first ensure the processing quality of mechanical parts.
Contact machining for many years, equipment accessories 45 # steel surface treatment, whether there is an impact on the dimensional accuracy of parts? 45 ᦇ blackening of steel has no effect on the dimensional accuracy, because blackening is a common means of chemical surface treatment. The principle is to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention. In the surface treatment, the dimension will not deform, so it will not affect the accuracy of parts.
In the process of machining, the parts with low appearance requirements need surface treatment, which can be blackened. In the machining industry, the surface blackening treatment of 45 ° steel parts is also called bluing. If the machining dimension of precision mechanical parts has accuracy requirements, different surface treatment processes can be selected according to the purpose of parts design. In the surface treatment process, 45 ° steel has blackening, chromium plating, nickel plating, zinc plating and other treatment. If the processing accuracy requirements on the production drawings are different, the reasonable surface treatment process should be selected.
In the field of machining industry, we often contact with the processing of aluminum alloy parts. Here is a brief introduction of the difficulties in processing aluminum alloy parts
In the process of machining, due to the influence of machining deformation on the dimension, form and position tolerance of parts, the machining method of high speed, low feed and low cutting depth is used to complete the machining of all associated dimensions of parts through one clamping, so as to reduce the deformation caused by excessive cutting force in the machining process and avoid the error caused by the non coincidence of machining datum and design datum, Improve the dimensional accuracy and shape and position accuracy of parts.
Problem: parts in the machining process, often due to internal stress and deformation, especially non-ferrous light metals such as aluminum, magnesium alloy processing. The frequent occurrence of warping, side bending and distortion caused by internal stress will seriously affect the processing quality and efficiency of parts, especially for thin-walled and thin-walled parts. How to minimize or eliminate the deformation of parts, ensure product quality and production efficiency, has been our processing technology topic!
Cause analysis: in the process of production and processing, in order to improve the processing and use performance of aluminum alloy, it is necessary to improve the strength through heat treatment (quenching treatment + aging treatment) before processing. The internal stress of the material produced in the quenching process is very large, and the aging process can not completely release the internal stress produced in the quenching process. In the subsequent machining process, new cutting stress is generated. With the continuous removal of materials, the balance state of internal stress is broken, and the internal stress is redistributed until the new balance process is reached, resulting in deformation, which makes the parts lose their due machining accuracy. Moreover, when the stress on the surface of the part exceeds the strength limit of the material, cracks will occur.
Solution: in view of the above reasons, the “nesting” method is used for processing thin-walled and thin-walled aluminum alloy parts“ The “nesting” method is a processing method that the parts are taken out from the blank after all dimensions are processed in one clamping. The process of raw materials includes milling upper surface, rough milling inner cavity, rough milling shape, finish milling shape, finish milling inner cavity, finish milling bottom surface, point (drill) hole, cutting and so on. Because the whole process is completed in one clamping, before cutting off, because the part is connected with the bottom of the blank material, the internal stress will not cause large deformation of the part, and the size of the part is stable in the whole process. When cutting, it is necessary to make the blank material and the part material have 0.1 mm adhesion on the bottom surface, so as to ensure that the part has enough strength to resist the cutting stress generated in the whole “nesting” process.
After the mechanical parts are cut from the blank, although the parts are deformed due to the stress release, the relative dimensions of the parts will not change. It only needs to increase the correction process to level the bottom surface, and all the dimensions and shapes can be restored to be correct.
The above is the knowledge of aluminum alloy processing technology. In the future processing, it can not only improve the processing efficiency and product quality, but also avoid the error caused by the non coincidence of design benchmark and process benchmark, avoid the compression of tolerance due to the conversion of dimension chain, and simplify the process of making process specification and parts processing.
In the domestic machining industry, CNC machining center is called CNC milling machine processing and computer gong processing. The main features of CNC machining are high precision, high efficiency and stable quality. CNC machining is very suitable for small batch and multi variety products. CNC machining in the production of different parts, only need to change the program, the use is very flexible. In addition to the above features, CNC processing also has the following main features
(1) High rigidity, in order to match the high precision of CNC system, CNC milling machine has high rigidity, CNC machining center can adapt to the high precision machining requirements.
(2) Light drag, turret (table) movement using ball screw pair, small friction, easy to move. The pressure angle of the special bearing for supporting both ends of the precision CNC machining lead screw is larger than that of the ordinary bearing, so it can be selected and matched before leaving the factory; The lubrication part of CNC milling machine adopts oil mist automatic lubrication, which makes CNC milling machine easy to move.
(3) General precision CNC milling machine processing three-axis linkage, according to different machine configuration, there are also four axis, five axis high precision CNC machining center. The main reason is high precision, small batch processing parts can multiple improve production efficiency. These are the main features of precision CNC machining.
In the machining industry, the simplest way to promote cooperation is to understand the processing fee first. In fact, the cost accounting of precision parts processing fee is very simple. It’s just a simple quotation method. You can calculate the price of raw materials and material density of parts. You can roughly calculate the material price of parts by looking at the size of drawings. Let’s take a look at the cost accounting formula of parts processing fee:
In the calculation of parts processing cost, we should know the weight of raw materials: we should also consider the machining allowance of raw materials, and increase the overall size by about 5-8mm. Process requirements: the size of parts requires high, the processing technology will be complex, and the processing cost will increase, especially the single piece processing. Number of machined parts: for the machining industry, small batch parts processing can save clamping time and improve production and processing efficiency. The difference in price is 3-5 times. Single piece processing is not suitable for batch quotation, and the final quotation is based on the processing technology on the drawing.
The above is about the cost accounting of mechanical parts processing fees.
In the mechanical processing industry, the price of general parts processing is calculated through the standard formula, and the processing cost will be appropriately increased in case of complex parts. There is a certain risk in complex precision parts, because if there is any problem in the processing technology, the dimensional tolerance of precision parts will be unqualified. At present, many precision parts are directly processed by CNC lathe or CNC, which can ensure the processing accuracy, save labor and improve the production and processing efficiency. Now many machining manufacturers have added CNC machine tools, let’s see how to calculate CNC processing fee
CNC processing, also known as computer gong processing, is mainly controlled by computer programming code. The main feature is high processing precision, small batch processing parts can improve production efficiency, but also save labor operation. CNC processing fee is generally calculated according to 60-70 yuan / hour. For high-precision parts, the processing fee is determined according to different processing technology.
When CNC processes small batch parts, the processing fee will be quite low. Because the batch parts can be repeatedly clamped, it can reduce a lot of programming time and improve the production efficiency. Machining manufacturers hope to have small batch processing, repeated clamping processing is OK. CNC processing fee how to calculate, generally calculated by the hour price. Precision parts with different requirements can be calculated comprehensively according to the processing technology.
Precision hardware processing technology processes include turning, milling, planing, grinding, clamping, stamping, forging and other methods.
Stamping: the pre made die is used for cold stamping, and the first step is sheet metal processing, that is, most of the processing materials are sheet metal, so the processing efficiency is relatively high and suitable for mass production.
The process of fine hardware processing technology is divided into engineering die and connecting die. Engineering die is also called single punch die. Some more complex parts need several sets of dies, and the connecting die splits the shape of the commodity into several parts in the cavity of the die. In this way, a punch processing stroke is a finished product. High speed continuous punch can process 300 or 400 products per minute.
Lathe: lathe belongs to precision machining machinery, which is divided into general lathe, active lathe, instrument lathe and computer lathe. After holding the material clip, it reverses and processes radially or axially by the turning tool.
Nowadays, active lathe and computer lathe are more and more widely used. Because both of them are fully active processing, the accuracy error caused by human operation is reduced to the lowest point, and the processing speed is fast, which is used for mass production. Most of today’s computer lathes are equipped with side reverse cutter and reverse reverse cutter, that is to say, milling can also be carried out on the lathe. The surface roughness of lathe is about ra0.4-1.6;
