July 2019 – Page 16 – CNC Machining & Turning, Milling, Metal parts

Brief introduction of drawing analysis process for metal parts

In metal processing, from the design drawings of parts to the qualified delivery of finished parts, a series of factors such as the arrangement of parts processing technology route, the selection of processing machine tools, the selection of cutting tools, positioning and clamping in parts processing are taken into account. The analysis and research of part drawings is mainly to carry out process review of parts, such as checking whether there are errors or omissions in the view, dimension labeling, technical requirements of design drawings, especially for parts with poor structural workmanship. If possible, the designer should communicate with the designer or propose modification suggestions, and the designer decides whether or not to do so. Carry out necessary modification and improvement. Here is a brief introduction to the analysis process of metal processing drawings.

First, the integrity and correctness analysis of part drawing.
The view of the parts should meet the requirements of the national standard, the position should be expressed clearly and accurately, the relationship between geometric elements (points, lines and surfaces), such as tangent, intersection and parallel, should be accurate, and all relevant dimensions should be marked completely and clearly.

Two, part technical requirements analysis

The technical requirements of parts mainly include dimension accuracy, shape accuracy, position accuracy, surface roughness and heat meter processing requirements. These technical requirements should be the limit value under the premise of ensuring the performance of parts. To analyze the technical requirements of parts, we mainly analyze the rationality of these technical requirements and the possibility of their realization, and focus on the analysis of the processing accuracy and technical requirements of important surfaces and parts, so as to prepare for the formulation of reasonable processing plans. At the same time, through analysis to determine whether the technical requirements are too strict, because too high accuracy and too small surface roughness requirements will make the process more complex, increase the difficulty of processing, and increase unnecessary costs.

Three. Analysis of dimensioning methods

Part dimensioning methods include partial annotation, concentration annotation and coordinate marking. For the parts processed on NC machine tools, the dimension on the part drawing should be labeled centrally or with the same reference (i.e. coordinate dimension) as far as possible, on the premise that the performance can be guaranteed. This not only facilitates the NC programming, but also facilitates the unification of design reference, process reference and programming origin.

Four. Part material analysis

On the premise of satisfying the function of parts, materials that are easy to purchase should be selected, the principle of proximity should be adopted when selecting materials, and precious and scarce materials should not be selected easily.

Five. Structural manufacturability analysis of parts

The structural technicality of parts refers to the feasibility and economy of manufacturing the parts designed under the premise of meeting the requirements of service performance. Good structural technicality will make parts easy to process and save costs and materials, while poor structural technicality will make processing difficult and increase costs, waste materials or even unable to process. Through the analysis of the structural characteristics, accuracy requirements and complexity of parts, the processing methods and the types and specifications of NC machine tools needed for parts can be determined.

What is operation

Whatever the industry, the first thing is to understand our services or products, how much ability do we have? How big is the market? What stage is it now? To fully understand oneself, it is not only one-sided, but also need to fully grasp the rhythm of the market, so as to make effective, valuable and meaningful decisions.

Maybe in the process of understanding, many people will point out and put forward their own opinions, for example, people do this, we can do the same as them; others can do this thing, we can do the same, and so on, if we stand in the perspective of everyone to think about the problem, all right. But for an operator, the ability to jump out of the planned circle, stand outside the circle and see problems, think about problems and think about their original intention is to consider what, as an operator, to learn to see the essence of the problem through phenomena, a simple understanding is to learn to see things essentially. Wait. Only when you know yourself clearly can you make reasonable decisions on the basis of what you know.

A qualified operator, according to the needs of users, will use simple, refined services or products to meet the needs of users. Commonly, operators think that the more information they push, the more users know. Therefore, constantly push services, product-related information, we must not know. Slowly, they will push their products to a blind alley.

But one thing is that in order to operate, we must have a clear positioning of our services and products, and then carry out a series of operations according to the point of demand. In general, we should try our best not to change the original decision easily. Once a decision is implemented, it means that we have invested a lot of energy in it. It is easy for others to shoulder the pressure of time and work.

This is not to say that the operation can not overthrow their previous wrong decisions, but to make themselves clear, often do not make some dispensable changes, if the reasons for the changes are unclear, vague, and even unable to convince themselves why to readjust the reasons for the changes, then how to make other changes? Are people convinced?

For example, to be a qualified operator, first of all, what you need to have is a continuous enterprising and learning attitude, because the Internet is not unchanged, what you have to do is to understand the news, understand the market, understand the product update, these things are not chat or look at can be mastered. Instead, we need to study, reflect and digest earnestly, so as to improve our thinking ability in operation.

In addition, doing business does not require you to know everything, but at least you can have a general understanding of what you are exposed to. For example, the operation process may involve some product design things, do not require technical knowledge, code writing, but must understand the most basic technical concepts and logic, so, with technical personnel. When communicating, you will find that there are some constructive suggestions in the process of not knowing anything and communicating, and the feedback they get is totally different.

There is also the need to understand themselves, to have a reasonable position for themselves, to know what occupation they are engaged in, what kind of abilities this occupation requires, and whether their current abilities meet the standards, how to improve their ability level, etc., to become a qualified operator, to learn how to grow up.

Note that the Internet industry should not be impetuous, because of the rapid development of the Internet, the rhythm becomes faster, but operators can not be affected by the environment and atmosphere around the Internet, we must understand where their most important capabilities are, at which stage, whether they have gone astray, is not it? Slow or fast steps lead to holes, and so on. Only when you are clear about yourself at all times can you move smoothly along the road of operation.

Classification performance of metal bellows

The performance, material selection and use of metal bellows are as follows:

Brass bellows

H80 H -60 -60 ~ +100 C has lower elasticity, greater hysteresis and greater aftereffect, and better solderability. It can be used as a measuring element in non corrosive media and instruments with low accuracy.

Tin bronze bellows

QSn6.5-0.1 *-60 ~+100 (?) has good elasticity, strength and corrosion resistance, less hysteresis and elastic aftereffect, better brazing performance, and is widely used as measuring elements.

Beryllium bronze bellows

QBe2 P-60 ~+150 (?) has little hysteresis and elastic aftereffect, high elastic stability, corrosion resistance and no magnetism. It is mostly used in high-precision measuring instruments.

stainless steel bellows

1Cr18Ni9Ti G -194 C ~ +400 C has high bending fatigue strength and corrosion resistance, and good weldability. It can be used as measuring, sealing, connecting and compensating elements in corrosive medium.

Material selection for sheet metal processing

Selection of materials

Sheet metal processing commonly used materials are cold-rolled sheet (SPCC), hot-rolled sheet (SHCC), galvanized sheet (SECC, SGCC), copper (CU) brass, copper, beryllium copper, aluminum sheet (6061, 5052, 1010, 1060, 6063, hard aluminum, etc.), stainless steel (mirror, wire drawing surface, fog surface), according to the role of the product, choose different materials. Generally consider the use and cost of the product.

1. cold rolled plate SPCC, mainly used in electroplating and baking parts, low cost, easy to shape, material thickness less than 3.2mm.

2. Hot-rolled sheet SHCC, material T (> 3.0mm), but also with electroplating, paint parts, low cost, but difficult to form, mainly for flat parts.

3. galvanized sheet SECC and SGCC. SECC electrolysis plate is divided into N material and P material. N material is mainly used for surface treatment and high cost. P material is used for spraying parts.

4. Copper; mainly used for conductive materials, its surface treatment is nickel plating, chromium plating, or no treatment, high cost.

5. Aluminum plate; generally used surface chromate (J11-A), oxidation (conductive oxidation, chemical oxidation), high cost, silver, nickel plating.

6. aluminum profile, complex section material, used in various inserts. Surface treatment is the same as aluminum sheet.

7. stainless steel; it is mainly used without any surface treatment, and the cost is high.

Graphic audit

In order to compile the technological process of parts, we must first know the various technical requirements of the part drawing, and then the surface examination is the most important link in compiling the technological process of parts.

1. check whether the map is complete.

2. figure view relationship, whether the label is clear, complete, dimensioning units.

3. assembly relations, assembly requirements for key dimensions.

4. the difference between the old and the new.

5. translation of foreign languages.

6. table code conversion.

7. feedback and burial.

8. materials.

9. quality requirements and process requirements.

10. official distribution of the map, the quality control chapter must be affixed.

Technical characteristics of cold heading and solutions to common problems

Cold upsetting is a forging process that uses dies to upset metal bars at room temperature. It is usually used to make the heads of screws, bolts, rivets, etc. It can reduce or replace cutting. The material for forging billet can be copper, aluminum, carbon steel, alloy steel, stainless steel and titanium alloy. Cold heading is usually carried out on a special cold heading machine, which is convenient for continuous, multi station and automatic production. On the cold heading machine, the cutting, upsetting, accumulation, forming, chamfering, twisting, shrinking and trimming processes can be completed sequentially. The following is a brief introduction to the common problems and solutions of the cold heading process.

1. What are the characteristics of cold heading technology?

(1) According to the theory of metal plastic deformation, a certain pressure is applied to the metal blank at room temperature to make it plastic deformation in the cavity and shape it according to the prescribed shape and size.

(2) It is necessary to select high-quality “plastic deformation” good metal materials, such as rivet screw steel, its chemical composition and mechanical properties have strict standards.

(3) cold heading bolts and nut forming machines have many models and series of machines. The equipment has reliable performance, high efficiency and stable product quality.

(4) the forming force of the product is large, and the power of configuration is high.

(5) good surface quality and high dimensional accuracy. Because of the cold work hardening in the upsetting process, the deformation should not be too large. Reduce cracking.

(6) cold heading technology is applicable to products with large quantities and various specifications so as to reduce costs.

Two. Matters needing attention in cold heading processing

(1) the corresponding fixture should be replaced according to the diameter of the steel bar.

(2) The mould and the central punch should be checked and confirmed to be free of cracks, and the concentricity between the upper and lower dies and the central punch should be corrected, bolts should be tightened, and safety protection should be done.

(3) After starting, it should run empty first, adjust the tightness of the upper and lower dies, calibrate the heading of the alignment die, and confirm the normal operation before it can be operated.

(4) the head should not be upset when the machine does not reach the normal speed. When the head size of the upsetting head is not uniform, the clearance between the punch and the fixture should be adjusted in time. The punch and guide block should be adequately lubricated.

(5) it is forbidden to replace shaft core, pin and change angle and speed regulation, nor to clean and refill.

(6) bending of steel bars exceeding the diameter specified in the nameplate is prohibited. When bending steel bars without cold drawing or with rusty skin, they should wear protective glasses.

(7) When bending high strength or low alloy steel bars, the maximum allowable diameter shall be converted according to the provisions of the mechanical nameplate and the corresponding mandrel shall be replaced.

Three. Performance requirements for special cold heading forming oils

(1) Excellent extreme pressure lubrication, high temperature resistance, extreme pressure and wear resistance, rust resistance and high temperature oxidation stability. Improving the precision and smoothness of the workpiece can prevent the sintering of the mould, satisfy the multi-position forming processing of standard and non-standard parts, and can be completely competent for cold heading stainless steel workpiece processing.

(2) Oil fume and “drifting fog” can be reduced to a minimum to meet the strict requirements of multi-die punching nuts with a strong die.

(3) It has good processing performance for products with large deformation, such as hollow, high strength bolts, sleeves, stainless steel hollow, semi-hollow rivets and so on.

(4) it can effectively protect the impact bar (punching needle) and die, prolong the service life and reduce the comprehensive cost.

(5) the heat dissipation is good, and the local temperature of workpiece and mold is too high during cold forming.

(6) high temperature resistance and good oil sludge. Low odor, low smoke, protect the operating environment.

(7) it has a certain degree of rust resistance, which can meet the rust prevention requirements in the process.

(8) it can meet the requirements of harsh cold heading stainless steel forming and large variant carbon steel forming.

Hydraulic characteristics

The basic function of the hydraulic circuit is to carry out easily controlled energy transfer in the form of liquid pressure energy.

From the perspective of energy transfer, hydraulic technology is roughly in the middle of mechanical energy transfer and electrical energy transfer.

From the transmission characteristics: mechanical transmission and hydraulic transmission device can be said to have fixed characteristics, on the contrary, hydraulic transmission device and electrical transmission device are the same, with the characteristics of CVT, in addition to constant power, but also easy to achieve constant speed and constant torque characteristics.

The characteristics of hydraulic technology can generally be summarized as follows:

(1) It is easy to carry out CVT and has a wide range of speed change, that is, it can easily adjust the force and torque in a wide range.

(2) Good control performance, that is, force, speed, position can be correctly controlled with a high response speed. In addition, for electrical, mechanical and other control methods have good adaptability, especially combined with electrical signal processing, can get good response characteristics;

(3) reliable operation and good operation performance;

(4) moderate flexibility in structure and characteristics;

(5) a standard element can be used to make circuits of arbitrary complex functions.

Related books

Related books

The reason for these characteristics is that the volumetric components are used as capacity converters, i.e. hydraulic pumps and actuators, and the lubricating oil (hydraulic oil) is used as working medium. The general disadvantage of hydraulic technology is also related to hydraulic oil. These shortcomings are summarized as follows:

(1) oil leakage;

(2) The contamination of hydraulic oil has an adverse effect on the characteristics of components and devices when special precise control is required. That is to say, the management of hydraulic oil has great influence on the reliability and the life of components.

Why helical gears are used in the manufacture of reducer

The main disadvantage of spur gears is that they generate vibration. Whether it is due to design, manufacture or deformation reasons, at the same time along the entire tooth surface may occur some changes in the shape of the involute. This will lead to a regular stimulus per tooth, which is usually very strong. The resulting vibration not only causes large loads on the gears but also causes noise. Another disadvantage is that the additional strength sometimes obtained by the engagement of two pairs of teeth in contact time cannot be utilized, because the stress is limited by the condition of the single tooth engagement in the cycle.

Helical gears can be seen as cylindrical gears with a set of flake gears misplaced so that each piece of contact is at different parts of the tooth profile, resulting in the compensation of each flake gear error, which is very effective due to the elasticity of the teeth, thus resulting in such a result that the error is less than 10 mm. The teeth of the gear can make the errors equalize, so it can run as smoothly as the teeth within 1 mm under load. Because at any instant, about half the time (assuming the degree of coincidence is about 1.5) there will be two teeth engaged, which brings additional benefits in terms of strength. Therefore, the stress can be established on the basis of 1.5 times the width of the tooth, not the width of the tooth.

It is difficult and inexpensive to manufacture and assemble a large number of thin spur gears, so they are made into gears that are connected together and the teeth are in the direction of helix. Helical gears are not like spur gears, which cause bad axial forces. But the benefits of vibration and strength far outweigh the disadvantages of axial thrust and slightly increased manufacturing costs. Therefore, helical gears are chosen instead of spur gears in the manufacture of reducers. For example, there are four series: R series coaxial helical gear reducer, K series helical bevel gear reducer, S series helical gear worm gear reducer, F series parallel shaft helical gear reducer.

Note 1:

What is spur gear: spur gear is the gear parallel to the rotating shaft. We only discuss the theory of parallel-axis gear transmission, so any cross-section perpendicular to the two gear shafts is exactly the same.

How to divide the steps of CNC machining

CNC machining is a kind of process method to process parts on CNC machine tools. CNC machining is consistent with traditional machine tools in general. It is an effective way to solve the problems of variable parts, small batch, complex shape, high precision and realize high efficiency and automatic machining. For a part with high complexity, high precision and need to be processed by CNC machine tools, the following is a brief introduction to the principle of CNC machining process division in Borun Petrochemical.

Process division method

(1) process the parts by clamping and positioning.

Due to the different structural shapes of each part and the different technical requirements of each surface, the positioning methods of each part are different in machining. When machining parts in general, they should be positioned in the inner shape and positioned in the shape when the parts are processed. The process can be divided according to different positioning methods.

(2) processing according to rough and Seiko sequence.

According to the machining accuracy, stiffness and deformation of parts, the process can be divided according to the principle of separation of rough and finish machining, that is, rough machining first, then finish machining. At this time, different machine tools or different tools can be used for processing. Usually in one installation, it is not allowed to finish machining one part of the surface of the part, and then reprocess the other surface of the part.

(3) processing according to centralized process.

In order to reduce the number of tool changes, shorten the running time of empty stroke and reduce unnecessary positioning errors, the machining process of parts can be divided according to the method of using the same tool to centralize the machining process. Use the same tool as much as possible to process all the parts that can be machined, and then replace another tool to process the rest of the part. This method is often used in special CNC machine tools and machining centers.

Two. The method of dividing work steps.

The division of work steps is mainly considered from two aspects: machining accuracy and production efficiency. Different cutting tools and cutting parameters are often needed to process different surfaces in a process. In order to facilitate analysis and description of complex parts, it is subdivided into work steps in the process. The principle of division is:

(1) The same surface is roughed, semi-finished and finished in turn, or all the surface is roughed and then finished separately.

(2) For parts with both milling plane and boring surface, they can be machined by milling plane before boring. By dividing the steps according to this method, the machining accuracy of high holes can be raised. Because the cutting force is larger when milling the plane, parts tend to deform. Milling plane before boring can restore its deformation for a period of time and reduce the influence of deformation on the accuracy of the hole.

(3) divide the steps according to the use of cutting tools. The turning time of the worktable of some machine tools is shorter than that of tool changing. The working steps can be divided according to the tool used to reduce the number of tool changing and improve the machining efficiency.

Two. Ways to improve cutting technology.

(1) design of high speed cutting tools

With the expansion of high-speed machining applications, the research of new tool materials, the improvement of tool design structure, the generation of new NC tool path strategy and the improvement of cutting conditions have also been improved.

(2) manufacture of high speed milling equipment

Ultra high speed cutting technology is the development direction of cutting process, and is also the product of the development of the times. High-speed cutting technology is one of the main development directions of cutting technology. With the development of basic technology, such as technology, microelectronics technology, new materials and new structures, it has advanced to a higher level.

(3) the development of CNC system is progressing smoothly.

Generally speaking, machine tool adaptive control can be divided into process adaptive control and geometric adaptive control, among which process adaptive control is studied more. Intelligent technology is used to realize intelligent decision-making, process adaptive control, error compensation intelligent control, motion trajectory optimization control of complex curved surface machining, fault self-diagnosis, intelligent maintenance and information integration under multi-information fusion, which will greatly improve forming and machining accuracy and manufacturing efficiency.

(4) research and development of special cutting oil

Special cutting oil is a kind of medium which must be used in NC cutting process. It plays the role of lubrication, cooling, cleaning and so on. Due to the continuous improvement of cutting tools, equipment and technology in high-speed cutting, new cutting oil usually uses vulcanized extreme pressure and anti-wear additives as its core component, which can effectively protect the cutting tools and improve the process accuracy in ultra-high-speed cutting process.

Points for attention in hydraulic motors

1. When the inertia of the driven parts is large, if it is required to brake or reverse or align in a short time, safety valve cushion should be set in the oil return circuit to prevent damage accidents caused by sharp hydraulic impact.

2. When using the quantitative motor, if you want to start and stop smoothly, you should adopt the necessary pressure control or flow control method in the loop design.

3. When the hydraulic motor is used as the power part of the lifting tool or the walking device, the speed limit valve must be set to prevent the heavy object from falling rapidly or the vehicle and other walking mechanism from overspeeding when it goes downhill, which causes serious accidents.

4. Because the hydraulic motor always leaks, so the hydraulic motor’s inlet and outlet will be closed to brake, it will still have a slow slip, when a long time of braking, should be set up to prevent rotation of the brake.

5. When starting at full load, we should pay attention to the starting torque value of hydraulic motor, because the starting torque of hydraulic motor is smaller than the rated torque, if neglected, the working mechanism will be unable to operate.

6. Because the back pressure (outlet pressure) of the hydraulic motor is higher than the atmospheric pressure, the motor’s oil drain pipe must be separately led back to the tank, and can not be connected with the return pipeline of the hydraulic motor.

CNC standard procedure for CNC programmers

As the representative of advanced productive forces in the machinery manufacturing industry, CNC machining has played an important role in the automotive, aviation, aerospace and mold industries after more than 10 years of introduction and development.

CNC programming is an important aspect affecting the quality and efficiency of CNC machining, especially in high-speed and precision machining. In the mechanical industry, because the level of CNC programmers is different, it is necessary to establish certain specifications to avoid low-level errors and repetitive problems.

First, numerical control machining programming flow.

The general process of NC machining programming includes: determining the basis of programming, establishing process model, defining machining operation, generating tool path, machining path simulation, post-processing, NC machining program simulation, NC machining program checking, issuing on-site processing and NC machining program finalization.

1. confirm programming basis.

CNC programming basis mainly includes three-dimensional model, engineering drawings and parts manufacturing instructions (NC process specification), through NC programming basis can be obtained the following information: parts information, NC machining process plan, NC machine tool type, clamping positioning mode, cutting tools, procedures and steps, processing program number and product processing status. Wait.

2. establish process models

Based on the three-dimensional model of parts and engineering drawings, the process model is designed, which mainly includes trimming of the three-dimensional model of parts, establishing process reference surface, establishing process positioning hole, pressing plate and position design, and machining surface allowance processing.

3. define machining operations to generate tool path.

Define the machining operation and generate the tool path. The main contents include: Define the programming coordinate system, fully consider the machining material characteristics, tool cutting characteristics, machine tool cutting characteristics and the material conditions of the parts to be removed, define the machining methods (including various tool running strategies, etc.) and process parameters (including remainder) according to the process requirements. Quantity, feed speed, spindle speed, tool path span, etc. and auxiliary attributes (including tool point, safety surface and CNC machine tool attributes) eventually generate tool path.

4. machining trajectory simulation verification

The main contents of simulation verification of machining path include: checking whether the definitions of cutting tools, machine tools, workpieces and fixtures are complete and the dimensions are accurate; checking machining operations, defining whether the dimensions of the parts to be achieved in each process are correct; checking the machining methods in the definition of machining operations (such as rough machining strategy, tool repair machining and cavity machining). Etc.

Whether it is correct and reasonable; Check whether there are over-cutting, undercutting or collision interference between NC machine tool worktable, machined parts, tools and fixtures; Check whether the process parameters are reasonable.

5. post processing

Postprocessing can be an independent processing process, or can be integrated with the tool location file generation process, according to the function of the processing software, choose the appropriate processing method, and for the post-processing there are the following requirements:

The special post-processing software should be selected to generate the special NC system processing program; the development or customization of the post-processing software should be combined with the specific control system and the type of machine tool motion structure; the post-processing software should ensure the full conversion of tool position processing information and meet the requirements of control system syntax; the post-processing software should be used to develop or customize the post-processing software. When necessary, the necessary annotation instructions are automatically added to the processing program.

6. simulation verification of NC machining process

On the basis of programming software or combining with the function of NC simulation software, verify every aspect of CNC machining program as far as possible to ensure the correctness of the final machining program, and record the corresponding simulation verification of CNC machining program.

The simulation verification mainly includes the following contents: checking whether the annotation information is correct in the machining procedure; checking whether the machining method is correct in the NC machining procedure; checking whether the tool size information is correct in the machining procedure; checking whether the part size information that each working procedure should achieve is correct in the CNC machining procedure; Check whether the tool compensation information is correct in NC machining program, check whether there are over-cutting, under-cutting or collision interference problems in CNC machining program, check whether the spindle speed and feed speed matches the current NC machine tool, etc.

7. proofreading of CNC machining program

The proofreading of NC program is totally different from the proofreading of process files. The program format is a coordinate point. If we proofread the program content line by line, it will take a lot of time and is impractical.

The proofreading procedure is mainly considered from the following aspects.

(1) model. Model is the basic element to ensure the correctness of the program. It is necessary to check the correctness of the model and analyze whether all the data of the model are consistent with the elements of process documents.

Coordinate system. Check whether the direction of the machining coordinate system is in accordance with the requirements of the process documents, whether it is easy to operate, whether the selection of the coordinate system is reasonable and whether it is easy to control the size.

Third, the processing strategy. The program generated by different machining strategies is totally different, and the amount of program is also different. The rationality of the analysis of machining strategy is mainly to control the tool path of the program, control the machining quality and efficiency.

(4) cutting tools. Tool materials, specifications and forms are determined according to part materials and parts processing position. Different tools directly affect the processing efficiency and quality.