April 2020 – Page 11 – CNC Machining & Turning, Milling, Metal parts

Advantages and disadvantages of CNC machining

CNC machining has the following advantages:

① The number of tooling is greatly reduced, and complex tooling is not required for parts with complex processing forms. If we want to change the form and size of the parts, we only need to modify the processing program of the parts, which can be used in the development and modification of new products.

② The machining quality is stable, the machining precision is high, and the repeated precision is high, which is suitable for the machining requirements of aircraft.

③ Under the condition of multi type and small batch production, the production efficiency is high, which can reduce the time of production planning, machine tool adjustment and process inspection, and reduce the cutting time due to the use of the best cutting amount.

④ It can be used to process complex surfaces which are difficult to be processed by conventional methods, and even to process some processing parts which cannot be observed. The disadvantage of NC machining is the high cost of machine tools and equipment, which requires high level of maintenance staff.

Technical problems of aluminum processing

There are many reasons for the deformation of aluminum parts, which are related to the material, shape and production conditions. There are mainly the following aspects: deformation caused by internal stress of blank, deformation caused by cutting force and cutting heat, and deformation caused by clamping force.

1、 Technological measures to reduce processing deformation

1 reduce the internal stress of blank

The internal stress of the blank can be partially eliminated by natural or artificial aging and vibration treatment. Pre processing is also an effective process. For the blank of fat head and big ear, because of the large margin, the deformation after processing is also large. If the surplus part of the blank is pre processed and the surplus of each part is reduced, not only the processing deformation of the subsequent process can be reduced, but also the internal stress can be released after pre processing for a period of time.

2. Improve the cutting ability of tools

The material and geometric parameters of cutting tools have an important influence on cutting force and cutting heat. The correct selection of cutting tools is very important to reduce the machining deformation of parts.

(1) Reasonable selection of tool geometry parameters.

① Front angle: under the condition of maintaining the strength of the cutting edge, the front angle should be larger. On the one hand, it can grind out a sharp edge, on the other hand, it can reduce cutting deformation, make chip removal smooth, and then reduce cutting force and cutting temperature. Never use a negative rake tool.

② Back angle: the size of the back angle has a direct impact on the wear of the back cutter face and the quality of the machined surface. The cutting thickness is an important condition to select the back angle. In rough milling, due to the large feed, heavy cutting load and large heat output, it is required that the heat dissipation condition of the cutter is good, so the back angle should be smaller. When finishing milling, it is required to have sharp edge, reduce the friction between the back face and the machining surface, and reduce the elastic deformation. Therefore, the back angle should be larger.

③ Helix angle: in order to make milling stable and reduce milling force, the helix angle should be selected as large as possible.

④ Main deflection angle: properly reducing the main deflection angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.

(2) Improve the tool structure.

① Reduce the number of milling cutter teeth, increase chip space. Because of the large plasticity of aluminum material, the large cutting deformation and the need for large chip space, the bottom radius of chip holding groove should be larger and the number of milling cutter teeth is less.

② Sharpen the teeth. The roughness value of cutting edge should be less than RA = 0.4um. Before using a new knife, it is necessary to use a fine oilstone to slightly grind the front and back of the knife teeth, so as to eliminate the remaining burrs and slight serrations when grinding the knife teeth. In this way, not only cutting heat can be reduced, but also cutting deformation is relatively small.

③ Strictly control the tool wear standard. After tool wear, the surface roughness of workpiece increases, the cutting temperature increases, and the deformation of workpiece increases. Therefore, in addition to the selection of good wear-resistant tool materials, the tool wear standard should not be greater than 0.2mm, otherwise it is easy to generate chip accretion. When cutting, the temperature of workpiece should not exceed 100 ℃ to prevent deformation.

3. Improve the clamping method of workpieces

For thin-walled aluminum parts with poor rigidity, the following clamping methods can be used to reduce deformation:

① For thin-walled bushing parts, if the three jaw self centering chuck or spring chuck is used to clamp from the radial direction, the workpiece will be deformed once it is loosened after machining. At this time, the method of axial end face compression with better rigidity should be used. Locate the inner hole of the part, make a self-made threaded through mandrel, insert it into the inner hole of the part, press the end face with a cover plate and back it with a nut. When machining the outer circle, the clamping deformation can be avoided and the satisfactory machining accuracy can be obtained.

② When machining thin-walled sheet metal, it is better to select vacuum sucker to obtain uniform clamping force, and then to process with a small cutting amount, which can prevent the deformation of the workpiece well.

In addition, the filling method can be used. In order to increase the technological rigidity of thin-walled workpiece, the medium can be filled in the workpiece to reduce the deformation of workpiece during clamping and cutting. For example, fill the workpiece with urea melt containing 3% – 6% potassium nitrate, after processing, immerse the workpiece in water or alcohol, then the filler can be dissolved and poured out.

4 reasonable arrangement of process

In high-speed cutting, because of large machining allowance and intermittent cutting, the milling process often produces vibration, which affects the machining accuracy and surface roughness. Therefore, NC High-speed machining process can be generally divided into: rough machining – semi finish machining – angle cleaning machining – finish machining and other processes. For parts with high precision requirements, sometimes it is necessary to carry out secondary semi finishing, and then finish machining. After rough machining, the parts can be naturally cooled to eliminate the internal stress caused by rough machining and reduce the deformation. The allowance left after rough machining shall be larger than the deformation, generally 1-2mm. During finishing, the machining allowance of the finished surface of the part shall be kept even, generally 0.2-0.5mm is the best, so that the cutter is in a stable state during the machining process, which can greatly reduce the cutting deformation, obtain good surface machining quality, and ensure the accuracy of the product.

Medical device processing

Medical equipment processing not only needs to meet the requirements of high precision and high surface brightness of parts, but also faces the challenge from difficult to process raw materials.

The products of artificial key include hip, knee, shoulder, elbow, wrist, ankle, shin, spine, etc. In the artificial critical processing industry, because it is related to the health and safety of human remains, there are quite high requirements for the processing accuracy, quality and generality.

In the medical industry, the manufacturing enterprises usually have the following requirements for tool suppliers:

1. Partners and joint design strength. The manufacturing enterprises of artificial critical products have a good understanding of the raw materials and design of artificial critical products, but they don’t have much experience in the detailed processing technology of products, so they usually form a strategic partnership with tool suppliers. In the process of new product research and development, the tool supplier enters the joint development, and more researches are made on the stability of processing cost and processing technology, and the controllability of product quality.

2. Quite specific use. The products of artificial critical industries are relatively stable, and the design and use of products are relatively specific. Although the products provided by different companies are different, due to the relatively unchanged human body structure, there will be no significant difference in the products. In this way, the product processing technology and quality assurance system are also relatively similar. This also poses a greater challenge to tool suppliers, constantly improving the quality of tools, improving the level of processing technology, reducing processing costs, and improving the stability and controllability of processing technology.

3. High quality requirements. Most of the artificial critical products need to be implanted into human body, so the raw materials and quality of the products have the highest requirements. In the same way, the same requirements will be put forward for the suppliers including the tool suppliers of the manual critical processing enterprises. In the grinding equipment, the grinding oil temperature, air temperature, tool temperature and grinding point temperature are all detected online. When the temperature is too high or insufficient, the system will automatically adjust the air conditioning system and correct the temperature, so as to maximize the control to ensure the accuracy, quality and generality of the tool and meet the requirements of the medical industry.

4. Product traceability. All artificial critical products have their specific numbers, which are used to track the use of products, so as to achieve the traceability of product quality. If there is a problem with a certain product, it is advisable to trace all batches of the same product and recall the same product. This requirement is certain for the medical industry. Shangao tool has its specific number for tracking. As long as you check the number of this tool, you can immediately track the production date, production equipment, production process, product detection, product transportation and other information of the product.

5. Product certification. Due to the unique use of medical industry, the access threshold for suppliers is also quite high. The supplier must also possess the product certification system to meet the requirements of the medical industry.

The raw materials at the artificial juncture are also improving with the development of the industry. The demand for raw materials meets the requirements of biocompatibility (no adverse effect on human body), bioconversion (the artificial juncture must be integrated with the surrounding tissues), and of course, it also includes the strength and elasticity of raw materials. Moreover, the raw materials required by people of different ages are definitely different, which are suitable for more activities and late hours of young people The recovery of human body and bones in the year of 2000 was slow.

Common raw materials for artificial key include titanium alloy, cobalt chromium alloy (containing cobalt chromium molybdenum alloy), stainless steel, UHMWPE, peek and ceramics, and the heat treatment of raw materials is different, such as forging and forging.

Different raw materials and different heat treatment methods have a huge impact on the machinability of workpiece raw materials. Shangao cutting tool also specially develops a targeted cutting tool and processing plan for different raw materials in the medical industry. For example, when machining titanium alloy, it is advisable to select jhp750 series high efficiency milling tools to remove the surplus in the fastest time. At the same time, this tool can also be used for finishing. For cobalt chromium alloy, jh141 series high-speed milling tools can be selected with unique coating to ensure the surface quality and processing life of the workpiece. Peek raw materials, more and more found in many carbon fiber raw materials are widely used in the artificial critical industries, the selection of a unique custom diamond coated tool greatly improves the efficiency, life and process stability of the tool.

The processing of UHMWPE raw materials, such as the joint surface used in the knee joint, has quite high requirements for the quality of the processed surface, such as RA < 0.20 μ m, and also has different requirements for the workpiece difference target. Seco jabro has developed a special Super meticulous finishing milling cutter, Premier finish, which will be delivered with a unique serial number, product certificate, inspection report, unique tool packaging, etc. for product tracking, and this cutter can also be used for regrinding to reduce processing cost. Customers choose this cutting tool, the efficiency can be increased up to 70%, the process is stable, and the cost of the cutting tool also drops more than 30%.

The medical critical industry is related to human health interest, and the market scale is huge, and the development potential in developing countries is more and more obvious, and it is not affected by the market operation cycle. Most of the overseas key market occupiers still set up branches in China and carry out production. In recent years, the production scale has increased dramatically. Chinese production companies are also trying to catch overseas companies outsourcing a large number of products to China in order to reduce costs

Factors affecting the machining accuracy of precision parts

As we all know, the reason why the processing of well-rounded parts is called well-rounded machining is precisely because of the high requirements of its processing procedures and processes, as well as the high requirements for the accuracy of products. The processing accuracy of well-rounded parts includes the accuracy of position, size, form, etc. today’s small compilation summarizes the following factors that affect the processing accuracy of well-rounded parts:

(1) The rotary run out of the machine tool’s spindle can produce certain deviation to the machining accuracy of the parts.

(2) The inaccuracy of the guide rail of machine tool can also cause the deviation of the workpiece form of the careful parts.

(3) Transmission parts can also cause workpiece machining deviation, which is also the most important factor of workpiece surface deviation.

(4) The difference of tool and fixture will also affect the accuracy of workpiece.

（5） In the process of machining and cutting, due to the change of the position of the stress point, the system will deform, which will lead to differences, and also can make the accuracy of the workpiece deviate from the standard.

(6) The difference of cutting force will also affect the accuracy of workpiece.

(7) In the process of machining, the process system will have certain thermal deformation under the action of various heat sources.

(7) The deformation of the process system caused by heating usually affects the accuracy of the workpiece.

(8) The deformation of the machine tool caused by heating will cause the deformation of the workpiece.

(9) The hot deformation of the tool will have a great influence on the workpiece.

(10) The workpiece itself is deformed by heating, mainly if it is deformed by heating in the cutting process

Conditions for precision milling of gantry

Gantry milling processing and milling fill the gap that carving milling machine can’t process large-scale mold in the current market. The machine has the advantages of average transmission, high rigidity, heavy body and large processing size, which can meet the requirements of carving and milling of most large molds in the market at present.

The tool path of gantry milling must be in accordance with the following strategies:

1. High speed machining should be based on down milling to reduce tool wear and improve machining accuracy.

According to the principle of shallow cutting and small layer depth, the correct layering route is selected to complete the correct intelligence of machining and the stability of load.

3 arc cutting should be added at the corner to prevent the sudden change of velocity vector target and the sharp change of tool load.

4 in the plane two-way cutting, it is possible to add arc transition between two adjacent tool paths, so as to make the tool move smoothly laterally. In the process of two-way cutting in space, it is advisable to select several extended transition modes, such as space circular arc cutter, space inner circular arc cutter, space outer circular arc cutter and “Golf” type transition cutter, which not only ensures the smoothness of cutter path, but also effectively prevents the phenomenon of turning and hard bending between two lines. This transition mode is widely used in high-speed milling of various curved surfaces.

5 to prevent the normal direction direct feed and retreat on the appearance, the spiral, arc and diagonal mode should be selected to ensure smooth feed and retreat.

In order to prevent the sharp change of the cutting load, the different ways are used to separate the steep wall and the non steep wall, which can increase the cutting speed and average the surface roughness of the parts.

Gantry milling processing conditions:

● prevent sharp changes in tool movement.

● prevent feeding and withdrawing on the appearance. Sink directly to the next depth in appearance milling. If it can’t sink directly, it can sink through spiral or slope.

● the infeed (Fz) of each tooth shall be equal to (AE).

● real cutting roughness milling is selected for gantry milling – the step distance is calculated by the roughness of the tool.

● the best surface machining quality can be achieved when the feed rate of each tooth is constant.

Do you understand the above Longmen milling content? If you have any other questions, please call us for consultation. We will sincerely serve for you

How to model and simulate the parts of automobile inspection tools

When the existing testing equipment of automobile parts in stamping or injection molding can not meet the requirements of testing, it needs to use the inspection tool accessories. However, when planning reflection, it is necessary to analyze the part products of the inspection tool accessories, check whether the 3D digital model of the product is the same as the 2D drawing of the product. The original data of the 3D digital model of the product is the entity, still the piece. The following two points are for the entity or What are the differences in the design process of the inspection tool for the slice.

1、 When the original data of 3D digital analog of automobile product is entity (i.e. the product already has thickness), it is better to use the datum plane (or lap plane) of the product as an offset datum, or the datum plane marked on the GD & T drawing of the product as the offset plane. In the design of imitation block, there are not many phenomena of target selection, which are usually well mastered.

2、 When the original data of 3D digital analog of automobile product is a piece (i.e. the product is a surface without thickness), the target of product thickness must be studied. Once the thickness target is definitely wrong, or there is no target to study the thickness, the product can not be put into the inspection tool for detection, resulting in the scrap of the imitation block of the inspection tool accessories.

Therefore, in the process of the design of checking tool parts, it is very important to analyze the product of automobile parts, especially when the original data of the product is a piece, it should be very concerned.

Problems in the design of fixture parts

The design of fixture parts is usually simple in structure, which makes people feel that the structure is not very complex. The more we find that the hydraulic fixture is widely used, which greatly simplifies the original mechanical structure. However, if we do not make a detailed study in the design process, there will inevitably be unnecessary difficulties:

1 blank allowance of the workpiece to be processed. The size of forming blank is too large, and interference occurs. So we must plan the rough drawing before design. Leave plenty of space.

2. Smooth chip removal of fixture accessories. Due to the limited machining space of the machine tool, the fixture is often designed in a compact space. At this time, it is often ignored that the iron chips accumulated in the dead corner of the fixture during the machining process, including the unsmooth outflow of chip liquid, which brings many difficulties to the later machining. Therefore, at the beginning of essence, we should study the problems in the process of machining. After all, the fixture will increase efficiency and be easy to operate.

3. Overall opening of fixture. Ignoring the opening, the manipulator is difficult to install, time-consuming and laborious, and the design is taboo.

4. Basic comment principle of fixture accessory design. Each set of fixture has to go through many times of clamping and loosening, so it may reach the user’s requirements at the beginning, but the fixture should have its accuracy maintenance, so do not design some equipment that is against the truth. Even if you are lucky now, it will not last forever. A good design should be tempered by time.

5. Interchangeability of positioning elements. It is important to wear the positioning elements, so it is necessary to study the quick and simple replacement. Do not design as larger parts.

The accumulation of fixture design experience is very important. Occasionally design is one thing, and in essence use is another. So good design is a process of accumulation and summary. The above content is introduced here first, you are interested, please pay more attention to us, and will bring you different knowledge at any time.

Characteristics of precision parts processing

Five axis linkage machining center is a machining center with high technology content and high weekly density, which is specially used to process complex curved surface. This machining center system has full weight lifting influence on aviation, sail sea, military, scientific research, sophisticated equipment, high-precision medical equipment and other industries in a country.

1、 What is a five axis machining center

Five axis linkage machining has the characteristics of high efficiency and high precision, and the complex machining can be completed as soon as the workpiece is clamped once. It can be suitable for the processing of present moulds such as auto parts, aircraft structural parts, etc. There is a big difference between five axis machining center and pentahedral machining center. Many people don’t know this. They mistakenly regard the pentahedron machining center as a five axis linkage machining center. Five axis machining center has x, y, Z, a, C five axis, XYZ and AC axis to create five axis machining, specializing in space surface processing, special-shaped processing, hollow processing, drilling, oblique hole, oblique cutting, etc. The “pentahedron machining center” is the same as the three-axis machining center, but it may as well do five faces at the same time, but it can not do special-shaped processing, such as drilling, cutting bevel, etc.

For the rest, the practical boundary of the five axis CNC machining center is quite ordinary. It is understood that the current five axis CNC machining center system is the only way to process impellers, blades, marine propellers, heavy-duty generator rotors, automobile wheels, large diesel engine crankshafts, etc.

2、 Advantages of five axis machining center

1. Reduce processing time and improve processing accuracy.

The biggest feature of the five axis machining center is that it is advisable to process all five surfaces by one-time clamping. That is the so-called processing angle avoidance. If it’s a linked bed, axis C can rotate endlessly, and axis a can rotate by 130 degrees. These characteristics of the equipment make it possible to process without interference.

The advantage of this method is that one-time clamping can not only finish the processing, but also prevent the repeated positioning deviation caused by repeated clamping. At the same time, it also saves a lot of time and improves the working efficiency. It can reduce the time from product to delivery and reduce the inventory.

2. Reduce equipment investment cost, workshop area and workshop number.

The five axis linkage machining center controls the compound machining machine, usually with turning performance, which can be included from lathe to milling machine to vertical mill. Everyone knows that the value of vertical mill equipment is quite high at present. After cost, processing beat and other accounting, we can find that the value of five axis is high. Before that, the majority of people’s production and processing may be based on engineering segmentation. The problem with such a production method is that there is a lot of waiting time that cannot be eliminated. However, the engineering intensive production represented by the five axis compound processing equipment only needs the early waiting time for debugging, and with the popularization of all kinds of complete machine simulation software in China at present, even if only the blank data is imported, the programming can be completed and the early planning can be greatly reduced. So at present, overseas auto parts and high-end manufacturing are basically based on five shafts.

3. No need for unique fixture, can complete automation.

Another prominent feature of the five axis is that the dependence on the fixture will be reduced. The rule workpiece can be clamped directly with three claws and four claws chuck, while the rule workpiece can be clamped with one side and two pins. At the same time, the five axis machining center can complete the automation of the workshop and reduce the number of people. For example, machining robot’s key point and base. In the past, horizontal plus and vertical plus combined processing were used. Now, only zero point tray and five axis linkage processing center are used to complete 24-hour operation processing.

Advantages of non-standard precision parts processing

The advantages of non-standard precision parts machining center is developed from CNC milling machine. The biggest difference between CNC milling machine and CNC milling machine is that the machining center has the strength of automatic interchangeability of machining tools. Through the installation of different purpose tools on the tool magazine, the machining tools on the spindle can be changed through the automatic tool change device in a clamping process to complete a variety of machining performance. The non-standard and sophisticated parts processing equipment is suitable for a large number of high-precision and complex processing, and it is more and more competent for arc, taper and other processing. The advantages of non-standard parts processing small non-standard parts processing from one to three digits, is through simple mold, soft mold, perhaps directly out of the processing.

The processing of non-standard precision parts is usually a normal machining process such as turning, milling, planing, grinding, pliers, etc., and the fitter’s blanking, drawing lines, drilling, tapping, etc. Representative industries include aviation, aerospace industry, ship industry, construction machinery industry, machine tool industry, etc. The typical representative of mass production is the automobile industry, while the new model and the first-class trial production of the automobile industry and the mold industry focusing on mass production service are still a single small batch production. The advantages of non-standard parts processing small batch production may well save time and raw material cost, and speed up the product market cycle. Small batch production is closely related to hand plate mold. Hand plate mold is the condition of small non-standard parts processing, while small non-standard parts processing is based on hand plate mold.

How to improve the efficiency of CNC machining

With the recent development of China’s machining and manufacturing level, CNC machining technology is still widely used. Many enterprises still possess the international advanced CNC machining equipment

However, the phenomenon of “heavy equipment light technology” exists widely

How to improve the efficiency and quality of machining

The falling technology level greatly affects the development of advanced equipment manufacturing strength

High advanced equipment can not fully develop its production strength, which means cost.

The above situation directly affects the market competitiveness of enterprises

Pay attention to processing technology and improve production efficiency

“Technology” is the core of machining;

Therefore, the emphasis on “technology” is a good way to improve the production efficiency;

Indeed, we will raise the technological level, complete efficient manufacturing, high-quality manufacturing and economic manufacturing, and achieve the sustainable competitiveness of the enterprise with high technology.

Conclusion: clamping method is the core factor of decision-making efficiency and quality control. So usually the first question many customers ask is the proportion of teachers and fathers in your workshop,