Category Archive Machinery industry

At present, digital AC servo system is widely used in CNC machine tools. The digital servo drive module and servo motor constitute a high precision angle closed-loop servo system. Its input is the command pulse given by the CNC system, and the output is the motor angle. Under the closed-loop control with optical encoder as feedback link, the rotation angle of motor shaft will strictly follow the change of command value, and the angular displacement of motor will be converted into the required linear displacement of worktable through gear pair and screw nut pair.

Although the digital servo system with rotation angle as output is a closed-loop system, the position control system composed of it is an open-loop system (or semi closed-loop system) from the perspective of taking the displacement of machine tool table as the final controlled value. Therefore, the position control accuracy is not only related to the performance of the control system, but also largely depends on the mechanical structure of the machine tool. In this way, the error of information transmission link, the error of mechanical transmission link and the influence of various non-linear factors in the system will make the table displacement deviate from the command value, and the open-loop system can not effectively correct it. Therefore, even if the conventional CNC machine and the machine use high-performance digital servo system, it is difficult to achieve high machining accuracy.

2、 Composition of digital full closed loop position control system

In order to solve the above problems, this paper proposes a digital full closed-loop position control method. Its basic idea is: on the basis of the digital drive of the moving parts of the machine tool, the digital measurement link which directly detects the final displacement of the moving parts is introduced to fully obtain and use the system information to count the motion of each coordinate of the machine tool from the perspective of feedback control The digital closed-loop system consists of various error sources and nonlinear links. In this way, the system can not only make the positioning accuracy of moving parts determined by the measurement accuracy of the detection link, but also make effective dynamic correction for the influence of various interference and non-linear factors on the displacement of moving parts, so that the actual displacement of the moving parts at any time always follows the change of the command value, so as to ensure the high dynamic and steady-state accuracy of the movement of the machine tool coordinates Degree.

The basic composition of the digital closed-loop position control system is shown in Fig. 2. The system uses grating as the linear displacement detection device to directly obtain the displacement information of the machine tool table. After preprocessing, the two-way displacement pulse signals with phase difference of 90 degrees are obtained. The frequency is directly proportional to the displacement speed of the worktable, and the number is the actual displacement of the worktable divided by the pulse equivalent. The displacement pulse is sent to the reversible counter for counting, and the count value in the counter represents the current actual position of the worktable. The function of the position controller in the system is to control the operation of the whole system according to the difference between the given position value and the position feedback value according to the digital control law designed in advance, so as to ensure that the displacement of the worktable strictly follows the instruction value.

3、 Dynamic structure and controller design of the system

The generalized object is composed of zero order holder, pulse generator, digital AC servo system and mechanical moving parts. Among them, the zero order holder plays a bridge style of connecting discrete link (digital controller) and continuous link. The task of pulse generator is to generate command pulse to control the operation of AC servo system according to the control signal given by the position controller, so this link is a proportional link.

AC servo system is a digital driving device in the system. From the macroscopic point of view, there is an integral relationship between the angle θ of servo motor and the command pulse frequency f, but the inertial characteristics between θ and F should be further considered from the microscopic point of view. The function of mechanical moving parts is to convert the rotation angle of the motor into the linear displacement of the worktable. If the influence of transmission error and nonlinear factors is treated as the dynamic disturbance to the system, the link can also be regarded as a proportion link. In this way, the transfer function of the generalized object can be expressed as a feedback channel after proper processing, although it includes detection device, pre-processing, information transfer, reversible counting and many other links, involving more complex information processing process.

But from the point of view of taking the actual position of the worktable as the input and the position feedback value (the count value in the reversible counter multiplied by the pulse equivalent) as the output, the feedback channel can be regarded as a proportional link, and its transfer function GF (s) = l can be made by proper design. Considering that the generalized object is a third-order system with an integral part, in order to make the closed-loop system composed of it have fast dynamic performance and no steady-state error of tracking slope input, PID controller is used as position controller

Digital mold technology has become the mainstream direction

In recent years, the rapid development of digital mold technology is an effective way to solve many problems in the development of automobile mold. The so-called digital mold technology is the application of computer technology or computer-aided technology (CAX) in the mold design and manufacturing process. The successful experience of applying computer aided technology in automobile die and mould enterprises at home and abroad is summarized

① Design for manufacturability (DFM) is to consider and analyze the manufacturability in the design to ensure the success of the process.

② The auxiliary technology of mold surface design, the development of intelligent surface design technology.

③ CAE aided analysis and Simulation of stamping process, predict and solve possible defects and forming problems.

④ The traditional two-dimensional design is replaced by three-dimensional mold structure design. ⑤ CAPP, cam and CAT technology are used in the manufacturing process of mould. ⑥ Under the guidance of digital technology, the problems in the process of die testing and stamping production are solved.

The rapid development of mold processing automation

Advanced processing technology and equipment is an important basis for improving productivity and ensuring product quality. In the advanced automobile mold enterprises, CNC machine tools with double worktables, automatic tool changer (ATC), photoelectric control system for automatic machining, and workpiece online measurement system are not uncommon. NC machining has developed from simple surface processing to comprehensive processing of profile and structural surface, from medium and low speed processing to high-speed processing, and the development of machining automation technology is very rapid.

High strength steel sheet stamping technology is the future development direction

High strength steel is widely used in automobiles because of its excellent properties in yield ratio, strain hardening characteristics, strain distribution ability and energy absorption. At present, the high strength steels used in automotive stamping parts mainly include bake hardening steel (BH steel), dual phase steel (DP steel), transformation induced plasticity steel (TRIP steel), etc. It is estimated that 97% of ulsab-avc will be made of high-strength steel, and the proportion of advanced high-strength steel in the whole vehicle will exceed 60%, and the proportion of dual phase steel will account for 74% of vehicle steel plate. Now a large number of IF steel based mild steel series will be replaced by high strength steel plate series, high strength low alloy steel will be replaced by dual phase steel and ultra-high strength steel plate. At present, the application of high strength steel plate for automobile parts in China is mostly limited to structural parts and beam parts, and the tensile strength of the materials used is mostly less than 500MPa. Therefore, it is an important problem to master the stamping technology of high strength steel sheet in China.

New mould products launched in time

With the development of high efficiency and automation of automobile stamping production, progressive die will be widely used in the production of automobile stamping parts. Progressive die is used more and more for the complex stamping parts with complex shape, especially for the small and medium-sized parts which need to be punched by multiple dies according to the traditional process. Progressive die is a kind of high-tech mould product, which is difficult in technology, high in manufacturing precision and long in production cycle. Multi position progressive die will be one of the key die products in China.

Die material and surface treatment technology will be reused

The quality and performance of die materials are important factors affecting the quality, life and cost of dies. In addition to a variety of high toughness and high wear resistance cold work die steel, flame quenching cold work die steel and powder metallurgy cold work die steel, the selection of cast iron materials in large and medium-sized stamping dies abroad is a development trend worthy of attention

Five axis parts processing is a kind of machining center with high technology content and high precision, which is specially used for machining complex curved surface. This machining center system has a significant influence on aviation, aerospace, military, scientific research, precision instruments, high-precision medical equipment and other industries of a country. At present, the five axis CNC machining center system is the only way to solve the problem of impeller, blade, marine propeller, heavy generator rotor, turbine rotor, large diesel engine crankshaft and so on.

Five axis parts machining multi-dimensional curved surface parts is a difficult point in cutting plus T. in addition to the application of multi axis machine tools, multi axis programming technology is the key. Reasonable setting of machining tool path is an important guarantee for the surface accuracy and dimensional accuracy of parts. Taking human head image processing as an example, this paper discusses and analyzes the practical application of five axis cutting to multi-dimensional curved surface parts.

The machining of five axis parts has the characteristics of high efficiency and high precision. It can adapt to the processing of modern molds such as auto parts and aircraft structural parts. There is a big difference between a five axis machining center and a pentahedron machining center. Many people don’t know about the five axis machining, mistakenly regard the pentahedron machining center as the five axis machining center. Five axis machining center has x, y, Z, a, C five axis, XYZ and AC axis form five axis linkage processing, good at space surface processing, special-shaped processing, hollowing out processing, drilling, oblique hole, oblique cutting, etc. The five axis machining center is similar to the three axis machining center, only it can make five faces at the same time, but it can’t do special-shaped machining, oblique hole drilling, cutting inclined plane and so on.

In our industry, we need to use a wide range of processes and manufacturing processes, there are all kinds of different products, we need to use different processes to process, Dongguan precision parts processing is one of them, so what is the comb angle polishing process of precision parts processing?

Fine parts processing is commonly used in daily necessities. For example, we consume a comb, and the comb is made by stamping. The edge of the comb is very sharp. We have to polish the sharp edges and corners of the comb. In this way, we will not hurt the human body in the process of application Harm.

Dongguan precision parts processing

When CNC lathe is used to process fine parts, it only needs to program the part graphics, process parameters and processing steps in the form of digital information and input them into the control system of the machine tool. After the calculation is stopped, it is converted into the command signal driving the servo mechanism, so as to control the harmonious action of all parts of the machine tool and automatically process the parts.

Generally speaking, the following methods are used by the mold parts processor:

1. Washing and cutting: mainly use milling cutter to mill the plane. 2. Grinding: mainly use grinding wheel to grind the surface of workpiece
2. Planing: it is mainly used for planing the surface of workpiece with planer.
3. Special processing: is the direct use of electrical energy, chemical energy and other processing methods.
4. CNC machining: mainly through digital information to control the machine tool, so that the parts and cutting tools to produce the required relative movement, from the surface to achieve parts processing.

The following methods are generally used in the processing of die parts:

1. Geometric accuracy the geometric accuracy of the Journal (roundness, cylindricity) should be limited within the range of diameter tolerance points. When the accuracy of geometric shape is high, the allowable tolerance can be specified on the part drawing.
2. The surface roughness can have different surface roughness values according to the different surface working parts of the parts. For example, the surface roughness of the bearing journal of the main shaft of the ordinary machine tool is ra0.160.63um, and the surface roughness of the matching journal is ra0.632.5um. With the increase of the machine speed and the improvement of the precision degree, the requirements of the surface roughness value of the shaft parts will become smaller and smaller
3. Dimension accuracy journal is the main surface of shaft parts, which affects the rotation accuracy and working state of shaft. The diameter accuracy of journal is usually it69 according to its application requirements, and the precision journal can reach it5.
4. Position accuracy mainly refers to the coaxiality of the matching Journal of the assembly transmission parts relative to the supporting Journal of the bearing, which is usually expressed by the radial circular runout of the matching journal to the supporting journal; according to the use requirements, the high-precision shaft is 0.0010.005mm, while the general precision shaft is 0.010.03mm. In addition, the coaxiality of the inner and outer cylindrical surface and the perpendicularity requirements of the axial positioning end face and the axis line are also included.

In the process of grinding machine processing, the surface of the workpiece often appears to have a ripple, which affects the accuracy and the appearance. According to experience, there are three situations:

There are irregular lines and scratches on the surface: This is mainly due to the problems of the grinding fluid and filtering system used, resulting in the particles and debris falling from the grinding wheel circulating in the grinding fluid to scratch the surface of the workpiece. At this time, the grinding fluid should be replaced or the filtering device should be added.

There are several reasons for the appearance of helix on the surface

1. When dressing the grinding wheel, the grinding wheel at the exit is convex, and the workpiece is just grinded to the surface by the convex point when it comes out of the grinding area, forming spiral pattern. The solution is that the grinding wheel at the exit can be trimmed more or the edge of the grinding wheel at the exit can be rounded with a file.
2. Small cracks appear in the alloy part of the tool plate supporting the workpiece, resulting in uneven surface and scuffing. The tool plate needs to be repaired or replaced.
3. The uneven bond hardness of grinding wheel leads to uneven wheel threshing. If the grinding wheel can not be improved after sanding, it is necessary to replace the grinding wheel.
4. The feeding speed or discharging speed is inconsistent with the normal speed of the guide wheel (it is easy to appear when there is an automatic feeding device). It is necessary to adjust the feed and guide wheel speed.
5. The relative position of the axis of the same grinding wheel deviates when the guide wheel is adjusted and R is hit, which needs to be re aligned.

Oscillation pattern on the surface: it is mainly caused by the vibration of the machine itself or the vibration in the grinding process of the workpiece.

1. The grinding wheel is clamped tightly, and the grinding wheel is not in stable operation. This requires new grinding wheel installation and balancing.
2. The bearing in the spindle is worn or improperly adjusted, which drives the grinding wheel to vibrate. The bearing clearance should be readjusted or replaced.
3. The vibration of other equipment is transmitted to the grinder to cause resonance, so it is necessary to keep away from other vibration sources or dig anti vibration ditch.
4. Due to the increase of the center height of the tool plate supported by the pad wood, the tool plate is not firm and vibrates when the workpiece passes through. The screws that hold the cutterhead need to be tightened.
5. The grinding wheel spindle is driven by the motor through the triangle belt. The length of the triangle belt is different or there is wear, which causes the vibration of the machine tool. Need to check and replace.
6. When the center of the workpiece is too high, the grinding wheel presses the workpiece to the cutter plate through grinding force, and the component force of the guide wheel is reduced, resulting in uneven force of the workpiece and vibration. At this time, lower the center height of the cutterhead.

The accuracy of scale is still the roughness accuracy, and the accuracy of form and position service level. The dimension accuracy of the machine tool can be controlled by 0.01mm, and the roughness can reach 1.6. For the shape and position service, such as coaxiality, concentricity, runout and straightness. Flatness, perpendicularity can ensure the following range;

The accuracy of outer circle is 0.01

Cylindricity 0.01/100

Flatness of end face 0.02/200

The accuracy of thread pitch is 0.06/300

Generally, the precision of machining mainly refers to four points

1. Scale public service
2. Public service of shape
3. Public service of bearing degree
4. Surface finish (as for the other largest solid scale flows, this is a concept that has only recently emerged.

You didn’t say that the ordinary lathe is a CNC lathe, which means the highest machining accuracy of the ordinary lathe. The CNC precision is higher, but this one is not certain. For example, the cylindrical cylinder service is 0.01-0.02MM. General lathe can also reach.

In addition to the accuracy of the outer circle, but also to see the requirements of the drawing requirements of the surface finish, for example, the cylindrical service 0.01-0.02 mm, finish in 1.6-3.2, then you can choose general lathe or CNC lathe, but the finish in 0.8 may be higher, then you can not choose a lathe, the choice of grinding machine processing.

In the case of CNC milling machine tool, sometimes you need to consider the machining center of the lathe, if you have higher requirements for the lathe perpendicularity, you may need to consider the machining center of the lathe.

General good point lathe turning processing can be up to 6 grade public service belt products.

Misunderstanding of high machining accuracy of CNC machine tools:

Generally, the precision of machining mainly refers to four points

1. Scale public service
2. Public service of shape
3. Public service of bearing degree
4. Surface finish (as for the other largest solid scale flows, this is a concept that has only recently emerged.

1 shear

1.1 check whether the material and thickness of the sheet are in accordance with the drawing, whether the surface of the plate is uneven and defective, pay attention to the direction of the grain and confirm the cutting sequence.

1.2 adjust the gap between the upper and lower cutters according to the thickness of the plate, adjust the position of the back stop, and check whether the cut material is accurate and whether the width of the two ends is the same.

1.3 in the process of shearing, it is often checked whether the size of the cut sheet (length, width, diagonal) conforms to the drawing.

1.4 the cut sheets shall be placed by category, stacked in a regular manner, marked with the title and size, so as to protect the board surface from damage.

1.5 when cutting small pieces of sheet metal, it must be cut after the pressing column of plate shearer, and pay attention to the safety of operation.

1. How to use plate shears

2.1 after the plate shears are started, several idling cycles are carried out to ensure that the plates with different thickness (t ≤ 6 mm) are cut under normal conditions, and the functions of the plate shears are understood.

2.2 it is necessary to adjust the blade clearance before cutting the plate. If the corresponding blade gap is not adjusted, the blade durability will be affected.

2.3 in the process of shearing, open the pressure gauge to investigate the oil pressure. When cutting 1.0 mm stainless steel plate, the pressure should be less than 1.5 MPa. It is not allowed to cut the plate with thickness greater than 6 mm in violation of regulations to avoid damage to the machine tool!

3 operation procedure

3.1 it is necessary for the operator to understand the general structure and function of the equipment, and it is forbidden to use the equipment beyond the function.

3.2 before starting the equipment, add oil according to the smooth rules of the equipment and check the oil volume of the oil cylinder.

3.3 the upper and lower blades should be adjusted before operation, and the blade gap should be confirmed according to the thickness of the shear steel plate. Generally, it is between 8-10% of the thickness of the plate to be cut, and each gap adjustment should be locked and adjusted according to the thickness of each plate. (refer to the gap adjustment reference table on the machine tool)

3.4 during the operation, it is forbidden to wipe the machine tool and the worktable, and it is not allowed to place sundries or things on it, so as to prevent the blade from being damaged by the edge of the pushing blade. It is necessary to avoid material rebound when pressing material.

3.5 always pay attention to the abnormal or failure of locking organization, gathering and scattering, braking and foot switch, and concentrate on cutting. In case of abnormal equipment phenomenon, stop cutting immediately, cut off power supply and inform maintenance personnel for maintenance.

3.6 according to the relevant rules, pay attention to safe and civilized production and keep the surrounding environment clean.

CNC lathe is a kind of high-precision and high-efficiency automatic machine tool. The use of CNC lathe can improve the processing efficiency and create more value. The emergence of CNC lathe makes enterprises get rid of backward processing technology.

The processing technology of CNC lathe is similar to that of ordinary lathe. However, since CNC lathe is a kind of clamping device, which can complete all turning process continuously and automatically, attention should be paid to the following aspects.

Reasonable selection of cutting parameters in CNC machining

For efficient metal cutting, machining materials, cutting tools and cutting conditions are the three main factors. These factors determine the processing time, tool life and machining quality. An economical and effective machining method must be a reasonable choice of cutting conditions.

Three factors of cutting conditions: cutting speed, feed and cutting depth directly lead to tool damage. With the increase of cutting speed, the tool tip temperature increases, resulting in mechanical, chemical and thermal wear. When the cutting speed is increased by 20%, the tool life is reduced by 1 / 2.

The relationship between feed condition and tool wear is very small. However, when feeding, the cutting temperature increases and the wear occurs. It has less effect on the tool than on the cutting speed. Although the influence of cutting depth on cutting speed and feed rate is not as great as that of cutting speed and feed rate, the hardened layer produced by cutting material will also affect the tool life when cutting at small cutting depth.

The user should select the cutting speed according to the material, hardness, cutting state, material type, feed rate and cutting depth.

According to these factors, select the most suitable processing conditions. The ideal state is to wear regularly and stably to reach the service life.

But in practice, the choice of tool life is related to tool wear, size change, surface quality, cutting noise, processing heat and so on. When determining the processing conditions, it is necessary to study according to the actual situation. For refractory materials such as stainless steel and heat resistant alloy, coolant or hard blade can be used

In the process design, the accuracy and efficiency are mainly considered. Generally, the principle of surface before hole, benchmark before others, roughness before refinement is followed. The machining center in a clamping, as far as possible to complete all machining surface processing. When machining holes with high position accuracy, special attention should be paid to the arrangement of hole processing sequence. If the arrangement is not proper, the reverse clearance of transmission pair may be brought in, which will directly affect the position accuracy. For example, when arranging the hole series processing sequence of the parts shown in Fig. 5.6A, if the machining is carried out according to the route shown in Fig. 5.6b, since the positioning direction of the hole 5.6 is opposite to that of the hole 1.2.3.4 in the Y direction, the reverse clearance in the Y direction will increase the error, thus affecting the position accuracy of the 5.6 hole and other holes. According to the route shown in Fig. 5.6c, the introduction of reverse clearance can be avoided.

A /) part drawing B /) processing route 1

c) Processing route 2

Figure boring processing route

In the process of machining, in order to reduce the number of tool changes, the centralized process of cutting tools can be adopted, that is, the corresponding parts of parts are processed with the same tool, and then the second tool is replaced to continue processing. However, for the hole system with high precision requirements, this method can not be adopted because of repeated positioning error when the parts are determined by the rotation of worktable.