Yearly Archive September 28, 2020

After the injection molding, the film and plastic are integrated. The wear-resistant material is on the outside. This process is mostly used in the mobile phone display screen. The plastic materials are mostly PC, PMMA, PBT, etc., which mainly have the function of wear resistance and scratch resistance. There is also a technology called IML (in-mold-lable), which is roughly the same as IMD, except that flim is pulled out like a punched tape after injection molding, which just transfers the printed pattern to the plastic parts, also known as in mold transfer.

There are two main types of IMD. One is PC and single chip. The other is pet, chain like (like film or printed instant noodle pockets).

The former finished product is merge PC chip, the latter only takes the ink on the pet chain, but PET material (chain, also known as foil) is not imported into parts by merge.

The former can only be screen printed because of the thick PC, so the effect is rough. For example, the front shield shape of Motorola v66 is already very delicate, while the latter can be printed with offset plate due to its thin pet, which is very fine, especially electroplating and transparent, fine metal and surface texture are very good, such as the front electroplating and black texture effect of Motorola V60.

For example, the control panel on Matsushita rice cooker mold is a typical IMD, which puts a silk screen printed PET film into the injection mold for injection molding. The materials are PC, transparent ABS and PMMA. After injection molding, the film and plastic are combined into one.

Nowadays, most of the outer screen lenses of mobile phones adopt IMD technology, and the cost is correspondingly increased. The requirements of mobile phone molds, especially transparent molds, are more stringent.

Generally speaking, there are two background reasons for using IMD,

1. Some effects of injection molding are difficult to simulate, such as the walnut automobile dashboard (car parts mold).
2. It is very difficult to integrate several effects on small pieces of parts. For example, the front triangle of moto V60 mold concentrates on electroplating, transparency and screen printing, but it also requires delicacy. Imagine that it is very difficult to use real plating, injection molding and splicing of transparent pieces.

Another method is to make the outer surface smooth and the inner surface rough, but there are some requirements for the mold.

In a broad sense, it refers to the process that all products can be manufactured by mechanical means; in a narrow sense, it refers to the process of making parts by special machinery such as the lathe, milling machine, drilling machine, grinding machine, stamping machine, die-casting machine, etc.

There will be some errors in machining. Let’s talk about the original error related to the initial state of the process system itself

① Principle error is the error of machining method.

② Geometric error of process system

The relative position errors between workpiece and tool exist in static state, such as manufacturing error of tool and fixture, adjustment error and installation error;

The relative position error of workpiece and cutter exists in the motion state, such as the spindle rotation error of machine tool, the guide error of guide rail, the transmission error of transmission chain, etc.

The deformation caused by the force effect of the process system, such as the deformation caused by the stress deformation of the process system and the deformation caused by the generation and disappearance of the internal stress of the workpiece.

② Deformation caused by thermal effect of process system, such as the error caused by thermal deformation of machine tool, cutting tool and workpiece. In the machining process, when the position relationship between the tool and the workpiece processing surface is reasonable, the machining surface accuracy can meet the processing requirements, otherwise it can not meet the processing requirements. CNC machining accuracy analysis is to analyze and study various factors when the machining accuracy cannot meet the requirements, that is, the possibility of various original errors, and take effective technological measures to overcome them, So as to improve the machining accuracy.

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