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High-speed, high-precision CNC machining and CAM technology for molds

Posted by: Fymicohuang 2021-07-29 Comments Off on High-speed, high-precision CNC machining and CAM technology for molds

Preface Moulds are important craftsmanship for the upgrading of products (such as automobiles, motorcycles, home appliances, etc.), and their manufacturing quality and cycle directly affect the quality and time to market of new products. Therefore, Mold research and development has also become an important link in the development of new products. In order to develop high-quality, short-period, and low-cost molds and mold companies that need to change models for new products, they have widely adopted advanced manufacturing technologies represented by CAD/CAE/CAM technology. Among them, the rapid development of high speed and high Precision Cnc Machining technology has attracted much attention from the mold industry. This article will introduce in detail the application of high-speed, high-precision CNC machining technology in mold manufacturing, and take Space-ECAD/CAM software as an example to introduce the CAM function that meets the high-speed, high-precision CNC machining of molds.

2 The concept and characteristics of high-speed machining. High-speed CNC machining is a high-efficiency, high-precision CNC machining method characterized by high spindle speed, fast feed, and small cutting depth and spacing. Traditional CNC machining often adopts the method of increasing the depth of cut to improve machining efficiency, and this machining method is often restricted by the rigidity of the machine tool, tool strength and rigidity, and it also has a great impact on the machining accuracy of the mold. Therefore, in the traditional mode The efficiency of CNC machining will be subject to many restrictions. High-performance, high-speed, high-speed digital processing provides a technical guarantee. High-speed machining is based on a very high spindle speed (such as 20 000r/min) and rapid feed (such as 10m/min) to achieve the purpose of improving processing efficiency. The efficiency of high-speed machining is not only reflected in the improvement of CNC machining itself, but the key is to improve the machining efficiency of the entire mold making process. The reason is that the use of high-speed processing technology can greatly improve the processing quality of the mold surface. If you use it! 10mm ball-end knife, the cutting distance is 0. Walking knife, the theoretical residual height left on the surface of the workpiece is only 0.001mm. In this case, if it is a cover mold, it does not need to be polished, and debug directly; if it is a plastic mold , Except that the concave fillets that are not processed by CNC machining need to be processed by EDM, the mold surface part of the cavity is slightly polished, and the trial work can be carried out, which greatly reduces the grinding and polishing time of the fitter.

The main advantage of high-speed machining is that it can cut a large amount of excess material in a single process, and can also achieve high machining quality, which greatly reduces the time spent in subsequent finishing, which greatly shortens the entire mold manufacturing cycle.

High-speed machining has the following characteristics: a. High spindle speed. As far as current technology is concerned, machining with a spindle speed exceeding 10 can be called high-speed machining. However, with the rapid development of high-speed machining technology, various machine tool factories have developed better-performing cnc machine tools, such as the UHS10 CNC machine tool spindle manufactured by Niigata Iron Works, Japan. The maximum speed is 100r/min.b. Cutting feed High speed. For processing cast iron or steel molds, the cutting feed rate can be regarded as high-speed processing of the mold. *The cutting feed rate of recently developed CNC machine tools far exceeds the value of 5m/min. For example, the cutting depth of the German XHC240 machining center’s maximum feed rate and high-speed machining is generally below 0.5mm. A small depth of cut is beneficial to reduce the cutting force, tool deformation and wear in the machining process.

The cutting pitch is less than 2mm. A small cutting distance can reduce the cutting force, deformation and wear of the tool during the cutting process, and it can also reduce the thermal deformation of the machine tool.

3 Factors that affect high-speed and high-quality processing of molds There are many factors that affect high-speed and high-quality processing of molds, but they are summarized as follows: product mathematical models, CNC machine tools, processing tools, and programming methods.

3.1 Product mathematical model High-precision, high-quality product mathematical model is the prerequisite and necessary condition for implementing high-speed and high-quality mold processing. Product modeling error mainly comes from the random error of data input, the approximation error of curve and surface, the tolerance of curve and surface smoothing and the error caused by improper method of constructing surface, especially the error caused by improper surface modeling method. The processing quality has the greatest impact.

3.2 CNC machine tools The performance of CNC machine tools directly affects the quality and efficiency of the processed parts. The parameters related to the machine tool that affect the quality and efficiency of mold processing include: positioning accuracy and repeat positioning accuracy of the machine tool, spindle speed and cutting feed rate, machine tool structure and rigidity, temperature compensation function and C7C control system performance.

3.3 Machining tools The impact of machining tools on the high-speed and high-precision machining of molds is second only to CNC machine tools. The parameters related to the machining tool that affect the quality and efficiency of mold processing include: the geometry and dimensional accuracy of the tool, the dynamic balance performance of the tool, the deformation and wear of the tool, and so on.

3.4 CNC programming Reasonably designing the CNC machining process of the mold and setting the processing parameters of each process is the prerequisite and guarantee for the implementation of high-speed and high-precision machining of the mold, and it is also the most dynamic factor that has the greatest impact on the quality and efficiency of mold processing. The content of the CNC machining process includes: the number of processes for the CNC machining of the part, the content of the process and the processing sequence, the tool usage of each process and the selection of processing parameters.

3.5 The alignment of the workpiece, the alignment of the clamping and the actual processing of the workpiece, the clamping and the actual processing also have a great impact on the high-speed and high-precision processing of the mold. If there is an error in the alignment, the error will be directly reflected On the processed part; if the positioning and clamping of the workpiece are improper, the part will produce large deformation, displacement and vibration during the processing, which will affect the processing accuracy of the processed part.

4 Technical requirements for high-speed and high-precision processing 4.1 Technical requirements for product mathematical model 8. Product mathematical model must be a good and unified mathematical model without missing or redundant surfaces.

B. The product mathematical model must not have data errors and surface shape errors.

4. The mathematical model of the product must meet strict geometric topological relationships, and geometric topological errors such as surface overlap, untrimmed surfaces, excessive gaps between surfaces, and tangent vector continuity or curvature continuity between the surfaces are not allowed.

The mathematical model of the product should be a smooth continuous model.

The surface in the mathematical model of the product should meet the requirements of the principle of parameter correspondence and surface smoothing.

4.2 Technical requirements for CNC machine tools 8. Machine tool performance CNC machine tools must have the characteristics of high performance and high precision. The specific parameters are machine tool positioning accuracy and repeat positioning accuracy, geometric position accuracy, spindle speed, feed speed, etc. b. Machine tool structure The machine tool must have sufficient strength, rigidity and stability in use, including: machine tool structure, guide rail form, spindle structure, bearing, cooling method, thermal deformation measures, and closed-loop control.

The machine tool control system should be able to automatically adjust the cutting feed rate according to the shape characteristics of the processed part (curvature distribution), that is, the so-called “look ahead” function; the thermal deformation compensation function of the machine tool; whether it supports the NURBS interpolation function Whether it supports the ability to transmit CNC machining data at high speed (such as whether it can be connected via Ethernet), etc. 4.3 Technical requirements for machining tools 8. With high geometrical shape and dimensional accuracy, the tool path required for CNC machining is through the CNC programming Auto technology Table 1 Auto cover mold CNC machining process parameters Process name The tool spindle speed/ c Table 2 Plastic mold CNC machining process parameters The tool spindle speed/c 0000.010.2-0.50.1-0.30 CMA software must be able to generate smooth, smooth and stable high-quality tool motion trajectories, which must be rich and practical Tool motion path generation and editing function. The following takes Space-ECAD/CAM system as an example to introduce the functions of CAM.

5 High-speed, high-precision mold CNC machining requirements for CAM function bookmark4 In order to achieve high-speed, high-precision CNC machining of molds, the selected tool shape and size are calculated. Therefore, the tool used in actual processing must be consistent in shape and size with the tool selected during programming, otherwise, these errors will be directly reflected on the workpiece to be processed, which affects the processing accuracy of the mold. b. It has good dynamic balance performance. Because high-speed machining is carried out under the condition of spindle speed above 10000r/min, the tool is required to have good dynamic balance performance. Tools used for high-speed machining should generally undergo a dynamic balance test.

To have good rigidity, tools with appropriate diameter-to-length ratio and tools with good rigid materials must be selected. For example, when finishing, use solid carbide surface-coated tools.

D. To have good wear resistance, a tool with good wear resistance must be used. At present, the tools used for high-speed machining mainly include solid carbide-coated tools, indexable machine-clamping blades, and blades such as TIN, TIC, TICN, TIAIN, CBN and other coated blades.

4.4 Technical requirements for programming 4.4.1 Reasonable determination of the CNC machining process. Mold CNC machining generally consists of four processes: rough machining, semi-finishing, root cleaning, and finishing. The high-quality mold surface often needs to be performed twice. Semi-finished. The purpose of mold roughing is to remove excess material on the surface of the blank at the fastest speed. Generally, large-diameter tools, large cutting distances, and large tolerances are used for cutting. Rough machining emphasizes the high efficiency of machining. The purpose of semi-finishing of the mold is to remove excess material on the mold surface at a faster speed and create conditions for the finishing of the mold. Generally, larger diameter tools are used for cutting with reasonable cutting spacing and tolerance values. Semi-finish processing emphasizes the unity of processing efficiency and quality. The surface of the mold after semi-finishing should be smoother and more uniform. Mold root removal processing refers to the removal of excess material at the intersection of the recessed parts of the processed part, which provides conditions for high-speed mold finishing. If the parts are not directly processed for finishing without root removal processing, it is difficult to achieve high speed of mold finishing. This is because after the mold surface is semi-finished, the machining allowance left at the profile with the radius of curvature greater than the radius of the tool is uniform, but at the concave intersection of the processed part, the radius of curvature is less than the radius of the tool. The machining allowance of the surface is much larger than the machining allowance of other parts. This part of the material must be removed before finishing the mold. Otherwise, in the finishing process, when the tool passes through these areas, the cutting force on the tool will suddenly increase and damage the tool. It can be seen from the analysis that the tool radius required for root removal processing should be less than or equal to the tool radius used in finishing. After root removal processing, finish machining is performed. When the tool reaches the concave intersection of the workpiece, the tool is in a suspended state that does not participate in cutting, which greatly improves the force of the tool at the concave intersection of the workpiece. It provides good cutting conditions for the high speed and high precision of mold finishing. *The latter is the finishing of the mold. The finishing usually uses small-diameter tools, small cutting distances, and small tolerances for cutting.

4.4.2 Reasonable determination of CNC machining process parameters CNC machining process parameters include: machining tools, machining tolerances, cutting depth, cutting distance, spindle speed, feed speed, machining allowance, etc. Table 1 is the numerical control machining process parameters of automobile panel molds. Table 2 is the numerical control machining process parameters of plastic molds. The content of these two tables is only, because different companies, different precision requirements of the mold processing process parameter setting methods will have greater differences.

5.1 Tool motion trajectory generation method Space-ECAD/CAM system provides users with more than 20 tool motion trajectory generation methods, mainly including: contour roughing and finishing, parallel roughing and finishing, casting roughing, straight Punching roughing, cycloid roughing, surface equidistant finishing, flat area finishing, residual amount processing, root removal processing, contour processing, area processing, free shape processing, projection processing, flow processing and other processing methods.

5.1.1 Contour roughing and finishing The contour roughing method refers to generating a set of Z planes according to the cutting depth specified in programming, and each Z plane cuts the blank and product model to determine the Z plane It is a method of generating tool motion trajectory according to the cutting distance in the processing area. The tool motion trajectory generated by this processing method is a set of contour curves. This is the most common method for roughing plastic molds. In order to meet the requirements of high-speed processing, the processing side has many control items: for example, the processing methods include down-milling and up-milling processing; the cutting methods include unidirectional parallel cutting, reciprocating parallel cutting and spiral cutting, The tool retraction methods include direct advance and retreat, advance and retreat along the vector direction, and spiral advance and retreat; crotch control methods include direct crotch mode, arc crotch mode and S-curve crotch step mode. Fillet can be automatically added to the dome of the tool motion trajectory to meet high-speed machining requirements; for CNC machining using insert-type fillet knives, in order to prevent the generation of unprocessed areas, the tool motion trajectory is optimized to generate * Optimize tool movement trajectory. Shown is the contour roughing tool motion path.

Contour rough machining tool motion path The contour finishing method refers to generating a set of Z planes according to the cutting depth specified in programming, and each Z plane cuts the product model to generate the tool motion path. This is the most common method for finishing plastic molds. In addition to the characteristics of the contour roughing method, it adds an option to control the quality of the tool motion path. This option can be based on the shape and characteristics of the processed part, in the sparse area of ​​the tool motion path, and the main tool Some sub-tracks are automatically added in the vertical direction of the motion track, and the crossing part between the tracks is removed, so that the processing can not only ensure the processing accuracy, but also ensure the processing efficiency. Shown is the contour line finishing tool motion path.

5.1.2 Parallel feed roughing and finishing The parallel feed roughing method refers to generating a set of Z planes according to the cutting depth specified in programming, and each Z plane cuts the blank and product model to determine the Z plane In the machining area, the tool motion path in the same parallel plane is generated according to the cutting distance in the machining area. This is a common method for rough machining of automobile panel molds. The control method of the tool motion path is similar to contour roughing. Shown is the tool trajectory for parallel roughing.

 

Parallel-traveling tool rough machining tool motion path Parallel-travel finishing method refers to generating a set of parallel planes according to the cutting distance and cutting direction specified in programming, and each parallel plane cuts the product model to generate the tool motion path. This is a common method for finishing molds of automobile panels. The control method of the tool motion path is similar to contour finishing. Shown is the tool trajectory for finishing parallel passes.

4 Parallel feed finishing tool motion path 5.1.3 Equal distance finishing along the surface The finishing equal distance on the surface refers to the tool motion track obtained by offsetting the surface of the machined part at an equal distance according to the offset value specified in programming. This is a common method used for finishing all kinds of molds.

This processing method can obtain satisfactory processing quality. Shown is the tool motion track of equidistant finishing along the surface.

5.1.4 Residual amount processing Residual amount processing refers to a processing method in which the unprocessed area left by the previous process is partially processed. The Space-ECAD/CAM system provides three residual processing methods.

Cleaning root processing refers to a processing method that removes the remaining material at the intersection of the concave direction of the product model. There are two types of root removal processing: one is pen-type root removal processing, which refers to the tool motion path generated by the tool along the concave intersection of the two curved surfaces and double-cut with the two curved surfaces; the second is regional root removal processing , It refers to the method of determining the machining area according to the tool radius specified in the previous process and the tool radius specified in this process, and generating the tool motion path according to the cutting distance. Shown is the tool motion path of area clean-up processing.

5.1.6 Direct ramming roughing Direct ramming roughing refers to a high-efficiency roughing method in which the tool makes a reciprocating linear motion along the direction of the tool axis to remove the internal material of the blank. It is particularly suitable for the roughing of large-scale cavity molds. Machining requires the machine tool and knife to have sufficient strength and rigidity. This processing method has been widely used in countries with developed mold industries such as Europe, America and Japan.

5.1.7 Cycloid roughing Cycloid roughing is a machining method that uses arc cutting, linear motion, and arc exit. This processing method can ensure that the tool bears a certain load and prolong the service life of the tool. It is especially suitable for rough machining of low-grade parts around the middle and high sides.

5.1.8 Projection processing Projection processing refers to a processing method in which the tool motion path path is first generated in a two-dimensional plane, and then the generated tool motion path is projected onto the processed surface. The application of this processing method is more flexible. If the method is used properly, it can generate the tool motion trajectory required for various processing.

5.1.9 Flow type processing Flow type processing methods are divided into single curve control flow type processing and hyperbolic control flow type processing.

The flow type processing method of single curve control is divided into offset type processing method and normal type processing method. The offset processing method refers to the tool obtained by using a certain curve (generally defined as a two-dimensional plane curve) as a reference, given an offset distance, and then generating a series of offset curves* and then projecting these curves onto the processed surface A processing method of motion trajectory. This kind of processing method is especially suitable for roughing and finishing of rotating surface parts. The normal processing method refers to a certain curve (generally defined as a two-dimensional plane curve) as a reference, given an offset distance, and then generate a series of normal offset straight lines, * and then project these straight lines onto the surface to be processed A processing method of the obtained tool motion trajectory.

The flow type processing method of hyperbolic control can be divided into interpolation type processing method and straight line type processing method. Interpolation processing method refers to a processing method in which the cutting distance is given by the selected two curves as the reference curve, and then a series of intermediate interpolation curves are generated, and then these curves are projected onto the surface to be processed to obtain the tool motion trajectory. Straight line type processing method refers to the selected two curves as the reference curve to give the cutting distance and then generate the ruled lines of the ruled surface formed by the two curves, and then project these ruled lines onto the processed surface. A processing method of the obtained tool motion trajectory.

5.2 Provide a variety of tool advance and retract functions The system provides users with multiple tool advance and retract functions, such as direct advance and retract methods along the given vector direction, and retract methods. Arc type advance, retract, and spiral type advance , Retraction method.

5.3 Provides a variety of crotch step control methods The system provides users with a variety of crotch control methods, such as direct crotch mode, arc crotch mode, curved crotch mode, etc.

5.4 Tool path path turning dome control In order to meet the requirements of high-speed cutting, the system automatically adds arcs at the tool path path turning dome to avoid drastic changes in the direction of machine movement during high-speed cutting.

5.5 The control system supports NURBS interpolation function In order to meet the requirements of high-speed cutting processing for transferring processing data, the control system supports NURBS interpolation function.

6 The application of high-speed and high-precision machining in mold manufacturing shows the solid model of the automobile crankshaft mold. The mold uses 4 processes to complete, namely rough machining, semi-finishing, root cleaning and finishing. The process parameter setting of each process is shown in Table 3. It shows the motion path of the finishing tool of the crankshaft mold.

7 Conclusion High-speed, high-precision CNC machining is a high-tech in mold manufacturing, and it is an indispensable processing technology to achieve high-quality and short-cycle mold manufacturing. With the continuous improvement of the performance of CNC machine tools and the goodness, the knife-use maintenance-Toyota Camry car airbag system maintenance Chang’an University Dai champion system failure, its self-diagnostic circuit can store and display the fault code. When repairing, the fault code can be extracted and checked and repaired according to the code. If there is no fault code but there is a fault sign, it can be checked and repaired according to the fault sign. If there is sometimes no fault code, it can be checked and repaired as an intermittent fault.

Subject headings Car safety gas maintenance In order to ensure the safety of the driver and the occupants, modern mid-to-high-end cars are equipped with anti-collision safety gas systems. When a front-end collision of the car occurs, if the deceleration exceeds the prescribed limit, the control system will The safety gas is detonated, and the safety gas is rapidly expanded to block the inertial force of the driver and occupants from forward impact to reduce injury. Now take the safety air system of the Toyota Camry car in Japan as an example to illustrate its structure, use and maintenance.

The safety air system of the Toyota Camry 94 car in Japan consists of steering wheel cushion (in contact with air), side air of the occupant (if installed), center air sensor, spiral cable, front left and front right air sensors, and on the dashboard Safety gas alarm indicator and other components, as shown. The safety gas is triggered by the electronic control module according to the collision table 3 Crankshaft mold CNC machining process parameters Process name The machining method adopts the tool spindle speed/r-min-1 feed rate/mm-min-1 cutting tolerance mm cutting depth/mm cutting With the improvement of spacing/mm machining allowance and material performance, as well as the continuous improvement of CAD/CAM software functions, this technology will become the mainstream CNC machining technology for mold CNC machining in the future.

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