High speed, high precision CNC machining and CAM technology

Foreword Mold is an important process for the replacement of products (such as automobiles, motorcycles, home appliances, etc.). The quality and cycle of manufacturing directly affect the quality and time-to-market of new products. Therefore, the development and development of molds has become an important part of the development of new products. Mold mold companies that need to develop new products for high quality, short cycle and low cost have adopted advanced manufacturing technologies such as CAD/CAE/CAM technology, which have developed rapidly in recent years. Precision Cnc Machining technology has received much attention from the mold industry. This article will introduce the application of high-speed and high-precision CNC machining technology in mold manufacturing in detail, and take Space-ECAD/CAM software as an example to introduce the CAM function that meets the high speed and high precision CNC machining of the mold.

2 High-speed machining concept and characteristics High-speed CNC machining is a high-efficiency, high-precision CNC machining method with high spindle speed, rapid feed, small cutting depth and spacing. The traditional mode of NC machining often uses the method of increasing the depth of cut to improve the machining efficiency, and this machining method is often restricted by the rigidity of the machine tool, the strength and rigidity of the tool, and the machining accuracy of the mold is also greatly affected. The efficiency of CNC machining is subject to many limitations. High performance, high speed, high speed and high speed provide technical support. High-speed machining is achieved by high spindle speed (eg 20 000r/min) and rapid traverse (eg 10m/min) for improved machining efficiency. The efficiency of high-speed machining is not only reflected in the improvement of machining efficiency of CNC machining itself, but the key is to improve the machining efficiency of the entire molding process. The reason is that the use of high-speed machining technology can greatly improve the processing quality of the mold surface. If you use it! 10mm ball-end knife with a cutting pitch of 0. The walking knife has a theoretical residual height of only 0.001 mm on the surface of the workpiece. In this case, if it is a cover mold, it does not need to be ground and directly debug; if it is a plastic mold In addition to the machining of the recessed corners in which the NC machining is not in place, the profile part of the cavity is slightly polished, and the test mode can be performed, which greatly reduces the dressing and polishing time of the fitter.

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

High-speed machining has the following characteristics: a. High spindle speed In the current technology, 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 CNC machines with better performance. For example, the maximum speed of UHS10 CNC machine tools manufactured by Sakamoto Niigata Iron Works is 100r/min.b. Cutting feed rate For machining cast iron or steel molds, the cutting feed rate can be considered as high speed machining of the mold. The cutting feed rate of the recently developed CNC machine tool far exceeds the value of 5 m/min. 5毫米以下。 The cutting depth of the high-speed machining of the high-speed machining of the XHC240 machining center in Germany is generally below 0. 5mm. Small depth of cut is beneficial for reducing cutting forces, tool deformation and wear during machining.

Cutting pitch below 2mm. The small cutting pitch reduces the cutting force, deformation and wear of the tool during the cutting process, while also reducing the thermal deformation of the machine.

3 Factors affecting high speed and high quality processing of molds Many factors affecting high speed and high quality processing of molds, but they are summarized as follows: product mathematical model, CNC machine tools, machining tools and programming methods.

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

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

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

3.4 NC programming Reasonable design of the CNC machining process of the mold and setting the processing parameters of each process is the premise and guarantee for the high speed and high precision machining of the mold, and it is also the most active factor affecting the quality and efficiency of the mold processing. The contents of CNC machining process include: the number of processes for CNC machining of the parts, the process content and processing sequence, the tool usage of each process and the selection of processing parameters.

3.5 The alignment of the workpiece, the clamping and the actual machining of the workpiece, the clamping and the actual processing also have a great impact on the high speed and high precision machining of the mold. If there is an error in the correction, this error will be directly reflected. If the workpiece is positioned and improperly clamped, the part will have large deformation, displacement and vibration during the machining process, which will affect the machining accuracy of the machined part.

4 Technical requirements for high-speed, high-precision machining 4.1 Technical requirements for the mathematical model of the product 8. The mathematical model of the product must be a good, uniform mathematical model that cannot have missing surfaces or redundant surfaces.

b. The product mathematical model cannot have data errors and surface shape errors.

4. The mathematical model of the product must satisfy the strict geometric topological relationship. Geometric topological errors such as overlapping surfaces, untrimmed surfaces, excessive gaps between surfaces, and tangential continuity or continuous curvature between surfaces are not allowed.

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

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

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

The machine control system should be able to automatically adjust the cutting feed rate according to the shape characteristics (curvature distribution) of the machined part, the so-called "forward look" function; the machine's thermal deformation compensation function; whether it supports NURBS interpolation function Whether it supports the ability to transfer CNC machining data at high speed (such as whether Ethernet connection is possible). 4.3 Technical requirements for machining tools 8. High geometric shape and dimensional accuracy The tool path required for NC machining is the tool spindle speed adopted by the numerical control programming in the CNC technology. c Table 2 Plastic mold NC machining process parameters Process name Tool spindle speed / c 0000.010.2-0.50.1-0.30CMA software must be able to produce smooth, smooth, stable high-quality tool motion track, must be rich and practical Tool motion trajectory generation and editing functions. The Space-ECAD/CAM system is taken 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 the mold, the tool shape and size selected at the time. Therefore, the tool used in actual machining must be consistent in shape and size with the tool selected during programming. Otherwise, these errors will be directly reflected on the workpiece being machined, which will affect the machining accuracy of the mold. b. Has good dynamic balance performance Because high-speed machining is carried out under the condition of spindle speed of 10000r/min or more, it is required that the tool has good dynamic balance performance. Tools used for high speed machining should generally be subjected to dynamic balance tests.

For good rigidity, it is necessary to use a tool with a suitable aspect ratio and a tool with a good rigidity. For example, when finishing, a solid carbide surface coating tool is used.

d. With good wear resistance, it is necessary to use a tool with good wear resistance. At present, the tools for high-speed machining mainly include solid carbide coated tools, indexable inserts, and blades with coated blades such as TIN, TIC, TICN, TIAIN, and CBN.

4.4 Technical requirements for programming 4.4.1 Reasonable determination of CNC machining process Mold NC machining is generally carried out by four processes: roughing, semi-finishing, root cleaning and finishing. It is often necessary to perform high quality mold surface twice. Semi-finished. The purpose of die roughing is to remove excess material from the surface of the blank at the fastest speed. Generally, large-diameter tools, large cutting pitches, and large tolerance values ​​are used for cutting. Roughing emphasizes the high efficiency of processing. The purpose of semi-finishing of the mold is to remove excess material of the mold surface at a faster speed to create conditions for finishing the mold. Generally, larger diameter tools are used, and the cutting distance and tolerance value are used for cutting. Semi-finishing emphasizes the uniformity of processing efficiency and quality. The semi-finished mold surface should be smoother and more uniform. Mold clearing processing refers to the removal of excess material at the intersection of the concave parts of the machined parts, which provides conditions for high-speed machining of the mold. If the part is directly finished without rooting, it is difficult to achieve high speed of mold finishing. This is because after the semi-finishing of the surface of the mold, the machining allowance left at the profile with a radius of curvature greater than the radius of the tool is uniform, but the radius of curvature at the concave intersection of the workpiece is smaller than the radius of the tool. The machining allowance of the surface is much larger than that of other parts. Before the mold is finished, this part of the material must be removed first. Otherwise, during the finishing process, as the tool passes through these areas, the cutting force experienced by the tool suddenly increases and damages the tool. It can be seen from the analysis that the tool radius required for root cleaning should be less than or equal to the tool radius used during finishing. After the rooting process, the finishing is performed. When the tool reaches the concave intersection of the workpiece, the tool is in a suspended state that does not participate in the cutting, which greatly improves the force of the tool at the concave intersection of the workpiece. It provides good cutting conditions for high speed and high precision of mold finishing. Finally, the finishing of the mold, the finishing is generally carried out using small diameter tools, small cutting pitch, small tolerance values.

4.4.2 Reasonable determination of CNC machining process parameters CNC machining process parameters include: machining tool, machining tolerance, cutting depth, cutting distance, spindle speed, feed speed, machining allowance, etc. Table 1 shows the numerical control processing parameters of automobile cover parts mold. Table 2 shows the process parameters of plastic mold CNC machining. The contents of these two tables are only for the difference, because of the different enterprises, the processing parameters setting method of the mold with different precision requirements will be quite different.

5.1 Tool trajectory generation method Space-ECAD/CAM system provides users with more than 20 kinds of tool trajectory generation methods, including: contour line roughing, finishing, parallel cutting rough, finishing, casting roughing, straight捣 roughing, cycloidal roughing, equidistant finishing along the surface, flat area finishing, residual processing, root cleaning, contour machining, area machining, free shape machining, projection machining, flow machining, etc.

5.1.1 Contour line roughing and finishing contour line roughing method refers to generating a set of Z planes according to the cutting depth specified during programming. Each Z plane cuts the blank and the product model to determine the Z plane. The machining area and then the tool movement path is generated according to the cutting pitch in the machining area. The tool movement path generated by the machining method is a set of contour curves, which is the most common method for roughing plastic molds. In order to meet the requirements of high-speed machining, the machine has many control items: for example, the machining method has a down-cutting process and an up-cut milling process; the pass mode has a single-direction parallel pass, a reciprocating parallel pass and a spiral pass, The retracting method has direct advancement and retraction, and advances, retracts, and spirals into and out of the tool along the vector direction; the step-by-step control mode includes direct stepping mode, arc stepping mode, and S-curve stepping mode. It is possible to automatically add rounded corners at the turning point of the tool movement to meet the requirements of high-speed machining. For CNC machining with insert-type fillet knives, in order to prevent the generation of unprocessed areas, the tool trajectory is optimized to generate Optimize tool trajectory. Shown is the contour trajectory of the roughing tool.

Contour line roughing tool motion trajectory contour finishing method refers to generating a set of Z planes according to the cutting depth specified during programming. Each Z plane cuts the product model to generate the tool motion trajectory. This is the most common method of finishing plastic molds. In addition to the characteristics of the contour line roughing method, it adds an option to control the tool's motion track quality. The selection can be based on the shape characteristics of the machined part, in the sparse area of ​​the tool motion track, and in the main tool. The vertical direction of the motion track automatically adds some sub-tracks, and the intersection between the tracks is removed, so that the processing can ensure the processing precision and ensure the processing efficiency. Shown is the contour trajectory of the finishing tool.

5.1.2 Parallel cutter roughing and finishing parallel cutter roughing method refers to generating a set of Z planes according to the cutting depth specified during programming. Each Z plane cuts the blank and the product model to determine the Z plane. The machining area is then generated in the machining area by the cutting pitch to generate the tool movement trajectory in the same parallel plane. This is a common method for roughing a car cover mold. The tool movement path is controlled in a similar manner to contour line roughing. The tool trajectory for parallel roughing is shown.

Flat walking knife roughing tool movement path parallel path finishing method refers to generating a set of parallel planes according to the cutting pitch and cutting direction specified during programming, and each parallel plane cuts the product model to generate the tool motion track. This is a common method for finishing automotive mold parts. The tool movement path is controlled in a similar way to contour finishing. Shown is the tool trajectory of parallel pass finishing.

4 Parallel pass finishing tool path 5.1.3 Asymmetric finishing along the surface Isometric finishing refers to the tool path obtained by the equidistant offset along the surface of the machined part according to the offset value specified during programming. This is a common method used for the finishing of various types of molds.

This processing method can achieve satisfactory processing quality. Shown is the tool trajectory of the facewise equidistant finishing.

5.1.4 Residual amount Processing Residual processing refers to a processing method that performs local processing on the unprocessed area left in the previous process. The Space-ECAD/CAM system offers three residual volume processing methods.

Clearing processing refers to a processing method that removes the remaining material in the concave line of the product model. There are two kinds of clearing root processing: one is the pen type clear root processing, which refers to the tool movement trajectory generated by the tool along the concave intersection line of the two curved surfaces and double cut with the two curved surfaces; the second is the regional clear root 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 the process, and generating the tool movement path according to the cutting pitch. Shown is the tool trajectory of the area clearing process.

5.1.6 straight-type roughing straight-type roughing is a high-efficiency roughing method in which the tool reciprocates linearly along the direction of the cutting axis to remove the internal material of the blank. It is especially suitable for the roughing of large cavity molds. Machining requires the machine and the knife to have sufficient strength and rigidity. This type of processing has been widely used in countries with developed mold industries such as Europe, America and Sakamoto.

5.1.7 Cycloidal Roughing Cycloidal Roughing is a machining method that uses arc cutting, linear motion, and arc exit. This machining method ensures that the tool can withstand a certain load and prolong the service life of the tool. It is especially suitable for roughing of intermediate high and low parts.

5.1.8 Projection Projection Projection refers to the processing method of generating the tool motion path in the two-dimensional plane and then projecting the track onto the surface to be processed to generate the tool motion track. This type of machining is more flexible, and if used properly, it can generate the tool trajectory required for various machining operations.

5.1.9 Flow type processing The flow type processing method is divided into flow type processing with single curve control and flow type processing with hyperbolic control.

The single-curve controlled flow type machining method is further divided into an offset type machining method and a normal machining type. The offset machining method refers to a tool movement obtained by giving a certain offset distance and then generating a series of offset curves based on a curve (generally defined as a two-dimensional plane curve) and finally projecting the curves onto the surface to be machined. A way of processing a trajectory. This type of processing is particularly suitable for the roughening and finishing of the rotating surface parts of the main surface of the part. The normal machining method refers to a certain curve (generally defined as a two-dimensional plane curve) as a reference, given an offset distance, and then generates a series of normal offset lines, and finally projects these lines onto the surface being machined. A method of machining the obtained tool trajectory.

The flow processing method of hyperbolic control can be divided into an interpolation type processing method and a straight line type processing method. The interpolation type processing method refers to a processing method in which a cutting curve is given with a selected two curves as a reference curve, and then a series of intermediate interpolation curves are generated, and finally the curves of the tools are projected onto the processed surface. Straight line type processing means that the cutting pitch is given with the selected two curves as the reference curve and then the straight lines forming the ruled surface formed by the two curves are generated, and finally the straight lines are projected onto the processed surface. A method of machining the obtained tool trajectory.

5.2 Provide a variety of infeed and retract function system to provide users with a variety of advance and retract function, such as direct advance, retract mode, along the direction of a given vector, retraction mode, arc type advance, retract mode and spiral type Retraction method.

5.3 Provide a variety of step-by-step control methods The system provides users with a variety of step-by-step control methods, such as direct stepping mode, arc stepping mode, and curve-stepping mode.

5.4 Tool Path Path Turning Control In order to meet the requirements of high-speed machining, the system automatically adds an arc to the tool path to avoid sharp changes in the machine tool's direction of motion during high-speed machining.

5.5 Control system supports NURBS interpolation function In order to meet the requirements of high-speed machining to transfer machining data, the control system supports NURBS interpolation function.

6 High-speed, high-precision machining in the mold manufacturing application shows a solid model of the automotive crankshaft mold, the mold is formed by four processes, namely roughing, semi-finishing, root cleaning and finishing. The process parameter settings for each process are shown in Table 3. The trajectory of the finishing tool of the crankshaft mold.

7 Conclusion High-speed, high-precision CNC machining is a high-tech of mold manufacturing, and is an indispensable processing technology for achieving high-quality, short-cycle manufacturing. With the continuous improvement of the performance of CNC machine tools and the good, knife-use maintenance - Toyota Camry car airbag system maintenance Changan University Dai champion system failure its self-diagnosis circuit can store and display the fault code. The fault code can be extracted during repair and checked and repaired according to the code. If there is no fault code but there is a symptom of failure, it can be repaired according to the fault symptom. If there is no fault code, sometimes it can be repaired according to the intermittent fault.

Key words car safety gas maintenance In order to ensure the safety of the driver and the occupants, the modern high-end cars are equipped with anti-collision safety gas system. When the car has a front-end collision accident, if the deceleration exceeds the specified limit, the control system will The safety air is detonated, and the safety air is rapidly expanded to block the inertial force of the driver and the occupant to strike forward to reduce the damage. Take the safety gas system of Sakamoto Toyota Camry as an example to explain its structure, use and maintenance.

The safety air system of the Sakamoto Toyota Camry 94 sedan, which consists of steering pad (contact with gas), occupant side air (if installed), central air sensor, spiral cable, left front and right front air safety sensors and dashboard The safety gas alarm indicator is composed as shown. The trigger of the safety gas is determined by the electronic control module according to the collision table 3 crankshaft mold NC machining process parameter process name processing tool spindle speed / r-min-1 feed speed / mm-min-1 cutting tolerance mm cutting depth / mm cutting The improvement of pitch/mm machining allowance and material performance and the continuous improvement of CAD/CAM software functions will become the mainstream CNC machining technology for future CNC machining.

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