Machinery industry – Page 7 – CNC Machining & Turning, Milling, Metal parts

Introduction of vertical CNC lathe

(1) Vertical CNC lathe vertical CNC lathe referred to as CNC vertical lathe, the lathe spindle is vertical to the horizontal plane, a large diameter circular worktable, used to clamp the workpiece. This kind of machine tool is mainly used for processing large complex parts with large radial size and relatively small axial size.

(2) Horizontal NC lathe horizontal NC lathe is divided into NC horizontal guide horizontal lathe and NC inclined guide horizontal lathe. The inclined guide rail structure can make the lathe more rigid and easy to remove chips.

Classification according to the basic types of machined parts

(1) Chuck type CNC lathe has no tailstock, which is suitable for turning disc (including short shaft) parts. The clamping mode is mostly electric or hydraulic control, and the chuck structure has adjustable claw or non quenched claw (soft claw).

(2) This kind of lathe is equipped with ordinary tailstock or CNC tailstock, which is suitable for turning long parts and disc parts with small diameter.

According to the number of turrets

(1) Single turret CNC lathe is generally equipped with various forms of single turret, such as four position horizontal rotation turret or multi position turret automatic rotation turret.

(2) Double turret CNC lathe this kind of lathe double turret configuration parallel distribution, can also be mutually vertical distribution.

By function

(1) The simple CNC lathe, which is formed after the feed system of ordinary lathe is transformed by stepping motor and single chip microcomputer, has low cost, but the degree of automation and function are relatively poor, and the turning accuracy is not high. It is suitable for the turning of rotary parts with low requirements.

(2) According to the turning requirements, the general CNC lathe is specially designed in structure and equipped with general CNC system. The CNC system has strong function, high degree of automation and machining accuracy, and is suitable for turning general rotary parts. The CNC lathe can control two coordinate axes, namely X axis and Z axis.

(3) On the basis of ordinary CNC lathe, turning center adds c-axis and power head. More advanced CNC lathe has tool magazine, which can control x, Z and C coordinate axes. Linkage control axes can be (x, z), (x, c) or (Z, c). Due to the addition of c-axis and milling power head, the machining function of this CNC lathe is greatly enhanced. In addition to general turning, it can be used for radial and axial milling, surface milling, drilling of holes and radial holes whose center line is not in the rotation center of parts.

Selection and use of CNC machining fixture

(1) According to the characteristics and processing needs of machining center, the commonly used fixture types include special fixture, modular fixture, adjustable fixture, group fixture and workpiece unified reference positioning clamping system.

(2) The high flexibility of machining center requires that its fixture structure is more compact and simple than ordinary machine tool, clamping action is more rapid and accurate, auxiliary time is reduced as far as possible, operation is more convenient, labor-saving and safe, and enough rigidity and flexibility should be ensured. Therefore, pneumatic and hydraulic clamping devices are often used.

(3) In order to keep all the surfaces to be machined fully exposed, the fixture should be open as far as possible, and the space position of the clamping element should be low as possible, so there must be space for the tool path.

(4) Considering the minimum distance between the machine tool spindle and the worktable and the clamping length of the tool, the installation position of the fixture on the machine tool worktable should ensure that the processing content of the workpiece can be completed within the stroke range of the spindle.

(5) Automatic tool change and worktable exchange can not interfere with the fixture or workpiece.

(6) Sometimes, the positioning block on the fixture is used when installing the workpiece. In the process of processing, in order to meet the processing requirements of the front, back, left and right stations and prevent interference, the workpiece can be removed after clamping. In this regard, we should consider the problem of maintaining the positioning accuracy of the workpiece after removing the positioning element.

(7) Try not to change the clamping point in the middle of machining.

(8) Determine the best position of parts on the machine tool table

Function introduction of engraving and milling machine

In terms of appearance and volume:

The volume of machining center is the largest, the volume of large 1690 machine is 4m * 3M, and that of small 850 machine is 2.5m * 2.5m; carving and milling machine is the second, and that of large 750 machine is 2.2m * 2m; carving machine is the smallest.

In terms of mechanical structure:

Machining centers generally use cantilever type, carving and milling machines and carving machines generally use gantry type structure, gantry type is divided into pillar type and fixed beam type, at present, carving and milling machines are mostly fixed beam type.

In terms of index data:

Spindle maximum speed (R / min): 8000 machining center; carving and milling machine is the most common 240000, high-speed machine is the lowest 30000; engraving machine is generally the same as carving and milling machine, engraving machine for high gloss processing can reach 80000, but it is not ordinary motorized spindle, but air floating spindle.

Spindle power: machining center is the largest, from thousands of watts to tens of kilowatts; carving and milling machine is the second, generally within ten kilowatts; carving machine is the smallest.

Cutting capacity: machining center is the largest, especially suitable for heavy cutting, roughing; carving and milling machine is the second, suitable for finishing; carving machine is the smallest. Engraving and milling machine

Speed: because the engraving and milling machine and engraving machine are relatively light, their moving speed and feed speed are faster than the machining center, especially the high-speed machine equipped with linear motor, the maximum moving speed can reach 120m / min

Accuracy: the accuracy of the three is almost the same.

From the processing dimension: the area of the worktable can better reflect this. The smallest worktable area (unit mm, the same below) of domestic machining center (computer gong) is 830 * 500 (850 machines); the largest worktable area of engraving and milling machine is 700 * 620 (750 machines), and the smallest is 450 * 450 (400 machines); engraving machine generally does not exceed 450 * 450, the common is 45 * 270 (250 machines).

In terms of application objects: machining center is used to complete the processing equipment of large amount of milling work pieces, large molds and materials with relatively high hardness, which is also suitable for roughening of ordinary molds; engraving and milling machine is used to complete the finishing of small amount of milling work pieces and small molds, which is suitable for copper and graphite processing; low-end engraving machine is inclined to wood, two-color board, acrylic board and other materials with low hardness Plate processing, high-end suitable for wafer, metal shell polishing.

It is generally believed that machining centers and engraving and milling machines can be used for both products and molds, while engraving machines can only be used for products.

Tool setting point and tool changing point of computer gong

When programming large-scale computer gongs, we should first consider the selection of tool point position,

The tool setting point is the starting point of tool movement relative to the workpiece in NC machining. Since the program is also executed from this point, the tool setting point is also called the program starting point or tool starting point.

When the machining accuracy is not high, some surfaces on the workpiece or fixture can be directly used as the tool face; when the machining accuracy is high, the tool setting point should be selected on the design basis or process basis of the part as far as possible, for example, for the part with hole positioning, it is more appropriate to take the axis of the hole as the tool setting point. The tool setting point must have a certain coordinate relationship with the positioning datum of the workpiece. In this way, the relationship between the machine tool coordinate system and the workpiece coordinate system can be determined. The choice of tool setting point for computer gong processing should be convenient for coordinate value calculation and tool setting.

During tool setting, the tool setting point should coincide with the tool position. The so-called tool position refers to the intersection of the tool axis and the tool bottom surface for flat end milling cutter; the ball end milling cutter refers to the ball center of the ball head part; the turning tool refers to the tool tip; the drill bit refers to the drill tip; the processing for the wire electrode cutting machine tool refers to the focus of the wire electrode axis and the part surface.

Stress and warpage analysis based on two-sided flow technique

According to the solidification effect of gate and the analysis results of packing pressure and temperature distribution

The stress and warpage analysis module calculates the stress changes with time in the wall thickness and plane direction of the product, and the shrinkage of the product along the wall thickness direction at the time of demoulding. Based on the double-sided flow technology, a special double shell element is used to predict the warpage of the product at the time of demoulding.

Function introduction of engraving and milling machine

In terms of appearance and volume:

In terms of mechanical structure:

In terms of index data:

Accuracy: the accuracy of the three is almost the same.

It is generally believed that machining centers and engraving and milling machines can be used for both products and molds, while engraving machines can only be used for products.

Technology standard of high speed computer gong

The machining center is an efficient and high-precision CNC machine tool. The workpiece can be processed in multiple processes in one clamping. At the same time, it is equipped with tool library and automatic tool change function. The rich functions of machining center determine the complexity of programming.

The machining center can realize the linkage control of three or more axes, so as to ensure the machining of complex surface. In addition to linear interpolation and circular interpolation, the machining center also has various functions, such as processing fixed cycle, automatic compensation of tool radius, automatic compensation of tool length, graphic display of machining process, man-machine dialogue, automatic fault diagnosis, off-line programming, etc.

Machining center is developed from CNC milling machine. The biggest difference between CNC milling machine and machining center is that the machining center has the ability to exchange machining tools automatically. By installing different tools on the tool magazine, the machining tools on the spindle can be changed through the automatic tool changing device in one clamping, and a variety of machining functions can be realized.

The broad meaning of benchmark is “basis”. The datum in mechanical manufacturing refers to the points, lines and surfaces used to determine the geometric relationship between the geometric elements on the production object. According to different functions and applications, datum can be divided into design datum and process datum, and process datum can be divided into process datum, positioning datum, measurement datum and assembly datum.

The technology of high-speed CNC machining is the premise to ensure the production of high-quality parts.

On lathe, the shape and size of the blank can be changed by the rotary motion of the workpiece and the linear or curvilinear motion of the cutter, and it can be processed to meet the requirements of the drawing.

Ordinary machine tools are more and more difficult to meet the needs of processing precision parts. At the same time, due to the improvement of production level, the price of CNC machine tools is falling from time to time. CNC precision parts processing mainly includes ultra precision turning, mirror grinding and grinding.

The primary premise of CNC precision parts processing is the accuracy of process datum. Datum on mechanical drawings are represented by capital letters a, B, C, D, etc. with a specific reference symbol with circle. When the reference symbol is aligned with the surface and its extension line or the dimension limit of the surface, the surface is taken as the datum. When the datum mark is aligned with the dimension line, it means that the solid center line of the dimension is taken as the datum. It is a more general statement that the process is accurate.

Assembly benchmark refers to the precision used to determine the position of parts in components or products during assembly. Measurement datum refers to the specification for the size and position of the machined surface to be measured during the inspection of parts. Positioning datum refers to the datum used for positioning the workpiece in the machine tool or fixture during machining.

What are the differences of CNC milling machine

The biggest difference of CNC milling machine is that the machining center has the ability to exchange machining tools automatically. By installing different tools on the tool magazine, the machining tools on the spindle can be changed through the automatic tool changing device in one clamping, so as to realize a variety of processing functions.

CNC machining center is composed of mechanical equipment and CNC system, which is suitable for processing complex parts. CNC machining center is one of the most widely used CNC machine tools with the highest output in the world. Its comprehensive processing ability is strong, the workpiece can complete more processing content after clamping at one time, and the processing accuracy is high. For the batch workpiece with medium processing difficulty, its efficiency is 5-10 times higher than that of ordinary equipment, especially it can complete the processing that many ordinary equipment can’t complete, and it is more suitable for single piece processing with complex shape and high precision requirements or small and medium batch multi variety production. It concentrates the functions of milling, boring, drilling, tapping and cutting threads on one equipment, so that it has a variety of technological means. Machining centers are classified into horizontal and vertical machining centers according to the spatial position of the spindle. According to the classification of process uses: boring and milling machining center, composite machining center. According to the special functions, there are single table, double table and multi table machining centers. Machining center of single axle, double axle, three axle and changeable headstock.

Types of CNC metal processing technology

Time effect elimination method

Aging elimination is a traditional method to reduce quenching residual stress. As aluminum alloy materials, especially aviation aluminum alloy materials, are very sensitive to temperature, the increase of aging temperature will obviously reduce the strength index, resulting in excessive precipitation of mgzn2 and other strengthening phases, resulting in over aging phenomenon. Therefore, aging treatment after quenching is usually carried out at a lower temperature (less than 200-250 ℃), which affects the stress relief effect (only 10-35%)

Mechanical stretching the principle of mechanical stretching is to apply a certain amount of permanent tensile plastic deformation to the quenched aluminum alloy plate along the rolling direction, so that the plastic deformation will occur after the superposition of tensile stress and the original quenching residual stress, so that the residual stress can be relaxed and released. The results show that more than 90% of the residual stress can be eliminated by mechanical stretching. However, this method is only suitable for the parts with simple shape, and it has high requirements on the microstructure uniformity of aluminum alloy sheet before drawing, so it is mostly used in aluminum processing plants.
Die cold pressing method

Die cold pressing method is to eliminate the residual stress of aluminum alloy die forgings with complex shape through strictly controlled limited cold shaping in a special finishing die. In fact, the term “die pressing” is not accurate enough, because its main mechanism is to make the local material of aluminum alloy die forgings subject to “tension” or “compression”. When the finishing die is pressed down, the finishing punch is embedded into the draft angle of the end face and edge (rib) of the aluminum alloy die forging, which actually causes the “tensile” effect on the web part of the die forging. Therefore, this method is to adjust rather than eliminate the overall stress level of the parts. It can release the residual stress in some parts of the aluminum alloy die forging and increase the residual stress in other parts.

Computer gong processing – how to make surface finish of parts

First of all, you need to ensure the stability of the lathe, that is, the fixation of the lathe, that is, whether the spindle will vibrate at high speed, and that the coolant is very important, Secondly, your cutting tool should be well ground, and the chip removal groove should be well opened to prevent the workpiece from being scratched due to poor chip removal, and the turning tool should be made into an arc angle when chamfering. In addition, the tool should not be resistant when loading.

Generally speaking, the more precise ones must go through the following steps: blanking, roughing, fine grinding, finishing and surface treatment.

Cutting. Generally, the work of cutting is handed over to the apprentice or the special staff, so the requirements of cutting are not high. Generally, 3-5mm allowance will be left for roughing. When laying down materials, too much allowance shall not be left to reduce the roughing time, and too little allowance shall not be left to prevent material waste due to insufficient allowance.
Rough. If it’s rough, you can also give it to an apprentice or a master who has not enough experience to operate it. The so-called roughing is to roughen the material and make the material smooth. Generally, a 0.2-0.5mm allowance is left for fine grinding. Too much allowance is not enough.
Fine grinding. This work should be operated by experienced masters. Fine grinding is to carry out precision machining on roughened materials, so as to ensure the perpendicularity and parallelism of the workpiece and prepare for the finish machining. Fine grinding is convenient, so we should pay attention to the precautions of grinding machine processing. For details, please refer to the internal grinder processing safety specification.
Finish machining. Master, must be master, must determine the order of machining, first understand the drawing requirements, determine the datum, select the fastest and most convenient processing steps.
Surface treatment. Generally, there is no surface treatment equipment. We need to choose our own high-quality surface treatment plant, and then match the spindle speed and feed speed. If your lathe doesn’t work very well, it’s recommended to buy some sandpaper to make it. When making sandpaper, it’s suggested to make it according to the working direction of the lathe tool, so as to make the texture better.

In order to ensure that the die steel has good original precision – the quality of the original die steel, in the manufacturing process, it is necessary to reasonably select high-precision processing methods, such as EDM, WEDM, CNC machining, etc., and pay attention to the accuracy inspection of the die steel, It includes the machining accuracy, assembly accuracy of die steel parts and the accuracy of die steel through the test and acceptance work. It is necessary to select high-precision measuring instruments as far as possible during the inspection. For those die steel parts with complex surface structure, if the ordinary ruler and vernier card are used, the accurate measurement data can not be achieved. At this time, the coordinate measuring instrument should be selected To ensure the accuracy of measurement data.

Advantages of machining center

After the workpiece is clamped on the machining center once, the digital control system can control the machine tool to automatically select and replace the cutting tool according to different processes, automatically change the spindle speed, feed rate, the movement path of the cutting tool relative to the workpiece and other auxiliary functions, and complete the multi process processing on several surfaces of the workpiece in turn. And there are a variety of tool change or tool selection functions, so that the production efficiency is greatly improved.

① The selection of die steel materials should not only meet the customer’s requirements for product quality, but also take into account the cost of materials and their strength in the set period. Of course, the selection should be based on the type of die steel, working mode, processing speed, main failure forms and other factors. For example: the main failure mode of blanking die is edge wear, so it is necessary to select the material with high surface hardness and good wear resistance; the stamping die mainly bears periodic load, which is easy to cause surface fatigue crack and lead to surface spalling, so it is necessary to select the material with good surface toughness; the drawing die should select the material with low friction coefficient; the die casting die should be selected due to the effect of cyclic thermal stress For injection mold, when the plastic parts are ABS, PP, PC and other materials, the mold steel material can be pre hardened and tempered steel; when the plastic parts are high finish and transparent materials, the corrosion-resistant stainless steel can be selected; when the products are in large quantities, the quenching and tempering steel can be selected. In addition, it is also necessary to consider the use of mold steel materials with less affinity with the parts, so as to prevent the mold sticking from aggravating the wear of mold steel parts, thus affecting the quality of mold steel.

② In the design of die steel structure, the structure should be compact and easy to operate, and the die steel parts should have enough strength and rigidity; when the die steel structure allows, the corners of each surface of die steel parts should be designed as fillet transition as far as possible to avoid stress concentration; for the die, cavity, part of punch and core, the combined or inlaid structure can be used to eliminate stress Appropriate protection measures shall be taken for the structure of the long and thin punch or core with concentrated force; for the cold stamping die, devices shall be provided to prevent the blockage of the parts or waste materials (such as spring pin, compressed air, etc.). At the same time, we should also consider how to reduce the impact of sliding parts and frequent impact parts wear on the quality of die steel.

③ In the design, it is necessary to reduce the scope of disassembly and assembly when maintaining a certain part, especially when replacing the vulnerable parts.

The manufacturing process of die steel is also an important part to ensure the quality of die steel, The processing method and precision in the manufacturing process of die steel will also affect the service life of die steel. The precision of each part directly affects the overall assembly of die steel. In addition to the influence of the precision of equipment itself, it is necessary to improve the processing method of parts and the technical level of fitter in the grinding process of die steel to improve the processing precision of die steel parts If the overall assembly effect of the die steel can not meet the requirements, the probability of the die steel in abnormal state will be increased, which will have a great impact on the overall quality of the die steel.

Collision detection of NC machining simulation system

Due to the high cost of NC machining, in order to save the cost, a NC machining simulation system is developed. NC machining simulation system can reduce or even completely eliminate the process of trial cutting and manual verification. Before the actual processing of new NC machining program, the programmer can use NC machining simulation system to carry out virtual machining environment and machining process on the computer, and detect the possible problems in the program design.

In the process of NC machining, it is easy to over cut, under cut and other phenomena. At the same time, the damage of the tool, or the processing of waste products, the interference and collision between parts and tools, tools and fixtures, tools and worktable, will cause a certain waste of cost to the production. The NC machining simulation system can simulate the relevant programs well and reduce the loss to the greatest extent.

Before the actual processing, the programmer can confirm whether the finished cutting product is consistent with the original design drawing through the simulation system, and can make better detail analysis.

collision detection

In the actual processing, five axis NC machining has more advantages than three-axis NC machining, can achieve a wider range, has faster material and efficiency, can reduce processing time and improve surface accuracy. However, because of the high degree of freedom of the two additional rotating shafts, it is easy to collide and damage the machine tool.

Therefore, before the actual processing, we need to use the NC machining simulation system to detect the collision. The main detection algorithms are as follows

The machine tool includes many parts, but the collision detection algorithm between different parts is similar. The simulation system takes the tool, workpiece and fixture as the main research object to detect the possible global collision.

According to the tool location, the grid voxel model of the cutter head scanning body and the grid voxel model of the cutter handle scanning body are solved respectively. The tool holder scanning body is used to detect whether there is a global collision between the tool, workpiece and fixture, and the tool head scanning body is used to calculate the intersection between the tool and workpiece.
A feature attribute of voxel model is cuboid envelope box, which is used for rough judgment. If the envelope box does not intersect, the objects surrounded in the envelope box must not intersect. At this time, the position data information of the object envelope box is updated, and other information remains unchanged, so as to prepare for the generation of the next cutter scanning volume and collision detection. Rough judgment can speed up the detection Speed.
Once a collision occurs, the system stops reading the data and reports the error information and the exact location of the collision. If there is no collision, the system will continue the teaching operation between the cutter head and the workpiece.