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The speed of CNC machine tool
With the improvement of the performance of the core processor of the CNC system, the feed speed limit of the high-speed machining center can reach 80 m / min, and the idle speed can reach about 100 m / min. At present, many automobile factories in the world, including Shanghai General Motors Company in China, have partially replaced modular machine tools with production lines composed of high-speed machining centers. The feeding speed limit of hypermach machine tool of Cincinnati company is 60m / min, the speed is 100M / min, the acceleration is 2G, and the spindle speed has reached 60000r / min. It takes only 30 minutes to process a thin-walled aircraft part, while it takes 3 hours for the same part to be processed on a general high-speed milling machine and 8 hours on a general milling machine. Due to the specialization of each component of the mechanism, under the development of professional spindle factory, spindle high-speed is increasingly popular. In the past only used for high-speed automobile industry models (15000 rpm or more), now has become a necessary mechanical product requirements.
ken. tang@chengcg.com
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Installation of gantry milling machine
What points should be paid attention to when machining and installing workpieces with gantry milling machine
When machining and installing workpieces with gantry milling machine, if it is necessary to use pad iron, a certain thickness of copper plate (about 5mm) should be padded between the pad iron and the worktable, and a thin copper sheet should be padded between the pad iron and the worktable to prevent the surface of the worktable and workpieces from producing marks. When using pad iron, pay attention to the pad iron and the fixing screw as low as possible, And the iron pad should be placed outside a certain area of the workpiece processing range, in order to avoid the damage caused by the impact of the iron pad on the tool head and tool chuck. When loading and unloading workpieces, it is necessary to handle them with care to reduce the friction and movement of workpieces on the worktable as far as possible. It is forbidden to drag workpieces on the worktable of the machine tool by using the edges and corners of many workpieces as support points (this will seriously scratch the worktable of the machine tool and affect the flatness of the worktable). It is forbidden to place tools such as socket, screw wrench, screw, rubber hammer, oilstone, file, etc. on the worktable of the machine tool to prevent damage Damage the working table of the machine tool. Operation method of gantry milling: before starting the machine, first check whether the lubricating oil is appropriate and whether the machine is in normal state, then turn on the machine power (turn the knob from “off” to “on” when turning on the machine power), then turn on the power switch of the control panel and turn out the emergency stop key.
After the machine is started, the origin of the machine tool will return and the tool magazine will return to zero. Before the origin return, check whether the position of the tool relative to the workpiece is safe, and then determine how to return the origin (the machine tool can return to the zero position according to the sequence of axes). Select zero return (machine tool origin return); select arc manual → press Magazing zero return (tool magazine return). Check the shift record to make clear today’s tasks and precautions. For each workpiece, check in advance whether the processing program is complete, whether the tools are complete and in good condition, number the tools, and write the tool number on the tool with a marker pen. Easy to check. According to the programmer’s requirements, prepare the workpiece and fixture, and determine the method of clamping the workpiece (the bottom of the work should be polished with an oilstone).
ken.tang @ chengcg.com
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Structure of gantry machining center
1 worktable
The worktable of gantry machining center is basically rectangular. Large castings such as worktable, bed, column, crossbeam and RAM are made of mihanna cast iron. The inner cavity of the castings is honeycomb composite arrangement structure. The design is advanced. All of them are treated by aging and secondary tempering to eliminate residual internal stress, stabilize the material, ensure the stability of workpiece processing accuracy and machine life.
2 Longmen
The gantry consists of a beam and two columns. It can be divided into three types: fixed beam, locking sectional lifting beam by positioning block and arbitrary lifting beam.
3 RAM
The structure of RAM can be divided into open type and closed type. The ram with open structure is clamped on the spindle box by pressing plate, and the cross-sectional area of ram is large; the ram with closed structure is clamped in the spindle box, and the cross-sectional area of ram is small.
4 tool magazine
There are three basic types of tool magazine: turret type, drum type and chain length type.
Attachment 5
The processing of large and complex parts usually needs a lot of accessories. The accessory head is specially designed according to the processing requirements of the workpiece, which is generally divided into right angle head, extended head, special angle head and universal head.
6 CNC system
The CNC system generally adopts SINUMERIK 840C and 840D of Siemens company of Germany or 31I series of FANUC company of Japan, and the CNC axis adopts full closed-loop control.
7 accuracy
The accuracy of machine tool refers to the original accuracy of machine tool without external load. The accuracy is usually expressed by the deviation between its opposite side and ideal state (error for short). The smaller the error is, the higher the accuracy is.
ken.tang @ chengcg.com
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Precision of computer gong forming
The content of mold precision includes four aspects: dimension precision, shape precision, position precision and appearance precision. Because the mold is divided into two parts: upper mold and lower mold, the position accuracy between the upper mold and the lower mold is the most important among the four kinds of accuracy.
3。 Mold precision is to serve the precision of products, high-precision products must be guaranteed by higher precision mold, mold precision generally must be higher than the precision of parts 2 or above.
Methods of improving die precision
1。 Precision guarantee of mould processing equipment
2。 Precision requirement of parts in mould manufacturing
①。 Mold material accuracy requirements
The processing tolerance of die steel shall be controlled within 300×300 + 0.005-0 ± 0.005300×500 + 0.01-0 ± 0.01500×800 + 0.01-0.01 ± 0.015800×1200 + 0.02-0.02 ± 0.02 ②. The accuracy requirement of die parts is a. Misumi guide pillar and guide sleeve series are used for guide parts affecting die precision, and the tolerance of superfinishing can be controlled within 0.002mm.
b。 The edge forming punch is made of Misumi standard material: SKD-11, hardness: 60-62hrc, edge shape: dregth punch is usually used for forming inner hole or cylinder shape of products. The precision of punching needle can be controlled within ± 0.01mm, and it can be about 2um for special requirements, and keep the mirror.
3。 The size of die gap is the main basis of die design and manufacturing accuracy. In order to ensure the product size accuracy, shape and position accuracy, and product quality (such as the quality of punch section and burr height), it is necessary to ensure the gap between the concave and convex dies.
4。 The construction precision of the mould is required. From the perspective of processing and assembly, the accuracy of mold base mainly includes the following aspects: a. The consistency of plane dimension and guide hole position of upper and lower formwork; B. Flatness and parallelism of large plane of formwork; C. Perpendicularity of guide hole to large plane; D. Perpendicularity between adjacent sides of formwork; e. The fitting accuracy between guide post and guide sleeve.
The main methods to ensure the accuracy of the mold base are as follows:
a。 One time processing method is that after the large plane of the template is processed, the upper and lower templates are clamped together, and the plane size and guide hole of two templates are processed at one time.
b。 One of the four guide holes is deviated from the symmetrical position to ensure the assembly orientation of the die.
c。 Datum is used for surface calibration.
d。 High precision guide post and guide sleeve are adopted.
e。 Improve the machining accuracy of parts.
②。 In order to ensure the accuracy of punch, from the perspective of processing and assembly, the accuracy of punch mainly includes: a. The shape and dimension accuracy of punch; B. Perpendicularity between adjacent sides of punch.
③。 From the perspective of processing and assembly, the accuracy of the die mainly includes: a. The shape and dimension accuracy of the die; B. Perpendicularity between adjacent sides of die; C. Perpendicularity of die side to large plane; D. Die position.
5。 The precision of forming processing is guaranteed. When processing the forming structure, whether it is processed by computer gong, EDM, WEDM or ordinary milling machine, coordinate processing method is adopted. The guarantee of the accuracy mainly depends on the accuracy of the machine tool and the accuracy of the operator’s calibration. It is considered that the concept of die precision should also run through the whole process of die design and manufacturing, just like the guidelines and guiding ideology of establishing enterprise product quality assurance and management system. In order to ensure the accuracy requirements of the closed loop of the die assembly dimension chain, strict control and management must be carried out on the key links and key factors affecting the accuracy of the die in the process of die manufacturing, outsourcing (including materials and standard parts) and the whole process of die assembly, die test, acceptance, packaging and transportation.
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The most efficient computer gong processing method
The so-called most efficient processing method is that when reprocessing, it can be completed quickly. Its completion effect can not be underestimated. All kinds of complex products can be completed. So what is the most efficient processing method for computer gong processing?
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 a tool library and has the function of active tool change. These abundant functions of machining center determine the disorder of programming of machining center.
The machining center can realize the linkage control of three or more axes, so as to ensure the tool to process the disordered surface. In addition to linear interpolation and circular interpolation, the machining center also has various functions, such as processing fixed cycle, active compensation of tool radius, active compensation of tool length, graphic display of machining process, man-machine dialogue, active fault diagnosis, off-line programming, etc.
Machining center is developed from CNC milling machine. The biggest difference with CNC milling machine is that the machining center has the ability to exchange machining tools actively. After installing different tools in the tool magazine, the machining tools on the spindle can be changed through the active tool changing equipment in one clamping, so as to realize a variety of processing functions.
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Computer gong processing to prevent collision
Under the condition of such high speed and structure, once the operator has no time to press the emergency stop button due to programming and operation errors, the tool has collided with the workpiece. In order to prevent machine tool and personal troubles, the following methods can be adopted in programming and operation (take FANUC system as an example).
The origin of the workpiece coordinate system set by the programmer should be outside the workpiece blank, at least on the workpiece surface.
Under normal conditions, the origin of workpiece coordinate system can be set anywhere, as long as the origin has a certain connection with the origin of machine coordinate system. But in practice, if the command value is zero or close to zero, the tool will point to zero or close to zero. In milling, the cutter will run to the table or fixture base surface; in turning, it will run to the chuck base surface. In this way, the tool will penetrate the workpiece and point directly at the reference plane. At this moment, if you want to move quickly, you will have trouble.
FANUC system generally set: when the decimal point is omitted, it is the minimum input unit, generally μ M. When the decimal point is omitted, the input value will be reduced to one thousandth. At this moment, the input value will be close to zero. Perhaps, due to other factors, the tool should be separated from the workpiece, but the practice is not separated from the workpiece and into the workpiece. In this case, the zero point of the workpiece coordinate system should be set outside the workpiece or on the base surface of the worktable (or fixture), and the result will be different.
Programmers and operators should be more careful about decimal points when writing programs.
FANUC system is the minimum setting unit when the decimal point is omitted, while most domestic systems and some European and American systems are mm when the decimal point is omitted, which is the input method of calculator. If you are used to calculator input method, there will be problems in FANUC system. Many programmers and operators may use both systems. In order to prevent the scale from getting smaller due to decimal point, decimal point should be added to the input program of calculator. But it’s not because of the habit of doing something like this.
In order to make the decimal point eye-catching, the isolated decimal point is usually written as “. 0” in programming. Of course, when the system is executed, the zero after the decimal point of the value is ignored.
When adjusting the workpiece coordinate system, the operator should set the reference point beyond the physical (geometric) length of all tools, at least on the tool position of the longest tool.
For the workpiece coordinate system on the workpiece installation drawing, the operator obtains it by setting the machine coordinate system offset on the CNC machining center. In other words, the operator sets a reference point on the CNC machining center, finds the scale between the reference point and the zero point of the workpiece coordinate system set by the programmer, and sets this scale as the workpiece coordinate system offset.
On the lathe, the datum point can be set on the base of turret rotation, the datum tool tip or other directions. If there is no additional movement, the zero of the programmer’s instruction is the zero position of the tool rest (CNC machining center) moving to the offset. At this moment, if the datum point is set at the base of turret rotation, the turret must collide with the workpiece. In order to avoid collision, the datum point of CNC machining center should not only be set outside the tool holder, but also outside all tools. In this way, even if the tool is installed on the tool holder, the datum point will not collide with the workpiece.
In CNC machining center, the datum points of X and Y axes are on the axis line of spindle. However, the reference point of the z-axis can be set at the spindle end or at a point other than the spindle end. If it is at the spindle end, when the command is zero, the spindle end will reach the zero position specified in the coordinate system. At this moment, the end key of the spindle end will collide with the workpiece: if the spindle is equipped with a tool again, it will collide with the workpiece. To ensure that there is no collision, the reference point on the z-axis should be set beyond all tool lengths. Even if no other motion is attached, the reference point will not hit the workpiece.
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Computer gong boring type processing
1、 Processing type:
- Hole processing:
- Drilling: before drilling on the machining center, the center drill must be used for positioning, and then the drill bit 0.5 ~ 2mm smaller than the drawing size shall be used for drilling, and finally the appropriate drill bit shall be used for finishing.
- Reaming processing: when reaming the workpiece, it is also necessary to use the center drill to locate, then drill with a drill 0.5 ~ 0.3mm smaller than the drawing size, and finally ream with a reamer. When reaming, pay attention to control the spindle speed within 70 ~ 180rpm / min.
- Boring: to boring the workpiece, first use the center drill to locate, then use the drill 1 ~ 2mm smaller than the drawing size to drill, then use the rough boring cutter (or milling cutter) to process to the left side of 0.3mm machining allowance, finally use the pre adjusted size of the fine boring cutter for fine boring, and the last fine boring allowance shall not be less than 0.1mm.
- Direct numerical control (DNC) operation:
- Before DNC NC machining, the workpiece should be clamped, the zero position should be set, and the parameters should be set.
- Open the processing program to transfer data in the computer for checking, then let the computer enter DNC state, and input the file name of the correct processing program.
- Press the tape key and the program start key on the machine tool, and the machine controller will flash LSK.
- Press enter on the computer to process DNC data.
2、 Contents and scope of workers’ self inspection:
- Before processing, the processor must see clearly the contents of the process card, know clearly the parts to be processed, the shape, the dimensions of the drawing and the processing contents of the next process.
- Before the workpiece is clamped, the blank size should be measured to see if it meets the requirements of the drawing. When the workpiece is clamped, it must be carefully checked whether its placement is consistent with the programming operation instruction.
- After rough machining, self inspection should be carried out in time to adjust the data with errors in time. The main content of self inspection is the position and size of the processing part.
(1) Whether the workpiece is loose or not;
(2) . whether the workpiece is correctly divided into parts;
(3) Whether the dimension from the processing part to the datum edge (datum point) meets the drawing requirements;
(4) The position and size of processing parts. After checking the position and size, measure the rough machined shape ruler (except arc).
- Finish machining can only be carried out after rough machining and self checking. After finishing, the workers should carry out self inspection on the shape and size of the processing parts: check the basic length and width of the processing parts on the vertical plane; measure the base point size marked on the drawing for the processing parts on the inclined plane.
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How to make precision parts
Numerical control tool is one of the preconditions to improve machining efficiency, its selection depends on the geometry of the machined parts, material state, fixture and machine tool rigidity. The following aspects should be considered:
(1) The cutting tool is selected according to the cutting performance of the part material. For example, turning or milling high strength steel, titanium alloy and stainless steel parts, it is recommended to choose indexable carbide tools with good wear resistance.
(2) The tool is selected according to the processing stage of hardware parts. That is to say, the roughing stage is mainly to remove the allowance, and the tool with better rigidity and lower accuracy should be selected. The semi finishing and finishing stages are mainly to ensure the machining accuracy and product quality of the parts, and the tool with high durability and high accuracy should be selected. The precision of the tool used in the roughing stage is the lowest, while the precision of the tool used in the finishing stage is the highest. If the same tool is selected for rough machining and finish machining, it is suggested that the tool eliminated from finish machining should be selected for rough machining, because the wear of tool eliminated from finish machining is mostly slight edge wear, and the coating is worn and polished. Continued use will affect the machining quality of finish machining, but has less impact on rough machining.
(3) According to the characteristics of NC lathe processing area, the tool and geometric parameters are selected. If the structure of the part permits, the cutter with large diameter and small ratio of length to diameter should be selected; the end edge of the over center milling cutter for cutting thin and ultra-thin wall parts should have enough centripetal angle to reduce the cutting force of the cutter and cutting parts. When machining soft material parts such as aluminum and copper, the end mill with slightly larger rake angle should be selected, and the number of teeth should not exceed 4.
When selecting the cutting tool, the size of the cutting tool should be adapted to the surface size of the workpiece. In production, end milling cutter is often used to process the peripheral contour of plane parts; when milling plane, cemented carbide blade milling cutter should be selected; when machining boss and groove, high speed steel end milling cutter should be selected; when machining rough surface or rough hole, corn milling cutter with cemented carbide blade can be selected; Ball end milling cutter, ring milling cutter, cone milling cutter and disk milling cutter are often used to process some solid surface and variable angle profile.
In free-form surface machining, because the end cutting speed of ball end cutter is zero, in order to ensure the NC machining accuracy, the cutting line spacing is generally very small, so ball end milling cutter is suitable for surface finishing. The end milling cutter is much better than the ball end milling cutter both in the surface processing quality and processing efficiency. Therefore, on the premise of ensuring that the parts can not be cut, the end milling cutter should be selected as far as possible when rough machining and semi finish machining curved surface.
In the machining center, all the tools are pre installed in the tool library, and the corresponding tool change action is carried out through the tool selection and tool change instructions of the NC program.
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Computer gong processing surface treatment:
- In terms of appearance, the machined surface of the parts shall not have obvious defects such as scratches and scratches.
- The surface of products processed by CNC lathe must be smooth, beautiful, no burr, no flash, etc
- In terms of quality, the machined surface of parts must meet the requirements of corrosion resistance, wear resistance and hardness.
In order to meet the accuracy of parts processing, it must also meet the surface technical requirements and appearance requirements. The parts we process can’t appear to be full of burrs. Here we introduce the surface processing requirements of CNC lathe
- In terms of appearance, the machined surface of the parts shall not have obvious defects such as scratches and scratches.
- The surface of products processed by CNC lathe must be smooth, beautiful, no burr, no flash, etc
- In terms of quality, the machined surface of parts must meet the requirements of corrosion resistance, wear resistance and hardness.
- Selection principle of cutting parameters
According to the cutting requirements, first determine the back cutting amount AP, then look up the table to get the feed, and then look up the table to calculate the main cutting speed u through the formula.
In many cases, we can use empirical data to determine the value of these three elements.
- Selection method of cutting parameters
Practice has proved that the selection of reasonable cutting parameters is related to many factors such as machine tool, cutting tool, workpiece and technology. The method of reasonable selection of processing amount is as follows:
In rough machining, it is necessary to ensure high production efficiency, so it is necessary to choose a larger back draft a. , larger feed rate,, low cutting speed u is selected.
When finishing, it is mainly to ensure the size and surface accuracy of the parts, so it is necessary to select smaller back feed AP, smaller feed, and higher cutting speed U.
In rough machining, it is necessary to give full play to the potential of NC lathe and the cutting ability of cutting tools. In the semi finish machining and finish machining of CNC lathe factory, how to ensure the machining quality should be considered, and on this basis, the productivity should be improved as much as possible. When selecting the cutting parameters, the CNC lathe factory should ensure that the cutting tool can complete a part or ensure that the durability of the cutting tool is not less than one working shift, at least not less than half a working shift. The specific value of CNC lathe factory should be selected according to the provisions in the machine tool manual, tool durability and practical experience.
(1) It’s a choice to take a knife on your back. The selection of back cutting amount should be determined according to the rigidity of machine tool, fixture, fixture and workpiece as well as the power of machine tool. In the case of the process system allows, as far as possible to choose a larger amount of back knife. In addition to the allowance left for the subsequent process, the rest of the rough machining allowance should be cut off as far as possible to minimize the number of tool runs.
Generally, on medium power machine tools, the back draft of rough machining is 8-10 mm (one side). The back feed of CNC lathe factory is 0.5-5 mm for semi finishing and 0.2-1.5 mm for finishing.
(2) The feed rate is determined. Feed rate refers to the change of tool feed direction in unit time. Numerical control lathe factory moving distance. The principle of determining the feed rate is: when the quality requirements of the workpiece can be guaranteed, in order to improve the productivity, a higher feed rate can be selected. When cutting, turning deep hole or finishing lathe, the CNC lathe factory should choose a lower feed speed. The feed speed should be adapted to the spindle speed and back feed.
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Notes for computer gong processing:
- Confirm the model, size and machining allowance of the blank according to the program sheet before operation, and remove sand and polish the blank
- After operation, confirm the position of the workpiece and the processing sequence, and complete the table comparison
- In the process of centring, if the “centring rod” is needed, the rotating speed is 501r / m. if the cutter is used, the rotating speed depends on the cutter. In this process, the data must be taken at the same height to ensure the accuracy of centring. After centring, the “G0 g54 x0 Y0” can be used for inspection
- Before formal processing, check and confirm the position of the workpiece and whether the data is correct
Precautions during processing:
- Before processing each program, it is necessary to strictly confirm whether the tool is consistent with the program
- When loading the tool, it is necessary to confirm whether the length of the tool and the selected tool holder are suitable
- In the same workpiece, each tool setting should be kept in the same area to ensure the accuracy of tool receiving
- Try to blow with air in roughing procedure and spray oil in smooth knife procedure
- Clean up the aluminum slag in the machine tool before light knife oil injection to prevent the aluminum slag from absorbing oil
- During the self operation of the machine tool, the operator is not allowed to leave the machine tool or check the operation status of the machine tool regularly. If he / she needs to leave midway, he / she must appoint relevant personnel to check
- If excessive machining allowance is found in the process of machining, it is necessary to use “single section” or “pause” to clear x, y and Z values, then mill them manually, and then swing them back to “zero” to let them run by themselves
- In case of tool collision during machining, the operator must stop the machine immediately, such as pressing the “emergency stop” button or “reset” button or setting the “feed rate” to zero
- Do not open the door when the machine tool is running to avoid flying knife or workpiece
- The workpiece must be cleaned and deburred in time
- At the end of work, the operator must make timely and accurate handover to ensure the normal follow-up processing
- Before turning off the machine, make sure that the tool magazine is in the original position and the XYZ axis stops in the middle position. Turn off the power supply and the main power supply on the operation panel of the machine in turn
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