Difference and Selection of CNC Milling Milling Milling
As a user, of course, it is necessary to select the right equipment. If it is improperly selected, not only can it not make money, but it also causes the bitter situation of working for the machine. So what kind of machine tool is a good machine tool?
Machine tools that can recover investment in the short term are good machines.
The design service life of CNC machine tools is generally 7 years, which is mainly based on the service life of CNC. This way the relationship between spending money and making money will directly affect your business. Therefore, careful analysis of function selection is a necessary condition for effective investment. .The term “CNC engraving and milling machine†has long been known abroad. Strictly speaking, carving is part of the milling process. It is always a question to ask yourself if you want to purchase a engraving machine or purchase a CNC milling machining center. In addition, there is currently a high-speed cutting machine (HSC MACHINE).
Or let us first find out the difference between the three models:1. CNC Milling and Machining Centers are used to complete the machining of large-diameter workpieces
2. CNC engraving and milling machines are used to complete smaller milling quantities, or soft metal processing equipment
3. High-speed cutting machine used to complete medium-sized milling and minimize the amount of grinding after milling
In-depth analysis of the structure of the above equipment can help us make the right choice
First, analysis and analysis from the mechanical point of viewThe machine's machinery is divided into two parts, the moving part and the non-moving part. Tables, slides, crossovers, etc. are moving parts, bed bases, columns, etc. are non-moving parts.
1, CNC milling machining centerNon-moving parts have very good rigidity
Mobile part of the steel requirements are very goodAdvantages: Heavy cutting;
Disadvantages: As the mobile part is also huge, at the expense of the flexibility of the machine, it is incapable of acting on small parts and fast feeds.2, CNC engraving and milling machine
Non-moving parts have good requirements for rigidityThe mobile part of the steel should be flexible under the premise of being as light as possible, while maintaining a certain degree of rigidity.
Advantages: Can be processed with finer processing and high precision. For high-speed machining of soft metalsDisadvantages: Heavy cutting is not possible due to poor rigidity.
3, high-speed cutting machine toolsNon-moving parts have very good rigidity
The mobile part has better steel requirements and is as light as possible.Advantages: It can carry out medium and small amount of cutting (for example, flat bottom knife with φ10 in general, and 0.75 for deep cutting depth of 45 steel (300));
Disadvantages: Under the correct use, it can be highly efficient, low cost, and minimize the amount of sanding. Improper use will immediately pile up the scrap of the tool.How to mechanically achieve the above requirements of light and rigid contradictions is the key to the mechanical structure.
1. The bed adopts a mesh structure with high and low ribs, and some directly use the hexagonal mesh structure of the honeycomb. 2. Ultra-wide columns and beams, we all know that the gantry-type structure has been the preferred structure for high-speed cutting equipment manufacturers because of its excellent symmetry and excellent steel properties.
3. The difference between the moving part and the CNC milling is that the distance between the guide rail and the guide rail is widened to overcome the problem of bad torque.4. In terms of materials, generally speaking, the use of Meehanite cast iron, which is the birth of cast iron, adds a certain proportion of silicon (Si) when pouring molten iron, thus changing the internal structure of iron, making it more resistant to punching, and significantly improving rigidity. .
5. The rigidity of the machine tool is mainly used to overcome the strong impact on the non-moving part when the moving part moves at a high speed, so the guide rail, the screw rod are required to be thicker, and the rigidity of the connection part is strengthened.
Second, analysis and analysis from the perspective of numerical control
1. The numerically-controlled system requires a general speed for the CNC milling center, and the spindle speed is about O to 8000 RPM.
2, engraving and milling machine. High-speed CNC system is required, and the spindle speed is about 3000 to 30000 RPM.
3, high-speed cutting machine tools require high-speed CNC system and excellent servo motor characteristics, spindle speed 1500 ~ 30000 RPM or so.
Third, programming software analysis
From the software point of view, CNC milling center, high-speed cutting machine milling machine can use standard CAD/CAM software such as: Mastercam Cimatron PE UG.
The milling machine usually thinks that Cimatron has a better tool path. The new version of the software fully considers the uniformity of the cutting amount at every moment of the cutting tool, especially the speed and roundness of the knife when entering and leaving the work, and the following difference algorithm at the inflection point. The following error (Following Error) makes the result and the design graphics more affiliated. The CAD part has just used a lot of intuitive three-dimensional solid modeling such as Solidworks and then transferred to CAM software through IGS for processing.
But don't worry, the development speed of CAD/CAM is much faster than the CNC's development speed. degree.
Fourth, automatic tool change tool magazine and automatic tooling requirements
The machining center is a decent term. The machining center is a numerical control device that is used to complete various processes in an automatic state. It is mainly for some fixed large-volume production operations. If we process a lot of holes and teeth, it must be every day. Do similar (a minimum of 200 batches or more) that must be selected machining center, for the mold industry and small batch production units must not be on the processing center, because too many manufacturers have to buy a machining center, when CNC milling The use of a tool magazine is very simple for the cost of the CNC system, but the spindle and the tool magazine, the air compressor and various tool holders will increase the cost, so the difference for one device is more than 100,000 yuan, and the programmer Be clear-headed. Otherwise, the tragedy will happen, and the problems will be increased a lot. With regard to efficiency, the use of machining centers should not be used for workpieces with less than one or two hundred production quantities, and the efficiency is too low.
What is a good way to improve efficiency, do not use the tool magazine, and will not cause artificial tool change error, only automatic tool setting system, a knife to the previous equipment, a button, the machine tool automatic tooling, direct processing, error in 0.001 ~ Within 0.003μm, compared with the automatic change of time, it can't be a little slower. If it is a machining center, there is no automatic tool setting machine tool and no tool magazine, but compared with the automatic tool setting tool, the efficiency in the latter is far higher than the former. Please note that the price of the best brand of the automatic tool setting tool is not more than 10,000 yuan (Marposs), and it is unlikely to be damaged. In this analysis, there is a large amount of labor for the domestic mold processing, as well as the processing of small batches of industrial parts. If the full consideration of the value of funds must not be used for processing center equipment, in addition, the domestic manufacturers of the magazine is still a lot of problems. Imports are also quite expensive. (The BT40's 10 magazines will not be less than RMB 100,000).
Fifth, the view of high-speed cutting equipment
The savvy processor will certainly take a lot of time to consider the machine tool's preparation time and the human factors caused by the loss, we always remember not to remind them in this regard. What we should do is how to give them higher processing efficiency from the processing time of the machine tool and to reduce their grinding time as much as possible. Even polished. The debut of high-speed cutting equipment is an event that stuns processors. Don’t think about its expensive cost (about 1.5 million yuan). From the use of it alone, I think it must be the old saying that it is a fragrant meat for some people and a poison for other people. Japanese and Europeans have spared no effort to promote the benefits of high-speed cutting so that people can use their equipment. Of course, some are not practical. The actual experience in the numerical control machine tool industry within 8 years told me that their cost should be about 60-70,000. Such a high rate of profit makes me see their essence. The gross profit of domestic CNC machine tools should be between 30 and 40%. This is a reasonable, upright profit. If you are willing to maintain their high profits I would not be able to earn more money at the same time. More to consider after-sales service and so on. I can't believe that their service can solve all the problems within 1 to 2 days. Because our existing technology can not achieve "solid fax."
From the perspective of revitalizing national industries, we should support the development of domestic machine tool factories. The essence of high-speed cutting is to walk the length of the tool in a short time. Everybody knows:
Distance = Speed ​​× Time
The fixed cutting method of the tool determines that if it is long, it means that it is not profitable. To increase the speed is to shorten the time.
High-speed cutting determines that it is not necessarily good because of the constraints of the current machine tool's own spindle and the tool used. At present, the common practice in foreign countries is that the first device does not use high-speed cutting, while the second or third device can consider this. equipment.
Successful practices such as:
A copy milling machine finishes most of the cutting amount (heavy cutting) while leaving a machining allowance of 2 to 3 mm, and quickly completes the remaining cutting amount on a high-speed machine tool. This has many advantages:
1) A lot of heavy cutting machine tools, processing fees are very low
2) The processing volume is large and the accuracy is not high enough to easily achieve
3) The tool is cheap
4) After turning into high-speed cutting, the cutting amount of the first knife is uniform because the processing object is close to the forming.
5) Fast and accurate forming
6) avoid too much grinding, with the precise size
7) The tool is expensive, but the time is short, the cutting amount is not great, and the performance price ratio is very good
8) A lot of nuances, such as small-angle conduction, etc., meticulous machining is completed at one time without using sparks to help
9) Excellent surface finish (mirror effect)
From this point of view, the coordination of the equipment is the way to win because the remaining amount of it is 2 to 3 mm. Therefore, two calibration G54 bezels on the work table to complete the workpiece clamping problem, and for the cutting A small amount of work is done directly on the high-speed machine.
Sixth, discuss the issue of the spindle
For NC milling and machining centers because of the requirement of low rotational speed and high torque, it is inevitable that the reduction ratio of the spindle transmission to increase the rotational speed of the torque is low and the accuracy is unavoidable. Therefore, it is not possible to use a tool with a small radius.
For the engraving and milling machine to spindle work in the 2 ~ 30,000 RPM can work, rotary precision is generally about 2 μ, or broken knife phenomenon is very serious, so we must use the motor spindle, the motor and the spindle is one. For the high-speed cutting equipment, the inner spindle is required, and at low speed, a certain torque must be used to maintain the spindle temperature.
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