The best way to overcome the difficulties of hard

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Overcome the difficulties of hard material processing

different from the traditional concept, it is not difficult to use the right machine tools and the right tools to process the quenched and hardened workpiece to 5 m. At present, tool suppliers have developed new tools that can withstand this processing condition, and machine tool manufacturers have also produced CNC lathes that can meet the required stiffness of these new tools. Similarly, hard material turning can promote production from the following aspects

save time. Turning hard materials takes less time than grinding to the final size specification, because the metal cutting rate of turning is higher than grinding, and multiple processes can be processed in one clamping. The operator can complete all processing with only one loading and unloading, thus realizing just in time production

to reduce costs and save time is to save money. Besides, using lathes to replace grinders means a lower total investment in machine tools

turning of hard materials with good quality is much better than grinding in ensuring dimensional accuracy and surface roughness. You can cart most hard materials to a total tolerance of 5 m, with a surface roughness of ra0.1 M. Of course, such precise surface quality requires special measures, but ra0.15 m-ra0.2 m is light and at one stroke

less processes turning hard materials can eliminate many forms of grinding, polishing and other finishing processes. It not only saves processing costs, but also makes more sense to take back many outsourced processing jobs and do them by yourself

waste less hard materials, turning waste is very few. Because the coolant used is the same as that used in normal turning, there is no need to add additional coolant, resulting in a small necessary waste. What's more, you can choose to carry out dry turning without coolant to avoid the waste of coolant and waste workpieces. Turning hard materials can also eliminate the troublesome problem of grinding waste residue - the waste residue recovery and treatment, which is labor-intensive and expensive

requirements for power and stiffness

in order to obtain the best effect in turning hard materials, the correct combination of machine tools and cutters is very important. For example, in a rough turning process, when we use a ceramic knife and use a cutting amount of 0.28 mm/min and a cutting amount of 1.9mm, we need to make the 15kw motor output 65% of the load of new materials. This lathe turns one end of the hardened steel piece with a diameter of 50mm to about 25mm, and also turns out the cone, arc radius and other complex shapes

although high power is required for large cutting, many users find that this is not the case in most cases. Because most of the processing of hard materials is finish machining. Generally, rough turning can be carried out on the ordinary screw lathe first, leaving 0 38mm allowance, and then finish machining with hard material turning technology after heat treatment

another requirement for turning hard materials is stiffness, including machine tools, cutting tools and workpieces, and any link in the machine tool device. If there is a lack of stiffness, it will cause tremor. In order to obtain the accuracy and dimensional tolerance comparable to grinding, the machine tool must have a particularly high stiffness from the machine bed. Compared with granite polymer, the traditional cast iron bed is not suitable for turning hard materials. The anti vibration ability of polymer bed is 20 times higher than that of cast iron, so that the vibration on the spindle is less than 1/3 of that installed on the cast iron bed

fully reducing the overhang is another weapon to reduce vibration. Theoretically, the workpiece clamping device should make the clamped workpiece as close to the spindle bearing as possible, and the tool should be as close to the turret body as possible without cantilever state. For this reason, a lathe capable of directly clamping spring collets in the spindle. The chuck seat keeps the workpiece away from the spindle bearing, which not only reduces the clamping force, but also increases the chance of vibration

new varieties of tools

ceramic knives and cubic boron nitride (CBN) knives are good for processing hard steel. These tools have developed rapidly in a short time. Some tool manufacturers claim that as long as the machine tool is used correctly, their tools can shorten the time of grinding by 300% and improve the cutting accuracy

ceramic knives recommended by these suppliers have negative rake angles and large t-chamfering, which only increases pressure on the tool workpiece interface. On the contrary, CBN can have or not such adverse t-chamfering according to the specific situation of the workpiece. For example, when CBN is used for intermittent cutting, a large t-chamfer is required to withstand vibration

the use of ceramic tools will be more and more common than CBN, which is due to its low cost and more cutting edges. However, they are very easy to crack when heated. In addition, if the blade is not polished properly, it is not suitable to carry out intermittent cutting. Although CBN is much more expensive than ceramics, it has much better cutting performance, high machining accuracy and longer service life

how to choose between these two tool materials is how to make the workpiece material, geometry, cutting speed and feeding people adapt to it. Some users usually don't stick to the comparison item by item, but take the cost of the tool for the same processing and how much benefit it can produce as the selection principle. These users rough turn the rust and iron scales left during heat treatment with low-cost ceramic knives, and then finish machining with better CBN knives. Generally speaking, if the hardening depth in the deformation measurement system is moderately greater than the depth of the material to be driven, CBN is the best choice

choose the correct processing method

from a practical standpoint, turning hard materials is a process closely related to the characteristics of the workpiece. It is especially suitable for cutting workpieces with complex geometric shapes such as intricate arcs, angles, and radii. You can use the method of programming turning with a single tool tip to complete the machining quickly and economically without having to buy a shaped grinding wheel for this purpose. According to experience, most hard materials are turned at a cutting speed of m/min and 0 13mm/min feed rate. The cutting depth of fine cutting is generally 0.08-0.5mm

therefore, how to control the purity of materials, as well as the heat treatment, rough turning and forming processes before turning, have become the decisive factors of the accuracy that this machining can achieve. If the workpiece hardness fluctuates by only three Rockwell hardness values (for example), the cutting pressure of the tool will change enough to make you unable to guarantee the dimensional accuracy of 5 m. Unstable hardness and uneven cutting depth will damage this kind of processing. Therefore, qualified materials should be used to maintain a constant metal cutting rate and ensure that the batch heat treatment hardness is within ± 1 or ± 2 HRC values

the length diameter ratio of the workpiece will also affect the ability of the machine tool to maintain tolerance accuracy. A typical fixed head lathe can achieve quite strict accuracy without tailstock for soft workpieces with a length diameter ratio of 5:l-6:1. Due to the hardness of the workpiece, the negative rake angle of the tool and the t-chamfer necessary for cutting hard materials, the pressure on the tool is quite large. Therefore, when the workpiece has no tailstock support, the length diameter ratio of the workpiece must be limited to 3:1-4:1

of course, this limit changes with the processing time - that is, the automatic control experiment of constant speed loading and constant speed displacement can also be carried out, that is, it changes with the material, hardness, roughness and accuracy requirements of the workpiece. We have previously turned workpieces with a diameter of 13mm and a length of 64mm without tailstock support, but the accuracy is very poor

tailstock can play a certain role, but it is a panacea to solve all problems for Africa. For example, the center cannot prevent the vibration of a workpiece with a diameter of 25mm and a length of 300mm. For this kind of workpiece, you can only use grinding. It is better to adopt grinding technology to ensure a more strict tolerance accuracy than 0.005mm. Although hard material turning cannot completely replace grinding, it can replace a considerable part, especially when the length diameter ratio of the workpiece is small and the shape is complex

when you need precision

after superior technology company (Rochester, N.Y.) moved to a new plant with an area of 2508.38m (2700ft), the boss added a new vmc700 vertical machining center, a hardinse CHNC lathe that has been used for 9 years, and 13 hardingeconquest CNC lathes that can finish turning hardened workpieces to the processing workshop with an annual output value of $2million. Among these machine tools, Mr. superior uses a row turret lathe for turning hard materials, that is, an ultra-high precision conquest GT lathe with an accuracy of 0.25 M

although this precision level is not required for every processing, "when you need it, it's very reassuring to know where to have this precision equipment." Mr. Tony shortino, vice president, said, "if I need to cut 0.51 m, I can do it."

the batch of tasks he assigned to the machine tool was 20000 surface hardened 50mm long and 13mm thick 12L14 steel parts. The hardness of the hardened layer is HRC, the cutting depth is 0.8mm, and the required shape and position matching tolerance is 0.005mm. CBN tools are used for turning hard materials. The tool must cut the hardened layer, with one side of 1mm

when conditions permit, the workshop also adopts hardened material turning technology to replace journal grinding, grinding after heat treatment and other surface finishing processes. After canceling these processes, sunerior not only saves money, but also purifies the environment due to the elimination of grinding dust. Mr. shortino finally said, "there is no special coolant or air filtration device here."

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