Milling of hard materials
Mr Cory greenwald encountered such a problem. He knows that the milling of hard materials has become a major problem when producing injection molds in factories. He knows how to create a studio by himself. Hard material milling method? , milling hard materials efficiently, consistently and confidently. As a mold workshop, he knew that he would encounter the milling problem of hard materials. It seems that they need such a professional processing workshop to solve the problem of milling hard materials, because they have neither enough time to process on their own machine tools nor are they ready to mill hard materials on their own equipment.
Unfortunately, when it comes to hard materials that need to be milled, many mold workshops are not prepared for it. They still use traditional mold processing methods. After they finished processing the molds, they had to spend a lot of manual time polishing the molds, and finally they had to spend time finishing, testing and deploying the molds point by point.
Mr. greenwald said that these extra working hours will make a huge difference between the competitive and non-competitive mold industries in the global market. ? He concluded:? If these mold workshops do not change their processing methods, it will be difficult for them to survive. ?
Mr. greenwald is convinced that the most important problem at present is to solve the milling problem of hard materials, especially small molds and core inserts. He said that the use of hard material milling technology can help the workshop to start processing hardened steel molds, and there is no or little need to polish the surface of the mold cavity. In this way, they saved several time-consuming and labor-intensive processing procedures in mold processing and production. He added that after using hard material milling technology, the machining level of the other side of the die can be improved to reach? Negative inventory? Conditions. That is to say, there is a small gap between the mating surfaces of the mold. In this way, when the die is put into the press for the first time, the final debugging time of the die can be greatly saved and the labor intensity can be reduced. But also prolongs the service life of the die and improves the running speed.
Mr. Greewald said: With proper application of hard material milling technology, the mold workshop can directly process the mold parts from the machine tool, then assemble them and finally install them on the injection molding machine, so that a good part can be produced in the first injection molding. After the milling technology of hard materials is adopted in the mold workshop, a lot of time and expenses are saved from the processing and debugging of injection molds. ?
So what are the requirements for using hard material milling technology? Mr. greenwald believes that the adoption of hard material milling technology needs a brand-new concept to solve the problem of how to process metals. The milling of hard materials requires the use of some kind of machine tool, some kind of cutter, tool rest and some kind of processing program software. These technologies should be put in place in time and fully coordinated.
Mr. greenwald said that as long as everything goes smoothly and we know how to cooperate with each other, the milling technology of hard materials will become a reliable and fruitful process. ? It turns out that the two vertical machining centers (specially used for milling hard materials) used in his workshop are actually running 24 hours a day, and few people need to participate in the operation.
The birth of mold processing workshop
How did Mr. greenwald become a respected practitioner and strong recommender of hard material milling technology? Here is an unusual story. At first, he was a production engineer, and later he took part in the management of the mold workshop in a mold factory in the suburbs of Detroit. One project he experienced was to install a machining center for milling hard materials of stamping dies for hot forging of metal connecting rods.
The result left a deep impression. The production of stamping dies has been shortened from 30 days to 6 days, far exceeding the hope of workshop owners, which is exactly what they want. Moreover, Mr. greenwald even found a kind of hard material milling technology with more development potential and cost saving.
Mr. Graig Sizemore, Mr. greenwald's friend in Detroit mold industry, is also very interested in this hard material milling technology. His factory, Cut-Rite EDM Company, specializes in advanced WEDM, and he is also looking for a milling technology for hard materials as a supplement or substitute for EDM. With the support of Sismore, greenwald founded a Hard Milling Solutions milling Company in Shelby, Michigan, which is located about 30 miles north of Detroit. Near Mr. Sismore's studio. Although Mr. greenwald is not trained as a mechanic or a mold maker like Mr. Sismore. His only experience is that he has a close cooperative relationship with his former boss in the milling technology of hard materials.
It is this reason that encouraged Mr. greenwald. As a production engineer, he knows enough about the milling of hard materials, and he realizes that he must make persistent efforts. The task before him is to learn hard practical knowledge, how to grind hard materials and how to equip a workshop so that it can work effectively. To this end, Mr. greenwald contacted Single Source Technology Company in auburn hills, Michigan, which is a distributor of machining centers and EDM equipment provided by Mu Ye Company (located in Mei Sen, Ohio) and other manufacturers. Single source technology company has been actively promoting high-speed machining and hard material milling machine tools in Detroit subway station area, and together with its former boss, it helped Mr. greenwald to establish a hard material milling factory.
He participated in the workshop high-performance machining technology training course in the single source technology company, which laid the foundation for his success in hard material milling technology. When Hard Milling Solutions started its business, an employee was responsible for operating the Makino V56 machining center.
Although Mr. greenwald started his work with the help of external forces, he soon realized that the milling of hard materials still needed to open up a new path on his own. Because this workshop was specially set up for milling hard materials, he began to undertake various tasks of milling hard steel with hardness as high as 60HRc. Some processing data tables provided by Single Source Technology Company laid the foundation for his work, but most of his work still needs practical experiments and trial cutting.
Now most of the work in the workshop is processing plastic injection molds, and most of the injection molds are tool steels H 13 and S7. The workshop also specializes in processing medical instrument parts, including forging dies, die parts, cavity inserts, powder metallurgy parts and any other parts with hardness as high as 65HRc. Now, a V56 vertical machining center has been added to the processing equipment in the workshop, and Mr. kevin hunt, a mold worker with 30 years' working experience, has been hired to take charge of the operation of this machine tool.
Because his workshop specializes in all milling tasks of hard materials, Mr. greenwald said that he has almost become a quite advanced expert in this field. Regardless of selfishness and selflessness, he hopes to see the hard material milling technology widely used by American mold manufacturers. As more and more factories invest in this technology, he is sure that the workload of their company will become bigger and bigger, especially some difficult jobs. More importantly, he believes that hard material milling technology is the future development direction of American mold manufacturing industry. He said:? Faced with more and more molds imported from low-wage countries, there is really no better way to make the mold manufacturing industry profitable. ?
The modules produced by Makino V56 vertical machining center are made of H 13 hardened tool steel. In this machining project, a spherical end mill with a diameter of 1.0mm is adopted, and the length-diameter ratio is 12∶ 1, which is the smallest machining tool. After using this kind of milling cutter, the machining ability of EDM machine tool is greatly reduced, and the polishing process is also saved for customers.
Grinding technology of hard materials suitable for walnut shell processing
Hard material milling technology is a branch of high-speed machining technology. The core of high-speed machining technology is to carry out multi-pass slight cutting in close steps, leaving only tiny tool marks on the machined surface. Its goal is to greatly reduce the subsequent processing requirements of the machined surface. For tools, in order to achieve effective chip load, it is necessary to greatly improve the tool feed speed and spindle speed to exceed the normal machining speed applied in traditional machining technology, so this technology is named high-speed machining. High-speed feed also greatly improves the tool feed, so the speed of machining workpieces is faster than that of traditional methods.
The milling technology of hard materials is one step ahead of the concept of high-speed machining. The combination of high-speed optical cutting and high-speed spindle can effectively cut hardened steel, thus maintaining the original characteristics of the material. At the same time, the small diameter round end milling cutter is used for short-distance high-speed machining, and the surface smoothness of the machined surface is close to the level of manual grinding and polishing. (According to Mr. Greenwald's report, if necessary, the surface finish can often reach the level of 10 ~ 12 rms by using hard material milling technology. Because steel is processed under hardened conditions, there is no need for subsequent processes such as heat treatment, stress relief or grinding. More importantly, this process can also replace many EDM processes with high processing cost.
Another advantage of using hard material milling technology is that it can ensure very accurate tolerance size (? 0.0004 inches), which is very precious for mold processing. The processed mold does not need to be trimmed point by point manually. Moreover, because there is no need for manual trimming after machining, the geometric shape of the die is completely consistent with the CAD design model. Moreover, the processing of the mold mating surface has reached the level without any finishing. Its concept is a slightly more accurate processing along the parting line, generally at one end of the mold cavity, making it slightly lower than the nominal size. In this way, when the mold halves are closed, there will be a little gap between the contact surfaces of the mold. However, the gap is very small (generally only 0.008in inch), so that some plastic can flow out during the injection process, but the mold can still be effectively closed. In addition, when molten plastic is injected into the mold, the gap can also allow air to be exhausted from the gap without pre-ventilation. The small contact pads on the corners continue to maintain this gap, otherwise, the closed curved surfaces cannot touch each other. Generally speaking, the interference between these mating surfaces must be solved in the process of point-by-point fitting, and now this problem no longer exists. When that mold core and the mold cavity are close, the interaction between surfaces is eliminate due to the gap, so that the parting surface is completely protected, and the produced part will not have flash.
Improve efficiency from the tip of the knife
Mr. greenwald said that, like any NC machining process, the milling technology of hard materials depends on high-performance machine tools, suitable tool and handle systems and effective tool running procedures. However, unlike other processing technologies, the interaction of these elements has a complex dynamic relationship, which is certainly not insurmountable. As long as new users make up their minds and are not afraid of difficulties, they can change this relationship and solve problems.
He pointed out that it may be a challenge to master the milling technology of hard materials. But there is a way to make your mind revolve around this goal. ? He said that the way to understand the milling technology of hard materials is to know how to protect the tool tip. ? Concentrate on making your tip cut safely and effectively. Knowing this, we can work in reverse thinking and understand the requirements of the system and the interaction between them. If all this can be managed in an orderly way, then the tip of the end milling cutter can be combined with the processed material and cut freely. Everything else can go smoothly step by step. ? He added that if any part of the system is ignored or interrupted, the tip of the tool will be affected and the whole process will fail.
The surface of the die cavity is completely milled in the hardened state, and the surface finish after machining is 12rms, which saves the time of point-by-point finishing and supporting machining without further machining by the fitter. The matching core also adopts hard material milling technology. After machining, the machining accuracy of the sealing surface on one side of the cavity reaches 0.0008in. With this mold, good parts can be produced for the first time.
Mr. greenwald listed several main factors that should be paid attention to when machining from the end milling cutter.
Tool: Hard milling solutions generally use round end milling cutter for rough machining, semi-finish machining and finish machining. Round-head milling cutter with two chip grooves is specially used for finishing, and these finishing tools are very key factors in the milling of hard materials. As a round end milling cutter for finishing, it must meet two key requirements: the cutter must have a nearly perfect radius and a cutting edge with almost no defects. The radius accuracy of the blade must be extremely high, so that no matter the height of the chip removal groove, the uneven state of metal chip removal will not be caused, so as not to affect the geometric shape and reduce the surface quality and the service life of the tool. The radius accuracy of end milling cutter for finishing in workshop should be at least? 5mm(？ 0.0004 inch). Round-head milling cutters with a diameter of 0.012 inch are occasionally used in the workshop, with a radius accuracy of? 0.0002 inch.
There must be some trace chips, fractures or other irregular shapes on the cutting edge of the chip removal groove. The appearance of these defects shows that accelerated wear will occur when they contact the workpiece. This situation will lead to rough surface and shorten the service life of tools. The service life of the tool is a very critical factor, because when the machine tool is unmanned, the workshop completely depends on the expected working period of the end milling cutter.
Suppliers such as OSG (Glendale Heights, Illinois) and NSTOOL (distributed by Single Source Technology Company in North America) can provide tools that meet the above specifications, but their prices are much higher than standard tools. It is absolutely necessary to use tools of this quality level, and the cost should not be a problem. Mr. greenwald said that these tools are the foundation of mold processing. Using them can save the polishing process and point-by-point finishing process of the mold. Adding these tools is a very important investment in the milling process of hard materials. ?
Tool shank: The tool shank can protect the radius of the end milling cutter and the quality of the blade. Mr. Greenwald is convinced that the handle installed in the hot sleeve with HSK interface can provide the best protection. The hot sleeve clamping method has extremely low offset, which is superior to any clamping method at present and minimizes the eccentric rotation of the tool. Because the offset error will lead to excessive cutting of the chip removal groove of the tool, the cutting load on the chip removal groove will increase, thus shortening the service life of the tool.
The hard milling solution adopts Harmo hot sleeve installation system. According to Mr. Greenwald, tools can be replaced and re-clamped in less than one minute, and then returned to the automatic tool changing device. According to his experience, the clamping deviation accuracy can reach below 0.000 1in by using the hot-fitting clamping method.
The company only buys balanced HSK handles to prevent unnecessary handling. HSK interface is a compulsory interface, because it is more durable and accurate than other taper sleeve clamping methods, and can be clamped to the spindle more safely.
Spindle: Just as the tool holder is used to protect the cutting edge and precise radius of the end milling cutter, the spindle is used to protect the integrity of the tool and tool holder assembly. Of course, the design of the spindle should also have the high-speed rotation performance required for milling hard materials. It is very important to control the heat and vibration generated by the spindle. Direct drive spindle (not driven by gear or belt) and its internal cooling mode are especially suitable for milling hard materials.
The spindles of these two V56 vertical machining centers installed in the hard milling solution have the above characteristics. The spindle speed of these two machine tools reaches 20000 rpm.
Structure of machine tool: When discussing the spindle of this kind of machine tool, we can discuss it separately from the overall structure of the machine tool, although they are all inseparable parts of the machine tool. Mr. greenwald said that there is no doubt that the machine tools used for milling hard materials must be very hard. ? Of course, its overall accuracy is also very important.
The thermal stability and rigidity requirements of the company's machine tools are specially designed and manufactured for its application purposes. Some structural features of this machine tool are different from general machine tools, including:
● Equipped with heavy-duty base and column (the weight of this machine tool exceeds 9072kg).
● Equipped with central cooling spindle.
● Install the linear roller bearing in the headstock.
● Double support screw.
Mr. greenwald said, in my opinion, the most important thing is to minimize the vibration and accumulated errors of the machine tool, which may affect the cutting accuracy of the tool. Whether we use the 0.5mm end mill with 40ipm or the 6mm end mill with 380ipm, the accuracy is always kept at110, but the variable effect of the system will be amplified, so all factors must be strictly controlled. ?
The CNC processor and servo system of this machine tool are also specially designed for milling hard materials. Its characteristics are as follows:
● Two sets of RISC processors, one of which is dedicated to the necessary data conversion, and turns the programmed tool machining route into a servo instruction.
● 120 block's forward-looking function to avoid tool stroke overshoot or undershoot.
● Through accurate positioning control, the feedback from the high-resolution encoder is effectively inserted.
● Grating can be fed back in increments of 50 nanometers.
Programming software
However, the performance of a rigid and responsive machine tool depends on the programming input of NC. In the milling of hard materials, Mr. Greenwald lacks this knowledge, but he has some research on CNC driven by tool path.
He explained:? The problem goes back to the point we discussed at the beginning. ?
When processing hardened materials, in order to ensure safe and accurate positioning cutting, the ideal fillet radius and cutting edge of the tool are very important, but it still depends on the machine tool. Smooth operation? . Therefore, most CAM software is not suitable for milling hard materials. The algorithm for generating the tool running route is not specially designed for this kind of hard material milling, because the latter requires stable and accurate movement according to tolerances, allowing the mold workshop to bypass all processing steps in the mold manufacturing process.
As Mr. Greenwald saw, the design of typical CAM software can quickly generate tool machining lines, so most system applications can effectively generate coded machining shortcuts. This software is very useful for general milling, because these shortcuts will not produce great efficiency. But the problem is, according to him, this advantage becomes a disadvantage in the milling of hard materials.
CAM-TOOL is used as programming software in their workshop. The software was developed by the Japanese and sold in the United States by North American Graphic Products Company. The company is located in Windsor, Ontario, and its new president is Randy Nash. Chris renaud is an expert in the sales and application software of this company, and has worked with hard milling solutions, so he is very familiar with the application of this software. He said:? Mr. Corey's workshop represents the demand for milling hard materials, especially the mold processing industry. ?
Mr Renaud said that the software could not create triangular geometric surface meshes, because these approximations would affect the accuracy of one millionth of an inch required for milling hard materials. On the contrary, this software can calculate the tool machining route according to the measuring points directly taken from the geometry. In fact, he said, these points can be connected by a mathematically specified curve that is most suitable for these points, and then the center points of each triangle distributed in the outline grid can be connected by a straight line segment, and then they can be compared with each other. Because the generated path is a series of curves, the motion defined in the tool machining path lacks steep changes in the direction of creating short segments. Trying to make the machine tool with micron feedback resolution move unambiguously along these line segments will definitely have adverse effects and put the machine tool in danger.
According to Mr Renaud's idea, there are other requirements for an effective tool processing line for hard material milling. They must:
● Control how the cutter moves forward and backward during cutting.
● By controlling the contact degree between the blade and the workpiece material, the chip load is kept constant.
● Provide constant inventory conditions for each roughing or finishing process in the future.
Mr Renaud said that the algorithm used to accurately analyze geometric shapes in machining mode is the key to achieve these goals. The machining route of the tool suitable for milling hard materials will not produce conditions contrary to the machining ability of the tool, so that the machining accuracy and surface smoothness of the die can fully adapt to the press.
A complete and accurate tool model is helpful for programming software to check the possible collision or gouging in the workpiece, and the accuracy can reach 100%, thus realizing unmanned cutting.
Concentrate all advantages
When there is no weak link between the tool tip and the programming software, the milling technology of hard materials can achieve the expected reliable purpose. It is for this reason that unmanned operation becomes feasible. This is the actual work that Hard Milling Solutions does every day. Mr. greenwald said that each of our machine tools works more than 100 hours per week on average, and most of them are unmanned. ? About 90% of the processing work is completely unattended. He said:? If you have to work in front of the machine tool, there is something wrong with the programming of the machine tool. ? He or Mr. Hunter will stand in front of the machine tool and pay close attention to the processing of materials when using a smaller tool for trial cutting, or when processing hard materials that have never been encountered before, so as to learn and master the working performance of the system.
However, he stressed that the daily unmanned operation mode is not an option or reward for milling hard materials. He said that the purpose of almost 24-hour uninterrupted operation of the machine tool is to recover the investment healthily and pay the cost of the machine tool itself. Unmanned operation embodies the goal of low labor input and high output of machine tools. Moreover, this process also replaces hundreds of hours of mold polishing and point-by-point finishing by locksmiths, which requires high labor costs.
For customers who buy molds, the benefits are obvious, so they are so eager to hope that the milling technology of hard materials should become an indispensable processing technology for mold manufacturers. In the mold manufacturing process, the use of hard material milling technology can replace some of the most expensive and time-consuming processing steps, and can eliminate or greatly reduce electrode milling, EDM, grinding, polishing, point-by-point dressing on the press and so on. For this reason, Mr. greenwald thinks that hard material milling is the key technology related to the success or failure of American mold workshops.
Their existence ensured his survival, because he knew that there were more milling tasks of hard materials waiting for him to complete, and there were more unusual difficulties waiting for him on the way forward.
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