To meet the needs of the automotive industry, tool manufacturers have also introduced milling cutters and inserts for milling cast iron and other materials. These tools and inserts have greatly improved machining efficiency and surface quality of parts.
I. QC milling inserts developed by Valenite to meet the needs of the automotive industry
In the early car production line, each station had to complete a process in a fixed cycle time. Then, the workpiece is transferred to the next station. This transfer can only be performed after the slowest process is completed. At this time, the cutting speed, feed rate, and number of passes per process are fixed. If a process requires a tool change, the entire production line must be stopped, so the impact of tool life on production efficiency is very prominent. Reiterman, product development manager at Valenite, proposed that tool life is half a class, one half class is not good, and tool life can reach a class steadily, making the tool change after work is the minimum requirement. The next goal is to increase tool life to 2, 3 or 4 shifts.
The use of high-hardness, high-strength tool materials with appropriate coatings is the primary measure to extend tool life. However, Reiterman believes that improving tool geometry is also an important means of increasing tool life, especially when milling cast iron. He pointed out that in the automotive industry, a range of alloy cast irons are processed, including grey cast iron, ductile iron and high density ductile iron. These cast irons have different processing characteristics. Among them, gray cast iron contains a reticulated hard structure, which is brittle. When machining, the tool is prone to chipping. Ductile iron and high-density ductile iron have certain plasticity, which can produce iron filings, but the cutting of the tool When it comes out, the workpiece will also produce "flanging", which will result in damage to the tip. Reiterman also pointed out that the same workpiece casting process is different, and its processing performance is also different. For example, a thin section and rapid cooling can result in a particularly hard, difficult-to-machine surface for the casting. In addition, the processing properties may vary depending on the batch being cast and the batch of the ingredients.
Valenite's newly developed QC milling cutter for machining cast iron has four cutting edges with a positive rake angle and several tip arcs between the main and minor cutting edges. A wiper blade is specially designed at the cutting edge.
The size of the tool nose arc is critical when milling or shallow deep milling. In this case, the radius of the tool nose should be larger than the depth of the cut, which results in a leading angle between the tool nose arc and the workpiece, which is good for avoiding chip edge chipping when machining cast iron. effect. The sharp edge is sensitive to vibration during machining of cast iron and is highly prone to chipping. Therefore, the cutting edge arc and the cutting edge at the main declination should be rounded. On the other hand, the function of the wiper is to remove the "crest" of the feed tool mark, which reduces the cutting ability of the wiper - making it less sharp and showing signs of squeezing on the machined surface. The front angle of the QC insert is positive, which can effectively reduce the cutting force and facilitate chip removal. According to the characteristics of the workpiece material, it is convenient to customize the most suitable milling cutter body to achieve the purpose of reducing cutting force, reducing heat accumulation and prolonging tool life. The use of QC inserts in different cast iron milling processes increases tool life.
Second, the Auto2000 milling cutter developed by Iscar for the automotive industry
Automotive production has undergone a digital transformation from the use of ancient rigid production lines to today's advanced flexible manufacturing systems. For the car itself, there is a trend of diversification of energy. This change directly affects the choice of automotive structures and automotive parts materials. Therefore, the automotive industry is looking for tools that are both easy to use and adapt to a variety of metallic materials. To this end, Iscar has developed a new range of milling cutters for the automotive industry, called the Auto2000 milling system. The feature is that the insert seat ring of the axial height of the positioning blade is finely ground, which can greatly save the adjustment time of the tool adjustment. The tool can be used for finishing, semi-finished grey cast iron, malleable cast iron and ductile iron commonly used in the automotive industry. The maximum depth of cut is 5mm. The blade is an octagonal Hanyang Technology Co., Ltd., each blade has 16 cutting edges, and the axial direction has a positive cutting groove, which reduces the cutting force. In addition, the rear of the tool tip has a wiper to improve the surface quality of the workpiece.
Third, the use of ceramic blades for milling
It is easy to adjust the cutting parameters by means of numerical control technology on a modular production line or a flexible machining unit (FMC), which is more conducive to giving full play to the full potential of advanced tools. According to Marshall, manager of milling cutters at Kennametal, silicon nitride is the best choice for milling gray cast iron for maximum productivity. Even at cutting speeds of 760 to 1370 m/min, the feed rate and tool life are comparable to those of cemented carbide.
After the National Precision Products Company (NPP) tried the Fx-perfect blade made of Kennametal's silicon nitride Kyon3500, it was considered that the tool life was still improved after the feed rate was increased by 3-4 times compared with the cemented carbide tool. For example, with a φ25.4mm solid carbide end mill, 300 pieces can be machined in one regrind, and more than 2000 pieces/edge or 16,000 pieces/piece are processed with a face milling cutter with a Kyon3500Fix-perfect blade of φ76mm.
According to NPP, ductile iron is more difficult to machine than gray cast iron, and the cutting speed needs to be adjusted. In the case where the metal removal rate per tooth is the same as that of the gray cast iron, the spheroidal graphite cast iron has a cutting speed of v=730 m/min, and the gray cast iron is processed, and the cutting speed is v=914 to 1219 m/min. Silicon nitride Kyon3500 tool material superior performance, although its price is more expensive than hard alloy, but the productivity gains are far more effective than the increase in tool costs. The key is that the machine power and rigidity are sufficient. Although ceramics can be used for milling to achieve high cutting speeds and long tool life, if the depth of cut reaches 3.8mm, the machine power is 20 horsepower. Therefore, only a small cutting speed can be reduced, and this does not give full play to the superior performance of the ceramic.
Fourth, the improvement of the geometric angle of the milling cutter
According to the experience of NPP, when the machine power is insufficient, the geometric angle of the tool can be correctly selected, and the production capacity of the low-power machine tool can also be expanded. For example, conventionally, cast iron milling cutters have negative axial and radial rake angles (double negative angle milling cutters). This negative geometric angle makes the cutting edge relatively strong. On the contrary, the positive and negative angle milling cutters (axial positive rake angle, radial negative rake angle) cut smoothly, which also reduces the machine power requirements and makes it easier to use advanced tool materials.
Depending on the grade and use of the insert, the cutting edge of the cutter insert can be sharp or it can be ground with a chamfer of 0.013 mm to 0.076 mm. For the Kyon 3500 ceramic insert, a 20° chamfer is ground and the chamfer width is 0.2mm to prevent the cutting edge from being damaged by the chip at high speed.
Kennametal's Fix-Perfect system is a product line that combines different positive and negative angles. Its characteristic is that because the blade adopts the vertical type, the lower part of the blade has strong physical support, which increases the blade strength. The negative axial rake angle forces the cutting force towards the spindle and the milling cutter works stably. Moreover, the negative axial rake angle allows the "impact point" that is first cut into the workpiece to leave the tip and protect the tip.
The Fix-perfect cutter has a scraping blade for roughing and finishing. The surface roughness is up to 32 (contour root mean square deviation), which reduces one finishing and reduces cycle time.
Fifth, the tool should adapt to the changes of various parts of the car
Due to the toughness of cast iron and its high compressive strength, and its ability to be cast into very complex shapes, it has been used in the manufacture of automotive engine casings and other parts. Later, under the promotion of CAFE (Corporate-average-fuel-efficiency), the use of heavy alloys was reduced on light vehicles. In 1980, according to the American Foundry Association, household cars were controlled at 600 pounds of cast iron. By 1999, the average had dropped by nearly half to 325 pounds and is expected to drop to 230 pounds in 2006. On the other hand, the aluminum industry analysis predicts that the application of automotive aluminum parts will increase by 50% in five years, from 250 pounds per vehicle in 2000 to 380 vehicles in 2005.
The processing of aluminum parts in mass production requires the use of polycrystalline diamond (PCD) tools. The chips generated during machining are the main cause of damage to the PCD tool.
To maintain the integrity of the cutting edge of the PCD tool, it is best to distribute the cutting load evenly to each milling cutter. Therefore, precision adjustment (especially axial) is an important means to extend the life of PCD milling cutters. For example, the Flex-Lok insert of the Ingersoll cutter allows fine adjustment of the vertical insert and then secures the insert with a barrel screw. In this way, the load on each insert on the milling cutter is balanced, resulting in the longest tool life.
The processing of aluminum alloys has special requirements on the geometrical angle of the tool. Aluminum alloys for the aerospace industry should use large positive rake angle cutters because of their high viscosity and low silicon content. For cast aluminum alloys with high silicon content in the automotive industry, It is not necessary to use a sharp front angle, but should be stable and durable. Therefore, most automotive manufacturers use aluminum alloys with small axial and radial positive rake angles.
In addition, some automotive parts are now hardened to increase productivity and reduce costs. For machining hardened ferrous metals, milling cutters with CBN or ceramic inserts are available.
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