Low-carbon and medium-carbon steel almost constitute the backbone of every workshop in its general engineering applications and manufacturing parts.
They are defined by the percentage of carbon in the steel. Low carbon “low carbon” steel is 0.15% to 0.30%, and medium carbon steel is 0.30 to 0.60%. According to a report from cnccookbook.com, low carbon steel has a wide range of uses due to its good machinability, weldability and low cost. Most grades can be cold-formed or hot-rolled. Low carbon steel is used for parts that may undergo surface hardening but whose core strength is not critical. Considering the preferential price of this material, manufacturers usually use it for high-volume parts such as screw machine parts, shafts, light-duty gears and wear-resistant surfaces, pins and chains. Other applications include weldments, gearboxes, transmission systems and general engineering parts.
However, mild steel has problems with turning, drilling and milling. They are soft, gel-like materials that often form long and problematic chips. Not surprisingly, the most common problem with handling these steels is how to break the chips. The answer can be found in chip control by feeding speed, depth of cut and selecting the geometry of the insert.
Medium carbon steel has balanced ductility and strength, and has good wear resistance to large parts, forgings and automotive parts. Medium carbon steels are stronger and harder than low carbon steels, but they are more difficult to form, weld and cut.
During the discussion, Director of Service and Application Engineering at Absolute Machine Tools in Lorraine, Ohio. Craig Adorni, Application Engineer of Absolute Machine Tool; Rich Ford, Senior Sales Engineer of Pittsburgh Kennametal Inc./MTI, outlined the method of choosing the right cutting tool and cutting data to meet the challenges of machining mild steel. Kennametal’s Engineering Calculator or NOVO’s proprietary cutting tool database provides online information about the correct cutting tool, insert geometry, processing speed and feed for the application.
Adorni pointed out obvious problems with drilling and chip breaking. “When you are drilling, when the chips start to accumulate on the tool and the tool holder, you can’t block the pile of chips, so you need to make sure to break the chips.”
Zunis believes that if the chip is not damaged, it will have a certain impact on automation. He said: “If the drill or tap leaves a pile of chips, they may prevent the robot from grasping the part.” “The best milling application will produce chips like popcorn, which can actually hold six to nine. Small chips like popcorn are flying around. They are not connected to each other and do not behave like long strings.
He continued: “However, for mild steel, you can end up with wood chips like an eagle’s nest, wrapped around the drill bit, and then thrown everywhere.” He pointed out that usually, the wind cannot remove the chips-the chips need to be removed. crumble. He said this can be done by increasing the feed rate or changing the geometry of the blade so that a small part of the chip will “essentially explode.”
Running at a higher feed rate seems attractive. “However, customers are often afraid of running newer machines at the appropriate feed rate because they are’old school’ and used to run too slow, which usually leads to excessively long chips,” Adorni said. “However, if you can increase the feed rate, it is easy to chip. Some machinists do not take into account the newer technologies of CNC, blades and tools, which are designed for tools designed or developed when a specific feed rate is reached Yes, so you can break or break the chips. But if you can’t get there and you don’t use the geometry of the tool as expected, you will get a large long chip that can cause problems in the tool changer.”
Sandvik Coromant of Fair Lawn, New Jersey, said the new cutting tool technology provides a better way to approach these steel grades. The company introduced a new type of cemented carbide grades GC4415 / GC4425 with second-generation Inveo coating. The new grade also provides ISO-shaped and proprietary bagged blades, suitable for mass production and mass production of low-alloy steel and non-alloy steel.
”The new grade is new in every way,” said Keith Brake, a turning expert at Sandvik Coromant. “We have improved the coating, substrate and post-treatment processes. These improvements provide us with a reliable and effective process for steel turning applications because these grades perform well in both roughing and finishing applications and increase tool life The new base material also enables GC4425 to perform well in intermittent cutting applications where other P25 inserts may encounter difficulties. All this adds to our customers better performance and tool life.”
Brake believes that in all machining applications, chip control is essential. This is especially difficult in soft materials such as mild steel (such as low carbon steel). “Uncontrolled chips can cause premature blade failure, scrapped parts, or most seriously injured employees. Sandvik Coromant has a variety of chipbreaker geometries, of which “LC” is the first for this type of application. This Combining chipbreakers with appropriate cutting data can produce excellent results.
He continued: “For customers who want to increase productivity, we have also released new grades in the CoroTurn Prime series.” “PrimeTurning is not a new technology, but we have noticed that tool life and new steel turning grades (especially The consistency of the 4425 CoroTurn Prime’B’ insert) has been significantly improved. For CoroTurn Prime, it is not uncommon for the roughing cycle to be reduced by 30%.” He also said that CoroTurn Prime does not require any auxiliary tools to create radius and Square shoulder.
Brake said that Sandvik Coromant has documented a case study of its GC4425 / GC4415 inserts, “In many steel turning applications of different materials, the grades have been released.” “The automotive and general engineering industries can make good use of the new grades. , But these grades are not limited to these areas. If you want to turn steel, GC4415 and GC4425 will provide improvements.”
Another problem with the stickiness of mild steel is that it tends to create a build-up edge (BUE) on the tool. Randy Hudgins, National Product Manager for Turned and Threaded Products, said Iscar USA in Arlington, Texas has used several different approaches to solve this problem. Iscar’s Sumo Tec surface treatment can smooth the top of the blade, making it easier for the material to slide on the blade, thereby preventing BUE. In addition, Iscar has recently developed a series of new chip formers for steel processing, from heavy cutting to finish cutting.
Hudgins said: “For our customers, the important help is the nomenclature of the chip forming machine.” “It enables the end user to easily identify and select the appropriate chip former. For example, let us use a dash M3P chip Former. The first letter M indicates the application of the medium, the third letter indicates the feed speed of the standard medium, and the last P indicates the material (steel). Iscar goes all the way to F1P, F indicates finishing, F indicates low feed Rate, P means steel.”
Chip control is essential in high-volume production industries such as automobiles, which use low-carbon steel for transmission shafts, steering shafts, and various shafts. why? The automotive industry relies on the use of a lot of robotics and cannot afford to stop production when cleaning the chips in the machine. According to Hudgins, this is especially true in places that require long continuous turns.
He said: “We have encountered many production machines for processing mild steel parts, including multi-spindle, dual-spindle and multi-spindle machines, as well as Swiss-style and CNC automatic lathes.”
As an alternative to conventional ISO turning inserts, Iscar has launched the CXMG Logiq4Turn product line, which doubles the cutting edge of positive bevel inserts for general turning applications. “This is an economical solution for 80° turning, and provides a double-sided positive four-edged cutting edge, which can easily replace a positive two-edged cutting edge. The dovetail shape is suitable for the unique groove design to ensure better insert positioning and stability. To ensure a longer blade life.” Hudgins said. “The holder can be with or without a through coolant channel.”
In addition, the new double-sided CXMG blade works similarly to the CCMT positive blade and can replace the standard CCMT blade. In some applications, such as long shafts, the positive geometry of CXMG can relieve a lot of pressure and still has strength, and because of the dovetail geometry, it can also replace standard negative CNMG blades.
Jack Burley, vice president of sales and engineering at BIG Kaiser Precision Tools, Hoffman Estates, Illinois, agrees that low-carbon steel is challenging due to its stickiness in hole machining processes such as drilling and boring. . “From my point of view, many companies believe that low-carbon steel is easy to process. This is based on their success in hole-making tools, usually drills and boring tools purchased from us. [However,] Low-carbon steel The low tensile strength of steel requires several items in the tool geometry to be able to successfully drill and boring. For the drilling depth, you really should have enough pressure to pass the coolant straight into the chips, with enough pressure to break the chips. “Burley said.
For deep hole drilling, coolant is particularly important, for example, in vertical deep hole drilling, the chips must be drained. “What I call deep hole drilling is four times the hole diameter,” said Zunis of Absolute Machine Tools. “Usually, a multiple of three times or less is considered normal, but if you want to cut 4 times, 5 times, or 6 times the chip diameter, you need to remove the chips from the hole.” Use high-pressure coolant when drilling. It is advantageous, but without sufficient feed speed, even the coolant will not help you damage the chips. Feed speed, depth of cut and the use of suitable inserts and tool holders are the main catalysts that cause chip breakage. “
Burley said that BIG Kaiser offers various types of drills, including carbide drills, spade drills and indexable drills. He added: “However, in the case of indexable drills, you need to break the chip feed too much, and may even exceed the capacity of the equipment.”
This is also true for hole processing in weldments of agricultural and construction equipment and mechanical frames that usually use mild steel. Burley said: “Metals are usually not as pure as they come from foundries, so you have to deal with many fragments in the material. These fragments may be difficult to process.” “In these areas, this is double trouble because when you look at the assembled parts When you are punching large, thin-walled workpieces, and these workpieces do not have a lot of structure behind them. When you start to push the weldment or frame, it will produce a little and rebound, which is very difficult on drills or boring tools. Especially when it comes to roughing. Over the years, our work has been researching different methods of handling such parts and holes, including circular milling of larger holes.”
Burley believes that boredom is another story. As the holes for fabricated weldments become larger, the workshop will not use drills to burn the holes, instead of drilling holes, but use double-edged milling cutters to use square inserts and double holes for balanced cutting to make holes. Countersinking on knives and machines is difficult, but with the right tools, the right feed and speed, and the right blades, the shop can use the application very effectively.
He said: “boringness brings its own special challenges.” “When the cutting depth is less than 0.020 inches (0.508 mm), the chip is almost impossible to break. It will start to wrap around the tool like shoelaces, giving the surface a smooth finish. And machining brings a lot of trouble. When you try to use different speeds and feeds and apply coolant, you will eventually get a higher feed rate and a deeper cutting depth. All these factors together lead to a higher surface finish And tighter tolerances.”
Last year, BIG Kaiser introduced a unique chipbreaker for fine boring mild steel. Burley said: “The ELM geometry of these blades can be reduced to a 0.008 inch (0.2032 mm) nose radius. The chip breaker has been pressed into the blade, so we can tightly take up the chips. Even a thin DOC, It can reduce chips less than 0.010 inches (0.254 mm). We can still roll the chips well, reducing the trouble of pulling the chips out of the holes.”