Low carbon steel and medium carbon steel form the backbone of almost every workshop operating in its general engineering applications and manufactured parts.
They are defined by the percentage of carbon in steel; low-carbon "low-carbon" steels range from 0.15% to 0.30%, and medium-carbon steels range from 0.30% to 0.60%. According to 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. Mild steel is used for surface hardened parts, but its core strength is not important. Considering the favorable cost of this material, manufacturers usually use it for high-volume parts such as screw machine parts, shafts, light-stressed gears, and wear-resistant surfaces, pins, and chains. Other applications include weldments, gearboxes, transmission systems and general engineering components.
However, mild steel has problems in turning, drilling and milling. They are soft, sticky materials that often form long, problematic fragments. Not surprisingly, the most common problem with machining these steels is how to break the chips. Through the choice of feedrate, depth of cut and insert geometry, the answer can be found in chip control.
Medium carbon steel has balanced ductility, strength and good wear resistance, and can be used for 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.
In a discussion, Dave Zunis, Director of Service and Application Engineering, Absolute Machine Tools, Lorraine, Ohio; Craig Adorni, Application Engineer, Absolute Machine Tools; and Senior Sales Engineer/MTI Rich Ford, Kennametal Inc., Pittsburgh, gave an overview of choosing the right cutting tool and cutting Data to deal with the challenges of low-carbon steel processing. Information about the correct cutting tool, insert geometry, processing speed and feed for the application can be accessed online at Kennametal’s engineering calculator or its NOVO proprietary cutting tool database.
Adorni pointed out obvious problems with drilling and chip breaking. "When you drill a hole and chips start to appear on the tool and the tool holder, you can't let those chip balls get in the way, so you need to make sure you break the chips."
Zunis said that if the chip is not damaged, then automation will definitely have an impact. "If the drill or tap leaves a pile of chips, they may prevent the robot from grasping the part," he said. "The best milling application will produce a kind of potato chips that look like popcorn, like small six or nine points you can hold in your hand. It will be small potato chips flying around like popcorn; they It is not connected to each other, nor is it like a long rope.
"But in the case of mild steel, you might end up with an eagle's nest-like chip, wrapped around the drill bit and thrown anywhere," he continued. He pointed out that under normal circumstances, the airflow cannot move the chips away-the chips need to be broken. This can be achieved by increasing the feed rate or changing the geometry of the blade so that the chips will fall off in small pieces, "basically making the chips explode," he said.
Running at a higher feed rate seems attractive. "But customers are usually afraid to run new machines at the proper feed rate because they are'old school' and are used to running machines too slow, which usually produces long chips," Adorni said. "However, if you can increase the feed rate... you are likely to break the chips. Some machinists do not consider the new technologies of CNC, blades and tools. These technologies are designed to or When developing a tool, you can break or break the chip. However, if you can’t get there and you don’t use the tool geometry as expected, you will get a large, long chip that can cause problems with the tool changer ."
The new tool technology provides a better way to deal with these steel grades. According to Sandvik Coromant of Fair Lawn, New Jersey, it has introduced a new cemented carbide grade-GC4415/GC4425 , With second-generation Inveo coating. The new material can provide ISO shapes and proprietary groove inserts, suitable for mass and mass production of low-alloy and non-alloy steels.
“The new material 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 reliable and efficient processes for steel turning applications, because these materials perform well in both roughing and finishing applications and have tool life. An increase of 25%. The new matrix also enables GC4425 to perform well in interrupted cutting applications where other P25 inserts may be difficult to handle. All of these provide our customers with better performance and tool life."
According to Brake, in all machining applications, having controlled chips is essential. This is especially difficult in softer, more viscous materials (such as low carbon steel). "Uncontrolled chips can cause premature blade failure, scrap parts, and worst of all, cause employee injuries. Sandvik Coromant has a variety of chipbreaker geometries. For this type of application, the first thing that comes to mind is " LC". This type of chip breaker combined with appropriate cutting data can produce excellent results.
"For customers who want to increase productivity, we also released new materials for the CoroTurn Prime series," he continued. "PrimeTurning is not a new technology, but we have noticed a significant improvement in tool life and consistency with new steel turning materials, most notably the 4425 CoroTurn Prime'B' insert. When using CoroTurn Prime, the roughing cycle is reduced 30% is not uncommon.” He also said that CoroTurn Prime can create radii and square shoulders without any auxiliary tools.
Sandvik Coromant has documented a case study of its GC4425/GC4415 inserts, "In many steel turning applications in many different materials, this grade has just been released," Brake said. "The automotive and general engineering departments can make good use of the new grades, but these grades are not limited to these areas. If you are turning steel, GC4415 and GC4425 will provide improvements."
Another problem with the stickiness of mild steel is that it tends to produce built-up edge (BUE) on the tool. According to Randy Hudgins, national product manager for turning and threading, Iscar USA, based in Arlington, Texas, used several different methods to solve this problem. Iscar's Sumo Tec surface treatment makes the top of the blade smooth, making it easier for the material to slip through the blade and preventing BUE. In addition, Iscar has recently developed a series of new chip conveyors for steel processing from heavy cutting to finish cutting.
"An important help for our customers is the nomenclature of our chip forming machines," Hudgins said. "It enables the end user to easily identify and select the correct chip forming machine. For example, let's take a dash M3P chip forming machine. The first letter M represents the media application, 3 represents the standard media feed rate, and the last P represents the material (Steel). Iscar until F1P, F means finishing, 1 means low feedrate, and P means steel."
Chip control is very important in mass production industries such as automobiles. Automobiles use low-carbon steel to manufacture transmission shafts, steering shafts, and various shafts. Why? The automotive industry relies on the use of a large number of robotics and cannot afford to stop production due to the removal of chips in the machine. According to Hudgins, this is especially true during long consecutive turns.
"We encountered various production machines for turning mild steel parts, including multi-spindle, dual-spindle and multi-spindle machine tools, as well as Swiss-style and CNC automatic lathes," he said.
As an alternative to traditional ISO turning inserts, Iscar has launched the CXMG Logiq4Turn product line, which doubles the cutting edge of positive rake inserts used in general turning applications. "This is an economical solution for 80° turning. It provides double-sided four-edge inserts, which can be easily replaced with two-edge inserts. The dovetail shape fits the unique groove design to ensure better insert positioning and stability, thereby ensuring better Long blade tool life," Hudgins said. "The tool holder can be with or without a cooling channel through the tool."
In addition, the operation of the new double-sided CXMG blade is similar to that of the CCMT positive blade and can replace the standard CCMT blade. In some applications, such as long shafts, the positive geometry of CXMG relieves 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 Tooling Inc. in Hoffman Estates, Illinois, agrees that low-carbon steel is challenging due to its stickiness in drilling and boring holes. "In my opinion, many companies believe that low-carbon steel is easy to machine. This is based on their success in hole-making tools, usually the drills and boring tools they buy from us. [However,] low-carbon steel Low tensile strength requires several factors in the tool geometry to be successful in drilling and boring. For the drilling depth, you really should direct the coolant with enough pressure to accurately guide the cutting to destroy the chips," Burley said .
For deep hole drilling, coolant is particularly important, for example in vertical deep hole drilling where chips must be removed. "The deep hole drill I'm talking about is four times the hole diameter," said Zunis of Absolute Machine Tools. "Usually, three times or less is considered normal, but if you want to machine 4 times, 5 times, or 6 times the chip diameter, you need to remove the chips from the hole. It is advantageous to use high-pressure coolant when drilling Yes, but if the feed rate is not enough, even the coolant will not help you break the chips. The feed rate, the depth of cut and the use of suitable inserts and tool holders are the main catalysts for chip breaking."
According to Burley, BIG Kaiser offers different types of drills, including carbide drills, spade drills and indexable drills. "However, in the case of indexable bits, the feed required to break the chips is very high and may exceed the capacity of the equipment," he added.
The same is true for the welding parts of agricultural and construction equipment and mechanical frames that usually use mild steel. "The way the metal comes out of the foundry is usually not very pure, so you have to deal with a lot of fragments in the material, which can be difficult to process," Burley said. "In these areas, this is double trouble, because when you look at the manufactured parts, you are putting holes into large thin-walled workpieces, which don’t have a lot of structure behind them. When you start pushing the weldment or the frame, it creates A little bit and rebound, which is very difficult on drills or boring tools, especially when roughing. Over the years, what we have done is to study different methods of handling such parts and holes, including rounding particularly large holes Milling."
According to Burley, boredom is a different story. As the holes of fabricated weldments become larger, the workshop will no longer use drills, but will burn the holes instead of drilling. Instead, use double cutters, square blades and double hole balanced cutting to drill holes. It is difficult to ablate holes in tools and machines, but with the right tools, the right feed and speed, and the right blades, the workshop can be applied very effectively.
"Fine diamonds themselves pose special challenges," he said. "When the depth of cut is less than 0.020" [0.508 mm], the chip is almost impossible to break, it will begin to wrap around the tool like a shoelace, in terms of surface finish and the tool's ability to accurately drill holes. When you try to use different speeds and feeds and apply coolant, you will end up with a higher feed rate and heavier cutting depth-all these factors combined, are not conducive to a higher surface finish and Tighter tolerances. "
Last year, BIG Kaiser introduced a unique chipbreaker for fine boring mild steel. "These inserts can be used with our ELM geometry as low as 0.008" [0.2032 mm] nose radius," Burley said. With 0.010" [0.254 mm], we can still coil the chips nicely and allow the chips to escape from the hole. Not so troublesome. "