Innovation promotes continued growth in the hard-car processing market

The need for hardened parts is always ubiquitous. Market forces show that consumers always expect all products to be durable, from car engines to hardened wheel drive shafts. For machine shops eager to gain a competitive advantage, the goal is to optimize the manufacturing process for these parts. Traditionally, hardened parts are subject to the grinding process, but now more often, turning is becoming a more cost-effective and more popular alternative.

Why is this? There are many specific reasons. For example, since the hard part turning process is in principle similar to conventional "soft" turning, the use of the same CNC lathe or turning center provides true processing flexibility. In addition, if the part structure changes, it is easier to change on a lathe than on a grinding machine; the lathe runs faster and the running cost is much lower than the grinding machine; the chip generated by hard part turning is more than the residue generated by grinding To be more environmentally friendly; hard parts often require no coolant, which further reduces waste disposal and recycling costs; the investment cost of using a lathe is usually much lower than that of a grinding machine; the grinding machine requires more support equipment, such as balancers and Dresser; lathe tools take up less space than grinding wheels.

These and other reasons have contributed to the rapid spread of hard-car processing in all industrial sectors. At present, hard-car processing is most commonly used for processing post-heat treated parts with surface hardness ranging from 55 to 68 HRc, usually involving hardened alloy steel, tool steel, case hardened steel, superalloy, iron nitride and hard chrome coated steel. Understandably, there are obviously many hard-car processing applications in the automotive industry, including transmission gears, fuel injection pump nozzles, bearing races, steering gears, brake discs, axles, camshafts, valve seats, pistons and cylinder liners, to name a few. Not all. The challenge for the industry is to obtain the most cost-effective part surfaces when machining these hardened parts. New advances in knives and their applications have made machining shops profitable and are taking harder machining to a higher level through innovative blade materials, geometries, design, positioning and clamping. Machine tools play an important role in the field of hard machining, but there is no doubt that the machining capability of cutting tools is the decisive factor in the success of machining.

The finishing touch

Since most of the processes in the field of hard machining are finishing, this requires higher dimensions, shape and indication of finish tolerances. The first indicator of excessive tool wear is usually that these tolerances are reduced, so choosing the right cutting tool and the right application becomes even more important. Most hard-car parts require an accuracy of approximately 10-12 microns and a surface roughness requirement between Rz 0.8 and 6.3.

In general, the harder the material, the lower the cutting speed and the shorter the tool life. When the hardness of the part exceeds a certain limit, it is necessary to use a harder tool material. In the lower hardness range (45-50 HRc), harder carbides perform satisfactorily and provide good cost efficiency, but for the more common hardness range (55-65 HRc), carbide Materials are generally not a practical solution.

When the workpiece material hardness exceeds 55 HRc, the properties of the CBN cutting edge make it excellent in most applications. In addition, the CBN material has a good toughness range, which makes it not only very suitable for finishing processes, but also a good choice for roughing and continuous and interrupted cutting. In general, in order to meet the material requirements of the workpiece, the tool material is required to have a higher hardness, and in order to withstand the mechanical load and resist common material performance degradation (such as flank wear and blade gingival), the tool is required to be different. Degree of resilience.

Blade processing is beneficial

Cutting edge processing is critical to ensuring the success of hard machining. For example, the chamfer angle of the cutting edge has a considerable effect on its toughness. All inserts used for hard machining should be chamfered as this is an important feature for ensuring tool performance. The chamfer is determined by the width and angle, where the chamfer can be sharp or honed. There are many different types of chamfers currently available, but the honed S-shaped edge protects the edge lines from chipping and cracking. Similarly, the S-shaped cutting edge is better suited for interrupted cutting and greater depth of cut, making it the preferred choice for hard machining.

The cutting edge of the CBN insert contains three variables: chamfer angle, chamfer width and cutting edge radius. They all have an impact on the process, the part and the blade itself. The greater the chamfer angle, the more cutting force is directed to the blade, thereby enhancing the cutting edge. The result of this is a compressive force that is suitable for the properties of the brittle hard tool material. In addition, the correct chamfering of the cutting edge for the actual machining process also helps to eliminate the crater wear of the tool.

Sandvik Coromant has recently made significant progress in CBN materials, and these advances offer many ways to further reduce tool wear, improve cutting edge safety, extend application range, and achieve higher feed rates and cutting speeds. For example, CN7015 and CB7025 materials now offer different grooved tools with larger chamfer widths (0.15 and 0.2mm) and larger chamfer angles (30 and 35°), which perform very well in interrupted cutting. The CB7525 insert series also features a large chamfer with a width of 0.2 mm (honing edge) for demanding intermittent hard-car machining applications.

Sword slant

Many of today's manufacturers have adopted these innovative materials, including Arvin Meritor, a US-based manufacturer that produces heavy-duty automotive parts for trucks, trailers and specialty vehicles, such as many hardened power transmissions. System parts and brake parts. Here, the chamfering of the cutting edge on the CB7025 insert has a huge impact on the performance of hard part turning. Arvin Meritor wants to improve the light roughing of gears, which are made of 8620 alloy steel with a skin hardened to 60-62 HRc, where shorter tool life often leads to many problems. The relevant dry cutting test was carried out on a Mori Seiki CNC lathe, which obtained 8 finished parts before the tool was changed (Arvin Meritor used a tool and passed the knife twice). However, after switching to the CB7025, Sandvik Coromant engineers recommended a double-cutting combination with roughing and finishing tools. The former roughs the inner diameter hole and the finished surface, while the latter only finishes the inner diameter.

The result is shorter cutting times and a five-fold longer tool life. Arvin Meritor now has more than 50 parts and is able to complete the entire batch before it needs to be replaced. In short, the solution allows the company to save more than $100,000 per year and more than 200 man-hours of production time per year. Now they have asked Sandvik Coromant to inspect all of its CBN processes on site.

CBN inserts offer potential cost savings and faster production cycles, making hard machining a veritable alternative to grinding. Because of the many commonalities between hard machining and standard turning, it is easily absorbed by most workshops. Coupled with the right machine tools, machining strategies and tool combinations, hard part turning can quickly increase the yield of a variety of small tolerance applications.

Self Drilling Screw

Self drilling Screw made of 410 stainless steel, high hardness (40 Rockwell C), steel process.