The machining of final contours is gaining importance
Journal : Werkzeug Technik, Edition 158 Subject area : Milling (with GeFo), AMB Author : Dr. Diethard Thomas, LMT Consultant Date : 10/6/2016
At the AMB in Stuttgart current trends such as digitized production, Smart Factory, additive 3D printing, resource and energy efficiency, and lightweight design with the related tool and material concepts took center stage as expected. But the traditional tool blade has not been forgotten. New geometries, cutting materials and coatings are the direct contact to the workpiece and are still govern quality, process reliability and, of course, production costs.
The optimum coating for every application (source : LMT Group)
Here, the machining of final contours - finishing - has gained particular importance. This applies especially to components with surfaces which perform an important function, such as workpieces used in die and mold making. Here, the smallest of surface defects can have a direct impact on the final product, e.g. visual defects on body parts.
Roughing as a general pretreatment has not gone out of style. But this preliminary process started being replaced some time ago by near net shape technology and, more recently, by additive 3D printing.
The solid carbide HSCline SuperFinish4 copy mill produces maximum quality (source : LMT Group)
The latest milling tools in LMT Tools Group's large product portfolio can display the finishing potential possessed by innovative tools when it comes to a wide range of processes from the milling of hardened materials to the production of top grinding quality.
The FinishLine Premium generates grinding-quality surfaces (source: LMT Group)
High-performance coatings - the key to service life and precision
High-performance coatings have a fundamental significance for machining : The coating has the closest contact with the workpiece and is therefore primarily challenged by force and temperature influences. Coating systems thus have a substantial productivity potential. Consistent development of application-specific high-performance coatings is a core competence at LMT Tools.
The 8 - cutting edge inserts of the MultiEdge T90 PRO8 reduce tool costs (source: LMT Group)
The high-performance coating Nanomold Red was specially developed in the coating center at LMT Kieninger (image 1) for the finishing of cold and hot-working steel, cast steel and hardened materials up to 65 HRC. Its 4-layer coating structure ensures top-quality coating adhesion, while heat is kept away for as long as possible – evidenced by long service lives.
The application area of the Nanomold Gold coating is on the left side of the diagram (image 1). It is the first choice for roughing and semi-smoothening of materials in the lower hardness range.
Another innovative example is the new "Nanomold Black" coating, which was presented for the first time at the AMB trade fair in Stuttgart. It has a performance spectrum between the two established high-performance coatings "Nanomold Gold" and "Nanomold Red" and covers a more universal range of application. Nanomold Black is ideal for smoothening and semi-smoothening steel, cast steel and cast iron up to a hardness of 56 HRC and can be used for both wet and dry machining.
HSCline SuperFinish2 and SuperFinish4 - top-quality hard milling
In addition to process reliability, a high surface grade and long service lives are essential for high cutting speeds when it comes to finishing. The VHM copy milling cutter HSCline SuperFinish2 sets new standards in exactly these areas, especially in the finishing of hardened steel between 56 – 65 HRC. Due to its high-precision cutting edge geometry with an optimized cutting edge preparation, significant tool life improvements can also be realized.
The new copy milling cutter HSCline SuperFinish4 by LMT Fette (image 2) was presented for the first time at the AMB. It has 4 cutting edges with a special S-cut. Compared with the already established HSCline SuperFinish2 with 2 cutting edges, the processing time can thus be reduced even more whilst simultaneously increasing the service life. This is particularly useful when processing larger components with a long processing time.
Its high-precision cutting geometry with defined cutting edge preparation enables a productivity increase of up to 40%. The spiral angle of 30° and the carbide shaft reduce the tendency to vibrate. In addition, the high dimension accuracy enables a significant surface quality increase thanks to a narrow radius tolerance of +/- 5 µm. The tool can also be used for the finishing of hardened steel up to 65 HRC and for the finishing and semi-finishing of high-strength steel.
FinishLine Premium – grinding-quality surfaces
The FinishLine Premium program features a larger number of teeth for all diameters above 12 mm as well as a reinforced base body design and the high-performance coating Nanomold Red. With this tool, users have a milling system which can produce grinding-quality surfaces. The grinding process is substituted, and finishing time and costs are reduced.
Its performance can be demonstrated with a practical example. The surface of a die for the car industry was processed using the material 1.2379 (X160CrMoV12) with a hardness of 58 HRC. The screw miller with a diameter of 32 mm (image 3) was used for this process. The inserts have 1 mm corner radii, the tooth feed is ft = 0.1 mm, and the cutting speed is vc =140 m/min. The final milling result, with a surface roughness of Ra = 0.09 µm, is impressive.
Tangential insert position – highest metal removal rate
For now, preliminary roughing will, of course, remain relevant. For these applications, tangentially positioned inserts, for example, guarantee an extremely stable milling process and facilitate the highest possible metal removal rate during roughing. If the insert geometry also has a positive rake angle, this soft cut also protects machine performance and increases tool life. LMT Fette combined these two advantages in two of the shoulder milling cutters at the AMB and generates maximum steel and cast material roughing and semi-smoothening productivity with the MultiEdge T90 PRO4 and MultiEdge T90 PRO8 designs.
The inserts in the MultiEdge T90 PRO4 have 4 cutting edges and feature an especially stable geometry which is simultaneously soft-cutting, allowing maximum axial infeeds of ap = 11.5 mm to be achieved consistently, even with larger tooth feeds.
The special inserts in the MultiEdge T90 PRO8 (image 4) have twice as many cutting edges. This increases customer benefit thanks to increased efficiency due to further reduced tool costs. The highest axial infeed is ap = 10 mm with adapted tooth feeds. The inserts in the tool displayed are coated with Nanomold Gold (see image 1 as well).
Both tool designs have specific cutting material alternatives for machining steel or cast iron. The name MultiEdge does not stand for the highly-effective number of cutting edges per insert, however. It stands for the high number of teeth due to the close pitch. This means that the largest tool diameter of 160 mm still has 20 inserts. The diameter palette of these new milling tools starts at 50 mm.
Performance can be demonstrated with a practical example. Components (general mechanical engineering) made of GGG50 were machined with the MultiEdge T90 PRO8 with the diameter d1 = 100 mm, the number of teeth t = 12 and a tooth feed of ft = 0.35 mm. The metal removal rate and service life were more than tripled, and machining time and machine costs were reduced by 60%.