New coatings and geometries are paving the way for previously unattainable peak performances during grooving and parting off operations. Their properties combine an exceptionally high level of toughness and wear resistance – something which is hugely advantageous in parting off operations. Walter AG is a company that possesses the range of products for these applications, which both seeks to improve process reliability and enhances tool life.
Grooving and parting off are types of turning operations which place unique demands on tools as a result of the conditions during machining. The company became seriously involved in this area a few years ago and has been able to use its experience in the field of cutting tool material development to integrate its innovative strength into other aspects of carbide tools.
The result of recent successful development work is a new tool family for grooving and parting off with specially developed geometries and carbide cutting tool materials. Here the carbide substrate and the coating produce the carbide grade. "Through further development, Walter has succeeded in enabling a further increase in the high-temperature wear resistance of PVD aluminium oxide coatings without compromising the toughness of the cutting tool materials", explains Gerd Kussmaul, Senior Turning Product Manager at Walter AG. The hardness of the optimised aluminium oxide is higher than its predecessor, which marks a significant improvement in wear behaviour. The friction on the rake face is lower thanks to an optimised surface structure, which in turn means a lower frictional temperature.
The Walter Tiger•tec Silver PVD cutting tool material has proven that wear resistance and toughness are not a contradiction. The Al2O3 layer functions as a protective heat shield and is characterised by a low thermal load for the micrograin carbide substrate. The inflow of heat into the carbide is also lower than in comparable products as a result of the Al2O3 layer. The silver indicator layer makes it easy to identify worn and unused cutting edges. This ensures that all cutting edges are used to optimum effect. The micrograin carbide substrate produces an extremely high cutting edge quality. The highly precise microgeometry also guarantees a consistent tool life. The low coating thickness of the PVD coating enables a sharp cutting edge to be achieved. "The decisive advantage in practice is a result of the extremely consistent tool life", says Gerd Kussmaul.
Sharp and defined cutting edges
A quartet comprising four carbide grades for recessing, grooving and parting off operations forms the future PVD aluminium oxide product range. The designations are WSM13S, WSM23S, WSM33S and WSM43S. These are universal cutting materials which are used primarily in the area of ISO-P, ISO-M and ISO-S materials. As a result of their distinctive hardness, cutting materials WSM13S and WSM23S are suitable for use under stable machining conditions, and particularly for ISO-S materials. The WSM23S is the universal cutting material for 50 percent of applications and for users who work with a wide variety of materials. The WSM43S cutting material is the first choice for unstable clamping arrangements, low cutting speeds when parting off to centre and interrupted cuts due to its excellent toughness properties. This means that the optimum carbide grade is available for every application.
When used in connection with the new parting off geometries, all four cutting materials offer a high level of performance and tool life, and essential process reliability when grooving. Particularly sharp and defined cutting edges can be achieved because the coating technology used has a low coating thickness.
Geometries ensure maximum precision
The good performance of cutting inserts is achieved by combining the carbide grades with the three CF6, CF5 and CE4 geometries specially designed for parting off. The CF6 geometry - "The sharp one" - is characterised by minimal burr and pip formation and is particularly suitable for small diameters and thin-walled tubes. The CF5 geometry - "The positive one" produces low burr and pip formation, covers the widest chip breaking area and is recommended as the first choice for parting off operations. The CE4 geometry - "The stable one" - has a stable cutting edge and features excellent chip contraction. All three geometries are available in a right-hand and left-hand version with a main cutting edge incline of 6 deg, 7 deg and 15 deg.
Unique 4-point clamping with parting blades
Depending on the machine type and machine adaptor, users require a range of different tools. "It is in this area that the new Walter Cut GX System is leading the way in precise parting off operations". During parting off operations, a distinction is made between small (diameter up to 12 mm), medium (diameter up to 40 mm) and large (diameter up to 110 mm) workpieces. The range comprises four tools and previously unseen innovations.
The G 1042 deep parting blade has an optimum insert seat design and features 4-point clamping. "The 4-point clamping principle is unparalleled when it comes to parting blades and generates a higher level of stability", explains Gerd Kussmaul. The self-clamping system is easy to use. The reinforced G 1041 parting blade features screw clamping and is available for both right-hand and left-hand tools as well as for a contra version.
The G 1011 monoblock tool is suitable for grooving, parting off and recessing. It has a low tool head height for easy chip removal and its clamping screw is accessible both from above and from below. The new XLDE monoblock tool provides easy access to the clamping screw, is available as a contra version and is ideally suited to small part production and the bar turning industry. "I use the XLDE monoblock tool primarily in multi-spindle machines and Swiss type auto lathes since there is only limited space available in the machine room", explains Gerd Kussmaul. "The clamping screw is inclined and facilitates simple insert replacement without having to remove the tool from the machine. This particular property helps to increase productivity."
The Walter Cut GX System was essentially developed for grooving, parting off and recessing, for all types of lathe. A cutting depth of up to 23 mm can be achieved during grooving operations with a diameter of up to 46 mm during parting off operations thanks to the double-sided cutting insert. Grooving and parting off to a considerable cutting depth using the same tool are also possible with a single-sided cutting insert.
"The key advantage of the new tool technology for grooving and parting off is the fact that it is a grooving system for all grooving applications and all standard tool types for grooving and parting off", says Gerd Kussmaul, summarising the properties of Walter Cut GX.
The high level of performance when using the new grooving tools can be demonstrated using the example of parting off a ball bearing race from workpiece material 100Cr6 (1.3505). "Here we are using cutting insert GX16-1E200N020-CE4 WSM33S - Walter Tiger•tec Silver - to achieve a tool life of 950 components, which is 111 percent higher than our competitors can offer", boasts Gerd Kussmaul. "As such, machining with the Walter product is characterised by a more consistent tool life, improved flatness of parted surfaces and excellent chip control." The G1011 monoblock toolholder was used as the tool. The entire system (tool, carbide grade and geometry) ensure maximum process reliability. "It is the unique development of a complete tooling system, that is to say tool holder, geometry and cutting tool material, that distinguishes us from other competitors on the market. Everything produced features state-of-the-art technology."
Additional information: Parting Off Bar Stock
It is essential to note during parting off operations that the tool should be as rigid as possible. The shank cross-section should be as large as possible, while the cutting depth should be as low as possible. This prevents vibrations which can have a negative impact on the quality of the tap and on the achievable tool life. In order to save material, the parting off should be as narrow as possible. This will also minimise cutting forces. Depending on the tool type, the ratio between the insert width and the cutting depth should not exceed 1/8, i.e. in the case of a 2 mm wide cutting edge, a maximum diameter of 32 mm should be parted off. The parting off operation should be performed as close as possible to the chuck or collet in order to prevent unnecessary vibrations.
One particular challenge faced by the parting off tools is the fact that when the maximum machine speed is reached, the cutting speed diminishes and decelerates down to zero in the centre. It is also no longer possible to access the coolant or lubricant in the cutting zone, which means high thermal and mechanical loads on the cutting edge. It is recommended that the parted off parts are tapped, since a component falling off and the wobbling that precedes this can damage the corners of the cutting insert, thus resulting in a fluctuating tool life which cannot be reproduced.
Parting off operations should always be performed with neutral cutting inserts wherever possible. The use of inclined cutting inserts does indeed reduce burr and pip formation, but at the same time has a negative impact on the tool life of the cutting sets and the quality of the parted off surface. It also has a negative influence on chip formation. In order to achieve particularly low burr and pip formation, it is possible to revert to ground cutting sets without corner radius.
