Efficient machining of PCD tools with multi-function machines

As the use of lightweight metal materials in the automotive and aerospace industries is increasing, the demand for superhard tools (such as PCD tools) for cutting such materials is also growing. However, the grinding process of PCD tools is expensive, complicated, time-consuming and laborious, which restricts the promotion and application of such tools.

The PCD tool is made by welding the PCD composite tip to a carbide insert or a shank base. When manufacturing such tools, the PCD tip and the carbide substrate need to be machined separately on different machines. The cemented carbide substrate is generally processed by a conventional grinding process; the PCD composite sheet is processed by a discharge etching process (wire cutting or today's focus: discharge grinding).

In order to simplify the processing of PCD tools and improve production efficiency, multi-functional machine tools have been developed that can perform grinding and discharge corrosion processing on PCD and PCBN tools with complex geometries and ultra-clear surfaces on the same machine. The key to this high-efficiency, versatile machine tool is the optimization of the spark generator, allowing the operator to precisely control the spark discharge to avoid damage to the workpiece surface and improve the quality of the machined surface. . Another feature of this new processing system is the high-sensitivity probe, advanced control software and simulation software for easy automated machining.

Germany's Walter AG has developed a multi-function machine called Helitronic Power+Diamond. This five-axis machine can perform both conventional grinding of carbide and high-speed steel substrates, and discharge grinding of PCD composite sheets, and can be easily converted between the two processing methods. Thanks to the double-machining function of the machine, the machining of cemented carbide substrates and PCD composites can be done in one installation, which facilitates the entry of smaller tool manufacturing companies into the PCD tooling market. The machine has sufficient rigidity to minimize machine vibration and ensure that the discharge interval between the tool and the electrode is kept constant. Conventional grinding and discharge grinding can share the same coolant/insulation supply system.

The Swiss company Ewag AG has introduced a multi-function grinding machine called ewamatic. The machine can grind the cemented carbide substrate and discharge corrosion of the PCD composite sheet in one installation. This processing method avoids the multiple loading and unloading process of transferring the workpiece from one machine to another during the processing of the PCD cemented carbide tool in the past, thereby reducing the cumulative error caused by multiple clamping. The ewamatic multi-function grinding machine is modular in design and allows the operator to use a circular arc and a tangential end face of the grinding wheel to edge a tool with equal or unequal relief angles. An important feature of the machine is the use of a star-shaped grinding head with six independent shafts (up to 12 grinding wheels). Grinding of the outer surface, cutting angle and cutting edge of the tool can be completed by adjusting the working head. The machine can machine cylindrical or conical PCD cutters with diameters of 0.1 to 35 mm and straight or helical teeth.

Germany's Vollmer Werke Maschinenfabrik GmbH has developed the QWD755/760 series of five-axis horizontal CNC wire-cutting machines by studying the PCS tool EDM process technology. This series of machines enables continuous wire-forming of stepped tools, forming tools and other complex shaped tools. The electrode wire on the fifth axis (E-axis) of the machine tool is installed in a horizontal position, which overcomes the defect that the workpiece wire is difficult to be processed by the vertical installation of the wire electrode of the conventional wire-cutting machine. The horizontally mounted electrode wire can realize radial and axial walking. Silk, so the contours of stepped tools and other complex tools can be shaped. In the one-time clamping of the workpiece, the rotary working head (E-axis and A-axis) can be cut in a wide range of angles. The optimized and improved spark generator allows the operator to precisely control the output power of the electro-erosion process, resulting in a machined surface roughness of ≤ Ra 0.2 μm. The machines are also equipped with simulation software, process control software and optimization software. The tooling range of the QWD760 machine is between the top centerline and the QWD755 machine. The machine does not have a tailstock and is suitable for machining PCD tools with long toolholders.

The Lach-Diamant branch of Jakob Lach GmbH in Germany introduced the redesigned Dia-Profile discharge grinding machine at the Ligna exhibition in Hanover in May 2003. This eight-axis machine is equipped with a new type of spark generator and drive shaft motor, which can achieve better surface quality than wire cutting when machining PCD tools. When machining a PCD tool with a wire-cutting process, the PCD loses some of its conductivity after brazing, while grinding the PCD with a Dia-Profile machine maintains its conductivity, which is important for optimizing the machined surface quality of PCD tools. The Dia-Profile machine uses a small radius graphite wheel (or copper wheel) to perform a discharge corrosion process on a given tool profile. The working principle of the grinding wheel is very similar to that of a CNC lathe. It first corrodes the rough profile of the PCD tool. The grinding wheel is then trimmed and then finished and repeated until the PCD tool reaches the desired surface finish.