EN
Tool steels used for molds in modern industries, like injection molding, die casting, stamping and forging, require both hardness and wear resistance to cope with stringent demands in their service. After heat treatment, tool steels used for mold making usually reach the hardness of 58-62 HRC, which makes them wear resistant yet hard to machine. The challenges of efficiently grinding hardened tool steels while keeping tight tolerances and fine surface finish are perennial problems for mold makers. Ordinary aluminum oxide wheels used for this application are fast in consumption, generate more heat and often require a number of dressing operations. Cubic Boron Nitride (CBN) wheels from Zhengzhou Ruizuan Diamond Tool Co., Ltd. actually offer effective solutions for both roughing and finishing operations on hardened tool steels.
Roughing Hardened Tool Steels with CBN: High Material Removal
Roughing operations on hardened molds primarily aim at removing bulk material as fast as possible while keeping any thermal damage on the workpiece to a minimum. Under heavy load, ordinary wheels are rapidly worn and dulled due to the high abrasive forces in the contact zone, causing the wheels to be overloaded, require high spindle power and eventually lead to surface burn or re-hardened conditions on the workpiece.
CBN's unique inherent hardness (second to diamond) guarantees that CBN abrasives can maintain sharpness even in demanding roughing conditions. Ruizuan metal bonded CBN wheels are specifically designed for high material removal grinding operations on tool steel workpiece hardened to 65 HRC. This means the metal bond effectively fixes the hard CBN grains while allowing them to cut, rather than rub the surface. The forces and power are reduced, while significantly more heat is removed from the cutting area than is generated. For the typical work removed (0.5-1.0 mm), Ruizuan CBN wheels can finish this task in roughly half the time of ordinary grinding wheels.
Finishing Operations: Achieving Mirror Surface Finishes
The final surface finish requirement on mold cavities, typically Ra 0.2–0.4 µm or finer with tight tolerance of 0.005 mm, cannot actually be achieved in any reasonable time with conventional abrasives, which need numerous dressing steps to maintain the intended form and profile over large work surfaces.
Ruizuan resin bonded CBN wheels with a fine grit size (B91, B76, B64) offer superior mirror finish to hardened tool steels. The soft cutting action of the resin bond produces fine surface finishes while reducing surface stress and subsurface damage. Thanks to consistent abrasive wear characteristics of CBN, the surface finish can be maintained relatively constant on large surface area within the same dressing. The stable bond structure allows long-duration finishing operations. In real mold finishing grinding, Ruizuan CBN wheels have repeatedly achieved Ra 0.2 µm finish without requiring secondary polishing operations.
Thermal Stability and Surface Integrity Protection
Tool steel molds are extremely sensitive to thermal damage during grinding. The heat generated will induce surface burn, re-tempering, re-hardening and residual tensile stress. These anomalies can ultimately affect the life span of molds, cause fracture and wear.
The extremely high thermal conductivity (1300 W/m:K) of CBN quickly dissipates the grinding heat away from the workpiece surface and into the wheel body and coolant. Ordinary abrasives trap the heat on the workpiece surface rather than transferring it. Zhengzhou Ruizuan carefully selects the grit size, concentration, and bond type ofCBN wheels to effectively reduce heat generation. With Ruizuan CBN wheels, even very sensitive tool steels can be ground with no risk of thermal damage; in some cases they can generate favorable compressive residual stresses to improve the mold fatigue resistance.
Cost Effectiveness and Productivity Gains
Compared with standard aluminum oxide and silicon carbide wheels, CBN wheels have a higher initial price, but the total cost of grinding hardened tool steel molds is significantly lower. A Ruizuan CBN wheel can grind thousands of mold components whereas the ordinary wheels can only produce a few hundred. Dressing operations are also significantly reduced, saving the mold maker substantial time for actual production. It is reported that switching to Ruizuan CBN wheels in one mold shop has reduced overall grinding costs by two thirds while productivity increased by 40%, with the rejection rate (caused by thermal damages) reduced by more than 50%. This represents a truly remarkable ROI.
Summary
Hardened tool steels actually used in molds demand both productivity and accuracy in their grinding operations. Zhengzhou Ruizuan Diamond Tool Co., Ltd. provides metal bonded CBN wheels for roughing of hardened tool steels and resin bonded CBN wheels for high-finish grinding applications, ensuring thermal stability, long wheel life, reduced costs and excellent part quality. With a reputation built since 2014, Ruizuan actually offers customized CBN solutions certified by CE, SGS, TUV, and ISO 9001. Contact Ruizuan for consultation on your mold grinding needs and trial our effective CBN wheels for tool steels.