Case Analysis and Optimization

Introduction

In the modern precision machining industry, Powder Metallurgy High-Speed Steel (PM HSS) is a critical material for tool manufacturing and high-precision part processing due to its outstanding wear resistance and high hardness. However, due to its material properties, achieving high-precision surface processing has become a key research challenge in the industry. Ceramic bond CBN grinding wheels, as superhard abrasives, offer an important solution to this problem. This case study focuses on the use of ceramic bond CBN grinding wheels to grind PM HSS, aiming to achieve the target surface roughness of Ra0.1μm.

1. Workpiece Material and Equipment Parameters

(a) Workpiece Material

The workpiece for this case study is powder metallurgy high-speed steel, which has a hardness of 64-66 HRC. This material is classified as a high-hardness, difficult-to-machine material, requiring highly advanced processing techniques and tool performance.

(b) Processing Equipment

A high-precision CNC grinding machine was used for the processing, which provides precise motion control and stable processing performance, ensuring the foundation for achieving precision grinding.

(c) Grinding Wheel Selection

Ceramic bond CBN grinding wheels were selected for this operation, with 800# and 1200# grit sizes chosen. The 800# grinding wheel was used for rough and semi-finish grinding, while the 1200# wheel was intended for finish grinding, aiming to achieve the desired roughness by combining different grits.

2. Grinding Process and Results

(a) 800# Grinding Wheel Results

When using the 800# ceramic bond CBN grinding wheel, the actual surface roughness achieved was Ra0.2μm. Both the grinding efficiency and wheel lifespan met the customer’s expectations. Although the surface finish was acceptable, it still fell short of the target Ra0.1μm, indicating that the 800# grinding wheel had limitations in further reducing surface roughness.

(b) 1200# Grinding Wheel Results

Upon initial use of the 1200# grinding wheel, after correction, the wheel showed good grinding results with an ideal surface finish. However, as the grinding continued, the grinding wheel started to experience “grinding failure” during the processing of the second part. Ultimately, the surface quality did not meet expectations, and the actual roughness was also Ra0.2μm. This indicates that while the 1200# grinding wheel initially performed well, it experienced stability issues during prolonged grinding.

3. Problem Analysis and Solutions

(a) Problem Analysis

Upon in-depth analysis, it was found that the main issue with the 1200# grinding wheel was its high hardness. When grinding high-hardness materials like PM HSS, the high hardness of the grinding wheel caused the cutting edges to quickly become dull, losing their cutting ability. Moreover, the high hardness of the wheel led to significant heat generation and friction during grinding, accelerating the wheel’s wear rate and affecting processing accuracy and surface quality.

(b) Solutions

• Reduce the Wheel Hardness: By lowering the hardness of the CBN grinding wheel, its cutting ability can be improved. A softer wheel allows for micro-fracturing of the cutting edges, forming new, sharp cutting edges, reducing grinding heat and friction, and thereby improving processing accuracy and achieving a finer surface roughness.
• Increase Grit Size: Consider using a coarser grit size. A coarser wheel provides larger abrasive spacing and better chip removal capabilities, enhancing the cutting ability of the wheel while reducing heat accumulation and preventing the grinding wheel from stalling.
• Adjust Equipment Parameters: The customer should fine-tune the CNC machine’s parameters, such as cutting speed and feed rate. Proper matching of cutting speed and feed rate will optimize the force and heat distribution during grinding, improving grinding performance and surface quality.

4. Advantages of Ceramic Bond CBN Grinding Wheels

Ceramic bond CBN grinding wheels have become increasingly popular in metalworking, especially for grinding hard materials. Their key advantages include:

• High Hardness and Wear Resistance: CBN (cubic boron nitride) has a hardness second only to diamond, making it ideal for processing high-hardness materials. Its excellent wear resistance ensures stability and durability during long-term grinding operations.
• Heat Resistance: Ceramic bond materials have excellent heat resistance, which effectively prevents thermal damage during high-temperature grinding. This ensures that the wheel maintains its shape accuracy and grinding performance even in high-heat environments, extending its lifespan.
• Precision Grinding Capability: Thanks to high-precision manufacturing and stable performance, ceramic bond CBN grinding wheels are capable of achieving micron-level surface roughness control, making them ideal for high-precision part processing in the precision machining industry.

5. Conclusion

This case study on grinding powder metallurgy high-speed steel highlights the significant impact of the grinding wheel grit, hardness, and equipment parameters on grinding performance. In practical applications, selecting the appropriate grinding wheel specification and optimizing processing parameters are key to achieving high-precision, high-efficiency grinding. Moving forward, Moresuperhard will continue to refine grinding technologies and optimize products and services, providing customers with better, more tailored grinding solutions to help the precision machining industry reach new heights.