Knowing how to sharpen knives is a crucial skill for anyone working with grinding tools. Understanding the basics of the materials, grinding machines, grinding wheels, and what parameters to look for during the operation is essential for achieving quality results. This guide will walk you through these fundamental aspects of knife sharpening.
I. Materials Used in Manufacturing
Common materials used in knife manufacturing and sharpening include High-Speed Steel (HSS), Powder Metallurgy High-Speed Steel (PM-HSS), Cemented Carbide (HM), as well as super-hard materials like PCD and CBN. HSS tools are known for their sharpness and good toughness, while HM tools exhibit high hardness but lower toughness. It's important to handle HM tools with care due to their susceptibility to chipping.
II. Grinding Machines
Given the hardness of knife materials, grinding is typically the method of choice for altering their shape. Common types of grinding machines used in manufacturing and sharpening include:
1. Groove Grinder: Used for grinding grooves or backs of tools like drill bits and end mills.
2. Point Angle Grinder: Specifically designed for grinding the conical point angles of drill bits.
3. Side Edge Grinder: Used to correct the side edges of drill bits.
4. Manual Universal Tool Grinder: Suitable for various tasks like grinding outer circles, grooves, backs, point angles, side edges, flat surfaces, and front cutting surfaces. This is commonly used for tools with complex shapes and in cases where quantities are limited.
III. Grinding Wheels
1. Abrasive Grains
Different types of abrasive grains in grinding wheels are suited for different tool materials. The size of the abrasive grain used depends on the specific part of the tool to ensure the optimal combination of edge protection and processing efficiency.
- Aluminum Oxide: Used for grinding HSS tools. It's cost-effective and can be easily shaped to suit complex tool profiles.
- Silicon Carbide: Used for dressing CBN and diamond wheels.
- CBN (Cubic Boron Nitride): Used for grinding HSS tools. Although more expensive, it's highly durable.
- Diamond: Used for grinding HM tools. It's costly but highly durable.
2. Wheel Shapes
Different wheel shapes are used to facilitate the grinding of various parts of tools. The most commonly used shapes include:
- Parallel Wheel (1A1): Used for grinding top angles, outer diameters, and backs.
- Dish Wheel (12V9, 11V9): Used for grinding spiral grooves, main and secondary cutting edges of milling cutters, and side edges.
- After a period of use, grinding wheels may need to be reshaped (including the flat surface, angles, and corner radius R). Regular cleaning to remove debris from between abrasive grains is essential for maintaining grinding efficiency.
1. Name Definitions
In the context of cemented carbide drill bits, the process of blunting the cutting edge is referred to as "reversing the edge." The width of this reversal is related to the material being cut and typically ranges between 0.03-0.25mm. Chamfering the edges (at the tip) is referred to as "reversing the chamfer."
In the case of end mills, the cutting edge on the peripheral surface is the main cutting edge, while the one on the end face is the secondary cutting edge.
2. Differences between HM and HSS Drill Bits
- HSS Drill Bits: Typically have a point angle of 118 degrees, sometimes exceeding 130 degrees. They have sharp edges and have relatively lower precision requirements.
- HM Drill Bits: Generally have a point angle of 140 degrees. Straight flute drills are often 130 degrees, and three-edge drills are typically 150 degrees. Their edges and tips (at the corners) are not sharp and are often blunted, known as "reversing the edge" and "reversing the chamfer." They have high precision requirements, and their side edges are often shaped into an S-form to aid chip breaking.
V. Sharpening Guidelines
1. Proper selection of grinding wheels (type and model).
2. For new tools, measure key geometric parameters and keep records, especially regarding the reversal, chamfer reversal, and side edge corrections of drill bits.
3. Input grinding wheel data before entering tool data.
4. After sharpening, measure the main parameters and make corrections after comparing them with the sharpening standards.
By following these sharpening techniques and guidelines, you'll have the knowledge to improve your knife grinding skills and increase the quality and consistency of your product output.
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