The passivation of tool edges is an under-appreciated but important issue. It is important because:The passivated tools are effective in improving edge strength, tool life and stability of the cutting process.

We all know that the tool is the “teeth” of the machine tool, the main factors affecting the cutting performance and tool life, in addition to the tool material, tool geometry parameters, tool structure, cutting dosage optimization, etc., through a large number of tool edge passivation experiments show that: a good edge type and edge passivation quality is also the premise of the tool can be faster and better for the premise of the cutting process.

What is passivation of the cutting edge of a tool?

Tool passivation is a process whereby a tool or insert is deburred, flattened, and polished after fine grinding and before coating, in order to improve tool quality and extend tool life.Its name is not yet standardized both domestically and internationally, but it is called “Edge Passivation”, “Edge Strengthening”, “Edge Honing”, “Edge Preparation” or “ER (Edge Radiusing) Processing”.

Why do I need to passivate my tools?

The cutting edge of a tool sharpened by ordinary grinding wheels or diamond grinding wheels has different degrees of microscopic notches (i.e., tiny chipping and notching). The former can be observed with the naked eye and ordinary magnifying glass, and the latter can be observed with 100 times (with 0.010mm scribe line) microscope, and the microscopic notch is generally 0.01-0.05mm, and the serious one is as high as 0.1mm or more.During the cutting process, the microscopic notch on the cutting edge of the tool is very easy to expand, which accelerates the wear and damage of the tool.

Modern high-speed cutting and automated tooling machines put forward higher requirements on tool performance and stability, especiallycoating tools must be passivated before coating in order to ensure a strong coating and a long service life.

Purpose of tool passivation

The purpose of passivation is to solve the defects of microscopic notches on the cutting edge of the tool after sharpening, so that the sharpness can be reduced or eliminated, and to achieve the purpose of smoothness, sharpness, durability and flatness.

Common Edge Forms

Sharp Blade

【Sharp Edge】 The tax edge formed naturally by the intersection of the front and back surfaces of the blade before and after sharpening, with a sharp edge, poor strength, and easy to wear. Generally used for finishing tools.

chamfered edge

【Chamfering Edge】 A very narrow, negatively angled edge is sharpened on the front face near the cutting edge, which greatly improves the strength of the cutting edge. Used for roughing and semi-finishing tools.

Vibration-dampening edge

【Vibration-dampening edge】A very narrow, negatively angled edge is sharpened on the back face near the cutting edge to increase the contact area between the tool and the workpiece during cutting and to eliminate vibration during the cutting process. It is used as a single-edged tool when the rigidity of the process system is insufficient.

Naked Edge

【Naked Edge】A narrow edge or strip with a 0° back angle is ground on the back face near the edge, which can play the role of supporting guidance and extrusion finishing, and is used for reaming knives, broaching knives and other multi-flute knives.

Inverted Blade

【Inverted Blade】Sharpening or passivating the rounded corners on the counterparts to increase the strength of the cutting edge and improve the life of the tools, which are used for all kinds of roughing and semi-finishing indexable tools.

Blunt cutting edges

The geometry of the passivation of the cutting edge has a great influence on the tool life: one is a rounded edge and the other is a waterfall edge.

Rounded Edge

Waterfall edge

【Rounded Edge】Forms a symmetrical arc at the corner of the cutting edge, which is used in more than 80% of tools for roughing and finishing.

【Waterfall edge 】The ratio of top surface to side surface at the corner of the cutting edge is generally 2:1, which is an asymmetric arc for severe impact machining.

Main effects of tool passivation

Rounding of cutting edges: Remove burrs from cutting edges and achieve accurate and consistent rounding.

Edge burrs cause tool wear and the surface of the workpiece becomes rough. After passivation, the edge becomes smooth, chipping is greatly reduced, and the surface finish of the workpiece is improved.

Uniform polishing of tool grooves improves surface quality and stock removal performance.

The flatter and smoother the surface of the groove, the better the chip evacuation, and the higher the cutting speed can be realized. The improved surface quality also reduces the risk of the tool seizing up on the material being machined. It also reduces the cutting force by 40% for smoother cutting.

Selection of passivation parameters

Through the development and production of passivation machines for insert blades, some preliminary rules have been learned. It is very important to select the edge type and passivation parameters for different machining conditions. Due to the different materials of inserts and different machining conditions, the parameters of the selected edge type and passivation shape are also different, otherwise the expected effect of extending the tool life will not be achieved. See the following table for recommended parameters:

Compared with the foreign edge passivation parameters, 70% of the passivation value of the tool is between 0.0254-0.0762. The maximum value: 0.127-0.2032mm. Maximum value: 0.127-0.2032mm Minimum value: 1/6 of a hair 0762mm, i.e. 0.0127mm Even with such a small passivation, the cutting edge of the tool is significantly strengthened.

Experience from a large number of passivation practices confirms this:

1）A sharper edge is not necessarily better, nor is a duller edge better.The best passivation values are determined for different processing conditions.

2）Edge passivation, in combination with edge profiling, is the most common and effective measure to improve edge strength and increase tool life and reduce tool costs.

3）Sharpening negative chamfers with micronized grinding wheels with small micro-notches (up to 0.005-0.010mm) and small passivation parameters (0.010-0.030mm) results in sharp and durable cutting edges.

Polishing of coatings

Removes protruding droplets produced after tool coating, improves surface finish, and increases lubricant adsorption.

The surface of the coated tool produces tiny protruding droplets, which increase the surface roughness, making the tool prone to greater frictional heat during the cutting process and reducing the cutting speed. After passivation and polishing, the small droplets are removed and many small holes are left behind, which can absorb more cutting fluid during machining, resulting in a great reduction of the heat generated during cutting and a great increase in cutting speed.