Grinding Quality of Negative Chamfering and Its Influence (Part 1)

Part1 Preface

The negative chamfering of the tool is usually to grind a negative rake angle plane with a width of about 0.1 to 0.2 mm at the cutting edge of the tool. By increasing the wedge angle of the tool to improve the strength of the tool, and optimizing the heat dissipation conditions of the tool, it can strengthen the cutting edge and make cutting. On the basis of a small increase in force, the durability of the tool is improved.

On a large number of carbide tools, ceramic tools, PCBN tools and various machine-clamped blades, the method of grinding negative chamfers is used to increase the strength of the blade.

In the previous articles, the author introduced the important role of negative chamfering on the cutting performance of PCBN tools, and successively introduced the influence of parameters such as the width, angle and even coating of the negative chamfering. Common important parameters are currently only left. The lower chamfer is passivated, and I can only temporarily press it because I haven't found a suitable paper.

In addition to these quantifiable parameters, in the actual production process, the impact of the grinding quality of the negative chamfer on the cutting performance of the tool is also very significant.

Part2 negative chamfering method

At present, the grinding of negative chamfering mainly relies on the imported CNC precision grinder for indexable tools and the ordinary grinder assisted by the special negative chamfering fixture.

It is generally believed that the quality of the negative chamfers ground by the CNC precision grinder is better, while the quality of the grinding by the special negative chamfering fixture assisted by the ordinary grinder is unstable, and may have the following adverse effects:

on the one hand

Causes problems such as sawtooth defects on the cutting edge of the tool and edges at the negative chamfer.

on the other hand

The surface of the negative chamfer shows different grinding marks of the grinding wheel.

Part3 test plan idea

3.1

test subject

This paper takes the tools obtained by two different grinding methods as the research object. The cutting performance of the tools ground by the special negative chamfer grinding fixture will be compared with that of the negative chamfer tools ground by the CNC precision grinder.

3.2

sampling phase

The quality of the negative chamfer mainly has a great influence on the initial wear of the tool. Therefore, when designing experiments to explore the influence of the quality of the negative chamfer on the cutting performance, the appropriate test parameters and the length of the cutting workpiece are selected by combining the wear curves obtained in the literature to ensure cutting. The process is in the initial wear phase.

03

Samples and Indicator Measurement Methods

In this paper, 2 negative chamfering fixtures with different principles are used to grind 6 PCBN negative chamfering tool samples, and the micron-level stereo microscope is used to obtain the image of the negative chamfer arc contour, and the tool tip is extracted, fitted and calculated with the help of MATLAB software. From the 2D contour data of the negative chamfer arc image, the overall negative chamfer arc at the tool tip and the arc of the negative chamfer at the actual cutting position (hereinafter referred to as the arc of the negative chamfer) are obtained.

04

Experimental procedure

By cutting and surfacing cobalt-based alloys, the influence of negative chamfering quality on workpiece surface roughness is qualitatively studied; with the aid of the overall negative chamfering and the radian of the negative chamfering at the actual cutting position, the effect of negative chamfering quality on workpiece surface roughness is quantitatively studied. The influence law of degree, tool wear and cutting force.

Part4 Cutting test design

In order to qualitatively and quantitatively explore the relationship between the quality of the negative chamfer and the cutting performance of the tool, the cutting performance test of the negative chamfering tool was carried out. 

The base material of the specimen is 316 stainless steel, and the surfacing layer is cobalt-based superalloy of Stellite Co12. The specific composition is shown in Table 1. The size is D165mm×250mm. .

The turning tool selects the DBW85 grade PCBN tool that has been ground negative chamfering by different devices. The radius of the tool nose arc is 0.8mm, the chamfering parameter is 0.2mm×-20°, the rake angle of the tool is 0°, and the clearance angle is 0°. When used with a special toolholder, the toolholder itself has a certain angle. When the tool is clamped on the toolholder for processing, it can meet the corresponding angle requirements. The MCLNR2020-12 toolholder was selected for the test. The actual working angle of the tool is shown in Table 2. 

The test cutting parameters are: cutting speed v=82.4m/min, feed rate f=0.1 mm/r, and back-cut amount ap=0.1 mm.

Experiments were carried out on a CA6140 lathe, with each tool cutting a 10mm length of workpiece material.

Dry cutting is used for cutting, YDGB-H05 piezoelectric quartz dynamometer is used to measure tool cutting force, YE5850B charge amplifier is used for signal processing and conversion, software Coinv DASP V10 is used to collect and process cutting force, TR200 surface roughness is used The measuring instrument measures the surface roughness after machining, uses the XSP-2C (60×) stereo microscope to obtain the appearance of the negative chamfer of the PCBN tool, and observes the wear condition and wear amount of the rake face and flank face of the tool after cutting. .

Part5 Test result index selection

Machining is mainly to obtain workpieces with surface quality that meets the requirements. Surface roughness is a parameter that directly reflects the quality of the workpiece. By measuring the surface roughness, the machining quality of the workpiece under different negative chamfering qualities can be known.

The cutting force in the cutting process is of great significance to the research of the cutting mechanism, and is closely related to the design and use of the tool, machine tool and fixture, and by detecting the cutting force during the cutting process of PCBN tools with different negative chamfering qualities, the cutting state of the tool can be understood. , Predict tool wear and workpiece quality.

Tool wear is an important indicator for measuring tool quality. By measuring tool wear after cutting, the influence of tool negative chamfering quality on tool life can be explored.

Article summary

Due to space limitations, in this article, we first use the negative chamfering manufacturing method to draw out its influence on the processing quality, and conduct an experimental design: it is planned to test the tools produced by the two manufacturing methods, and the surface roughness will be measured. , cutting force and tool wear as indicators to analyze the difference in cutting performance. The next article will reveal the conclusions and conclusions for everyone, so stay tuned.