How to choose a turning tool for thermal spraying workpieces?

01 August 2022
Thermal spraying are widely used in metal surface strengthening, workpiece after thermal spraying, the surface hardness can reach 50 to 55 HRC, general high up to 70 HRC, and most of the coating on the surface of the demand is higher. the surface after spray to cold working, some large machining allowance or restricted to large cylindrical grinding machine equipment, often used in car generation grinding machining method.
1. The type of thermal spraying materials 
(1) Types of thermal spraying materials:
Thermal spraying commonly used spraying powder including nickel base, iron base and cobalt base alloy powder, according to different coating hardness, respectively applied to repair and protection of mechanical parts; 
Spray thickness can be from 0.01 to a few millimeters; The hardness is generally above 50HRC.
General machining allowance and spraying thickness can be used for grinding; On the contrary, instead of grinding car is an economic choice.
CBN Inserts
2. Tool selection for turning thermal sprayed workpieces
(1) When the hardness of the thermal spray coating is less than HRC45, the carbide tool material can be selected. The commonly used grades are YS30, YG3X, etc., and the line speed can be selected as νc=40 m/min.
(2) When the hardness of the thermal spray coating is greater than HRC45, ceramic or CBN cutters can be used; ceramic cutters and welded composite CBN cutters are often used in finishing due to their poor impact resistance (the cutting depth is preferably within 0.3mm).
(3) When the hardness of the thermal spray coating is greater than HRC55, CBN tools can have better tool life and processing efficiency.
Ceramic Inserts
3. Cutting parameters of the tool
(1)When using carbide cutting tools, the cutting depth is usually aO=0.15~0.6mm. The higher the hardness of the surface layer, the smaller the aP should be. aP=0.05~0.1mm during fine turning.
The feed rate is generally taken as f=0.1~1mm/r, and f should be smaller during fine turning.
The first speed is generally selected according to the hardness of νc=40 m/min; when the hardness of thermal spraying is HRC45-65,choose the carbide tool and the linear speed is better at νc=10 m/min.
(2)When using ceramic cutting tools, the cutting depth is generally controlled within 0.2mm, and the feed rate is about 0.1mm/r; however, the linear speed can be increased to about 3 times that of the original cemented carbide.


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