High-efficiency and high-precision machining method for zirconia ceramic materials
1. ELID superfinishing
ELID is the abbreviation of Electrolytic Online Dressing Grinding Method. It applies a grinding wheel composed of metal bond and super-hard micro-diamond (or CBN) abrasive, and at the same time electrolytically sharpens the grinding wheel during the grinding process, so that the grinding wheel is always kept sharp, thus ensuring ultra-precision grinding under high efficiency conditions Therefore, it is an advanced method for mirror grinding of brittle materials (such as ceramics, glass, silicon and iron oxide, etc.).
The high material removal rate grinding of zirconia ceramic materials by ELID method can greatly reduce the grinding cost. When reasonable grinding wheel dressing parameters are used, the grinding force can be reduced by 1 to 2 times compared with the traditional grinding method, and the grinding force can remain almost unchanged during the continuous grinding process (Fig. 1), which is conducive to improving the Material removal rate and ensure the stability of machined surface quality.
ELID’s grinding wheel dressing steps are:
- 1) Reshaping the grinding wheel, using a 100# grinding wheel to hit the grinding wheel at 300r/min;
- 2) Mechanical trimming, trimming with 400# Al2O3 grinding wheel at 300r/min;
- 3) Electrolytic pre-trimming, electrolytic trimming at 300r/min and 90V for 30min;
- 4) ELID trimming in grinding process, voltage 60V, current IP=6A, circuit closing and disconnecting time τo=τoff=μs.
Grinding of precision ceramic balls
The accuracy of ceramic balls has a great influence on the running accuracy and high speed of ceramic bearings. The tolerance grade of ceramic balls used in precision and ultra-precision spindle bearings is G5, the diameter variation and spherical error of the balls are ≤0.13μm, and the surface roughness is Ra0.02μm. In order to efficiently ensure that the accuracy requirements are met, the machining points are as follows:
- 1) It is necessary to go through multiple processes such as coarse, fine, ultra-fine grinding and polishing, and gradually reduce the abrasive particle size, grinding pressure and grinding speed (Table 1) from coarse to fine, and gradually extend the grinding time.
- 2) Reduce the grinding pressure and reduce the beating of the grinding disc (or use a very low grinding speed), which can effectively reduce the surface roughness and waviness.
- 3) The abrasive should follow the principle of adding a small amount frequently.
- 4) The material of the ceramic ball should be sintered Si3N4 (HIPSN) or ZrO2 by hot fluid isostatic pressing with dense and small defects.
- 5) Adopt conical grinding method to improve grinding efficiency. The upper grinding disc shown is tapered, so that the ceramic balls have a large spin angle (>45º) during grinding, so that the ceramic balls can fully spin to enhance the rotary sliding, so the grinding efficiency is higher than the usual V-groove grinding method.