Fundamental Study Of The Biological In-process Dressing(BID) For The Copper-based Matrix Diamond Tools

The metal-bonded fine diamond tools with high precision stability and durability is strongly recommended as alternative in precision machining of hard and brittle materials,but it is confronted with dressing difficulties and problems.The traditional mechanical dressing method is dif?cult to control the dressing intensity for reasonable grit protrusion due to the high accuracy requirement.Besides,mechanical damages of the bond and grains are induced by the impact between the abrasive tool and the dresser.The new types of methods such as electrical discharge dressing and electrolytic in-process dressing are able to dress fine-grained wheels.However they have its disadvantages: requirement of a complex and expensive control system,control difficulty,environment pollution and so on.This research project,based on the fundamental principles of biomachining,a new,green and controllable dressing method for copper based fine diamond tools is proposed,which is named as “Biological In-process Dressing,?BID?”.The conceiving,principle,technique,process of the BID were systematically studied.The main works and important conclusions are as follows:?1?The biomachining experiment of copper?Cu?,cobalt?Co?,iron?Fe?,tin?Sn?,and tungsten?W?were experimentally studied using Acidithiobacillus ferrooxidans.The results showed that the metals can be removed in biomachining except tungsten,the removal amounts of the metals appeared good linear relationship with time.The basic removal principle of pure metal is that the the bacteria firstly oxidize Fe²⁺to Fe³⁺as an oxidizer then realizing the removal of the metals by corrosion.The experiment revealed that the material removal rate?MRR?of pure metal was mainly affected by the electrochemical corrosion resistance of the material.However,the generation of a reaction layer of several ten microns could reduce the MRR for the pure Co.?2?The biomachining experiment of four binary powder mixtures?Cu-Co,Cu-Fe,Cu-Sn,and Cu-W?were experimentally studied using Acidithiobacillus ferrooxidans.The results showed that the removal amounts of the four copper based binary powder mixtures appeared good linear relationship with time as well.The experiment reveals that the removal mechanisms between binary powder mixtures and pure metal removal are different,and the element in the powder mixtures is selectively removed by the galvanic corrosion cell of binary metals.In addition to the erosion effect,the corrosion resistance of intermetallic compound produced in the powder mixtures and powder particles fall off will affect the removal efficiency of the powder mixtures.?3?The effects of temperature,shaking rate,pH value and bacteria concentration on the MRR,MRR stability and surface roughness were investigated using Taguchi methodology,and the optimum combination of process parameters was obtained.It is found that there is a good linear relationship between MRR and Fe³⁺concentration in a certain range.?4?Combined with the research results mentioned above,a biological in-process dressing system was designed and made.It can provide space for the growth of microorganism by a packed-bed bioreactor,and the cell-free culture supernatant could be filtered from the microorganisms cultured and continuously sprayed onto the surface of the diamond tool to conduct the dressing process.The possibility of dressing diamond tools was proved by through groups of grinding and polishing experiments.?5?The coarse lapping processing of quartz glass and sapphire were performed by coarse-grained Cu-Co matrix pad.During the lapping of quartz glass with BID,the protrusion height of the diamond grits has improved significantly,with has reached 60% of the grit size.The MRR increased nearly 10 times with BID,but the surface quality decreased.During the lapping of sapphire with BID,the protrusion height of diamond grits maintains at about 1/3 of the grit size.The lapping surface qualities were improved under different Fe³⁺concentration,but the MRR were hard to increase even with high Fe³⁺concentration.The results show that,in the the process of BID,the bond material removal amount should fit the diamond grit wear.Increasing the Fe³⁺concentration could improve the removal rate of bond material,but it also easily lead to a too high protrusion height resulting a low machining quality and shorter tool life.?6?The fine lapping processing of sapphire was performed by fine-grained Cu-Co matrix pad.With BID,the protrusion height of the diamond grits has improved.The MRR of sapphire was improved with the increasing of Fe³⁺concentration,the highest value about 10 times was obtained in this paper,meanwhile the machining surface roughness?S_a?was decreased to 50-70 nm.It should be noted that the machining surface quality is correlative to an optimal Fe³⁺concentration.?7?The fine grinding processing of sapphire was performed by fine-grained Cu-Co matrix wheel.With BID,the grinding force has dropped about 2/3.The machining quality can be significantly increased,and the lowest machined surface roughness?S_a?of sapphire was 32 nm.This research project reveals the biomachining mechanism of binary powder mixtures.And on this basis,the dressing method for copper based diamond tools was proposed and the feasibility was provided.Compared with other dressing method,this technology possesses many advantages such as low cost,low energy consumption,high efficient,controllable,and environment friendly.The research provides a new way to dress metal based diamond tools,and it offers technical support for the high efficiency and precision processing of brittle and hard materials by metal based diamond tools.