| Titanium-Zirconium-Niobium alloy(Ti-Zr-Nb alloy)has the advantages of high specific strength,low elastic modulus,good biocompatibility,non-toxicity and corrosion resistance.It is an ideal substitute for the currently used vanadium-titanium alloy.However,β-type Ti-Zr-Nb alloy is a typical difficult drilling material due to its low elastic modulus and sticking characteristics.In this paper,Ti-Zr-Nb alloy dental materials have many problems such as severe knife sticking,poor drilling quality,and fast tool wear.The holes in dental implants are used as the research object,and AlTiN coated hard alloy twist drills with a diameter of 2mm are used for the new type.A single-factor small hole drilling experiment was performed on a β-type Ti-Zr-Nb alloy.The dental implant is equipped with a small hole as its prototype,and a 2 mm diameter AlTiN coated hard alloy twist drill is used for the new type.A single-factor small hole drilling experiment was performed on a β-type Ti-Zr-Nb alloy.Using experimental research methods,drilling parameters(cutting speed and feed rate),drilling methods(pecking and conventional drilling),and cooling methods(dry cutting,flooded cooling,cryogenic cooling,minimum quantity lubrication(MQL)and cryogenic minimum quantity lubrication(CMQL))were studied the effects on axial drilling force,vibration,drilling quality,chip shape,and tool wear.It provides experimental reference and theoretical support for the small-hole drilling application of the new β-type Ti-Zr-Nb alloy.The main conclusions of this article are as follows:(1)Drilling force and dynamic characteristics of a new P-Ti-Zr-Nb alloyWith the increase of cutting speed,the thrust force has an overall decrease and gradually tends to a stable change trend.When the feed speed increases,the thrust force increases continuously.The overall thrust force of conventional drilling is slightly smaller than peck drilling.Under five different cooling methods,the thrust force under the MQL condition is the smallest.with the increase of the number of drill holes,the thrust force under different cooling modes is increased,among which the thrust force of the dry cutting and the cryogenic cooling method rises fastest,and the other three types of cooling force increase slowly.Under different drilling parameters,it was found that the vibration amplitude increases with the increase of cutting speeds or the decrease of feed rates,which is opposite to the change of thrust force.In MQL cooling method,the amplitude of vibration in X and Z directions is the smallest and they are 0.0287m/s~2 and 0.0471m/s~2,respectively.(2)Drilling quality of a new β-Ti-Zr-Nb alloyThe effect of different drilling parameters on the surface roughness is not obvious.The average surface roughness at Vc=30m/min and f=20mm/min is the minimum,which is Ra=1.213μm.Among the five different cooling methods,the minimum inner wall surface roughness was 1.319μm for the flooded cooling.And slight softening at the surface of the inner wall of the hole was observed at cutting speeds of 40m/min and 45m/min,respectively.The softening degrees were 4.1%and 5.6%,respectively.During the dry cutting and cryogenic cooling processing,slight work hardening occurred near the hole wall,and the hardening degree was 5.1%and 6.7%respectively.Under the five cooling methods,the largest of the average value of the small hole entry burr was the cryogenic cooling method,reaching 100μm.The average hole entrance burr height of MQL cooling method is only 44μm.In MQL cooling mode,the surface quality of the small hole is the best,the surface material is less adhered,and the material of the hole wall is obviously coated by dry cutting and cryogenic cooling.The overall hole size accuracy of the conventional drilling is better than that of the peck drilling.When the cutting speed is 25m/min and the feed speed is 15mm/min,the hole diameter deviation of the conventional drilling is the smallest.In different cooling methods,the hole diameter is the closest to the drill bit diameter in the MQL cooling,and the hole diameter accuracy is the best.(3)Chips formation mechanism of drilling new β Ti-Zr-Nb alloyAnalyzing the chips of the new β-Ti-65Zr-20Nb alloy found that,from the macroscopic appearance of the chip,the chip shape of conventional drilling is mainly continuous long-band curled chips and closely overlapping continuous long-band chips.The chip morphology of peck drilling is mainly continuous short spiral conical and folding-type chips.The maximum length of the chip becomes smaller as the cutting speed increases.From the microscopic topography of the chips,as the feed rate increases,the pitch of the serrated fringes on the free surface becomes smaller,the twisting deformation increases,and the cracks generated by the chips at the edges and inside become less.The difference in the microscopic morphology of the chips under different drilling modes is not big.(4)Tool wear characteristicsThe effect of different cooling methods on the flank wear of AlTiN coated carbide twist drills was studied.From the tool wear curve,it can be found that after drilling 30 holes,the drill bit under dry cutting and low temperature cooling has appeared serious damage and chipping,and loss of drilling ability.After drilling 150 holes in the cooling methods of MQL,CMQL cooling and flooded cooling,the flank wear of drill bit does not exceed 40μm,and a small amount of MQL and flooded cooling methods of wear was very close,they are 32.31μm and 32.51μm,respectively.Carbide bit-coated drills exhibited micro-disintegration after drilling 150 holes under trace MQL,cryogenic cooling,and flooded cooling,and it also found to that the drill used in the flooded cooling showed obvious oxidation.From the energy spectrum analysis diagram,it can be seen that after 150 holes were drilled,the drill bit was adhesion wear in the MQL cooling method,and the bit was diffusion wear in the CMQL and flooded cooling methods.All three cooling methods have abrasive wear and oxidation wear. |
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