dc.description.abstract | Due to the high hardness and wear resistance, WC–Co cemented carbides have been used extensively for metal cutting and wear application tool materials in the manufacturing industry; Tungsten carbide (WC) offer essential hardness and abrasion resistance, and cobalt (Co) as combining tungsten carbide and offering toughness that the cemented carbide needs . The ultra hard alloy of tungsten carbide has good hardness,corrosivity and abrasion resistance; But in the powder metallurgy industry, while producing cemented carbide with the traditional mechanical presses or hydraulic presses, the production technology bottlenecks faced are mainly three: First, the product’s cracking defect after sintering Second, the product’s size defect after sintering due to shrinkage Third, the product’s deformation after sintering cause squareness defect
This research is to study the case company after introducing new servo-motorized electric press , how to employ the servo numerical control function for upper punch, die and core rod movement curve simulation and intelligence program generator function , combine with finite element method modeling simulation ,Taguchi method and respond surface methodology for robust experimental design , after carry on the pressing parameter optimization experiment, succeed in overcoming above-mentioned powder metallurgy three technical bottlenecks for cemented carbide production. The following conclusions can be drawn based on the experimental results in this study.
First, improving the product’s cracking defect after sintering by pressing parameter optimization
Using servo-motorized electric press servo numerical control function for upper punch, die and core rod movement curve simulation ,apply the findings of FEM modeling for spray nozzle density distribution related to cracking, put into under filling movements and pressurize synchronously movements and two section holding pressure that can reduce stress and density change during blank compacting period . Besides, modify powder feeding shoes to fill out powder by twice can help to improve powder filling density uniform, in the early pressing stage which powder is still loose , the movement and interaction of the die and upper punch have little effect on product for whether have cracking defect after sintering, but when the powder density gradually increasing while pressing period, especially in the final stage , the synchronization control upper punch top pressing down and die of floating upward, precisely control and adjustment of interaction between the punch and die movement curve ,is the most critical point for spray nozzle product whether have cracking defect after sintering .
Second, improving the product’s size defect after sintering by pressing parameter optimization
Taguchi method and Response Surface Methodology(RSM) was employed to analyze and optimize pressing parameter for conveyor scraper and improve the L size precision of the scraper product after sintering, the best pressing parameter decided by dual response surface methodology are pressing height H =3.5 mm and pressing weight W =22.445 g, can get L length from 50.18 mm to 50.32 mm which meet with the length tolerance between 50.1-50.4 mm. Via Analysis of Variance (ANOVA) analyzing showing significance value of powder variation value is far greater than pressing high and pressing weight significance value , so the powder variation can be neglected to the influence of L length after sintering. Set up the tooling movement curve via the optimization pressing parameter, the conveyor scraper product’s L length can meet the size tolerance after sintering, so can reduce the re-grinding cost for L size larger than 50.4 mm and reduce the L size defect scrap lost amount for L size smaller than 50.1 mm.
Third, improving the product’s squareness defect after sintering by pressing parameter optimization
The action will be applied via using servo-motorized electric press numerical control function for punch and die movement curve simulation to improve the hammer product’s squareness defect after sintering, the best pressing parameters are as following: powder feeding shoe should be the forward direction, put the inclined plane of the hammer product on the contact surface of the graphite tray, do not put aluminum paper, adjust profile filling dx3 and dx4 parameter as 70% to adjust the amount of powder to fill before and after the die cavity and thus can improve the problem of uneven powder filling, adjust the die movement curve setting, increase powder filling in the middle of the die and increase the upper punch pressure. At the same time, through this study found that the hammer product’s squareness and flatness after sintering are mainly affected by product’s contact surface and direction related to graphite tray, put aluminum paper on product’s contact surface with graphite tray, although the uneven surface of the product can be improved, but it will cause the product after sintering easily deformed and affect squareness of the product.
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