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本科畢業(yè)設(shè)計(jì)論文
題 目 ______拋丸機(jī)斗式提升機(jī)的設(shè)計(jì)______
專業(yè)名稱____機(jī)械設(shè)計(jì)制造及其自動(dòng)化___
學(xué)生姓名________王志偉______________
指導(dǎo)教師_________張永紅_____________
畢業(yè)時(shí)間_____二零一四年六月__________
畢業(yè)設(shè)計(jì)（論文）英文資料翻譯
Micro Shot Blasting of Machine Tools
學(xué) 院：西北工業(yè)大學(xué)明德學(xué)院
專 業(yè)：機(jī)械設(shè)計(jì)制造及自動(dòng)化
班 級(jí)： 161003班
姓 名： 王 志 偉
學(xué) 號(hào)： 103359
指導(dǎo)老師： 張 永 紅
2014年 6 月
Micro shot blasting of machine tools for improving surface finish and reducing cutting forces in manufacturing
D.M. Kennedy *, J. Vahey, D. Hanney
Faculty of Engineering, Dublin Institute of Technology, Bolton Street, Dublin 1, Ireland
Received 5 January 2004; accepted 3 February 2004
Available online 13 April 2004
Abstract
Micro blasting of cutting tips and tools is a very effective and reliable method of advancing the life of tools under the action of turning, milling, drilling, punching and cutting. This paper outlines the ways in which micro blasted tools, both coated and uncoated have benefited from shot blasting and resulted in greater productivity, lower cutting forces, improved surface finish of the work pieces and less machine downtime. The process of micro blasting is discussed in the paper. Its effectiveness depends on many parameters including the shot media and size, the mechanics of impact and the application of the shot via the micro shot blasting unit.
Control of the process to provide repeatability and reliability in the shot blasting unit is discussed. Comparisons between treated and untreated cutting tools are made and results of tool life for these cutting tips outlined. The process has shown to be of major benefitto tool life improvement. 2004 Elsevier Ltd. All rights reserved.
Keywords: Micro shot blasting; Surface finish; Machine tools
1. Introduction
Many modern techniques have been developed to enhance the life of components in service, such as alloying additions, heat treatment, surface engineering, surface coating, implantation processes, laser treatment and surface shape design. Processes such as thin film technology, plasma spraying, vacuum techniques depositing a range of multi-layered coatings have greatly enhanced the life, use and applications of engineering components and machine tools. Bombardment with millions of micro shot ranging in size from 4 to 50 lm with a controlled process can lead to dramatic operating life improvements of components. Standard shot peening was first used in a production process to extend the life of valve springs for Buick and Cadillac engines in the early 1930s [1,2] but prior to this it was a well known process used by blacksmiths and sword makers overtime to improve the toughness of the cutting edges of their tools and weapons. Today, cutting tips and tools can be greatly improved by the process of micro shot blasting their surfaces to induce compressive residual stresses. The operating life of tools such as drills, turning tips,milling tips, punches, knife edges, slicers, blades, and a range of other working parts can also benefit from this process.Standard components, such as springs, dies, shafts, cams, and dynamic components in machines and engines can be enhanced by this process. The fatigue life of compressor components for example, treated by shot peening have increased dramatically as reported by Eckersley and Ferrelli [3]. Other factors such as improved fatigue resistance, micro crack closure, reduced corrosion and an improved surface finish can also be designed into components as a result of this the peening process. Not only can improvements be made to the surface finish of the cutting tips and tools but also the surface finish of the work pieces machined with these tools have improved as a result of this technique. Engineering materials such as tools steels, carbides, ceramics, coated carbides, through to polymers and even rubbers (elastomers) can benefit. The key requirement for this process is to develop anautomated micro blasting process to fit inside a spraybooth or standard shot blasting booth. Shot material, size and mass, operating pressures, operating velocities, kinetic energy, density and coverage time will need to be perfected and optimised for a range of materials. The process is a line of sight method but can be applied to complex surface shapes such as the tips of drill bits.
2. Method of operation
One of the primary ways that components fail in ervice is through fatigue. This is closely associated with cyclic stresses and accelerated by tensile stresses, micro crack propagation and stress corrosion cracking. Cracks reduce the cross section of a material and eventually it will fail to support the applied loads. One simple method of reducing failure by fatigue is to arrest these tensile stresses by inducing compressive stresses into a surface. The benefits obtained with shot peening are a direct result of the residual compressive stresses produced in a component. A typical shot striking a surface is shown in Fig. 1. Any applied tensile loads would have to overcome the residual compressive stresses before a crack could initiate as described by Almen [4].
Poor machining of materials can result in residual stresses accruing at the surface. Rough surfaces have deeper notches, where cracks can initiate due to tensile stress concentrations at these points. Many standard machining processes such as grinding, milling, turning, and coating processes such as electroplating induce residual tensile stresses in surfaces and this can lead to early failure of components. Further tensile loading in service would lead to early failure and this can be prevented by shot peening and micro blasting of component surfaces. Micro shot blasting will change the following in a materials surface:
(i) resistance to fatigue fracture;
(ii) resistance to stress corrosion;
(iii) a change in residual stresses;
(iv) modification of surface finish.
It is a cold working process involving bombarding powders such as ceramics, glass and metals of mainly spherical shapes against surfaces and can be used in conjunction with other processes. The main stages involved in this dynamic process include elastic recovery of the substrate after impact, some plastic deformation of the substrate if the impact pressure exceeds the yield stress, increased plastic deformation due to an increase in impact pressure and finally some rebound of the shot due to a release of elastic energy. Some critical design characteristics of the micro shot peening process include the shot size, shape, hardness, density, durability, angle of impact, velocity and intensity. All of these parameters will influence the residual compressive stresses produced in the substrate.
3. Experimental work
Tool materials such as Tungsten Carbide, High Speed Steels used in milling and turning tools were subjected to the micro peening process using different shot media (ceramic and glass bead) and shot size. Tests prior to and following the blasting process were conducted to ascertain any improvements resulting from the process.
The micro shot peening unit is shown in Photo 1 it incorporates an air filter, pressure regulator and gauge, air flow regulator, pressurised blast media container and a venturi blast nozzle for directing the stream of micro shot. The unit is PLC controlled and a stepper motor, used to drive a lead screw, is used to move the blast nozzle across the sample in order to control media shot coverage.
The blast nozzle can also be rotated to allow shot media to strike the samples at different angles. Tests undertaken include surface finish and roughness measurement, machining tests on standard lathes and mills, hardness tests, cutting forces on turning operations, tool wear and the determination of surface finish of the work pieces machined. Figs. 2 and 3 show a typical high speed steel (HSS) tip prior to and following the micro shot peening process using ceramic bead at a pressure of 5.5 bar.
4. Experimental results
Testing of treated and untreated cutting tips and tools was conducted on HSSs for turning and milling as well as coated and uncoated carbide inserts. A dynamometer was used to measure cutting forces on the turning tool (Lathe). The cutting process consisted of a depth of cut of 2 mm on a standard bright mild steel specimen over a length of 750 mm while milling tests consisted of machining a 25_25_150 mm piece of mild steel using a depth of cut of 1 mm with a slot milling cutter of 18 mm diameter. Surface roughness measurements were conducted on the machined components prior to and after machining to establish whether the treated cutting tips had superior performance to the untreated tips. Micro Hardness testing was also carried out to establish if there was any increase in surface hardness due to the micro shot peening process. The impact angle of the shot was set at 90_ as this provides the optimum compressive layer [5]. The shot velocity on impact with a surface is largely dependent on the nozzle size, the air pressure and the distance from the substrate. The exposure time was adequate to give sufficient coverage of the substrate and this was determined by the Almen strip saturation time, work piece indentation time and visual appearance. Harder materials such as carbides will obviously require longer exposure time or harder shot media. The micro peening media used was a ceramic bead of approximately 40 lm diameter providing high impact strength and hardness (NF L 06-824, approximately 60 HRc).
4.1. Micro hardness tests
Combined Vickers micro hardness tests gave the results in Table 1. for both treated and untreated HSS cutting tips.
4.2. Surface roughness values
In all surface roughness tests conducted, the micro blasted surface gave an improved surface roughness value. Surface roughness and profile tests were carried out on both a Talyor Hobson Tallysurf instrument and a non contact surface profileometer. Surface roughness details of a typical untreated HSS cutting tip and a treated one are shown in Figs. 4 and5 and Table 2 shows the results of surface measurement values for other cutting tips and tools and workpieces. Fig. 6 shows an uncoated carbide cutting tip which was not subjected to micro blasting. The flank wear was measured using an optical microscope and the value recorded was 150 lm after 676 s of machining. Fig. 7 shows an uncoated carbide tip subjected to micro blasting. The flank wear in this case is only 90 lm for the same machining time.
and5 and Table 2 shows the results of surface measurement values for other cutting tips and tools and workpieces. Fig. 6 shows an uncoated carbide cutting tip which was not subjected to micro blasting. The flank wear was measured using an optical microscope and the value recorded was 150 lm after 676 s of machining. Fig. 7 shows an uncoated carbide tip subjected to micro blasting. The flank wear in this case is only 90 lm for the same machining time.
4.3. Dynamometer tests
Figs. 8 and 9 show the comparison for Dynamometer results for HSS in the treated (micro blasted) and untreated states with relevant comments.
Similar profiles are shown for coated and uncoated turning tips in both the treated (micro blasted) and untreated conditions in Figs. 10–13. In all cases, the micro blasted tips provided an increase in cutting tip life with lower cutting forces recorded.
5. Conclusions
This research work has shown that micro shot blasting of cutting tips and tools has a very positive effect on component surfaces by increasing toughness, operating life, improving hardness and surface finish. From the tests conducted, it is obvious that the process affects the residual stresses at or near the surface in a beneficial way by inducing compressive stresses on the substrates tested. The micro blasting process is very simple to apply and economical to use. The mechanical properties of the substrates will determine the type of treatment, i.e. shot hardness, velocity and duration of application in order to obtain maximum benefits from this process. In some cases, authors have reported a 4– 10 fold improvement in fatigue life in a range of dynamic machine parts subjected to standard shot blasting. Further testing will need to be conducted at the micro shot blasting stage to obtain similar benefits. Other applications for the micro blasting process are currently being investigated and rubber based products that are subjected to fatigue and wear are being tested in order to remove the surface voids that act as stress concentrations in these materials.
References
[1] Impact. Bloomfield, CT: Metal Improvement Company; Fall 1989.
[2] Zimmerli FP. Heat treating, setting and shot-peening of mechanical
springs. Metal process; June 1952.
[3] Eckersley JS, Ferrelli B. Using shot-peening to multiply the life of
compressor components. In: The shot peener, International newsletter
for shot-peening surface finishing industry, vol. 9, Issue No.
1; March 1995.
[4] Almen JC. J.O. Almen on hot blasting. General motors test, US
Patent 2,350,440.
[5] Champaigne J. Controlled shot peening. Elec Inc., Report; 1989.
制造業(yè)用于提高表面光潔度和減少切削力的拋丸清理機(jī)
摘要
在旋轉(zhuǎn)，銑削，鉆孔，沖孔和切削運(yùn)動(dòng)中，微拋丸切削技巧和工具是一種提高工具壽命的非常高效并且可靠的方法。本文概述了應(yīng)用微拋丸工具的方式，微拋丸對(duì)有無(wú)鍍膜工件的益處，并且創(chuàng)造了更大的生產(chǎn)力，降低了切應(yīng)力，提高了工件的表面光潔度，減少了機(jī)器的停機(jī)時(shí)間。本文對(duì)微拋丸過(guò)程進(jìn)行了討論。它的效率取決于包括彈丸媒體和型號(hào)在內(nèi)的許多參數(shù)，碰撞力學(xué)和通過(guò)微拋丸單元的彈丸的應(yīng)用程序。對(duì)控制流程提供的可重復(fù)性和可靠性的爆破裝置進(jìn)行了探討。處理和未經(jīng)處理的刀具的做出了對(duì)比，切割技巧對(duì)刀具壽命的影響做出了概述。這個(gè)過(guò)程體現(xiàn)了提高工具壽命的主要好處。
2004愛(ài)思唯爾有限公司保留所有權(quán)利。
關(guān)鍵詞:微噴丸清理,表面光潔度;機(jī)床
介紹
許多現(xiàn)代技術(shù)已經(jīng)開(kāi)發(fā)出來(lái)加強(qiáng)服務(wù)組件的壽命，例如添加合金，熱處理，表面工程，表面涂層，移植過(guò)程，激光治療以及表面外形設(shè)計(jì)。例如薄膜技術(shù)，等離子噴涂，沉淀多層涂料的真空技術(shù)都大大加強(qiáng)了壽命，工程和應(yīng)用程序組件和機(jī)床使用。通過(guò)控制過(guò)程用數(shù)以百萬(wàn)計(jì)的大小在4到50微米的微拋丸撞擊可以顯著提高組件的使用壽命。標(biāo)準(zhǔn)噴丸技術(shù)首次使用時(shí)在20世紀(jì)30年代提高別克和凱迪拉克引擎氣門彈簧的生產(chǎn)過(guò)程中，但在此之前該技術(shù)就是被鐵匠和刀制造商所熟知的來(lái)提高他們工具和武器切削刃韌性的過(guò)程。當(dāng)今，切割技巧和工具可以通過(guò)微拋丸清理它們的表面的過(guò)程來(lái)引導(dǎo)壓縮參與應(yīng)力而被大大提高。鉆頭，車削頭，銑削頭，沖頭，刀刃，切片機(jī)，葉片以及一系列的其他工作部分都可以受益于該過(guò)程。
機(jī)器和引擎中的標(biāo)準(zhǔn)組件，例如離合器，柴油機(jī)，軸，凸輪以及動(dòng)態(tài)組件等都可以通過(guò)該過(guò)程提高。由Eckersley和Ferrelli所述，例如壓縮機(jī)組件的疲勞壽命通過(guò)拋丸處理可以顯著增加。其他因素，例如抗疲勞強(qiáng)度，微裂紋閉合，減少腐蝕以及提高表面光潔度都可以被作為噴丸的結(jié)果而被設(shè)計(jì)進(jìn)組件當(dāng)中。不僅可以做到切削刀具表面光潔度的提高，而且由這些刀具加工的工件的表面光潔度作為該技術(shù)的一個(gè)成果也得到了提高。工程材料中，例如工具鋼，硬質(zhì)合金，陶瓷，涂層硬質(zhì)合金，通過(guò)聚合物甚至橡膠（彈性物）都可以受益。這個(gè)過(guò)程的關(guān)鍵要求是開(kāi)發(fā)一個(gè)自動(dòng)化微拋丸的工藝過(guò)程來(lái)適用于噴漆柜或者標(biāo)準(zhǔn)拋丸位置。
拋丸材料，大小和質(zhì)量，操作壓力，操作速度，動(dòng)能，密度，覆蓋時(shí)間都要被完美優(yōu)化一系列材料。這個(gè)過(guò)程是一種視線方法卻可以應(yīng)用于復(fù)雜外形例如鉆孔。
操作方法
服務(wù)組件損壞的主要原因之一是疲勞使用。這是與循環(huán)應(yīng)力密切相關(guān),加速了抗拉應(yīng)力，微裂紋擴(kuò)展和應(yīng)力腐蝕開(kāi)裂。裂紋減少材料的橫截面，最終它將無(wú)法支持應(yīng)用加載。減少疲勞的失敗的一個(gè)簡(jiǎn)單方法是通過(guò)誘導(dǎo)壓應(yīng)力到表面來(lái)停止這些拉伸應(yīng)力。拋丸加工直接產(chǎn)生的好處是一個(gè)組件產(chǎn)生的殘余壓應(yīng)力。典型的鏡頭的表面是圖1所示。在由阿爾門[4]描述的裂紋出現(xiàn)之前，任何應(yīng)用拉伸加載將不得不克服殘余壓應(yīng)力。
不良的加工材料會(huì)導(dǎo)致殘留表面壓力積累。粗糙表面有更深層次的等級(jí)，在這些點(diǎn)，由于拉應(yīng)力會(huì)產(chǎn)生裂紋。
許多標(biāo)準(zhǔn)磨削，銑削、車削和涂層工藝?yán)珉婂兊燃庸み^(guò)程，在表面產(chǎn)生殘余拉應(yīng)力，這可能會(huì)導(dǎo)致早期失效的組件。進(jìn)一步拉伸加載服務(wù)會(huì)導(dǎo)致早期失效，這可以防止噴丸加工和微拋丸組件表面。
微拋丸處理將改變以下材料表面：
1. 抗疲勞斷裂；
2. 抗應(yīng)力腐蝕；
3. 殘余應(yīng)力的變化；
4. 修改的表面光潔度。
這是一個(gè)包括轟擊粉末的冷加工過(guò)程，例如陶瓷，玻璃，金屬表面的主要是球形的形狀并且可用于與其他進(jìn)程。參與這一動(dòng)態(tài)過(guò)程的主要階段包括彈性恢復(fù)后的基質(zhì)影響，如果壓力超過(guò)屈服應(yīng)力的影響而使得一些基體的塑性變形，由于彈性能量的釋放，在影響最后噴丸的一些反彈的壓力，增加了塑性變形。一些關(guān)鍵設(shè)計(jì)微噴丸加工過(guò)程的特性，包括噴丸的大小、形狀、硬度、密度、耐久性、角度的影響、速度和強(qiáng)度。所有這些參數(shù)會(huì)影響產(chǎn)生的殘余壓應(yīng)力。
實(shí)驗(yàn)工作
應(yīng)用與銑削和車削工具中的工具材料如碳化鎢，高速鋼，是受到微噴丸過(guò)程使用不同的拋丸媒體和拋丸大小。測(cè)試之前和之后進(jìn)行了拋丸過(guò)程確定造成的任何改進(jìn)過(guò)程。
微噴丸加工單位是圖1所示包含一個(gè)空氣過(guò)濾器，壓力調(diào)節(jié)器，和壓力機(jī)，空氣流量調(diào)節(jié)器，壓力容器拋丸媒體，文丘里噴嘴來(lái)指導(dǎo)微流噴射。此單位是PLC控制和步進(jìn)電機(jī)，用于驅(qū)動(dòng)絲杠，用于移動(dòng)拋丸噴嘴來(lái)控制拋丸噴射媒體。噴嘴也可以允許旋轉(zhuǎn)，讓媒體達(dá)成樣品在不同角度噴射。包括表面光潔度和粗糙度進(jìn)行測(cè)試測(cè)量、車床加工測(cè)試標(biāo)準(zhǔn)，碾磨，硬度測(cè)試，切削應(yīng)力，刀具磨損，加工的工件表面光潔度測(cè)定。圖2和圖3是一種典型的高速鋼之前和在5.5bar壓力下用陶瓷珠微拋丸加工過(guò)程之后的情況。
實(shí)驗(yàn)結(jié)果
經(jīng)過(guò)處理和未經(jīng)處理的切割技巧和工具在高速鋼上進(jìn)行車削和銑削以及有涂層或沒(méi)涂層的嵌入合金的測(cè)試。在車刀上用測(cè)力計(jì)測(cè)量切削力。切削過(guò)程用一個(gè)標(biāo)準(zhǔn)為2毫米低碳鋼試樣，其長(zhǎng)度為750毫米，銑削時(shí)測(cè)試用加工一塊25*25*150毫米低碳鋼，加工1毫米的深度，槽銑刀直徑18毫米。表面粗糙度的測(cè)量分別在機(jī)械零部件加工之前和之后進(jìn)行，以此來(lái)確定切削技巧治療是否比未經(jīng)處理的技巧帶來(lái)更優(yōu)越的性能。微硬度測(cè)試也測(cè)試了在微噴丸加工過(guò)程之后是否能增加表面硬度。噴射角度在90度的影響是提供了最佳抗壓層[5]。噴射速度的影響很大程度上是依賴于表面噴嘴的大小,空氣壓力和基質(zhì)之間的距離。曝光時(shí)間是適當(dāng)?shù)慕o予足夠的覆蓋率的基質(zhì),這是決定于阿爾門帶飽和時(shí)間，工件縮進(jìn)時(shí)間和視覺(jué)外觀。堅(jiān)硬的材料,如碳化物將顯然需要更長(zhǎng)的曝光時(shí)間或噴射媒體。微噴丸媒體使用的陶瓷珠直徑約40 微米提供高沖擊強(qiáng)度和硬度。
微硬度測(cè)試
處理和未經(jīng)處理的高速鋼切削技巧結(jié)合維氏顯微硬度測(cè)試結(jié)果在表1列出。
表面粗糙度值
在所有表面粗糙度進(jìn)行的測(cè)試中，微拋丸處理可以得到一個(gè)改進(jìn)的表面粗糙度值。
一個(gè)典型的未經(jīng)處理的高速鋼刀片和一個(gè)處理的表面粗糙度的細(xì)節(jié)如圖4所示，圖5以及表格2顯示了其他切削表面測(cè)量值的結(jié)果。
圖6顯示了一個(gè)裸露的硬質(zhì)合金刀片并沒(méi)有受到微拋丸噴射。側(cè)面磨損是由光學(xué)顯微鏡測(cè)量的，數(shù)值是在加工676s以后記錄的，數(shù)值是150微米。圖7顯示了一個(gè)裸露的硬質(zhì)合金受到微拋丸處理。相同的加工時(shí)間，本例中的側(cè)面磨損只有90 微米。
測(cè)功器測(cè)試
圖8和圖9顯示測(cè)功器的比較處理和未經(jīng)處理的高速鋼的狀態(tài)與相關(guān)評(píng)論的結(jié)果。
類似的顯示有涂層和無(wú)涂層的以及在經(jīng)過(guò)處理(微拋丸)和未經(jīng)處理的資料在圖10 – 13。
在所有情況下，微拋丸技巧提供了一個(gè)刀片在較低的切削力工作的壽命增加記錄。
結(jié)論
本研究工作表明,微噴丸的技巧和工具組件通過(guò)增加韌性、使用壽命、提高硬度和表面光潔度對(duì)表面有非常積極的影響。從實(shí)驗(yàn)中可以看出，很明顯,這一過(guò)程通過(guò)在基質(zhì)上影響殘余應(yīng)力達(dá)到或接近表面以有益的方式誘導(dǎo)壓應(yīng)力。微拋丸過(guò)程是非常簡(jiǎn)單的應(yīng)用和非常經(jīng)濟(jì)的?；宓臋C(jī)械性能將決定處理的類型,即硬度、速度、應(yīng)用程序時(shí)間來(lái)獲得這一過(guò)程的最大受益。在某些情況下，作者報(bào)道受到標(biāo)準(zhǔn)拋丸提高4到10倍疲勞壽命的動(dòng)態(tài)機(jī)器零件。需要進(jìn)行進(jìn)一步測(cè)試在微丸清理階段獲得類似的好處。
其他為了消除表面孔隙的橡膠產(chǎn)品受到疲勞和磨損的微拋丸處理程序測(cè)試目前正在測(cè)試當(dāng)中。