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南京理工大學(xué)泰州科技學(xué)院
畢業(yè)設(shè)計(論文)外文資料翻譯
系 部： 機(jī)械工程系
專 業(yè)： 機(jī)械工程及自動化
姓 名： 周平
學(xué) 號： 05010156
(用外文寫)
外文出處：International Conference on Spray
Deposition and Melt Atomization
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附件1：外文資料翻譯譯文
噴射成形加工
對于注射成型和沖壓成型模具的應(yīng)用
摘要
快速凝固加工工藝（RSP）是一種適合于生產(chǎn)注塑模具和沖壓模具的噴射成形技術(shù)。這種方法把快速凝固加工和網(wǎng)狀材料加工結(jié)合在一個單步執(zhí)行。這種噴射堆積成型的方式取代了常規(guī)模具制造中使用的昂貴的機(jī)械加工方法，并減少了周轉(zhuǎn)時間。此外，快速凝固抑制碳化物的析出和增長、促使鐵素體工具鋼被人工老化，為代替?zhèn)鹘y(tǒng)熱處理提供了獨特的益處。噴射成形工具鋼H13描述了熱處理過程中的材料性能和微觀結(jié)構(gòu)的轉(zhuǎn)變。
引言
注塑模具和沖壓模具，以及相關(guān)的工具常被用來制造我們每天都在家里或工作中使用的塑料和金屬部件。這一加工出所希望的零件形狀（模芯和型腔）的過程包含鍛制工具鋼或者金屬鑄件毛坯，增加冷卻通道、排氣孔和其他機(jī)械性能，接著是磨。許多注塑模具和沖壓模具需進(jìn)行熱處理（奧氏體化/淬火/回火）以改善金屬性能，接著是最后的研磨和拋光以實現(xiàn)期望的效果[1]。
模具的傳統(tǒng)制造方法是非常昂貴和費時的，因為：
1.每一個定制的產(chǎn)品，都反映了所需零件的形狀和結(jié)構(gòu)。
2.用于制造模具的材料是難以被機(jī)械加工的。對于長期生產(chǎn)來說，工具鋼產(chǎn)業(yè)是其骨干產(chǎn)業(yè)。加工工具鋼是資本密集型設(shè)備，因為個別加工步驟往往需要專門的加工設(shè)備。
3.機(jī)械加工必須精確。許多個體零件必須正確裝配和校正才能使最終產(chǎn)品正常運行。
注塑模具的費用因規(guī)模大小和復(fù)雜程度，從大約1萬美元到30萬美元以上不等，并有3到6個月的制造周期。零件檢查和資格認(rèn)證可能需要額外的3個月。大型傳輸機(jī)器的壓鑄模具和制造汽車車身面板的金屬板沖壓模具成本可能會超過100萬美元。制造周期通常大于40周。每年一個大型汽車公司投資約10億美元在制造部件進(jìn)入其新的轎車和卡車生產(chǎn)線上。
噴射成形為降低成本和減少制造時間提供了巨大的可能性，省去了很多如加工、研磨、拋光的單步工序。另外，噴射成形提供了強(qiáng)有力的手段來抑制合金元素的凝固和碳化物的形成，在大多數(shù)鐵素體工具鋼中都能創(chuàng)造有利的亞穩(wěn)相。因此，相對較低的溫度處理沉淀硬化可用于制造特定性能的金屬，如硬度，韌性，抗疲勞強(qiáng)度和剛度。本文介紹了噴射成形技術(shù)對于生產(chǎn)H13工具鋼的注塑模具和沖壓模具的應(yīng)用，以及低溫?zé)崽幚硭鶐淼暮锰帯?
快速凝固加工工藝
快速凝固加工工藝（RSP），是一種適合生產(chǎn)注塑模具和沖壓模具的噴射成形技術(shù)[2-4]。這種方法把快速凝固加工和網(wǎng)狀材料加工結(jié)合在一個單步執(zhí)行。從CAD軟件到高精度工具鋼所使用的一個合適的快速原型（RP）技術(shù)解釋了一般概念上所涉及模具設(shè)計轉(zhuǎn)換，如立體平板印刷。一般是用氧化鋁或熔融石英把一個模板轉(zhuǎn)變?yōu)橐粋€澆注陶瓷。緊接著是用噴射成形噴一層厚厚的工具鋼（或其它合金）沉積物在模板上的方式獲得所需的形狀、表面紋理和細(xì)節(jié)。由此合成的金屬塊冷卻到室溫與模具分離。通常，沉積物的外表面被加工成方形，在一個控股塊中能夠被用來作為插入物，如MUD結(jié)構(gòu)[5]。在一個機(jī)器工作的情況下，加工總周轉(zhuǎn)時間大約是3天。注塑模具和沖壓模具的這種生產(chǎn)方式已被用于塑料注塑和沖壓模具的原型和生產(chǎn)運行。
快速凝固加工工藝一個很大的好處是，它讓制造注塑模具和沖壓模具的過程成為設(shè)計周期前期的一部分。真正的原型零件用相同的生產(chǎn)加工計劃可以被制成預(yù)定形狀、尺寸和性能。若零件是合格的，它能像普通零件一樣被用于生產(chǎn)加工。使用數(shù)字化資料庫和RP技術(shù)可以很容易的修改設(shè)計上的內(nèi)容。
實驗步驟
氧化鋁基陶瓷（Cotronics780[6]）是漿體通過硅橡膠模具或格式機(jī)冷凍模具鑄造的。完成后，陶瓷模型脫離模具，在干燥室烘干并冷卻到室溫。H13工具鋼是由在內(nèi)部設(shè)計和建造的溫度約100°C、壓力由有工作臺刻度的收斂/發(fā)散噴霧嘴控制的氮氣保護(hù)層中誘導(dǎo)融化的。噴霧裝置在惰性氣體中能最大限度地減少漂浮狀態(tài)的氧化液滴，因為它們存放的加工模式比率大約是200公斤/小時。氣體到金屬的質(zhì)量流量比大約是0.5。
對于延伸性和硬度的要求，噴射成形材料用電火花加工來去除表面0.05毫米厚的熱影響區(qū)。在沒有氮氣的火爐中對樣品進(jìn)行熱處理。為防止脫碳，每個涂有氧化硼的樣品都放置在一個密封的金屬箔包內(nèi)。把樣品放在400至700°C的溫度范圍內(nèi)人工老化，隨后空冷。常規(guī)熱處理H13鋼的是在1010°C的溫度持續(xù)30分鐘使它奧氏體化，隨后空冷，再在538°C的溫度兩次回火。
在室溫下，微硬度測量使用的是平均每10微刻度讀數(shù)的M型維氏硬度測試儀。工具鋼被腐蝕（3％硝酸浸蝕液）的微細(xì)結(jié)構(gòu)的光學(xué)評估使用奧林巴斯的PME-3金相顯微照片和安瑞1830年電子掃描顯微鏡。相成分通過能量分散光學(xué)（EDS）分析。超范圍噴涂粉末的分析由麥奇克系列微粒分析器在來篩去200微米的粉末樣品覆蓋的粗糙表面。樣品密度由利用阿基米德原理工作的梅特勒天平（型號AE100）的排水量來測試。
用INEEL（國家工程與環(huán)境實驗室）開發(fā)的一維計算機(jī)章程用來評價多相流在自由射流噴嘴的表現(xiàn)。該章程的基本數(shù)值技術(shù)解決了穩(wěn)態(tài)氣流場通過合適網(wǎng)格，全氣動和強(qiáng)力耦合之間的水滴和運輸氣體的保守變量的方法和采用液滴相的拉格朗日公式。液態(tài)金屬噴射系統(tǒng)耦合的氣體力學(xué)，包括熱傳遞和摩擦在內(nèi)。該章程還包括一個允許液滴冷卻和升溫的非平衡凝固模型。該章程用于描述用射流噴嘴噴出的氣體和霧化液滴的溫度和速度變化情況。
結(jié)果與討論
噴射成形是一個有效的快速制造技術(shù)，它讓工具鋼注塑模具和沖壓模具的生產(chǎn)變得簡單。每個零件都是用快速原型機(jī)器通過陶瓷模板噴射成形的。
粒子和氣體的狀態(tài)
圖1給出了噴射H13工具鋼的粒子聚集頻率和累積頻率分布圖。中央塊狀直徑被確定的56微米為插補尺寸的50％的累積頻率。這些面積平均直徑和體積平均直徑是分別被計算出的53微米和139微米。幾何標(biāo)準(zhǔn)偏差是1.8，sd=(d84/d16)1/2 ，d84和d16是粒子直徑相應(yīng)的84％和16％的累積量。
圖1 噴射H13工具鋼的粒子聚集頻率和累積頻率分布
圖2給出了在射流噴嘴里多相流場速度的計算結(jié)果（圖2a），和H13工具鋼的凝固體分?jǐn)?shù)線（圖2b）。氣體速度增長至激震前沿位置時會急劇下降，最終在噴嘴外成倍衰退。小水滴很容易被速度場干擾，在噴嘴內(nèi)加速噴嘴外減速。在達(dá)到其終級速度后，較大的水滴（～150微米）因為其較大的動力受流場干擾較小。
眾所周知，目前的噴射成形高速粒子在噴嘴（103-106開/秒）和大部分沉積物（1-100開/分）的冷卻速度[7]。大多數(shù)粒子在噴射中經(jīng)歷了復(fù)輝而造成的凝固體分?jǐn)?shù)大約是0.75。計算出的從噴嘴噴出的或小（～30微米）或大（～150微米）的凝固體分?jǐn)?shù)，如圖2b。
圖2 氣體和微粒在射流噴嘴里多相流場。(a)速度分布圖 (b)凝固體分?jǐn)?shù)線
噴射成形沉積
這種高溫提取率模式降低了因腐蝕而影響工具表面質(zhì)量。這是相對靈活的，澆注陶瓷材料的模式將取代難以令人滿意的常規(guī)金屬鑄造過程。通過合適的加工條件，噴射成形模具模式可以制造出優(yōu)質(zhì)的表面質(zhì)量。表面粗糙度因成型表面的質(zhì)量而定。商業(yè)漿體生產(chǎn)的適合許多成型應(yīng)用的鑄造陶瓷的表面粗糙度大約是1微米。沉積工具鋼在鋼化玻璃上產(chǎn)生的定向反射面拋光粗糙度大約是0.076微米。在初電流階段，一個普通的機(jī)床來重復(fù)性空間噴射成形模具大約是±0.2％。
化學(xué)性質(zhì)
H13工具鋼的化學(xué)性質(zhì)要求是使材料承受溫度、壓力、磨損和熱循環(huán)等要求苛刻的應(yīng)用，如沖壓模具。這是最流行的沖壓模具合金也是全球第二受歡迎的塑料注塑工具鋼。這種鋼以低含碳量（0.4％）來提高韌性，以中等含鉻量（5％）來提供良好的抗高溫軟化性，以1％的硅含量來改善抗高溫氧化性，以少量鉬和釩（約1％）形成穩(wěn)定的碳化物來提高耐磨性[8]。噴射成形前后對H13工具鋼的成分分析。表1給出的結(jié)論，說明在合金補充后沒有顯著的變化。
表1 H13工具鋼的組成
化學(xué)成分 C Mn Cr Mo V Si Fe
常規(guī)H13鋼 0.41 0.39 5.15 1.41 0.9 1.06 Bal.
噴射成形H13鋼 0.41 0.38 5.10 1.42 0.9 1.08 Bal.
微觀結(jié)構(gòu)
在H13的工具鋼中發(fā)現(xiàn)的碳化物的大小、形狀、類型和分布是取決于加工方法和熱處理的。一般的商業(yè)鋼，機(jī)械廠會在使用之前退火處理和熱處理（奧氏體化/淬火/回火）。典型的奧氏體化溫度大約是1010°C，在空氣或油中淬火，并在540至650°C仔細(xì)回火兩次或三次，以獲得與要求相符合的硬度、抗疲勞強(qiáng)度和韌性。
商業(yè)用的鍛造鐵素體工具鋼因為鋼鐵廠的鑄塊慢慢冷卻形成粗糙碳化物而不能被沉淀硬化。與此相反，快速凝固的H13工具鋼因為合金增加的原因在很大程度上解決了這個問題，并更均勻地分布于模型[9-11]。其性能可以被人工老化或常規(guī)熱處理改變。
人工老化的一個好處是它繞開常規(guī)熱處理過程中具體的容積變化而導(dǎo)致的工具變形的發(fā)生。這些具體的容積的變化發(fā)生在從奧氏體向鐵素體轉(zhuǎn)為回火馬氏體的模型轉(zhuǎn)換階段，必須在模具設(shè)計的初期說明。然而，不是總能得到可靠預(yù)測的。補充的這部分，從設(shè)計和生產(chǎn)的角度看可能是可取的，經(jīng)常不包括像材料在淬火中奧氏體化或變形時有大幅衰退的趨勢。因為它沒有相變，噴射成形工具鋼不遵守人工老化期間的工具失真。
參 考 文 獻(xiàn)
[1] R. G. W. Pye, Injection Mould Design, John Wiley & Sons, NY, p. 14, 1989.
[2] Rapid Prototyping & Tooling State of the Industry - 1998 Worldwide Progress Report, Terry T. Wohlers, Wohlers Associates, Inc., p. 22, 1998.
[3] Kevin M. McHugh, “Fabrication of Tooling Inserts Using RSP Tooling Technology,” Proceedings of Moldmaking ‘99 Conference, Communication Technologies, Inc. Columbus, OH, May, 1999, p. 383.
[4] B. Hewson, J. Folkestad, and K. M. McHugh, “Qualifying Rapid Solidification Process Tooling: Justifying Cutting Edge Technology,” Proceedings of Rapid Prototyping and Manufacturing ‘99 Conference, The Society of Manufacturing Engineers, Dearborn, MI, April, 1999, p.75.
[5] Master Unit Die Quick-Change Systems, Greenville, MI
[6] Cotronics Corporation, Brooklyn, NY.
[7] E. J. Lavernia and Y. Wu, Spray Atomization and Deposition, John Wiley and Sons, New York, NY, p. 291, 1996.
[8] Tool Materials, ed. J. R. Davis, ASM International, Materials Park, OH, P.139, 1995.
[9] K. M. McHugh, “Microstructure Transformation Of Spray-Formed H13 Tool Steel During Deposition and Heat Treatment,” Solidification 1998, Edited by S. P. Marsh, J. A. Dantzig, R. Trivedi, W. Hofmeister, M. G. Chu, E. J. Lavernia, and J.-H Chun, The Minerals, Metals, & Materials Society, P. 427, 1998.
[10] Kyeong Ho Baik, Eon-Sik Lee, Woo-Jin Park, and Sangho Ahn, “Formation of Eutectic Carbides in Spray Cast High Speed Steel,” Proceedings of the Third International Conference On Spray Forming, Cardiff, UK p. 251, (1996).
[11] K. Bhargava and A. N. Tiwari, “Effect of Rapid Solidification and Heat Treatment on D2 Tool Steel,” Internat. J. Rapid Solidification, 7, 51 (1992).
附件2：外文原文
Spray-Formed Tooling
For Injection Molding and Die Casting Applications
Abstract
Rapid Solidification Process (RSP) Tooling is a spray forming technology tailored for producing molds and dies. The approach combines rapid solidification processing and net-shape materials processing in a single step. The ability of the sprayed deposit to capture features of the tool pattern eliminates costly machining operations in conventional mold making and reduces turnaround time. Moreover, rapid solidification suppresses carbide precipitation and growth, allowing many ferritic tool steels to be artificially aged, an alternative to conventional heat treatment that offers unique benefits. Material properties and microstructure transformation during heat treatment of spray-formed H13 tool steel are described.
Introduction
Molds, dies, and related tooling are used to shape many of the plastic and metal components we use every day at home or at work. The process involves machining the negative of a desired part shape (core and cavity) from a forged tool steel or a rough metal casting, adding cooling channels, vents, and other mechanical features, followed by grinding. Many molds and dies undergo heat treatment (austenitization/quench/temper) to improve the properties of the steel, followed by final grinding and polishing to achieve the desired finish [1].
Conventional fabrication of molds and dies is very expensive and time consuming because:
? Each is custom made, reflecting the shape and texture of the desired part.
? The materials used to make tooling are difficult to machine and work with. Tool steels are the workhorse of industry for long production runs. Machining tool steels is capital equipment intensive because specialized equipment is often needed for individual machining steps.
? Tooling must be machined accurately. Oftentimes many individual components must fit together correctly for the final product to function properly.
Costs for plastic injection molds vary with size and complexity, ranging from about $10,000 to over $300,000 (U.S.), and have lead times of 3 to 6 months. Tool checking and part qualification may require an additional 3 months. Large die-casting dies for transmissions and sheet metal stamping dies for making automobile body panels may cost more than $1million (U.S.). Lead times are usually greater than 40 weeks. A large automobile company invests about $1 billion (U.S.) in new tooling each year to manufacture the components that go into their new line of cars and trucks.
Spray forming offers great potential for reducing the cost and lead time for tooling by eliminating many of the machining, grinding, and polishing unit operations. In addition, spray forming provides a powerful means to control segregation of alloying elements during solidification and carbide formation, and the ability to create beneficial metastable phases in many popular ferritic tool steels. As a result, relatively low temperature precipitation hardening heat treatment can be used to tailor properties such as hardness, toughness, thermal fatigue resistance, and strength. This paper describes the application of spray forming technology for producing H13 tooling for injection molding and die casting applications, and the benefits of low temperature heat treatment.
RSP Tooling
Rapid Solidification Process (RSP) Tooling, is a spray forming technology tailored for producing molds and dies [2-4]. The approach combines rapid solidification processing and netshape materials processing in a single step. The general concept involves converting a mold design described by a CAD file to a tooling master using a suitable rapid prototyping (RP) technology such as stereolithography. A pattern transfer is made to a castable ceramic, typically alumina or fused silica. This is followed by spray forming a thick deposit of tool steel (or other alloy) on the pattern to capture the desired shape, surface texture and detail. The resultant metal block is cooled to room temperature and separated from the pattern. Typically, the deposit’s exterior walls are machined square, allowing it to be used as an insert in a holding block such as a MUD frame [5]. The overall turnaround time for tooling is about three days, stating with a master. Molds and dies produced in this way have been used for prototype and production runs in plastic injection molding and die casting.
An important benefit of RSP Tooling is that it allows molds and dies to be made early in the design cycle for a component. True prototype parts can be manufactured to assess form, fit, and function using the same process planned for production. If the part is qualified, the tooling can be run in production as conventional tooling would. Use of a digital database and RP technology allows design modifications to be easily made.
Experimental Procedure
An alumina-base ceramic (Cotronics 780 [6]) was slurry cast using a silicone rubber master die, or freeze cast using a stereolithography master. After setting up, ceramic patterns were demolded, fired in a kiln, and cooled to room temperature. H13 tool steel was induction melted under a nitrogen atmosphere, superheated about 100°C, and pressure-fed into a bench-scale converging/diverging spray nozzle, designed and constructed in-house. An inert gas atmosphere within the spray apparatus minimized in-flight oxidation of the atomized droplets as they deposited onto the tool pattern at a rate of about 200 kg/h. Gas-to-metal mass flow ratio was approximately 0.5.
For tensile property and hardness evaluation, the spray-formed material was sectioned using a wire EDM and surface ground to remove a 0.05 mm thick heat-affected zone. Samples were heat treated in a furnace that was purged with nitrogen. Each sample was coated with BN and placed in a sealed metal foil packet as a precautionary measure to prevent decarburization.Artificially aged samples were soaked for 1 hour at temperatures ranging from 400 to 700°C, and air cooled. Conventionally heat treated H13 was austenitized at 1010°C for 30 min., air quenched, and double tempered (2 hr plus 2 hr) at 538°C.
Microhardness was measured at room temperature using a Shimadzu Type M Vickers Hardness Tester by averaging ten microindentation readings. Microstructure of the etched (3% nital) tool steel was evaluated optically using an Olympus Model PME-3 metallograph and an Amray Model 1830 scanning electron microscope. Phase composition was analyzed via energy-dispersive spectroscopy (EDS). The size distribution of overspray powder was analyzed using a Microtrac Full Range Particle Analyzer after powder samples were sieved at 200 μm to remove coarse flakes. Sample density was evaluated by water displacement using Archimedes’ principle and a Mettler balance (Model AE100).
A quasi 1-D computer code developed at INEEL was used to evaluate multiphase flow behavior inside the nozzle and free jet regions. The code's basic numerical technique solves the steadystate gas flow field through an adaptive grid, conservative variables approach and treats the droplet phase in a Lagrangian manner with full aerodynamic and energetic coupling between the droplets and transport gas. The liquid metal injection system is coupled to the throat gas dynamics, and effects of heat transfer and wall friction are included. The code also includes a nonequilibrium solidification model that permits droplet undercooling and recalescence. The code was used to map out the temperature and velocity profile of the gas and atomized droplets within the nozzle and free jet regions.
Results and Discussion
Spray forming is a robust rapid tooling technology that allows tool steel molds and dies to be produced in a straightforward manner. Each was spray formed using a ceramic pattern generated from a RP master.
Particle and Gas Behavior
Particle mass frequency and cumulative mass distribution plots for H13 tool steel sprays are given in Figure 1. The mass median diameter was determined to be 56 μm by interpolation of size corresponding to 50% cumulative mass. The area mean diameter and volume mean diameter were calculated to be 53 μm and 139 μm, respectively. Geometric standard deviation, sd=(d84/d16)? , is 1.8, where d84 and d16 are particle diameters corresponding to 84% and 16% cumulative mass in Figure 1.
Figure1. Cumulative mass and mass frequency plots of particles in H13 tool step sprays.
Figure2 gives computational results for the multiphase velocity flow field (Figure 2a), and H13 tool steel solid fraction (Figure2b), inside the nozzle and free jet regions. Gas velocity increases until reaching the location of the shock front, at which point it precipitously decreases, eventually decaying exponentially outside the nozzle. Small droplets are easily perturbed by the velocity field, accelerating inside the nozzle and decelerating outside. After reaching their terminal velocity, larger droplets (?150 μm) are less perturbed by the flow field due to their greater momentum.
It is well known that high particle cooling rates in the spray jet (103-106 K/s) and bulk deposit (1-100 K/min) are present during spray forming [7]. Most of the particles in the spray have undergone recalescence, resulting in a solid fraction of about 0.75. Calculated solid fraction profiles of small (?30 μm) and large (?150 μm) droplets with distance from the nozzle inlet, are shown in Figure 2b.
Spray-Formed Deposits
This high heat extraction rate reduces erosion effects at the surface of the tool pattern. This allows relatively soft, castable ceramic pattern materials to be used that would not be satisfactory candidates for conventional metal casting processes. With suitable processing conditions, fine surface detail can be successfully transferred from the pattern to spray-formed mold. Surface roughness at the molding surface is pattern dependent. Slurry-cast commercial ceramics yield a surface roughness of about 1 μm Ra, suitable for many molding applications. Deposition of tool steel onto glass plates has yielded a specular surface finish of about 0.076 μm Ra. At the current state of development, dimensional repeatability of spray-formed molds, starting with a common master, is about ±0.2%.
Figure 2. Calculated particle and gas behavior in nozzle and free jet regions.
(a) Velocity profile.(b) Solid fraction.
Chemistry
The chemistry of H13 tool steel is designed to allow the material to withstand the temperature, pressure, abrasion, and thermal cycling associated with demanding applications such as die casting. It is the most popular die casting alloy worldwide and second most popular tool steel for plastic injection molding. The steel has low carbon content (0.4 wt.%) to promote toughness, medium chromium content (5 wt.%) to provide good resistance to high temperature softening, 1 wt% Si to improve high temperature oxidation resistance, and small molybdenum and vanadium additions (about 1%) that form stable carbides to increase resistance to erosive wear[8]. Composition analysis was performed on H13 tool steel before and after spray forming.Results, summarized in Table 1, indicate no significant variation in alloy additions.
Table 1. Composition of H13 tool steel
Element C Mn Cr Mo V Si Fe
Stock H13 0.41 0.39 5.15 1.41 0.9 1.06 Bal.
Spray Formed H13 0.41 0.38 5.10 1.42 0.9 1.08 Bal.
Microstructure
The size, shape, type, and distribution of carbides found in H13 tool steel is dictated by the processing method and heat treatment. Normally the commercial steel is machined in the mill annealed condition and heat treated (austenitized/quenched/tempered) prior to use. It is typically austenitized at about 1010°C, quenched in air or oil, and carefully tempered two or three times at 540 to 650°C to obtain the required combination of hardness, thermal fatigue resistance, and
toughness.
Commercial, forged, ferritic tool steels cannot be precipitation hardened because after electroslag remelting at the steel mill, ingots are cast that cool slowly and form coarse carbides. In contrast, rapid solidification of H13 tool steel causes alloying additions to remain largely in solution and to be more uniformly distributed in the matrix [9-11]. Properties can be tailored by artificial aging or conventional heat treatment.
A benefit of artificial aging is that it bypasses the specific volume changes that occur during conventional heat treatment that can lead to tool distortion. These specific volume changes occur as the matrix phase transforms from ferrite to austenite to tempered martensite and must be accounted for in the original mold design. However, they cannot always be reliably predicted. Thin sections in the insert, which may be desirable from a design and production standpoint, are oftentimes not included as the material has a tendency to slump during austenitization or distort during quenching. Tool distortion is not observed during artificial aging of spray-formed tool steels because there is no phase transformation.
References
[1] R. G. W. Pye, Injection Mould Design, John Wiley & Sons, NY, p. 14, 1989.
[2] Rapid Prototyping & Tooling State of the Industry - 1998 Worldwide Progress Report, Terry T. Wohlers, Wohlers Associates, Inc., p. 22, 1998.
[3] Kevin M. McHugh, “Fabrication of Tooling Inserts Using RSP Tooling Technology,” Proceedings of Moldmaking ‘99 Conference, Communication Technologies, Inc. Columbus, OH, May, 1999, p. 383.
[4] B. Hewson, J. Folkestad, and K. M. McHugh, “Qualifying Rapid Solidification Process Tooling: Justifying Cutting Edge Technology,” Proceedings of Rapid Prototyping and Manufacturing ‘99 Conference, The Society of Manufacturing Engin
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