矩形開關(guān)外殼罩殼的注塑模具設(shè)計-抽芯塑料注射模含10張CAD圖
矩形開關(guān)外殼罩殼的注塑模具設(shè)計-抽芯塑料注射模含10張CAD圖,矩形,開關(guān),外殼,罩殼,注塑,模具設(shè)計,塑料,注射,10,cad
注塑模具之模具設(shè)計與制造
模具是制造業(yè)的重要工藝基礎(chǔ)，在我國，模具制造屬于專用設(shè)備制造業(yè)。中國雖然很早就開始制造模具和使用模具，但長期未形成產(chǎn)業(yè)。直到20世紀80年代后期，中國模具工業(yè)才駛?cè)氚l(fā)展的快車道。近年，不僅國有模具企業(yè)有了很大發(fā)展，三資企業(yè)、鄉(xiāng)鎮(zhèn)（個體）模具企業(yè)的發(fā)展也相當迅速。
雖然中國模具工業(yè)發(fā)展迅速，但與需求相比，顯然供不應(yīng)求，其主要缺口集中于精密、大型、復(fù)雜、長壽命模具領(lǐng)域。由于在模具精度、壽命、制造周期及生產(chǎn)能力等方面，中國與國際平均水平和發(fā)達國家仍有較大差距，因此，每年需要大量進口模具。
中國模具產(chǎn)業(yè)除了要繼續(xù)提高生產(chǎn)能力，今后更要著重于行業(yè)內(nèi)部結(jié)構(gòu)的調(diào)整和技術(shù)發(fā)展水平的提高。結(jié)構(gòu)調(diào)整方面，主要是企業(yè)結(jié)構(gòu)向?qū)I(yè)化調(diào)整，產(chǎn)品結(jié)構(gòu)向著中高檔模具發(fā)展，向進出口結(jié)構(gòu)的改進，中高檔汽車覆蓋件模具成形分析及結(jié)構(gòu)改進、多功能復(fù)合模具和復(fù)合加工及激光技術(shù)在模具設(shè)計制造上的應(yīng)用、高速切削、超精加工及拋光技術(shù)、信息化方向發(fā)展。
近年，模具行業(yè)結(jié)構(gòu)調(diào)整和體制改革步伐加大，主要表現(xiàn)在，大型、精密、復(fù)雜、長壽命、中高檔模具及模具標準件發(fā)展速度高于一般模具產(chǎn)品；塑料模和壓鑄模比例增大；專業(yè)模具廠數(shù)量及其生產(chǎn)能力增加；“三資”及私營企業(yè)發(fā)展迅速；股份制改造步伐加快等。從地區(qū)分布來看，以珠江三角洲和長江三角洲為中心的東南沿海地區(qū)發(fā)展快于中西部地區(qū)，南方的發(fā)展快于北方。目前發(fā)展最快、模具生產(chǎn)最為集中的省份是廣東和浙江，江蘇、上海、安徽和山東等地近幾年也有較大發(fā)展。
雖然我國模具總量目前已達到相當規(guī)模，模具水平也有很大提高，但設(shè)計制造水平總體上落后于德、美、日、法、意等工業(yè)發(fā)達國家許多。當前存在的問題和差距主要表現(xiàn)在以下幾方面：
（1）總量供不應(yīng)求
國內(nèi)模具自配率只有70%左右。其中低檔模具供過于求，中高檔模具自配率只有50%左右。
（2）企業(yè)組織結(jié)構(gòu)、產(chǎn)品結(jié)構(gòu)、技術(shù)結(jié)構(gòu)和進出口結(jié)構(gòu)均不合理
我國模具生產(chǎn)廠中多數(shù)是自產(chǎn)自配的工模具車間（分廠），自產(chǎn)自配比例高達60%左右，而國外模具超過70%屬商品模具。專業(yè)模具廠大多是“大而全”、“小而全”的組織形式，而國外大多是“小而?！薄ⅰ靶《?。國內(nèi)大型、精密、復(fù)雜、長壽命的模具占總量比例不足30%，而國外在50%以上。2004年，模具進出口之比為3.7:1，進出口相抵后的凈進口額達13.2億美元，為世界模具凈進口量最大的國家。
（3）模具產(chǎn)品水平大大低于國際水平，生產(chǎn)周期卻高于國際水平
產(chǎn)品水平低主要表現(xiàn)在模具的精度、型腔表面粗糙度、壽命及結(jié)構(gòu)等方面。
（4）開發(fā)能力較差，經(jīng)濟效益欠佳
我國模具企業(yè)技術(shù)人員比例低，水平較低，且不重視產(chǎn)品開發(fā)，在市場中經(jīng)常處于被動地位。我國每個模具職工平均年創(chuàng)造產(chǎn)值約合1萬美元，國外模具工業(yè)發(fā)達國家大多是15～20萬美元，有的高達25～30萬美元，與之相對的是我國相當一部分模具企業(yè)還沿用過去作坊式管理，真正實現(xiàn)現(xiàn)代化企業(yè)管理的企業(yè)較少。
隨著全球經(jīng)濟的發(fā)展，新的技術(shù)革命不斷取得新的進展和突破，技術(shù)的飛躍和發(fā)展已經(jīng)成為推動世界經(jīng)濟增長的重要因素。市場經(jīng)濟的不斷發(fā)展，促使工業(yè)產(chǎn)品越來越向多品種、小批量、高質(zhì)量、低成本的方向發(fā)展，為了保持和加強產(chǎn)品在市場上的競爭力，產(chǎn)品的開發(fā)周期、生產(chǎn)周期越來越短，于是對制造各種產(chǎn)品的關(guān)鍵工藝裝備——模具的要求越來越苛刻。?一方面企業(yè)為追求規(guī)模效益，使得模具向著高速、精密、長壽命方向發(fā)展；另一方面企業(yè)為了滿足多品種、小批量、產(chǎn)品更新?lián)Q代快、贏得市場的需要，要求模具向著制造周期短、成本低的快速經(jīng)濟的方向發(fā)展。計算機、激光、電子、新材料、新技術(shù)的發(fā)展，使得快速經(jīng)濟制模技術(shù)如虎添翼，應(yīng)用范圍不斷擴大，類型不斷增多，創(chuàng)造的經(jīng)濟效益和社會效益越來越顯著。??快速經(jīng)濟制模技術(shù)與傳統(tǒng)的機械加工相比，具有制模周期短、成本低、精度與壽命又能滿足生產(chǎn)上的使用要求，是綜合經(jīng)濟效益比較顯著的一類制造模具的技術(shù)，概括起來，有以下幾種類別快速凝固加工技術(shù) 表面成型制模技術(shù)澆鑄成型制模技術(shù)擠壓成型技術(shù)?
快速凝固加工工藝現(xiàn)在應(yīng)永最多的是快速凝固加工工藝。
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)。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）的微細結(jié)構(gòu)的光學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（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，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。
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。幾何標準偏差是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工具鋼的凝固體分數(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數(shù)大約是0.75。計算出的從噴嘴噴出的或?。ā?0微米）或大（～150微米）的凝固體分數(shù)。
圖2 氣體和微粒在射流噴嘴里多相流場。(a)速度分布圖 (b)凝固體分數(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，一個普通的機床來重復(fù)性空間噴射成形模具大約是±0.2％。
化學性質(zhì)
H13工具鋼的化學性質(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，說明在合金補充后沒有顯著的變化。
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。
6
外文翻譯：
Injection moulding for Mold Design and Manufacture
The mold is the manufacturing industry important craft foundation, in our country, the mold manufacture belongs to the special purpose equipment manufacturing industry. China although very already starts to make the mold and the use mold, but long-term has not formed the industry. Straight stabs 0 centuries 80's later periods, the Chinese mold industry only then drives into the development speedway. Recent years, not only the state-owned mold enterprise had the very big development, the three investments enterprise, the villages and towns (individual) the mold enterprise's development also quite rapidly.
Although the Chinese mold industrial development rapid, but compares with the demand, obviously falls short of demand, its main gap concentrates precisely to, large-scale, is complex, the long life mold domain. As a result of in aspect and so on mold precision, life, manufacture cycle and productivity, China and the international average horizontal and the developed country still had a bigger disparity, therefore, needed massively to import the mold every year .
The Chinese mold industry except must continue to sharpen the productivity; from now on will have emphatically to the profession internal structure adjustment and the state-of-art enhancement. The structure adjustment aspect, mainly is the enterprise structure to the specialized adjustment, the product structure to center the upscale mold development, to the import and export structure improvement, center the upscale automobile cover mold forming analysis and the structure improvement, the multi-purpose compound mold and the compound processing and the laser technology in the mold design manufacture application, the high-speed cutting, the super finishing and polished the technology, the information direction develops .
The recent years, the mold profession structure adjustment and the organizational reform step enlarges, mainly displayed in, large-scale, precise, was complex, the long life, center the upscale mold and the mold standard letter development speed is higher than the common mold product; The plastic mold and the compression casting mold proportion increases; Specialized mold factory quantity and its productivity increase; "The three investments" and the private enterprise develops rapidly; The joint stock system transformation step speeds up and so on. Distributes from the area looked, take Zhujiang Delta and Yangtze River delta as central southeast coastal area development quickly to mid-west area, south development quickly to north. At present develops quickest, the mold produces the most centralized province is Guangdong and Zhejiang, places such as Jiangsu, Shanghai, Anhui and Shandong also has a bigger development in recent years.
Although our country mold total quantity had at present achieved the suitable scale, the mold level also has the very big enhancement, after but design manufacture horizontal overall rise and fall industry developed country and so on Yu De, America, date, France, Italy many. The current existence question and the disparity mainly display in following several aspects:
(1) The total quantity falls short of demand
Domestic mold assembling one rate only, about 70%. Low-grade mold, center upscale mold assembling oneself rate only has 50% about.
(2) The enterprise organizational structure, the product structure, the technical structure and the import and export structure does not gather
In our country mold production factory to be most is from the labor mold workshop which produces assembles oneself (branch factory), from produces assembles oneself the proportion to reach as high as about 60%, but the overseas mold ultra 70% is the commodity mold. The specialized mold factory mostly is "large and complete", "small and entire" organization form, but overseas mostly is "small but", "is specially small and fine". Domestic large-scale, precise, complex, the long life mold accounts for the total quantity proportion to be insufficient 30%, but overseas in 50% above 2004 years, ratio of the mold import and export is 3.7:1, the import and export balances the after net import volume to amount to 1.32 billion US dollars, is world mold net import quantity biggest country .
(3) The mold product level greatly is lower than the international standard
The production cycle actually is higher than the international water broad product level low mainly to display in the mold precision, cavity aspect and so on surface roughness, life and structure.
(4) Develops the ability badly, economic efficiency unsatisfactory our country mold enterprise technical personnel proportion low
The level is lower, also does not take the product development, and frequently is in the passive position in the market. Our country each mold staff average year creation output value approximately, ten thousand US dollars, overseas mold industry developed country mostly 15 to10, 000 US dollars, some reach as high as 25 to10, 000 US dollars, relative is our country quite part of molds enterprises also continues to use the workshop type management with it, truly realizes the enterprise which the modernized enterprise manages few
To create the above disparity the reason to be very many, the mold long-term has not obtained the value besides the history in as the product which should have, as well as the most state-owned enterprises mechanism cannot adapt the market economy, but also has the following several reasons: .
The mold material performance, the quality and the variety question often can affect the mold quality, the life and the cost, the domestically produced molding tool steel and overseas imports the steel products to compare has a bigger disparity. Plastic, plate, equipment energy balance, also direct influence mold level enhancement.
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.
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.
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