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致謝
本科畢業(yè)設(shè)計(論文)
題目：洗衣機排水管道某零件的注射模具設(shè)計
系 別： 機電信息系
專 業(yè)： 機械設(shè)計制造及其自動化
班 級：
學 生：
學 號：
指導教師：
2013年 5 月
洗衣機排水管道某零件的注射模具設(shè)計
摘要
本次設(shè)計詳細介紹了洗衣機排水管道某零件的注塑模具設(shè)計，主要包括塑件材料的分析與設(shè)計方案的論證；注塑機的選擇；成型零件的設(shè)計；側(cè)向分型與抽芯機構(gòu)的設(shè)計；導向機構(gòu)的設(shè)計；脫模機構(gòu)的設(shè)計；溫度調(diào)節(jié)系統(tǒng)的設(shè)計，以及模具各部分的計算和校核等。本次設(shè)計的方案為一模兩腔，塑件材料選用了丙烯腈－丁二烯－苯乙烯共聚物（ABS），澆口形式選用了側(cè)澆口，模具結(jié)構(gòu)為直接分型——推桿推出機構(gòu)。同時運用了PRO/ENGINEER軟件設(shè)計模具三維圖。
關(guān)鍵詞：注塑模具，塑料，模具設(shè)計，抽芯機構(gòu)
Design of the injection mould for a part of the washing machine drain pipe
Abstract
The detailed design of the injection mold design of a washing machine drainage pipe parts, mainly includes the analysis and design of the plastic injection machine choice demonstration;forming part design; design side parting and core pulling mechanism; design of steering mechanism; demoulding mechanism design; design of temperature control system the portion of the mold, and the calculation and verification. The design scheme for a mold two cavity, acrylonitrile - butadiene - styrene copolymer with plastic material (ABS), gate form the side gate, the die structure for the direct type -- push rod ejecting mechanism. At the same time using the PRO/ENGINEER software design of 3D graph.
Key Words: Injection mould, plastic, mold design, core-pulling mechanism
目 錄
1緒論 1
1.1題目背景 1
1.2塑料模具的發(fā)展概況 1
1.3塑料模具的發(fā)展前景和趨勢 2
2塑件分析 3
2.1塑件的結(jié)構(gòu)分析 3
2.1.1塑件三維圖 3
2.1.2塑件二維圖 3
2.1.3精度分析 3
2.2塑件的材料分析 4
2.2.1塑件材料 4
2.2.2材料的特性 4
2.2.3 ABS的工藝特性 4
2.2.4 ABS的成型工藝 4
2.3塑料的成型工藝 5
2.4注射成型的過程 5
2.4.1成型前的準備 5
2.4.2注射成型過程 5
2.4.3制品的后處理 5
3方案論證 6
3.1方案論證 6
3.2采用方案 6
4注射機的選擇 7
4.1確定零件的體積 7
4.2注射機的選擇及參數(shù) 7
4.2.1注射機的類型 7
4.2.2注射機的主要技術(shù)參數(shù) 8
4.3注射機的校核 8
5分型面的選擇 10
5.1分型面選擇原則 10
5.2分型面設(shè)計 10
6澆注系統(tǒng)設(shè)計 11
6.1澆注系統(tǒng)作用及要求 11
6.2澆注系統(tǒng)的布置 11
6.3主流道設(shè)計 11
6.3.1主流道設(shè)計要求 11
6.3.2主流道計算 11
6.4分流道設(shè)計 12
6.4.1分流道設(shè)計要求 12
6.5澆口設(shè)計 12
6.5.1澆口類型 12
6.5.2澆口的位置 13
6.5.3澆口的選擇 13
6.6冷料穴設(shè)計 13
6.7澆口套和定位圈設(shè)計 14
6.7.1澆口套的設(shè)計 14
6.7.2定位圈的設(shè)計 14
7成型零部件設(shè)計 15
7.1成型零部件材料選擇 15
7.2成型零部件結(jié)構(gòu)設(shè)計 15
7.2.1型腔結(jié)構(gòu)設(shè)計 15
7.2.2型芯結(jié)構(gòu)設(shè)計 16
7.3成型零件尺寸計算 16
7.3.1影響制品尺寸精度的因素 16
7.3.2成型零件工作尺寸計算 17
7.3.3成型型腔壁厚計算 19
8導向機構(gòu)設(shè)計 20
8.1導柱的設(shè)計要求 20
8.2導柱的選擇 20
8.3導套的設(shè)計和選擇 20
9側(cè)向分型抽芯機構(gòu)設(shè)計 22
9.1抽芯機構(gòu)的類型 22
9.2抽芯距和抽芯力的計算 22
9.2.1抽芯距 22
9.2.2抽芯力 22
9.3斜導柱和斜滑塊設(shè)計 23
9.3.1斜導柱 23
9.3.2斜滑塊 23
9.3.3楔緊塊 24
10脫模機構(gòu)設(shè)計 25
10.1脫模裝置 25
10.2脫模機構(gòu)設(shè)計原則 25
10.2.1設(shè)計原則 25
10.2.2脫模力的計算 25
10.3頂桿頂出機構(gòu)的設(shè)計 26
10.3.1頂桿頂出機構(gòu)的設(shè)計要求和特點 26
10.3.2頂桿強度的計算 26
10.4復位裝置 27
11溫度調(diào)節(jié)和排氣系統(tǒng)設(shè)計 28
11.1溫度調(diào)節(jié)系統(tǒng)設(shè)計 28
11.1.1溫度調(diào)節(jié)對制品質(zhì)量的影響 28
11.1.2冷卻系統(tǒng)的設(shè)計原則 28
11.1.3冷卻系統(tǒng)的結(jié)構(gòu) 28
11.2排氣系統(tǒng)設(shè)計 29
12模具總體設(shè)計 31
12.1模具工作過程 31
12.2模具選用材料及熱處理 31
12.3環(huán)保和經(jīng)濟技術(shù)分析 32
13結(jié)論 33
參考文獻 34
致謝 35
畢業(yè)設(shè)計（論文）知識產(chǎn)權(quán)聲明 36
畢業(yè)設(shè)計（論文）獨創(chuàng)性聲明 37
0
1緒論
1.1題目背景
塑料模具的設(shè)計和制造水平反映了機械設(shè)計和加工的水平，模具的設(shè)計已應用了當代先進的設(shè)計手段。各行各業(yè)對模具需求量的增大，增加了大量的模具設(shè)計與制造的技術(shù)人才。本課題為中等以上難度的塑料模具設(shè)計，從模具的結(jié)構(gòu)設(shè)計，各種參數(shù)的設(shè)計與計算，材料的選擇與處理，零件的加工工藝方案的制訂，三維造型等均得到一定的鍛煉。
一個描述電鑄鎳殼在注塑模具的應用的技術(shù)研究
摘要：在過去幾年中快速成型技術(shù)及快速模具已被廣泛開發(fā)利用. 在本文中,使用電芯作為核心程序?qū)λ芰献⑸淠＞叻治?。通過差分系統(tǒng)快速成型制造外殼模型。主要目的是分析電鑄鎳殼力學特征、 研究相關(guān)金相組織，硬度，內(nèi)部壓力等不同方面，由這些特征參數(shù)以生產(chǎn)電鑄設(shè)備的外殼。最后一個核心是檢驗注塑模具。
關(guān)鍵詞：電鍍；電鑄；微觀結(jié)構(gòu)；鎳
1. 引言
現(xiàn)代工業(yè)遇到很大的挑戰(zhàn)，其中最重要的是怎么樣提供更好的產(chǎn)品給消費者,更多種類和更新?lián)Q代問題。因此,現(xiàn)代工業(yè)必定產(chǎn)生更多的競爭性。毫無疑問，結(jié)合時間變量和質(zhì)量變量并不容易。因為他們經(jīng)常彼此互為條件；先進的生產(chǎn)系統(tǒng)將允許該組合以更加有效可行的方式進行，例如，如果是觀測注塑系統(tǒng)的轉(zhuǎn)變、 我們得出的結(jié)論是，事實上一個新產(chǎn)品在市場上具有較好的質(zhì)量它需要越來越少的時間快速模具制造技術(shù)是在這一領(lǐng)域，中可以改善設(shè)計和制造注入部分的技術(shù)進步。快速模具制造技術(shù)基本上是一個中小型系列的收集程序，在很短的時間內(nèi)在可接受的精度水平基礎(chǔ)上讓我們獲得模具的塑料部件。其應用不僅在更加廣闊而且生產(chǎn)也不斷增多。
本文包括了很廣泛的研究路線，在這些研究路線中我們可以嘗試去學習，定義，分析，測試，提出在工業(yè)水平方面的可行性，從核心的注塑模具制造獲取電鑄鎳殼，同時作為一個初始模型的原型在一個FDM設(shè)備上的快速成型。
不得不說的是,先進的電鑄技術(shù)應用在無數(shù)的行業(yè)，但這一研究工作調(diào)查到什么程度，并根據(jù)這些參數(shù)，使用這種技術(shù)生產(chǎn)快速模具在技術(shù)上是可行的。都產(chǎn)生一個準確的，系統(tǒng)化使用的方法以及建議的工作方法。
2. 制造過程的注塑模具
薄鎳外殼的核心是電鑄，獲得一個充滿epoxic金屬樹脂的一體化的核心板塊模具(圖1)允許直接制造注射型多用標本，因為它們確定了新英格蘭大學英文國際表卓華組織3167標準。這樣做的目的是確定力學性能的材料收集代表行業(yè)。
該階段取得的核心[4]，根據(jù)這一方法研究了這項工作，有如下：
a,用CAD系統(tǒng)設(shè)計的理想對象
b模型制造的快速成型設(shè)備(頻分多路系統(tǒng)). 所用材料將是一個ABS塑料
c一個制造的電鑄鎳殼，已事先涂有導電涂料(必須有導電)。
d無外殼模型
e核心的生產(chǎn)是背面外殼環(huán)氧樹脂的抗高溫與具有制冷的銅管管道。
有兩個腔的注塑模具、 其中一個是電核心和其他直接加工的移動版。因此,在同一工藝條件下，同時注入兩個標準技術(shù)制造，獲得相同的工作。
3 獲得電殼:設(shè)備
電鍍是電解質(zhì)時電流的化學變化，電解所形成的直流電有兩個電極，陽極和陰極。當電流流經(jīng)電路，在離子溶液中轉(zhuǎn)化為原子。
電鍍液用于這項工作是由氨基磺酸鎳400 毫升/升,氯化鎳(10克/升)、硼酸(50克/升),allbrite SLA(30毫升/升),allbrite703(2毫升/升)。選擇這種組合主要原因是我們考慮注塑模具程序是玻璃纖維。氨基磺酸鎳讓我們獲得可以接受的內(nèi)部壓力(測試不同工藝條件結(jié)果,而不是最佳工藝條件約2兆帕最高為50兆帕)。不過,這種內(nèi)部壓力是由touenesulfonamode衍生物和甲醛水溶液使用的ALLbrite添加劑的結(jié)果。
這種添加劑也增加了殼的阻力。 Allbrite703是一種可生物降解水溶液表使用劑氯化鎳，有利于解決金屬統(tǒng)一分布在陰極，提高導電性的問題。硼酸作為PH值緩沖區(qū)。
該設(shè)備用于制造殼的測試如下：
● 聚丙烯:600毫米×400毫米×500毫米的尺寸
● 三聚四氟乙烯電阻器,每一個有800W
● 具有機械攪拌系統(tǒng)的陰極
●循環(huán)和過濾系統(tǒng)用的泵和聚丙烯過濾器。
● 充電整流器 最大強度在連續(xù)50個A和連續(xù)電流電壓介于0至16伏
● 籃鈦鎳陽極(鎳硫回合電解鎳)純度99%以上
● 氣體注入系統(tǒng)
一旦電流密度( 1-22A/dm），溫度(35至55℃)和pH值，已經(jīng)確定，執(zhí)行參數(shù)以及測試的進程部分不可改變。
4 獲得硬度
電殼硬度的測試一直保持在相當高的很穩(wěn)定的結(jié)果。如圖2，可以看到：電流密度值2.5到22A/dm，硬度值介于540到580高壓，PH值為4+-0.2和溫度為45攝氏度，如果PH減少到3.5和溫度為55攝氏度，硬度為520以上，高壓低于560.這一測試使常規(guī)組成不同于其他氨基磺酸鎳，允許其經(jīng)營更加廣泛，然而，這種operatyivity將是一定的取決于其他因素，如內(nèi)部壓力，因為他可能的變異。
改變PH值，電流密度和溫度等，另一方面，傳統(tǒng)的硬度氨基磺酸鎳承受的高壓在200-250之間，遠低于取得的一個實驗結(jié)果的電壓。對于一個注塑模具，硬度可以接受的起點300高壓這是必須考慮的，注塑模具中最常見的材料，有改善鋼（290高壓），整體淬火（520-595高壓），casehardened鋼鐵（760-8--高壓）等，以這樣一種方式，可以看到，注塑模具硬度水平的鎳是殼內(nèi)的高范圍的材料。因為這是一個負責內(nèi)部壓力的塑料注射液，這種方式與環(huán)氧樹脂灌漿將遵循它，相反對低韌性的殼補償，這就是為什么它是必定盡可能的外殼厚度均勻，并沒有重要的原因，如 腐蝕。
5 金相組織
為了分析金相結(jié)構(gòu)、電流密度、溫度主要變化. 在正面橫向部分（垂直沉積）對樣品進行了分析，為了方便地封裝在樹脂，拋光。銘刻，在不同階段的混合乙酸和硝酸。該時刻間隔15,25,40,50之后再次拋光, 為了在金相顯微鏡下觀察奧林巴斯PME3-ADL3.3X/10X
必須要說的是，這一條規(guī)定顯示了圖片之后的評論，用于制造該模型的殼在FDM快速成型機里融化的塑料材料（澳大利亞統(tǒng)計局）鞏固和解決了該階層。后來在每一個層，擠出的模具都留下一個大約0.15毫米直徑橫向和縱向的線程。因此，在表面可以看到細線表面頭部的機器。這些西路將作為參考信息解決鎳的重復性問題。重復性的模型將作為一個基本要素來評估注塑模具的表面紋理。
表1測試系列：
表1. 檢驗系列
系列
pH
溫度(℃)
電流密度A/mm2
1
4.2?±?0.2
55
2.22
2
3.9?±?0.2
45
5.56
3
4.0?±?0.2
45
10.00
4
4.0?±?0.2
45
22.22
圖3說明該系列第一時刻表面的樣本
它顯示了流道起點的頻率復用機，這就是說，又一個很好的重復性。它不能仍然要注意四舍五入結(jié)構(gòu)。在圖4 系列2，經(jīng)過第二次，可以看到一條線的流道的方式與以前的相比不太清楚。在圖5系列3雖然第二次時刻開始出現(xiàn)圓形晶結(jié)果是非常困難的。此外，最黑暗的部分表明時刻不足的進程和組成。
這種現(xiàn)象表明，在低電流密度和高溫條件下工作，得到更小的晶粒尺寸和殼重現(xiàn)性好，就是所需要的足夠的應用程序。
如果分析橫向平面進行的沉積，可以在所有測試樣品和條件增長的結(jié)構(gòu)層（圖6），犧牲一個低延展性取得令人滿意的高機械阻力，最重要的是添加劑的使用情況，氨基磺酸鎳液的添加劑通常創(chuàng)建一個纖維和非層狀結(jié)果[9].這個問題表明在任何情況下改變潤濕劑，由于該層結(jié)構(gòu)的決定因素是這種結(jié)構(gòu)的應力減速器（ALLbriteSLA)。另一方面，她也是測試的層狀結(jié)構(gòu)不同厚度中的電流密度.
6 內(nèi)部壓力
殼的一個主要特點是應該有其應用，如插入時要有一個低水平的內(nèi)部壓力。測試不同的溫度很電流密度，所采取的措施取決于陰極彎曲張力計法。A鋼測試控制使用側(cè)固定和其他自由度固定（160毫米長，12.7毫米寬，0.3毫米厚）。金屬沉積只有在控制了機械拉伸力（拉深或壓應力），才能計算內(nèi)部壓力。彈性的角度來看，斯托尼模型應用，假定鎳基質(zhì)厚度，對部分鋼材產(chǎn)生足夠小（3微米）的影響。在所有測試情況下，一個能夠接受的應用程序在內(nèi)部壓力在50兆帕的極端條件下和2兆帕的最佳條件下產(chǎn)生。得出的結(jié)論是，內(nèi)部壓力在不同的工作條件和參數(shù)沒有明顯的變化條件下。
7 校驗注塑模具
試驗已進行了各種代表性熱塑性材料如聚丙烯、高密度聚乙烯和PC、 并進行了注射部件性能的分析，如尺寸，重量，阻力，剛度和柔性。對殼的力學性能進行了拉伸破壞性測試和分析。大約500個注射液在其余的條件下，進行了更多的檢驗
總體而言, 為分析一種材料，重要的是注意到行為標本中的核心和那些加工腔之間的差異。然而在分析光彈注入標本（圖7）有人注意到不同的國家之間張力存在兩種不同的類型的標本，是由于不同的模腔熱傳遞和剛度。這種差異解釋了柔性的變化更加突出的部分晶體材料，如聚乙烯和聚酰胺6.
有人注意到一個較低的柔性標本在的高密度聚乙烯分析測試管在鎳核心的情況下，量化30%左右。如尼龍6這個值也接近50%。
8 結(jié)論
經(jīng)過連續(xù)的測試，注塑模具在不同條件下檢查的氨基磺酸鎳液使用添加劑。這就是說塑性好，硬度好和摩擦力好的層狀結(jié)構(gòu)，已取得的力學性能是可以接受的。借鞋缺陷的鎳殼將部分取代環(huán)氧樹脂為核心的注塑模具，使注入的一系列中型塑料零部件達到可接受的質(zhì)量的水平。
畢業(yè)設(shè)計（論文）中期報告
題目：洗衣機排水管道某零件的注射模具設(shè)計
系 別 機電信息系
專 業(yè) 機械設(shè)計制造及其自動化
班 級
姓 名
學 號
導 師
2013年 3 月 19 日
1.設(shè)計（論文）進展狀況
在本階段，主要完成的是畢業(yè)設(shè)計中的外文翻譯、模具裝配草圖、完善了塑件的二維零件圖以及對該塑件更深層次的分析和理解。
1.1二維零件圖
通過對零件的更深入的理解，在初期的零件二維圖的基礎(chǔ)上更加完善了零件的二維圖，使零件圖完整同時可以表達清楚零件的結(jié)構(gòu)。
1.2模具裝配草圖
初步完成了模具的裝配草圖，對裝配圖有了一個基本的認識和理解。
1.3外文文獻翻譯
通過工具翻譯了一篇與模具相關(guān)的外文文獻，使自己對國外的模具研究有了一個認識。
1.4設(shè)計方案
經(jīng)過研究和討論，對設(shè)計方案有了更加完善的結(jié)果，模具采用上下開模的方式，采用一模兩腔的結(jié)構(gòu)，對稱放置，一次成型；澆注采用側(cè)澆口，同時澆注；由于該塑件上具有與開模方向不一致的孔，所以要設(shè)計側(cè)向抽芯機構(gòu)，在開模的同時進行側(cè)向抽芯；同時也需要脫模機構(gòu)，在開模后將塑件頂出；在定模和動模之間要有導桿，保證動模定模能夠正確的開合。
2.存在問題及解決措施
2.1沒有很好的掌握和理解模具裝配的知識，模具裝配圖存在一些問題，具體的計算沒有完成
2.2對注射機的了解還不夠，沒有完成相應的計算及校核；同時對塑件和模具的理解還不到位等。
2.3對模具的側(cè)向抽芯的設(shè)計存在不合理的地方，對側(cè)抽芯機構(gòu)認識和理解不夠深刻。
2.4模具的流道和澆注設(shè)計做的不夠，缺乏這方面知識的學習。
接下來的時間里，需要對自己掌握不好的地方重點研究和理解，參考資料對自己較少涉及的方面重點學習，同時要與同學和老師多溝通交流，進一步加深對模具設(shè)計的理解以及把所學的理論知識運用到實際設(shè)計中去。
3.后期工作安排
11—12周，完成注射機的選擇及校核，通過計算逐步完善模具裝配圖。
13—15周，完成模具裝配中所有的零件設(shè)計同時畫出所有零件圖；同時對模具進行三維剖析，做出模具的開合結(jié)構(gòu)圖。
16—17周，撰寫畢業(yè)論文。
18周，整理資料，準備答辯。
指導教師簽字：
年 月 日
A technical note on the characterization of electroformed nickel shells for their application to injection molds
——Universidad de Las Palmas de Gran Canaria, Departamento de Ingenieria Mecanica, Spain
Abstract
The techniques of rapid prototyping and rapid tooling have been widely developed during the last years. In this article, electroforming as a procedure to make cores for plastics injection molds is analysed. Shells are obtained from models manufactured through rapid prototyping using the FDM system. The main objective is to analyze the mechanical features of electroformed nickel shells, studying different aspects related to their metallographic structure, hardness, internal stresses and possible failures, by relating these features to the parameters of production of the shells with an electroforming equipment. Finally a core was tested in an injection mold.
Keywords: Electroplating; Electroforming; Microstructure; Nickel
1. Introduction
One of the most important challenges with which modern industry comes across is to offer the consumer better products with outstanding variety and time variability (new designs). For this reason, modern industry must be more and more competitive and it has to produce with acceptable costs. There is no doubt that combining the time variable and the quality variable is not easy because they frequently condition one another; the technological advances in the productive systems are going to permit that combination to be more efficient and feasible in a way that, for example, if it is observed the evolution of the systems and techniques of plastics injection, we arrive at the conclusion that, in fact, it takes less and less time to put a new product on the market and with higher levels of quality. The manufacturing technology of rapid tooling is, in this field, one of those technological advances that makes possible the improvements in the processes of designing and manufacturing injected parts. Rapid tooling techniques are basically composed of a collection of procedures that are going to allow us to obtain a mold of plastic parts, in small or medium series, in a short period of time and with acceptable accuracy levels. Their application is not only included in the field of making plastic injected pieces [1], [2] and [3], however, it is true that it is where they have developed more and where they find the highest output.
This paper is included within a wider research line where it attempts to study, define, analyze, test and propose, at an industrial level, the possibility of creating cores for injection molds starting from obtaining electroformed nickel shells, taking as an initial model a prototype made in a FDM rapid prototyping equipment.
It also would have to say beforehand that the electroforming technique is not something new because its applications in the industry are countless [3], but this research work has tried to investigate to what extent and under which parameters the use of this technique in the production of rapid molds is technically feasible. All made in an accurate and systematized way of use and proposing a working method.
2. Manufacturing process of an injection mold
The core is formed by a thin nickel shell that is obtained through the electroforming process, and that is filled with an epoxic resin with metallic charge during the integration in the core plate [4] This mold (Fig. 1) permits the direct manufacturing by injection of a type a multiple use specimen, as they are defined by the UNE-EN ISO 3167 standard. The purpose of this specimen is to determine the mechanical properties of a collection of materials representative industry, injected in these tools and its coMParison with the properties obtained by conventional tools.
Fig. 1.?Manufactured injection mold with electroformed core.
The stages to obtain a core [4], according to the methodology researched in this work, are the following:
(a) Design in CAD system of the desired object.
(b) Model manufacturing in a rapid prototyping equipment (FDM system). The material used will be an ABS plastic.
(c) Manufacturing of a nickel electroformed shell starting from the previous model that has been coated with a conductive paint beforehand (it must have electrical conductivity).
(d) Removal of the shell from the model.
(e) Production of the core by filling the back of the shell with epoxy resin resistant to high temperatures and with the refrigerating ducts made with copper tubes.
The injection mold had two cavities, one of them was the electroformed core and the other was directly machined in the moving platen. Thus, it was obtained, with the same tool and in the same process conditions, to inject simultaneously two specimens in cavities manufactured with different technologies.
3. Obtaining an electroformed shell: the equipment
Electrodeposition [5] and [6] is an electrochemical process in which a chemical change has its origin within an electrolyte when passing an electric current through it. The electrolytic bath is formed by metal salts with two submerged electrodes, an anode (nickel) and a cathode (model), through which it is made to pass an intensity coming from a DC current. When the current flows through the circuit, the metal ions present in the solution are transformed into atoms that are settled on the cathode creating a more or less uniform deposit layer.
The plating bath used in this work is formed by nickel sulfamate [7] and [8] at a concentration of 400?ml/l, nickel chloride (10?g/l), boric acid (50?g/l), Allbrite SLA (30?cc/l) and Allbrite 703 (2?cc/l). The selection of this composition is mainly due to the type of application we intend, that is to say, injection molds, even when the injection is made with fibreglass. Nickel sulfamate allows us to obtain an acceptable level of internal stresses in the shell (the tests gave results, for different process conditions, not superior to 50?MPa and for optimum conditions around 2?MPa). Nevertheless, such level of internal pressure is also a consequence of using as an additive Allbrite SLA, which is a stress reducer constituted by derivatives of toluenesulfonamide and by formaldehyde in aqueous solution. Such additive also favours the increase of the resistance of the shell when permitting a smaller grain. Allbrite 703 is an aqueous solution of biodegradable surface-acting agents that has been utilized to reduce the risk of pitting. Nickel chloride, in spite of being harmful for the internal stresses, is added to enhance the conductivity of the solution and to favour the uniformity in the metallic distribution in the cathode. The boric acid acts as a pH buffer.
The equipment used to manufacture the nickel shells tested has been as follows:
? Polypropylene tank: 600?mm?×?400?mm?×?500?mm in size.
? Three teflon resistors, each one with 800?W.
? Mechanical stirring system of the cathode.
? System for recirculation and filtration of the bath formed by a pump and a polypropylene filter.
? Charging rectifier. Maximum intensity in continuous 50?A and continuous current voltage between 0 and 16?V.
? Titanium basket with nickel anodes (Inco S-Rounds Electrolytic Nickel) with a purity of 99%.
? Gases aspiration system.
Once the bath has been defined, the operative parameters that have been altered for testing different conditions of the process have been the current density (between 1 and 22?A/dm2), the temperature (between 35 and 55?°C) and the pH, partially modifying the bath composition.
4. Obtained hardness
One of the most interesting conclusions obtained during the tests has been that the level of hardness of the different electroformed shells has remained at rather high and stable values. In Fig. 2, it can be observed the way in which for current density values between 2.5 and 22?A/dm2, the hardness values range from 540 and 580?HV, at pH 4?±?0.2 and with a temperature of 45?°C. If the pH of the bath is reduced at 3.5 and the temperature is 55?°C those values are above 520?HV and below 560?HV. This feature makes the tested bath different from other conventional ones composed by nickel sulfamate, allowing to operate with a wider range of values; nevertheless, such operativity will be limited depending on other factors, such as internal stress because its variability may condition the work at certain values of pH, current density or temperature. On the other hand, the hardness of a conventional sulfamate bath is between 200–250?HV, much lower than the one obtained in the tests. It is necessary to take into account that, for an injection mold, the hardness is acceptable starting from 300?HV. Among the most usual materials for injection molds it is possible to find steel for improvement (290?HV), steel for integral hardening (520–595?HV), casehardened steel (760–800?HV), etc., in such a way that it can be observed that the hardness levels of the nickel shells would be within the medium–high range of the materials for injection molds. The objection to the low ductility of the shell is compensated in such a way with the epoxy resin filling that would follow it because this is the one responsible for holding inwardly the pressure charges of the processes of plastics injection; this is the reason why it is necessary for the shell to have a thickness as homogeneous as possible (above a minimum value) and with absence of important failures such as pitting.
Fig. 2.?Hardness variation with current density. pH 4?±?0.2, T?=?45?°C.
5. Metallographic structure
In order to analyze the metallographic structure, the values of current density and temperature were mainly modified. The samples were analyzed in frontal section and in transversal section (perpendicular to the deposition). For achieving a convenient preparation, they were conveniently encapsulated in resin, polished and etched in different stages with a mixture of acetic acid and nitric acid. The etches are carried out at intervals of 15, 25, 40 and 50?s, after being polished again, in order to be observed afterwards in a metallographic microscope Olympus PME3-ADL 3.3×/10×.
Before going on to comment the photographs shown in this article, it is necessary to say that the models used to manufacture the shells were made in a FDM rapid prototyping machine where the molten plastic material (ABS), that later solidifies, is settled layer by layer. In each layer, the extruder die leaves a thread approximately 0.15?mm in diameter which is compacted horizontal and vertically with the thread settled inmediately after. Thus, in the surface it can be observed thin lines that indicate the roads followed by the head of the machine. These lines are going to act as a reference to indicate the reproducibility level of the nickel settled. The reproducibility of the model is going to be a fundamental element to evaluate a basic aspect of injection molds: the surface texture.
The tested series are indicated in Table 1.
Table 1.
Tested series
Series
pH
Temperature (°C)
Current density (A/dm2)
1
4.2?±?0.2
55
2.22
2
3.9?±?0.2
45
5.56
3
4.0?±?0.2
45
10.00
4
4.0?±?0.2
45
22.22
Fig. 3 illustrates the surface of a sample of the series after the first etch. It shows the roads originated by the FDM machine, that is to say that there is a good reproducibility. It cannot be still noticed the rounded grain structure. In Fig. 4, series 2, after a second etch, it can be observed a line of the road in a way less clear than in the previous case. In Fig. 5, series 3 and 2° etch it begins to appear the rounded grain structure although it is very difficult to check the roads at this time. Besides, the most darkened areas indicate the presence of pitting by inadequate conditions of process and bath composition.
Fig. 3.?Series 1 (×150), etch 1.
Fig. 4.?Series 2 (×300), etch 2.
Fig. 5.?Series 3 (×300), etch 2.
This behavior indicates that, working at a low current density and a high temperature, shells with a good reproducibility of the model and with a small grain size are obtained, that is, adequate for the required application.
If the analysis is carried out in a plane transversal to the deposition, it can be tested in all the samples and for all the conditions that the growth structure of the deposit is laminar (Fig. 6), what is very satisfactory to obtain a high mechanical resistance although at the expense of a low ductibility. This quality is due, above all, to the presence of the additives used because a nickel sulfamate bath without additives normally creates a fibrous and non-laminar structure [9]. The modification until a nearly null value of the wetting agent gave as a result that the laminar structure was maintained in any case, that matter demonstrated that the determinant for such structure was the stress reducer (Allbrite SLA). On the other hand, it was also tested that the laminar structure varies according to the thickness of the layer in terms of the current density.
Fig. 6.?Plane transversal of series 2 (×600), etch 2.
6. Internal stresses
One of the main characteristic that a shell should have for its application like an insert is to have a low level of internal stresses. Different tests at different bath temperatures and current densities were done and a measure system rested on cathode flexural tensiometer method was used. A steel testing control was used with a side fixed and the other free (160?mm length, 12.7?mm width and thickness 0.3?mm). Because the metallic deposition is only in one side the testing control has a mechanical strain (tensile or compressive stress) that allows to calculate the internal stresses. Stoney model [10] was applied and was supposed that nickel substratum thickness is enough small (3?μm) to influence, in an elastic point of view, to the strained steel part. In all the tested cases the most value of internal stress was under 50?MPa for extreme conditions and 2?MPa for optimal conditions, an acceptable value for the required application. The conclusion is that the electrolitic bath allows to work at different conditions and parameters without a significant variation of internal stresses.
7. Test of the injection mold
Tests have been carried out with various representative thermoplastic materials such as PP, PA, HDPE and PC, and it has been analysed the properties of the injected parts such as dimensions, weight, resistance, rigidity and ductility. Mechanical properties were tested by tensile destructive tests and analysis by photoelasticity. About 500 injections were carried out on this core, remaining under conditions of withstanding many more.
In general terms, important differences were not noticed between the behavior of the specimens obtained in the core and the ones from the machined cavity, for the set of the analysed materials. However in the analysis by photoelasticiy (Fig. 7) it was noticed a different tensional state between both types of specimens, basically due to differences in the heat transference and rigidity of the respective mold cavities. This difference explains the ductility variations more outstanding in the partially crystalline materials such as HDPE and PA 6.
Fig. 7.?Analysis by photoelasticity of injected specimens.
For the case of HDPE in all the analysed tested tubes it was noticed a lower ductility in the specimens obtained in the nickel core, quantified about 30%. In the case of PA 6 this value was around 50%.
8. Conclusions
After consecutive tests and in different conditions it has been checked that the nickel sulfamate bath, with the utilized additives has allowed to obtain nickel shells with some mechanical properties acceptable for the required application, injection molds, that is to say, good reproducibility, high level of hardness and good mechanical resistance in terms of the resultant laminar structure. The mechanical deficiencies of the nickel shell will be partially replaced by the epoxy resin that finishes shaping the core for the injection mold, allowing to inject medium series of plastic parts with acceptable quality levels.