压铸过程中模具表面温度变化研究综述

1、Surface temperature of tools during the high-pressure die casting of aluminium 高压铝压铸成型过程中模具表面温度的变化abstract: The objective of this work was to determine the temperature experienced within a pressure die-casting tool during alunimium part production. It was important to determine the temperature profi

2、le of the production process so that an accurate thermal cycle could later be simulated. The research overcame several challenges of this aggressive environment to show that the surface temperature of a die could be obtained from an H13 steel tool running on an aluminium pressure die-casting machine

3、. The results show that the surface of a typical aluminium pressure die-casting tool heats to 400-450C within approximately 1s and cools to 150-200C within approximately 20s 。摘要：此次工作的目标是为了测定在生产铝件产品时压铸模具内部温度的变化情 况。重点是确定产品在生产过程中模具的温度变化曲线，并且描绘出精确 的热量周期曲线。研究需要克服恶劣工作环境的挑战，从而得出在铝压铸 机中应用 H13 钢材制作的模具浇注系统的情况

4、下， 压铸模具表面温度的变 化情况。研究结果显示出普通的铝压铸模具温度达到 400450 度时大约需 要1s,而冷却到150200度时大约需要20s的时间。Keywords: surface temperature, tools, high-pressure die casting, aluminium关键字：表面温度 模具 高压压铸 铝1 IntroductionIn cold-chamber die casting, the molten material is forced into the die via a hydraulic plunger-piston in three cont

5、rolled phases producing high-quality castings. The process can be used with zinc-, magnesium-,aluminium-,and copper-based alloys.1 、简介对于冷室压铸成型, 熔融的材料是通过冲头作用挤压进入到模具中, 通过对 三个阶段的控制能够生产出高质量的制件。这种成型方法能够使用的材料为以 锌、镁、铝、铜为基体的合金。Phase1 is termed take up and slowly pushes the aluminium towards the die with min

6、imum turbulence.阶段 1 是压铸开始并且缓慢将铝液推动进入模具,从而得到最小的铝液波 动。Phase2 is the injection phase (filling of the die cavity). The cold-chamber pressure die-casting process typically casts aluminium alloys which are injected at 700-750C depending on the die geometry. This phase has to be fast enough to prevent chi

7、lling while the alloy is filling the die. The speed of this phase is approximately 10 m/s and typically takes 0.05-0.1s; however, speeds can be as high as 100m/s. During this phase, any gases are expelled via machined vents in the die and through the parting line.阶段 2 是注射阶段(充填模具型腔) 。冷室压铸成型普遍使用铝合金，其能

8、 够在温度为 700750 度时充填入压铸模的型腔中，形成几何形状。这一过程必 须足够快速， 并且要防止合金充填模具时发生急剧的冷却。 这一阶段的速度大约 是 10m/s ，并且普遍的充填时间为 0.050.1s ；甚至速度可以提高到 100m/s 。 在此阶段，型腔中的气体都要经由模具中的机械装置或者是通过分型面排出型 腔。phase 3 is the compaction phase, as the alloy solidifies in the cavity it begins to shrink away from the surface of the die. The force a

9、pplied to the alloy (50-70 N/mm2) reduces this effect and reduces the size of inclusions and porosity caused by air, trapped during injection. The die is usually water cooled and the surface sprayed with water-based die lubricant, causing thermal shock.阶段 3 是压实阶段。这一阶段中型腔中合金开始凝固， 并且从模具型腔表面 位置处开始收缩。当对

10、型腔中的铝液施加一定的压力时( 5070N/mm2 )，能够 减小体积收缩， 能够减小内部部件的尺寸变化， 并且能够消除由于气体和收缩造 成的内部孔洞。模具通常采用水冷， 并且表面采用水基润滑剂进行喷雾， 这都造成模具的热 量波动。The most important properties required of materials for die-casting tools are resistance to thermal fatigue and resistance to softening at elevated temperatures. Resistance to softenin

11、g is required to withstand the erosive action of molten metal under high injection pressures and speeds. The performance of die-casting dies is related to the casting temperature of the work metal, the thermal gradients within the dies, and the frequency of exposure to a high temperature. During the

12、 high-pressure die casting of alumunium the die has to withstand severe operating conditions such as high pressure and rapid temperature fluctuations and, over time, tool failure occurs 2,3. In actual die casting, the dominant tool failure mechanism is thermal fatigue cracking 4. Initially molten me

13、tal contacts the die and causes the surface temperature to increase above that of the interior of the die 5. The die face starts to expand; however, the cooler underlying layer resists this expansion creating a temporary compressive stress layer 6,7. When the casting is removed, the die surface star

14、ts to cool and, as it does, the surface shrinks or contracts. The surface cools more quickly than the interior of the die; this places the subsurface of the die into residual tensile stress, which is made worse by the application of die lubricant 8. During further cycling, the die surface is subject

15、ed to alternating compressive and tensile stresses that result in plastic deformation 9. Continued cycling reduces the yield strength of the tool, causing increased residual tensile stresses to develop and cracks to initiate. This type of cracking is more prevalent in aluminium and brass die casting

16、 because of the higher temperatures and resulting thermal shock by the molten metal.压铸模具材料需要的很多重要性能都是为了抵抗热疲劳和高温软化。 抵抗软 化是需要在高压和高速的情况下经受住熔融金属的侵蚀作用。 压铸模具的性能是 与成型金属的铸件温度、 模具内部的热量梯度和高温产生的频率密切相关的。 在 高压铝压铸成型过程中模具要经受严峻的工作条件， 比如高压、 迅速的温度波动 和疲劳、模具失效。在目前的压铸成型中，首要的模具失效形式是热疲劳开裂： 首先熔融金属接触模具导致模具表面温度激增， 并超过模具的内部温度

17、， 导致模 具表面开始膨胀； 但是表层下的冷却系统发挥作用抵抗这种膨胀， 并形成了临时 的可压缩应力层， 当铸件被取出后， 模具表面开始冷却， 在这样的情况下导致表 面收缩或者造成尺寸的缩减。 表面的冷却与模具内部相比要快速的多， 在这些位 置的模具表面下产生了残留的拉伸应力，而模具润滑剂的应用使得情况发生恶 化。经过较长的周期， 模具表面是受交互的压缩和拉伸应力的影响， 结果产生了 塑性变形， 这使得模具的屈服应力减少， 残留的拉伸应力增加， 并导致其持续增 长直至裂纹的产生。 这种裂纹的形式在铝和铜的压铸成型中是非常普遍的， 因为 在成型过程中都是经受了熔融金属的高温和热冲击。To und

18、erstand how a tool material behaves when subjected to thermal fatigue it is important to know the process temperature cycle (heating rate, cooling rate, temperature difference, mean temperature, cycle duration, etc.).了解模具材料受热疲劳影响所产生的变化， 这对于理解加工中温度的周期变 化是非常重要的(加热速率、冷却速率、温度差异、平均温度、周期持续时间等 等)。Persson 4

19、,10 investigated the thermal fatigue temperature profiles and conditions of brass pressure die casting and developed a test method. The die s surface temperature during casting was measured by four probes in a production die for tube couplings. The probes had a diameter of 16mm which housed a small

20、cylindrical test disc behind which K-type thermocouples ( with thin wires of diameter 0.13mm) were spot welded to the back of the discs. The thicknesses of the discs were 0.25, 0.5, 2, and 5mm.The temperature of the molten brass was 980C and was used with a cycle time of 30s during which the die was

21、 closed for 10s and opened for 20s. Water at 20C circulated continually in the die and the surfaces were lubricated. The shot mass of each casting was 1.6Kg with a peak casting pressure of 164Mpa.Persson 研究热疲劳温度曲线，并以铜的压力压铸件为研究对象，研究出一 套测试方法。 在铸造期间通过应用四个探针对生产中模具的管路进行耦合，发现模具表面温度是存在规律变化的。探针的直径是 16mm ，它的

22、前端是小的圆柱 型的测试薄片，后面是 K 型热电偶(细的金属线的直径是 0.13mm )，它焊接在 薄片的后面。测试薄片的厚度分为0.25mm 、0.5mm 、 2mm 、5mm 。熔融铜的温度是980度，并且使用30s的周期时间，其中模具的闭合时间是10s,而开 模的时间是20s。在模具中使用20度的水进行冷却，并且对模具的表面进行润 滑。在采用 164Mpa 极限压铸压力的情况下，使每个制件的射出质量保持在 1.6Kg 。During the first few cycles (less than 20) the tool ramped up from room temperature t

23、o steady state of 300C. Persson et al. 11 described a typical die surface temperature cycleas follows: ”When the 980C melt makes contact with the tool, the tool material is heated within about 0.35s from around 300C to a maximum temperature of around 750C at a surface depth of 0.25mm ”. “Until the t

24、ool is opened, cooling occurs by heat conduction into the bulk of the tool. Die opening and simultaneous cast ejection give rise to an additional heat loss through irradiation and convection. ”在最初的几次循环周期内 (少于 20 次)，模具温度急剧的由室温上升到 300 度的状态。 Persson 等人的出了典型的模具表面温度周期变化曲线，如下：当 980 度的熔融物与模具接触时，模具材料内部距离模具表

25、面 0.25mm 以内的区 域，在大约 0.35s 的时间内从大约 300 度升高到大约 750 度的最高温度。“直到 开模时，都会通过热传导的方式对模具内部进行冷却。 当模具打开和制件顶出时， 又会通过辐射及热传导的方式使模具造成更多的热量损失。 ”Bounds 12 investigated the thermal behaviour of the zinc pressure die-casting process by measuring the temperature of the die to obtain the operating conditions. J-type miner

26、al-insulated thermocouples were placed through the die block and die surface so that they would be in contact with the casting, and additional thermocouples were positioned 2.5mm behind the die surface. The zinc solidus was at 380C, the liquidus at 386C, and the casting alloy temperature, prior to i

27、njection, was 410C. The report detailed a problem with the response rate of the thermocouples.Bounds 是通过测量锌压力铸造时处于工作状态的模具温度， 来进行其热行 为的研究。首先将 J 型矿物绝缘热电偶通过模板放置在模具表面， 使其与制件相 接触，其它的电偶将被防止在距离型腔表面 2.5mm 的位置处。锌的凝固温度是 380 度，而其液化温度是 386 度，当合金温度为 410 度时进行注射，所得到的 报告详细的记录了热电偶的响应速率这一问题。Aluminium pressure die-cas

28、ting research regarding die temperature is limited. However, Perssons 4 research estimated the aluminium die surface temperature to be 520C. Srivastava et al. 6 stated that a typical die surface temperature reaches a maximum of 457C and can be cooled to 107C.铝压铸研究的模具温度范围比较狭窄， Persson 估计铝压铸模具表面温度是 52

29、0 度。 Srivastava 等人提出普通模具表面最高温度为 457 度，并且其能够冷 却到 107 度。Research has shown that on average the external surface temperature of the shot sleeve directly below the pouring hole reached 350C while the internal temperature reached between 480C and 500C 13. The shot sleeve removes a significant amount of h

30、eat from the molten aluminium prior to injection. When injected, the aluminium formed a skin on impact with the die and the mass of the die cooled the metal so rapidly that the surface temperature never reached the aluminium pourtemperature 14,15. This was confirmed by Oberg et al. 16 who stated: Al

31、though the die is hot, metal entering the die is cooled quickly, producing layers of rapidly chilled, dense material about 0.015 in (0.4mm) thick in the metal having direct contact with the die cavity surface”; this istermed the skin effect.研究表明，当模具内部温度达到 480 度至 500 度之间时，料缸下部浇注口 的外表面平均温度可以达到 350 度。在

32、注射前铝液中相当大数量的热量在加料 室中被损耗，当注射时，铝液形成外壳使其避免受到模具和模具质量的影响产生迅速冷 却，因此可以使得表面温度达到铝液灌注时的温度。这个理论已经被 Oberg 等 人所证实： 虽然模具是热的， 金属进入模具后快速冷凝， 与模具型腔表面相接触 的金属迅速冷却并形成由密集材料组成的凝固层，该层厚度大约为 0.015 英寸 ( 0.4mm )。这被称作：外壳效应。2 EXPERIMENTAL PROCEDUREA series of tests was planned to establish the temperature profile of an aluminium

33、 pressure die-casting toll surface, under production conditions.2 实验过程 通过一系列的实验建立起在生产条件下铝压铸模具表面的温度曲线。Obtaining a temperature profile was a difficult process because of the high pressures and speed of solidification in the pressure die-casting process. The main problem was locating and securing the t

34、hermocouples in position on the surface of the die. They had to be located and secured such that they resisted being pushed back into the bolster owing to the injection pressure; otherwise aluminium would escape from the cavity.在压铸过程中由于铝液是在很高的压力和速度下进行凝固， 所以对于温度曲 线的建立将是十分困难的。 主要的问题是在模具的表面如何放置热电偶， 并且能

35、 够保护其安全工作， 这需要热电偶能够在后退时受到模架的支撑来抵抗注射压力 所产生的推力，此外还必须能够防止铝液从型腔中溢出。In order to be relevant to normal practice a typical industrial aluminium pressure die-casting tool was required than could be modified to accommodate thermocouples. The tool needed to be manufactured from H13 tool steel (standard die ma

36、terial) to ensure that the thermal characteristics of the tool were accurate.为了顺利进行相应的实验， 不但要具有改良的热电偶， 同时也必须应用工业 级的铝压铸模，模具需要应用 H13 钢料来制作，这样能够保证模具具有良好的 热性能。A typical production H13 multi-cavity (four) aluminium die-cast tool was chosen. This was a tool for a clutch housing. The tool consisted of five

37、 inserts, three on the moving half (Fig.1(a) and two on the fixed half; this arrangement made tool modification easier since they could easily be removed from the bolster an d, if damaged, replaced. The cast ing had a shot mass of 250g with runner and biscuit and all four comp onents (Fig.1(b), and

38、an in dividual comp onent had a mass of 14g (Fig.2).图1（a）模具动模侧；（b ）离合器机壳制件挑选出一套典型的H13钢料制作的多型腔（四型腔）铝压铸模具，这是一 套离合器机壳模具。模具模仁是由五个部分镶拼组成，其中三个部分在动模侧（如 图1（a），两个在定模侧。这样的设置使得模仁能够容易的从模架中拆卸下来， 而且如果损坏，也能够更容易的进行更换。铝压铸制件包括浇注系统、料柄和四 个部件的射出质量是250g （如图1（b）,单个部件的质量是14g （如图2所 示）。图2“ Dyson ”离合器机壳图片The casting alloy use

39、d was AI-8% Si-3% Cu or LM24 (BS 1490 or ASTM B85-03). The alloy is com monly used for pressure die casti ng because its material properties are well suited to the process. Aluminium is prone to hydrogen absorption when molten, which can cause porous casting; this was resolved by modifying the alloy

40、 in the furnace by degassing. The aluminium was degassed by bubbli ng n itroge n through the molte n alloy. The alloy also required flux ing (Foseco, Coverall 11); this separated the dross from the molten aluminium so that is rose to the surface, creati ng a protective layer that hydroge n could not

41、 pen etrate. The dross was only removed at the begi nning of the casti ng process. A sample of molte n alu minium was take n in order to test the gas level using a hydroge n gas an alyzer; it was found to contain 0.15-0.25cm3 of gas per 500g, which was within typical casting limits.铸件合金由8%的铝、3%的硅、铜或

42、者LM24(BS 1490或者ASTM B85-03) 组成。由于该材料的属性与压铸成型过程非常匹配，所以这种合金普遍的应用于压铸部件。由于在熔融状态时防止了铝液对氢的吸收， 所以它能够用于防渗制件， 但是这必须在熔炉中通过抽气的方法来熔炼合金。合金同样需要进行提纯，这需要从熔融的铝液中祛除渣滓，使得铝液的表面呈现玫瑰色，这样在表面建立起一 道保护层，使得氢不能够进入到铝液内部。所以熔炼过程开始时产生的渣滓必须 要进行祛除。熔融铝液的样品需要应用氢气分析器来测定气体的含量水平，它的极限测试值为能够测试出金属液试样内部每500g里0.150.25cm3 的气体含量。表1压铸机参数参数值|机器类型

43、Frech DAK 125 SDV最大冲头速度（阶段1）0.15m/s最大冲头速度（阶段2）0.8m/s阶段2开始位置140mm阶段3开始位置270mm最大射出长度315mm最大模具锁模力125t合金LM24注入温度750C模具加热温度180C模具涂覆材料Delta Cast 333 R3周期时间2024s冲头直径50mm浇口位置处速度2.48m/s射出质量250g系统压力105barThe machi ne used had to be large eno ugh to accommodate the size of the die and the shot mass. A Frech DA

44、K125 SDV cold-chamber mach ine was used. The mach ine parameters are show n in Table 1 with the casting cycle shown in Fig.3. For consistency of die cooling, the automated die lubricator on the mach ine was utilized. The die lubrica nt (release age nt) was Aches on DeltaCast 333 release 3, at a temp

45、erature much higher tha n 20-25C; this was sprayed on to the die surface immediately prior to each shot, through six no zzles for 3s.动作响应开模舀汤注射凝固开模顶出脱模剂涂覆12s1s58s1s3s3s3s3s图3压铸成型周期压铸机的选择必须能够拥有足够的容模空间并且能够提供足够的射出质量,在这里使用法国产型号为DAK125 SDV的冷室压铸机进行实验。机器参数如表 1所示，一个周期中各个阶段的时间设置请见图 3。在机器中对模具实行持续的 冷却并自动进行模具润滑

46、剂的涂覆。润滑剂采用的是 Acheson DeltaCast 333型号3，其比其它产品的工作温度要高出2025度，润滑剂将在每一次注射前通过六个喷嘴在3s的时间内快速的喷散在模具的表面上。As in product ion, the die was in itially heated to approximately 150C with a gas lance and 50 shots run through to heat the die to the operat ing temperature.在生产中，应用喷枪使模具的初始温度达到150度，并且需要经过50模次的射出使得模具整体热量均

47、匀，达到工作温度。Measuri ng the surface temperature was difficult and several attempts and test adaptati ons were con ducted. An in itial attempt to determ ine the surface temperature of a die resulted in an aluminium blowout, causing considerable loss of time because the die had to be disassembled clea ned

48、, repaired, and reassembled. It was obvious from the first attempt that the thermocouples required relocation, resulting in the machining of the bolster and the insert, to secure two calibrated min eral-in sulated K-type en d-gro und thermocouples of 0.25mm diameter by means of a collet. The size of

49、 the thermocouples was importa nt because, the smaller the diameter of the wire, the faster is the react ion speed. A compromise had to be made; if the thermocouple is too small, it would be destroyed an d, if it is too large, its resp onse rate would be too slow. The thermocouple tips were positi o

50、ned at the die surface to allow direct con tact with the molte n alumi nium as it en tered the die. Temperature-se nsitive paints were placed in the biscuit and runner system of the alu minium die cast tool as these areas are typically subjected to the most heat (Fig.4.). However, it was found that,

51、 as the alu minium was being forced dow n the runn ers, it washed the paints away. The locati on of the paints was cha nged to the overflow regi on of the die, to solve this problem. The thermocouples were conn ected via a compe nsati ng cable to a computer data logger con trolled by Nati onal In st

52、rume nts LabVIEW TM version 5.1.1 software. It en abled several thermocouples to be conn ected at once. The data could also be loaded into Microsoft Excel.图4模具动模侧中热电耦和感热材料的位置测量模具的表面温度是困难的，需要经过一些尝试，并且需要对测试的条件 进行记录和整理。最初的试验是确定铝液喷出时模具表面温度数值， 结果对模具 进行了拆解、清理、修复和装配，浪费了大量的时间。通过最初的测试，开始对模架和镶块进行加工，用以保护两个直径为0

53、.25mm的具有矿物绝缘端盖的 K型热电偶，将其用底座进行固定。热电偶的尺寸是非常重要的，比较小的电线直 径能够提供更快的反映速度，但是如果热电偶过小，它将容易受到破坏；如果热 电偶过大，它的响应速率将会很慢。热电偶的尖端位置需要放置在模具表面并直 接伸入到模具中与熔融的铝液相接触。在铝压铸模具的料柄和流道区域涂覆感热 涂料，因为这些是遭受到巨大热量的影响的典型位置（如图4所示）。然而通过实验发现，铝液充填产生的压力作用于流道系统中，它将涂料冲到远处，涂料甚 至出现在模具的溢流区域，这是需要解决的问题。热电偶需要经由均衡导线通过 Natio nal In strume nts LabVIEW

54、TM 5.1.1版本的软件与计算机数据记录控制器相连接。它能够一次连接多个热电偶，所得到的数据能够转化为 Microsoft Excel 格式。3 RESULTS3、实验结果Figure 5 shows the results obta ined from the first test. Unfortun ately the thermocouple in the runner failed when the die was warmed to 250C as it was directly next to the gas lance. The thermocouple in the hott

55、est area (biscuit) survived and the test continued show ing that the surface temperature of the die reached 350 ?C and cooled to between 150 and 200?C with a typical cycle time of 20 -24 s. How-ever, the paints suggested that the surface temperature was between 399 ?C and 454?C. It was clear that th

56、e reaction time of the thermocouples was too slow because of thelarge wire diameter and the in sulati on. Hence, the results obta ined were n ot represe ntative of the surface temperature in an alumi nium pressure die-cast ing cycle because the thermocouples were not able to measure the temperature

57、sufficie ntly rapidly.SOD3503002502001SDf I J J- vf k T X xj f、|、1、777*I7100010203040506070 9QTime (s)id0 1001110120图5压铸过程中模具表面温度变化图（料柄区域）图片5显示了最初实验的结果。当模具温度达到 250度时由于流道中的热 点耦直接受到气体喷枪的作用，所以导致其发生失效。在比较热的区域中的热电 偶未受影响，并且继续测试显示出在一个为 2024s的成型周期内模具表面温度 达到了 350度，并冷却到150度到200度之间。然而涂料显示的表面温度却在 399度至454度之间，这是

58、由于热电偶具有较大直径并且绝缘的关系，造成了反 应迟钝使得温度存在偏差。因此，由于热电偶没有十分迅速的测出模具表面温度, 使得测量的结果并没有真正代表铝压铸成型周期内模具的真实表面温度。To overcome the problem in the previous experiment, several fiberglass-insulated K-type ope n-en ded thermocouples, with a wire diameter of 0.3 mm, were stuck to the surface of the die. These thermocouples have a faster rea