压铸过程中模具表面温度变化研究.docx

1、压铸过程中模具表面温度变化研究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 tem

2、perature pro 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

3、machine. 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

4、况下，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 controll

5、ed 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 minimum turb

6、ulence.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 chilling while

7、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，其能够在温度为700750度时充填

8、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 applied to the alloy (50-70 N/m

9、m2) 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。当对型腔中的铝液施加一定的压力时（5070N/mm2），能够减小体积收缩，

10、能够减小内部部件的尺寸变化，并且能够消除由于气体与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 softening is required to withstand the erosive actio

11、n 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 high-pressure die casting of alumunium the

12、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 metal contacts the die and causes the surface

13、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 starts to cool and, as it does, the surface shri

14、nks 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 subjected to alternating compressive and tensile st

15、resses 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 because of the higher temperatures and resu

16、lting 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与高温软化。抵抗软化是需要在高压与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与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、迅速的温度波动与疲劳、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，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

17、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与拉伸应力的影响，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与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与热冲击。To understand how a tool material behaves when subjected to thermal fatigue it is imp

18、ortant 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 4,10 investigated the thermal fatigue temperature profiles and conditions of brass

19、pressure die casting and developed a test method. The dies 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 cylindrical test disc behind which K-type thermocouples（with thin wires of diameter

20、 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 closed for 10s and opened for 20s. Water at 20C circulated continually in the die an

21、d 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

22、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 to steady state of 300C. Persson et al. 11 described a typical die surface temperature cycle as follows:” W

23、hen 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 tool is opened, cooling occurs by heat conduction into the bulk of the tool. Die opening and simultaneous c

24、ast 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。当模具打开与制件顶出时，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。”Bou

25、nds 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 mineral-insulated thermocouples were placed through the die block and die surface so that they would be in contact with the casting, a

26、nd 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 injection, 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

27、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-casting research regarding die temperature is limited. However, Perssons 4 research estimated the aluminium die surface temperature to be 520C. Sriv

28、astava 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520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

29、the pouring hole reached 350C while the internal temperature reached between 480C and 500C 13. The shot sleeve removes a significant amount of heat 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

30、 so rapidly that the surface temperature never reached the aluminium pour temperature 14,15. This was confirmed by Oberg et al. 16 who stated: Although 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 me

31、tal having direct contact with the die cavity surface”; this is termed 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与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

32、寸（0.4mm）。这被称作：外壳效应。2 EXPERIMENTAL PROCEDUREA series of tests was planned to establish the temperature pro an aluminium 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 pro 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 thermocouples 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 pr