注塑工艺设计2.天津.jul2009

1、注塑工艺设计,徐昌煜 Charles Hsu 先进成型技术学会 创会理事2009年7月13日 于天津市,注射成型周期 Injection Molding Cycle,Mold temperatures are important in determining final part finish and molded-in stress levels. Cold molds are more difficult to fill, necessitating high injection pressure and melt temperature. Heated molds generally produce a part with a better finish and lower molded in stress. Because of the high heat distortion temperatures of engineering thermoplastic resins, parts are ejected easily at higher temperatures.The

2、 midpoint of the suggested range will generally give good results with respect to part appearance and cycle time. Higher mold temperatures can result in better flow, stronger knitlines and lower molded-in stresses. Using lower than the suggested mold temperatures will generally result in higher molded-in stresses and compromise(危及) part integrity.,模温 Mold Temperature,As a general rule, residence time should be as short as possible when molding near the maximum suggested melt temperature.When pro

3、cessing near, or at, the upper limit of the melt range, the shot weight should approach 80 to 90% of the cylinder capacity of the machine. If the cylinder temperature exceeds the upper limit of the suggested melt range, thermal degradation of the resin and loss of physical properties may result.,熔胶温度 Melt Temperature,A relatively small increase in screw speed (RPM) or back pressure can result in a dramatic increase in melt temperature with no change in controller set point. It is suggested that

4、melt temperatures be measured using hand-held pyrometers. These measures should be taken on the thermoplastic melts after the machine is on cycle.Increased melt temperatures will reduce viscosity and increase resin flow, thus providing for longer flow for thin wall sections and help produce lower residual stress. When higher melt temperatures are used, reduced barrel/residence times are needed to minimize any degradation of the resin.,熔胶温度 Melt Temperature,Screw speeds (RPM) should be adjusted t

5、o permit screw rotation during the entire cooling cycle without delaying the overall cycle . Low screw speeds will help reduce glass fiber damage during plastication when molding reinforced grades. Suggested screw speed is dependent on screw diameter. Optimum linear velocity of screw O.D. is typically 8 inches (202.4 mm) per second. RPM = (60 x 8 inches/second or 202.4mm/second)/( x screw diameter). For example, for a 3 inch (75.9 mm) diameter screw: 3 (screw Dia.) x 3.1416 = 9.4248 divided into

6、 8 inches (202.4 mm) per second (optimum linear velocity) x 60 = 51 RPM.,螺杆转速 Screw Speed,Back Pressure A back pressure of 50 to 100 psi (0.35 to 0.7 MPa) is suggested to help ensure a homogeneous melt and maintain consistent shot size. Higher back pressures used to improve melt mixing result in higher melt temperatures and possibly degradation due to excessive shearing of the resin.,背压 Back Pressure,The fastest fill speed possible provides longer flow, fills thinner wall sections, and helps to

7、create a better surface finish. Slower fill is suggested for sprue-gated and edge-gated parts to help prevent gate blush, splay and jetting. In thick wall parts 0.2 inches (5.06 mm) and up slow fill helps reduce sinks and voids.,射速 Injection Speed,Injection Pressure The actual injection pressure will depend on variables such as melt temperature, mold temperature, part geometry, wall thickness, flow length, and other mold and equipment considerations. Generally, the lowest pressures which provide

8、 the desired properties, appearance, and molding cycle are preferred. Ideally, injection pressure should vary to maintain the intended ram speed. This is called “velocity controlled injection“ and provides the molder a much more robust and respectable process than controlling injection pressure during fill.,射压 Injection Pressure,射压对充填时间变化曲线 Injection Pressure vs Fill Time,DVD盒的翘曲及锁模力需求Warpage and Required Clamp Force of a DVD Box,DVD盒, PP, 广东省珠海市, 2002.8.6.,DVD盒, PP, 2型腔模, 注射时间: 1.8秒 公称厚度1.3mm,

9、铰链厚度0.18mm,产品简介,产品：DVD Box 材料：PP 产品尺寸(展开) 284x191x9.4mm 产品尺寸(合上) 136x191x14mm 模具为一出二。,产品壁厚分布如上图所示，公称壁厚为1.3mm，侧壁壁厚为1.8mm、1.6mm和0.8mm，中间铰链处最小厚度为0.18mm。,方案比较表,保压切换位置为99%,保压压力为切换时注射压力的80%.模温设定8C； 料温设定260C,* 第1项没有采用优化的螺杆注射曲线，和使用优化曲线者(第7项)比，射压高出了13%以及锁模力多出了39%。 * 第2项至第11项采用优化的螺杆注射曲线。,U型曲线(注射压力vs注射时间),DVD盒(PP) 模温设定8C； 料温设定260C,对应最小射压的注射时间为1.2秒。,U型曲线(锁模力vs注射时间),对应最小锁模力的注射时间为0.6秒。,DVD盒(PP)模温设定8C； 料温设定260C,Programmed injection is suggested for parts with small gates (pin gates and subgates). A slow inject

10、ion rate can be used at the start to help eliminate gate blush, jetting, and burning of the material. Once underway, speed can be increased to fill the part. Maintain constant melt front velocity, and slow near end of fill to optimize part quality.,螺杆速率 Ram Speed,螺杆速度对行程曲线 Ram Speed Profile,螺杆速度对行程设定的影响,MFV & MFA的定义,熔胶前沿速度 Melt-Front Velocity (MFV) 熔胶前沿截面积 Melt-Front Area (MFA),前沿速度 Melt Front Velocity,MFV的调整,由于大部分的模具几何外型都相当复杂，固定的螺杆速度不太可能提供固定的熔胶前沿推进速度。 每当型腔的截面积改变时，该区域的充填速度就可能比其他区域充填的还要快，上图中表示的，就是在一定的入口速度下，熔胶前沿推进速度在入子的两侧突然加快的情形。 这将会造成在上图中入子的两侧产生高剪切应力，可能会导致成品的翘曲变形。,

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