Injection molding

Replies

• 

  Ernesha

  njection molding (British English: moulding) is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity. [1] After a product is designed, usually by an industrial designer or an engineer, molds are made by a moldmaker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars.
  File:injection Molding.png
• 

  ronvieky

  Interesting. But too basic. Thanks anyways. I need calculations, and Modelling of the machine. Thanks for the effort. Its more than anyone else could do... 😀
• 

  Ernesha

  Injection molding is a method of fabricating plastic parts by utilizing a mold or cavity with a shape and size identical to the part being produced. Molten polymer is injected into the cavity, resulting in the desired part upon solidification. The mass production capability of injection molding offers low production cost, but start-up costs can be significant because of the high costs of the injection molding machine and the mold itself. Injection molds are typically made from steel alloys and can require several months and tens of thousands of dollars to develop. Lower cost and shorter development time, therefore, have been an important focus in the injection molding community. Stereolithography, with Its capability to produce tools quickly and economically, offers a potential solution.
• 

  Ernesha

  Ejection Force Modeling
  Current ejection force equations are insufficient to apply to SL molds (e.g., 5-8). For instance, they apply only to restricted geometries and shapes and fall to account for the properties and characteristics of SL tools. More noticeably, the mechanical interlocking due to the characteristic stair stepping of SL molds has been only partially investigated and accounted. For example, Glanvill's model for ejection force (8) assumes a perfectly rigid, smooth male core with a plastic part shrinking onto it (Eq 1).
  P = [S.sub.t] X E X A X [mu]/d(d/2t - d/4t X [gamma]) (1)
  where P is the ejection force; E is the modulus of the plastic part; A is the total area of contact between the part and the mold in the line of draw; [mu] is the coefficient of friction between the plastic and the metal; d is the diameter of the circle of circumference equal to the length of the perimeter of the part surrounding the male core; t is the thickness of the part; [gamma] is the Poisson's ratio of the plastic; and [S.sub.t] is the thermal contraction of the plastic across the diameter d (the coefficient of thermal expansion x temperature difference between softening point and ejection temperature X d).
  This deficit prompted the need for a new model that is versatile and acceptably accurate. The model for ejection force is developed by combining the contributions of major contributing factors, namely the thermal shrinkage and the inherent stair-step profile of SL tools. This is shown mathematically in Eq 2.
• 

  Ernesha

  [F.sub.Ejection] = [F.sub.fric,therm] + [F.sub.def,stair] (2)
  where [F.sub.fric,therm] and [F.sub.def,stair] denote ejection force components due to thermal shrinkage and stair-step, respectively. These ejection force components are developed below.
  Ejection Force Due to Thermal Shrinkage ([F.sub.fric,therm])
  For a general mold with a core feature, [F.sub.fric,therm] can be estimated using the thick-walled cylinder approximation (9, 10) as shown in Eq 3.
  [FORMULA NOT REPRODUCIBLE IN ASCII] (3)
  where is the [F.sub.fric,therm] is the ejection force due to thermal shrinkage; [mu] is the friction coefficient; SA is the surface contact area parallel to the ejection direction; [DELTA]T is the change in temperature from injection to ejection points; r is the hydraulic radius (2*area/perimeter); E is the Young's modulus: [upsilon] is Poisson's ratio; and m, p are subscripts denoting mold and part, respectively. In regard to [DELTA][T.sub.p], the Young's modulus of the part's material is significant only at a temperature lower than the glass temperature [T.sub.g,p]. Therefore, the thermal strain due to part cooling should be included only after the part cools below [T.sub.g,p]. In other words, [DELTA][T.sub.p] = [T.sub.g,p] - [T.sub.e,p]. where [T.sub.e,p] denotes the ejection temperature of the part.
  Ejection Force Due to Stair-step ([F.sub.def,stair])
  The layered nature of the SL process leads to the stair-step phenomenon. In previous research, the effect of the stair-steps was usually lumped into the value of the friction coefficient, [mu]. This approach does not take advantage of the well-defined structure of the stair-step profile. Also, simply using [mu] as the proportionality coefficient between the normal load and the ejection force ([F.sub.e] = [mu]*N) implies that friction is proportional to the normal load, which is not the case for polymers (5, 11). In this study, the effect of stair-step on ejection force was considered separately from the frictional value. [F.sub.def,stair] represents this effect, Previous research (3, 12) suggested that the part and mold must deform elastically to make ejection possible. The ejection force component [F.sub.def,stair] is the force necessary to elastically deform the mold and the part to overcome the overlap. In order to formulate [F.sub.def,stair] the stair-step profile was modeled and the overlap, [delta], was quantified as follows.
  Modeling of Stair-step Profile of SL Tools.
  As the laser beam draws the boundary contours of the CAD model, it generates the parabolic-cylinder-shaped "cured lines" that form the stair-like structures on the surface of the SL tool (13). The overlap created by this stair-step can be quantified using the equation of the curing bullet profile (Fig. 2) as seen in Eqs 4 and 5. The latter equation represents the practical form.
  [delta] = [L.sub.w]/2(1 - [square root of ([C.sub.d] - l/[C.sub.d])])
  = [W.sub.o] * [square root of (0.5 * ln[[square root of (2/[pi])]([P.sub.L]/[W.sub.o][V.sub.s][E.sub.c])])] * ( 1 - [square root of ([C.sub.d] - l/[C.sub.d])]) (4)
• 

  Ernesha

  is this fine or you need more
• 

  ronvieky

  Girl On fire!!!
  
  Hey, thanks, miss cummins, i wonder where you got this info from. hope you can share the link , or ebook. What year are you in? and which Branch?
• 

  raghav.shet

  Hi dude.
  
  Check this link for basic to advance moulding.
  #-Link-Snipped-#
  
  Cheers
  
  Raghav
• 

  ronvieky

  Awesome... thanks... raghav.. and Ernesha... both... 😀
• 

  jinkejie

  ronvieky

  Awesome... thanks... raghav.. and Ernesha... both... 😀

  Nice topic, inisider really! I am running a factory check out my website: who need to make plastic products just contact me freely.
• 

  skyma

  there is a good place for injection molding manufacturers as there are so many injection molding manufacturers and much knowledge for injection molds. we are the injection molding manufacturer from Shanghai China. if you need,
  
  
  PS:- Contact Admin if you want to advertise on CE.