Question

3) Meld lines are formed when two separate flow fronts meets. These are preferred over weld lines as they will normally result in improved structure. In manufacturing, the Weld line or Meld line is the 'knit line where two flow fronts meet and there is the inability of two or more flow fronts to "knit" together, or "weld", during the molding process. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. These are considered molding defects. a) How may the effect of weld and meld lines be reduced? b) Describe the process of single screw injection molding c) What are the three phases of injection molding? d) Why would an extra 15% volume of material be recommended during the pressurization phase? e) why may a large volumetric change of about 25% be observed after the pressurization phase? 1. Melt fronts approach 2 Weld line forma 3. Meld line forma Meld Line Weld Line Met Met Met Met

Answer 1

a.This can be done by changing the polymer injection location or altering wall thicknesses to set up a different fill time.

b.

Stationary Movable Platen Platen Mol d Plates Nozzle Rotating and Barre Injeconrue Reciprocating Screw Cha mber

c.Step 1: Product Design

There are many objectives to design : function, aesthetics, manufacturability, assembly, etc

Step 2: Mold Design

After the design has been tested and destined for further production, the mold needs to be designed for injection mold manufacturing

Step 3: The Manufacturing Process

Thermoset or thermoplastic material in granular kind is fed through a hopper into a heating barrel. The plastic is heated to a preset temperature and driven by an outsized screw through the gate(s) and into the mould. Once the mould is crammed, the screw can stay in situ to use applicable pressure for the length of a preset cooling time. Upon reaching this time, the screw is withdrawn, the mould opened, and therefore the half ejected. Gates can either shear off mechanically or be manually removed. This cycle can repeat over and over, and may be wont to produce many thousands of components during a comparatively short quantity of time.

d. In the pressurization phase the packing of mold material is increased such that more material is accomodated in the same volume. Hence it is recommended to have a greater volume flow in molding.