Table of Contents
What Causes Flow Lines? Flow lines are often the result of variations in the cooling speed of the plastic as it flows in different directions through the mold. They also can occur when you’re creating pieces of differing thicknesses, as the thinner areas cool before thicker areas are fully filled, causing flow lines.
What causes flow marks in injection molding?
Flow marks, also known as flow lines, are molding defects that can occur in the manufacturing process of injection molding. They commonly occur when there is a large variation between cooling speeds of sections of the material as it flows through the mold.
How do you prevent weld lines in injection molding?
Avoid weld lines in areas which need strength, or which need to appear smooth. This can be done by changing the polymer injection location or altering wall thicknesses to set up a different fill time. With a different fill time, flow fronts may meet at a different location and therefore the weld/meld line will move.
How can you prevent jetting?
Avoiding jetting To avoid jetting, mould geometry and process conditions have to be altered to induce laminar flow within the cavity, filling from the gate end as an unfolding melt front rather than an uncontrolled jet of melt. Reducing overall injection speed will help.
How do you fix injection molding problems?
Redesign the mold with wider channels or gates for better flow. Increase injection speed or pressure or choose a thinner base material to improve flow. Increase mold temperature to prevent material from cooling too rapidly. Add additional air vents or enlarge existing vents in the mold to allow trapped air to escape.
How can I reduce my flow marks?
Ⅲ. Countermeasures Increase the nozzle diameter. Increase the nozzle temperature. Increase injection speed. Increase injection pressure. Raise the cylinder temperature. Reduce the cushion. (Reduce the charging amount.).
What is the parting line in injection molding?
The parting line is where the two halves of the mold meet around the parameter of the part. All parting lines need to seal properly when the mold is clamped in a molding machine. If the parting lines are too loose or have excessive wear, the mold will “leak” plastic over the parting line during the molding process.
What is a meld line?
Meld lines are formed when two separate flow fronts meets. These are preferred over weld lines as they will normally result in improved cosmetics and structure. In a meld line, the plastic comes together at an angle greater than 135 degrees.
What are welding lines called?
In manufacturing, the Weld line or Knit line or Meld line is the line where two flow fronts meet when 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.
What causes jetting?
Causes: Jetting occurs mostly when the melt temperature is too low and the viscosity of the molten plastic becomes too high, thereby increasing the resistance of its flow through the mold. When the plastic comes in contact with the mold walls, it is rapidly cooled and the viscosity is increased.
How the jetting problem can be solved?
Remedies. Optimize gate design and position. Direct the melt against a metal surface by repositioning the gate or use an overlap or a submarine gate. Use a tab or fan gate to slow down the melt with a gradually divergent flow area.
What is back pressure in injection molding?
Back Pressure in an injection molding process is often defined as “the resistance of the screw to recover as the metering section pumps molten plastic through the non-return valve to the front of the screw.” When this position is reached, the screw will stop rotating.
How do you know if you have injection mold?
A clear indication as to whether an object has been injection moulded is its complexity, signs of feed points (see Fig. 1) or ejector pin marks (see Fig. 2). Nearly all, complex three-dimensional plastic components are injection moulded.
How do you prevent warp in injection molding?
Solution: Increase residence time by adding time to the cooling process of the cycle. This will ensure the material receives the proper amount of residence time and eliminate mold warping. If the barrel temperature is too low, the resin is not able to heat up to the proper flow temperature.
How do you reduce injection pressure?
Select a different material with a lower viscosity, which requires less injection pressure to fill the mold. Increase the melt temperature to reduce the viscosity. This reduces the injection pressure required to fill the mold.
What is the minimum pressure allowed to be given to the injection molding process?
The volume of material is not counted among important factors. 7. What is the minimum pressure allowed to be given to the injection molding process? Explanation: None.
How can I improve my sink mark?
A) Sometimes sink marks can be reduced by increasing the packing pressure along with the holding time and slowing the injection speed. This will depend on the location of the gates relative to the thicker wall sections and whether there is sufficient time to fill all areas of the cavity before the gate freezes off.
What is nozzle drooling?
When nozzles are moved away from the mold after injection molding has been carried out, trickles of plastic from the sprue gate occur. This trickle of plastic is generally called the drooling (trickling), which is said to be caused by residual pressure stored in the sprue and runner.
Where is the parting line?
The parting line of a die cast component represents where the two different sides of the mold come together. This line often (but not always) marks the border between the inside and outside of the part. The location of the parting line indicates which side of the die is the cover and which is considered the ejector.
How do I create a parting line?
To create a parting line: Click Parting Lines (Mold Tools toolbar) or Insert > Molds > Parting Line. In the Parting Line PropertyManager, set options, then click .
How do you choose a parting line?
The first step for determining parting line is to select an appropriate parting direction. One set of alternatives for the parting direction is generally provided by the centrelines of the minimal bounding box of the casting. Other alternatives are given by the direction of normal to large faces in the casting.
What is meant by balanced runner system explain with figure?
A naturally balanced runner system is a runner configuration where there is an even flow length from the tip of the sprue to the end of each cavity with symmetrical cross-sectional shapes. See Figure 2.
