Top Molding Interview Questions Part – 2

61. What is runner?

Connecting member between gate and sprue bush.

62. What is gate?

Connecting member between impression and runner.

63. How can we calculate the cycle time of mold?

Cycle time Tc=m*3600/P
Where ,Tc =minimum cycle time obtainable
M=mass of the shot
P=plasticizing capacity of the machine with the particular polymer being molded (kg/h)

64. What is parting surface?

The surface where top and bottom half closed together and prevents the loss of plastic material from the impression.

65. What are the types of parting surface?

Flat and non flat

66. Name the types of non flat parting surfaces?

Straight, stepped and angular.

67. What do you meant flash ?

If the parting surfaces are not properly matched, the molding material from the impression will escape through the gap. This escaped melt is called the flash.

68. Why do we provide vent in mold?

Vents are provided in the mold to allow such air to escape freely. The vent is a shallow slot not more than 0.05 mm deep and 3mm wide. If the depth is more, the plastic material can pass through the slot and leave a flash mark.

69. What are the types of runner ?

Fully round
Rectangular
Hexagonal
Trapezoidal
Modified trapezoidal

70. Explain briefly about sprue gate ?

When the molding is directly fed from a sprue or secondary sprue, the feed section is term as sprue gate.The main disadvantage with this type of gate is that it leaves a large gate mark on the molding. This sprue gate is used only for single impression molds.

71. What is rectangular gate?

This is the general purpose gate and it is a rectangular channel machined in on mold plate to connect the runner to the impression.

72. Write a short note about fan gate?

Fan gate can be considered as the other type of edge gate but it does not have a constant width and depth. The fan shape spreads the flow of the melt as it enters the impression and a more uniform filling is obtained with less flow marks and surface finish.

73. What is tab gate?

This is particular gating technique for feeding solid block types moldings. This is mainly used to avoid undesirable jetting on the molded part.

74. What is overlap gate ?

It can be considered as a variation of basic rectangular edge gate and is used to feed certain type of molding. In this type of gate we have a better control over the flow rate. Main disadvantage is that it leaves big remnant mark after degiating.

75. What is diaphragm gate ?

This gate is used for single impression tubular shaped moldings on two plate molds.

76. What is ring gate?

The function of this gate is identical to that of a diaphragm gate. This type of gate is used for tabular type moldings when more than one impression is required in a simple two mold.

77. What is film gate?

This is a long rectangular type edge gate and it is used for large thin walled components to assist in the production of warpage free products.

78. What is pin gate?

Used for 3 plate mold and under feed mold. Small degating mark will be there.

79. What is round edge gate?

This gate is formed by machining a matching semi circular channel in both mold plates between the runner and impression.

80. What is submerged gate?

Automated degating with less mark also called as sub surface gate or submarine gate.

81. What is winkle gate?

This is a curved variation of the subsurface gate and for that reason it is sometimes called a “curved subsurface gate” or “curved tunnel gate”.

82.What are the types of injection techniques ?

Pin injection
Sleeve injection
Stripper bar injection
Blade injection
Valve injection
Air injection
Stripper ring injection
Stripper plate injection

83. What is Pin injection ?

This is the most common and simple type of injection. The molding is ejected by the application of a force by ejector pins.

84. What do you meant by sleeve injection ?

In this method, the molding is ejected by means of a hallow ejector pin which is called sleeve.

85. What is stripper bar injection?

This method of injection is suitable for thin wall box type moldings because of the effective injection area obtainable are greater.

86. What is blade injection ?

The main purpose of blade ejector is for the injection of very slender parts such as ribs and other projections which cannot be satisfactorily ejected by the standard type of ejector pin.

87. What is valve injection ?

A valve ejector is basically a large diameter ejector pin. It is used for the injection of large components.

88. What is air injection ?

This is the simplest to install. It is easy to connect to the fixed or moving half. The medium of actuation is compressed air.

89. Explain briefly stripper ring injection?

The stripper ring is a local stripper plate and it is used on molds with one or two impression only. The stripper ring is made to seat in the mold plate.

90. What is stripper plate injection?

This injection technique is used mainly for the injection of circular box type moldings and for moldings with thin wall sections.

91. Name the methods used for actuation of stripper plate?

Tie rod actuation
Length bolt actuation
Chain actuation
Direct actuation

92. Define shrinkage ?

When a hot plastic cools inside a mold, it contracts by an amount depending on the material being processed and the final product is smaller than the mold size is called shrinkage.

93. What are the factors which affect the increase in shrinkage ?

Increase of material temperature.
Increase of mold temperature.
Increase in wall thickness.
Low injection pressure .

94. What are the factors which effect the decrease in shrinkage ?

Low melt and mold temperature
High injection pressure
Long injection time
Presence of filler materials and its content

95. What is undercut molding?

A molding which has a recess or projection is termed as an undercut molding

96. What do you mean external undercut?

Any recess or projection on the outside surface of the component which prevents its removal from cavity is termed an external undercut

97. Name the methods of split actuation?

Finger cam actuation
Dog leg cam actuation
Cam track actuation
Spring actuation
Hydraulic actuation

98. How can we calculate finger cam length?

Finger cam length =(M/Sin Q) +(2c) l Sin 2Q

Where

M= split movement

Q=angle of finger cam

L=working length

C =clearance

99. Where we use side core and side cavity ?

A side core is a local core which is normally mounted at right angled to the mold axis for forming a hole or recess in the side face of a molding. The side cavity performs a similar function to the side core, in that it permits the molding of components which are not in line of draw. This element allows the components with a projection or projections on one or more of their side faces.

100. Where we use form pin straight action method ?

For the components which has internal undercut on one side of the wall.

101. Where we use form pin straight action method ?

We use form pin straight action method for the components which has internal undercut throughout the wall

102. What is single daylight mold ?

When a basic mold is opened, there is only one space or “daylight “ between the two mold halves. This is called a single daylight mold.

103. Explain about double daylight stripper plate mold ?

A stripper plate mold consists of a fixed plate, a moving mold plate and a stripper plate. There are two day light when opened. This is called double daylight stripper plate mold.

104. What is underfeeding mold?

An underfeeding mold is the one in which the feed system is arranged to feed into the underside of the component.

105. What are the types of injection molding defects ?

Sinkmark, Streaks, Blisters/Bubbles, Weld line, Ejector marks, Cold weld, Jetting, Warpage

106.Define sink mark ?

Sink marks are the localized contractions or the depressions on the surface of the moldings.

107. What is blister or bubbles ?

Hollows created on or in the molded part.

108. What is weld line ?

It is the witness marks of two or more melt flow fronts at their joining zone.

109.What is jetting ?

It is the prominent in-homogeneous snake like strands on the surface of molding.

110.What is warpage ?

Warpage is the deviation of the mold part from its required shape.

111.What is bulk factor?

Bulk factor is defined as the ratio of the volume of the loose powder to the volume of the molded part.

112. What are the types of compression molds?

Flash mold
Fully positive mold
Semi positive mold
Landed positive mold

113. Write a short note about performs ?

Performs are small pellets or tablets of molding material that are formed to shape in a special performs mold at room temperature. Curing won’t takes place only densification.

114. Name the types of transfer molds ?

Pot transfer mold
Plunger transfer mold

115. What is die casting?

Pressure die casting is the process in which the molten metal is forced under high pressure into a cavity in a metal disc with in fraction of a second and allowed to solidify.

116. What are the types of die casting ?

Hot chamber process
Cold chamber process

117.Write the differences between hot chamber and cold chamber processes ?

Hot chamber process

The plunger and cylinder are submerged in the molten metal in the holding furnace.

After shot, plunger is forced the molten metal through the nozzle.

Since both plunger & goose neck are submerged in the molten metal, it refills automatically when the plunger is withdrawn.

For casting metals that melt at lower temperature such as zinc and lead.

Cold chamber process

Molten metal is ladled into the cold chamber.

After ladling, the plunger advanced to force the metal in to the die.

Each time, we have to ladle the molten material in to the chamber.

For casting metals that melts at high temperature such as aluminum, magnesium and brass.

118. What are the types of die casting defects ?

Cold defects
Hot defects
Miscellaneous defects

119. Example for cold defects ?

Lack of fill, cold shut, severe chill, chill, flow lines

120. Examples for hot defects ?

Soldering, cracks, broken part, bent part, heat marks or shrinkage pits.