Month: October 2019

Pressure Die Casting

Content.

  1. Introduction
  2. Cold chamber Die casting
  3. Advantages & limitations of cold chamber Die casting
  4. Application of cold chamber die casting
  5. Hot chamber – gooseneck type
  6. Hot chamber – plunger type

Introduction

History:

  • Pressure Die casting is believed to have begun sometime during middle of 19th century.
  • According to records, Sturges patented the first manually operated pressure Die casting machine during 1849.
  • Various compositions of tin & lead were first Die casting alloys.
  • Their importance and use declined with the development of zinc alloys & the Mg a Cu followed.

Introduction content

  • Pressure Die casting types:
  • Cold chamber pressures die casting.
  • Hot chamber pressure die casting.

Specialty of Die casting process:

A “metallic mold” is used to prepare sand mold with which larger number of casting are made. The metallic mold is known as “die”.

Cold chamber Die casting

  • In this machine, the metal is melted separately in the furnace and transferred to these by means by small ladle. After closing the die, the molten metal is forced into the die cavity by a hydraulically and pressure is maintained till solidification. These machines can either have vertical plunger or horizontal plunger for forcing molten metal into die These machines can either have a vertical plunger or flat plunger for driving liquid metal into biting the dust.
  • Advantages & limitations

Advantages of cold chamber die casting:

Straightforward development Thus the expense of the gear isn’t extremely high.

Limitations of cold chamber Die casting:

Slower cycle time due to the need to transfer the molten metal from furnace to the cold chamber machine. Hence, the rate of production will be less.

Alloys cast with cold chamber die casting:

  1. Aluminum alloys:

A360 alu die casting, A383, A384, A290, A413, A418, A380 aluminum die casting,

  • Zinc alloys with larger proportion of aluminum:

ZA-12, ZA-27

  • Magnesium alloys:

AZ91D, AM60A, AS41A

  • Copper alloys

Hot chamber pressure die casting

Hot pressures die casting types:

  • Gooseneck air injection type
  • Submerged plunger type

Goose neck air injection type

In this machine, the goose neck container is operated by lifting mechanism. Initially it is submerged in molten metal and filled by gravity, and then it is raised so as to bring the nozzle in contact with die opening and is looked in that position. Compacted air at that point powers the metal into the bite the dust and weight is kept up till hardening. When solidification is complete, the goose neck is lowered down and casting is removed by ejector pins after opening the dies.

Plunger type

I this machine, the goose neck type container always remain immersed in metal pot. The molten metal from metal container is forced inside the die with help of plunger submerged in molten metal comes up and fills the cylinder and when plunger moves down, the metal is forced into die. The moveable die platen is synchronized such that when plunger is moving up, the moveable die platen moves away and casting is removed.

Gravity die casting

Content:

  1. Introduction
  2. Die casting machine
  3. Gravity die casting
  4. Advantages compared to sand molding
  5. Limitations
  6. Applications

Introduction:

  • Die casting process

Main drawback of sand molding process:

Mold needs to prepare for each casting produced.

The specialty of die casting process:

A “metallic mold” is used to prepare sand mold with which larger number of casting is made. The metallic mold is known as “die”.

Die casting process:

  • Mold material: metal or alloy.
  • Types of die casting process:
  • Gravity Die casting (permanent molding).
  • Pressures die casting.
  • Cold chamber pressure Die casting
  • Hot chamber die casting
  • Unlike gravity die casting in pressure die casting the molten metal is forced into a permanent mold cavity under pressure.
  • The pressure varies from 20 to 2000 kg/sq.cm. And is maintained till the solidification stage is reached. The weight is for the most part acquired by compacted air or using pressurized water.
  • Die casting machines
  • Die casting machines perform the following functions.
  • Holding the two die halves firmly together. Closing the die
  • Injection molten metal into the die casting mold
  • Opening the die
  • Ejecting the die casting out of die

Gravity Die casting

  • The casting is called gravity die casting because the molten metal is poured into the mold under gravity only, no external pressure is applied to force the liquid metal into the mold cavity (opposite to die casting).

Permanent molds

  • Permanent molds are made of grey cast iron in two halves (having high resistance to thermal shocks), alloy steels (for very high temp. and withstanding surface erosion) or non-ferrous alloys.
  • The inner surface of the molds is coated first with refractory and with lamp black or core oil. This is done in order to reduce the chilling effect on cast prevents the adherence of molten metal to the mold.
  • Pouring cups, risers, gates, sprues are present in the mold.

Advantages

  • Compared to sand casting following are merits
  • Closer dimensional tolerances.
  • Smoother surface and better appearances.
  • Fine-grained metal structure. (Because of the chilling effect.)
  • Mass production is more economical.
  • Low shrinkage and gas porosity.

Think – “climate toys can be delivered with this procedure.”

 Limitation

  • Lasting mold costs were substantially more than sand for
  • Suited for small/ medium-sized non-ferrous casting only.
  • Several defects like stress and surface hardening may be produced due to surface chilling effect.
  • Since the gating system is cut in mold halves, once machined, it cannot be changed.
  • The extremely high temp of molten metal makes this method unsuitable for steel casting.

Applications

  • Carburetor bodies.
  • Refrigeration casting.
  • Oil pump bodies.
  • Connecting rods and automotive pistons.
  • Typewriter segments, etc.