Used Die Casting Machines - Metalworking Machinery for Sale — 77

The Working of Die Casting Machine

Die or mould cavities are made up of hardened tool steel which have been previously machined to the exact shape or near net shape of the die cast parts which is responsible for the high degree of accuracy and repeatability of the die casting process. The most common metals used are non-ferrous metals such as aluminum, zinc, and magnesium alloys. Less frequently, copper and copper alloys such as the brass are used because of their higher melting temperatures. Metal housings for a variety of appliances and equipment are mostly die cast. Some of the common die cast parts include propellers, gears, bushings, pumps, valves, pistons, cylinder heads, and engine blocks. 

Process of Die Casting Machines

The die casting process is composed of five major stages:

Clamping – The first and foremost step is the preparation and clamping of the die unit. It is composed of two die halves which are attached to platens on the die cast machine. One of the halves is called as the cover die which is mounted on a stationary platen while the other half named as the ejector die is fixed on the movable platen. Each half is cleaned and lubricated well prior to the process and sufficient pressure is to be applied to keep both of them intact.

Injection - The molten metal, which is maintained at a particular temperature in the furnace, is then transferred into a chamber where it is injected into the closed die cavity. Injection time is always kept very low in order to prevent early solidification of any part of the metal.

Cooling – As soon as the molten metal is injected into the die cavity, it will start cooling and get solidified. The die unit should not be opened until sufficient cooling time is permitted and the casting is completely solidified. The thumb rule is that when the casting is required to have greater wall thickness, the amount of cooling time is more.

Ejection – After predetermined amount of cooling time, the casting is pushed out of the die cavity with the help of an ejection mechanism.

Trimming – The unwanted excess material called as the flash which has solidified along with the casting, must be trimmed off either manually by cutting or sawing, or with the help of a trimming press. 

Types of Die Casting Machines

There are two principle types of die casting machines predominantly used in the industrial environment. They are: 

• Hot chamber type
• Cold chamber type 

The hot chamber type is used for the lower melting temperature alloys like zinc, tin and lead while the cold chamber machine is used primarily for the other alloys owing to their higher melting temperatures such as aluminium, brass and magnesium. In both the machines, the metal is contained in an open holding pot which is placed into a furnace, where it is melted to the necessary temperature. In hot chamber machines, the molten metal then flows into a shot chamber through an inlet and a plunger, powered by hydraulic pressure which typically ranges from 1000 psi to 5000 psi, thereby forcing the molten metal through a gooseneck channel eventually into the die. However in the case of cold chamber type machines, holding pot is kept separate from the die casting machine and the molten metal is ladled from the pot for each casting, rather than being pumped. The injection unit in a cold chamber machine is almost similar to that of the one in the hot chamber machine except that it does not comprise of a gooseneck channel. The injection pressure required in cold chamber process is comparatively quite high varying from 2000 psi to 20000 psi. Die casting machines are usually rated by clamping force capacity. The clamping systems can use either hydraulic, pneumatic, mechanical, or a combination of any of these systems. Sometimes, this type of metalworking machinery are rated by the shot weight capacity of the injection system as well. 

High pressure die casting machines are used to force molten metal under high pressure into a mould formed from a pair of hardened steel dies. The advantages of this process are a high degree of dimensional accuracy, thereby reducing or even completely eliminating any necessity for secondary machining; the smoothness of the cast surfaces; a rapid rate of production; the ability to cast thinner walls and include inserts; and the high tensile strength that results in the finished product. 

Hot chamber die casting machines use a reservoir of molten metal which is forced into the die by means of a pneumatic or hydraulic piston. This method results in fast cycle times, but it can only be used with metals that have low melting points. It cannot be used with aluminium. For this metal cold chamber die casting equipment such as aluminium die casting machines are used. Here the metal is melted in a furnace that is separate from the machine and then fed into the machine's injection cylinder or shot chamber. From here it is forced into the die by means of a pneumatic or hydraulic piston.

Buying Used Die Casting Machines 

Due to these considerable advantages there is a very healthy market for used die casting machines, which can easily be picked up at used industrial equipment second hand market. Die casting machines fall into two types; hot chamber or cold chamber, and are rated by their clamping force, which in most cases is between 2,500 and 25,000 kilograms, something that is well worth bearing in mind if you're looking for used die casting machines for sale. The die casting machine manufactures make them with heavy duty use in mind, they create them to last and with low maintains operating. When you will buy the used die casting machine you will know that the machine will still be fully operational. Big companies and factories change these machine often, so you might buy a used casting machine that probably haven't been in use for long time. 

Die Casting Machine Manufacturers

Though it has several notable advantages, it is a slightly expensive process because of the high tooling costs. Only certain alloys can be cast using this process. It is not viable to produce certain type of alloyed castings. Size and volume restrictions on castings that can be die casted also prevails. TOSHIBA, KURTZ ERSA, YIZUMI, BÜHLER, GRUBER Systems, IMR, COLOSIA, FOMET, PACMAR and IDRA are some of the well-known providers of die casting machines in the world.