Squeeze Casting
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| (a) Direct Squeeze Casting |
Squeeze casting can be defined as a hybrid casting process which gives
fine homogeneous grain casting with forging and die casting properties
without gas and shrinkage defects.
Squeeze casting gives the advantages of high-pressure die casting providing better heat treatment, welding and forging qualities.
Due to less molten metal turbulence while pouring and slow squeezing of metal during solidification any gas entrapped and porosity is eliminated completely.
It is a high-yield process giving near-to-net shape reducing wastage of material.
When pressure is applied to the molten metal during solidification size of the grain decreases giving a very dense and robust structure.
Along with improved tensile strength, elongation, tensile strength, compressive strength, ductility, toughness, wear and tear properties and fatigue life.
Squeeze casting does not give any added advantage over the forging process. Mechanical properties are the same as forging only difference is squeeze casting is done in one step only with cores giving high surface finish components.
If the same complex shape is to be produced by the forging process it is difficult to manufacture it. This process applies to both ferrous and non-ferrous metals.
There are two types of squeeze casting processes.
- Direct squeeze casting.
- Indirect squeeze casting.
Indirect squeeze casting resembles a process similar to die casting with the difference that molten metal is injected at a slow speed and metal is solidified under pressure resulting in a fine refined-grained casting structure without any gas porosity.
During this process, solidification takes place while metal is been squeezed between the die giving high-quality dendrites grain casting.
The net volume of molten metal required in this process is close to the final casting as compared to the sand casting and die casting making this process highly economical.
Squeeze casting is also called liquid forging, extrusion casting, liquid metal forging and liquid pressing. This is a permanent expandable mould process,
Squeeze casting is of two types, direct squeeze casting and indirect squeeze casting process.
The direct squeeze casting process is performed on the vertical squeeze casting machine and indirect squeeze casting is performed on vertical and horizontal machines.
In an indirect squeeze casting machine molten metal is injected slowly at a lower velocity through a large gating system as compared to die casting slowly cooling the molten metal once the die is full. Molten metal is planar-filled in the die cavity. This process is done on horizontal ram.
Squeeze Casting Types
The squeeze casting process can be classified into two types.
- Direct squeeze casting process.
- Indirect squeeze casting process.
Direct Squeeze Casting
What is direct squeeze casting? Discuss the working and method of direct squeeze casting in a step-by-step process suitable diagram, animation, method and working?
Direct Squeeze Casting Animation
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| (b) Direct Squeeze Casting Animation |
Direct squeeze casting animation is shown above in (b). This process explains the direct squeeze operations such as pre-heating the die, pouring operation and a squeeze of punch into the die cavity.
I have explained all the steps of direct squeeze casting below in detail with diagrams.
Direct Squeeze Casting Step-By-Step Process Explained With Diagram
STEP 1: Cleaning, Lubrication of Die And Pre-Heating Die
Before the casting process starts the die is cleaned to remove any leftover molten metal, bits and broken parts from previous casting.
After this, the water-based lubricants are sprayed on the dies. Graphite lubricants are effective for cast iron dies. For steel ceramic coating agents are used.
Application of lubricants reduces the molten metal to solder the die reducing blisters, scaling and surface texture defects.
Pre-heating of die mould is done as shown below in diagram (c).
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| (c) Pre-Heating Direct Squeeze Casting Die |
STEP 2: Pouring Operation In Direct Squeeze Casting
Before the pouring operation starts the die is preheated to avoid molten metal sticking/freezing to the surface of the die as there will be a huge temperature difference between mould and die.
The pouring operation starts with filling the die cavity with the ladle as shown below in diagram (d).
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| (d) Pouring Molten Metal In Squeeze Casting Die |
The amount of molten metal required in the ladle is equal to the volume of the final casting and additional metal that is to be machined after solidification.
The temperature of the molten metal is kept in mind considering the transfer time of metal from the furnace to the die cavity with the ladle.
The temperature of molten metal should be adequate to eliminate defects such as cold shut and misrun.
STEP 3: Squeezing Operation In Direct Squeeze Casting
Once the die cavity is filled with molten metal squeezing operation starts. This process starts with a punch ascending towards the die as shown in diagram (e).
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| (e) Squeeze Operation |
Squeezing of the metal takes place at the zero fluid temperature, zero fluid temperature can be defined as the temperature below where metal loses its fluid properties.
The pressure of 55 N/㎟ to 170 N/㎟ is applied depending on the size, shape, complexity, and wall thickness of the casting. Temperature during this process is maintained between 180℃ to 300℃.
When the punch ascends towards the molten metal, the metal starts solidifying and getting squeezed between the die walls.
During this process, new grains are formed in the final casting resulting in grain-refined casting products.
Very low pressure will give incomplete dimensions casting as the molten metal will not squeeze in all sections of the die. Very high pressure will cause casting to tear in the die.
Very low temperatures in the system including pre-heating dies, punch temperature, die temperature and molten metal pouring temperature will cause cold labs and fatigue to the die and punch as the molten metal will not have required viscosity during the flow of molten metal in the die cavities.
Very high temperatures in the system will cause die and casting to weld and solder each other. At such a high temperature will cause hotspots in the final casting.
STEP 4: Ejecting Soldified Squeezed Casting Out of The Die
After casting is solidified the casting is ejected out of the die with the help of an ejector pin.
Care must be taken that casting is fully solidified before casting is ejected from the die to avoid damage to the final casting.
Mechanical robotic arms are used to remove the casting from the die.
The final solidified casting for the above casting designs looks similar to the following casting as shown below in diagram (f).
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| (f) Final Squeeze Casting |
Indirect Squeeze Casting
Indirect Squeeze Casting Animation
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| (g) Indirect Squeeze Casting Animation |
This casting process can be done horizontally and vertically with ram. This process may look like die casting but there is a difference in how metal is injected in this process.
This process starts with cleaning and lubricating the die and finally ejecting the final casting once the casting is solidified.
Indirect Squeeze Casting Step-By-Step Process Explained With Diagram
STEP 1: Cleaning The Die, Pre-Heating and Spraying The Lubricant
The closed die is cleaned and air blown to remove any excess remaining molten metal from the previous cycle.
Dies are pre-heated up to 200℃ and spray lubricated with graphite to avoid blister and soldiering of the die and molten metal.
STEP 2: Injecting And Solidification In Indirect Squeeze Casting
Molten metal in the dies is injected through a thick gate in the die cavity. Die is allowed to fill with the molten metal slowly. The rate at which the molten metal fills the die is slow squeezing the metal in the die slowly.
The molten metal which follows from the injecting nozzle squeezes the previously injected metal in the die creating a compact highly dense porosity-free casting.
This molten metal passes through a gating system such as a sprue, runner, gate and ingate to reach the mould cavity as shown in the diagram (h).
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| (h) Indirect Squeeze Casting |
A better thin and complex shape can be produced using indirect squeeze casting w.r.t direct die squeeze casting. This process is done mostly on a hydraulic press.
A runner and gates are not required for the direct squeeze casting process as metal is poured directly into the die but for indirect squeeze casting gating system is ulized so that molten metal can be injected in the die cavity without any turbulence by the injecting nozzle.
The thickness of the runner system and in-gates used in this casting process are thicker as compared to the die-casting process.
Laminar filling of molten metal reduces blowholes and porosity in casting.
STEP 3: Ejecting Molten Metal Out
Once molten metal is solidified in the die, the casting is ejected from the die mould with an ejector pin after opening the die.
This casting then goes through a secondary manufacturing process trimming the flash and any uneven surface.
Squeeze Casting Ingots/Casting Material List
What materials are used in the squeeze casting process for producing casting?
Metals used In the squeeze casting process for manufacturing final casting are as follows:
This process can be applied to ferrous and non-ferrous metals. Both pure and alloy metal can be cast.
Low to medium-temperature metals can be used as they are suitable for dies giving dies longer life and eliminating warping defects in casting.
The majority of casting produced here is from aluminium because of economic and environmental reasons.
But other forms of metals are also used in this process, I have listed them below:
| Alloy Metals | Non-alloy Metals |
|---|---|
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Squeeze Casting Die Material And Characteristics
Dies used in this casting process are made from cast iron, tool steel and grey cast iron.
Die used during the squeeze casting process needs to undergo casting and forging operations at the same time.
Dies needs to sustain high thermal temperature, hot strength, thermal shock, thermal fatigue, high thermal conductivity and high-temperature resistance.
Along with thermal capabilities, mechanical properties such as mechanical strength, toughness, ultimate tensile strength, refined structure high formability and ductility become equally important.
During direct squeeze casting dies and punches need to sustain the forces acting on them while in indirect squeeze casting need to sustain the pressure of molten metal on the inner walls of the die.
The life of these dies is much shorter as compared to die casting and investment casting dies as they are not subjected that much to mechanical and thermal stress at the same time for every cycle.
Squeeze Casting Defects
If process parameters are not controlled following defects are formed in the final casting are explained below:
| Squeeze Casting Defects | Cause of Defect |
|---|---|
| a) Cold Shut | If the temperature of the die is not hot enough molten metal will solidify early to give cold shunt defects. |
| b) Porosity | Laminar flow while pouring, solidification temperature and squeeze pressure need to be aligned to form porosity-free casting. |
| c) Misrun | A common defect in squeeze casting formed in the thinner casting section. Designing thicker sections eliminates misrun. |
| d) Oxide Inclusions | If the molten metal has inclusions such as dross and oxides, it will be trapped in the final casting. Direct squeeze casting does not have a runner and skim bobs for trapping foreign material. Molten metal needs to be filtered beforehand to avoid oxides in casting. |
| e) Hot Tears | Molten metal when solidified along two adjacent sections of different thicknesses tends to cause thermal stress and result in thermal cracks called hot tears. |
| f) Cold Laps | When the previously chilled casting section overlaps with the new fresh molten metal, sections are not cooled and fused properly and are called cold laps. |
| g) Stickness | Molten metal sticks to the cold surface of the die if the die is not pre-heated to the desirable temperature before pouring operation. |
Advantages And Disadvantages of Squeeze Casting
Squeeze Casting Advantages
- Metal matrix composites can be easily produced with isotropic properties having better wear resistance.
- It is a hybrid liquid forging and casting process giving advantages to both with fewer gas defects.
- Porosity is eliminated in the final casting.
- Lightweight weight strong casting can be produced.
- Very little machining is required after the final casting is taken out of the die after squeezing. This process saves secondary manufacturing costs.
- Components produced from squeeze casting have better wear and tear properties.
- Mechanical properties are better than die casting, sand casting and investment casting.
- A better surface finish can be obtained even for irregular shape casting.
- Only if the process can be automized productivity can be improved but without any control over solidification and squeezing time. During automation, a huge impact is only on the pouring and casting ejection operation.
- For automated processes only labour cost is low.
- The final product is free from the fin.
- No visibility of parting line over final casting produced by direct squeeze casting.
- Direct casting equipment and setup are less complex and costly.
- Flexibility in producing ductile and elongated components.
- Difficult to manufacture complex shapes from direct squeeze casting.
- Machine setup and the overall cost are lesser than the high-pressure die casting or forging process.
- Gives forging properties to the final casting components.
- Cores can be used to produce cavities, channels and internal holes in the casting.
- Precision casting can be produced with better dimensional tolerances.
- A lot of alloys can be worked with wide freezing range temperatures.
- Fine and high-quality grain structure with defect-free microstructure.
- Metal matrix composites can be manufactured.
- Thin-wall casting products can be manufactured.
- Molten metal waste in this process is minimized, casting yield of squeeze casting is higher than in sand casting and die casting processes.
- Sharp counter-casting components can be manufactured.
- This is a pattern-free casting process with reusable mould that can produce multiple castings with a single die only without using any pattern.
- Products manufactured from this casting are more acceptable for the heat treatment process to improve their hardness, ductility, toughness and other mechanical properties for final casting application.
- The foundry space required for squeeze casting setup is compact, small and reliable.
- Composite, fibre-reinforced casting, bimetals and alloy casting can be produced using ferrous and non-ferrous casting.
- The metal density and strength-to-weight ratio of the casting are better than the sand casting process.
Squeeze Casting Disadvantages
- Only particular shapes of casting can be formed with less flexibility over the shape.
- Limitations over the size of the casting as the squeezing operation is involved.
- Process parameters of squeeze casting such as mould temperature, alloy temperature, pressure during solidification and solidification rate need to be controlled to form desirable casting.
- Pouring and slowly squeezing of molten metal operations is time-consuming giving lesser productivity.
- Close control over process parameters such as plunger pressure, the temperature of molten metal and solidification rate are required to manufacture high-quality sound squeeze castings,.
- The life of the die is shorter than the die-casting dies because of the high pressure induced on the die surface by the plunger.
- Indirect casting equipment, machines and setup are more costly.
- A proper combination of process parameters such as squeeze pressure and temperature needs to be controlled to get desirable casting.
- It cannot be used for mass production of castings, the cost of manufacturing dies, tools and plungers needs to satisfy the quantity of the customer's order.
- A better complex shape can be produced from indirect squeeze casting.
- Precision over the process is required to produce sound casting. For example, premature cooling of the casting can produce cold laps defects.
- Cycle time is higher as molten metal needs to be poured and squeezed as liquid metal solidifies.
- Rework, repair, care and maintenance of squeeze casting dies is more as compared to die casting process.
- The die needs to be properly worked to reduce alignment and mismatch in the final casting.
- Flexibility and versatility in the tooling is very low compared to the sand moulding process.
- High cost due to complex tooling. The initial investment in this process, machines, inspection and tooling is high.
- There is a limitation over the size and length of the casting as compared to die casting.
Squeeze Casting Application
- Diesel engine pistons and cylindrical blocks.
- Barrel heads and shells.
- Stainless steel blades.
- Engine propellers.
- Alloy wheels.
- Engine case and gearbox case.
- Super alloy disk.
- Wheel inserts and brackets.
- Automotive disk brake.
- Arms of suspension.
- Piston and cylinders.
- Pots, hub flanges. and rotors.
- Bushes flywheel and clutch housing.
- Brake drums and connecting rod.
- Frame joints in the automotive industry.
- Steering knuckles.
- Gears, control arms and domes.
- Chasis frame.
- Hydraulic brake valves and cylinders.
- Air conditioning, pump and compressor components
Squeeze Casting Conclusion And Summary
This process and invention dates back to Russia in the 1950s for producing hybrid pressurized metal matrix solidified casting with low shrinkage and porosity due to pressure applied by the upper punch.
Later this process gained popularity in Japan, China, the United Kingdom, United States of America for producing automobile components made from aluminium as the components are more reliable than the traditional casting process in terms of mechanical properties.
The net volume of molten metal required in this process is close to the final casting as compared to the sand casting and die casting making this process highly economical.
Early this process was applicable for only non-ferrous metals but now high-temperature ferrous metals are also used as there is advancement in the die material.
This process replaced iron, pressed steel and cast iron with aluminium reducing the weight and material cost of the manufactured casting components.
This process can take place vertically, horizontally, at low pressure, at high pressure, without a vacuum and with a vacuum pump.
This process can produce casting with the highest mechanical properties having casting and forging qualities with better surface texture with the least secondary manufacturing process required.
Vacuum squeeze casting can produce casting with less porosity, air trapped inside, pinhole defects and blister.