Die Casting

Die casting - we provide youwith perfect tool tempering

Precise temperature control is essential throughout the entire die casting process. We can support your production processes with suitable temperature control units to ensure optimal and efficient control. Our Tool-Temp temperature control units are used for a wide range of different die casting methods.

Controlling the die temperature with Tool-Temp - proven and reliable

A temperature control unit is used to heat the die and maintain it at the required temperature, i.e. the defined operating temperature. Temperature control units bring consumers up to the required temperature by circulating a liquid heat transfer medium and maintaining the desired temperature using a constant controlled cycle of heating and cooling. Ensuring a stable die temperature ensures uniform high quality cast parts, optimised cycle times as well as a longer service life.

The die temperature is the key factor influencing the dissipation of heat from the molten material as well as for filling the mould and for the proper setting of the cast part. A common source of defects in die casting is not having the die at the optimum temperature. This problem can be avoided by using one of our temperature control units.

Die temperature control in die casting
When producing die cast parts, being able to control the thermal processes in the die plays a key role. Each die should therefore be heated up to the required casting temperature before production starts. This generally has the effect of increasing the useful life of dies. The die is subjected to more gentle stresses if the temperature difference between the casting temperature and die itself is as small as possible. Casting with a die that is cold, or insufficiently pre-heated, can result in high stresses on the tool surface as well as poor quality of the cast part.

Key factors for effective temperature control of the die are the temperature control unit, a suitable heat transfer medium and the tempering channels in the die. The tempering channels must be sufficiently large to ensure fast circulation and a minimal loss of pressure in the die. Selecting the right temperature control unit depends on the design of the channels in the die. The temperature control unit must be sufficiently powerful to regulate the temperature of the die and remove heat. The heat transfer medium plays a significant role in ensuring optimal temperature regulation. The better the heat transfer properties of the medium used, the more efficiently large amount of heat can be moved. Due to the high temperatures involved, die casting often uses oil heat transfer mediums. Tool-Temp’s recommended heat transfer medium is TOOL-THERM SH-3. This is a mineral based, temperature stable oil for use up to 360°C.

Stable heat balance
Optimising die temperatures for even temperature distribution and a peak temperature reduction on the surface can delay the onset of tool damage, particularly the development of fire cracks, and thus significantly increase the service life of the die. Part quality and cycle times also greatly depend on the heat balance of the casting die. High wastage in die casting is also associated with insufficient die temperatures.

Die casting -we provide you withperfect die tempering

The pump integrated into the unit moves the heat transfer medium from the tank to the die casting mould and back again. A temperature sensor measures the temperature of the medium and passes this value to the controller. This then regulates the temperature of the medium and thus also indirectly the temperature of the die. If the temperature in the die rises, a solenoid valve is activated by the controller to open the cooling water circuit, allowing cold water to flow through the heat exchanger until the temperature of the medium, and therefore the die, has returned to the target value. If the die temperature is too low, electrical heating elements are activated instead.

In order to guarantee quality requirements of cast parts such as surface finish, die filling, and dimensional accuracy, as well as optimising cycle times and the service life of dies, a temperature control unit is an indispensable piece of equipment.

For controlling the temperature of the die in die casting processes, we recommend two different systems depending on the choice of heat transfer medium:

  • Pressurised water temperature control units up to 160°C
  • Oil temperature control units up to 360°C

Pressurised water temperature control units up to 160°C – 6 kW to 48 kW heating power
Pressurised water temperature control units are closed systems in which static pressure increases the boiling point of the water in the circuit to 140°C or 160°C. Tool-Temp pressurised water units feature an expansion tank. This allows operations under low pressure conditions and guarantees stable temperature regulation. We strongly recommend against using pressurised water units for processing magnesium due to the risk of burning. To ensure easy die changes, Tool-Temp pressurised water units provide a die evacuation feature. Using pressurised air, some models can even dry rinse the die channels. Pressure release guarantees that hydraulic connections can be safety disconnected and also forces process water through the cooling water outlet.

Oil temperature control units up to 360°C – 8 kW to 48 kW heating power
Oil units have a closed hot oil circuit along with a cold oil container. The content of the expansion tank in Tool-Temp oil temperature control units remains cold during operation. It is therefore not possible for the heat transfer oil to evaporate or foam over into the unit. The heating elements are designed to prevent cracking of the oil. The heat exchanger in the cooling water circuit is proven limescale-free with guaranteed reliability and longevity.

Tool-Temp oil devices feature a die evacuation function. Switching to vacuum operation sucks the heat transfer medium into the expansion tank. The expansion tanks are sufficiently large as to absorb the return flow volume.

The advantages of Tool-Temp temperature control units for die casting
Tool-Temp temperature control units stand out for being extremely robust. Units are capable of withstanding the tough conditions associated with die casting.

Durable magnetically coupled pump: The pump with magnetic coupling developed by Tool-Temp is resistant to liquids that are aggressive, corrosive and filled with particulate matter and constitute a robust, high-performance key component. The pumps are produced exclusively at Tool-Temp’s main factory in Switzerland.

Temperature measurement on the tool: Tool-Temp temperature control units can regulate based on either the tank temperature or the tool temperature. Digital flow measurements and pressures are clearly visualised on the unit and act as a key parameter for reproduceable production quality.

Heating and cooling with oil allows for very high temperatures and therefore generates fewer areas of high material tension in the tool. Using oil for temperature control does however require larger channels in the mould so that enough oil can circulate to guarantee optimum heat transfer. The lower heat transfer coefficient of oil compared to water and the reduced amount of heat that can thus be transferred is compensated for by using higher temperatures. When working with magnesium, oil is the only proven and technically reliable alternative.

Advantages of Tool-Temp oil temperature control units – pumps for use in die casting
The pumps used by Tool-Temp have been specially design for the technical properties required of the temperature control units. Materials were evaluated based on the following criteria: good dry-running properties in the event of foreign objects entering, chemical resistance, particularly chloride, and dry-running behaviour. Bronze demonstrates significant advantages in these areas compared to alternatives such as V2A or brass. It is for this reason that we have chosen bronze as our primary material for pumps.

We develop and produce our own bronze pumps. These are available with either a sliding ring seal or sealless magnetic coupling depending on your requirements. The primary advantage of using pumps with a sliding ring seal is their resistance to metallic particles and contamination in the medium. Magnetically coupled pumps do not have a seal, are resistant to wear, and maintenance-free. Due to their sealless magnetic operation, they do not leak and the medium cannot leak out.
General advantages of Tool-Temp pumps: Robust materials, shafts and bearings are oversized, gap dimensions are maximised and improve the ability to cope with contamination in the medium, electromechanical durability thanks to the optimum choice of materials, powerful motors and thermal resistance.

The pump is constructed and integrated into the system in such a way that reliable operation within the operating conditions can be guaranteed and cavitation prevented.

Advantages of Tool-Temp oil temperature control units – robust and large dimensions
Tool-Temp temperature control units have been conservatively designed and constructed. Our heating elements are subjected to low loads so that the surface temperature of the elements is as low as possible. The oil also flows around the heating elements at high speed. This practically eliminates the risk of the heat transfer medium overheating and prevents early ageing and cracking within the unit.

Due to the fact that our oil units are not pressurised, it is ‘only’ the effective pump pressure of the system and the application that is used. Using pressurised oil systems risks additional pressure affecting the unit and attached consumers due to the inclusion of inert gases (e.g. nitrogen). This can lead to high levels of wear and tear in various components such as hoses, pipes and valves in the temperature control unit itself.

Advantages of Tool-Temp oil temperature control units – non-scaling heat exchangers
The heat exchangers used in Tool-Temp oil units are designed so that they empty themselves as soon as cooling is no longer active. This significantly reduces limescale build up, allowing the maximum cooling capacity to be achieved long term. A check valve in the line to the cooling water outlet also prevents limescale and dirt from accumulating in the cooling circuit from backflowing water where the process does not exert any counterpressure.

Safety-related components in Tool-Temp units are:

  • Temperature controller
    The temperature controller in combination with the temperature sensor records the current oil temperature. The actual temperature is compared with the defined target temperature. The controllers sends a command to heat or cool in order to achieve the target temperature. The maximum temperature can be defined and specified in the temperature controller.  If this value is exceeded, the electronic safety thermostat is triggered so that no further heating commands are sent and a warning lamp lights up. This electronically protects the unit from excess temperatures.
  • Mechanical safety thermostats
    Our units additional feature capillary tube thermostats to protect against overheating. A mechanical safety thermostat is set +5°C higher than the permitted maximum temperature. If this safety thermostat is triggered, all heating elements are shut off. If the temperature continues to rise for any reason, a second mechanical safety thermostat is triggered which shuts off the unit with the disconnection of main contactor K1. This second capillary thermostat is set to +10°C above the maximum temperature as standard.
    Mechanical safety thermostats are also built into water-cooled units. One protects against excess temperature, the other ensures a minimum operating temperature (frost protection thermostat). The frost protection thermostat protects the unit by preventing the water circuit from freezing.
  • Circuit breakers
    Tool-Temp temperature control and water cooling units are fitted with circuit breakers. Circuit breakers are used to protect lines from damage caused by heating due to high a current. The circuit breakers are triggered in the event of a short circuit. Shut-off occurs within a matter of milliseconds by means of an electromagnet. Once triggered, the circuit breakers must be manually reset.
  • Main switch
    All units in our sales catalogue have a main switch. The main switch acts as an emergency shut-off or emergency stop function. The main switch fully disconnects our units from the electrical supply. On certain large units, e.g. TT-708 Y, the main switch features overcurrent protection as protection for the installation. Our main switches must be manually operated.
  • Dual level monitoring
    Tool-Temp oil units monitor the minimum and maximum fill level. Two float gauges measure the corresponding oil volumes. If the fill level is too low, the indicator lamp illuminates to signal to the operator that the minimum fill level has been reached. The pump shuts off to prevent dry-running. As soon as the level is once again at a permitted or sufficient level, the indicator lamp goes out and the unit and pump start up again automatically. If the fill level is too high, another indicator lamp illuminates and the unit is prevented from overflowing. As soon as the fill level has been reduced, the lamp goes out and the pump starts up automatically.

Pressurised water units have the advantage that they can be used with smaller mould channels with a smaller heat exchange area. The temperature differences at the tool are thus improved, but can still lead to stresses within the tools and cause stress cracks. Wastage when starting up the die casting machines due to the tool temperature is reduced considerably compared to units using cold water. Due to its high thermal capacity and better heat transfer, water offers some significant advantages for cooling processes and counteracts the problem of mould channels being too small.

Avoid using pressurised water with systems being used to work with magnesium. A leak in the mould can lead to liquid magnesium igniting, thus causing extensive damage. Magnesium and water trigger energetic chemical reactions, including explosions, that can damage both the tool and the machine.

Advantages of Tool-Temp pressurised water systems – safe and robust construction
Tool-Temp temperature control units have been conservatively designed and constructed. Our heating elements are subjected to low loads so that the surface temperature of the elements is as low as possible. The oil also flows around the heating elements at high speed and the minimum fill level is monitored. If the fill level is too low, the indicator lamp illuminates to signal to the operator that the minimum fill level has been reached. The pump shuts off to prevent dry-running. The unit automatically fills via the cooling water inlet until a sufficient level has been reached. The indicator lamp goes out and the pump starts up again automatically. Tool-Temp places great value on ensuring robust construction. Pressurised water systems exclusively make use of permanent pipe joints. These are made using highly automated bending machines at the plant in Sulgen. The housing is fully enclosed so that zero contamination can take place. Starting with the design phase, special attention is given to the materials used. Without exception, stainless steel is used at every single point that will come into contact with water.

Tool-Temp products offer additional process safety in the form of safety valves that trigger if abnormal operating conditions are detected. A safety valve opens if the system pressure is too high. The pressure is channeled out through the cooling water outlet. If the pressure still continues to rise, a second safety valve opens which releases the pressure into the open air.

The following safety elements are also integrated into all pressurised water units from Tool-Temp:

  • The check valve prevents water from flowing backwards if the pressure in the circuit is higher than the mains supply pressure.
  • Two safety valves monitor the rising pressure. The first valve switches off the heating, the second opens the circuit when the pressure is too high to force a drop in pressure.
  • The manometers show both the system and pump pressures.
  • The flow rate sensor monitors circulation of the circulation medium to the consumer.
  • The pressure release ensures that the temperature control circuit is depressurised before the unit is decoupled from the consumer. When the unit is unpressurised (solenoid valve open) and the temperature is below 80°C, the consumer can be emptied using suction.

Experts are divided on whether water or oil is the best solution for heating and cooling equipment. As a manufacturer of both types of unit, we tend to see more advantages in using oil for temperature control. These advantages include the longer service life of the tool mould as well as the ease of maintaining oil-based heating and cooling units. The disadvantages associated with the need for larger mould channels when using oil can be worked around during the tool design phase using suitable tool design concepts.

The use of oil-based units offers many advantages for high tool temperatures:

  • High operating temperatures
  • Less stress resulting from temperature differentials
  • Longer mould service life
  • Lower maintenance costs

In order for these advantages of oil temperature control units to be fully exploited, there must be sufficient circulation of the medium in the tool. It is for this reason that Tool-Temp units are fitted with flow measurement sensors.

Whether more cooling or more heating is required during the die casting process, depending on the dimensions of the parts being cast. Smaller parts are generally heated, and larger parts are cooled. Tool-Temp units are designed to have a very low surface load on the heating elements (W/cm2) in order to prevent the oil from overheating and avoid the oil ageing too fast.

The heat exchangers are designed in such a way that once the cooling process has ended, the heat exchanger empties itself to prevent limescale and dirt from building up. Two different types of pump are available: conventional pumps with a sliding ring seal and sealless magnetically coupled pumps.

Oils can be either mineral-based or synthetic liquids. Mineral oils can be used with temperatures up to approx. 270°C. Most synthetic oils can be used up to around 320°C. Few options are available for temperatures between 320°C and 360°C. Tool-Temp recommends the synthetic heat transfer medium Marlotherm SH, as well as its own TOOL-THERM SH3. TOOL-THERM SH3 is a mineral oil heat transfer medium that can withstand high temperatures up to 360°C.

When using thermal oils at temperatures above 250°C, coke-like deposits can form in pipes and especially in the tank area. When such residues are present, oils will age more quickly and turn acidic. They also become easier to ignite as the cracking products1 that are released lower the viscosity and the flash point of the oil. Tool-Temp recommends regularly checking the quality of the oil and replacing it if necessary.

When producing die cast parts from aluminium, zinc and magnesium, being able to control the thermal processes within the tool mould is critical to ensuring efficient and high-quality work. A stable heat balance and a reduced peak temperature on the surface of the mould help prevent early damage to the tool mould such as stress cracks and increase its longevity significantly. Also: High wastage in die casting is also associated with insufficient mould temperature control.

Die casting is an industrial process in which molten metal is poured or pushed into a steel mould. In this fully automated process, the molten metal (aluminium, zinc or magnesium) is injected into the tool mould at a pressure of 1500 to 1200 bar. It is primarily used for large batch production. Advantages of die casting include excellent reproduceable precision of moulded parts, the complexity of the shape of parts, as well as the wall thickness and cost-effectiveness. The heavy mechanical forces associated with the process, e.g. locking force, temperature variations, wear caused by extreme forces when striking the molten metal, require expensive machines and die casting moulds. The required peripheral equipment such as various types of mould spray machines, heating and cooling units for controlling the temperature of the mould as well as equipment for removing and ejecting the cast part, provides for a high degree of automation in the process. Tool-Temp supports its customers in this demanding process by offering heating and cooling solutions adapted to meet their individual requirements. Cooling these complex tool moulds can be carried out using oil or water. The wide range of products available from Tool-Temp includes temperature control systems for both cooling mediums that can also be integrated into the machine control system if needed.

There are two variants of the die casting process:

  • Cold chamber die casting
  • Hot chamber die casting

The key difference between the two variants lies in how the molten metal is delivered for the casting process. Which methods is chosen depends on the melting point of the material being used.

3.1. Hot chamber process
Hot chamber die casting machines consist of a press onto which the mould is mounted and a directly connected furnace with dosing unit. The molten material sits in a melting pot. The piston is lowered into the injection unit and pushes molten material from the pressure chamber via the gooseneck and nozzle into the mould cavity. After injection, the piston returns to its original position. At the same time, the cavity opens and the workpiece is ejected from the ejector mould half. One cycle lasts between 3 and 9 seconds, depending on the size of the workpiece.

The casting unit is in constant contact with the molten material. In order to avoid exerting excessive forces on the moulded parts that are above technical thresholds, the process temperature in the hot chamber process is limited to < 500°C. This means that only metal alloys with a low melting point can be used. Zink and tin alloys are the most common options. Where higher temperatures are used, constant contact between the molten material and casting unit is not possible. Such constant contact would increase wear, reduce the safety of the process due to the build up of slag and seals, and chemically contaminate the molten material casting unit as a result of diffusion processes from within the moulded parts.

3.2. Cold chamber process
Cold chamber casting machines consists of just the injection unit into which the casting die is integrated and must be externally fed with molten metal. Dosing before each shot is carried out manually or using a melting furnace with dosing robot. Before each shot, the required amount of molten material is filled into the casting chamber. The molten material is then pressed into the closed casting die cavity at up to 200 m/s. The metal cools quickly so that the tool can be opened and the workpiece ejected. Cycle times upwards of 30 seconds are not uncommon for the cold chamber process. Commonly used alloys include mostly aluminium, copper and magnesium-based alloys. Unlike the hot chamber process, the separation of the casting unit (chamber, piston) from the reservoir of molten material means that thermal stress is cyclically interrupted. Process temperatures are, however, very high, restricting the service life to between approximately 50,000 and 200,000 shots (aluminium).

3.3. Other processes
Other casting processes exist besides the two above:

3.3a Acurad process
The Acurad process is used for workpieces that need thick walls where minimising trapped gas is critical. Unlike conventional die casting, the molten material is moved at low pressure through a sprue with a relatively large diameter. The molten material moves with a laminar flow into the casting die, evenly removing gas from the mould and thus ensuring minimal gas remains trapped in the material. Once the casting die has been filled, a second piston applies pressure to the molten material as it solidifies in order to reduce porosity. This process is unsuitable for thin-walled workpieces due to the longer time taken to fill the die.

3.3b Vacuum die casting
In vacuum die castings, the die is evacuated before each shot. The molten material is then shot into the airless cavity where it quickly hardens. Evacuation causes a reduction in gas content within the molten material. Vacuum die casting allows the production of weldable and heat-treatable aluminium die cast parts as the oxygen content has been reduced to a minimum.

3.3c Thixotropic die casting
Thixotropic die casting involves pouring the material in a semi-molten state. In this state materials behave more like a solid when not subjected to any external influences. In the event that the material experiences any shear stresses, it flows and becomes malleable. This state can be achieved with various alloys within a certain narrow temperature range. In the thixotropic state, materials exhibit a particularly advantageous structure. The grain is exceptionally fine and the material does not liquify when poured, meaning that there is no drastic change to its volume, thus preventing shrinkage porosity. This process is, however, associated with high raw material costs due to the need for very specific alloys in order to ensure the a reliable process. Precise control of the temperature in serial process is also very difficult.

Release agents and auxiliary materials have important roles in the die casting process.
The use of release agents in die casting is necessary in order to easily remove the cast parts from the mould, achieve a high level of quality and to ensure external cooling of the mould surface. Carefully selection of the right product is of the highest priority. Consequences of using the wrong release agent can include: reduced productivity due to longer spray times, increased rates of wastage due to a porous structure, defects from the ejection process, poor coating adhesion, difficulty in cleaning due to separating agent residues in the mould cavity and frame, or even a production shut down due to metal becoming stuck in the cavity. Release agents used in aluminium casting are usually liquid and applied in the form of a spray. Both water-based and water-free release agents are available.

Water-based release agents
Water-based release agents usually consist of water in oil emulsions. The water acts as the carrier matrix and evaporates due to its relatively low boiling point, cooling the surface layer of the tool. The emulsion allows for even application of the highly viscous active ingredients.

Microspraying is a new method being used to reduce resource usage. A very small volume is sprayed onto the mould surface. This has the advantage that no water is needed to dilute the release agent, meaning that there is no need to expensively dispose of waste water. Cycle times are also reduced and there is no need to be concerned about alternating thermal loads on the mould. The service life of the mould can also be significantly lengthened.

Water-free release agents
These agents use low viscosity oil or a solvent as the carrier. The function of the carrier substance is similar to that of water, acting primarily to ensure even distribution. Spraying a flammable mist onto the hot mould, however, presents a fire risk, as well as a posing a danger to the environment.

With regard to part quality, mould service life and efficiency of the casting process, it is not just the release agents and auxiliary materials that play crucial roles – temperature control / cooling of the mould is also of utmost importance.

There are many applications that even today are still solely cooled using water and heated with gas burners or infrared heating.

Technical and economical reasons have led to most of these being replaced with heating and cooling systems that operate using oil temperatures up to 360°C or pressurised water up to 180°C.

  • Heating with gas burners / infrared heating, cooling with cold water
  • Heating and cooling with heat transfer oil up to 360°C
  • Heating and cooling with pressurised water units up to 160°C / 230°C

The main disadvantage of this type of temperature control lies in the large temperature differences and the stresses this generates within the tool. This has a negative affect on the service life of the tool as well as having to bring the tool back up to the required temperature after each interruption in the production process. Large increases in start up times and the rate of wastage are to be expected. This variant is usually chosen where the mould channels are too small, making the use of a temperature control system impossible.

Using temperature control units, with either water or oil, offers a range of benefits over this variant.

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