Metals and alloys: the conditions under which the transition from solid to liquid state occurs
Would you like to know how the metal melting process occurs? Fully understanding this physical phenomenon will be very difficult if you do not know the importance of temperature. (If you don’t believe it, try melting iron with a camping stove)
In this article, you will discover what happens to solid metals during the process, what the melting temperatures of the most important metals are and, above all, why these data concern not only those who design a mold, but also those who design the automation that processes that metal immediately after casting.
At TREBI, we deal with this every day: knowing the melting temperature of metals and in particular the temperature of a casting is not an academic detail; it is a parameter that directly influences how a robotic cell must be built.
How the melting of metals and alloys occurs
Those who work in the metal processing sector know very well what melting is, at least in practical terms. To be honest, I doubt this phenomenon is totally unknown even to those who—for work—deal with something else entirely. However, not everyone knows (or remembers) what happens to metals during melting from a physical point of view.
I will make a premise right away: I am not a physicist and I do not intend to give lessons of any kind; however, I want to explain to you in a simple way what melting is and how it occurs.
The melting process consists of the transition of a matter from a solid state to a liquid state following the achievement of a certain temperature. Okay, we’re with you so far. But, at a structural level, what happens inside metals when they absorb heat?
You should know that, at room temperature, atoms and molecules maintain a bond with each other within the crystal lattice; with the absorption of the heat of fusion, however, they begin to agitate and the bonds are broken upon reaching a certain temperature. Their state, therefore, changes by virtue of the disintegration of the particles.
Read also: Steel copper plating: how to ensure an optimal result
The melting temperature of metals is a peculiar characteristic: it means that every metal has a very precise melting temperature, which determines the change of state from solid to liquid. In reality, there is something else that influences this phenomenon: pressure. I will specify the role of this factor shortly; before doing so, however, I want to clarify that metal alloys have a melting temperature that varies based on the percentage of pure metals of which they are composed.
Steel, for example, despite being composed mainly of iron, does not melt at the same temperature as this element. But now, let’s see how pressure affects the metal melting process.
Melting temperature and melting point: what changes?
A moment ago I told you that every metal has a certain melting temperature. True. However, it is correct to specify that this temperature, for convenience, is indicated taking atmospheric pressure into account. This means that the melting temperature is influenced by the pressure to which the matter is subjected.
In the same way, the melting point is also a thermodynamic state that depends on pressure. To be precise, it is the phase in which the actual melting process occurs and a metal passes from a solid to a liquid state. Once the melting point is reached, the temperature remains stable by virtue of the absorption of heat—called latent heat—by the material.
Until the change of state is completed, therefore, the temperature stops rising; once the metal reaches the liquid state, however, it starts to increase again.
Table of melting temperatures of the main metals
The substances present in nature that can be subjected to a melting process are many; therefore, in the following table, the melting temperatures of the metals most used in the foundry are shown.
| METAL | MELTING TEMPERATURE IN DEGREES CELSIUS |
| Lead | 327 |
| Steel | 1.350 |
| Zinc | 420 |
| Aluminum | 660 |
| Gold | 1.064 |
| Silver | 962 |
| Iron | 1.535 |
| Chromium | 1.857 |
| Copper | 1.083 |
| Tin | 232 |
| Bronze | 900 |
| Brass | 1.015 |
| Platinum | 1.769 |
Read also: Working cycle of aluminum profiles: main techniques
Why are melting temperature and melting point important concepts to consider even downstream of the casting? It is simple and at the same time intriguing. The casting, once extracted from the mold, does not instantly return to room temperature: the latent heat released during solidification keeps the part hot for a time that depends on the mass, geometry, and the metal itself. It is an aspect that we at TREBI always evaluate during the design phase of a robotic cell: a manipulator that picks up a still-hot casting works in very different conditions from one that handles a part at room temperature.
The importance of post-melting in the foundry: metal temperature management.
As you well know, once the liquid state is reached, a metal can be introduced into a mold using various techniques; the most used in the foundry are gravity casting and die casting. Once cooling is complete and the metal is returned to a solid state, however, the objects created with the molds present overflows, burrs, and sharp edges, not to mention the risers.
To eliminate them, it is necessary to perform various finishing operations such as:
- cutting of risers;
- belt sanding;
- grinding;
- sanding;
- filing.
Not all of these operations, however, must necessarily wait for the complete cooling of the part. In aluminum die casting, for example, it is established practice to shear the casting gates when the casting is still hot, even around 200°C. Similarly, in many processes, even deburring or gate cutting can be performed hot, immediately after extraction from the mold, without waiting for the part to return to room temperature.
Knowing the melting temperature of metals and the melting point is important, just as it is important to define the temperature at which subsequent processing is done.
Working hot, when the process allows it, brings a significant production advantage: overall cycle times are reduced because there is no need to wait for natural cooling before moving to finishing, and the deburring phase can be integrated directly into the continuous flow starting from the press.
This, however, also involves precise design choices for those who create the automation. A hot operation requires grippers, tools, and safety systems dimensioned for those temperatures, in addition to careful management of the sequence and timing, to ensure that the part is processed in the correct thermal window without compromising either the finishing quality or the integrity of the robotic system. It is an aspect that we address directly during the design phase of TREBI robotic cells, evaluating case by case if and when it is convenient to process the still-hot part, based on the type of alloy, the geometry of the casting, and the customer’s production cycle.
Performing these procedures manually causes various inconveniences both for you and for the customers; production timelines are never reliable, material waste is copious due to the many defective parts that do not pass quality control and do not faithfully respect the geometries requested by the customer. Furthermore, with manual deburring, it is impossible to standardize products because every piece—even if imperceptibly—will be different from the others.
Robotic deburring solves these problems. With the automation of finishing and deburring processes, in fact, you will have the certainty of producing quality metal components in precise cycle times because robots, unlike humans, work according to preset parameters and are not subject to drops in concentration or fatigue.
The TREBI point of view: why metal melting temperature is not just a foundry data point
In our field experience, the melting temperature and the resulting thermal conditions influence three very concrete aspects of robotic automation, often underestimated during the design phase:
1. Robot protection. When a manipulator works in close contact with still-hot castings, with furnaces, with die-casting lines, or in environments where ambient temperatures are high, the robot itself must be protected. It is not enough to choose a cobot or an anthropomorphic robot suitable for the payload: specific covers and protections are needed for the joints, cables, and electronic components, otherwise the reliability of the system over time suffers. This is a topic we address together with specialized partners, choosing case by case the most suitable protection solution for the thermal context of the plant.
2. Finishing quality depends on temperature control, not just the applied force. In satin finishing and brushing, for example, if the temperature on the part rises too much during processing—due to prolonged friction or uncalibrated process parameters—surface defects can emerge that compromise aesthetics and, in some cases, material properties. Correcting the design of speeds, contact pressure, and processing cycles of a robotic finishing cell also means keeping local overheating of the part under control, not just the final visual result.
3. The choice of tools and abrasives must take the metal into account. In the grinding of investment castings, for example, not all abrasive materials behave the same way on different alloys: a tool suitable for steel can wear out rapidly or generate excessive heat on a softer alloy, with negative effects on both part quality and the tool’s useful life. For this reason, during the design phase of a robotic machine tending system for grinding, the choice of wheels, brushes, and process parameters is always calibrated to the type of metal being processed.
In summary, metal melting temperature is not just a technical data point from a table: it is the starting point upon which the quality of the casting, cooling times, and, downstream, the way that part must be handled, deburred, and finished depend. Every metal and every alloy behaves differently under heat, and this difference affects the entire production chain, including automation.
This is where TREBI’s experience, particularly in industrial robotics for foundries, comes into play. Designing an effective robotic cell does not just mean choosing the right robot: it means understanding how the processed metal behaves thermally, what protections are needed to ensure system reliability over time, and which process parameters avoid surface defects or premature tool wear. It is an approach born from the knowledge of materials even before robotics itself, allowing us to build tailored solutions for every type of alloy and process—from the deburring of die-castings to the finishing of delicate components, up to the robotic machine tending of machine tools.
If you are evaluating how to automate a foundry or metal finishing process, the first step is precisely this: understanding the characteristics of the material you work with, to design a robotic system that is truly reliable within your production context.
Contact us: let us analyze your plant’s needs together and find the robotic automation solution best suited to your process.
