Why are plates installed on both the upper and lower sides of the hydraulic press workbench
Why are plates installed on both the upper and lower sides of the hydraulic press workbench
First of all, the hydraulic press requires extremely high pressure when pressing coins, especially for some customers who press patterns directly on silver coins without annealing, which requires a lot of pressure. The metal blank is pressed into the required shape and pattern, and the upper and lower plates of hydraulic press workbench play the role of protecting the workbench to avoid direct high pressure damage to the equipment. (Assuming that the pressure used by the customer is too high, the plate is directly damaged, and the cost of replacing the plate is lower.)
The overprinting plate will increase the hardness of the plate surface, that is, the plate needs to be hardened to withstand repeated high-pressure impacts and extend its service life. At the same time, it ensures that the details of the pressed coins are clear and reduces deformation caused by wear.
Disperse pressure: The plate can evenly disperse the huge impact force applied by the hydraulic press, avoid the workbench or die from directly bearing concentrated stress, and extend the life of the equipment.
Reduce wear: Metal blanks are easy to scratch the die under high pressure. The plate acts as a buffer layer to reduce direct wear of the die and reduce maintenance costs.
In addition, considering metal flow, the surface treatment of the plate may help control the direction of metal flow under high pressure, ensuring that the fine parts of the pattern can be accurately reproduced without burrs or underfill. The plate may also act as a buffer to evenly distribute pressure and prevent excessive local stress from causing coin defects.
Surface treatment optimization: The plate is treated with overprinting (such as hardening, polishing or engraving microstructures) to ensure that pressure is evenly transmitted, making the patterns of gold and silver coins clearer and the details sharper.
Controlling metal flow: Specially textured plates can guide the metal blanks to flow in a predetermined direction under high pressure, avoiding edge cracking or incomplete pattern filling.
Adapt to different specifications:
Quick replacement: the plate can be flexibly replaced for gold and silver coins of different sizes or patterns to improve production efficiency.
Adjust thickness: fine-tune the pressing space by plate thickness to adapt to different thicknesses of blanks or special process requirements (such as multi-layer composite coins)
Special functional requirements:
Anti-counterfeiting marks: Some plates may be pre-engraved with microtext, secret marks, etc., which are transferred to the coin surface synchronously during pressing to enhance anti-counterfeiting.
Thermal management: If high-temperature pressing is involved (such as special processes for commemorative coins), the plate may use heat-resistant materials or built-in cooling channels to regulate temperature distribution.
In summary, the role of the plate may include protecting equipment, improving the accuracy of coin patterns, controlling metal flow, extending the life of the die, and ensuring uniform pressure distribution. The specific process of the overprinting process needs to be further confirmed, but the core reason should be to improve product quality and production efficiency.
Q2: How is the plate processed?
In the process of stamping gold and silver coins with the hydraulic press machine, the processing technology of the stamping plate is very critical, which is directly related to the dieing quality, die life and production efficiency of the coins. The following are common processing methods and technical details of stamping plates:
- Material selection and pretreatment
– Material: Plates are usually made of high-hardness, high-wear-resistant alloy tool steel (such as H13, D2) or stainless steel. Titanium alloy or ceramic composite materials may be used in some special scenarios.
– Forging and annealing: The raw materials need to be precisely forged to eliminate internal defects, and the hardness must be reduced through annealing to facilitate subsequent mechanical processing.
- Surface hardening treatment
– Nitriding/Carburizing: A high-hardness nitride layer or carburizing layer (hardness can reach HRC 60 or above) is formed on the plate surface through chemical heat treatment (such as gas nitriding, ion carburizing), which significantly improves wear resistance and compressive strength.
– Laser quenching: Use high-energy laser to quickly heat and cool the plate surface locally to form an ultra-hard martensitic structure while maintaining the toughness of the matrix.
- Precision machining and polishing
– CNC engraving: The plate surface needs to be machined with micron-level concave and convex textures (such as relief, anti-counterfeiting secret marks) that complement the coin pattern, which needs to be completed by high-precision CNC machine tools (CNC) or electrical discharge machining (sparking).
– Mirror polishing: Use diamond paste or chemical mechanical polishing (CMP) to polish the working surface to Ra < 0.1μm to ensure uniform pressure transmission and reduce scratches on the coin surface.
- Coating and surface modification
– Diamond-like carbon coating (DLC: DLC coating is applied on the plate surface by physical vapor deposition (PVD), which has high hardness (HV 2000-4000), low friction coefficient (<0.1) and anti-adhesion properties.
– Titanium nitride (TiN) coating: Gold TiN coating can improve surface corrosion resistance and reduce cold welding between metal blanks and plates.
– Microtexturing: Micron-scale grooves or pits are processed on the surface by laser or photolithography technology to guide metal flow or store lubricants (such as graphene dispersion).
- Stress relief and dimensional stabilization
– Cryogenic treatment: Soak the plate in liquid nitrogen at -196℃ for more than 24 hours to eliminate residual stress and stabilize the microstructure to prevent deformation during long-term use.
– Aging treatment: For aluminum alloy or titanium alloy plates, artificial aging (such as 120℃ insulation for 8 hours) is used to improve dimensional stability.
- Functional treatment
-Pre-coating of release agent: Spray fluorinated polymer (such as PTFE) or nano-ceramic release agent on the plate surface to avoid precious metal adhesion.
– Thermal management design: For scenes that require heating and pressing (such as special-shaped commemorative coins), heating elements or cooling channels can be integrated inside the plate, and the heat conduction efficiency can be improved by aluminum plating on the surface.
Technical trade-offs in practical applications
– Cost and performance balance: For example, DLC coating has superior performance but high cost, and may only be used in the production of high-value-added commemorative coins.
– Adaptability adjustment: For different metals (gold is softer and silver is more brittle), the plate hardness needs to be designed differently – the gold coin stamping plate may use a higher toughness material, while the silver coin plate focuses on fatigue resistance.
Summary
The processing of the embossing plate is a multidisciplinary precision engineering project, covering material science, surface engineering and precision manufacturing technology. Through the above process, the plate can not only withstand thousands of tons of impact pressure, but also accurately reproduce the micron-level pattern on the coin surface. Modern mints will even design customized plates for each new set of coins, and combine digital twin technology to simulate the embossing process and further optimize the processing parameters.
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