Titanium Commemorative Coin

 Commemorative coin usage scenarios: legal commemoration, corporate customization, event commemoration, etc.

 Determine the core pattern: figures, landmarks, patterns

 Text: denomination/theme slogan, signature, serial number

 Specifications: common diameters are 25/30/40mm, thickness 1.5~3mm

 The designer completes the 2D rendering and specifies the relief height: titanium commemorative coins are recommended to have a relief height ≤0.8mm, far lower than silver commemorative coins (1.2~1.5mm)

 Edge tooth style: straight teeth, slanted teeth, rolled lettering teeth, for anti-counterfeiting

 Surface process zoning: mirror surface, sandblasting, and color printing areas.

Convert the 2D rendering into a 1:1 high-precision 3D engineering drawing, marking all dimensional tolerances, relief angles, and fillet radii; process engineers conduct manufacturability verification, eliminating design details that cannot be processed with titanium.

Organize a review by design, process, and customer representatives to confirm the visual effect of the drawings, process feasibility, and specifications. After modifications, the final production drawings (including 2D unfolded drawings, 3D solid models, and process requirements) are issued as the sole basis for mold making and production.

Use 3D printing (resin/wax) to create a 1:1 commemorative coin sample to visually verify the proportion and visual effect of the pattern and text. After confirmation, proceed to the mold-making stage. 

The original mold is the initial carrier of the commemorative coin's design. Due to the simple design of titanium commemorative coins, CNC precision engraving is primarily used, with manual engraving only suitable for high-end custom/artistic designs:

 CNC Precision Engraving: The final 3D drawing is imported into a five-axis CNC engraving machine. A cemented carbide engraving tool is used to engrave a 1:1 commemorative coin original mold on a brass blank. The engraving accuracy is controlled to within ±0.005mm to ensure the completeness of the relief, text, and pattern details.

 Manual Engraving: A senior engraver manually engraves the brass blank, suitable for niche artistic designs. This process is more time-consuming but results in a more artistic texture.

The original mold is a single piece. A ​​harder master mold is needed, created through electroforming, to serve as the basis for producing multiple working molds. The titanium commemorative coin master mold uses 304/45 stainless steel and undergoes heat treatment. The steps are:
 Polish, clean, and coat the brass original mold with a release layer to ensure a clean surface.
 Use the electroforming nickel/copper process to deposit a 0.5~1mm thick metal layer on the surface of the original mold, then peel it off to obtain the negative mold of the original.
 Attach the negative mold to a steel blank, and replicate the stainless steel master mold through hot forging/cold pressing, followed by vacuum quenching heat treatment to increase hardness to HRC58~62, enhancing wear resistance.

The working mold is the mold directly used for stamping the titanium commemorative coins. Due to the high wear on the mold caused by titanium stamping, multiple sets of working molds are needed. The material is tungsten carbide. The steps are:
 Replicate the pattern from the stainless steel master mold onto the tungsten carbide blank through cold extrusion to obtain the tungsten carbide positive/negative mold;
 Precisely grind and polish the tungsten carbide mold to remove machining marks, ensuring that the surface of the stamped titanium commemorative coin is free of burrs and the pattern is clear;
 Assemble the mold: Integrate the upper mold, lower mold, edge tooth mold, and positioning mold into a complete stamping mold assembly, and install it on the mold base, ensuring that all components are centered to prevent pattern misalignment during stamping.

The first trial stamping is performed using small titanium blanks to verify the mold's pattern reproduction accuracy and dimensional precision. The core objective is to address the issues of oversized dimensions and pattern misalignment caused by springback during titanium stamping:
 If the diameter of the trial part is too large, the process engineer will fine-tune the mold dimensions and optimize the stamping parameters;
 If the pattern is blurry or partially unformed, the mold will undergo localized precision polishing, and the stamping pressure will be adjusted;
 Once the trial parts pass inspection, the mold is officially finalized, a mold inspection report is issued, and mass production begins.

A cold-rolled pure titanium Gr2 plate with a thickness 0.1-0.2mm greater than the finished product is selected. It is cut into circular titanium blanks 5-8mm larger than the diameter of the commemorative coin using a CNC laser cutting machine/precision shearing machine. After cutting, edge burrs are removed to prevent scratching the mold.

If the commemorative coin thickness is <1.5mm, to obtain a blank with the required accuracy, the titanium blank is lightly cold-rolled using a two-roll cold rolling mill, controlling the deformation to ≤15%.

The titanium blank is placed in a vacuum annealing furnace and held at a temperature of 700-750℃ for 1-2 hours, then cooled to room temperature in the furnace. This eliminates internal stress from cold rolling and increases room temperature plasticity to over 25%, preventing cracking during stamping; the vacuum environment prevents oxidation of the titanium blank.

The annealed titanium blank is precision-ground on both sides using a double-sided grinding machine to remove the slight oxide layer on the surface, ensuring a flatness of ≤0.005mm on both sides and a thickness deviation within ±0.01mm, providing a uniform blank for stamping.

The precision-ground titanium blank is placed in an ultrasonic cleaning machine and cleaned with anhydrous ethanol + deionized water to remove abrasives and oil stains. It is then dried in a hot air drying oven at 60℃ to obtain a clean, oxide-free, and precisely sized titanium stamping blank for use.

The hardened alloy mold assembly is installed on a 100-200 ton CNC hydraulic press. The mold is calibrated using the press's high-precision positioning system to ensure the upper mold, lower mold, and edge tooth mold are aligned; the titanium blank is placed in the mold's positioning groove for precise positioning of each blank.

Titanium is prone to sticking to the mold during stamping, leading to scratches and defects on the commemorative coin surface. Therefore, a special high-temperature lubricating film for titanium alloy stamping is evenly sprayed on both sides of the titanium blank. The film is thin and uniform to avoid covering the mold patterns and resulting in unclear details.

Titanium commemorative coins do not use hot stamping, but instead use 3-4 passes of cold stamping to gradually form the shape. The stamping pressure is gradually increased with each pass to prevent cracking of the titanium blank and mold damage from a single high-pressure stamping. During stamping, the press slide speed is controlled at 5-10 mm/s; the low speed reduces titanium springback and improves pattern conformity.

After stamping, the excess material from the commemorative coin blank is trimmed using a special cutting die to obtain the precise diameter; simultaneously, the edges are rolled using an edge tooth rolling die to form the designed edge teeth. The rolling pressure is controlled to ensure uniform teeth without missing teeth. At this point, a titanium commemorative coin blank with complete patterns and edge teeth is obtained. The blank surface has residual lubricating film and slight stamping marks, requiring further surface finishing.

The titanium commemorative coin blank is immersed in an alkaline degreasing solution at 50-60°C for 5-10 minutes to remove the stamping lubricant film; after rinsing with deionized water, it is immersed in dilute nitric acid for 1-2 minutes to remove slight stamping oxidation spots, and finally thoroughly rinsed and dried.

According to design requirements, the commemorative coin undergoes mirror polishing/sandblasting/brushing to achieve zoned surface effects:

Fine polishing is performed using diamond polishing paste with a CNC double-sided polishing machine, achieving a surface roughness of Ra≤0.02μm and a mirror effect;

CNC sandblasting is performed using alumina micro-powder to achieve a matte finish;

Unidirectional brushing is performed using a nylon brushing wheel to obtain a brushed texture;

Utilizing the anodic oxidation light interference effect of titanium, a dense titanium dioxide passivation film is formed on the titanium surface. The film thickness is controlled by adjusting the voltage, and different film thicknesses produce different colors due to the reflection and interference of light.

Manual visual inspection to remove commemorative coins with surface scratches, oxidation spots, missing teeth, or blurred patterns.

All initially qualified coins undergo comprehensive testing using professional instruments. All indicators must meet the requirements of the production drawings:

Diameter, thickness, and relief height are measured using a 2D image measuring instrument, with a deviation of ≤±0.02mm;

Surface roughness of the mirror/sandblasted areas is measured using a roughness tester, meeting design requirements;

Titanium purity is tested using an X-ray fluorescence spectrometer to ensure it is Gr1/Gr2 pure titanium without impurities;

24-hour salt spray test using a salt spray testing machine, ensuring no corrosion or discoloration on the surface;

Surface hardness is measured using a Vickers hardness tester, ensuring HV≥200 to prevent deformation.

During mass production, 1% to 3% of each batch is sampled (a minimum of 50 coins). If the sample fails the inspection, the entire batch is inspected, and defective products are removed. After a successful inspection, a product quality inspection report is issued, indicating batch number, material, process, and test results.

Qualified commemorative coins are placed in transparent acrylic protective cases (with built-in shock-absorbing foam pads). High-end collector's editions use vacuum sealing to ensure isolation from air and dust. The acrylic case is labeled with the coin's theme, specifications, and material.

According to customer requirements, individually packaged commemorative coins are placed in customized collector's albums or gift boxes. The gift box includes a product certificate, quality inspection report, and collector's instructions, detailing the production process, titanium material characteristics, and collectible value.

The packaged commemorative coins are stored in a temperature- and humidity-controlled warehouse (temperature 20±5℃, humidity ≤60%), categorized and stored by batch. A warehousing ledger is maintained, recording the batch number, quantity, production date, and test results for subsequent traceability during outbound shipments.