How a Glass Substrate Becomes a Phone Cover: A Full Breakdown of the 3D Glass Cover Manufacturing Process

Engineering

Confirm whether the customer's drawings can be produced, create in-house drawings, film and confirm the process flow. Drawings and film must have production dates and numbers. When revisions are made, update them promptly and收 recycle old drawings and film. Issue work orders and track the entire sample line.

 

CNC Cutting

Material requirements: The glass material must be 3D curved glass. When sheet glass enters deep processing, the first step is to follow the customer's drawing dimensions, which allow for processing allowance (generally 0.1 mm per side) and input the data into a CNC glass substrate cutting machine for rough blank production, commonly known as cutting.

Notes: The glass cutting machine must be able to efficiently perform straight-line, round-hole and curve cutting. This can greatly save processing time in subsequent cover glass CNC forming, polishing and other steps, also it is highly positive for improving production efficiency and reducing production costs in the cover glass industry. The first step is the same as for ordinary cover glass.

 

CNC Precision Carving of Glass (Edge Grinding)

CNC precision carving of glass uses the grinding wheel groove of a precision engraving machine to grind the edges of the rough glass and remove allowance. Drill bits are used to chamfer and drill the glass raw material, and fine grinding wheels are used for precision processing of the outer shape and camera holes to meet final product requirements. Processing accuracy reaches 0.01 mm.

 

Grinding and Polishing

Add polishing powder and through a lapping tool under a certain pressure, create complex relative motion with the processed surface to grind the glass raw material to the required thickness and polish it to a mirror-like surface.

 

Cleaning

Different processing companies use different cleaning stages. Generally, cleaning is required after edge grinding, then grinding and polishing are performed again.

The main purpose is to clean away residual waste on the surface, usually using ultrasonic cleaning.

 

Thermal Bending Process

Thermal bending is one of the most core and also one of the most difficult processes in 3D glass manufacturing. Glass with a precision-carved shape and holes placed in a graphite mold, the mold is then placed in a thermal bending machine. After preheating, pressing and cooling, the glass forms into curved glass inside the mold. The dimensions of the curved glass depend on the graphite mold design. The appearance after forming depends on the forming process and the graphite mold design. The performance of the thermal bending machine has a crucial impact on forming. The most important thing is that the temperature inside the furnace must be uniform during the forming process and that the glass is heated evenly, avoiding stress cracking. The heating furnace is usually equipped with 16–22 temperature points inside to monitor temperature uniformity.

The specific operation process is during operation, nitrogen protective gas is introduced and air is prevented from entering. The furnace temperature is controlled at 700–750°C. The time the product stays in the furnace depends on the stations of the thermal bending machine, generally about 20–40 minutes. Because glass is not a crystalline substance and has no fixed melting point, it is a glassy inorganic compound. As the temperature rises, it gradually softens. The softening point is usually around 600°C. The softening point is the temperature at which the glass products we see in daily life begin to soften.

 

Glass thermal bending molds generally use graphite material. This is because graphite has high hardness, good electrical conductivity, radiation resistance, corrosion resistance, good thermal conductivity, and low cost. It also has high-temperature resistance. Its performance changes in the opposite way from metal as temperature rises: the higher the temperature, the harder it becomes. In this way, there is no problem of deformation. Therefore, using graphite material to make glass thermal bending molds not only greatly reduces production costs, but also greatly reduces mold processing difficulty. The mold body is solid, and the material is mainly graphite. The mold body is a graphite concave rectangular body, and the mold cavity is a preset curved surface. Among them, the mold cavity and push plate are finely polished. The mold body thickness is 5 to 30 mm. This effectively ensures material stability and dimensional consistency at high temperatures, improving product yield and good product rate.

Graphite thermal bending mold manufacturing process:

Step 1: Select suitable graphite material. Try to choose graphite with high purity and high density. Otherwise, the mold is prone to oxidation and collapse during high-temperature thermal bending. This way, oxidation will not occur during thermal bending processing, nor will bubble holes appear. Another point is that the service life of the mold will be greatly improved.

Step 2: After the graphite material is cut in the cutting room, it enters the CNC computer gong processing center for forming and engraving. Carbon CNC computer gong requires fast processing speed and high precision. The precision of products hot-pressed by this kind of mold can reach the thermal bending processing precision of 0.025 mm announced at new product launch events.

Step 3: After the mold is formed, it can be taken to a polishing machine for final graphite polishing. After polishing is completed and dimensions are inspected by a three-dimensional measuring instrument, it can be put into production.

 

Double-Sided Sweep Polishing

After thermal bending, the product surface must be polished. A cashmere wheel is used. By adjusting the speed of the upper and lower polishing wheels, the pressure on the product, and the time control, and with the aid of grinding powder or foam liquid, the glass product surface is finely polished to achieve a transparent and flawless finish.

Note: The parameter settings of the sweep polishing machine are very critical. Incorrect parameters may cause damage to the main reduction gearbox on the sweep polishing machine. At the same time, if the polishing powder quality is too poor, the yield of polished glass sheets will be low, and not only sand spots but also wave patterns may appear.

 

Quality Inspection

Multiple layers of quality inspection processes are required. 3D glass inspection needs to be based on process requirements. Generally, two inspections are required: one for appearance and dimensions before tempering, and another for appearance and warpage deformation monitoring after tempering because stress release causes extended curvature changes.

 

Chemical Strengthening

Use high-purity potassium nitrate solution mixed with a matching catalyst, generally for 4–6 hours at 450°C for high-temperature tempering treatment.

The principle is: potassium ions and sodium ions on the glass structure surface undergo ion exchange to form a strengthened layer. Hardness can reach 7H, improving the glass's scratch resistance, impact resistance, and other capabilities.

 

UV Transfer Printing (Adding Texture)

UV transfer printing, in simple terms, means adding texture. Here it refers to the GDF process, which transfers texture or digital graphics onto the glass explosion-proof film (generally PET material). There is no pixel loss during the transfer process.

 

Coating (PVD)

The purpose of coating is to prevent fingerprints and oil stains from adhering easily and to make them easy to wipe off. The surface is smooth, comfortable to the touch, and not easy to scratch. It increases the wear resistance of the glass surface.

The specific anti-fingerprint treatment process is as follows:

 

Pretreatment: Use weak alkaline cleaning agents or solvents to remove oil, moisture, and other stains on the substrate surface. Ultrasonic cleaning gives better results.

 

Apply AF liquid to the product surface to form a film.

 

Baking: After spraying, take out the glass and place it in an oven (120°C, 30 min). Adjust to the best conditions according to specific requirements and product conditions.

 

Cleaning: After the product is cleaned, the finished product is packaged.

 

Screen Printing, Spraying, or Exposure and Development

Make a screen plate for product LOGO characters, adjust ink, and use positioning fixtures to print the characters on the concave surface of the product. Dry by baking, apply fixtures, adjust paint, titanium crystal black / ceramic white, and spray reciprocatingly. Dry by baking.
The process equivalent to screen printing is exposure and development, which is currently a relatively new process.

 

Lamination

This process attaches the already decorated explosion-proof film to the glass cover.

 

Protective Film Application

 

Packaging

Clean, inspect, and package products that have completed effect processing and meet customer requirements. Use low-viscosity protective film for packaging. No bubbles are allowed during film application.