2. Product Analysis

2.1 Structural Features of the Grinder Housing

2.2 Film – Coating Requirements

3. Jili Company’s Processing Flow

3.1 Pre – processing Preparation

1. Design Communication and Confirmation
   • Have in – depth communication with the customer to obtain the detailed 3D design model of the coffee grinder housing and specific film – coating requirements, such as the film thickness (0.15mm) and glossiness (reaching 90% mirror effect).
   • Organize internal design and process teams to discuss and develop an initial processing plan, and repeatedly confirm details with the customer to ensure the plan meets their needs.
2. Material Procurement and Inspection
   • Purchase high – quality silver – gray PET film materials and conduct strict quality inspections. The inspection items include tensile strength (required to be ≥150MPa), peel strength (peel strength with the aluminum alloy substrate ≥10N/cm), and temperature resistance (stable performance at – 20℃ – 60℃), ensuring the materials meet processing and usage requirements. At the same time, prepare aluminum alloy blanks for CNC processing and conduct inspections on hardness, purity, etc.

3.2 CNC Machining

1. Rough Machining of the Housing
   • Use a five – axis CNC machining center to rough – machine the aluminum alloy blank. According to the design model, quickly remove most of the excess material to initially form the shape of the grinder housing. During processing, optimize the tool path and use a layered cutting method to reduce the impact of cutting force on the workpiece and prevent deformation. Select cemented carbide tools and set appropriate cutting parameters, such as a spindle speed of 8000r/min, a feed rate of 800mm/min, and a cutting depth of 1.5mm.
2. Finish Machining of the Housing
   • After rough machining, perform finish machining. Replace with a high – precision milling cutter to finely machine detailed parts such as the curves and installation positions on the main body, ensuring the dimensional accuracy is controlled within ±0.03mm. For the part connected to the hopper, use a combination of boring and milling methods to ensure the dimensional accuracy of the connection part for a tight fit with the hopper. Meanwhile, machine the flatness of the base, ensuring the flatness error does not exceed 0.02mm to ensure the stability of the grinder during placement.
3. Surface Treatment
   • After finish machining, perform surface treatment on the housing. First, use a sandblasting process to form a uniform and fine rough texture on the housing surface to increase the adhesion between the film and the housing. The sandblasting uses alumina sand with a particle size of 0.2 – 0.3mm and a sandblasting pressure controlled at 0.4 – 0.5MPa. After sandblasting, clean and dry the workpiece to remove surface impurities and moisture.

3.3 Film – Coating Workflow

1. Pre – coating Prep

• Preheated the housing (40℃) in a dust – free room for better film bonding.
• Cut PET film 5mm larger than the housing for edge wrapping.

2. Hot – Press Coating

• Applied the film via hot pressing: Temperature 120–130℃, pressure 0.8MPa, speed 30mm/min.
• Rolled the film to remove air (preventing bubbles) and manually adjusted for curves/angles.

3. Edge Trimming & Sealing

• Trimmed excess film and wrapped edges to the housing back for a neat, durable finish.
• Inspected for defects (e.g., bubbles) and used pinhole  /heating to fix issues.

3.4 Quality Control

1. Appearance Check: Inspected for smoothness, uniform gloss, and edge neatness under natural light.
2. Dimensional Testing: Used a CMM to verify mount/connector tolerances.
3. Performance Tests:
   • Scratch Resistance: Tested with an H2 pencil (500g force, 45° angle—no visible scratches).
   • Environmental Stability: Exposed to -20℃ (12h) and 60℃/90% humidity (24h)—no peeling/blistering.

4. Challenges & Solutions

4.1 Complex Curve Adhesion