Jili Company’s Plastic CNC Machining Case: Customized Production of Precision Circular Injection – Molded Parts
1. Project Background
In the context of diverse manufacturing needs in industry, sectors such as electronics and automobiles have increasing demands for the precision and complexity of precision plastic components. Jili Company, specializing in CNC machining, has, by virtue of its technology and experience, undertaken a customized machining project for a circular injection – molded part (similar to the plastic part in the figure with multiple connection structures and porous positions). It aims to create key components for an automotive electronics equipment manufacturer. This part is used in the vehicle – mounted sensor system, needs to adapt to complex installation environments, and has strict requirements for dimensional accuracy and structural integrity.
2. Part Analysis
（1）Structural Features
The part in the figure is a circular plastic component with a hollow bowl – like main body. It is equipped with multiple sets of connection blocks and positioning columns, and there are 8 precisely machined holes. It includes a hollowed – out central area for component nesting and circuit threading. The connection blocks and positioning columns are responsible for the positioning and fixing functions during component assembly, which have extremely high requirements for dimensional matching to ensure the stability of subsequent assembly with other electronic components.
（2）Material Properties
Polyetheretherketone (PEEK) engineering plastic is selected, which has the characteristics of high temperature resistance (long – term use temperature up to 260 °C), chemical corrosion resistance, high mechanical strength, and low hygroscopicity. It is suitable for complex environments such as the automotive engine compartment to ensure the long – term stability of components. At the same time, due to the high material cost and processing difficulty, strict control of the CNC process is required.
3. Jili’s CNC Machining Process
（1）Pre – production Preparation
- Design Collaboration : The customer provides a 3D model. Engineers at Jili deeply analyze the design. Considering the characteristics of PEEK, they evaluate processing difficulties (such as the tendency of the material’s toughness to cause tool chipping and dimensional thermal deformation during processing), and collaboratively optimize details with the customer. They define standards such as a dimensional tolerance of ± 0.02mm and a surface roughness of Ra 0.8μm.
- Process Planning : Based on the part structure, a segmented process of “rough machining – semi – finishing – finishing” is planned. According to the characteristics of holes and connection blocks, cemented carbide – coated tools (such as a Φ3mm end mill for narrow groove processing) are selected. The tool path is simulated through CAM software to avoid interference in the processing of connection blocks and positioning columns. Cutting parameters are preset (for rough machining: rotational speed 8000r/min, feed rate 0.2mm/r; for finishing: rotational speed 12000r/min, feed rate 0.1mm/r).
（2）Machining Execution
- Blank Preparation : High – quality PEEK bar stock is purchased and inspected for internal defects by ultrasonic flaw detection. It is then cut into a blank of Φ80mm × 40mm (with a 3mm machining allowance reserved) and placed in a constant – temperature drying oven (80 °C for 2 hours) to remove moisture and avoid deformation after processing.
- CNC Machining Operations
- Rough Machining : High – speed CNC milling is used, and a layered cutting strategy is adopted to remove most of the,quickly milling out an approximate contour. The cutting depth is controlled at 1.5mm to reduce the load of subsequent finishing. The spindle temperature is monitored in real – time, and an air – cooling system is used to maintain stability and prevent material softening due to overheating.
- Semi – finishing : A high – precision ball – nose end mill is used to refine the contours of connection blocks and positioning columns. Pilot holes are pre – drilled for hole positions, and the coaxiality of hole positions is controlled within 0.03mm. For the hollow area, a circular tool path (step distance 0.05mm/step) is used to avoid tool vibration affecting the inner wall flatness.
- Finishing : A precision CNC lathe (equipped with an on – line measuring probe) is used to perform combined reaming and boring processing on hole positions to ensure hole diameter accuracy. The surface of connection blocks is milled with a small step – over (0.05mm/step) to achieve a surface roughness of Ra 0.8μm. During processing, the workpiece temperature is monitored every 30 minutes with an infrared thermometer to compensate for thermal deformation errors.
（3）Quality Control
- In – process Inspection : After rough machining and semi – finishing, a coordinate measuring machine (accuracy 0.001mm) is used to sample and inspect key dimensions (such as connection block spacing and hole position coordinates), generating real – time data reports. A machine vision system is used to identify processing burrs and chipping on – line, triggering tool compensation or shutdown adjustment.
- Final Inspection : After processing, full – size inspection is carried out, covering more than 20 dimensional parameters. A salt spray test (simulating the outdoor environment of automobiles) is carried out to verify corrosion resistance, and a tensile testing machine is used to test the tensile strength of connection blocks (compliance value ≥ 50N). Fluorescent penetrant inspection is carried out on the surface to detect cracks, and a complete quality inspection report is issued.
4. Challenges and Solutions
（1）Material Processing Difficulties
PEEK has high toughness and is prone to tool adhesion and built – up edge during processing. Jili adopts a “low – temperature cutting fluid + spiral – edge tool” solution. The cutting fluid (containing special lubricating additives) flushes the tool in real – time to reduce adhesion. The spiral – edge design improves chip evacuation efficiency, the tool life is extended by 30%, and the processed surface quality is significantly improved.
（2）Dimensional Accuracy Assurance
The part structure is complex, and thermal deformation is likely to affect accuracy. Through a “processing – inspection – compensation” closed – loop system, according to real – time temperature data, the tool path is dynamically adjusted during the finishing stage, and the final dimensional tolerance is stably controlled within ± 0.015mm, which is better than the customer’s initial requirements.
5. Project Achievements
- Delivery Quality : 500 qualified parts are delivered on schedule, with a dimensional qualification rate of 99.2% and a surface defect rate of 0.3%. After the customer’s assembly test, the assembly yield of the sensor system is increased to 98.5%, far exceeding the level of previous suppliers.
- Technical Precipitation : A standard CNC machining process for complex circular plastic parts (with multiple connection structures and porous positions) is formed, and a library of high – precision processing parameters for PEEK materials is accumulated, providing technical support for similar projects in the subsequent automotive electronics and high – end equipment fields.
This case demonstrates Jili Company’s technical strength in plastic CNC machining. From in – depth part analysis to precise whole – process control, it provides a replicable customized solution for the machining of complex plastic parts in the industry.
