How do Plastic Injection Molding Manufacturers Perform Dimensional Control

During the injection molding process, product dimension control is a crucial link. In order to ensure the dimensional accuracy and quality stability of the product, it is necessary to carry out comprehensive control from multiple aspects such as mold design, process manufacturing and production management. The following are some specific experiences and suggestions for the control of the molding dimensions of injection molded products:

1. Control of mold design by plastic injection molding manufacturers

Mold structure and materials: First, you need to understand the requirements of the mold structure, materials, hardness and precision in detail. Including whether the shrinkage rate of the molded plastic material is correct, whether the 3D size modeling of the product is complete and reasonable, etc.

Appearance influencing factors: Comprehensively consider the appearance problems of injection molded products such as shrinkage holes, flow marks, draft angles, weld lines and cracks.

Simplify processing: Simplify the processing method of the mold as much as possible without affecting the function and appearance of the injection molded parts.

Parting surface selection: The selection of parting surface must be appropriate, which is convenient for mold processing and ensures smooth molding appearance and deburring operations.

Ejector method: Select the appropriate ejector method (such as ejector, unloading plate, ejector sleeve, etc.) according to the actual situation, and ensure that the position of the ejector and unloading plate is appropriate.

Core pulling mechanism: The side core pulling mechanism should be adopted appropriately to ensure flexible and reliable movement without jamming.

Temperature control: Select the appropriate temperature control method according to the characteristics of the plastic product, such as temperature control oil, temperature control water or coolant circulation system, and ensure that the size, number and position of the coolant hole are reasonably designed.

Gate form: Reasonably select the gate form, material channel and feed port size to ensure the appropriate gate position and size.

Heat treatment and standard parts: Consider the influence of heat treatment deformation of various modules and cores, and whether the selection of standard parts is appropriate.

Injection parameters: Ensure that the injection volume, injection pressure and clamping force of the injection molding machine meet the requirements, and the details such as nozzle R and gate sleeve aperture must also be matched appropriately.

2. Control of process manufacturing

Although full consideration has been given in the design stage, various problems may still occur in actual production. To ensure that production meets the original design intention, the following measures should be taken:

Equipment selection: Select economical and applicable machine tools and equipment, and formulate 2D and 3D processing plans.

Tooling and fixtures: Reasonable use of tooling and fixtures to assist production, optimize tool use, reduce product deformation, control shrinkage fluctuations, avoid demolding deformation, improve mold manufacturing accuracy, reduce errors, and maintain mold accuracy stability.

Error analysis: Referring to the data provided by the British Plastics Association (BPF), mold manufacturing errors account for about 1/3 of the total error, mold wear errors account for 1/6, mold shrinkage imbalance errors account for 1/3, and the error of inconsistent predetermined shrinkage and actual shrinkage accounts for 1/6. Therefore, the mold manufacturing tolerance should be controlled below 1/3 of the molded part size tolerance.

3. Control of plastic injection molding companies during the production process

After plastic parts are formed, geometric dimensions may fluctuate, which is normal, but needs to be controlled:

Temperature control: Different grades of plastics require different temperatures, and care should be taken when using plastics with poor fluidity or mixed materials. Plastic materials should be controlled within the optimal flow value range, and mold temperature control is more complicated. The cooling system needs to be designed according to the geometric shapes, sizes and wall thickness ratios of different molded parts to maintain the mold at a low temperature, shorten the injection cycle, improve efficiency, and keep the mold temperature stable to ensure dimensional accuracy.

Pressure and exhaust: Injection pressure and clamping force should be determined during debugging to ensure that the air and plastic gas in the mold cavity and core gap can be discharged. Poor exhaust will lead to problems such as insufficient filling, weld marks or burns. For the case of thick walls around thin-walled parts, excessively high or low mold temperatures will cause corresponding defects, and exhaust groove design is crucial.

Dimension compensation: Plastic parts may be deformed due to temperature changes and pressure release after demolding. They can be adjusted through auxiliary fixtures. Remedial measures should be taken in time after the molded parts are ejected from the mold to allow them to cool and shape naturally to obtain good correction effects.

In summary, the above-mentioned control measures can significantly improve the stability and accuracy of the molding dimensions of injection molded products.