Plastic Molding in China
Compared with stamping mold and die casting mold, plastic molding has 5 development features in China.
1. Cavity and core showing tridimensional molded surface
External and internal shape of plastic parts is directly formed by cavity and core. These complicated tridimensional molded surfaces have larger processing difficulty, especially blind hold molding surface processing. If traditional processing methods are adopted, it not only requires workers with high technical level, many auxiliary tools, but also requires long processing cycle.
2. Higher requirements for precision, surface quality and service life
At present, dimensional precision of common plastic parts is required to IT6-7, surface roughness Ra0.2-0.1mm. Dimensional precision of matching plastic molding parts is required to reach IT5-6, and surface roughness should be below than Ra0.1mm. Roughness of laser disc recording surface should reach to level of mirror finishing, 0.02-0.01mm. So, the surface roughness of mold should be lower than 0.01mm. Plastic injection mold having long service life is essential for improving efficiency and reducing cost. Now, the service life of injection mold is required to be used for more than one million times. Precise injection mold should use mold base having large rigidity to increase thickness of template, increasing bearing post or cone setting element to prevent mold from deforming after being pressed. Sometimes, internal pressure can reach to as high as 100MPa. Ejector is an important factor having influence on product deformation and dimensional accuracy. For this, the ejection points must be chosen for even demold. The structure of high precise injection mold mostly uses splicing and full splicing which requires that processing precision and interchangeability of mold parts should be highly improved.
3. Long technological process and limited manufacturing time
For plastic molding parts, most of them are composed into complete parts with other parts. And in many cases, other parts have been finished, urgently waiting for plastic parts. The requirements for shape and dimensional precision of products are high, and characteristics of resin materials are varied. Repeat trial and modification are needed after manufacturing mold, making limited development and delivery time.
4. Distributed design and manufacturing
Making mold is not the final objective. The users come up with design of final products, and the mold manufacturers design and making mold based on users’ requirements. In most of cases, injection molding is also carried out by other manufacturer. So, product design, mold design and product manufacturing are carried out in different places.
5. Professional division of labor, dynamic combination
Mold manufacturing has few batches, generally one piece production. However, mold needs a lot of standard parts, including mold base and centre. All of parts cannot be finished solely by only one manufacturer. Besides, manufacturing technology is complicated. The utilization of common equipment and CNC equipment is imbalanced.