With the rapid development of mold industry in recent years, moreover, new technology, new manufacturing process continue to expand and progress, from traditional experience to software application, it has been a qualitative change.
Due to the widely use of CAD, CAM and CAE , it opens up space for our mold and mould product geometric size control technology; meanwhile, a great variety of mould and product, the market demand differs greatly in the shape, size, material, structure, etc. All aspects of large changes and high requirements make it encountered many problems and difficulties in the production, then It is a hard nut to crack on how to effectively control the mold and product geometry.
Different types of molds and products have different control techniques and methods.Here I would like to talk something about plastic injection molding products,speak of it, plastic injection mold is inextricable. 3 aspects would be listed below:
Firstly, Mold Design
1, Fully understand many users’ technical requirements on mold structure, materials, hardness, precision, including plastic Shrinkage and product 3D size modeling, to make reasonable analysis.
2,Every aspect of the impact of apperance shall be taken full consideration, such as injection molding products shrinkage, flow marks, dial gradient mode, welding lines and cracks.
3, Try to simplify the mold manufacturing methods on the premise of without prejudice to the function of plastic injection products and patterns.
4, It shall be carefully selected on whether it is appropriate of the parting surface or not and on the deburring of the mold processing, forming appearance and forming parts.
5, Whether it is proper on the ejector mode, using the putter, unloading plate, ejecting sleeve or other ways, and whether it is appropriate on the location of the putter and on unloading plate.
6, Whether it is appropriate and reliable of the side core-pulling mechanism or not and there should be no clamping stagnation.
7, How to choose the methods of temperature control, which is more benefit for the plastic parts; what is the structural circulatory system fit for the oil, water, and cooling liquid together with the size, number and location of the coolant hole?
8, Gate type, feed path and feeding hole size, location and size of the running gate
9, Various types of modules and core deformation of the impact of heat treatment and the selection of standard parts
10,Whether it is sufficient of the injection molding machinery injection volume, injection pressure and clamping force, whether it is adequate of nozzle R, sprue bushing aperture or not.
And so on, make a comprehensive analysis from the initial stage of product, it should be strictly controlled.
Secondly, Manufacturing Process
Though full consideration will be taken in design phase, but there are still a lot of problems and difficulties in production period. We have to meet the design as much as possible in the production to identify more effiective and more economical and reasonable technics measure.
1. Select economic machinery equipment as 2D and 3D processing solution.
2, may also consider the appropriate tooling fixture in the production of auxiliary preparation work, the rational use of cutting tools to prevent deformation of plastic parts, to prevent product shrinkage fluctuations, to prevent product demold deformation, improve mold manufacturing accuracy, reduce errors, to prevent changes in mold accuracy, etc., a series of production process requirements and solutions.
3, Here refer to the British Plastics Association (BPF) of the causes of the size error of the forming parts and the proportion of its allocation:
A mold manufacturing error of about 1/3, B mold wear error of 1/6, C formed plastic parts caused by the uneven shrinkage errors of about 1/3, D The inconsistency of predetermined and actual shrinkage, its errors of about 1/6.
The total errors = A + B + C + D, thus mold manufacturing tolerances should be forming parts tolerance of 1/3 or less, otherwise the mold is difficult to guarantee the geometric dimensions of forming parts.
It is a common and frequent circumstance that the fluctuation of geometric size after forming of plastic parts:
1, The material temperature, mold temperature control.
Different grades of plastic must be different temperature requirements, plastic materials, poor mobility and the use of two or more mixture will have a different situation, plastic materials should be controlled in the best flow In the range of values, these are usually easy to achieve, but the mold temperature control is more complex, different forming parts geometry, size, wall thickness ratio of different cooling system has certain requirements, mold temperature to a large extent Control the cooling time;
So try to maintain the mold in a status of permissible low temperature, in order to shorten the injection cycle, improve production efficiency, mold temperature changes, then the shrinkage will change, mold temperature remains stable, dimensional accuracy is stable, thus preventing the deformation of plastic parts, poor gloss, cold spots and other defects, so that the physical properties of plastic in the best condition, of course, there is a debugging process, especially multi-cavity mold forming parts is more complex.
2, The adjustment of pressure and exhaust:
Injection pressure, clamping force matching should be determined when debugging the mold in the mold cavity and the cavity formed by the gap in the air and plastic generated by the gas must be discharged from the exhaust slot outside the mold, if the row Gas is shortage, it will occur underfill, resulting in welds or burns, these three forming defects sometimes occur occasionally in the same location;
When the thickness of the wall around the wall of the forming part exists, the mold temperature is too low, the filling will be insufficient. When the mold temperature is too high then there will be burns, usually in the burn site will also have weld marks, exhaust slot often will be ignored, generally in a small state, so usually if the burr is not existed, the depth of the exhaust shoulder shall be as deep as possible, the back of the shoulder to open a larger size of the ventilation slots in order to pass through the shoulder after the gas Can quickly discharge the mold, if there is a special need to open the exhaust slot in the mandrel, the reason is the same, one does not appear waste side, the second is to play a good effect on the line quickly.
3.The supplement of size of the injection molding parts
Due to the difference of shape and size, and changes of temperature and decompression, some plastic parts will be deformed and warpped after demould.Then some auxiliary tooling fixture can be used to adjust immediately to take remedial measures after demould of forming parts, until it is cooling, performance will be better. If the entire injection molding process maintain a strict management, then the size of injection molded parts will be in an ideal control.