How to control the size of injection molding products?

1, mold design control
1, we must first fully understand the technical requirements of the mold structure, materials, hardness, accuracy and other users, including whether the shrinkage rate of the forming plastic material is correct, whether the 3D size of the product is complete, and reasonable processing analysis.

2, the injection molding product shrinkage, flow marks, dialing mold slope, weld lines and cracks and other aspects of the appearance of various places to fully consider.

3, without interfering with the function of the injection molding product and the design of the premise, as far as possible to simplify the mold processing method.

4, the choice of parting surface is appropriate, the mold processing, forming appearance and forming parts to burr must be carefully selected.

5, whether the pushing method is appropriate, the use of push rod, discharge plate, push sleeve or other methods, the position of the push rod and discharge plate is appropriate.

6, the use of side core-pulling mechanism is appropriate, flexible and reliable action, there should be no card lag phenomenon.

7, the temperature control method is easy to use for plastic products more suitable for temperature control oil, temperature control water, coolant, etc. What kind of structure circulation system is used, and whether the size, number, position, etc. of the coolant hole is appropriate.

8, the form of the gate, the size of the material channel and the feed port, the location and size of the gate are appropriate.

9, all kinds of modules and mold core heat treatment deformation effect and the selection of standard parts is appropriate.

10, Injection Molding Machine injection volume, injection pressure and clamping force is sufficient, nozzle R, gate sleeve aperture is appropriate.

And so on these aspects of comprehensive analysis preparation, from the initial stage of the product should be subject to strict control.

II. Control of process manufacturing
Although the design stage has been fully considered and arranged, there will be many problems and difficulties in actual production. We should try our best to meet the original intention of the design in the production, and find out the more effective and economical technological means in the actual processing.

1, choose the economic adaptation of the machine tool equipment, for 2D and 3D processing program.

2, can also consider the appropriate fixture for auxiliary preparation in production, The reasonable use of the tool, to prevent the product part deformation, to prevent the shrinkage of the product part fluctuations, to prevent the product part demoulding deformation, improve the precision of the mold manufacturing, reduce the error, to prevent the mold accuracy changes, etc., a series of production process requirements and solutions.

3, here to mention the British Plastics Association (BPF) formed part size error cause and proportion of the distribution:

A: the mold manufacturing error is about 1 / 3, B the error caused by the mold wear 1 / 6C the error caused by the uneven shrinkage of the formed part is about 1 / 3, D An error of about 1 / 6 due to the discrepancy between the predetermined shrinkage rate and the actual shrinkage rate
The total error = A + B + C + D, so it can be seen that the die manufacturing tolerance should be less than 1 / 3 of the tolerance of the forming part, otherwise the die can not guarantee the geometric size of the formed part.
III. General Production Controls
The fluctuation of the geometric size of the plastic part after forming is a common problem and a phenomenon that often occurs:

1, the control of material temperature and mold temperature, different grades of plastic must have different temperature requirements, poor fluidity of plastic materials and the use of more than two kinds of mixtures will have different situations. The plastic material should be controlled within the optimal flow value range, which is usually easy to do, but the control of the mold temperature is more complicated. The different geometry, size and wall thickness ratio of the forming parts have certain requirements for the cooling system, and the mold temperature controls the cooling time to a great extent.

Therefore, try to keep the mold in the allowable low temperature state, in order to shorten the injection cycle, improve production efficiency, the mold temperature changes, then the shrinkage rate will also change, the mold temperature remains stable. The dimensional accuracy is stable, so as to prevent the deformation of the forming parts, poor gloss, cooling spots and other defects, so that the physical properties of the plastic is in the best state, of course, there is a debugging process, especially the multi-cavity mold forming parts are more complex. Therefore, the mold temperature cannot be changed at will during the production process, and the mold temperature should be set within the recommended temperature range of the material.

2, pressure and exhaust adjustment control:
The appropriate injection pressure, clamping force matching should be determined during the commissioning of the mold, The air in the gap between the mold cavity and the core and the gas generated by the plastic must be discharged from the exhaust groove outside the mold, such as poor exhaust will appear insufficient filling, resulting in weld marks or burns;

These three kinds of forming defects sometimes appear in the same part occasionally, when the thin wall around the thin wall part of the forming part exists, the shrinkage mark will appear when the mold temperature is too low, If the mold temperature is too high, there will be burn phenomenon, usually at the same time there will be weld marks in the burned part, the exhaust groove is often ignored, generally in a small state, so usually as long as there is no burr; The depth of the exhaust shoulder is as deep as possible, and the rear of the shoulder is provided with a larger size vent slot so that the gas passing through the shoulder can be quickly discharged out of the mold. If there is a special need to open the exhaust slot on the ejector rod, the reason is the same, one is not to appear flying edge, the other is to vent quickly can play a good effect on the line.

The depth of the exhaust shoulder is as deep as possible, and the rear of the shoulder is provided with a larger size vent slot so that the gas passing through the shoulder can be quickly discharged out of the mold. If there is a special need to open the exhaust slot on the ejector rod, the reason is the same, one is not to appear flying edge, the other is to vent quickly can play a good effect on the line.


3. Supplementary shaping control of the size of injection molded parts
Some plastic parts due to the shape and size of the different, after the release of the temperature and pressure changes, The deformation and warpage of different situations will occur, and then some auxiliary fixtures can be adjusted, and remedial measures can be taken in time after the forming part is out of the mold, and better correction and adjustment effects can be achieved after the natural cooling and setting. If strict management is ensured throughout the injection molding process, the dimensions of the injection molded parts are ideally controlled.