Key points of molding dimension control for injection mold products

With the rapid development of mold industry in recent years, and the continuous expansion and progress of the application scope of new technologies and processes, there has been a qualitative change from the accumulation of traditional experience to the application of software development.

The wide application of CAD, cam and CAE has opened up a space for the rise of the geometric dimension control technology of our molds and mold products. Due to the great difference in the market demand of molds and mold products, there are many kinds, and the great changes and high requirements in the shape, size, material, structure and other aspects, we have encountered many problems and difficulties in the production process of molds and products, Among them, how to effectively control the geometric dimensions of the mold and products is very intuitive in front of us.

There are different control technologies and methods for different types of molds and products. Today, I am here to talk about some experience on the dimensional control of injection molding products. When talking about injection molding products, I must also talk about injection molds. Generally, I start from the following aspects.

1、 Control of mold design

1. First of all, we should fully understand the technical requirements of users in many aspects, such as mold structure, material, hardness, precision, etc., including whether the shrinkage of formed plastic material is correct, whether the 3D dimension modeling of the product is complete, and conduct reasonable processing and analysis.

2. Full consideration shall be given to the shrinkage cavity, flow mark, mold pulling inclination, weld line, crack and other places that have an impact on the appearance of injection molded products.

3. The processing method of the mold shall be simplified as much as possible without hindering the product function and pattern shaping of the injection molded parts.

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4. Whether the selection of parting surface is appropriate, careful selection shall be made for die processing, forming appearance and deburring of formed parts.

5. Whether the pushing method is appropriate, whether the push rod, discharge plate, pushing sleeve and other methods are used, and whether the positions of the push rod and discharge plate are appropriate.

6. Whether the use of side core pulling mechanism is appropriate, the action is flexible and reliable, and there should be no stagnation.

7. Which method of temperature control is more suitable for plastic products, which structure circulation system is used for temperature control oil, temperature control water and coolant, and whether the size, quantity and position of coolant holes are appropriate.

8. Whether the gate form, the size of the material channel and the feed gate, the gate position and size are appropriate.

9. Whether the influence of heat treatment deformation of various modules and mold cores and the selection of standard parts are appropriate.

10. Whether the injection volume, injection pressure and clamping force of the injection molding machine are sufficient, and whether the nozzle R and the sprue sleeve aperture match properly.

And so on, which should be strictly controlled from the initial stage of product parts.

2、 Process manufacturing control

Although it has been fully considered and arranged in the design stage, many problems and difficulties will occur in the actual production. We should try our best to conform to the original intention of the design in the production and find out more effective, more economical and reasonable process means in the actual processing.

1. Select economical and suitable machine tools and equipment for 2D and 3D processing schemes.

2. A series of production process requirements and solutions can also be considered, such as appropriate tooling and fixtures for auxiliary preparation during production, rational use of cutting tools, prevention of deformation of product parts, fluctuation of shrinkage rate of product parts, prevention of demoulding deformation of product parts, improvement of mold manufacturing accuracy, reduction of errors, prevention of changes in mold accuracy, etc.

3. Here is the reason for the dimensional error of formed parts of the British Plastics Association (BPF) and the distribution of its proportion:

A: Die manufacturing error is about 1/3, B error caused by die wear is about 1/6, C error caused by uneven shrinkage of formed parts is about 1/3, D error caused by inconsistency between predetermined shrinkage and actual shrinkage is about 1/6

Total error =a+b+c+d, so it can be seen that the manufacturing tolerance of the die should be less than 1/3 of the dimensional tolerance of the formed part, otherwise the die is difficult to ensure the geometric dimension of the formed part.

3、 General production control

The geometric dimension fluctuation of plastic parts after forming is a common problem and often occurs:

1. The control of material temperature and mold temperature requires different temperature requirements for plastics of different brands. The poor fluidity of plastic materials and the use of more than two kinds of mixtures may occur. It is usually easy to control the plastic materials within the range of the best flow value. However, the control of mold temperature is more complex. Different shapes, sizes and wall thickness ratios of formed parts have certain requirements for the cooling system, The mold temperature controls the cooling time to a great extent;

Therefore, try to keep the mold at an allowable low temperature, so as to shorten the injection cycle and improve the production efficiency. If the mold temperature changes, the shrinkage rate will also change. If the mold temperature remains stable, the dimensional accuracy will be stable, so as to prevent the deformation, poor gloss, cooling spots and other defects of the formed parts, and make the physical properties of the plastic in the best state. Of course, there is a debugging process, In particular, multi cavity die forming parts are more complex.

2. Pressure and exhaust adjustment control:

The proper injection pressure and the matching of the clamping force should be determined when debugging the mold. The air in the gap formed by the mold cavity and core and the gas generated by the plastic must be discharged from the exhaust slot out of the mold. If the exhaust is not smooth, insufficient filling will occur, resulting in weld marks or burns. These three kinds of forming defects sometimes occur at the same part occasionally;

When there is a thick wall around the thin-walled part of a shaped part, insufficient filling will occur when the mold temperature is too low, and burns will occur when the mold temperature is too high. Usually, weld marks will appear at the burned part at the same time, and the exhaust slots are often ignored and generally in a small state. Therefore, generally, as long as there is no burr, the depth of the exhaust shoulder should be as deep as possible, and a large vent slot should be set at the back of the shoulder, So that the gas passing through the shoulder can be quickly discharged out of the mold. If there is a special need to open an exhaust slot on the ejector rod, the principle is the same. First, there is no flash, and second, the gas can be discharged quickly to achieve good results.

3. Supplementary shaping control of injection molded parts

Due to different shapes and sizes of some plastic parts, different deformation and warpage will occur with the change of temperature and pressure loss after demoulding. At this time, some auxiliary tooling fixtures can be used for adjustment. Remedial measures can be taken promptly after the formed parts are out of the mold. Good correction and adjustment effects can be achieved after they are naturally cooled and shaped. If strict management is ensured in the whole injection molding process, the size of injection molded parts will be well controlled.



About Huizhou Dj Molding Co., Ltd

Dj Mold is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.

Person: James Yuan
Company: Huizhou Dj Molding Company Limited
Add:  LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Tel: 86-752-6682869
Email: [email protected]


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