Basic knowledge of precision mold

With the society development, precision molds have got into life deeply.  And many people would be more familiar with plastic mold, but they may do not know much about precision mold-a kind of plastic mold. Today, Huaye Precision Mould will introduce the basic knowledge of precision molds to you.

plastic precision molding part-sprue and runner

First, the concept of precision molds

A mold is a tool that uses its specific shape to form a product with a certain shape and size. It has a decisive influence on the manufacturing quality and cost.

Mold products are everywhere in our daily life and as well as all areas of society.

The manufacturing level of precision mold has become an important indicator of a country’s product manufacturing level, and determines the quality, efficiency and development ability of new products to a great degree.

Second, several common terms for precision molds

1.Sprue

Plastic enters the mold cavity through the sprue-also known as the mainstream. The dissolution injection nozzle sleeve connects the nozzle and the mold, and has formed a standard part. Some thinner molds of the mother template do not need to be sleeved, and the dissolution injection port is directly drilled on the mold.

2.Cold-slug well

The temperature of the molten plastic at the front end of the nozzle is relatively low to form the cold slag. A hole opened on the male mold core at the end of the feed inlet to prevent cold slag from entering the cavity and blocking the flow channel. In order to pull the condensation from sleeve when mold is open, a pull rod (on the ejector pin) is generally provided at the end of the cold cavity.

3.Runner

The runner is the connection part of main runner, which is the channel for the plastic to flow into the mold cavity. It can send the plastic to the gate at a faster speed under the condition of minimal pressure loss. Its main types are: round, semicircular. rectangle and trapezoid. The ratio of the surface area or side area of ​​the runner to its cross-sectional area is required to be minimal.

4.Gates

It is the connecting part between the runner and the cavity, also the last part of the gating system. It is to make the molten plastic enter the mold cavity at a faster speed. After the cavity is full, the gate can be quickly cooled and closed to prevent the uncooled material in the cavity from flowing back.

5.Vent

When the mold is completely closed, the cavity and runner are filled with air. Air must be expelled from the mold during injection, otherwise it will burn, filling disatisfy, burr, bubble and silver wires.

6.Ejection device

It is a device that ejects the product from the mold and an important part of the mold, also known as the ejection mechanism. Its form and launch method are related to the shape, structure and plastic characteristics of the product. Its parts are ejector pins, push plates, ejection blocks, slant tips, barrels, cylinders or cylinders, gears, etc. There is a clearance fit between the kernels, the surface area is as large as possible, and it is set at a place that does not affect the appearance and function. Pay attention to the demolding balance.

7.Mold cavity

The mold cavity is to dig a frame on the template in order to embed the mold core, mainly in terms of saving materials and processing convenience. Some molds with large parting surface breaks will directly process the product part on the template without digging the mold cavity. The mold core mainly refers to the product part of the mold. Its accuracy and material requirements are higher than the mold base. Its shape and form have different requirements for different molds which is the most important part of the entire mold.

Third, Design ideas for precision molds

The quality of molds mostly depend on mold design. In addition to requiring the designer to have a wealth of theoretical knowledge and experience, it is also important to consider carefully before designing:

1. Understand the product drawing

Whether the mold opening conditions are available: draft, shrinkage and deformation, whether it can be ejected.

2. Confirm product material

There are many types of plastic. Confirm the material to determine the shrinkage rate and understand the fluidity to determine the nozzle and runner design.

3. Mold material 

According to different plastic and product requirements, choose the suitable mold steel in order to meet the quality and mold life requirements, which requires designers to have sufficient understanding of plastic and steel.

4. Molding machine specifications

Understand the clamping pressure, injection capacity, mold height, positioning ring size, nozzle radius and die hole position.

5. Mold cavity and its arrangement

Determined the mold base and standard part by projected area, shape, accuracy, output and benefits of the product.

6. Sprue 

Hot runner, adiabatic runner, no runner, direct glue (two-plate mold), indirect glue (three-plate mold) and other methods.

7. Gate types 

There are many kinds of gates, which are different according to the needs. Pay attention to whether the gate has appearance requirements and flow, balance, connection lines, exhaust issue. And whether the gate size is enough to fill the entire product.

8. Parting line

It is an important part of mold design, which can be used flexibly by designers. We must consider product appearance, ejection method, mold processing, etc.

9. Mold core 

We must consider the appearance, processing methods, mold strength, demolding methods, cooling methods, fluidity, exhaust and other issues.

10. Undercut

There are sliders, oil (gas) cylinders, motors, inclined tips, forced demoulding and other special methods, this part has the most changes and complicated design.

11. Ejection

Multiple ways: thimble, flat tip, secretary extinguishers, pallet, slider, the second paragraph ejected, oil (gas) pressure. Pay attention to demolding balance, mold strength, appearance, function and cooling effect.

12. Vent

It is very important to ensure the quality of the product. Exhaust in various forms to prevent the product from vacuum adsorption then the mold cannot be opened.

13. Cooling

Cooling has a great impact on mold production, and the design is more complicated. It is necessary to consider not only the cooling effect and consistency, but also the influence of the cooling system of the overall mold structure.

14. Processing method 

All mold designs must take into account the feasibility of mold processing to have practical value. Otherwise, it will be a failed design without the experience of on-site mold manufacturing.

15. Mold drawing

Drawing the mold drawing according to the above concept, including assembly drawing, part drawing and related processing drawing. In the drawing process, the coordination between the various systems of the mold is further improved to become perfect.

16. Proofreading and auditing

When complete the mold design, it is necessary to cooperate with the customer and relevant personnel to carry out a proofreading and audit to conduct a comprehensive inspection of the overall structure, processing feasibility, and omissions in the drawing process, soliciting customer opinions, and avoiding design errors. The mold is difficult to manufacture and use, and even scrapped.

If you want to make a good-quality plastic mold or know more knowledge about precision mold,

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