Basic Knowledge Of Injection Molds

- Mar 15, 2019-

Basic knowledge of injection molds


Mold classification

Introduction to injection molding principle
Introduction of 7 large-scale injection molds and basic structure of molds
Hot runner mold introduction
Introduction of ordinary (cold) runner injection molding principle
Introduction to common injection molds
Mold design process and key points
Mold test precautions
Basic knowledge of mold verification


Mold classification:

According to molding materials: metal molds and non-metal molds
Here are the following types of molds by molding material.
     Metal material mold: casting mold, die-casting mold, stamping die (bending, punching, blanking, stretching, shaping, flanging, etc.), forging die (hot forging, cold rolling, rolling, drawing, extrusion) and so on.
     Non-metallic materials are divided into: plastic molding die (extrusion, blow molding, injection molding, compression molding, gas assist, vacuum blister, etc.), rubber mold, glass mold, ceramic mold, etc.


 Injection molding principle:

1. The dried plastic pellets enter the molding machine barrel through the molding machine hopper
2. The plastic particles become molten under the action of the heating of the heating sheet and the shearing heat generated by the screw rotation.
3. The molten plastic is gathered in the head part of the molding machine, and the metering
4. The screw stops rotating and is changed to the forward direction to squeeze the plastic melt.
5. The plastic enters the mold casting system and then flows into the mold forming cavity.
6. Cooling and solidifying the plastic through the heat transfer of the mold itself and the cooling system added to the mold
7. After the cooling is completed, the mold is opened, and the ejector system of the molding machine pushes the product out, and the screw of the molding machine retreats to start the next measurement of the plastic melt.




Injection mold 7 system introduction:

Seven injection molding systems: gating system, guiding system, forming system, core pulling system, ejection system, cooling system, exhaust system.

1. Gating system: mainstream road, split runner, gate, cold well.
2. Guide system: guide column, guide sleeve, positioning block, etc.
3. Molding system: mold, inserts, etc.
4. Core pulling system: slider, skew pin, etc.
5.Eject system: thimble, top block, etc.
6. Cooling system: heat dissipation of the mold itself, cooling of the waterway.
7. Exhaust system: the matching clearance of each insert of the mold, the thimble with the clearance, and the additional exhaust groove.

Hot runner mold introduction:
Hot runner mold features

Why is there such a hot runner technology? What are the benefits of hot runner technology? Engineers familiar with the injection molding process know that conventional injection molding often has the following disadvantages:
a. difficult to fill; b. thin-walled parts are easily deformed; c. waste of runner raw materials; d. quality of injection molded parts of multi-cavity molds are not equal.

The emergence of hot runner technology provides a more complete solution to these problems. In general, the use of hot runners has the following benefits:
Shorten the molding cycle

Save plastic materials

Mold design process and key points
1. Product image data and CAD technical requirements (2D&3D)
2. Product shrinkage rate
3. Forming machine beer machine information
4. Product Evaluation Analysis (DFM)
5. Mold flow analysis
6.2D Layout
7.3D Layout


 Product evaluation

Product evaluation is a pre-assessment of product structure, flesh thickness, draft, parting line, thimble arrangement, risk, etc., and is a written form of communication with customers.
See DFM specifically

For structural designers, it would be helpful to be able to arrange mold layouts to grasp the mold price.

Attention points in the mold test process:

1. Whether the mold opening and closing mold is smooth.
2. Whether the mold is ejected smoothly, whether the product can be automatically dropped
3. Pay attention to the gate position and feeding method of the mold, as well as the size of the gate and the size of the cavity (choose the appropriate pressure, speed, and amount of material).
4. After the mold is warmed up, open and close the mold several times, and carefully check whether all the joints of the mold are too hard. If there is no one to continue.
5. When testing the mold, first try the short shot product (confirm the bonding line and exhaust).
6. Let the quality personnel determine the size and appearance after the product is full.


Thank you for your attention!


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