As a mold engineer, do you know all these five little knowledges?

Time:2022-01-14 09:12:32 / Popularity: / Source:

1. What is difference between crystalline and amorphous plastics?

(1) Crystalline is a solid in which internal particles (molecules, atoms, ions) of minerals are arranged regularly to form a certain lattice structure, which is called crystalline (crystal). Result of regular arrangement of particles is shown as regular geometric shapes. Most minerals in nature are crystals.
(2) Amorphous: Any solid with irregular arrangement of particles (molecules, atoms, ions) inside a mineral without a lattice structure is called non-crystalline (or non-crystalline). This type of minerals is not widely distributed, and there are few types, such as volcanic glass.
Crystalline plastics are: PE, PP, POM, PA6, PBT, PET, PA66, PA6T, PA11, PA12
Amorphous plastics include: ABS, PVC, PMMA, PS, PC, PPO, PSF, PES, PAI, PEI

2. What are your commonly used die steels? What are differences between different steels? What is difference between NAK80 and S136? What are characteristics of NAK80? If mold core uses H13, what material is used for lifter, and why?

Commonly used die steels: P20, 718, 718H, S136, S136H, NAK80, NAK55, 738, 738H, S55C, H13, SKD, alloy beryllium copper, DF2, 8407, 2311. NAK80 does not require heat treatment, pre-hardened steel, with a hardness of more than HRC30, good mirror effect, good electrical discharge machining, and better weldability. Suitable for electrodes and polishing molds, NAK80 polishing material has obvious grain lines. 
S136 needs heat treatment, hardness HRC48-52, high mirror finish, good polishing performance, suitable for PVC, PP, EP, PC, PMMA. If mold core uses H13, lifter uses DF2.
hot runner molds 

3. What is key point in mold design?

Key points in mold design:
1 Overall layout of mold is reasonable, 2 selection of parting surface 3 layout of runner, selection of glue inlet 4 ejection device 5 arrangement of water 6 selection of exhaust 7 pay attention to draft angle when parting mold, extraction of inserts, treatment of rubbing angle, and shrinkage of material. 8 processing drawing should be detailed, but simple.
Can be demoulded! Easy to process! Easy to eject!
H13 is 2344 in Europe and SKD61 in Japan.   
H13 is a soft material. Hardenability and wear resistance of material are very good. It is generally used in molds with more than 300,000 shots. After heat treatment, it can reach 56HRC. Generally, commonly used hardness is between 48~56HRC.
For general lifter materials, surface hardness is required to be high, and inside must have a certain degree of toughness. Therefore, if mold core is made of H13, when it is hardened to 52HRC, lifter roof can be pre-hardened such as NAK80. Generally, large companies require that mold core material cannot be same material as lifter. If customer clearly specifies same material, it must be 5HRC or negative 5HRC higher than mold core material after heat treatment to prevent burns or bites during molding process and improve its wear resistance.
Generally, it is not recommended to use 420 type for lifter, because it is stainless steel, it is easy to burn to death.
Focus is on structure.
If structure is simplified as much as possible, but quality of mold is to be guaranteed, company will make the most profit. When we receive a product, the first problem is to find the largest parting surface, roughly determine front and rear molds, then analyze structure of front mold and rear mold on the basis of this parting surface: inserts, row positions, lifters, and other auxiliary mechanisms. After structure is clear, next step is to consider processing to determine rationality of structure: inlay or not; should be CNC or wire cutting; should be CNC or engraving, etc. Structure affects processing, processing involves cost and delivery time.
So how do we simplify mold structure as much as possible?
On the one hand, when reviewing product with customers, it is necessary to focus on problem of mold release caused by product and whether to improve product;
On the other hand, whether to hold a meeting in company before mold design, solicit a variety of feasible structure suggestions. Determine final plan from perspective of processing and customer requirements.

4. What should be paid attention to when designing hot runner molds?

(1): Orientation of hot runner system.
(2): Rationality of cooling.

5. What should be paid attention to when designing thread unloading mold? What's point?

Thread mold should pay attention to number of turns, pitch and direction of screw, focus is on how to prevent rotation.

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