Question: Prehardened mould and throughly harden mould

MINGYU MOULD:

1. Pre-hardened mould
   The prehardened mold refers to the hardness below 44HRC. The steel used in the inner mold can be used without heat treatment. The injection mold is called prehardened mold. For example, the inner mold is made of P20 steel, ace, 420H steel. Aluminum, beryllium copper, etc.
   2. throughly harden mould
   The throughly harden mold refers to the hardness above 44HRC. The steel used in the inner mold is heat treated, such as carburizing and quenching, to meet the requirements of use. Such an injection mold is called a hard mold. For example, the inner mold is made of H13 steel. The hardness of 420 steel, S7 steel and other molds is determined according to the clamping stress of the parting surface. When the mold clamping stress of the parting surface is 3.5 T/in2 or less, the pre-hardened mold steel having a hardness of HRC45 or less can be selected. When the mold clamping stress of the parting surface is 5 T/in2 or more, the hardness of the selected steel must be HRC45 or more.
   3. In addition to the large difference in the life of the mold, the soft and hard molds generally have no difference to the product, the manufacturing cost of the soft mold is low, and the manufacturing cost of the hard mold is high. Soft models are widely used in Asian countries, including Taiwan, Japan, East Asia and other countries and regions. Hard molds are the most widely used in Europe and North America. For some molds, it is necessary to make a hard mold to have a long life, such as injection molding a mold containing glass fiber raw materials.

the centering ring (locating ring) is for fixing the position of the mold sprue and the nozzle of the injection molding machine.

it is for storing the material which come inside the the mold at the beggining and the temperature is little low

Molds can be generally divided into plastic molds and non-plastic molds. Non-plastic molds include: casting molds, forging molds, stamping molds, die-casting molds, and plastic molds. They are further divided into injection molding molds and blowing molds according to different production processes and production products. The compression molding die, the transfer molding die, the extrusion molding die, the thermoforming die, and the rotary forming die can be divided into three types according to the different types of the casting system: a large sprue mold, a small sprue mold, and a hot runner mold.

Germany: HASCO Japan: FUTABA (double leaf) USA: DME China: LKM

45# S50c 718 738 718H
738H P20 2316 8407 H13
NAK80 NAK55 S136 S136H SKD61

Instead it is part thickness distribution with respect to injection point (gate) towards the extreme point on the melt flow path i.e, last fill point. A good injection molding part thickness should always decrease (not uniform) along the flow path and that thickness decrease magnitude is the prime factor responsible for sink marks.

Basically injection (processing) pressure and temperature are primarily polymer and then mold and machine dependent. i.e., injection melt state variables., So part form / features have very less to do with setting injection melt state.However a good control to prevent sinks can be achieved by increasing packing intensification rate, this technique can considerably compensate thickness distribution variance also, which is quite often.

Here are some advantages and reasons for choosing:

• Easy manufacturing. All operations in milling, and saving up to 2/3 actual time if made by aluminum instead of steel.
• Weight plays more important role (example in bigger sized molds and with many loose inserts to be inserted manually, it is easy to handle).

So the Aluminum tooling is cheaper than steel tooling.

There are many kind of steel, for long runs production, a durable mold is required, the tool steel must be selected properly, for small volume production, steel selection can be as economic as possible as long as it meet the requirement of production demands.

How to choose the injection mold steel? Important steel properties include:

• Ease of machining
• Dimensional stability after heat treatment
• Wear resistance
• Surface finish
• Corrosion resistance

To decide an injection mold for unpredictable demand, I would see whether more cavities will change the mold base size. If part size is small and volume is low, a 2 cavities and 4 cavities mold may use the same mold base (hence use the same machine tonnage), then it may be wise to have a 4 cavity-capable mold with only 2 cavity cut, like a bridge mold.

However, I am still a little bit doubtful on the saving we can gain by just not cutting the remaining cavity. Building a small injection mold is still the 1st preference. Then we may end up with 2 small molds, which is more expensive. However, the second mold is a duplicate mold which will not need to design, program, and go through various mold modification as the first mold. Furthermore 2 small injection molds are sometime more flexible for production planning compared to one big mold.

It’s a small plastic injected piece that will be submitted to short period of time (2 seconds) of high temperature (95-105ºC approx.) in every cycle; this high temperature is produced by a filament where electric current passes through (like a house light bulb but hotter) for no more than 2 seconds in the process cycle. A complete process cycle last for about 45 seconds where the piece has time to cool off again. This plastic piece has to work for about 45-50 complete process cycles.

I have used ULTEM (SABIC innovative plastics) PEI (polyetherimide) in high thermal service components such as hard drive parking ramps, insert molded side looking LED optics, motion sensor windows, and missile fuse optics in the past with good success. It also has high lubricity and it is easily used in molds designed for both commercial and engineering grade materials with shrinkage of 0.005 to 0.007in/in.. It comes in a variety of application grades with a 94VO rating.

We understand that with plastic parts, weight is the best method of controlling the process capability. Is there a guideline or standard for defining the tolerance?

The most common method is:
Shot to shot weight variation calculated as (three standard deviations) divided by (average weight) must be less than 1% and should be less than 0,5%. In general it is possible to achieve 0,1-0,4% weight variation using scientific molding.