(1) The relationship between injection pressure and plastic parts.

If the shape, material used is different, then the injection pressure we choose is different. It can classified as follows,

1.The injection pressure is lower than 70MPa, it can be used for good liquidity plastic, the shape is easy, and the thickness is large.
2.The injection pressure is 70-100MPa, it can be used for low viscosity plastic
3.The injection pressure is 100-140MPa; it can be used for medium viscosity plastic.
4.The injection pressure is 140-180MPa, it can be used for high viscosity plastic, the wall thickness is thin and high precision.
5.The injection pressure is higher than 180MPa, it can used for high viscosity plastic, the shape is unique and high precision
(2) How to choose injection pressure

When injection molding, how to choose injection pressure is very important. The injection pressure has the relationship with the plastic performance, plastify temperature, mould temperature, product shape and product precision. For one product injection molding, if the injection pressure is too high, it will be easy to occur flash and difficult to demoulding. What’s more, it will affect the injection life.

If the injection pressure is too low, the melting will be difficult to be full the cavity and will not moulding. Therefore, injection pressure has the high demand for the injection molding machine.

Posted By:Thomas Ruan
Email:thomas@kuntaimould.com

•Steel cost for Injection Mould
•Tooling cost for Injection Mould
•Labors and management cost for Injection Mould
•Tax+profits
Normally, steel cost is around 20 to 60%, this percentage is based the mould size, mould precision situation, steel type and mould structure.

Tooling cost is based on the injection mould dimension requirements,mould size, the mould maker will consider his tooling machines’ depreciation costs.

Labors and management cost is based the mould manufacturing lead time

(1) Unreasonable Structure design lead to crack and how to avoid

In the design of mould structure, unreasonable structure design, for example, bolt hole is too closer to the edge will decrease the strength; the corner is not smooth , causing stress concentration, all these reasons will lead to mould crack during molding process. For this structural cracks, because the mould has already done, it is not possible to change structure, we can only add frame to strength it.

(2) unreasonable heat treatment result in cracking in mould and how to avoid

There are many parts in mould, such as cavity and core, guide bush, guide pillar, all these need heat treatment, to improve the abrasive resistance and prolong the mould life. But if we choose unreasonable heat treatment condition, makes big difference between spare parts material. This difference will lead to crack. For this, we should pay more attention to the heat treatment condition, controlling the heat operating strictly

(3) The less stiffness of mould and how to avoid

Injection mould wills under big pressure when it works, if the stiffness is not big enough, mould crack will easyly appears. To solve this problem, we also should notice the mould structure, must ensure big stiffness and strength of mould

(4) High brittleness of the mould material will make mould crack and the method to avoid.

Some material with high brittleness, we heat the material slightly, the HRC will be very high, Such as carbon steel material. So we should choose material with excellent toughness to manufacture mould.

1
Disassemble the mold using a screwdriver to disconnect the parts. Separate the parts that are most susceptible to corrosion and contaminate build-up. These include the front and rear clamp plates, bubbler plates, bushings, water lines and wear plate grease grooves.

2
Spray the pieces of the mold with a cleaning spray, or place them in a solvent bath. More abrasive cleaning chemicals may work more quickly, but they will also cause wear and tear on the mold that can shorten its life.

3
Scrub the mold with a stiff brush to remove the contaminants, then wipe dry.

Cleaning With Dry Ice Pellets
1
Connect a dry-ice pellet blasting system to an air line near your mold. A double-line system introduces the pellets at the spray nozzle, while single-line systems introduce them at the hopper and offer a more powerful spray.

2
Disassemble the mold and strongly secure the parts to be cleaned. The force of the dry-ice pellet impacts can easily knock over unsecured parts, possibly damaging them.

3
Ensure the area is clear. These guns spray dry ice at 900 feet per second, which can cause severe injury.

4
Put on safety gear. This includes a face mask, gloves and an apron as well as ear protection that can block the 102-decibel noise produced by the sprayer.

5
Turn on the air line and squeeze the trigger to spray the parts. The dry ice will dissolve on impact, taking residue with it. This method, however, may not be very effective at rust removal.

Cleaning Molds Ultrasonically
1
Disassemble the mold and immerse the parts in a detergent solution. The exact type of detergent depends on what kind of contamination is to be removed. Heavily alkaline solutions like sodium hydroxide are very effective with most contaminants, but are dangerously caustic. Mildly acidic solutions are better for rust, but will turn steel gray.

2
Connect an ultrasonic generator to a shop power line. This generator transforms regular current into the very high frequencies necessary for ultrasonic cleaning.

3
Attach transducers to the bottom and sides of the tank. These transducers will vibrate at the high frequencies coming in from the generator, which produces tiny bubbles in the water that impact the mold pieces with force enough to strip away contaminants, while leaving the metal mold undamaged.

4
Set the timer on the generator, and walk away. The cleaning process will proceed on its own.

Human nature

— Unauthorized or unintentional interference with the operation of control elements

—- Uncontrollable corrective actions that lead to deviations from set data (e.g., manual opening and closing)

—- Lack of sufficient monitoring devices (no control display, therefore subjective assessment)

Environment

— Local temperature variations (during the day, seasonal)

— Changes in humidity

— Contamination

Technology

— Reproducibility of mechanics, hydraulic system, and control elements

— Mold defects

— Temperature (oil, barrel, mold), primary cause

— Inter-batch variations in the materials (comparable with melt-temperature effects)

—Fluidity of material, feeding behavior

Of the negative effects, human nature can be assumed to be the most important. The difficulty of performing the necessary control manually is a significant factor in the production of rejects or interior product quality. This is usually followed by a mould of inferior design and its temperature control (heat exchanger), which leads to temporal and local fluctuations. Frequent causes of imperfections are wrongly dimensioned runners and gates or the hot-runner manifold and inadequate temperature regulation. Every other disturbance is significant but takes second place to those expressly mentioned here.

Thus, important steps towards quality improvement, and especially quality constancy, can be made by eliminating the causes of adverse effects, e.g., by increasing the degree of automation, monitoring, and quality of design before complicated open-loop or closed-loop control systems are adopted. Besides mere sequence control measure aims to reduce the effects of disturbances on quality as much as necessary and keep them tolerable limits. Every expense, which show up clearly in accounting, should be measured against the achievements made in this direction.

Two methods are generally used to reduce cutting forces and to smooth the shock impact of heavy loads. Keep in mind that during a piercing operation with proper clearance, complete fracture occurs when the punch has penetrated one-third the material thickness.

1.By stepping punches one-third the material thickness, they can cut individually. Typically using three punches of the same diameter stepped properly you use one-third the total tonnage required to do all three simultaneously.
2.Adding shear to the die or punch equal to one-third the material thickness reduces the tonnage required by 50% for that area being cut with shear applied; note that share is applied to the die member that contacted the scrap. Therefore, deformation due to the shear angles does not affect the part.
In piercing, the direction of the shear angles must be such that the cut precedes from the outer extremities of the counter forward the center. This avoids stretching the material before it is cut free.