Injection Mould Construction

A molding according to the function of each of its parts can be divided into four sections 1. Introductory part of the plastic nozzle into the cavity cavity 2. penunjuang system (support system) 3. demolding system 4. heat transfer system

Mold Base Standard Part

In the manufacture of injection mold, mold base is an integral part, mold maker can make your own mold base or buy a standard mold base, the system of the mold base can be adjusted with the construction standards required, both for the two plate and three plate, stripper plate ejectors, hot runner and mold base for a screw, when the entire standard mold base is not there to meet the new final step is to make a special mold base.

Injection Mould Classification

classification or types of mold injection very depend on what we need to make the plastic parts, because every parts have specific and unique design. when design molds we must see what the influencing factor like geometry, number of cavities, ejection principle, plastic material and shape of part.

Injection Mold Cooling

This section is the most important part of the overall mold cylcle time, because in one cycle time, the process of heat exchange to spend about 70-80% of the total cycle time, thus setting the optimal heat transfer system will greatly affect the quality and cycle time of a product.

Undercut System : Cam, Angular, Lift Cavity, Loose core

cavity and core, and its derivatives when there are undercut on product, design and construction of a good core cavity and in accordance with the requirement could increase the life of tooling itself, reduce material consumption, reduce dependence on maintenance inserts, and can reduce the cost of making the mold so the mold cost per products also declined.

Saturday, February 23, 2008

Direct Gate or Sprue Gate

What is Gate ?
The entrance through which molten plastic flows into the cavity of the mold from the runner. This is where the flow or melting of molten plastic is controlled by control type of gate or gate dimension. It is positioned at the thickest area of a part.
other function of gate is the gate makes it easier for the runner, which will be unnecessary after molding, to be separated from the part.is recommended to consider gating options early in part design.

Direct Gate
direct gate or sprue gate we can define as connecting directly end sprue to the molding and used as a gate,
this type of gate is commonly used for single cavity molds, where sprue feeds the material to cavity molds directly rapidly with minimum pressure drop.

this type of gate is applied to molding of boxes or cups like bathtub, plastic bucket, and others, particularly large sized products. like at the picture above, shown cups product with direct gate before cutting.

Dimensions and Construction

from picture below we can concluded that direct gate is very easy to design,

from picture above the construction of direct gate is one parts with the product, after injection process, the sprue will cut manually.
parting line between cavity and core can directly placed at top surface of product or more lower from top surface product, it very depending of product shape and characteristics.
starting sprue diameter is controlled by nozzle of injection

- then, make sure the diameter of sprue orifices must be larger than nozzle exit diameter, choose from 1-2 mm or about 1/32 inch.
- give taper at the sprue from orifice diameter to product about 1-3 degree, it is will made the product demolded from cavity side more easy.
- in general the diameter of the gate much greater than the thickness of the product.

Advantages
- Low cost of design.
- The injection pressure was reduced due to direct cavity filling.
- Simple way to design gate and runner system.
- easy design and maintenance.

Disadvantages
some disadvantage of direct sprue are:
- since excessive stress is left easily around the gate, cracking often starts around the gate.
- when using non standard sprue tapers, will more expensive with little gain.
- gate mark left on part surface after runner of sprue trimmed of.
- This gate type can only produce one part per shot.
- The gate has to be cut manually by a cutter.
- Not applicable in little size product.

Monday, February 11, 2008

Basic Functions of Mold Base Parts

A mold plate is any plate required to built a complete mold, in all plate use for molds have the main requirements, they are :
1. Good corrosion resistant
2. Good Machinability.
3. Easy to clean
3. Good heat transfer.
4. Homogeneity of steel.
5. Easy ability.
6. Low Cost.

at picture below you can see 3 plate mold base type with closed position, basically 3 plate type and 2 plate type has some main plate, see explanation about mold construction type to understand more,


explanation below based on number at those picture
1. Fixed Clamping Plate or Top Plate
Holds The fixed side of the mold to attached at the fixed platen of the injection machine. at this plate will attach locating ring, eye bolt, and sprue bush.
2. Runner Stripper Plate
this plate only used in 3 plate molds type, the function is to cut resin from nozzle in top of sprue bush, and pull the runner by runner locking pin.
3. Fixed Mold Plate or Cavity plate.
use to hold cavity side of product, leader pin, support pin, Puller bolts, and Angular pin when slider attached.
4. Movable Cavity Plate or Cavity plate
it used to attach core side of product, return pin, leader bush and slider core if needed.
5. Back up Plate or Support plate
used to support cavity plate, attach the hole for return pin's spring, and cooling channel when in cavity plate can not make it.
6. Spacer Block
Mounted between the movable clamping plate (bottom plate) and the movable cavity plate to give space and allow the ejector plate to move when ejecting the
part. the required length of spacer block depend on ejector stroke that needed to eject product.
7.Ejector retainer plate
to hold the ejector, Z pin, shoulder bolts,and give space to ejector leader pin and support pillar.
8. Ejector Plate
Pushes the ejector pins and return pins, connected with ejector rods.
9. Movable Clamping Plate or Bottom plate
Holds The movable side of the mold like spacer block, support plate, cavity plate and ejector mechanism to the movable platen of the injection machine.


and look at picture below, shown 3 plate molds type in opening position, but at picture below, Bottom plate or movable clamping plate is number 7, number 8 is ejector retainer plate, and number 9 is ejector plate.




Saturday, February 9, 2008

Paralel and series Cooling methode at flat type plate of Mold Base

almost mold designer know that cooling is biggest part that effect cycle time of injection mold, a good design in cooling will make heat exchange between resin after injected and mold will reduce cycle time and give good product.
at flat type of mold base plate like stripper (Plate number2) plate between top plate and cavity plate, top plate it self, and support plate after core plate, at the top plate cooling not always used, it very depend on resin type,and product shape.
the picture below shown some flat mold base that we can use parallel or series cooling methods


How about core and cavity of Mold base ?


we can use both type of cooling series and parallel when design cooling at core and cavity plate, but you must careful place the cooling, because beside cavity molds it self, they are ejector at the core plate then sprue and runner system at cavity plate. the construction and how to connecting cooling at mold plate with cavity mold cooling will discuss later.

Parallel Cooling Channel
picture below shown parallel cooling channels concept























basic mold base cooling have four parts, they are :
1. Main Cooling pipe
commonly cooling pipe make by drilling using bore,the longer drilled hole, it recommended have length about 6 mm if using long nipple joint to connect with outer tube, if using nipple or inner joint plug each cooling pipe minimum have 12 mm.
2. stopper plugs, like at slider cooling and cavity cooling stopper plugs is prevent water or oil coolant flow to undesirable way.
3. Inner stopper plugs, the function is same as stopper plugs, but assembly methods and location is different, it assembled at inner of cooling pipe.

parallel cooling channels are drilled straight trough supply manifold cooling pipe, due the parallel design flow characteristics, the flow rate along various cooling will different, because each cooling pipe have their own flow resistance. as a results, cooling of the mold will not uniform. so it's clear that parallel circuit of cooling in molds are very poor flow rates.

Series Cooling
picture below shown basic series cooling construction and methods






















the parts is same with parallel cooling type, but the construction is different, at the series cooling channel types, it connected in single loop from the coolant inlet until its outlet, we can configure the flow by adjust the inner stopper plug type.
when design it is recommended to use same size of diameter cooling, because it's can maintain the turbulent flow, turbulent flow enables heat to be transferred more effectively.

Long and Shorts Nipple joint plug Assembly methods

considering mold base material strength,closer distance between two nipple plug type are not advisable, look at picture below

assembly between long type and shorts type is different, by using long type minimum length from both side is 6 mm, except for little diameter hole, less then 5 mm, smaller length spacing my be acceptable.
Short nipple joint types almost assembly in inner mold base, because of that minimum length space is 12,5 mm, although 10 mm my acceptable but will difficult to assembly it using hand.