Tài liệu Mold Selection P6 ppt

The following reasons make it desirable for the mold to run automatically: reach into the molding area, there is a safety hazard, even with all the safety features on today’s machines..

When considering the use of stack molds, especially for fast cycling products,

special measures must be planned to remove the huge amounts of products

Depending on the shape of the product, these measures could be any of a

number of controlled ejection methods, conveyors, stackers, packing

ma-chines etc

Figure 4.70 shows a typical cup stacker The stacker is positioned at the rear

of the molding machine It consists of an unscrambling vibratory conveyor

(A) that receives the randomly ejected, scrambled containers from under

the mold The cups are then elevated to the orienting section (B) and moved

to the stacking section (C), where they are counted to the required stack

length The stack is moved to the staging table (D) From there the stacks are

removed by hand and packed into boxes Production, depending on product

size, ranges from 2,400 to 12,000 pieces/hour

Figure 4.71 shows a typical lid stacker for round lids, in a range from 3 to

6.5 in diameter The randomly ejected lids are moved by in-press conveyors

onto a twin-disc unscrambler (A) The lids are then single-filed from each

disc and oriented ready for stacking in two lanes up the elevating conveyor

(B), to the stacking system “waterfall” (C) Next, the flow is split again and

four lanes (D) enter the spin bar stacking section (E) Stacks are cut to length

ready for transfer to the tray loading section (F) The automatic tray feeder

(G) moves the cardboard trays under the stacked lids, four stacks at a time,

and moves the loaded boxes to the unloading station (H) from where they

are hand packed into cartons

Figure 4.72 shows a (CHSV) retrieval, transfer, and stacking system, seen

from the side, where the molding machine would be located Arms enter

between the open 2 × 8 container stack mold Eight suction cups face the

cores in each level The ejected containers are held in these cups, which then

retract out of the molding area Another array of suction cups in the

Figure 4.70 Typical cup stacker

(Courtesy: CBW)

A

B

C

D

E

F G

H

Figure 4.71 Typical lid stacker for round lids

(Courtesy: CBW)

“out-side” position picks up the cups from the transfer arm After two shots, the receiving station rotates and stacks the cups to a predetermined number From there, the 16 stacks per level move on a conveyor to the packing station

4.1.9 Semi or Fully Automatic Operation?

With extremely rare exceptions, every mold can run automatically “Auto-matic” in this context means that the mold cycles without an operator’s intervention, such as opening the safety gate to remove the products, or lubricating (spraying) the molding surfaces, and so forth The following reasons make it desirable for the mold to run automatically:

reach into the molding area, there is a safety hazard, even with all the safety features on today’s machines Safety features have been known to fail and, worse, they have been deliberately tampered with or voided to save costs to repair a problem The best and safest policy is to have no operator near the operating parts of the machine Note that in general, mold operators employed to “run” a machine are often not educated in machine operations and are therefore more difficult to train in safe procedures around a machine Usually, well-trained setup personnel are employed to install the molds and to get the machine up to production They are better educated and well trained on the job and are less likely to run the machine in an unsafe condition or to condone unsafe practices

Figure 4.72 CHSV retrieval, transfer, and

stacking system (Photo courtesy: CBW, USA)

 Quality of product Uniformity of the quality of product depends much

on the uniformity of the cycle time Some operators are more skilled

than others, but even with the same operator, the time to open the safety

gate, to remove the product, and to close the gate before starting the next

cycle can vary greatly, depending on the time of the day or night, the

length of time working on the machine, and is affected by fatigue and

boredom If the product tends to hang up in the mold, or worse, if a

portion of the piece sticks in the core or the cavity and must be removed

with a tool (e.g, with a pointed piece of brass wire), it may take a while

before the mold can be restarted These undesired stops and variations

in the molding cycle affect the melt quality and the cooling temperatures

in the mold and can result in unequal quality of the product Also, if

such stoppages are too long, the extruder and any plastic in the mold

may have to be purged, before the mold can be restarted

labor force required to operate the molds To be operated most

eco-nomically, molding machines should be run uninterrupted, 24 hours a

day, for at least 5 days a week Many plants operate 7 days a week and

never stop a machine, except for mold changes and scheduled mold and

machine maintenance The problem is that absenteeism can create labor

shortages, which are difficult to control and affect the continuous

operation of a machine

reason for running fully automatic, but in fact this reason is much less

significant than the others given above With very few exceptions, every

mold can be designed so that it will run fully automatically The problem

is sometimes that the mold has been designed correctly to run

auto-matically, but was installed and set up poorly so that it will not eject

properly, as intended

4.1.10 Insert Molding

There are many applications where “inserts” must be used in a mold Here,

we will highlight a few examples (see Fig 4.73) The real challenge is to design

these molds to run automatically

Inserted labels at the bottom of products There are different methods of adding

labels to the mold before it closes Label insertion is always done automatically,

often with multi-cavity molds They use automatic label dispensers reaching

into the molding area and placing the label into the cavity or on the core

while the mold is open for ejection

Inserted labels at the sidewalls of products More difficult is the application of

labels on the sidewalls of containers, which are usually tapered, with little or

large draft angles Figures 4.74 and 4.75 show a typical system for applying

labels on the side of containers Figure 4.74 shows a view (from the rear of

the machine) of an automatic inserting mechanism, attached to a standard Figure 4.73 Variety of plastic lids withlabels applied automatically in the molds

B

C

D

E

Figure 4.74 View (from the rear of the

machine) of an automatic inserting

mechanism (Courtesy: Hekuma)

Operator side

Fixed plate Inserting labels Taking out cups

2 cavities 2 cavities 4 cavities 8 cavities

Movable plate

Takeout-head

of EDAT for cups

Inserting-head

of EDAT for labels

Cavities arrays: cups

Cup stacking

Pivoted chute for manual packaging

Horizontal stackingstation

Taking over labels

High speed side entry robot HELI 1-1700

560

1420 6388

Electric cabinet

Overhead cable trunking Label separation

Label magazine refilling position

Label preforming Push and wind device (Patent depending)

Non-operator side Label magazine refilling position

1000

Ferromatic

K 155 D

Figure 4.75 Schematic of the system

shown in Fig 4.74 (Courtesy: Hekuma)

A C B D

Figure 4.76 Molded box

molding machine The mold (A) can be seen behind the tie bars In the

foreground, left, is the dispensing mechanism (B) for the pre-formed

cup-shaped label blanks (C) Vacuum in the transfer arm (D) picks up the inserts,

ready for the next cycle After the mold arrives in the open position, the arm

moves the inserts into a position opposite the cavities (left) and the vacuum

changes to air pressure to push the inserts into the cavities At the same time,

the opposite face of the transfer arm receives the finished products as they

are ejected from the cores and holds them with vacuum When the transfer

arm arrives in the OUT position, the finished products are then air ejected

and stacked to the right (E)

Figure 4.75 schematically shows the same system as in Fig 4.74, including

other features, which are not visible in the photo It shows the label magazines,

the label separating, and the label pre-forming devices, and the stacking of

the finished products The top right corner gives layouts of molds suitable

for this operation with 2, 4, 6, or 8 cavities

Printed strips Some molds feed printed strips through the cavity side of the

mold and cut the label as the mold closes This too is performed in a fully

automatic mold

Paper and plastic containers Some products (e.g., low-cost boxes) consist of

a printed cardboard blank in a shape that, when folded, forms a box As the

mold closes, the core folds the cardboard while pushing it into the cavity

Plastic is then injected so that the cardboard along the open joints and corners

is sealed by narrow, thin, molded plastic These molds run also fully

auto-matically, with a dispenser supplying the blanks to the open mold

Figure 4.76 shows a molded box (A), consisting of printed cardboard bottom

and sides, but with a molded plastic rim (B) and plastic edges (C) Also shown

is the flat cardboard blank (D), which is fed automatically into the mold

Metal inserts The inserts can be loaded with independent robots or with

dispensing and inserting attachments to the mold Unfortunately, there are

still molds for which the inserting is done by hand or with suitable loading

boards, requiring an operator at the machine

Wire inserts Molding plastic over electrical connectors and electrical wires is

a special industry This is done manually by using shuttle molds with at least

two cavities (or cores), depending on the design of the product and the mold

While one mold half with the inserts is in the molding position, an identical

mold half is outside the molding area, where an operator places the inserts

into their respective locations This is done mostly in vertical clamp machines,

so that the shuttle can slide horizontally in and out of the molding area

This is relatively safe, because the (sitting) operator never needs to reach

into the molding area The molding cycle is usually fairly long and the operator

has ample time to place the inserts before the next shot is ready; the finished

products are removed when the other shuttle reaches the OUT position,

4.2 Summary

Up to this point, we have learned about the things to be considered by the decision maker in order to make the proper selection of a mold, i.e., how to look critically at the product, the importance of the expected production and productivity, and how to select the type of mold (and molding machine) most suitable for the job All this applies to the technology of injection molding as it stands today, but is also valid for any future developments in this field The most important principles are always common sense, simplicity and safety, and the target to produce the best product, at the best quality and the lowest cost