How to design fan gate in thermoplastic injection mold

fan gate, is a gate spreading toward in to cavity, basically this gate is thin similarly with previous gate (film gate) and is used in same purpose with film gate. with the gate construction it permits rapid filling of large parts or fragile section mold area with large entry area. it is used to create uniform flow into wide parts.
Purpose
1. thereby keeping the cross sectional area constant.
2. This ensures a constant and more even plastic flow into the cavity into a wide area at a slow injection speed, minimizing backfilling and reducing imperfections and stresses in the part.
3. used for thick-sectioned moldings and enables slow injection without freeze-off.
4. favored for low stress moldings or where warpage and dimensional stability are main concerns.
5.The melt velocity will be constant.
6.The entire width is being used for the flow.
7. The pressure is the same across the entire width

Construction and Design



side View

The gate should taper in both width and thickness, to maintain a constant cross sectional area, although at picture below thickness is doesn't tapered.



Dimension
the land thickness can be vary thin relative to the part thickness because the gate is very wide.the maximum thickness should be no more than 80% of the part thickness. if the parts very thin like 0,8 mm, you can also use 0.7 mm fan gate thickness, but when rubber is used as material parts, use 100 % of the thickness parts is more easy to control flow and product quality. The gate width varies typically from 6 mm up to 25% of the cavity length.in large parts is often use fan gate as wide as the parts it self.

Simulation Picture
all picture below based on injection simulation process, using material PS ASAHIPS 693 : Asahi Chemical
other data are
==== Machine setup ====

Melt temperature = 503.15 K
Mold temperature = 323.15 K
Fill time = 0.08 s
Packing/Holding time = 4.24 s
Cooling time = 7.72 s
Packing/Holding pressure = 12627300.00 Pa

==== Machine specification ====

Required clamp force = 27647.70 N
Required shot size (GPS) = 0.01 kg

Simulation results

mold time filling in seconds


time to cool after injection
from below picture we can learn where is the best position to make cooling layout, after you make cooling layout, enter the cooling simulation process to your parts. if the distribution is same in all shape of part (unless runner and gate) your design is good to realize.


Pressure distribution



all picture is enabled to enlarge, click the picture to enlarge.

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Film Gate Design (flash gate)

Film gate also called flash gate is very thin compare to another gate, this thin gate like film which have parallel runner before the gate, this type of gate used for straight edges. picture below shown film gate with main parts.


in generally this gate used in thin and flat requirement, like flat mobile phone cap, ipod cap and others. but sometimes this gate is not likely going to have a flat flow front, the make flow material more stable and flat, make temperature molds more higher than usual, but cycle time will also higher.

here is film gate from top view


Dimension
recommended dimension is approximately 0.2 mm to 0.6 mm in thick, the land area (parallel runner) is also be kept small approximately 0.6 mm - 1 mm depend the large and weight of product.

Other Design
picture below shown other design of film gate, with more reliable and easy in process.

look the different model of film gate, and different design of parallel runner.
picture below shown simulation of plastic flow from those design

and the last picture shown time that needed to cooling the melt plastic in mold


from the picture above we can choose the right place to make cooling pipe, the red color marks mean need more time to cool the product.

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Tab gate design in Mold

general construction of tab can see at picture below


basically melted material is fed to this gate from a separate primary gate (after runner), the function of the gate typically is employed for flat and thin parts to reduce the shear stress in the cavity, Tab gate able to used in various material plastic such us ABS, PS, acrylic, PP, PVC, Polycarbonate. SAN and other which has relatively low fluidity. at this type of gate, the high shear stress generated around the gate that trimmed after molded. this gate sometimes also called the collision gate.

Function in Product and General Rule
The thickness of tab gate should be the same as the part wall, yo can also make more thin, but when designed parts for cosmetic parts if preferred that the thickness is same with the product thickness.
rule number two is, make the gate as center as possible in the product side, but you must consider the product size and shape.
basically minimum tab width is about 6,5 mm and the tab thickness minimum is 75 % from the thickness product


for more picture and drawing view,please look at picture below

(Top View of Tab Gate)






(Front view of Tab Gate)





(Side View of Tab Gate)

each picture is able to enlarge by clicking the picture.

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side gate, edge dimension design

edge gate is the simplest type of gate and is used wherever the product can or must be gated from parting line. it's designed commonly for injection machine attended by operator, because the product must separated from the runner system by hand with the aid of side cutter.

Dimension
Picture below shown ideal configuration and practical gate, suggested dimension for general application of edge or side gate are


Runner width and Height for side gate or edge gate is preferred that height is about 0,7-0,8 from width of runner. the width of runner very depending on product size and weight, it from 3 mm until 7 mm in width ( product mass until 200 gram in maximum).
Gate width and height is about W=3h,with W is width and h is height (look at Herbert Rees, Mold Engineering, pg 159) but this rule can't applied for all part or product form, specially for thick product that have large in width such us panel and cover, when design the dimension of gate take the rule that height of gate is must about 75 % from the parts thickness, Suggested take 0,6 until 0, 7 from parts thickness, but specially for elastomer material take more large about 80-90 % from parts thickness.
T is gate width, for product mass until 200 gr, suggested take 1 until 5 mm in width , for the very large product some times have width until 12 mm.
C is Land of gate from runner, the length is should be no more than 1,5 mm. also preferred make taper before gate land, in that picture taper are change with R in both side, make R, taper or not is depend on side gate size and form.


Picture 1.A

Picture 1.B

both those picture shown edge gate or side gate with different design, application, parting line, taper and R system. taper from bottom runner to gate land have various dimension, the taper in picture 1A is enough large, about 30-45 degree, in picture 1B taper is about 10-20 degree.

beside those type of side gate, they are still various type of side gate or edge gate, will upload in other post.

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