Project 2
CREATION OF MOLD FOR CPU FAN BEZEL
INTRODUCTION
Molding is a process in which a molten or liquid material is poured into a mold and allowed to set or freeze. There are many types of molding process out of which injection molding is widely used. Injection Molding is a manufacturing process for producing parts in large volume. It is most typically used in mass-production processes.
Injection molding is a manufacturing process for producing parts by injecting molten material into a mold. Molded products are obtained by injecting plastic material molten by heat into a mold and then cooling and solidifying them.
OBJECTIVE
To create a mold for CPU fan bezel with ejectors and sliders if needed. And also to create the guide, runner, air vents and cooling channels. Assuming the material to be ABS.
METHODOLOGY
Step 1- Decide a tooling direction and do a draft analysis and decide the core and cavity side.
Step 2- Increase the size of the model to account for the shrinkage.
Step 3- Create a parting line on the core cavity separation.
Step 4- Create a shut off surface.
Step 5- Create a parting surface.
Step 6- Core and cavity surfaces are created.
Step 7- Create a core and cavity blocks.
Step 8- To create other features like the gate and runner system, ejector pins, air vents and cooling channels.
DESCRIPTION
Parting line-
A 'parting line' is the line of separation on the plastic part where the two halves of the plastic injection mold meet.
Parting surface-
A parting surface is a surface that separates the mold block into two parts – the core and the cavity.
Ejector pins-
Ejector pins apply a force to eject a part from the mold, and in some cases can leave marks. Once the mold is opened, the pins extend into the mold cavity, push the part out, and then retract, allowing the mold to close and be refilled.
Sliders and Cams-
Sliders and cams are moving parts within the mold that allow or restrict access to particular areas within the tooling (and thus facilitate the desired shape of the part). The use of sliders or cams can facilitate ejection of certain areas of plastic that might otherwise be trapped in the tooling.
Sprue, Gate and runners-
Sprue-
This is the contact point between the machine and the mold. The sprue has a concave spherical seat where the molding machine nozzle tips seats off.
Runner-
The plastic flows from the sprue into the runner system. The runner is the channel that feeds directly into the gate of each part.
Gate-
the plastic flows from the sprue into the runner system. The runner is the channel that feeds directly into the gate of each part.
Cooling channel-
cooling channel is a cooling passageway which follows the shape or profile of the mould core or cavity to perform rapid uniform cooling process for injection moulding or blow moulding processes.
Air vents-
Vents are cuts within the mold steel that allows air to escape. Air inside of the mold must be allowed to escape so that the plastic can fill the entire space. If air fills the cavity then it would lead to defect in the component.
Steps for making the core and cavity block-
1.
Decide the tooling direction and then do the draft analysis. Usually the draft angle of 0.5º is given.
Then decide the core and cavity side.
While deciding the core and cavity side we also see the number of ribs or any feature on both side and the side which has more number of features is taken as the core side and the other side and the cavity side.
This is done because the core side has ejector pins, so we eject the component easily without it getting stuck.
2.
Use the scale command to increase the size of the model to account for the shrinkage.
Here the material used is ABS and the shrinkage percentage for ABS is 0.6%
So, we will make the model 1.006 times bigger than the model given to us.
3.
Use the parting line command to create the line on the core and cavity separation.
4.
We need to close or fill the surface for creating the core and cavity block. Use the shut off surface command to fill the holes.
5.
For the parting surface we use the parting surface command to create a surface.
6.
Create the core and cavity surface. Use the move/copy bodies tools to copy the parting surface and the knit one of the surfaces with the surface body for the core and the other surface with the surface body for the cavity. By doing this two surface gets created for the core and cavity mold.
7.
Go to the assembly part file and insert the part where the surfaces are created. Create two new parts for the core and cavity mold.
The width of the mold depends on the size of the ejector plates. Besides the ejector plate there is also the spacer blocks the standard size of the spacer block is 45mm. Also we add 50mm more in the width for the bottom support. Considering the sprue at the centre the mould is designed.
The length should be atleast 50 mm distance from the component.
The thickness of the block depends upon the cooling channels. The distance between the cooling channel and core block is kept at 40mm. The thickness is considered from the top most part of the block to the bottom flat base of the block.
8.
Create ejectors pins. Create a sketch for the ejector pin. Pin ejector system of type 1 is created. Pins are generally placed near the ribs and sidewalls.
There should be minimum distance of 1 mm between the pin and outer boundary.
Using this sketch extrude it to a certain distance and then using the same sketch extrude cut the mold to create path for the ejector pin.
Relief is provided from a distance of 10mm onwards. Use the extrude cut option to remove the surface for the relief.
On the bottom face of the ejector pin draw a sketch for the ejector plate and then extrude it to 10mm. Also provide a clearance for the ejector pin in the ejector plate. Below that create another sketch and extrude it to 15mm for ejector back plate.
9.
In this step sliders are designed. The slot for which the slider is required is in the cavity area. So first we edit the cavity region. Use the sketch tool and sketch the surface on the top plane which comes under the undercut and then create a reference plane upto which the slider is needed. Then use the split command to split the body so that we get a body of the slider as well as that of the cavity.
A wedge is provided on the slider so that it can interlock with the cavity block.
Height should be 2/3rd and angle is taken as 30º.
Then fill up the remaining gap using sketch and extrude command and for giving the cavity the shape of the slide, make a copy of the slider bodies and then use the combine command, in that select subtract option to subtract the copy of slider body with the main body.
In the assembly file insert a new component for the slider and import the solid body of the slider which was saved. Then using the save combine command edit the core block and fill the remaining gap.
10.
In this step we make the guide rails for the slider to move. The guide rail should have enough width to fit the washer. Create the guide rail in the core block using extrude command. Now since the guide rail was made in the core block, make cavity for the guide rail in the cavity block.
11.
In the assembly file create a new part for the washers. Draw the sketch for the washer with diameter of 16mm and then extrude it. Then we create a bolt to and then use sketch driven pattern to copy it along the slider and washers.
Use the hole wizard to create a tapped hole on the core block.
After creating this, edit the cavity block too to create a cavity for the washer and the bolt.
12.
Locking mechanism is created on the core block. Create sketch on the core mold for the locking mechanism and the use the cut extrude command to cut from the core mould. Then travel distance of the slider is taken as 45mm, so while creating the slot for the slider it then made at a distance of 45mm from the slot in the core.
13.
Create a sprue, runner and a gate. First thing is to edit the cavity block and create a sketch a circle at the centre and extrude cut it. This cut is for the proper alignment of the nozzle. Now we make a sprue and make sure that it is tapered and it will extend throughout the surface. A sprue puller is provider in the core block.
Then for the runner we make a line sketch and extrude it 4.5mm thick in the thin feature without merging it with the core block. Give a draft of 10º, then give a fillet in the bottom of 2mm.
Sketch for the gate in the shape of a trapezoid and extrude it to 0.5mm. now for the bottom part of the gate, we give a draft of 40º. Sketch and use the intersection curve command so that the remaining material can be removed using the cut extrude command. Use the fillet tool. Combine the gate and sprue and then with the help if the same combine using the same combine tool select subtract and subtract the gate and runner body from the core mold.
14.
While making a cut for the air vent we make a 0.002 mm cut and a 1mm cut, since we cannot do a cut of 1mm directly for the air vent connected to the cavity. If we do that and make a cut of 1mm directly then the molten plastic will flow in the sir vents too.
So we make a cut of 0.02mm adjacent to the vent, it is big enough for the sir to passand not big enough for the molten plastic.
We have to create a channel for the air trapped in the vents to escape.
15.
For the colling channel we follow the serial cooling channel since the flow rate is same and it causes uniform cooling. We use the hole wizard command and in that we use the socket head cap screw and then make the channel accordingly.
Result-
CONCLUSION
With the help of this project we got to learn about procedure and the parameters we need to follow while designing a mold for the component.