Week 9 Challenge

AIM:

To create the core-cavity blocks, sliders and inserts for the plastic component.

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.

 

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.

 

Inserts-

It is a separate block that would be inserted in the main block to form the complete core block. Some feature in the block cannot be cut using the current tool available. So we use inserts.

PROCEDURE:

CPU fan case-

 

Steps for making the core and cavity block-

Step 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.

Step 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.

Step 3-

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. For the holes near the rib we select the option ‘no fill’, since if a surface is created there then there would be a sharp edge at ab acute angle which be difficult to tool.

Step 4-

Use the parting line command to create the line on the core and cavity separation. While selecting the lines the following should be taken into the consideration-

• Minimum sliders

• Matching draft- making sure that there is no direct steel to steel rubbing between the core and cavity blocks by making sure that none of the core and cavity block overlap each other at 90º. The draft should be almost 7º.

We the sketch and split line command to separate the surface and can use it for selecting the parting line.

Step 5-

For the parting surface since it has a 3D profile, use the ruled surface command. Extend the surface using the ruled surface command. Then for the curved edges use lofted surface and then knit them all together using knit surface.

Step 6-

Create the core and cavity surface. Use the move/copy bodies tools to copy the parting surface and before knitting the surface we have to create extra surfaces for the holes which was left. Fill the hole by using rules surface and fill surface command such that there are no sharp edge with an acute angle. Use the move/copy bodies to copy that surfaces too

Then knit one of the surfaces and the surfaces at the ribs 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.

Step 7-

Go to the assembly workbench and insert the part we created and make new part for the core and cavity,

Whenever we have a part with 3D profile, we don’t make the entire mold block with 3D profile. We only the the 3D profile upto some distance near the main component and the rest of the block will have a 2D profile.

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.

For 3D profile the distance between the component and the block should be atleast 30mm. The length of the block should always start from the sprue position which is at the centre.

Use the extrude command and then use the cut with surface command to create the core and cavity block separately.

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.

Reliefs are created on the core and cavity blocks using the move surface command so that there wouldn’t be any steel to steel rubbing at 90º

 

Step 8-

In this step sliders are dsigned.one of the slot for which the slider is required is in the core area and the other is in the cavity area. So for the first slider we edit the core region. Use the sketch tool to sketch that region and then make a reference along that. 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. Then we edit the slider in such a way that it fills all the gap and the mold can be formed.

The width of the slider should be such that it accommodates the finger cam and the washer.

Height of the wedge should be 2/3^rd and angle is taken as 30º.

Then save the slider separately.

To cut some material for the newly edited slider in the core. Then use the combine command, in the subtract the cavity with the copy of the slider, in this way. Now to fill in the excess cavity on the cavity block use the extrude command and move face command to fill in the excess cavity. Then use the combine command, in the subtract the cavity with the slider.

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 cavity block.

For the second component the undercut is in the cavity region. But there is a feature too which is in both the blocks. So make to spilt solid and when we get do separate bodies in the core and cavity region, insert a new part file and import the bodies and then combine it together. After this the same steps are followed which was used in making the previous slider.

Step 9-

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.

Step 10-

In the assembly file create a new part for the washers. Draw the sketch for the washer with diameter od 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.

Step 11-

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 pf the slider is taken as 35mm, so while creating the slot for the slider it then made at a distance of 15mm from the slot in the core.

Step 12-

Inspect the region in the core block which and see which feature cannot be cut using the tool in the core block. Use the sketch command and sketch around that and then make a reference plane. When we have inserts on the block then keep atleast 40mm distance between the insert and base of the block. Use the split command so separate it from the main core body.

 

Result

 

CONCLUSION;

With this we got to learn about the core and cavity block for a component having 3D profile using solidworks.