Week 8 - Challenge 5 - Core & Cavity Design

Aim

To create the Core and cavity design for the switch bezel along with the parting surface and parting line in catia v5.

Parting surface

A parting surface is a surface that separates the mold block into two parts – the core and the cavity.It is a surface portion of both mould plates adjacent to the impression which butt together to form a seal. and prevent the loss of plastic material from the impression.

Requirements

• parting surface should facilitate mold making
• parting surface should be helpful for mold venting
• The parting surface should be located at the largest section a plastic part
• parting surface should be helpful for mold release / product ejection
• parting surface should ensure the precision requirements of the plastic product
• parting surface should be selected to meet the appearance requirements of the plastic product
• The deisgn of the mold should be as simple as possible and side core must be avoided as it increases the cost
• Dimensional accuracy
• Ensure adequate venting.

Parting line

It is a line that splits the mold into two parts – the core and the cavity. It is the line of separation on the plastic part where the two halves of the plastic injection mold meet.

Reuirements and considerations

• Parting line Shape
• Mold Clamping force
• Products' Appearance & Quality
• Easy to Process mold components
• Conducive to venting

Draft

Draft is the amount of taper for molded or cast parts perpendicular to the parting line. It also a slant that is applied to each side of most features of an injection molded part By applying appropriate draft angle the mold will be easier to remove and it also accounts for thermoplastic shrinkage in Injection molding. The draft may also alter the form and fit of the part during assembly.

A draft of minimum of 0.5 degree draft per side is recommended. For textured sidewalls use an additional 0.4 degree draft per 0.1mm depth of texture. But maintaning the minimum draft could be costly during manufacturing hence an optimum draft angle of 3 degree could be maintained.

Draft Direction

Outward Draft

In this model the draft is provided in the outward direction so that if the flash occurs it happens at the Class B surface which could be removed by some manual process. It also does not affecct the appearance since it is hidden below the class A surface. If inward draft is provided then the flash would occur on the class A surface which would reduce the appearance of the part which is undesirable.

Tree strucutre

Create the Tooling axis

X direction

The cut section is taken and since there is no other surface to intersect we give the required draft angle from the horizontal.

Y direction

The centre point of the lower surface is chosen and vertical line is drawn passing through the point.

Bisecting line

The bisecting line is used to create a line bisecting the two reference lines created in normal direction. The bisecting lines helps us to achieve the average draft angle between the two reference lines.

The tooling axis is obtained by using an bisecting line from the X and Y direction.

Publish

In the next step publish the tooling axis and Class A surface so that we can access it easily and use it for further creation of surfaces or thick body.

Draft Analysis

Once the tooling axis is created the draft analysis can be done. For viewing the draft analysis results we need to change the view parameters into customise mode enabling only the material.

Go to insert-analysis-feature draft analysis.

The compass option is used to choose the tooling axis. The color coding shows the result of the draft analysis done. The limits of the draft angle can be changes according to the needs.

Types of the modes in the analysis

A single limt can be chosen to show the positive or negative draft

Multiple limits can also be set based on the requirements

The draft angle value can be found at any given point of the surface. For this case 3 degree is chosen as the optimum angle and we can see that the entrire model has positive draft angle highlighted in green color. Zero draft angle would have been shown in red color and negative draft in blue color.

Class A Surface Draft Analysis

Core and Cavity design

Core design

parting surface

The class A surface is extrapolated and trimmed with the class C surface to get the required output and the it is splitted to get the parting surface

The sketch for extrude

The surface is extruded and upper surface is filled and required trim is done. the final core(in orange)output is obtained using close surface.

Core output

The similar steps are used to get the cavity but the lower half is kept and lower surface is filled and the trim, close surface operations are done to get the required output.

Parting line

Final core and cavity

Core in brown color

cavity in light brown color

parting surface in light red color

Tooling axis in yellow dotted line

parting line in blue dotted line

the switch bezel part in orange color

Conclusion

Thus the core and cavity design along with the parting surface and parting line is done for the switch bezel and the draft analysis has been done in catia v5.