A Definitive Guide to DFM Success Machining Issue IV Jan2015

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Subtitle

2 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Machining Design Guidelines

Milling Rules

Issue IV, Jan 2015


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Welcome once again to another issue of DFM Guidebook!

Milling is one of the most flexible and well known method of

machining. Due to the high tolerances and surface finishes that milling

can offer, it is ideal for producing parts with precision features and

shapes.

Milling is typically used to produce parts that are not axially symmetric and DFM guidelines

recommend avoiding sharp internal corners inside pockets when it is to be manufactured using

milling process.

In this issue we cover important design guidelines for Milling such as Deep Radiused Corners, Sharp

Internal Corners, Tool Accessibility, Narrow Regions in Pockets, Side and Bottom Radius, Tool

Clearance Check and Angular Milling Faces.

If you missed reading previous issues of DFM Guidebook, please visit our website, www.dfmpro.com

Rahul Rajadhyaksha Senior Product Manager Geometric Limited


Contents

Deep Radiused Corners ........................................................................................... 6

Sharp Internal Corners ............................................................................................ 7

Tool Accessibility ..................................................................................................... 8

Narrow Regions in Pockets ..................................................................................... 9

Side Radius and Bottom Radius ............................................................................ 10

Tool Clearance Check ............................................................................................ 11

Angular Milling Faces ............................................................................................ 12


Deep Radiused Corners

Flute engagement in the milling operation is important because it directly influence the forces. When the axial depth of cut is increased, the length of engaged flutes increases, and the milling forces also increase. Longer end mills are prone to breakages and chatter, requires longer machining time and results in increased tool vibrations. Vibration creates uneven wear on cutting tools and thereby shortens tool life. Designers should design milling areas such that longer end mills are not required to machine it.

Example


Sharp Internal Corners

Rounded corners provides number of advantages such as less stress concentration on part and tool, few operational steps and reduced scrap rate.

Sharp inside corners cannot be produced by milling and require more expensive machining methods like EDM. When designing a three-edged inside corner, one of the inside edges should be radiused. It is advised to avoid sharp corners and use fillets and radii.

If a sharp corner is required for mating clearance, then drilling a separate relief hole as shown below may serve the purpose.


Tool Accessibility

Features should be accessible to the cutting tool in the preferred machining orientation.

Example


Narrow Regions in Pockets

It is recommended to avoid features that are too close to each other such that the gap between them is too narrow to allow milling cutter to pass through them. If narrow regions are unavoidable, then they should not be very deep.

The size of the milling cutter is constrained by the smallest distance between the faces of the feature. Small diameter cutters are prone to breakage and chatter. Hence larger diameter, shorter cutters are generally preferred.

Example


Side Radius and Bottom Radius

Use of standard side radius and bottom radius for milling features will ease manufacturing of milling features with standard available milling tools. For reducing, machining cycle time and tool setup cost, it is recommended to avoid non-standard side radius and bottom radius.

As a general guideline use single standard side radius and single standard bottom radius.

Example


Tool Clearance Check

Machining Features or slots should be accessible to the cutting tool in the preferred machining direction and at the same time there should not be any clash between tool holder and component while machining the feature.

Tool clash with components leads to adverse effect like tool damage, component damage, and it will be unsafe for machine operator as well.

Example


Angular Milling Faces

Side and bottom faces of milling features separated by bottom fillet should be at 90 to each other to allow production with an end mill having bottom corner radius. Machining of angular faces require multi-axis machining, which leads to higher machining cost.

It is recommended that side and bottom faces of milling features separated by bottom fillet should be at an angle 90 to each other.

Example

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A Definitive Guide to DFM Success Machining Issue IV Jan2015