2 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Assembly Design Guidelines Issue XIX, Aug 2016

3 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

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4 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Welcome to another issue of the DFM Guidebook. This issue of DFM Guidebook will focus on design for assembly guidelines.

This time we will not be talking about DFM. On the other hand we will cover some aspects of DFA or Design for (ease of) Assembly. Consideration of assembly issues during early design stage shortens product development time, minimizes development cost, and ensures a smooth transition into production with minimal rework. If a product contains fewer parts it will take less time to assemble, thereby reducing assembly costs. With each part there is an opportunity for a defective part and an assembly error. As the number of parts increases, the probability of a perfect product goes down exponentially. In addition, if the parts are provided with features which make it easier to grasp, move, orient and insert them, this will also reduce assembly time and assembly costs. Additionally, there are many assembly related issues which occur on the shop floor and can be avoided during the design stage. Read the guidebook to understand rules for: Hole Alignment, Hole to Slot Alignment, Slot parameters based on thread size, Interference Detection, Fastener Clearance, Fastener Accessibility, Fastener Engagement Length, Minimum Clearance between Components and Check for Preferred Components. If you have any feedback or questions on DFM guidebook, please write to us at info@dfmpro.com Happy Reading…. Regards DFMPro Marketing.

5 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Contents

Hole alignment .............................................................................................................. 6

Hole and Slot pairs......................................................................................................... 7

Hole to Slot Alignment ............................................................................................................ 7

Slot Parameters based on Hole Thread Size ........................................................................... 8

Interference Detection .................................................................................................. 9

Fastener Guidelines ..................................................................................................... 10

Fastener Accessibility ............................................................................................................ 10

Fastener Clearance ............................................................................................................... 11

Fastener Engagement ........................................................................................................... 12

Recommended Thread Connection .............................................................................. 13

Check Contact Material................................................................................................ 14

Check Preferred Components ...................................................................................... 15

6 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Hole alignment

Hole alignment plays a major role in assembly design. Holes are used for insertion of fasteners, dowels,

cables, etc.

It is recommended that, holes in connecting parts should be collinear to avoid difficulties in assembly.

Blocked holes and unused holes which lead to increase in manufacturing cost should be avoided.

7 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Hole and Slot pairs

Slot holes are used in single-direction accurate joints. This is typically used where the alignment

tolerance along the length of the slot is not critical.

Hole to Slot Alignment

Correct hole to slot alignment id provided for proper position of the slot with respect to the threaded

hole in the adjacent part. This should be measured by slot position center to the threaded hole axis.

It is recommended that, hole should collinear and at the center of a slot. If the hole is not at the center

of the slot, then it may leads to misalignment in future adjustment.

8 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Slot Parameters based on Hole Thread Size

Slot parameters (Slot width and length) should be maintained as per the corresponding threaded hole

sizes. These slots will act as clearance holes.

It is recommended that, for ease of manufacturing, slot parameters should be in standard sizes.

9 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Interference Detection

To achieve desired functionality and ease of assembly interference between assembly components

must be avoided. Interference detection is most useful in complex assemblies, where it can be difficult

to visually determine whether components interfere with each other.

Failure to avid interference may result in rework and engineering changes.

10 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Fastener Guidelines

A fastener is a mechanical component which is used to join two or more parts/components together.

Fasteners play a major role in assemblies.

Fastener Accessibility

Fasteners should be easily accessible for assembly and disassembly.

It is necessary to ensure sufficient space around the fastener head for spanners, wrenches, bits for ease

of fastening or extraction. Also, a designer should provide sufficient space axially for insertion and

removal of fastener into the holes.

11 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Fastener Clearance

For the ease of insertion of fasteners there should be sufficient clearance between non-threaded parts

and the fasteners (radial clearance).

Also, it is advised to provide sufficient gap between bolt and bottom of the hole or the next component

(axial clearance) to absorb excessive tightening load if any.

A = Axial Clearance , B = Radial Clearance

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Fastener Engagement

The axial distance through which the fully formed threads of both the nut and bolt are in contact is

called the fastener (thread) engagement length.

It is recommended that, engagement between the internal and external thread should be long enough

to provide adequate cross-sectional thread area. Insufficient thread engagement results in a tensile

failure of the bolt rather than thread stripping. To achieve the required strength, there should be

sufficient engagement between fastener and the component.

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Recommended Thread Connection

The threads on male (external) and female (internal) sides of a threaded connection should be of

compatible types/forms. It is recommended to use only the compatible thread types/forms on male

and female sides of a threaded connection to avoid issues like improper connection, cracks, stress

ruptures etc. during functioning.

Designer should select right threads (standard and size) in both male and female parts. For example, If

the male part thread is metric thread (M8 X 1.0) female part should have metric thread (M8 X 1.0).

In some cases, even though thread standard and sizes are same but male thread is fine thread and

female part thread may coarse thread, designer has to avoid such mismatches.

14 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Check Contact Material

Compatible contact material is one of the critical criteria in assembly design. Material properties

determine, how the parts react to the structural or thermal loads applied. While selecting material,

designer need to consider density, thermal conductivity, Specific heat, Coefficient of thermal expansion

and so on.

Metal oxidizes in presence of oxygen. Atmospheric effects and thermal cycling accelerates this process,

when moisture is present. To avoid chemical reactions like oxidization or corrosion etc. contact

materials should be compatible.

SURFACE CONTACT Examples LOWER UPPER SURFACE

SURFACE GAL ZINCALUME COLORBOND S/STEEL ALUMINIUM COPPER ZINC LEAD

GAL YES NO NO NO NO NO YES Y/NC

ZINCALUME YES YES YES Y/NC YES NO YES NO

COLORBOND YES YES YES Y/NC YES NO YES NO

S/STEEL Y/NC Y/NC Y/NC Y/NC Y/NC Y/NC Y/NC Y/NC

ALUMINIUM YES YES YES Y/NC YES NO YES Y/NC

COPPER Y/NC Y/NC Y/NC YES YES NO YES Y/NC

ZINC YES NO NO NO NO NO YES Y/NC

LEAD Y/NC Y/NC Y/NC Y/NC Y/NC Y/NC Y/NC YES

NOTE : YES CONTACT ACCEPTABLE

Y/NC CONTACT ACCEPTABLE BUT NOT DIRECT METAL CONTACT

NO NO DIRECT METAL CONTACT

15 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS

Check Preferred Components

In most organizations, similar products with different versions or series are produced by way of

modification or replacement of components. This is done with a purpose of making the product

available with various features at different costs based on market demand.

In such cases, it is important to ensure the presence of preferred and allowed components in the final

assembly based on the product or series. Goal is to exclude disallowed components from the final

assembly of a particular product version or series. Also, sometimes, materials assigned for disallowed

component are deemed obsolete by organizations. Hence, it needs to be ensured that such

components are not be shipped with the final assembly.