Designing guide

MECHANICAL DESIGN PROCEDURE:

 1.  At first a design scheme (lay-out/concept) is drawn in which the shape of the part being designed and the nature of its connection with other elements are presented in a simplified form while the forces acting on the part are assumed to be either concentrated or distributed in conformity with some simple law.

    o    Decompose the physical concept into sub-assemblies and components, determine the Geometric arrangement of component and establish dimensional relationships between components.

    o            Decide which components are standard and which must be designed.

    o           Select manufacturing process to be used for each designed component.

2. The forces acting on the part in the process of machine operation are then determined;

3. The necessary material is selected and the allowable stresses are found accounting for all the factors that affect the strength of the part;

4. The dimensions of the part, required by the design criteria (strength, rigidity, wear resistance etc.) corresponding to the accepted design scheme, are determined;

5. Finally the drawing of the part is made indicating all dimensions, accuracy of manufacture, surface finish and other information necessary for the manufacture of the part.

The Product Design Specification [PDS]:

The Product Design Specification is the necessary information required to effectively define architecture and system design in order to give the development team guidance on architecture of the system to be developed. The Product Design Specification document is created during the Planning Phase of the project. Its intended audience is the project manager, project team, and development team. Some portions of this document such as the user interface (UI) may on occasion be shared with the client/user, and other stakeholder whose input/approval into the UI is needed.
The Product Design Specification (PDS) comprises quantitative statement of what you want to design prior to starting to design it. In other words, the specifications of the PDS should be largely independent of any specific embodiment of your product, so multiple solution concepts are possible.The purpose of the PDS is to ensure that your design actually addresses your customer needs. This is essential if your product is to succeed.

Typical content of PDS:

Factors to be considered for Preparing PDS:

A. Product design & performance issues..

·         Expected product size and weight

·         Expected product performance requirements

·         Operational requirements.

·         Speed (Continuous or discontinuous)

·         Loadings likely encountered

·         Product power requirements.

·         Product shelf life.

·         Product service life.

·         Expected product service environment.

·         What is the operating temperature range

·         What is the operating humidity range

·         Subject to shock loading?

·         Will the product be exposed to dirt or other contaminants (corrosive fluids, etc.)

·         Will there be any anomalies in power/fuel available for this product?

·         How will the product be treated in service?

·         What impact will the product have on its environment?

·         Expected product safety requirements.

·         Potential sources of product liability litigation.

·         Potential operator hazards.

·         Potential manufacturing and assembly hazards.

·         Potential for misuse/abuse.

·         Expected product reliability standards and requirements.

·         What level of reliability can we expect for this product?

·         Expected product ergonomic requirements -- customer requirement

·         Which user/operator features are desirable in this product?

·         Are there problem areas for users/operators? Can we design around them?

·         Expected product aesthetics -- customer requirement

·         Expected product maintenance requirements.

·         Can product be maintenance-free?

·         If routine maintenance is required, can it be done by the owner/operator?

·         Will professional maintenance be required?

·         Possible off-the-shelf component parts.

·         Which parts of this product be purchased instead of being made by us?

·         Is the quality and reliability of purchases parts adequate for this design?

·         Material requirements..

·         What are the strength requirements?

·         What are the rigidity/compliance requirements?

·         Is product weight of importance?

·         Expected product recycling potential and expected disposal

·         Does the disposal of this product constitute an environmental hazard?

·         Can parts of this product be effectively recycled by existing processes?

·         Manufacturing process requirements and limitations.

·         Is protection from the environment necessary?

·         Is there a customer preference for a particular finish?

·         How do we minimize environmental impact?

·         Product packaging requirements.

·         Can we use environmentally friendly packaging and packing materials?

·         How much packaging and packing materials are really necessary?

·         Applicable codes and standards to be checked.

·         Patents to be checked.

·         Processes to research/benchmark. (special processes needed for fabrication?)

B. Market issues...

·         Potential customer base

·         Who will buy this product? Why?

·         Have you listed all potential classes of customers?

·         Can we tap into a new segment of the market? How?

·         Market constraints on product.

·         Who is buying this type product? (customer base)

·         What is currently selling?

·         What is currently not selling?

·         Expected product competition (These will be benchmarked)

·         What are the strengths of each competing product? Can we incorporate them?

·         What are the weaknesses of each competing product? Can we improve?

·         What are the market shares of competing products?

·         Target product price -- OEM and MSRP

·         Target production volume and market share.

·         Is there a market for this product? How do you know?

·         Is the potential market sufficiently large to justify investment in a new product?

·         Is the new product sufficiently better than the competition?

·         Expected product distribution environment.

·         How will the packaged product be treated in shipping, storage, and on the shelf?

·         Are adequate shipping facilities available?

·         Will installation require a professional?

C. Capability issues....

·         Company constraints on product design, manufacture, and distribution.

·         What are our manufacturing capabilities?

·         Should we manufacture ourselves or outsource?

·         Schedule requirements -- time to market.

·         When should we have this product to market to capture maximum market share?

·         How much time should we allocate to design?

·         How much time do we need to implement a manufacturing process?

Development Of Product Specification:

Improvement Of Product Specification:

Materials Selection:

The selection of a material for a machine part or structural member is one of the most important decisions of the designer.  There are systematic and optimizing approaches to material selection. Here, for illustration, we will only look at how to approach some material properties. One basic technique is to list all the important material properties associated with the design, e.g., strength, stiffness, and cost. This can be prioritized by using a weighting measure depending on what properties are more important than others. Next, for each property, list all available materials and rank them in order beginning with the best material; e.g., for strength, high-strength steel such as 4340 steel should be near the top of the list. For completeness of available materials, this might require a large source of material data. Once the lists are formed, select a manageable amount of materials from the top of each list. From each reduced list select the materials that are contained within every list for further review. The materials in the reduced lists can be graded within the list and then weighted according to the importance of each property.  

Selection of Material Depends on following factors,

·         Material Properties

                         The expected level of performance from the material 

·         Material Cost and Availability

Material must be priced appropriately (not cheap but right)

            Material must be available (better to have multiple sources)

·         Processing

Must consider how to make the part, for example:

Casting

Machining

            Welding

·         Working Environment and Serviceability

         Wear And Corrosion

·         Durability and Maintenance