Manufacturing processes for selection in mechanical design

What are the most commonly used manufacturing processes for mechanical design . A detailed look and importance of design for manufacturing.

Manufacturing process

The method through which raw materials are transformed into a final product

Why is selection of manufacturing process important for product development?

From a business perspective of product development, the returns of a product depend on

  • Cost of the product
  • Volume of sales of the product

Both aspects are driven by the selection of the manufacturing process as cost of per piece depends on the rate of raw material and the higher the scale of production the lower the per piece price will be due to “economies of scale”. Depending on the sales of product an investment in the manufacturing process infrastructure is done. Selecting a process which is not capable of reaching the predicted volumes is a loss and so is a process which is more than capable of the volumes but is underutilized.

The input for the process selection is obviously the design intent i.e. the product design.

Types of Processes:

Common manufacturing processes

Injection molding:

Molten material is injected through a nozzle into a hollow cavity, the molten materials takes the shape of the hollow cavity in the mould and then cool down to become the final part.

Materials: Thermoplastics and elastomers

Sheet metal forming :

A sheet of metal is bent, shaped and cut in variety of ways to generate different types of shapes. Like bending of paper sheets.

Materials:

Steel, Aluminum, Tin in the form of rolled sheets

Pros:

A very large variety of shapes and sizes can be made using multiple techniques for forming.

Sheet metal products are always a lightweight option over bulk deformation or machined parts. They give the best strength to weight ratio for most applications.

Cons:

Dimensional accuracy of parts is one of the major concerns with sheet metal forming

Almost all thin components exhibit spring back which is the elastic deformation of bent sheets. Similar to the tendency of a paper sheet to retain its shape once folded.

Most used for: From Automotive body panels to body panels of aircraft, Kitchen utensils, industrial products. Sheet metal products are one of most ubiquitous parts today.

Casting:

Molten material is poured into a mould cavity made with sand and allowed to cool , molten material solidifies into the final part which is then removed by breaking the sand mould

One of the oldest and most widely used processes for making mechanical components.

Materials: Molten Steel, aluminium and other metals

Pros:

A wide variety of shapes can be made

Cheap process does not require costly equipment

Huge parts can be made efficiently without major overhead.

Cons:

Dimensional accuracy is not as high as other processes

There are higher chances of internal defects

Strength of the parts is suspect and inferior to Forged parts.

Most used for:

Large machine components, Base of machines like Lathe. Aluminium sand castings are used in aerospace applications.

CNC machining:

Material is strategically removed from a block of material using cutting tools which are controlled through a computer program.

Materials:

Most metals are machinable.

Thermoplastics like Nylon.

Ceramics

Pros:

  • Highly precise and accurate process with dimensional tolerances in microns or lower.
  • Rapid set up and running time

Cons:

  • Size of the parts is limited by the Machine tool
  • Intricate and hollow parts are difficult to make.

Most used for: Machining is the quintessential manufacturing operations used in every application of machines. Either the complete part is made through machining or post processed after another process like Forging or casting.

Selection of process

Parameters for process selection:

  • Nature of design – The shape and geometry of the design.
  • Volume of production – The number of parts to be produced annually and monthly.
  • Cost – Cost incurred through investment in the process equipment as well as per part cost.
  • Materials compatibility – The compatibility of materials selected with the process. Material and process selection often go hand in hand
  • Lead time – The time required to Bring a part to production from a design.
  • Process capability – The repeatability, reproducibility, accuracy and precision of the process
  • Availability due to logistics – Not all processes are available everywhere in the world.

Assembly

Earlier sections dealt with the process of creating apart from shaping, melting or forming raw materials. Most products are assemblies of multiple parts. These parts need to be joined with each other to form an integral whole.

The joining methods can be permanent or temporary.

Types of joining:

  • Fits
    • Press fit
    • Loose fit
  • Fasteners
    • Threaded fasteners
  • Rivets
  • Welding or brazing
  • Adhesives

Tolerances

One of the major contributors to the overall quality of the product is the tolerance of the design features.


The tolerance is basically the range of deviation a certain dimension of the part can vary in while retaining the function.

Not all process can maintain the same tolerances. Decision on tolerances for features in a design is done considering process capability and importance of those features have to the function of the product. Tolerances play big roles in how parts fit and assemble.

Why knowledge of manufacturing is required for design

Design of a product is not an isolated activity anymore, designers need to work increasingly with manufacturing engineers to work out the process selection and design modification for the best results.

Since manufacturing is the thing driving the cost of the product, the designer should know how to best design the part so that he/she can make the best use of the manufacturing process and not compromise on function.

What should the designers know?

  • The possibilities of design with the process
  • The limitations of the process
  • The capability of the process in terms of tolerance
  • The assembly sequencing of the product.
  • Direct and indirect Consequences of design changes on the process

Design for manufacturing and assembly

DFMA is the combination of two methodologies; Design for Manufacture, which means the design for ease of manufacture of the parts through the earlier mentioned processes and Design for Assembly, which means the design of the product for the ease of assembly.

DFMA is an integral part of the product development effort.

Today products are

  • Tending to become more complex
  • Made/required in increasingly large number
  • Intended to satisfy a wide variation in user population
  • Required to compete aggressively with similar products
  • Required to consistently high quality

The costs associated with design modification during production are very high, hence manufacturing inputs have to be taken at every stage of design before it is sent out for production.

Concept of Concurrent engineering

Concurrent engineering, also known as simultaneous engineering, is a method of designing and developing products, in which the different stages run simultaneously, rather than consecutively. It decreases product development time and also the time to market, leading to improved productivity and reduced costs.

Involving the manufacturing engineering team early in the design process so that decisions in design concerning manufacturing can be taken upfront to avoid major updates after design is committed.

  • Competitive Advantage- reduction in time to market means that businesses gain an edge over their competitors.
  • Enhanced Productivity- earlier discoveries of design problems means potential issues can be corrected soon, rather than at a later stage in the development process.
  • Decrease Design and Development Time- make products which match their customer’s needs, in less time and at a reduced cost






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Categories: DFM