Design for Manufacturing and Assembly

In the past few decades, research into design thinking has engendered a new wave of methodologies in product design and manufacturing processes. These methodologies have saved billions in product development and ensured lower cost, higher competition and greater product reliability.

Among these methodologies, one of the most prominent ones, Design for Excellence (DFX), has since fragmented into smaller focus areas such as Design for Manufacturing (DFM), Design for Assembly (DFA), Design for Manufacturing and Assembly (DFMA), Design for Supply Chain (DFSC) and so on. In DFX, a focus such as cost, quality or ease of manufacturing is chosen and the product’s design is improved in regards to that aspect.

This article will explore the role of Design for Manufacturing and Assembly (DFMA or DFM/A) in product design. DFMA represents a harmonious combination of Design for Manufacturing (DFM) and Design for Assembly (DFA), both of which we have discussed in separate articles previously.

What Is Design for Manufacturing and Assembly?

DFMA stands for Design for Manufacturing and Assembly. It is an engineering methodology that focuses on optimising the manufacturing and assembly aspects of a product. Both of these aspects have a high impact on the final product’s quality and cost.

Factors such as raw materials, manufacturing processes, volume, machinery, tooling, precision, number of parts and their complexity, labour and skills, automation potential, etc, are all very influential in product development. By optimising these factors alone, companies can drop the initial cost estimates by over 50%. This is the main intention of implementing DFMA principles.

In DFMA, the product design is continuously modified while keeping certain end goals in mind to arrive at a product that requires less time, money and effort to produce.

The Need for DFMA Methodology

Why do we need DFMA when we already have DFM and DFA? Let us start by reviewing our understanding of each.

Design for Manufacturing is concerned with maximising the manufacturing ease of a product. It employs techniques that make manufacturing faster, cheaper, and easier by improving the design and the manufacturing process.

On the other hand, Design for Assembly works to simplify, shorten and mistake-proof the assembly process. Principles such as poka-yoke, combining and standardising parts are all examples of DFA application.

Both DFM and DFA have similar objectives. They both aim to reduce material requirements, cost and time-to-market. But there are times when the two may work against each other. A net gain from DFM could lead to a net loss in DFA, essentially making the gain worthless.

Let’s take the example of combining parts from DFA “guidebook”. If fewer individual parts lead to a part that is expensive or difficult to manufacture, we gain little benefit from this DFA technique as DFM is affected negatively. Similarly, many DFM guidelines can reduce the effectiveness of a DFA technique.

To avoid such occurrences, it was prudent to look at the two methodologies of DFM and DFA together. This is how DFMA came to be. It uses DFA and DFM in tandem to arrive at an optimum product design. DFMA can help us leverage the advantages of both these methodologies without the disadvantages of either.

Benefits of DFMA

A well-structured DFMA application provides both short-term and long-term advantages. These advantages are indispensable to the creation of a sound product that can beat modern-day competitors. Some of the amazing benefits of DFMA are:

Shorter time to market

Time to market is defined as the duration between the idea generation phase and the introduction of a product to the market. Ideally, you’d want this time to be as short as possible. DFMA significantly reduces the time to market by simplifying the manufacturing processes and the assembly steps.

Lower product development cost

An efficient DFMA at the initial phase reduces the development costs by thinking ahead of time and resolving possible issues that may crop up later.

One of the leading experts on concurrent engineering and Design for Manufacturing, Dr. David Anderson explains that in DFM there is a “Rule of 10” which states that it costs 10 times more to fix defects at every successive stage of assembly. Thus, if rectifying a part defect costs x prior to assembly, it will cost 10x at sub-assembly, 100x at final assembly, 1000x at the distributor stage and 10.000x if the part has reached the customer.

DFMA removes the need for downstream design changes. It also recommends adding provisions for features that the manufacturer may want to add to a product at a later point in time.

Reduced wastage

DFMA aims to eliminate waste from the product and assembly design. It reduces the wastage of materials, motion, inventory and overprocessing. It also minimises defect risks and wait time by eliminating redundant manufacturing and assembly steps and unnecessary features.

Greater product reliability

Due to the high focus on preventing defects and increasing the benefit-cost ratio (BCR), DFMA products naturally become highly reliable and durable. The fewer number of parts in a DFMA-conscious product also helps to reduce the failure rate.

Quality control

DFMA improves communication and teamwork between different teams in a manufacturing setup. A well-coordinated product development effort between designers and manufacturing engineers, for instance, informs both teams about the best practices of each department to reach a certain end goal. This ensures a higher quality product within the allotted budget.

DFMA Principles

DFMA is a vast methodology and many books have been written on this subject. It consists of a variety of principles. The application at hand is evaluated in light of these principles to create a DFMA-conscious product.

It is crucial that DFMA starts at the concept creation phase. The design stage is the most influential in determining many aspects of the product such as the quality, reliability and final price. Any decisions taken at this stage have far-reaching effects. Some of the common principles in DFMA that can be applied to a wide variety of products are as follows:

Simple design

Keeping the design simple is one of the tenets of design for manufacture and assembly (DFMA). A designer must strive for a clear and efficient product design. Removal of unnecessary features and components must be a priority.

Such a design is usually easier to manufacture and assemble. It also requires lower investment costs and relatively less time to manufacture and repair, if the necessity arises.

A complicated product geometry is unattractive besides being uncomfortable to use. You will find that it is actually more complex to create a simple design than a complex one. Remember the adage “Simplicity is the ultimate sophistication.”

Opt for a modular design

A modular design breaks a product down into various modules, each of which performs a certain function. Such modules reduce the number of parts present in a family of products. For instance, a single laptop battery may be used in a number of different laptops. Same goes for other components such as a smartphone camera module. This type of design process has a positive effect on time to market, inventory, cost, customisation, sustainability and the possibility of future upgrades.

Easy and efficient fasteners

Most products require the use of some kind of fasteners and there’s a variety of options available on the market. Many fasteners may appear cheap on paper but their installation can be expensive and time-consuming. Moreover, fasteners can create a bottleneck in a factory’s manufacturing setup, often restricting production volume.

DFMA optimises the fastening process by recommending affordable fasteners that are also easy and cheap to install. Wherever possible, it prefers the use of snap-fit fastening methods. For a stronger bond, rivets can be chosen over screws. Due consideration to fastening methods can reduce manufacturing costs, waste, product weight and space requirements.

Poka-Yoke

Poka-yoke refers to the use of mistake-proofing techniques to improve the accuracy rates of assembly and manufacturing operations. The intention is to correct errors and defects as close to the source as possible by installing automatic/manual interlocks that prevent incorrect manufacturing and assembly of product parts. These interlocks ensure that a component can only be assembled in the correct orientation. Using asymmetry in product structure is one of the ways to ensure this. However, it must be noted that symmetrical products are easier to manufacture and assemble.

Reduce the number of parts

Reducing the number of parts is one of the most popular techniques in DFMA as in DFM and DFA. There are many advantages to this.

Each part draws from your team’s bandwidth logistically and financially. It will require specific tooling and fixtures. More parts will require more prototypes, manufacturing, individual analysis and assembly steps. It is always a good practice to consolidate part functions wherever possible.

Fewer parts reduce the amount of time required in manufacturing and fastening processes. It also reduces the assembly time and the chances of incorrect assembly.

Use standard parts

Standard parts are readily available, they’re also cheaper and have greater reliability than custom-made parts. DFMA advises preferring the use of standardised components wherever possible.

Be aware of process limitations

Many designers are unaware of suitable manufacturing processes and their capabilities when designing a product. By improving communication between different teams, DFMA ensures that designers make decisions that suit more economical manufacturing methods.

Use suitable tolerances

Tight tolerances can be very difficult to achieve. They require expensive production and measurement methods. Furthermore, parts with tighter tolerances are difficult to assemble. This increases the assembly costs through increased labour costs and scrap rates.

Wherever possible, the tolerances should be as loose as possible to keep the price down while maintaining functionality.

Other DFMA techniques

In addition to the above principles, some other DFMA techniques that improve the manufacturing and assembly ease are:

• Remove flexible parts

• Implement automation into the production process or make provisions for future automation potential

• Make modifications for an easy assembly

• Give due consideration to how the part will be handled and oriented during assembly and manufacturing operations

• Design multi-functional parts