The design and development of products require not only the management of basic concepts of conventional mechanical design but the proper selection of materials and manufacturing processes that allow obtaining items that meet the functional requirements of high quality and with the possibility of being acquired at low costs. For this reason, it is essential to work in multidisciplinary teams.
This involves both the client’s attributes and the engineering and process variables. It helps in idea generation and implementation of techniques that facilitate teamwork and guide designers to obtain the right path for the design process.
Design for manufacturing and assembly (DFMA)
The decisions taken in the design phase commit 70% of the cost of the product. If you want to reduce the costs of a product, a possible line of action would be required for the optimization of the product design.
Design for manufacturing and assembly is a methodology used as part of the design and integrated products and processes development (IPPD), which, based on rules and principles, guide the design team to create concepts of parts that are easy to manufacture, have an economic structure maintaining their quality, and easy to assemble.
Currently, the largest and most profitable global companies do use DFMA techniques and tools to:
#1 Analyze the management cost chain.
#2 Simplify products and improve quality
#3 Improve communication between design, manufacturing, shopping and management.
#4 Cut manufacturing and assembly costs
These methodologies and tools were introduced in the industry by Dr. Boothroyd and Dr. Dewhurst in 1983. In fact, they are the owners of the registered trademark “DFMA.”
Since then, companies from the world such as the automotive industry, agricultural machinery, computers, instrumentation, furniture, and more have cut millions of dollars from their manufacturing and assembly costs by applying these techniques.
Accepted gradually, it is called simultaneous or concurrent engineering.
Principle Implications in The Design
#1 Life cycle
Design taking into account everything that the product will go through in its life cycle. The product life-cycle management helps to have a perception of the associated manufacturing and assembly costs. It also determines the associated costs of the different modules throughout the different stages of the cycle of life.
Modules imply an implicit simplification of products, in subgroups that allow distributing the project in subprojects or subcontracting parts. This facilitates not only the assembly of the modules but also the diagnosis of malfunctions and therefore, maintenance and repair.
#2 Organization of teams
The design teams are organized by a project manager who drives the project in all its areas, relying on committees of experts. Responsible for all stages of the product life cycle, the project manager should not overlook the aspects that could be important in stages close to the launching of the product to the market.
With a little room for manoeuvre and associated costs that this would entail, organization of teams also provide the space for the creativity of the teams of work and innovation.
#3 Product architecture
Starting from the specifications, the approach towards the design and architecture of the product should be kept common among the products of the same family or range, taking into account its functions and possibilities to structure it in different modules
Miller & Edgard propose models of modularization grouped into four categories:
• Reuse of knowledge in design
• Customization in manufacturing
• Configuration of variants in the mounting
• Adaptation after manufacture
#4 Design and development
Advancing in the conceptual design, of materialization and detail of product, you have to know the new manufacturing technologies with computer support as well as those of rapid prototyping or rapid manufacturing, without neglecting traditional.
Trust that the subcontracting of components of the market with or without modifying is a strategy to take into account. Further, while designing the product, it is convenient to take into account the symmetries, effect of the thicknesses and dimensions of the parts, of the tolerances and the difficulties of access and vision to evaluate with precision its influence and use them effectively.
For assembly operations, it is advisable to design using the following techniques:
• Structure in modules
• Decrease complexity
• Establish a basic element
• Limit the addresses of mounting
• Facilitate the composition
• Simplify the unions
The expression design for manufacturing (DFM) is often applied to a process that follows certain rules in order to facilitate the design of differentiated parts for an efficient process.
The DFM has been applied for years and it is evident that this information is very valuable for the designers, however, if these rules are considered as a principle of manufacturing guidelines the results are generally unsatisfactory. This is because the efficiency of the manufacture of each piece requires that the orientation tends to the simplicity of each piece.
#1 Structure in modules
It consists of grouping the different functions that a product must fulfill, or the different sequences of its manufacture, in modules connected by mechanical interfaces, material flow, energy flow, and clearly defined signal flow.
#2 Decrease complexity
It is based on reducing, on the one hand, the number and variety of the pieces that make up the product; and on the other hand, the mechanical interfaces and material flow from station to station.
#3 Establish a fundamental element
The assignment of the title “base element” to one of the parts makes it easier to handle a reference with which to handle the other components. Regularly this helps to strengthen the unions and the structure of the product.
#4 Limit mounting directions
The aim is to reduce the directions of the product during assembly, if possible, to only one. Having changes of direction and even a double direction on the assembly line represents an unproductive manipulation that in the automation is transformed into the difficulty of operation and cost of the equipment.
#5 Facilitate the composition
It depends on the orientation of the pieces and the establishment of symmetries that facilitate handling during assembly. This helps to reduce the orientation and manipulation times of the pieces as well as the care in their dimensions and thicknesses.
#6 Simplify the unions
It is said that the joints and connections between the pieces represent a great aspect within the times and costs of the assembly, besides affecting the product in multiple aspects (resistance, weak structural points, poor aesthetics and more)
The satisfaction of any need implies having gone through a design process; The material selection process is a crucial step to guarantee the satisfaction of the calculations foreseen in the design.
It is important to mention that not all manufacturing processes are compatible with all materials. So the authentic is to arrive at a combination of material and manufacturing process.
The study of a DFMA case is the qualitative evaluation of the process to which it was designed or redesigned, for this normally the comparison of the standard assembly times is made as an indicator of improvement. The evaluation mainly falls on the following two aspects and their derivatives.
Design or redesign the product taking as its objective the ease and quality of the assembly, in short, the reduction of costs (without forgetting the functional point of view, the primary purpose of the product).
The main recommendations for the design of a new product (or redesign of an existing product) in relation to assembly, are:
#1 Replace a part or components with materials different from the original.
#2 Choose the material for a new product.
#3 Choose the material for a better design.
#4 Choose a material to meet a need raised.
As mentioned above, the most important part of the concurrent engineering is to establish transfunctional product development teams that have the necessary knowledge and technical information to ensure that all the requirements of a new design are addressed.
The alternative approach for DFM located in pieces is in principle to focus on the product structure and try to reach the consensus of the team regarding the design structure.
The DFA (design for assembly) then challenges the product development teams to reduce the time and costs needed to assemble the product, no doubt a powerful way is by reducing parts in the product.
Within the DFA, a series of data are used with the manipulation and insertion times based on the dimensions and symmetries of the pieces as well as the complete fixing methods. After capturing these measurements, penalties are added that represent the difficulties that may arise during assembly.
This is defined as:
DFA index = (Nm × tm) / ta X 100
Where Nm = theoretical minimum quantity of pieces
Tm = minimum assembly time per piece
Ta = estimated total assembly time
In reality, many times, there will be no material that meets all the requirements, often several comply with the specifications.
It is important to have a list with the qualification of the properties to make sure we consider all the factors.
If none of the materials meets the requirements, then it will be necessary to redesign the product.
Some of its most significant specific objectives are:
- Facilitate manufacturing and assembly operations
- Reduce manufacturing and assembly costs
- Reduce investment and tooling costs
- Optimize the use of manufacturing and assembly tools and equipment
- Reduce management costs
- Increase manufacturing flexibility
- Increase the configurability of the products
- Decrease the time of the introduction in the market
- Reduce intermediate warehousing, dispatch and occupation of spaces in general.
Proposals to eliminate the steps of a manufacturing and assembly process should be analyzed to document for the DFA process.
The minimum number of pieces that can be used to determine a DFA index includes not only the evacuation of possible redundancies of the number of pieces but also the assembly difficulties of the design that is analyzed. It consists of choosing the most suitable material for a specific engineering application.