Design for manufacture and assembly in construction: a review

TL;DR: In this paper, a comprehensive review of DfMA in construction, its prospects and challenges in particular, seems absent from the literature, and the possible perspectives of DMA with a view to providing implications to the construction industry.

Abstract: Design for Manufacture and Assembly (DfMA) is known as both a philosophy and a methodology whereby products are designed in a way that is as amenable as possible for downstream manufacturing and assembly. As construction is moving towards a combination of offsite prefabrication and onsite assembly, DfMA is gaining momentum in this heterogeneous industry. Nevertheless, a comprehensive review of DfMA in construction, its prospects and challenges in particular, seems absent from the literature. This study reviews the processes and principles of DfMA and explores the possible perspectives of DfMA with a view to providing implications to the construction industry. It was found that DfMA in construction has been interpreted from three perspectives: (1) a holistic design process that encompasses how structure or object will be manufactured, assembled and guided with DfMA principles; (2) an evaluation system that can work with virtual design and construction (VDC) to evaluate the efficiency of manufacturing and assembly; and (3) a game-changing philosophy that embraces the ever-changing prefabrication and modular construction technologies. This study suggests that development of design guidelines, forming multidisciplinary team, use of VDC systems and understanding the lean principles are factors that could further enhance the successful application of DfMA in construction.

Summary

Introduction

• A report from KPMG (2016) cautioned ‘offsite manufacturing alone will not overcome the challenges the construction industry is facing, to do so requires a partnership with an integrated design process, like the Design for Manufacture and Assembly (DfMA) method’.
• DfMA method is commonly known as methodological procedures for evaluating and improving product design for both economic manufacturing and assembly.
• Unlike the increasing uptake of lean thinking (originated in manufacturing) by construction firms to improve the construction process, very few studies (Fox, Marsh, & Cockerham, 2001) attempted to shed light on best practices of design engineers, the building designer’s counterparts in manufacturing, in the design stage such as the DfMA method.

DfMA: concept

• The key principle is to produce a design with fewer parts as well as designing the parts which remain easy to assemble (Stoll, 1986).
• In Layman’s term, DFM aims to design parts that are easier, cheaper and more efficient to manufacture (Emmatty & Sarmah, 2012).
• Boothroyd (2005) outlined the original DfMA analysis method which provided methodological procedures for evaluating and improving product design for both economic manufacturing and assembly.

DfMA: process and principles

• The typical DfMA process can be arranged into stages, as summarized in Figure 1.
• At this stage, DfM is assisted with guidelines for standardization, component design and component assembly to reduce total manufacturing cost.
• The third approach which is most recently developed is the automation of the entire process.
• The system can be developed in a way that a design can be analysed, evaluated, and then optimized repeatedly by applying the rules to improve the design quality after each iteration.
• It is particularly important that the DfMA Figure 1.

DfMA in construction: a research gap

• Construction on site is portrayed by Ballard and Howell (1998) as a combination of fabrication and assembly.
• Rather, it was the complete and consistent interchangeability of parts and the simplicity of attaching them to each other (Crowley, 1998).
• Since Koskela (1992) brought the production theory into construction, much has been written about the lean concept and lean tools to make the site assembly efficient (Tommelein, 1998).
• The focus of lean is predominately focused on the construction process.
• Given the limited source of DfMA in the construction literature, this paper attempted to explore what are the emerging interpretations of DfMA in construction, what typical benefits that DfMA could bring to the construction industry along with the challenges associated with the DfMA adoption in construction.

Method

• A study examining the DfMA in construction is overdue.
• This study uses existing literature to examine the construction perspectives to DfMA concept.
• Following on the steps of conducting a systematic literature review outlined by (Tranfield, Denyer, & Smart, 2003), the first step in the systematic review was to identify the research.
• Knowing these criteria, the search was performed in March 2019; articles published by then and appearing in the database were considered.
• Cost reductions by eliminating need to re-work incorrectly assembled parts 1. Design for simple part orientation and handling Cost reductions due to non-valueadded manual effort or dedicated fixturing 1.

DfMA: a systematic process

• First, DfMA is viewed as a systematic procedure, which can add value to the construction/production process by standardizing component and reducing design variabilities (Goulding et al., 2015).
• Step 3 – the manufacturing phase is the final step which comprises of three activities: (1) factory assembly, (2) releasing the manufactured components by signing-off the production checklists, and (3) on-site installation.
• It is interesting to see this method encourages designers to capture the production experience from past projects and use it during design.
• It is good to have structured steps or guidelines to perform DfMA process given this method is just taking place in the construction industry.
• In Luiten and Fischer’s (1998) words, DfMA changes the traditional sequential process to a process where design and manufacturing are reciprocally dependent.

DfMA: an evaluation model

• Secondly, DfMA is the development of an evaluation method.
• The scoring system allows product designer and building designer, in the case of buildability, to take advantage of the opportunity to redesign based on the numerical values.
• To achieve that, a performance index was created to evaluate to what extent the design could achieve the predefined criteria, which is given a factor of relevance (R), and a grade (G).
• Moreover, Gbadamosi et al. (2019) identified a list of assessment criteria – based on the DfMA concept and lean construction principles – for the design optimization of assembly.

DfMA: prefabrication technologies

• Lastly, DfMA was closely associated with prefabrication (Laing O’Rourke, 2013), to which a bundle of gamechanging technologies that can be applied (BCA, 2016).
• A closer examination of Table 3 shows that the examples of DfMA technology range from material (CLT), to component (integrated prefabricated M&E), to assembly (precast and prefabricated elements), to module (PBU and PPVC) in about four levels.
• This has been well documented through wealth literature when DfMA is viewed as technology.
• It was reported, the first major benefit of DfMA is a significantly reduced construction programme (Laing O’Rourke, 2013) followed by better quality and safety.
• RIBA (2013) found a 20−60% reduction in construction programme time, and greater programme certainty.

Challenges

• Boothroyd (1994) used a metaphor ‘over-the-wall’ approach to describe the design process where the designer throws the design over a wall to the manufacturing engineers who then have to deal with the various manufacturing problems arising because they are not involved.
• Unlike their counterparts in manufacturing, the building designers have not been provided with equivalent methodologies, but rely on the varying experience of individuals (Fox et al., 2001), and some think in frames (Atkin, 1993).
• No feedback from construction is possible.
• Overlook something which may be worth having (Atkin, 1993).
• These are the main challenges for DfMA taken as a process or evaluation model.

Design guidelines

• Clearly the above observation suggests that DfMA has not been consciously applied in construction.
• Edwards (2002) concluded that design guidelines are one of the main sources of explicit knowledge on the practice of design.
• Therefore, qualitative and general principles of DfMA, together with Koskela’s (2000) flow principles, can be a good reference point for construction firms to customize their own DfMA guidelines.
• Other principles can be triggered by tasks or events as the design proceeds (Edwards, 2002).
• DfMA development including prefabricated service risers, prefabricated services horizontal distribution units and packaged plantrooms .

Multidisciplinary team

• Many researchers (Ashley, 1995; Omigbodun, 2001) emphasized that the DfMA practice is applied by a multidisciplinary, including design engineers, manufacturing engineers, shop floor mechanics, suppliers’ representatives, and specialists in production support, maintainability, and reliability.
• Syan and Swift (1994) wrote the chief among the underlying imperatives of DfMA approach is the team or simultaneous engineering approach in which all relevant components of manufacturing system, including outside suppliers, are made active participants in the design effort from the start.
• Similarly, Song, Mohamed, and AbouRizk (2009) agreed that early involvement of subcontractors and suppliers do face challenges in the contracting practices, but their case studies (Song et al., 2009) showed that fabricators are able to provide design assistance in optimization, modularization, and standardization in the early design stage.
• Dainty, Briscoe, and Millett (2001) proposed an integrated contractual system that ensures a parity of responsibilities and obligations would be desired.
• Chen and Lu (2018) acknowledged it is challenging to balance between benefits/ value derived from multi-disciplinary team to integrate knowledge as extensively as possible.

Building information modelling (BIM)

• Historically, one of the DfMA thrusts is the development of a variety of computer-based and/or computer-aided design programs (i.e. CAD software) (Stoll, 1986).
• The advantage of computer support is that it aids the DfMA evaluation procedure by prompting the user, providing help screens in context and by conveniently documenting the analysis (Leaney, 1996).
• This novel design approach, as Yuan et al. (2018) claimed, realizes the coordination of building designers, manufacturing designers, and assembly professionals.
• Again, the challenge here is the quality of the data or information that needed for BIM to assist the building designer to evaluating alternative designs as Fox et al. (2001) did caution that building designers have limited confidence over information (i.e. price books, 10 S. GAO ET AL. manufacturer data) when they get it.
• Often, their decision-making of materials selection is likely to be based on rule-of-thumb instead of quantified comparisons of alternatives.

Synergy of DfMA and Lean construction

• It has been noted that the key characteristics of DfMA rules are in line with the heuristic principles of flow concept of production as put forward by Koskela (2000).
• As Koskela (2000) implied other things being equal, the very complexity of a product or process increases the costs beyond the sum of the costs of individual parts or steps.
• Kremer (2018) noted, not only is parts standardization important to DfMA, the removal of elements and a reduction in the number of overall parts assist in reducing time in manufacturing and improving efficiency.
• Furthermore, Gbadamosi et al. (2019) found waste minimization is another common factor underpinned by DfMA and lean construction.
• By understanding what these wastes (non-value added) activities are, it would be more meaningful to assist designers in understanding what kind of inefficient motions, and operation are associated with manufacturing and assemble.

Conclusion

• There are two main areas of manufacturing that construction can benefit from (Kagioglou et al., 1998), namely new product development and the operational/ production processes.
• Much has been discussed on the second area.
• This study begins with a review of DfMA in the manufacturing, and notes DfMA takes manufacturing and assembly into account during the product design, but also these considerations must occur as early as possible.
• It extends the previous work of Fox et al. (2001) and Gerth et al. (2013), which only focus one of the perspectives discussed above, by proposing the application of DfMA in construction need to embrace these three perspectives holistically.
• Early involvement or teamwork avoids many of the problems that arise.

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Design for manufacture and assembly in construction: a review
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Design for manufacture and assembly in
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Design for manufacture and assembly in construction: a review
Shang Gao
a
, Ruoyu Jin
b
and Weisheng Lu
c
a
Faculty of Architecture, Building and Planning, The University of Melbourne, Melbourne, Australia;
b
Division of Built Environment and Civil
Engineering, School of Environment and Technology, University of Brighton, Brighton, UK;
c
Department of Real Estate and Construction, Hong
Kong University, Hongkong, People’s Republic of China
ABSTRACT
Design for Manufacture and Assembly (DfMA) is known as both a philosophy and a methodology
whereby products are designed in a way that is as amenable as possible for downstream
manufacturing and assembly. As construction is moving towards a combination of offsite
prefabrication and onsite assembly, DfMA is gaining momentum in this heterogeneous industry.
Nevertheless, a comprehensive review of DfMA in construction, its prospects and challenges in
particular, seems absent from the literature. This study reviews the processes and principles of
DfMA and explores the possible perspectives of DfMA with a view to providing implications to the
construction industry. It was found that DfMA in construction has been interpreted from three
perspectives: (1) a holistic design process that encompasses how structure or object will be
manufactured, assembled and guided with DfMA principles; (2) an evaluation system that can work
with virtual design and construction (VDC) to evaluate the efficiency of manufacturing and
assembly; and (3) a game-changing philosophy that embraces the ever-changing prefabrication
and modular construction technologies. This study suggests that development of design guidelines,
forming multidisciplinary team, use of VDC systems and understanding the lean principles are
factors that could further enhance the successful application of DfMA in construction.
ARTICLE HISTORY
Received 1 May 2019
Accepted 22 August 2019
KEYWORDS
Design for manufacture and
assembly (DfMA);
construction; design;
prefabrication; assembly;
lean construction
Introduction
Many studies have explored various aspects of prefabri-
cation, or otherwise known as offsite manufacturing,
including its business models (Goulding, Rahimian,
Arif, & Sharp, 2015; Pan & Goodier, 2011), barriers
and constraints (Blismas, Pendlebury, Gibb, & Pasquire,
2005; Mao, Shen, Pan, & Ye, 2013), benefits (Blismas,
Pasquire, & Gibb, 2006) and opportunities (Arif, Gould-
ing, & Rahimian, 2012; Goodier & Gibb, 2007). How-
ever, a report from KPMG (2016) cautioned ‘offsite
manufacturing alone will not overcome the challenges
the construction industry is facing, to do so requires a
partnership with an integrated design process, like the
Design for Manufacture and Assembly (DfMA)
method’. DfMA method is commonly known as meth-
odological procedures for evaluating and improving
product design for both economic manufacturing and
assembly. Unlike the increasing uptake of lean thinking
(originated in manufacturing) by construction firms to
improve the construction process, very few studies
(Fox, Marsh, & Cockerham, 2001) attempted to shed
light on best practices of design engineers, the building
designer’s counterparts in manufacturing, in the design
stage such as the DfMA method. As Dewhurst (2010)
noted, ‘what we have forgotten along the way is that
the design of the product itself ultimately controls the
total cost’. DfMA can guide cost reduction efforts
early in the product design process, so that product’s
full potential of lean production can be realized since
some potential manufacturing problems and assembly
issues have already been addressed in the design. The
aim of this paper is to review critically the concepts
and principles of DfMA, to discuss the perspectives of
DfMA in the construction industry, and to suggest
key strategies for better implementation of DfMA in
construction.
Review of DfMA
DfMA: concept
There are two components of DfMA, design for manu-
facture (DfM) and design for assembly (DfA) (Bogue,
2012; Otto & Wood, 2001). DfM is principally concerned
with making individual parts, DfA addresses the means
of assembling them (Bogue, 2012). The research on
DfA is pioneered by Boothroyd and Dewhurst (1987)
© 2019 Informa UK Limited, trading as Taylor & Francis Group
CONTACT Shang Gao shang.gao@unimelb.edu.au
BUILDING RESEARCH & INFORMATION
2019
https://doi.org/10.1080/09613218.2019.1660608

who conducted a series of studies considering the assem-
bly constraints during the design stages. This helps avoid
the manufacturing and assembly issues in the down-
stream stages of the product development (Emmatty &
Sarmah, 2012). Based on the premise that the lowest
assembly cost can be achieved by designing a product
that can be economically assembled by the most appro-
priate assembly system. The key principle is to produce a
design with fewer parts as well as designing the parts
which remain easy to assemble (Stoll, 1986). The fewer
the number of parts, the greater is the probability that
all of them will be placed correctly (Bridgewater, 1993).
To achieve that, Boothroyd and Dewhurst’s(1987) hand-
book introduced various ratings for each part in the
assembly process based on the part’s ease of handling
and insertion. According to Emmatty and Sarmah
(2012), the parts do not satisfy the following criteria
should be eliminated: (1) the part moves relative to all
other parts already assembled during the normal oper-
ation of the product; (2) the part must be of a different
material, or must be isolated from all other parts already
assembled; (3) the part must be separate from all other
parts already assembled. In the construction context,
the implication of DfA concept is to consider how
aspects of the design can be designed in a manner that
minimizes work on site, and in particular, avoids ‘con-
struction’ (RIBA, 2013). An example would be designing
a handrail system that allows half landing lengths to be
quickly installed into sockets which are pre-positioned
in the stair structure (RIBA, 2013).
DfM, on the other hand, compares the use of selected
materials and manufacturing processes for the parts of
an assembly, determines the cost impact of those
materials and processes, and finds the most efficient
use of the component design (Ashley, 1995). In Layman’s
term, DFM aims to design parts that are easier, cheaper
and more efficient to manufacture (Emmatty & Sarmah,
2012). O’Driscoll (2002)defined DfM as the practice of
designing products with manufacturing in mind, with
its goal is to reduce costs required to manufacture a pro-
duct. Interestingly, O’Driscoll (2002) argued that the
principle of DfM is at least 200 years old, citing LeBlanc,
a Frenchman, devised the concept of interchangeable
parts in the manufacture of muskets which were pre-
viously individually handmade (Bralla, 1999). For con-
struction, DfM is the process of designing in a manner
that enables specialist subcontractors to manufacture sig-
nificant elements of the design in a factory environment
(RIBA, 2013). Panelized system such as claddings have
been designed in this manner for years, and now the
emerging hybrid systems (i.e. pods) and modular build-
ings (i.e. fully factory-built houses) also pertain to the
DfM concept.
From the above descriptions of DfM and DfA, it was
felt that these two disciplines are appropriate to be con-
sidered together, as one term – DfMA (Bogue, 2012).
This is because products now are complex and the ability
to assemble them eff
ectively is equally critical. Constance
(1992)
noted that DfMA was a management and soft-
ware tool enables designers to consider a product’s
material selection, design, manufacturability, and assem-
bly up front. Boothroyd (2005) outlined the original
DfMA analysis method which provided methodological
procedures for evaluating and improving product design
for both economic manufacturing and assembly. When
DfMA was introduced to manufacturer such as Douglas
aircraft in California, it was labelled as a design review
method that identified the optimal part design, materials
choice, and assembly and fabrication operations to pro-
duce an efficient and cost-effective product (Ashley,
1995). The goal is to provide manufacturing input at
the conceptualization stage of the design process in a
logical and organized fashion.
DfMA: process and principles
The typical DfMA process can be arranged into stages, as
summarized in Figure 1. Boothroyd (1994) has noted
that DfA should always be the first consideration, leading
to a simplification of the product structure. This is fol-
lowed by the economic selection of materials and pro-
cesses and early cost estimates. In this process, cost
estimates for original design and new (or improved)
design will be compared, in order to make trade-off
decision. Once the materials and processes have been
finally selected, a more thorough analysis for DfM can
be carried out for the detailed design of the parts. At
this stage, DfM is assisted with guidelines for standardiz-
ation, component design and component assembly to
reduce total manufacturing cost.
Fox et al. (2001) noted that design engineers are pro-
vided with standard design improvement rules or guide-
lines in workbooks and standard design evaluation
metrics in manuals for evaluating a design with respect
to its ease of assembly. If a concept is compatible with
these guidelines, one can be reasonably assured that
the design will be fairly well in the subsequent detailed
analysis (Otto & Wood, 2001). In this manner, a feed-
back loop is provided to aid designers measuring
improvements resulting from specific design changes
(Boothroyd, 2005). Afterwards, the best design is taken
forward to a more thorough analysis for DfM, where
the detailed design for the parts will be performed (Boot-
hroyd, 1994).
According to Bogue (2012), there are three means of
applying a DfMA process. The first is to follow a general
2 S. GAO ET AL.

set of non-specific and qualitative rules or guidelines and
require someone (most likely designers and engineers) to
interpret and apply them in each individual case. The
aim is to encompass a diversity of products, processes
and materials. Table 1 provides an example of such
DfMA guidelines and their associated benefits. Similarly,
Stoll (1986) outlined ten DfMA principles and rules: (1)
minimizing total number of parts, (2) developing a mod-
ular design, (3) using standard components, (4) design-
ing parts to be multifunctional, (5) designing parts for
multi-use, (6) designing parts for ease of fabrication,
(7) avoiding separate fasteners, (8) minimizing assembly
directions, (9) maximizing compliance, and (10) mini-
mizing handling.
A close examination reveals that despite these guide-
lines/principles from various reference points, they
share substantial similarities, such as minimization,
standardization, and modular design to be the key
characteristics of DfMA principles. This is in line with
the heuristic principles of Koskela’s(2000) flow concept
of production: (1) simplify by minimizing the number
of steps, parts and linkages, (2) increasing flexibility,
and (3) increasing transparency. As Koskela (2000)
noted: ‘simplification can be realized, on one hand, by
eliminating non-value-adding activities from the
production process, and on the other hand by reconfi-
guring value-adding parts or steps’. The implication of
this heuristic principle, in the context of DfMA, is for
designers to rethink their designs as to what extent
the criteria that they applied in their designs would
affect the production and assembly that may cause
extra motions.
The second method employs a quantitative evaluation
of the design. The rationale is that each part of the design
can be rated with a numerical value depending on its
‘assemblability’ (Bogue, 2012). Subsequently, the num-
bers can be summed for the entire design and the result-
ing value is used as the guide to evaluate the overall
design quality. Another evaluation tool is based on a
100-point method with demerit marks being given for
factors which hamper the ease of assembly.
The third approach which is most recently developed
is the automation of the entire process. It relies on com-
puter software. Quantitative analysis can be applied to
the design, followed by constructing an expert system
employing the general design rules. The system can be
developed in a way that a design can be analysed, evalu-
ated, and then optimized repeatedly by applying the rules
to improve the design quality after each iteration. In this
connection, it is particularly important that the DfMA
Figure 1. Typical stages in a DfMA procedure. Source: Boothroyd (2005 ).
BUILDING RESEARCH & INFORMATION 3

Frequently asked questions

Q1. What are the contributions in "Design for manufacture and assembly in construction: a review" ?

This study reviews the processes and principles of DfMA and explores the possible perspectives of DfMA with a view to providing implications to the construction industry. This study suggests that development of design guidelines, forming multidisciplinary team, use of VDC systems and understanding the lean principles are factors that could further enhance the successful application of DfMA in construction. 

Q2. What is the role of DfMA in building design?

In the modern-day construction industry, with the rise of prefabrication and BIM, building designers should be working closely with engineers and fabricators, in a multidisciplinary team, to develop DfMA guides and evaluation metrics and digitally incorporated them into 3D model so that such useful information can assist building designers evaluating alternative designs. 

Q3. How many minutes of assembly time did Chen and Lu (2018) save?

In addition, Chen and Lu (2018) reported the DfMA-oriented curtain wall (CW) design was able to save more than seven minutes in assembly time for one CW unit with better workmanship. 

Q4. What is the advantage of computer support?

The advantage of computer support is that it aids the DfMA evaluation procedure by prompting the user, providing help screens in context and by conveniently documenting the analysis (Leaney, 1996). 

Q5. What is the importance of programs and design software?

Kremer (2018) noted programs and design software is an important platform required to deliver a DfMA value proposition that allow for assessment, design and adjudication of parts and elements that constitute the individual units. 

Q6. How many articles were published in the last two years?

It is worth mentioning that 9 out of 26 articles (34.6%) were published in the last two years (2018–2019), indicating that DfMA only recently become a popular topic. 

Q7. What is the definition of a typical building project?

In Luiten and Fischer’s (1998) words, typical building project with a sequential or linear product development process where communication is only possible one way from designers to builders. 

Q8. What was the first recommendation for DfMA?

It was first recommended as a key recommendation during the International Panel of Experts (IPE) for Construction Productivity and Prefabrication Technology in 2014, where the panel called for fundamental changes and stronger measures in the 2nd construction productivity roadmap to achieve its target of 20–30% productivity improvement. 

Q9. What is the role of easy assembly in the decision-making process?

Rashidi, Samali, Ronagh, and Mortazavi (2018) noted the level of easy assembly can be a decision-making factor to determine the level of prefabrication. 

Q10. What is the importance of integrating knowledge into the design process?

But more importantly, the client organization and the architect need to accept that contractor and/or subcontractors can bring added value to their design process. 

Q11. What are the main components of the DfMA-oriented design process?

Yuan et al.’s (2018) work mentioned manufacturing simulation, transportation simulation, and assembly simulation are added into the DfMA-oriented design process.