Design for Assembly: Reducing Manufacturing Costs

Understanding Design for Assembly: A Strategic Approach to Cost Reduction

In today's competitive manufacturing landscape, Atlantic Canadian companies face increasing pressure to deliver high-quality products while maintaining tight margins. Design for Assembly (DFA) represents one of the most powerful methodologies available to mechanical engineers seeking to reduce manufacturing costs without compromising product integrity. By systematically analysing and optimising how components fit together during the design phase, companies across Nova Scotia and the broader Maritime region can achieve significant cost savings while improving product reliability.

Design for Assembly is a systematic approach that focuses on simplifying product structure, reducing the total number of parts, and ensuring that remaining components are easy to assemble. When implemented correctly, DFA can reduce assembly time by 40-60%, decrease part counts by 30-50%, and lower overall manufacturing costs by 20-40%. These aren't merely theoretical figures—they represent real-world results achieved by manufacturers who have embraced this methodology.

The Core Principles of Design for Assembly

At its foundation, DFA operates on several key principles that guide engineers toward more manufacturable designs. Understanding these principles is essential for any engineering team looking to implement DFA effectively in their product development process.

Minimise Part Count

The most fundamental principle of DFA is reducing the total number of parts in an assembly. Every component added to a design introduces additional costs through procurement, inventory management, handling, and assembly operations. A rigorous DFA analysis asks three critical questions about each part:

• Does the part move relative to other parts during normal operation?

• Must the part be made from a different material than adjacent parts for functional reasons?

• Does the part need to be separate for assembly or service access?

If a part doesn't satisfy at least one of these criteria, it becomes a candidate for elimination or consolidation with adjacent components. Studies have shown that the average mechanical assembly contains 30-50% more parts than theoretically necessary, representing substantial cost reduction opportunities.

Design for Ease of Handling

Parts must be designed to facilitate easy handling by assembly workers or automated equipment. This includes considerations such as part symmetry, size, weight, and the presence of features that could cause tangling or nesting. Components weighing more than 4.5 kilograms typically require two-handed handling or mechanical assistance, significantly increasing assembly time. Similarly, parts smaller than 6 millimetres become difficult to grasp and position accurately.

Design for Ease of Insertion

The insertion process—bringing parts together and securing them—represents a significant portion of total assembly time. Optimal designs incorporate self-locating features such as chamfers, tapers, and guide surfaces that reduce the need for precise positioning. Standard engineering practice recommends chamfers of 0.5-1.0 millimetres at 45 degrees for most insertion operations, with larger chamfers (1.5-2.0 millimetres) for blind assemblies where visual alignment isn't possible.

Quantitative Analysis Methods in DFA

Effective DFA implementation requires rigorous quantitative analysis to identify improvement opportunities and measure the impact of design changes. Several established methodologies provide frameworks for this analysis.

The Boothroyd-Dewhurst Method

Developed at the University of Massachusetts, the Boothroyd-Dewhurst method remains the most widely used DFA analysis technique. This approach assigns time penalties to various part characteristics and assembly operations, enabling engineers to calculate a design efficiency metric. The theoretical minimum assembly time is compared against the estimated actual assembly time to generate an efficiency percentage, with most initial designs scoring between 5-15% and well-optimised designs achieving 30-60% efficiency.

The method utilises standardised tables that assign handling times based on part size, symmetry, and features that affect grasping. For example, a part that is symmetric about both axes of insertion might have a handling time of 1.5 seconds, while an asymmetric part requiring orientation could require 3.0-4.0 seconds. These seemingly small differences compound dramatically across thousands of assemblies.

Lucas DFA Methodology

Developed in the United Kingdom, the Lucas method takes a slightly different approach by categorising parts as either "A" parts (essential functional components) or "B" parts (candidates for elimination). This binary classification simplifies the initial analysis and helps teams quickly identify the most significant opportunities for part consolidation.

Practical Applications and Case Studies

The principles of DFA translate directly into tangible improvements across virtually every manufacturing sector. For companies in Atlantic Canada, where manufacturing operations often compete against larger central Canadian and international facilities, these efficiencies can be crucial for maintaining competitiveness.

Electronics Enclosure Redesign

Consider a typical electronics enclosure assembly that initially comprises 24 individual parts including the housing, cover, fasteners, gaskets, and internal mounting components. A systematic DFA analysis might reveal opportunities to:

• Integrate multiple mounting bosses directly into the injection-moulded housing, eliminating 6 separate standoffs

• Replace 8 individual screws with 4 quarter-turn fasteners, reducing fastening time by 60%

• Consolidate the gasket and cover into a single overmoulded component

• Add snap features to eliminate 4 additional fasteners

The resulting design might contain only 12 parts—a 50% reduction—while simultaneously improving weatherproofing performance and reducing assembly time from 4.5 minutes to 1.8 minutes per unit.

Agricultural Equipment Applications

Nova Scotia's agricultural sector, particularly in the Annapolis Valley and surrounding regions, relies heavily on specialised equipment that must withstand harsh operating conditions while remaining serviceable in the field. DFA principles applied to agricultural machinery design can yield significant benefits:

• Modular subassembly design enabling faster field repairs

• Standardised fastener selections reducing inventory requirements

• Tool-free access panels for routine maintenance points

• Self-aligning bearings and bushings simplifying replacement procedures

Marine Equipment Considerations

The Maritime provinces' extensive fishing and marine industries present unique DFA challenges due to corrosive saltwater environments and the need for reliability in remote operating conditions. Effective DFA for marine applications prioritises:

• Minimising dissimilar metal contacts to prevent galvanic corrosion

• Designing for assembly and disassembly with cold, wet hands or gloves

• Incorporating visual and tactile alignment features for poor-visibility conditions

• Selecting fastener types appropriate for repeated service intervals

Material and Process Selection for Optimal Assembly

DFA considerations extend beyond part geometry to encompass material selection and manufacturing process decisions. The choice of materials and processes directly affects assembly characteristics and overall product cost.

Polymer Components and Consolidation Opportunities

Modern engineering polymers enable consolidation strategies that were previously impossible with traditional materials. A single injection-moulded component can integrate features that might require 10 or more separate metal stampings, castings, and fasteners. Common consolidation opportunities include:

• Living hinges replacing separate hinge pins and bushings

• Snap-fit features eliminating threaded fasteners

• Integrated cable management channels

• Moulded-in colour eliminating painting operations

• Textured surfaces replacing separate grip components

While tooling costs for injection moulding can be substantial—ranging from $15,000 to $100,000 or more for complex tools—the per-unit cost savings often justify these investments for production volumes exceeding 5,000-10,000 units annually.

Sheet Metal Design Optimisation

For lower-volume production common in Atlantic Canadian manufacturing, sheet metal fabrication often provides the most economical solution. DFA principles for sheet metal assemblies include:

• Designing self-locating tabs and slots for accurate positioning during welding

• Incorporating bend reliefs and corner reliefs to prevent material tearing

• Standardising bend radii to minimise tooling changeovers

• Designing for laser or waterjet cutting to eliminate secondary operations

Fastener Selection and Reduction Strategies

Fasteners represent a disproportionate share of assembly time and cost in most mechanical products. Studies consistently show that fastening operations account for 30-50% of total assembly time, making fastener reduction one of the highest-impact DFA strategies.

Fastener Standardisation

Many assemblies suffer from fastener proliferation—using multiple sizes, types, and drive styles without functional justification. A systematic fastener audit often reveals opportunities to reduce variety by 40-60% without compromising performance. The benefits extend beyond assembly time to include:

• Reduced inventory carrying costs

• Fewer tools required on the assembly line

• Lower risk of incorrect fastener installation

• Simplified service procedures for end users

Alternative Joining Methods

Modern manufacturing offers numerous alternatives to traditional threaded fasteners, each with specific advantages for particular applications:

Snap-fit features provide permanent or semi-permanent joints with zero additional hardware and assembly times under 2 seconds. Properly designed cantilever snaps can achieve pull-out forces of 50-200 Newtons, suitable for many structural applications.

Adhesive bonding distributes stress across large areas, eliminates stress concentrations from fastener holes, and can join dissimilar materials. Modern structural adhesives achieve shear strengths of 20-30 MPa, rivalling traditional mechanical fasteners.

Ultrasonic welding creates permanent joints in thermoplastic components within 0.5-2 seconds, ideal for high-volume production of sealed enclosures.

Implementing DFA in Your Organisation

Successful DFA implementation requires organisational commitment beyond individual engineering decisions. Companies achieving the greatest benefits typically follow structured implementation approaches.

Cross-Functional Team Engagement

DFA works best when designers, manufacturing engineers, assembly technicians, and procurement specialists collaborate from the earliest design stages. Manufacturing personnel often possess invaluable tacit knowledge about assembly difficulties that may not appear in formal documentation. Regular design reviews with cross-functional participation identify issues when changes are least expensive to implement.

Prototype and Pilot Assembly Evaluation

Physical prototypes remain essential for validating DFA improvements. Timing actual assembly operations, documenting handling difficulties, and measuring defect rates during pilot production provide objective data for design refinement. Video recording of assembly operations enables detailed analysis of worker motions and identification of subtle inefficiencies.

Continuous Improvement Integration

DFA should integrate with broader continuous improvement initiatives rather than functioning as a standalone activity. Tracking metrics such as parts per product, assembly time per unit, and first-pass yield creates accountability and demonstrates the business value of DFA investments.

Partner with Expert Engineering Support

Implementing effective Design for Assembly requires both technical expertise and practical manufacturing experience. Whether you're developing a new product or seeking to reduce costs in existing designs, professional engineering analysis can identify opportunities that deliver measurable returns.

Sangster Engineering Ltd. brings decades of mechanical engineering experience to manufacturers throughout Nova Scotia and Atlantic Canada. Our team understands the unique challenges facing regional manufacturers and provides practical, implementable solutions that balance theoretical optimisation with real-world constraints. From initial DFA analysis through detailed design development and manufacturing support, we partner with clients to achieve their cost reduction and quality improvement objectives.

Contact Sangster Engineering Ltd. today to discuss how Design for Assembly principles can reduce your manufacturing costs while improving product quality. Our Amherst, Nova Scotia office serves clients throughout the Maritime provinces and beyond, delivering professional engineering services that drive competitive advantage in demanding markets.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.