Designing with Assembly Variants

 

Introduction

When designing a product that requires assembly, it is common to have multiple variants of the product to accommodate different features, components, or configurations. For example, a desk chair may come in variants with different seat materials, armrest types, caster wheels, etc. The design process needs to account for these variants to ensure all product configurations work as intended and can be efficiently manufactured and assembled. In this article, we will explore strategies and considerations when designing products with assembly variants.

Modular Design

A modular design approach is key for managing complexity and variety when designing product families and assembly variants. The goal is to break the product down into discrete modules or components that can be mixed and matched to create the desired product configurations.

For example, a modular desk chair may have separate interchangeable modules for the:

• Seat (mesh, fabric, leather)
• Backrest (mesh, plastic, upholstered)
• Armrests (fixed, adjustable, no arms)
• Base/wheels (plastic, metal, casters, glides)

With clever modular design, a large variety of chair models can be assembled from a smaller set of common components.

Benefits of Modular Design

There are several benefits to modular design when dealing with assembly variants:

• Simplifies manufacturing - Common components can be mass-produced for use across multiple product variants. Less unique parts to manufacture.
• Simplifies inventory - Fewer total part numbers to stock for assembly. Reduces variability in the supply chain.
• Enables customization - Customers can tailor the product by selecting preferred modules. Allows mass customization.
• Facilitates upgrades - Modules can be switched out to upgrade or alter the product configuration.
• Simplifies assembly - Assembly workers build each variant from familiar common modules. Easier to learn and faster to assemble.
• Isolates testing - Modules can be independently tested and qualified. Critical for quality control.

Modular Design Strategies

Here are some useful strategies when architecting a modular product family design:

• Identify the most variable product dimensions or features the modules should accommodate. The desk chair example has clear variability in seat, backrest, armrests.
• Group less variable features into shared modules when possible. The base/wheels is often standard across chair models.
• Define clean module-to-module interfaces. Physical and functional. Allows interchangeability.
• Minimize inter-dependency between modules. Avoids complex interactions across variants.
• Standardize connection methods between modules. Ex: fasteners, locating features. Consistency aids assembly.
• Utilize common parts/materials within each module grouping where possible. Reduces part proliferation.
• Seek to maximize module commonality across product variants where feasible. Leverage re-use.
• Use modular simulation models to evaluate product performance. Verify critical functions met.

Thoughtful modular architecture is key for managing complexity for assemble-to-order or engineer-to-order type product strategies.

Assembly Process Design

The assembly process itself needs to be designed to efficiently handle combining the various modules into their numerous configurations. Some key considerations:

Assembly Line Configurations

• Mixed-model lines can assemble different variants intermixed. Maximizes flexibility but can increase complexity.
• Dedicated lines are simpler but less flexible. Group lower volume variants on dedicated specialty lines.
• Reconfigurable lines strike a balance. Sections of the line are reconfigured as needed for product changeovers. Adds cost for reconfigurability.

Workstation Design

• Arrange workstations according to assembly sequence of base modules. Similar variants will follow similar routing.
• Position modules within easy reach for operators to grab, orient and attach to subassemblies. Optimizes ergonomics and motions.
• Clearly label, orient and present modules to aid visual inspection and assembly. Mistake-proof if possible.
• Standardize fastening methods at each station. Repeating actions improves operator intuitiveness and rhythm.

Tooling and Fixtures

• Design fixtures to locate, support and restrain modules for assembly in multiple configurations. Quick changeover is vital.
• Develop common bases, pallets or frames to assemble modules on. Promotes flexibility across variants.
• Utilize quick connect/disconnect fastening methods for module connections. Ex: cam locks, quarter turns, magnets. Speeds assembly and reconfiguration.
• Provide sufficient tooling sets at each station for the range of fastener types encountered. Organize tools for easy selection.

Material Supply

• Kit modules required for each variant’s assembly sequence. Deliver modules just-in-time to point-of-use.
• Kanban systems help regulate and trigger module component replenishment to assembly processes.
• Smart factories can use RFID, barcodes, AGVs to deliver correct modules to stations. Automates material supply.

Efficient assembly of product variants requires meticulous process design and optimization.

Quality Control Planning

Another vital consideration is developing robust quality control procedures when dealing with high product variety from multiple module combinations.

Strategic Inspection Points

Determine critical inspection points:

• Receiving inspection of individual modules and raw materials
• In-process inspection of subassemblies at key stages
• Final end-of-line audit of completed variants
• Periodic audits of modules in inventory

Focus on locations where defects are likely introduced or able to be detected.

Control Plans

Define detailed control plans for each product configuration:

• Inspection criteria such as dimensions, tolerances, specifications, functional criteria
• Tools or gauge requirements
• Sample size and frequency
• Reaction plans if defects detected
• Documentation methods

Standardize plans across common modules and assembly steps when possible.

Automated Testing

Leverage automation for inspection where feasible:

• Vision systems to verify form, fit and cosmetic defects
• Gauging fixtures to confirm dimensional conformance
• Functional testing stations to validate performance
• Leak, pressure, vibration tests for robustness

Automated testing provides rapid objective evaluation 24/7.

Traceability

Maintain traceability of individual modules:

• part numbers
• serial numbers
• manufacture dates
• inspection/test records

Critical for tracking quality issues to root causes. Helps contain potential recalls.

With diligent quality control planning, high quality and reliability can be maintained even across thousands of product configurations.

Lifecycle Considerations

Lastly, it’s important to consider the impact of variants when designing products and assembly processes.

Services and Maintenance

• Service manuals must provide instructions for all fielded configurations.
• Diagnostics may need programming for the range of possible feature sets.
• Replacement parts inventory grows with greater product variety.
• Technicians require training to service diverse configurations.

Upgrades and Enhancements

• Existing modules may need redesigned to accommodate upgrade needs.
• New modules designed must be backwards compatible with old configurations.
• Field upgrade kits simplify modifying existing installed variants.

Phase-Outs and Obsolescence

• Module commonality aids extending life of aging product platforms.
• Declining demand for niche variants can trigger phase outs.
• Proactively define phase-out plans as variants near end of life.

Recycling and Disassembly

• Disassembly may need to flexibly handle diverse configurations.
• Common fasteners, labels, materials aids separating modules for recycling.
• Modular design can extend product lifecycle through re-use of modules.

Conclusion

Designing products with assembly variants creates additional complexity across the product lifecycle. A well architected modular design is key to maximizing flexibility and commonality. Assembly processes need to be optimized to efficiently handle multi-configuration production. And comprehensive quality control plans are essential to deliver consistent and reliable product quality across high variation. When executed deliberately, assembly variants can be leveraged to satisfy diverse customer needs, enable mass customization and simplify manufacturing.

Key Takeaways

• Utilize modular architecture to create product family platforms
• Standardize and reuse common modules across variants
• Design flexible assembly lines and workstations
• Develop robust quality control procedures for complex configurations
• Carefully consider lifecycle impacts of high product variety

Frequently Asked Questions

What are the pros and cons of designing products with assembly variants?

Pros:

• Allows customization to meet diverse customer needs
• Modules enable mass configuration options from fewer unique parts
• Platform designs maximize re-use and commonality
• Simplifies manufacturing, inventory management and assembly
• Facilitates upgrades and enhancements

Cons:

• Increased complexity in product, assembly process, quality control
• Proliferation of part numbers and configurations
• Higher costs for modular components and flexible assembly
• Supply chain challenges managing high mix inventory
• Service and maintenance more complex across configurations

How can you simplify assembly of multiple product variants?

• Utilize a modular architecture to break product into interchangeable modules
• Design product/modules for easy orientation and assembly
• Standardize assembly steps, connections and tooling where possible
• Create flexible assembly stations that can handle multiple configurations
• Kit and deliver needed modules just-in-time to each workstation
• Implement visual cues, mistake-proofing, and ergonomic best practices

How does modular design impact design for manufacturability (DFM)?

Modular architecture complements DFM principles:

• Standardized modules with common parts reduces unique components
• Designed for ease of assembly and connection
• Human factors considered for component handling
• Designed for reliability and quality
• Modules designed for optimal packaging and transport
• Accommodates flexible, low-cost processes and tooling
• Enables just-in-time assembly with minimal inventory

How can quality control be implemented for high variety assembly?

• Define strategic inspection points at critical steps
• Create control plans for each module and product configuration
• Leverage automation for inspection where possible
• Maintain traceability of individual modules
• Focus on defect detection and containment
• Standardize procedures across common modules/assemblies
• Require thorough documentation at each inspection point
• Ensure failed samples trigger reaction plans to address issues

How should end-of-life be handled for assembly variant products?

• Module commonality makes extending product lifecycle easier
• Phase out niche variants with declining demand first
• Reuse any reusable modules in next generation products
• Plan ahead for phase-outs and communicate to suppliers/customers
• Structure bills of materials to simplify configuration management
• Design modules to ease disassembly for maintenance and recycling
• Provide upgraded replacement modules to extend existing product life