Ken YoussefiUC Berkeley*Design for Manufacturing and Assembly

UC Berkeley

Design for manufacturability (also sometimes known as design for manufacturing or DFM) is the general engineering art of designing products in such a way that they are easy to manufacture.

Design for manufacturing (DFM) is design based on minimizing the cost of production and/or time to market for a product, while maintaining an appropriate level of quality. A primary strategy in DFM involves minimizing the number of parts in a product.

DFM describes the process of designing or engineering a product in order to facilitate the manufacturing process in order to reduce its manufacturing costs.

Design for Manufacturing and Assembly

Ken YoussefiUC Berkeley*Design for Manufacturing and AssemblyDesign for manufacturing (DFM) is design based on minimizing the cost of production and/or time to market for a product, while maintaining an appropriate level of quality. The strategy in DFM involves minimizing the number of parts in a product and selecting the appropriate manufacturing process.

Design For Assembly (DFA) involves making attachment directions and methods simpler.

UC Berkeley

"Design for Manufacture" (or DFM) means the design for ease of manufacture of the collection of parts that will form the product after assembly and

"Design for Assembly" (or DFA) means the design of the product for ease of assembly.

Thus, "design for manufacture and assembly" (DFMA) is a combination of DFA and DFM.

UC Berkeley*

UC Berkeley

Steps to be taken when using DFMA during designThe DFA analysis is first conducted leading to a simplification of the product structure.

Then, using DFM, early cost estimates for the parts are obtained for both the original design and the new design in order to make trade-off decisions.

During this process the best materials and processes to be used for the various parts are considered.

Once final selection of materials and processes has occurred, a more thorough analysis for DFM can be carried out for the detail design of parts.

DFM Method1. Estimate the manufacturing costs.2. Reduce the costs of components.3. Reduce the costs of assembly.4. Reduce the costs of supporting production.5. Consider the impact of DFM decisions on other factors.

*DFMA Method

1. Estimate the Manufacturing CostsKen YoussefiUC Berkeley*

UC Berkeley

Elements of Manufacturing Cost of a Product

Manufacturing Cost of a ProductComponent Costs (parts of the product)Parts purchased from supplierCustom parts made in the manufacturers own plant or by suppliers according to the manufacturers design specifications

Assembly Costs (labor, equipment, & tooling)

Overhead Costs (all other costs)Support Costs (material handling, quality assurance, purchasing, shipping, receiving, facilities, etc.)Indirect Allocations (not directly linked to a particular product but must be paid for to be in business)

Fixed Costs vs. Variable CostsFixed Costs incurred in a predetermined amount, regardless of number of units produced (i.e. setting up the factory work area or cost of an injection mold)

Variable Costs incurred in direct proportion to the number of units produced (i.e. cost of raw materials)

2. Reduce the Cost of ComponentsUnderstand the Process Constraints and Cost DriversRedesign Components to Eliminate Processing StepsChoose the Appropriate Economic Scale for the Part ProcessStandardize Components and ProcessesAdhere to Black Box Component Procurement

Redesign costly parts with the same performance while avoiding high manufacturing costs.Work closely with design engineersraise awareness of difficult operations and high costs.Understand the Process Constraints and Cost Drivers

Redesign Components to Eliminate Processing StepsReduce the number of steps of the production processWill usually result in reduce costsEliminate unnecessary steps.Use substitution steps, where applicable.Analysis Tool Process Flow Chart and Value Stream Mapping

Choose the Appropriate Economic Scale for the Part ProcessEconomies of Scale As production volume increases, manufacturing costs usually decrease.Fixed costs divided among more units.Variable costs are lower since the firm can use more efficient processes and equipment.

Standardize Components and ProcessesEconomies of Scale The unit cost of a component decreases as the production volume increases.Standard Componentscommon to more than one productAnalysis tools group technology and mass customization

Adhere to Black Box Component ProcurementBlack boxonly give a description of what the component has to do, not how to achieve itSuccessful black box design requires clear definitions of the functions, interfaces, and interactions of each component.

3. Reduce the Costs of AssemblyDesign for Assembly (DFA) indexIntegrated Parts (Advantages and Disadvantages)Maximize Ease of AssemblyConsider Customer Assembly

DFA SystemsBoothroyd Dewhurst DFM & AMunro & Assoc. (Design Prophet/Profit)Others

Design for Assembly Index

Determining the Theoretical Minimum Number of PartsDoes the part need to move relative to the rest of the assembly?Must the part be made of a different material from the rest of the assembly for fundamental physical reasons?Does the part have to be separated from the assembly for assembly access, replacement, or repair?

Advantages of Integrated PartsDo not have to be assembledOften less expensive to fabricate rather than the sum of each individual partAllows critical geometric features to be controlled by the part fabrication process versus a similar assembly process

Minimize Ease of AssemblyPart is inserted from the top of the assemblyPart is self-aligningPart does not need to be orientedPart requires only one hand for assemblyPart requires no toolsPart is assembled in a single, linear motionPart is secured immediately upon insertion

Consider Customer AssemblyCustomers will tolerate some assemblyDesign product so that customers can easily and assemble correctlyCustomers will likely ignore directions

4. Reduce the Costs of Supporting ProductionMinimize Systemic Complexity (inputs, outputs, and transforming processes)Use smart design decisionsError Proofing (Poka Yoke)Anticipate possible failure modesTake appropriate corrective actions in the early stagesUse color coding to easily identify similar looking, but different parts

5. Consider the Impact of DFM Decisions on Other FactorsDevelopment TimeDevelopment CostProduct QualityExternal FactorsComponent reuseLife cycle costs

DFMA provides a systematic procedure for analyzing a proposed design from the point of view of assembly and manufacture. This procedure results in simpler and more reliable products that are less expensive to assemble and manufacture. In addition, any reduction in the number of parts in an assembly produces a snowball effect on cost reduction because of the drawings and specifications that are no longer needed, the vendors that are no longer needed, and the inventory that is eliminated. All of these factors have an important effect on overheads, which, in many cases, form the largest proportion of the total cost of the product.DFM and DFA Benefits

DFMA tools also encourage dialogue between designers and the manufacturing engineers and any other individuals who play a part in determining final product costs during the early stages of design.

This means that teamwork is encouraged and the benefits of simultaneous or concurrent engineering can be achieved.

The savings in manufacturing costs obtained by many companies who have implemented DFMA are astounding.

DFM and DFA Benefits

*DFM and DFA BenefitsIt reduces part count thereby reducing cost. If a design is easier to produce and assemble, it can be done in less time, so it is less expensive. Design for manufacturing and assembly should be used for that reason if no other.

It increases reliability, because if the production process is simplified, then there is less opportunity for errors.It generally increases the quality of the product for the same reason as why it increases the reliability.

Less parts to design, document, reviseLess Bill of Material (BOM) cost, parts to receive, inspect, store, handleLess labor and energy to build productGets into the customers hands fasterLess complexitySimpler assembly instructionsHigher qualityHigher profit margin

DFM and DFA Benefits

More competitive in the marketplace

Quantitative method to assess design

Communication tool with other engineering disciplines and other departments (Sales, etc.)

Greater role for other groups while still in the engineering phase such as Manufacturing

Since almost 75% of the product cost is determined in the engineering phase, it gives a tool to attack those hidden waste areas before committing to a design

Fact: Fasteners typically account for 5% of BOM cost, yet contribute to 70% of the labor cost!

DFM and DFA Benefits

The design stage is very important in product design. Most of the product lifecycle costs are committed at design stage.

The product design is not just based on good design but it should be possible to produce by manufacturing as well. Often an otherwise good design is difficult or impossible to produce.

Typically a design engineer will create a model or design and send it to manufacturing for review and invite feedback. This process is called a design review.

If this process is not followed diligently, the product may fail at the manufacturing stage.

DFM and DFA

UC BerkeleyDFM and DFADFM and DFA starts with the formation of the design team which tends to be multi-disciplinary, including engineers, manufacturing managers, cost accountants, and marketing and sales professionals. The most basic approach to design for manufacturing and assembly is to apply design guidelines. You should use design guidelines with an understanding of design goals. Make sure that the application of a guideline improves the design concept on those goal.

UC Berkeley

If these DFM guidelines are not followed, it will result in iterative design, loss of manufacturing time and overall resulting in longer time to market. Hence many organizations have adopted concept of Design for Manufacturing.

Depending on various types of manufacturing processes there are set guidelines for DFM practices. These DFM guidelines help to precisely define various tolerances, rules and common manufacturing checks related to DFM.

DFM and DFA

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesMinimize part count by incorporating multiple functions into single parts. Several parts could be fabricated by using different manufacturing processes (sheet metal forming, injection molding). Ask yourself if a part function can be performed by a neighboring part.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesModularize multiple parts into single sub-assemblies.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesDesign to allow assembly in open spaces, not confined spaces. Do not bury important components.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesParts should easily indicate orientation for insertion. Parts should have self-locking features so that the precise alignment during assembly is not required. Or, provide marks (indentation) to make orientation easier.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesStandardize parts to reduce variety.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesDesign parts so they do not tangle or stick to each other.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesDistinguish different parts that are shaped similarly by non-geometric means, such as color coding.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesDesign parts to prevent nesting. Nesting is when parts are stacked on top of one another clamp to one another, for example, cups and coffee lids

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesDesign parts with orienting features to make alignment easier.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesProvide alignment features on the assembly so parts are easily oriented.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesDesign the mating parts for easy insertion. Provide allowance on each part to compensate for variation in part dimensions.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesDesign the first part large and wide to be stable and then assemble the smaller parts on top of it sequentially.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesIf you cannot assemble parts from the top down exclusively, then minimize the number of insertion direction. Never require the assembly to be turned over.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design GuidelinesJoining parts can be done with fasteners (screws, nuts and bolts, rivets), snap fits, welds or adhesives.

UC Berkeley

Ken YoussefiUC Berkeley*DFM and DFA Design Guidelines

UC Berkeley

Ken YoussefiUC Berkeley*Minimizing the Number of PartsTo determine whether it is possible to combine neighboring parts, ask yourself the following questions:If the answer to all questions is NO, you should find a way to combine the parts. Must the parts move relative to each other?Must the parts be electrically or thermally insulated?Must the parts be made of different material?Does combing the parts interfere with assembly of other parts?Will servicing be adversely affected?

UC Berkeley

Ken YoussefiUC Berkeley*Minimizing the Number of PartsThe concept of the theoretical minimum number of parts was originally proposed by Boothroyd (1982). During the assembly of the product, generally a part is required only when;A kinematic motion of the part is required.A different material is required.Assembly of other parts would otherwise be prevented.If non of these statements are true, then the part is not needed to be a separate entity.

KISS Keep It Simple Stupid

UC Berkeley

Ken YoussefiUC Berkeley*DFM Design GuidelinesAnother aspect of design for manufacturing is to make each part easy to produce.The up to date DFM guidelines for different processes should be obtained from production engineer knowledgeable about the process. The manufacturing processes are constantly refined.

UC Berkeley