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10 Principles of Design for Manufacturability in Mechanical CAD

10 Principles of Design for Manufacturability in Mechanical CAD

Standardize Parts

When designing mechanical parts in CAD, using existing standardized parts whenever possible is a key principle of design for manufacturability (DFM). Standardized parts refer to commonly used off-the-shelf components that are readily available from suppliers and distributors. These include fasteners like screws, nuts and bolts, bearings, gears, springs, shafts, belts and more.

By using standardized catalogue parts rather than custom-made components, designers can achieve several benefits:

  • Reduced costs - Standard parts have already been designed, tested and optimized by manufacturers. Using them eliminates the need for custom tooling and process development, thereby reducing manufacturing costs significantly. Standard parts are also produced at scale, bringing cost advantages.

  • Shorter lead times - Obtaining standard catalogue components from established supply chains is much faster than having to design and manufacture custom parts. This enables faster time-to-market.

  • Improved quality - Since standard parts are thoroughly tested and proven, quality issues are minimized compared to new custom parts. Reliability is higher.

  • Simplified inventory - Keeping stock of standard catalog parts in inventory enables quick assembly versus waiting for custom parts to be made.

  • Interchangeability - Standard parts from multiple vendors are designed for interoperability, enabling flexibility in sourcing.

Therefore, by maximizing the use of proven standard components, designers can optimize the manufacturability of their mechanical designs while minimizing costs and lead times. Exceptions would be for parts that require tight tolerances or unique performance characteristics. But for most common components, leveraging standard catalogue parts is a best practice in DFM.

Minimize Part Count

Reducing the number of parts in a design is a key principle for optimizing manufacturability. The goal should be to simplify the design as much as possible by minimizing the part count.

Fewer parts in an assembly mean:

  • Lower material costs - Less raw material is needed if part count is reduced

  • Reduced assembly time - Assembling a product with fewer parts takes less time and effort

  • Lower inventory costs - Less parts to store and manage in inventory

  • Improved quality - Minimizing part count increases reliability by reducing the number of possible failure points

  • Higher production output - A lower part count enables faster and higher volume manufacturing

Some ways to minimize parts in a design include:

  • Combining multiple parts into single unified parts

  • Eliminating fasteners by using snap-fits, integrated hinges, or monolithic solutions

  • Using common parts across assemblies rather than unique parts

  • Analyzing the design to remove unnecessary parts that do not contribute to functionality

The goal should be to simplify and streamline the design while still meeting the product requirements. Though it may require more upfront design effort, minimizing the overall part count pays dividends when it comes to manufacturability, cost reduction, and quality improvement. This principle applies across industries including automotive, aerospace, consumer electronics, medical devices, and industrial machinery. Every part eliminated improves manufacturability.

Minimize Reorientation of Parts

Design parts in a way that makes them easy to assemble without needing to reorient them frequently during the assembly process. Parts that require minimal manipulation or repositioning to assemble can greatly reduce overall assembly time and cost.

When designing parts, aim to:

  • Maintain a consistent orientation of parts from start to finish of assembly.

  • Design parts that self-locate or only fit together in the proper orientation.

  • Avoid complex, multi-axis insertion directions that require reorientation.

  • Enable vertical stacking or in-line assembly without re-gripping parts.

  • Standardize handing and orientation of similar part types.

Parts that need flipping, rotating or re-gripping during assembly require additional operator time, increase changeover actions, and introduce opportunities for errors. Limiting part reorientation streamlines workflows, reduces assembly complexity and minimizes non-value added motions. This improves manufacturing efficiency and reduces overall assembly costs.

Some examples of design techniques to minimize reorientation of parts includeadding assembly features like chamfers or tapers to guide parts into position, using gravity or automated feeding for vertical stacking, designing parts symmetrically so orientation does not matter, and standardizing part handling procedures. Applying these design principles results in manufacturing processes that are simpler, faster and more cost effective.

Define Acceptable Surface Finishes

When designing parts for manufacturability, it is important to define the required surface finishes based on the function of each part. The surface finish has an impact on the dimensional accuracy and tolerances needed for the part to operate as intended.

Specifying overly tight tolerances and smooth surface finishes increases manufacturing time and cost. This is because achieving very smooth surfaces requires additional processing steps and tighter process control. For parts like bearings or sealed surfaces, smooth finishes are essential. But for many other parts, a rougher finish is acceptable and more economical.

On the other hand, loose tolerances and coarse finishes can reduce quality in certain applications. For example, loose tolerances between mating parts may lead to poor fit, more vibration and other issues. Overly rough finishes cause excessive friction and wear in moving components.

To optimize cost and quality, designers should carefully specify the necessary surface finish based on the function and operating conditions of each part. Non-critical surfaces can have looser tolerances and coarser finishes. Critical surfaces like bearing surfaces and fits between parts should have tighter tolerances and finer finishes.

Choosing the right balance avoids unnecessary manufacturing steps to create unneeded finishes. This minimizes cost while still achieving the required performance and quality. Defining appropriate surface finishes for each part's function is a key principle of design for manufacturability.

Create Modular Assemblies

One of the key principles of design for manufacturability is to break down products into modular assemblies whenever possible. This involves designing components in a modular way using standardized interfaces and parts.

Modular design enables several benefits:

  • Interchangeability - Modules can be swapped out and interchanged easily without affecting the rest of the system. This simplifies service and repair.

  • Upgradability - Modules can be upgraded individually without having to redesign entire products. This makes upgrading simpler and more cost-effective.

  • Reusability - Modules can be reused across multiple products and product generations. This improves design efficiency and reduces costs.

  • Customization - Products can be customized by mixing and matching modules. This allows product variants to be developed faster.

  • Simplified Assembly - As modules are pre-assembled, final assembly is faster with fewer steps.

  • Serviceability - Issues can be isolated to specific modules which can be easily replaced. This improves field serviceability.

To leverage these benefits, mechanical designers should identify opportunities to develop modular components using standard interfaces like fasteners. Matching modular interfaces enables them to be easily connected and disconnected.

Common examples include creating sub-assemblies for electronics, pneumatics, hydraulic systems, sheet metal enclosures, and mechanisms. Using modular design improves manufacturability, quality, and service life of products.

Streamline Manufacturing Processes

When designing parts and products, it is important to select manufacturing processes that are well-suited to the particular design geometry and intended production volume. Attempt to minimize manufacturing steps and operations that provide no added value or function.

The goal is to streamline the manufacturing process as much as possible to reduce cycle times and costs. For low to medium volume production, processes like injection molding, casting, and CNC machining are typically good options for mechanical parts. For higher volumes, sheet metal fabrication and extrusion are often preferable.

Evaluate the part geometry and features early when selecting the optimal manufacturing process. Avoid unnecessary changes in orientation and handling during manufacturing by designing parts and products suitable for the process capabilities. Minimal changes in orientation enable continuous workflow and automation.

Also, minimize secondary machining operations, drilling/tapping operations, deburring, and other non-value added steps. Design parts with tolerances, surface finishes, and features that align with the primary manufacturing process as much as possible. Consider the limitations of the manufacturing method chosen.

Overall, choosing manufacturing processes wisely based on volumes and design can significantly reduce cycle times, changeovers, errors, and costs. It enables the creation of products optimized for manufacturing.

Consider Process Limitations

When designing parts in CAD, it is important to take into account the capabilities and limitations of the manufacturing processes that will be used. Understanding the processes available, as well as their strengths and weaknesses, ensures the part design is optimized for the selected manufacturing method.

Some key factors to consider for common manufacturing processes:

  • Machining - Features like deep pockets or complex 3D geometry can be difficult to machine. Avoid thin, unsupported walls and features like threads in drilling directions.

  • Injection molding - Limit undercuts, uniform wall thickness is ideal. Simple, two-piece molds are most cost effective.

  • Casting - Rounded corners, draft angles and uniform wall thickness help flow of material into mold. Avoid complex geometries.

  • Sheet metal - Optimize bend radius, access gaps. Limit number of bends and features. Account for material grain direction.

  • Stamping - Simple shapes with uniform wall thickness work best. Limit intersecting geometry. Deep draws increase tooling complexity.

  • Forging - Rounded edges and generous fillets reduce material cracking. Uniform sections prevent uneven cooling.

Keeping manufacturing processes in mind while designing in CAD ensures the geometry is optimized. Simple, manufacturable designs reduce costs and speed up production. Analyzing manufacturability early also prevents late-stage redesigns that can delay projects. By considering process capabilities during CAD, designers can avoid creating complex, expensive designs that are difficult or impossible to manufacture.

Use Suitable Tolerances

When designing parts in CAD, it is important to apply suitable tolerances based on the part's function and other requirements. Tighter tolerances generally increase manufacturing cost, while looser tolerances may negatively impact quality, safety or performance.

There are several key factors to consider when defining tolerances:

  • The function of the part and how tolerances impact performance. For example, tolerances for a bearing raceway must be tight to allow smooth rotation. But the housing may have looser tolerances with no functional impact.

  • How parts will mate together. Make sure clearances between mating parts are adequate. Too tight may cause jamming, too loose can reduce precision.

  • Manufacturing process capabilities. Processes like machining and injection molding have inherent limitations on achievable tolerances. Understand these and design accordingly.

  • Measurement and inspection capabilities. Looser tolerances are easier to measure and reduce rejection rates.

  • Material properties can dictate tolerances needed. For example, plastics shrink as they cure.

  • Cost implications of tight vs loose tolerances. In general, tighter tolerances require more precise tooling and processes, increasing costs.

Set tolerances with both function and manufacturing in mind. Strike a balance between tight enough to ensure quality while not being excessively tight to inflate costs unnecessarily. Work closely with manufacturing engineers to define and validate appropriate tolerances. Perform tolerance stack-up analysis for assemblies. Revisit tolerances as needed during prototyping and testing. Following these DFM principles will help optimize the relationship between tolerances, costs and quality.

Design for Easy Assembly

Design for easy assembly should be a primary consideration in mechanical design and CAD. Incorporating features that aid in part orientation and simplify assembly can significantly reduce assembly time and cost.

There are several techniques that can be used to optimize parts for easy assembly:

  • Providing lead-in chamfers and tapers to aid part mating and orientation. The chamfers and tapers help guide parts into position and alignment.

  • Using self-locating features like pins, bosses, and snap fits to position parts correctly without the need for additional alignment steps. These features can speed up assembly by automatically aligning parts.

  • Color coding parts and/or adding visual indicators for foolproof orientation. Clear visual cues make assembly intuitive and prevent errors.

  • Designing symmetric parts that do not require orientation alignment. Symmetric parts can be assembled without concern for orientation.

  • Minimizing fastener types and incorporating fastener capturing features to prevent loose fasteners. Different fastener types slow down assembly.

  • Standardizing part handing and orientations for subassemblies. Consistent orientations simplify assembly instructions and training.

  • Optimizing the sequence of assembly operations to maximize efficiency. The optimal build sequence minimizes changes in part orientation.

Following DFM principles like these when designing mechanical parts in CAD software ensures the end designs are optimized for fast, simple assembly without errors or rework. It results in significant cost reductions in production by minimizing assembly labor, training, documentation and quality control needs.

Poka-Yoke (Mistake Proofing)

Poka-yoke, also known as mistake proofing, is an important DFM principle that involves designing parts in a way that prevents errors during manufacturing or assembly. The goal is to use efficient methods to avoid simple human mistakes that result in defects.

Some common poka-yoke techniques used in mechanical design and manufacturing include:

  • Designing parts so they cannot be assembled incorrectly. For example, using asymmetrical part geometries so parts only fit together one way.

  • Incorporating guide features like pins, channels or chamfers to aid in correct part alignment during assembly.

  • Using sensors and markers on parts that can detect issues and stop the manufacturing line.

  • Adding step-by-step visual instructions for assembly at workstations.

  • Using different connector sizes or shapes to prevent use of wrong cables or fasteners.

  • Enabling foolproof inspection systems to identify defects early.

The benefits of poka-yoke design features are:

  • They prevent errors from occurring rather than detecting them later.

  • They eliminate the need for inspection and rework, improving quality.

  • They reduce overall manufacturing costs due to less scrap and faster processing.

  • They guide workers to the proper assembly sequence and orientation.

Poka-yoke techniques demonstrate how simple design considerations can mistake-proof products and result in higher reliability. Mechanical designers should leverage poka-yoke principles like part asymmetry, guides, sensors and instructional design to eliminate errors in manufacturing and assembly. This can create substantial improvements in quality and productivity.

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