Multidisciplinary Engineering Senior Design Project Project Card Guide Redesign and Manufacture Preliminary Design Review November 11, 2005 Project Sponsor: Dwayne Niewiemski Team Members: Bill Rowe Brad Good Laren Olson Team Mentor: William Scarbourgh Acknowledgements: Dr. Wayne Walter Kate Gleason College of Engineering Rochester Institute of Technology

Project Overview

Project Background Data Systems (MDS) has designed a printed circuit board (PCB) chassis Chassis is 1U high and can have up to eight PCB assemblies slid into the front of the chassis and mounted into a backplane assembly To support the PCBs, MDS is using a custom designed aluminum extrusion as a PCB card guide Having difficulties when the PCB extrusion guides are fastened onto the chassis To mount the card guides to the chassis and cover, MDS uses flat-head machine screws (21 in total to complete the assembly)

Project Background Cont. To keep costs down, the card guide is not tapped for each machine screw The screw forms the thread while being fastened into the aluminum extrusion The problem is when the screw is trying to “catch” into the aluminum extrusion to form the first thread The screw is walking up and down the slot of the card guide If the screw is not centered in the chassis hole, the screw head will not sit flush into the countersink

Major Needs of the Sponsor Reduce the total number of screws Make the chassis easier to assemble Come up with solutions to grounding issues and reduce cost Make board removal and maintenance easier Modify or get rid of the small faceplate

Major Needs of Sponsor Cont. Have fewer screws on the faceplates Have screws on the faceplate that do not get lost or discarded Have self taping screws to hold the aluminum extrusions in place A working prototype Tests proving the worth of the prototype

Project Schedule Gantt Chart – Used to keep design team on a strict schedule – To prevent time loss – To prevent team from getting side-tracked

Gantt Chart Events Allocated Time (weeks) Prob. Def. & Brain Storming Spec. & Mock up Function Anal. & Research Design Concept & Scope Detail Drawing Prototype Construction Prototype Testing Feasibility Analysis Re-design & Modifications Prototype Construction Prototype Testing Feasibility Analysis Presentation & Validation

Order Winners Reduce the total number of screws Make the chassis easier to assemble Come up with solutions to grounding issues and reduce cost Make board removal and maintenance easier Modify or get rid of the small faceplate Have fewer screws on the faceplates

Order Winners Cont. Have screws on the faceplate that do not get lost or discarded Have self-taping screws to hold the aluminum extrusions in place Maintain thermodynamic efficiency and improve if possible Be reliable Be user friendly

Needs Assessment Concept Development Detailed I-DEAS Drawings Preliminary Budget Methods of Analysis Technical Data Report (PDR)

Needs Assessment Cont. A working Prototype Tests performed on the Prototype Final Report / Group Binder / Log Book

Concept Development and Feasibility Assessment

Concept Development Concept Development Process – Objective Tree – Process of Proposed Design – Brainstorming – Research

Objective Tree PCB Chassis QualityEfficiencyCost Effectiveness Dura.Easy to Maintain Resis. to Corrosion Easy to Produce Low Maintenance Affordable to Produce Affordable to Customer Easy to Modify Easy to Repair More Access. Fewer Screws Panel is Easier to Access Boards are Easier to Replace

Process of the Proposed Design

Concept Development Cont. Solutions for solving structural assembly issues – Using only self-threading screws no guiders – Using self-threading screws with guiders

Concept Development Cont. Self-threading screws no guiders – Problem: The machine screws that secured the sheet metal into place do not sit well in the extrusions Machine screws ride up and down on the extrusion and give operators a lot of problems during the manufacturing process

Concept Development Cont. – Solution: To have machine screws replaced by self-threading screws

Concept Development Cont. Using self-threading screws with guiders – Problem: Too many screws on the chassis Cost Same as the last concept

Concept Development Cont. Solution: – Guiders punched into the sheet metal – Self-threading screws

Concept Development Cont. Solutions for solving grounding and faceplate issues: – Hairpin Clips with edges on extrusions – Redesign of extrusions with edges – Redesign of extrusions with an offset from the backplane – Captive screws instead of machine screws – Rubber bumpers – Faceplate clip

Concept Development Cont. Hairpin clips with edges on extrusions – Problem: Customer had difficulties using the current face- plate design Customer would lose the screws that fastened the PCB to the chassis Loose screws could cause a short circuit or would allow the PCB to slide out of the chassis altogether Expensive grounding clips on the circuit board

Concept Development Cont. Solution: – Hairpin clips will hold the PCB into place – To dislodge the PCB from the extrusion and the chassis, all you would have to do is pinch the ends of the hairpin – Mounted in such a way that they ground the circuit board

Concept Development Cont. Redesign of extrusion with edges – Problem: Expensive $0.12 clip are being used on current design The PCBs need to be grounded to pass FCC regulations

Concept Development Cont. Solution: – Redesign the extrusions – The edge for the aluminum extrusions touches the bottom and top of the gold strips on the circuit board – This removes the need for the expensive clips

Concept Development Cont. Redesign extrusions with an offset from the backplane – Problem: Current grounding design is expensive.

Concept Development Cont. Solution: – Cause a slight amount of misalignment between the backplane and the PCB when they connect to one another – Creates an upward force on the back end of the PCB

Concept Development Cont. Captive screws instead of machine screws – Problem: Customer had difficulties using the current face- plate design Customer would lose the screws that fastened the PCB to the chassis Loose screws could cause a short circuit or would allow the PCB to slide out of the chassis altogether

Concept Development Cont. Solution: – Replace the thumb screws that hold the faceplate into place with captive screws – Captive screws by design are held to the chassis by a spring mechanism

Concept Development Cont. Rubber Bumpers – Problem: Expensive $0.12 clip are being used on current design The PCBs need to be grounded to pass FCC regulations

Concept Development Cont. Solution: – Attaching the rubber bumpers to the PCBs – The bumpers apply a vertical force on the circuit boards and in doing so ensure the boards are grounded

Concept Development Cont. Faceplate Clip – Problem: MDS’s circuit boards has an optional attachment Attach the two faceplates attached to one another because there is not an extrusion separating the two boards Not attractive More Screws

Concept Development Cont. Solution: – Use a U-shaped metal fixture to hold the two boards together – Use one screw to hold them together

Feasibility Assessment Feasibility Assessment Chart – Ranks the concepts – Ranks them according to important factors

Feasibility Assessment Chart

Feasibility Assessment Cont. Feasibility assessment for concepts solving structural assembly issues – Using only self-threading screws no guiders – Using self-threading screws with guiders

Feasibility Assessment Cont. Self-threading screws no guiders Pros – Similar to the original design – Fixes assembly issues – Screw sit well in the extrusion – Save on labor because less time to assemble Cons – Cost: Machine Screws= $0.03 Self-threading screws= $0.09 – Do not get rid of any of the screws Ranking on Feasibility Assessment Chart= 5 th

Feasibility Assessment Cont. Self-threading screws with guiders Pros – Uses the original design chassis with guiders – The guiders will be punched while the sheet metal is bent into its final shape – Will restrict the lateral movement of the extrusions during assembly – Will allow the assembler to spend less time screwing the screws into place – Fewer screws Cons – Untested – Self-threading screws cost more then machine screws – Punching is an added cost Ranking on Feasibility Assessment Chart= 2nd

Feasibility Assessment Cont. Feasibility assessment for concepts solving grounding and faceplate issues: – Hairpin Clips with edges on extrusions – Redesign of extrusions with edges – Redesign of extrusions with an offset from the backplane – Captive screws instead of machine screws – Rubber bumpers – Faceplate clip

Feasibility Assessment Cont. Hairpin Clips with edges on extrusions Pros: – Solves some of the grounding issues – Cost Hairpin: $0.05 Thumb screw: $0.06 – Edges on extrusions might create more contact for ground the PCB Cons: – Edges are untested – Hairpins are untested – Edges might damage PCBs Feasibility assessment chart ranking= 1st

Feasibility Assessment Cont. Redesign of extrusions with edges Pros: – Same cost – May solve EMI – Easy to do Cons: – Not a tested – Damage PCBs with edge – Does not solve faceplate issues Feasibility Assessment Chart Ranking= 7th

Feasibility Assessment Cont. Redesign of extrusions with an offset from the backplane Pros: – Same cost – Four points of solid contact which meet the grounding requirements – Simple (less=more) Cons: – Unproven – Does not solve faceplate issues Feasibility Assessment Chart Ranking= 4th

Feasibility Assessment Cont. Captive screws instead of machine screws Pros: – Will not come off the chassis – “user friendly” Cons: – Cost: Thumb screws: $0.06 Captive screws: $1.49 – Does not fix grounding problem Feasibility Assessment Chart Ranking= 8th

Feasibility Assessment Cont. Rubber Bumpers Pros: – Cost Adhesive rubber bumpers: $0.07 Grounding clips: $0.12 – PCB is grounded Cons: – Unproven – Does not solve faceplate problems Feasibility Assessment Chart Ranking= 3rd

Feasibility Assessment Cont. Faceplate Clip Pros: – Cheap – Fewer screws – The boards are even more secure Cons: – Untested – Not much of a change Feasibility Assessment Chat Ranking= 6th

Feasibility Assessment Conclusion Do not use: – Captive Screws – Edges in Extrusions Two Prototypes – Prototype A (safe) will have: Redesign of extrusion Self-threading screws No guiders Offset from the backplane – Prototype B (risk) will have: Redesign of extrusion Self-threading screws Guiders Rubber bumpers Faceplate clip Hairpin

Analysis and Conclusions

Cost Analysis Prototype Part Numbers: Prototype Costs: DesignTotal Number of Parts Current Design186 Prototype A175 Prototype B178 DesignTotal Cost Current Design$90.40 Prototype A$91.13 Prototype B$91.46

Assembly Efficiency The manual assembly efficiency: Current DesignPrototype APrototype B %14.588%14.500%

Anticipated Design Challenges/Risks Prototype A (safe design): – Redesign of extrusion – Self-threading screws – No guiders – Offset from the backplane Challenges/Risks – Cost must be kept low – Has not been Tested – Working with the Vendor to get cheap and actuate pieces

Anticipated Design Challenges/Risks Cont. Prototype B (risk) will have: – Redesign of extrusion – Self-threading screws – Guiders – Rubber bumpers – Faceplate clip – Hairpin Challenges/Risks: – Cost – Not tested – Hairpins may not hold PCB in place – Faceplate clip may be unnecessary

SD II Project Plan Follow EDGE design process – Gantt Chart Order prototype components Assemble prototypes Test and troubleshoot the prototypes Select the best design Present a final design to Sponsor and at the Final Review

References Boothroyd, Geoffrey, Peter Dewhurst, and Winston Knight. Product Design for Manufacture and Assembly. New York: Marcel Dekker, “Do-It-Yourself dot com.” Home Improvement, Repair, Remodeling, and Hardware Store. 30 October “Fastenal.” Industrial and Construction Supplies. 30 October “McMaster-Carr.” Supply Company. 30 October “Metal-Grip.” Your Trusted Fastener Source. 30 October “Mouser Electronics.” Electronic Component Distributor. 30 October Rutledge, John phD. Dr. John Rutledge Blog. 7 November “Stainless Fasteners.” Industrial Directory. 30 October

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