Parametric Design of Mechanical Systems: A Case Study on Bolt and Belt Pulley Design, Slides of Computer-Aided Design for Engineers

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ParaMetric

Design

OutLine  ParaMetric Design

• Design phase info flow
• Parametric design of a bolt
• Parametric design of belt & pulley
• Systematic parametric design
• Summary

Information Flow

Special Purpose Parts: Features Arrangements Relative dimensions Variable list Standard Parts: Type Variable list

Parametric Design variable values Design e.g. Sizes, dimensions Materials Mfg. processes Performance predictions Overall satisfaction Prototype test results

Detail Design Product specifications Production drawings Performance Tests Bills of materials Mfg. specifications

ConFig Design

Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected]

Engineering 11

Real Life

Application

3x00 Seismic Protection Analysis Plan

• Measure/Calc Weight and Center of Gravity
• Consult S2/§19 for Lateral Loading Criteria (0.63g)
• Consult Mechanical Design Drawing for Seismic Structural- Element Location & Configuration
• Use Newtonian Vector Mechanics to Determine Force & Moment Loads
• Use Solid-Mechanics Analysis to Determine Fastener (Bolt) Stresses
• Use Mechanical-Engineering & Materials Properties to determine Factors of Safety

BMayer

3x00 Seismic Loading & Geometry

BMayer

Loading Geometry Detail

Bracket Stress Analysis

• Analysis Parameters
  1. Assume Failure Point at M6 or M10 Bolts
  2. FOUR (4) Angle Brackets With a total of 8 Connecting & Anchor Bolts, Resist Shear
  3. Two Bolts Per Point, Each Bolt Bears 50% of Load
  4. Bolt Axial-PreLoad is negligible (Snug-Fit)
  5. Shear Load Per Restraint Point = 500lb/2.22kN
  6. Use Von Mises Yield Criteria: S (^) sy = 0.577Sy
• Results

2.22 kN

Bolt Bolt Ssy Load Stress,^ τ^ Factor of Size & Fcn Material (MPa) (MPa) Safety M6 Connector SS-304 139.1 13.84 10. M10 Anchor SS-304 139.1 4.74 29. 3x00_Seismic_Analysis_0202.xls Docsity.com

ParaMetric Bolt Design

• From Analysis Determine Failure Mode as AXIAL TENSILE YIELDING (E45)
• The Configuration Design Sketch

d

L

LT

shank

head

threads

Load Load

Use Engineering Analysis

• Using ENGR36 Methods Determine the Bolt Load as 4000 lb (4 kip)
• Thus the “Functional Requirement” for the Bolt

Fp ≥ 4000 lbs

 To Actually Purchase a Bolt we need to Spec a DIAMETER, d , and a length, L  Find d Using the FR & Stress-Eqn

p

AS (^) p Fp A S

4000 lbs = ≥ 4000 lbs ⇒ ≥

Design DECISION

• We Now need to make a Design Decision – We get to CHOOSE - Bolt MATERIAL  Gives Proof Stress - Bolt DIAMETER  Gives Supporting Area
• In this Case Choose FIRST a Grade-5, Carbon-Steel Bolt with S p = 85 000 psi (85 ksi)

Spec Bolt

• We can PICK any Grade-5 Bolt with a Diameter >0.245” - To Keep down the Bulkiness of the Hardware choose d = ¼” (0.25”)
• Thus We Can Specify the Bolt as
  • Grade-
  • ¼-20 x 6”
    • CHOOSE Coarse Thread (the “20”)
    • CHOOSE a Bolt Length of 6” based on size of Parts Connected

Forward & Inverse Analysis

• As Design Engineers we Can approach the quantitative Functional Requriments (FR’s) in Two Ways

1. Forward ≡ Guess & Check

• Set the ENGR-Spec and then Check if the FR is Satisfied (The Seismic Case)
• e.g; Guess a ½-12 Grade-2 bolt & chk S (^) p

2. Inverse

• Start with FR and Use Math & Science to effectively DETERMINE the ENGR-Spec