P16682: AATech GE90 Tube Trim
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

Planned

Completed

Not Completed

Outstanding action items:

Phase Activities

Detailed Design Phase

Detailed Design Phase

Review

Customer Requirements

Customer Requirements

Engineering Requirements

Engineering Requirements

Preliminary System Design

System Overall View (old)

System Overall View (old)

Overall system-level view

Overall system-level view

Prototyping, Engineering Analysis, Simulation

Tolerance Stack-Up

The end stop is fixed directly to the rotary tabletop. In the worst case, its allowable deviation from the center of rotation is 0.0175 inches. The total deviation from the center for all stacked parts cannot exceed this allowance in the worst case.

The deviation is given by:

The base plate fixture is fixed to the rotating plate, which is in turn fixed to the rotary tabletop. Because its X-position is adjustable, the relevant deviation is in the Y-direction. However, because it is not a datum fixture, its allowable deviation must be measured relative to the end stop. The total allowable deviation between the base plate fixture and the end stop is 0.0125 inches in the Y-direction.

The deviation is given by:

In each case, the deviation of the component is the total distance between the actual geometric reference of the part and the ideal position of that reference, relative to the part below it. For the rotary tabletop, the deviation is measured to the center of rotation of the rotary table.

With all parts designed so that dimensions are measured from the geometric reference, the expected deviations will be equal to the machining tolerances.

The plate will be waterjetted; its expected tolerances are:

The end stop will be CNC-machined; its expected tolerances are:

The rotary table will be purchased; its measurement accuracy for the centering is:

With these tolerances, the maximum deviation of the end stop from the center of rotation will be:

The base plate fixture will be composed of a purchased aluminum extrusion, a purchased slide table, and a manufactured base fixture, with respective tolerances of 0.003 inches, 0.003 inches, and 0.005 inches; the total deviation is:

The Y-tolerance in the fixturing is:

Based on these tolerances, our system is expected to be able to machine the part to within the required tolerances.

The Y-tolerance of the pin assembly only needs to be such that the spring stop contacts the inner tube in the worst case, as the Y-position will not be easily adjustable after machining. The spring stop plate is 0.63 inches wide, so the Y-tolerance in the pin assembly’s position relative to the end stop is:

Based on the above machining tolerances, we do not expect this tolerance limit to be a major area of concern.

The Z-tolerance of the tool is controlled relative to the base plate fixture, as that is where the outer tube height is dimensioned to. During assembly of the system, the bottom of the cutting disk will be calibrated to a specific height relative to the datum dowel in the base plate fixture. The tool mount height will then be locked in place so that it cannot be adjusted beyond the indexing required in the course of normal operation.

With the cutting height locked relative to the datum, the only tolerance in the Z-position will be in the calibration piece itself:

The calibration block will be CNC-machined; its expected tolerance is:

Based on this tolerance, we expect to be able to maintain an acceptable tube height.

Cutting Speed

The linear cutting speed [inches/second] for a tool with a certain outer radius r [inches] and angular velocity w [radians/second] is given by:

The rotating table adds or subtracts some additional linear speed, depending on the direction. For an angular velocity of approximately 6 rpm (0.628 radians/second) and an outer radius of the outer tube of 0.125 inches, the worst case for the linear cutting speed is to subtract 0.0785 inches/second from the tool speed.

The material of the tube will have some minimum required linear cutting speed. The combined worst-case linear speed will have to exceed this in order for the machining operation to be successful. The cutting disc on the dremel is currently replaced when its diameter is 0.5 inches or less, so for a range of angular velocities, the worst-case cutting speeds are given below:

Dremel Speed Worst-Case Cutting Speed
25000 rpm 654 in/s
30000 rpm 785 in/s
35000 rpm 916 in/s
40000 rpm 1047 in/s

Data on the required cutting speeds for operations of this type have been difficult to locate. However, the current operation can successfully cut the outer tube at a dremel speed of approximately 35000 rpm, so using the same cutting disc at the same speed will ensure the material can be cut.

Push-Plate Force Rate

To move the inner tube away from the cutting tool while the outer tube is being cut, a spring-loaded push-plate is attached to the tool mount. Experimentation shows that at least 5 lbf is required to move the inner tube when it is resting against the outer tube. From this position, less than 15 lbf is required to move it to the opposite wall of the outer tube.

The cutting disk has a maximum radius of 0.5 in and a minimum radius of 0.25 in. The spring will be more compressed when the cutting disk is smaller, so it will exert more force on the inner tube. The spring will need to be compressed when it contacts the inner tube when the disk is at its maximum radius; otherwise, it will exert no force.

Based on these constraints, and with two springs of equal force rates, the limits for the equilibrium extension, full compression, and spring constant are as follows:

Equilibrium Extension Full Compression Minimum k Maximum k
0.25 in 0.5 in 10 lbf/in 15 lbf/in

Ergonomic Assessment

Humantech scoring - results based on old process:

Drawings, Schematics, Flow Charts, Simulations

Overall System

Overall system-level view

Overall system-level view

Rotary Table

Part Fixture

Tool Mount

Stress Analyses

Bill of Material (BOM)

Test Plans

The test plan is meant to address all of the engineering requirements. Testing will be completed in two steps: the first step will be to collect data after the bending operation to make sure the parts are within the allowable ranges for the cutting operation.

The second step will be to run the same parts through our process and collect data on the final dimensions.

Ideally, these tests would be run on three sets of at least thirty parts each, run at two different times by two different operators. However, we are allowed only a limited number of parts for testing and validation purposes, so we will use as many as possible.

Design and Flowcharts

Risk Assessment

Risk Assessment

Risk Assessment

FMEA

Design FMEA

Design FMEA

Design Review Materials

Plans for next phase

Detailed Design Phase

Detailed Design Phase

Lessons Learned


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