Universal Fixturing System for Cast-Iron Parts

OVERALL DESIGN CONCEPT

Task: Build a fixturing system that can universally clamp/grasp pre-processed cast-iron parts with arbitrary topology; part volume is no larger than that of a shoe box 

Elements

1. Servo actuated ball bearing adaptive vise (servo operates camshaft)

2. Mechanical rotation mechanism operated by direct drive servo motor

3. Aluminum extrusion T-Slot frame as iterative R&D platform (allows modular mounting) 

4. Friction-based mechanisms for first iteration → bearings added with testing and wear

Settled Upon Option: 2 DOF Ball Bearing Adaptive Vise

Top 5 Design Requirements: Robust Mechanisms (mechanical integrity), Repeatable Integrated Workflow, Modularity (quick changes), Design Scalability, Cost 

INSPIRATION

• “Restoring a Giant Fractal Vise”

  • An alternative to the actual fractal vise, this system is simpler and more robust. It makes use of simple, linear jaws and a ball bearing reservoir for part retention.

• Practicalmachinist.com forum post on the Adaptive Vise

  • Mention in comments of having “machined many castings with this vise…I cannot recall any part that has slipped or moved while machining”

T-Slot Slides (above): These slides use a UHMW plastic slip system and are the easiest to implement for a first iteration. Wear is a potential issue with this slide system but the vise does not experience significant forces against the slides. Rather, these forces are largely experienced in the fore/aft motion. Testing is required to ensure that this system will work well. Roller bearings are the other option. 

INTEGRATION PLAN

The original workflow (shown in website animation) is largely maintained with this universal fixturing design. Although, once the arm grabs and transports the part from the conveyor to the camping location, I plan to include a slight change. The system might encounter an issue where if both sides of the vise were to actuate forward at the same time, one side might come into contact with the cast-iron part prior to the other side. This is a big issue because the part in question could be knocked off from its electromagnetic bond with the arm. To mitigate this, the system must offer support on a 3rd face (underneath) prior to the clamping operation.

Highlighted in green below is a vertically actuating platform that offers underside support as soon as our arm brings the cast-iron part into the central location. Making the assumption that the part is not centered between either end of the vise, the vertically actuating platform will offer support so the adaptive vise can clamp correctly. One side might come into contact first, but this is no longer an issue.

The underside platform will actuate down when the vise needs to rotate and back up when the part needs to be grinded. Pressure and vibration from the grinder will surely push the clamped part out of place if underside support does not exist, so this addition becomes necessary. The underside platform will also need force feedback to ensure proper clamping force and mitigate the risk of damaging our arm and/or the electromagnetic system. Servo feedback on all actuating mechanisms will need to exist and these systems should integrate with our central hardware. 

VALIDATION STRATEGY

1. Theoretical Validation

   1. Run through as many cycles of the workflow as possible, identify all issues from these cycles and iterate upon them

   2. FMEA: Identify incompetencies in the design to assist with testing focus

   3. Extraneous testing such vibration tests

2. Simulations and CAE

   1. FEA: System-wide simulations to ensure integrity of the vise and its integration with the T-Slot frame. Invented mechanisms such as the rotation system are of utmost importance for simulation (alongside physical iterative testing)

   2. Thermal Analysis: The foundry environment is thermally dynamic

   3. Note: Only so much can be learned from simulation. This is the type of system that would strongly benefit from rapid physical iteration

3. Testing, Experiments, and Iteration

   1. Build prototypes as fast as possible and run them with the rest of the workflow

      1. Apply various loads to prototypes to test for durability. Record this testing in a datasheet for continuous improvement/validation

   2. Material Testing: try different materials where it makes sense to and measure subsequent performance (comparative analysis)

   3. Electrical/harness integration testing: Make sure system is clean and wires protected

4. On-Site Testing and Validation

   1. Install device in customer foundry and begin testing (replicate this environment as closely as possible at office prior to onsite)

   2. Operations: Conduct full-scale operation and monitor for any issues on objectives of interest (make sure device can clamp all parts in question, issues with actuation, etc.)

   3. Adjustment/Optimization: bring all necessary tools and be able to make adjustments onsite (relative to issues that we see most often in testing)

5. Documentation & Reports (including field/service)

   1. Report: create a detailed report on all validation processes and iteration

   2. Develop installation procedure and General Purpose manual for field service

6. LSS Continuous Improvement

   1. Employ industry Lean Six Sigma continuous improvements techniques to ensure reliability and integrity of the entire robotic automation system.

   2. Look into documents on continuous improvement measures for RAAS (robotics as a service) companies. I’ve seen some theory of this on Linkedin.

CONSIDERATIONS

Friction from moving parts

• There are several degrees of freedom in the first iteration of my design that do not make use of bearings. This was intentional for the purpose of gauging wear of certain systems and whether or not the inherent friction will actually be a benefit to the integrity of the system (given satisfactory amounts of power and torque from the actuators

• I do have a design in mind for integrating bearings. This will be simple with additive iteration

Size of the T-Slot frame

• In the next iteration, the T-Slot frame should be larger. There are some concerns with the lack of space for actuators and the camshaft which is used to reset the vise jaws

• Simple, parametric change

Servo feedback and data-driven repeatability

• Generally, lower cost servo actuators might not have high enough mechanical advantage for a high torque application such as a vise. The torque specs for various motors must be analyzed and compared to the general torque requirements for securely clamping

URLs (for external parts used in assembly)

• M10 Bolts Mcmaster, M10 Nuts

• 15 series TSlot

• TSlot sliding sleeve bearing for central plate

• Stepper Motor (sample for the sake of CAD)

• T-Slot Framing Flush Bracket