Design of a truss structure to strengthen hoist rails
During my Master’s course, I had the opportunity to intern at Kenworth, the largest truck manufacturing company in North America. I interned at their Renton Plant in Washington during my summer term. During my internship, I overlooked the daily production of the sleeper cabs for the trucks and noticed that the hoist tracks had started to deform which made the hoist in-operational for the major portion of the day. To overcome this and impart more strength, I designed a simple truss structure which could be used as a superstructure to the rails and increase the strength along with making it more efficient.
Relevant Skills
Solidworks, PTC creo, Ansys Mechanical & prototyping
Project Duration
June 2020 - September 2020
Understanding the problem
The over head hoist system is used to transport heavy parts throughout the plant. It is used to transport the powertrain parts from their engine construction room into the frame and chassis build area. As the production rate has been ramped up to meet the increased demand for the new efficient and reliable trucks, the system was configured to carry 18000lbs and has been quite reliable through the time. The wear and tear however had deformed the rails which regularly caused production line snags and increased maintenance. To help improve the structural rigidity of the rails and add reduce the downtime, I designed a simple truss superstructure which would be retrofitted onto the existing hoist.
Solution
Improving the structural rigidity was of paramount importance. We decided that the most effective way forward was to provide structural support to the existing rails. The support would improve on the overall strength of the hoist system and also reduce the maintenance required for the rails. The structure would be manufactured at the plant itself before being retrofitted onto the rails. I found that a simple truss structure would be a good way to improve the rigidity of the system. It could be manufactured in-house using simple channels and rectangular beams for the cross members.
Designing a retrofitted truss superstructure
To begin with the design of the truss structure, we first began with a few hand sketches of the truss and understanding the forces that act on the members. I then proceeded to turn those drawings into 3D Models using Solidworks and PTC Creo. To design the internal members of the truss structure, I computed free body diagrams for each of the joints in the truss.
I modeled these members using Solidworks and used weldment tools to generate a complete 3D CAD design. The members of the truss were designed to be all 1 m long with internal angles at 60˚. The cad model was also analyzed using Ansys. Based on the results we obtained from the hand calculations, I chose steel square tubing having a 40 mm X 40 mm and a thickness of 4mm.
Cad Design
I designed the truss support structure using Solidworks Weldment workbench. The structure would be retrofitted on top of the overhead hoist and will be welded into place. The structure would help carry loads up-to 4000 lbs and would be operated remotely by the operator. The support structure would also be easy to maintain and would be constructed in-house by the plant production and maintenance crew. The total length of the truss is 4m long and 1m wide with a height of 0.7 m. All the members are 40mm X 40mm square tubing and all internal angles are equal.
Generating a truss structure on Solidworks Weldment using stainless steel square tubing
All the members of the truss structure were 1 m in length with all internal angles at 60˚
Structural Analysis
The truss structure was further analyzed using ANSYS to understand the maximum deformation and maximum equivalent stress acting on the body. As the truss structure would be retrofitted onto the the hoist, we consider it to utilize fixed supports. The major load gets distributed between the verticals and the weight acts at the Centre of Gravity. A fine mesh of 20mm was created which gave us a few interesting results.
Total Deformation Results
Equivalent Stresses Results
Reflections
Some of my major Takeaways from my experience at Kenworth were:
Diverse team, multiple perspectives: It was an amazing experience working with a hugely diverse team with people from varying backgrounds. Each one of us brought our own specialized skill set and approached the project in different ways. I understood that in order to work on a design for a project, it is crucial to have a complete view of the project and approach the project from a holistic perspective.
North America’s largest trucks: It was a very humbling experience to see, manage and execute the production of Kenworth Trucks. The trucks use parts of the best quality and are built in a clean and organized environment. It was quite an exhilarating experience driving these powerful trucks around the closed testing track at the PACCAR Technical Center.
Efficient testing: The emphasis on quality and safety by Kenworth was very encouraging. The design for the truss structure was analyzed multiple times and redesigned to improve the safety features of the structure. It was also interesting to see how a mock up of the structure was also built to test the fit and finish after retrofitting.
Setting daily goals: I found that by setting goals for myself on a daily basis helped me to organize my schedule in an efficient way and incorporate all of my responsibilities into my daily schedule. This helped me stay on top of all deadlines and was able to better prepare for design reviews and weekly reports.