Low-Cost-Truss

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How to Design & Build Ultra-Low Cost Truss Structures

New Article: The Most Advanced Product Development Course
by the author of all 50 DFM article in this site

Trusses have always been the highest strength/weight,
and now can be the lowest cost


The high strength per weight at low cost would be valuable for:
 

Antenna frames for optical and radio telescopes that are (as with most of these examples)  are stronger, lighter, use less material, and cost much less without needing welding  or skilled labor. 

Chasses for trucks, semi-tractors, farm equipment, Earth-moving equipment, etc.

Chasses for racing cars and trucks, which has been used since Maserati developed the “birdcage” space frame in the early 1960's. which consisted of 200 welded tubes that reinforces in high stress areas! The techniques of this page need no welding, no reinforcing, and, with more efficient layout may need up to five times fewer tubes because they follow load paths (as discussed below) so they cost so much less that these design innovations could evolve  into production models.

Long span structures that support heavy loads, like railroad cars and locomotive chasses and elevated rail structures (see first truss shape example below)

Light-weight structures that have to accelerate fast as may be needed to move challenging masses fast.

Solar mirror supports, which will save cost and lower material consumption for solar fields that have hundreds of heliostats and enable much higher mirror mounts that direct more sunlight at towers, that could be lower for a given sunlight directed.

Anchoring and concentrated loads
in aerospace structures that benefit from load-path analysis

Low-cost machine frames that can be backward “drop-in” replacements for nard-to-build weldments: This is the focus on the Steel Reduction Workshop.
 


How to optimize DFM for the highest strength per weight on the lowest fabrication cost, material cost, and overhead cost:
 

For most of the opening opportunities listed above and more, the major .
strategies are the following DFM techniques:

AUTOMATED FABRICATION
 

Design system architecture to be all fabricated on automated CNC machine tools (milling machines, lates, swagging machines, etc) with pre-fab parts rigidly and precisely by DFM techniques described below.


DESIGNING THE OPTIMAL TRUSS SHAPE
 

Synthesize the optimal truss shape in the following these examples from simple planar truss to 3D space frames:
 

2D Planar Trusses.

The Warren Truss:

The three equalateral triangle Warren truss has several times  strength per weight ratio than a flat beam because  flat beam stresses are always much higher near the center, whereas trusses can be designed so that each strut has the same load and they are much lower, as shown in the client example at the right.

 

A simple but higher version of this is the "King Post" truss, that consists of two right-angle  triangle.  On the other hand, more triangles in Warren truss would be lower but less efficient than catenary trusses, (discussed below)  which is the most efficient truss for spans.


The Catenary Truss

A very efficient truss for supporting uniform loads is the "catenary truss.”

A catenary is the shape formed by a chain hanging between two level points.  Ancient builders would trace this shape and build masonry domes and arches using this shape because the loads would transfer cleanly along columns of blocks without needing any sideways stresses, This catenaries are  very efficient. Some of the machinery catenary trusses presented below also have the  catenary in compression and do not need sideways bracing.  Trusses with the catenary in tension can be designed to have constant stress, thus being made in one piece.

Structurally, the catenary truss is the ideal beam because the catenary shape matches the load curve for beams that are supported at the ends, thus providing the greatest strength for the least material, the lightest weight, and the lowest cost.  This type of truss is utilized in the most advanced bridges   The inverse of this is a suspension bridge in which the catenary is a long cable with smaller cables connected to the bridge surface.  Catenary trusses, as shown below, can be utilized as cost-efficient frame work that need to support weights (loads) over challenging distances, especially for sub-frames that need to be light for accelerations. This may be the best design approach for long beams like large machinery or frames for the lightest railroad tracks.

Uniform loadc atenary
Truss with
constant-stress
lower "strap"

 

 

This truss geometry will support a uniform load, like on a floor or a road bed, and exert a constant stree on the  lower "strap" that supports the truss at each end.    Therefore, the strap can be the same thickness and be made of one piece of metal or composite carbon fiber. 

See Figure 16.4 from Chapter 16, "Finding Efficient Forms for Trusses," from Design of Building Trusses, by James Ambrose,  Professor of Architecture, USC.  1994, John Wiley & Sons.

Catenary  supporting
constant stress
"bridge" member

 

 

 

In this truss, a true catenary arch member supports the a constant stress "bridge"  surface member, which can be made from a one piece of metal of composite carbon fiber, which greatly simplifies construction.  The inverse of the catenary could be suspended from two towers, like the Golden Gate Bridge.  Note that no diagonal struts would be needed, which would also simply machinery construction.  See Figure 16.7 from the above reference, in Chapter 16, "Finding Efficient Forms for Trusses,"

Like all trusses discussed above, all the parts can be built automatically on ordinary CNC machine tools.  assembled by non-skilled labor, and retain neat treatments or cold-rolled strength of the raw materials.

      

3D SPACE FRAMES

 

Space frames are three dimensional trusses that are fully triangulated and can resust linear forces in all directions and resist torsion along all axes.  The     simplest space frams is the tetrahedron which can support a point load on three struts (like a camera on a tripod.

 

The Octahedron

The Octahedron is  a true space frame that will support a solid object on the top triangle while it and the truss is supported on the bottom triangle.

 

 

 

MORE EXAMPLES AND CONCEPTS

Truss Frame with Bearing Mounts for Shaft.  
© 2018 by Dr. David M. Anderson.

Two "tripods" can be bolted to any truss (in this case, the above octahedron) to mount other structures like mount bearing blocks to rigidly support machine shafts, axles, pivots, or any rotating members.  The bearing blocks have bearing mount surfaces bored and reamed and also tapped holes on the outer surface on which to bolt the struts.
      The tripod mounts result in fully triangulated rigidity and is much stronger per weight than the usual techniques us using heavy plates or weldments to mount bearings
    If a single structural mount was needed, one tripod could be utilized with an appropriate mounting surface.
       Any subassembly could be bolted to any side or multiple sides of any basic truss frame for functionality, for instance, bearing blocks, in any plane.


The Strategy

The strategy would be to commercialize proven parts with backwards compatible replacements with the same functionality and strength (possibly enhanced) with much less total cost and weight. This would provide cost reduction now on existing products. This would also encourage a leap-frog strategy where these low-cost parts could then become the basis for new generation products.

The specific strategy to eliminate the abovementioned costs would be to create an optimized concept/architecture for constant-stress trusses and structures (which, by definition, use the least material) with the following steps.

The Approach

The approach would be based on the following premises:

Fabrication. All machined parts would be small enough to be set up and made quickly on readily-available CNC machine tools in a single setup (Guideline P14 in the DFM book, which specifies that all operations should be done in one setup on versatile CNC machine tools).
            Welded parts would be limited to those that are small enough to be machined after welding by the typical in-house machine tools. This may be appropriate for bearing blocks and other junction parts if not feasible to machine from a single block.

Assembly. Precise alignment of these assembled pieces would be assured by the programmable part manufacture.

Mass Customized Tooling.   Dr. Anderson has written two books on mass customization, and had experience designing flexible tooling as Manager of Flexible Manufacturing at Intel's Systems Group and his own Anderson Automation, Inc.  Based on all this, his workshops show how to design flexible processes that can programmably offer variety with less cost, time, space, weight, and material usage.
        The general principles of mass customizing process design are  summarized on the web article  shows flexible processes for electronics (Figure 1) and  flexible processes for fabricated products (Figure 2)  at http://www.build-to-order-consulting.com/mc.htm .  Another big benefit of flexible tooling is that it enables spec changes or customer-induced changes to be implemented faster than with inflexible designs built in hard tooling, thus keeping them off the critical path.


Steps for Reducing Cost on Large Parts and Assemblies:

• Identify existing loads, directions, and attachment points, which would then be graphically represented. In a workshop setting, these could be projected from a active CAD screen or printed on several sheets of large paper with dark lines for the next step.

• Brainstorm on various ways to support these loads, with many ideas sketched on many printouts.

• Then optimize the design of these parts for manufacturability and currently engineered manufacturing strategies for trusses, assembling plates and bar stock, and "space frames."

Trusses consist of struts and nodes:

Struts. Purely tension members could be made of rods; compression struts must be  axisymmetric with the load path and wide enough to resist buckling. This favors tubing with threaded holes at the end to bolt to the node blocks. Very thick-wall tubing could be plugged with threaded disks that could be joined to the tubing with an automatically welded low-heat axisymmetric weld.  For smaller thick-wall thickness, a clean, inexpensive strut could be made by swagging down the ends to just past the tap diameter for tapping threads that could then be bolted to the node blocks. 

Swagged tubes are shown in the illustrations above (in grey), which can be inexpensively procured from a swagging shop.  In one application, a swaged tube cost $40 for a 25 inch long tube, 2.5" OD, with an 1/8" wall that that included drilling-and-taping and facing off for a precision length (wall thickness can go up to 1/4" and higher).  The swagged struts can be made quite large and strong, as was pursued in workshops for Caterpillar's underground coal mining front loaders Finmechanica's four-axle trailers and other workshops indicated by the blue hyperlinks on the client page.  In workshop exercises, Dr. Anderson leads a company team to brainstorm on many concepts for struts-and-nodes to support all the hardware in a frame or structure. 
         The nodes would have bolt holes for the struts and all hardware that bolts to the structure.

Node Blocks. Each node block would be designed and dimensioned so that all operations for node attachment and and object mounting holes would be made in one setup (Guideline P14) on an ordinary CNC machine tool.  Families of similar parts could be machined on flexible fixtures that would be able to make all parts in the family without setup delays and extra cost.  The illustrations below show spherical nodes (in red) for clarity.  Actual nodes would each be milled out of bar stock using various DFM design techniques to attach the struts and all the hardware that needs to be supported.  Dr. Anderson helps companies design these through  consulting after the workshop and through remote consulting and design studies.

 

Workshop

This one-day workshop will apply unique DFM principle to large parts  for half the cost or better and significantly less steel consumption.

This is the most effective way to reduce cost on existing products because it focuses the most effective half-cost DFM principles on the least manufacturable module in industrial machinery: structures and frames, which usually are hogged out of large blocks or are welded and then go to straightening, grinding, and drilling on mega-machines (see cost savings summarized below).

The workshop will show a small group of your people how to quickly design backward-compatible replacements that can “drop in” to existing product designs for significant near-term cost savings without needing a full product development cycle.
 

Workshop Format


The group would explore some of the most promising opportunities in the workshop to the point where they look feasible and it is clear how to proceed at which point responsibility could be assigned to pursue each opportunity.

The group would also identify future opportunities to be explored later based on pre-workshop research that will have identified some opportunities. Opportunities will be summarized and then the workshop group will vote on them for a baseline prioritization of opportunities.

Pre-workshop company research should also plot steel cost from the time current products were designed and extrapolate price trends into the future.

Audience. Product development team with all designated and potential members, with at least one person representing each function and one person knowledgeable about each proposed candidate structure. The workshop would benefit from close proximity to the physical structures being analyzed. 

Prerequisite:  When a DFM class is give, workshop attendees should attend the two-day DFM seminar first.   For a stand-alone workshop, the prerequisite would be be familiarity with the original part, its brackets, and everything that attaches to them, CAD skills, and familiarity with the parts welding process, and company or vendor machine shop operations.  


Alternative: Consulting with company CAD engineer.

        An alternative would be ask Dr. Anderson to do the above as a design study on a consulting basis, working with relevant company engineers and/or CAD engineers.  The joint effort would present the most promising approaches for the company to evaluate, select, and implement.  Dr. Anderson is particularly effective for complex parts that could benefit from more manufacturable design concepts and concurrently engineered low-cost tooling and processing.  He is in a unique position to do machining/welding tradeoffs, since he once had his own machine shop and has done welding since his college years.

        He also has to-scale CAD models for other layouts, like front and rear wheel loader frames, on which he will work exclusive with the first mover to contact him.  Because of his ethics code (from the Institute of Management Consultants) he will avoid conflicts-of-interest by not working with direct competitors, so that means first-come-first-serve for enlisting his considerable experience on these techniques that  he originated.  See client engagements that included this Steel/Cost Reduction workshop, as indicated by blue hyperlinks on his  clients page.  For clients with new challenges, he has a vast library of generic struts already drawn.

All of these principles on DFM can be included in
your
customized class and workshop on DFM or
Advanced Product Development class 

 

If you want to discuss Trusses by phone ot e-mail, fill out this form:

Name

Title/Position

Company/Division

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Phone number

e-mail address

Type of products


 Other challenges, goals, and opportunities:
 

   To Submit, first enter "12" and hit "Enter" to bypass Robo Filter (required field)
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         If your company makes any products that have similar opportunities, contact Dr. Anderson for your own proposal for workshops or design studies that will show you how greatly lower the cost of your hardest-to-design parts.  As a Certified Management Consultant (CMC), Dr. Anderson's high ethical standards  prevent  him from doing this for direct competitors, which means the first to bring him in gets a unique competitive advantage. 


To discuss this further, contact:

Dr. David M. Anderson, P.E.; CMC; Fellow, ASME
HalfCostProducts.com
www.design4manufacturability.com
www.build-to-order-consulting.com
1-805-924-0100; anderson@build-to-order-consulting.com

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