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How to design low-cost replacement frames for substantial cost savings now on existing products and/or base next generation products on these low-cost parts..

Text and illustrations Copyright © 2017 by David M. Anderson 

Case Study Example # 1: Low-Cost Rectangular Machine Frame

     This low-cost machine frame can be bolted together rigidly and precisely from parts fabricated on ordinary CNC machine tools. 

    The nodes (not shown) would be the fabricated blocks through which bolts connect their struts and mounts for all machinery components that need to be anchored in that area.  

    The outer edges of a rectangle frame are shown, to which covers could be attached to.

    Interior components and sub-frames would be supported by struts coming from the he main frame nodes discussed below and triangulated to other existing nodes. 

        It is important to note that such a frame replaces both the existing frame and all the existing brackets to support components and sub-frames,   

This eliminates all the problems of welded frames: skill demands, warpage, and post-weld machining on a mega-machine big enough to machine all mounting holes into a warped frame.  One ten foot cube semiconductor frame has to do this twice!

Case Study Example # 2: Low-Cost Machine Frame to Support an Object or Machine

   The low-cost machine frame concept shown bolts to the existing framework of the supported object or machinery   either directly through adapter blocks, shown on each corner of the grey  framework.

    The truss are built as specified below and the trusswork is a fully triangulated space frame that mounts to the floor on three points to install and align quickly and avoid the overconstraints common in all four-point frame mounts.  This truss frame needs could be backward compatible with an existing four-point mounting arrangement, with one new floor mount.  If the supported object can be  supported by three mounts, then the frame would be the simpler octahedron, as illustrated below in the comparison to a square welded frame.


   

Case Study # 3 Example: Commercial vehicle frames. These principles could apply to "work vehicles" whose frames have to support heavy loads, like engine/transmission units for work trucks, engine/generator units for locomotives or portable power plants, buckets or dump bodies for earth-moving equipment, combine equipment and engines for farm equipment, or the loads for heavy-haul trucks or trailers.

The illustration compares the typical heavy, expensive flat frames with light, inexpensive truss framework: The typical flat frames (shown on top) may be supported by I-Beams or channels (in the  case of Semi-trucks) that would have to be very heavy to support heavy loads in the middle of long frames, especially if they were only a few inches high.  Welded frames could be thicker, but at a high cost for steel and skilled labor; for instance, one wheel-loader frame is made from 300 pieces welded together to form the two pivoting frames.

 For large trucks, there are so many weight saving opportunities because the thickness of  a channel frame is determined by the loads around the bolt holes, but since the channel plate must have constant thickness, most of this steel is "loafing" and thus much heavier than necessary.

The Better Way:   On the other hand, in the simplified truss beam example shown in the lower illustration, the truss struts follow the “load paths” for the most efficient structure possible, meaning the lowest weight, and cost, possible for a given load. The design approach is described next. Easy manufacturing processes  are described  further below.

       Detailed Description.  Specifically, the approach would be to replace the usual heavy channels or welded frames with a 3-D truss, consisting of struts and nodes, as described below. Struts would be sized for their specific loads, as shown in the drawing where the longer struts have a greater diameter.  The truss would provide the lightest possible frame for a given strength because its struts would align with all the load paths between axle mounts (shown by half-round cylinders in both drawings). engine/transmission mounts, fifth wheel mounts, cab/body/bed mounts, piston pivots, tank mounts, dumping bodies, and everything else that mounts to a truck frame. The nodes would be placed at all of these mounting locations and the struts would connect them, even if they are not co-planar. This would eliminating all the separate brackets now needed to do this ( One long-time engineer at Freightliner called it a "bracket company" because different brands of purchased components needed different brackets).   CNC machine tools would fabricate all the nodes from bar stock blocks with all the holes and mounting surfaces needed for struts and mounted parts, which could be automatically mass customized for different engines and axles.

            The low-cost truss frame would be backward compatible and designed to "drop in" to your current vehicles, thus providing cost, steel, and weight reduction now and then become the foundation for next generation designs.
            Because the truss would follow the load paths, it would be the lightest possible structure for a given strength, called a constant-stress structure with no excess material that is 'loafing." 

Most of the workshops that  Dr. Anderson has done were for big structures with big loads, like the underground mining front-loaders for Caterpillar, four-axle missile trailers for Italy's Finmeccanica’s DRS division in the U.S., and many large machine frames, like the first two CAD models above. Clients that held these workshops, or the consulting equivalent, are indicated by blue hyperlinks to this page at the client list page.
              

Case Study #4 example: Low-cost Backhoe Boom Replacement for Weldment

The low-cost assembly (upper CAD model) replaces the heavy welded boom (lower photo)

The assembled replacement is a truss, which is the lightest structure for a needed strength, so it uses a fraction of the steel, and material cost, compared to a structure made of heavy plate. The truss is built automatically on ordinary CNC machine tools and assembled by non-skilled labor, as discussed below.  Note that the heavy load exerted by the boom piston is connected to the thick "elbow" structure with the load supported at the ends of two tetrahedrons.  This CAD model and more machine frames  below were drawn by Dr. David M. Anderson, copyright © 2016.  He also has to-scale CAD models for other layouts, like front and rear wheel loader frames, which he will work exclusive with the first mover to contact him

The conventional design in the photo is made by welding many large heavy plates, which has high skill demands and weakens the steel in the heat-affected-zone.. In order to provide accurate mounting holes and surfaces, which is essential for industrial machinery frames, the warped weldment must be machined on an expensive mega-machine with very high hourly costs for positioning, machining, repositioning, and inspections, not to mention transportation and queuing delays.

Low-cost manufacturable replacements can be designed to be back-ward compatible with expensive versions thus offering the following leap-frog strategy:

  • Providing near-term cost reduction without spending the cost, resources, and calendar time for a new product development cycle.

  • Becoming the basis for a next-generation development.
     

This one-day workshop applies very effective DFM principles to large, heavy, or hard-to-build parts for major reduction in cost, material usage, and build  time. These improved designs could then be retrofitted onto current products or used as a basis for new designs.  

The workshop will show how to develop backward-compatible substitutes that will replace expensive weldments, castings, or unnecessarily heavy machined parts with more steel-efficient parts comprised of assemblies of CNC-machined parts that are rigidly and precisely assembled by various DFM techniques.  

Such a manufacturable structure could be based on assembled plates or, for larger structures, look like this illustration, which will be described below in the discussion of trusses that follow the load paths for the highest strength per weight ratio.


Major Cost Reduction for Welded Assemblies

The most applicable large welded assemblies should be analyzed for opportunities at the conceptual level with the goal of avoiding the following costs:

  • high-skill labor cost to weld plus other labor to position, fixture, straighten warpage, and grind.  Skilled labor shortages raise costs and can delay production and lower quality.  Note that welding acute angles (e.g. in welded trusses or diagonal bracing) requires extra skill to get enough heat between diverging members.   For military and mission-critical applications, these  kind of welds require a special certification.

    • high steel usage and cost at a time when steel prices are rising and will continue to rise for raw material and transportation costs both for incoming materials and outgoing products.

    • the cost and delays for annealing the weldments or the risk of fractures from residual stresses.

    • the imprecise and labor intensive practice of mounting parts in slots or large holes and then aligning them manually, or

    • machining large parts after welding, which may require large machine tools and furnaces to anneal them, which:

  • • are very expensive to buy or have high hourly charges to outsource

    • usually involve labor-intensive on-line setups which adds more time to expensive machine charges and delays the flow

    • may involve transportation and queuing delays.

• loss of strength in the heat affected zone from welding and annealing, thus requiring more steel compared to steel used at its full cold-rolled strength.

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 states 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.


Steps for Reducing Cost on Large Parts and Assemblies:

• Identifying 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.

• Brainstorming 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 wide and axisymmetric with the load path to resist buckling. This favors tubing with threaded holes at the end to bolt to the node blocks. Thick wall tubing could be plugged with threaded disks that could be joined to the tubing with a low-heat axisymmetric weld. For smaller wall thickness, a clean, inexpensive strut could be made by swaging down the ends to just past the tap diameter for tapping threads that could then be bolted to the node blocks.  Swaged tubes are shown in the illustration (in grey), which can be inexpensively procured from a swaging 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 attachments 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 show spherical nodes (in red) for clarity.  Actual nodes would each be milled out of bar stock using various design techniques to attach the struts and all the hardware that needs to be supported.  Dr. Anderson helps companies design these through on-site consulting after the workshop and through remote consulting and design studies.

 

Comparisons with welded cubes. The usual orthogonal welded frame (like the one on the right) needs much skilled labor to weld, which results in a warped structure that must have holes drilled after welding on an expensive mega-machine for large structures.  Plus all 8 corners would have to be ground for appearance or sanitation.  And this is without diagonal bracing, which would require 6 more braces and 12 more welds, all of which will induce residual stresses that will reduce the load capacity or require more material.
      By contrast, the truss (on the left) has all parts machined automatically on ordinary CNC machine tools.  The struts are assembled to 6 nodes precisely and rigidly by unskilled labor.  The simplest truss, the octahedron, is shown, although trusses can be designed to accept any geometries of mating attachments, like existing rectangular objects. 
       For mounting loads, orthogonal frames, like the one shown on the right, usually need many extra brackets to attach hardware to the frame. This is so common that one long-term engineer at a commercial truck company described it as a  bracket company!
       With trusses, the nodes also serve as all the mounts for all the mounted hardware, since all the struts and  nodes can be uniquely fabricated (this is called mass customization)  so that a node is next to every hardware mount. Trusses have inherent diagonal bracing and can support loads without any warpage, overconstraints, or residual stresses.

Truss Frame with Bearing Mounts for Shaft.   © 2016 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.
 

Catenary Truss.  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 railroad engines and passenger cars. 

            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.

            This illustration shows a physical model, which can produce many ideas quickly and can be passed around in meetings..  These model parts are made by ZomeTool, which was designed by PhD mathematicians for molecular biologists and structural engineers in addition to being widely available as toys (see http://www.zometool.com/science/ ).

            In this model, the red spheres (like in the above CAD models) represent the nodes that connect the struts and are also the mounting blocks for objects.  The black spheres support the ends of the beam and anchor it.

 

 

 

 

 

 

 

 

 

Next Example: The Zig-Zag Truss for Long Structures.  Similar techniques can be used to create a

"zig-zag (Warren) truss for booms, masts or long structures.
       Additional truss members in a perpendicular plane can provide
lateral stiffness.  Similarly, three strut columns could provide lateral and torsional stiffness.  These will be the lightest and strongest structures possible without the cost, excess steel, and difficult machining of long channels/bar-stock and without the warpage, distortion, imprecise hole locations, and skill demands of welded trusses. 

     
The Results

The results would be much lower cost from:

• quick machining on readily-available CNC machine tools

• quick setup concurrently engineered for whole part families to further reduce machine time

• quick assembly with accuracy assured by programmably machined features

• higher strength per weight (meaning higher strength per material cost) because of:

• more structurally efficient designs (lower stresses to support a given applied load)

• all material would remain at cold-rolled strength and heat-treated strengths could be preserved
 

These truss structures would provide the absolute lowest weight for a needed strength.


Cost Reduction for Large Machined Parts

For fabricated parts now made of excessively thick steel, the workshop group would start by identifying the loads and load paths. Then we conceive of structural shapes that match the load paths, which is will probably not be a constant cross-section slab that has a lot of understressed material that leads to unnecessary cost and weight. Then we brainstorm on optimal assemblies of CNC-machined parts whose cross-sections are matched to the load, thus approaching constant-stress parts, which have the highest strength per weight. This would be accurately and rigidly assembled by various DFM techniques in which the precision is entirely determined automatically by the CNC machines. 

These techniques include DFM Guideline A3, in which mating parts would be aligned to sub-mill tolerances by inexpensive pairs of round and diamond dowel pins in reamed holes. Parts could be designed to be self-fixturing or simple fixtures could be concurrently engineered to hold parts during alignment and clamp together for fastening.  Aligned parts would then be bolted/riveted together with appropriate bolt strength, torque settings, and retention strategies.

Cost Reduction for Large Cast Parts

Cast parts require expensive tooling and lengthy and costly setups, which usual force the OEM to order a large batch to amortize the setup costs,  but this violates lean production principles and makes it hard to do build to order (see http://www.build-to-order-consulting.com/sbto.htm).    For large or complex castings, there may be a limited supplier base who can cast them, thus causing transportation costs, shipping delays, and possibly queues for busy suppliers.  For example, for a certain size of large Diesel engine blocks, there are only two suppliers in the world who can make them.  Further, castings all require machining, which may require an expensive mega-machines for large castings, which may also incur lengthy setups, queues, and delays to ship large castings to shops with mega-machines.

The workshop group would start by identifying the loads and load paths. Then we conceive of structural shapes that match the load paths. Then we brainstorm on optimal assemblies of CNC-machined plates whose cross-sections are matched to the load, thus approaching constant-stress parts, which have the highest strength per weight. This would be accurately and rigidly assembled by various DFM techniques, like Guideline A3 mentioned above.

The above techniques could replace many hard-to-make large parts and fasten multi-part assemblies.

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 would 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:  workshop attendees should attend the two-day DFM seminar first.   Work could proceed immediately with design studies (next point), which could be followed by an in-house seminar or webinar.


Alternative: Consulting Design Studies

        An alternative would be ask Dr. Anderson to do the above as a design study on a consulting basis, working with relevant design 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.

Workshops Done and Proposed:

     Dr. Anderson has already done workshops for low-cost frames for: underground coal mining vehicles; four-axle trailers for heavy loads; large paper converting machinery; 12' high box-makers; dock-scale natural gas compressors; fuel-cell back generator port block; framework for large ASRS warehouse; low-cost joints in a 400' long window glass vacuum chamber; cabinetry strategy to accept off-the-shelf enclosure modules; and nuclear plant worst-case scenario filters.
       Dr. Anderson has personally done both welding and owned his own machine shop, and, thus, is a good position to advise on tradeoffs between welding and machining.  See sixth paragraph of his credentials page.

       He has proposed this workshop or consulting studies for:

  • Many low-cost frame and structures for industrial machinery (like CAD model above)

  • Molding machinery foundations (CAD model available)

  • Large medical equipment gimbals (CAD model available)

  • Semi-truck chasses

  • Very large dump-trucks

  • Wheel-loader (wheeled front loader) (CAD model available)

  • framework for farm machinery

  • Mobile (distributed) power plant chasses

  • Diesel engine blocks (concept sketch available)

  • Long-span structures that support heavy loads, like railroad cars and locomotive chasses (physical model available)

  • Llight-weight long-span structures for high-speed motion (physical model available)

             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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