By Executive VP and Co-founder of Quickparts.com Inc.
Low-Volume Layered Manufacturing, LVLM for short, is a design-through-manufacturing method already known by different names in the short time is has been an option. Whether you call it ‘Rapid Manufacturing’ (RM) or the term coined by The Society of Manufacturing Engineers (SME), ‘Direct Digital Manufacturing,’ LVLM has the potential to re-define the way machines and products are designed.
Fig. 1-Rapid Prototyping (RP) machines now use materials strong enough for use as production parts.
This technique provides a method to improve quality, and decrease costs and lead times of products and machines. It reduces cost by eliminating tooling and assembly part count through part consolidation. It increases the efficiency of your development process because you can manufacture new, slightly different parts in just a few days. Use of LVLM methods enable faster and better machine designs, and quicker machine deployment.
A closer look
LVLM is the method of using Rapid Prototyping (RP) equipment to manufacture end-use parts. RP machines make parts through additive fabrication. Parts are made from the bottom up by adding material to the build space. This layer-by-layer process nearly eliminates all part design constraints or rules that exist with traditional manufacturing processes like CNC machining and injection molding.
Currently there are three RP technologies (figure 1) that can manufacture parts suitable for use as end-use parts: FDM® (Fused Deposition Modeling), SLS® (Selective Laser Sintering), and SLA® (Stereolithography).
Each RP technology has its strengths and weaknesses. To be a viable replacement for traditionally manufactured parts, layered manufacturing parts must meet application needs for strength, function, accuracy, and appeal. All three current technologies, FDM®, SLS®, and SLA® meet those needs. Selecting the best one for an application depends entirely on your needs. If strength is a part need, you may find that FDM and SLS systems have a slight edge over SLA systems. All three systems make parts that meet tolerance and accuracy requirements. SLA systems, however, offer the best surface smoothness and manufacture parts the fastest. SLS systems resist heat more than FDM and SLA systems.
original robotic wrist is ‘consolidated’ into a single part,
manufactured using the SLA® process in high-impact ABS-like material.
The original design called for three plates, three standoff posts, and
two adapters, for a total of eight parts, not including the screws. In
addition to reducing part complexity, layered manufacturing also
eliminated tooling for those eight parts.
From expertise in constraints …
Traditional design has always required a good understanding of the constraints the manufacturing process imposes on parts. Training courses in design-for-manufacturing (DFM) and design-for-assembly (DFA) have helped provide the needed knowledge of these constraints.
For example, parts that will be made by CNC machines must not have narrow, deep pockets because the rotating cutter of the machine cannot cut such features. Parts designed for injection molding need drafted walls in the direction of the tool movement to release the part from the tool after molding. Injection molded parts must also be free of undercut or die-locked features. The DFM and DFA rules exist to enforce the constraints of the part’s manufacturing process.
One reason for the delay in the broad adoption of layered manufacturing techniques is insufficient expertise in how to design parts and assemblies that take advantage of the design freedoms it provides.
…to expertise in flexibility
Layered manufacturing enables a part to be made from the bottom up, layer-by-layer, significantly reducing design constraints. Those narrow deep pockets, for example, are not a problem. Similarly, you can include reverse draft in your part, or handle internal, hidden channels.
Part design is no longer compromised by machine tooling. Often, parts requiring an investment in tooling become locked in an un-changeable design to avoid the cost of re-working the tooling or making new tooling. Layered manufacturing, however, does not involve a process that requires expensive, long-lead-time tooling. Thus, it encourages active re-design as you iteratively learn what works and what does not.
This capability not only handles intricate product designs, it promotes product flexibility, allowing customers to change features or continuously improve products without penalty. Since parts made with layered manufacturing have no tooling commitment, changes can be made on the fly based on customer or performance feedback. Such proactive evolution helps engineers stay focused on customer needs.
In addition, LVLM enables a design to be manufactured within a few days of creation. Thus, companies no longer need to face a warehouse full of obsolete products, and instead, can reap the benefits of tighter inventories.
To take advantage of layered manufacturing, engineers need to shift their design process. For example, many manufacturing processes force the use of multiple parts because they cannot accommodate certain types of complexity. LVLM, on the other hand, lets you consolidate parts, combining several parts in an assembly into a single part.
For example, consider the robotic arm (figure 2). The original design for the wrist consists of three plates, three standoff posts, and two adapters, for a total of eight parts, not including the screws. With layered manufacturing, that assembly is combined into a single part; a part that would be impossible to make with CNC or molding methods. Layered manufacturing eliminated tooling for those eight parts, and the bill-of-materials is reduced by seven parts.
Made to fit
Layered manufacturing excels when parts are designed to be made together. This is a new way to think about design-for-assembly. Look at the hand of the robotic arm of figures 3 and 3A. Its original design requires separate parts for each finger, palm pads, joint pins, and washers. The layer-based manufacturing version, however, provides a complete single hand part that
still meets the product requirements for function, accuracy, and strength.
In this example, 15 separate parts are reduced to one, which reduces inventory. The design also eliminates unique tooling for each of the parts, which reduces cost and lead time. Changing the hand “on-the-fly” to suit customer needs, such as shrinking or expanding its size, is simple.
In most cases of layer-based manufacturing, if you can design the part in 3D CAD software, then you can manufacture the part in an RP machine.
LVLM, the robotic hand was designed to be manufactured in the RP
machine as a single assembly, with the movable parts designed with
clearance and ‘grown’ together. This assembly is manufactured with the
SLS® process in glass-filled nylon.
enables you to go from design concept to 3D CAD to production parts,
without design constraint or tooling investment, but with the freedom
to consolidate parts and design for one-build assemblies.
All manufacturing processes have limitations, even layer-based manufacturing. The most notable limitations involve the capabilities of the materials used to make parts.
Rapid Prototyping machines have been making parts for more than 15 years, but only recently have the materials been strong enough for end-use commercial applications. Medical and food grade ABS, polycarbonate, Nylon, and epoxy, all offer mechanical properties on par with production injection molded plastics.
Surface finish can be a limitation too. LVLM parts cannot produce a smooth surface finish comparable to CNC machined or molded parts. Tolerances in layer-based manufacturing are good and well established based on part size. However, they are not quite as good as CNC or molded parts.
To successfully use layerd manufacturing, it’s important to clear your mind of previously learned constraints. Instead, imagine parts with obscure organic shapes, or with internal volumes. Consider past approaches and the constraints improsed by other manufacturing processes and ask what parts can be consolidated into one.
Then, identify a candidate project, such as a current sub-assembly. Apply the layered manufacturing principles to create a design free from constraints. DW
Filed Under: Digital manufacturing, Materials • advanced